Neutrinoless double beta decay

<h2 id="history">History</h2>

The Italian physicist <a href="/facts/Ettore_Majorana/3SzGKHSx">Ettore Majorana</a> first introduced the concept of a particle being its own antiparticle in 1937.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> Particles of this nature were subsequently named after him as Majorana particles. 
In 1939, <a href="/facts/Wendell_H._Furry/A9gUnnus">Wendell H. Furry</a> proposed the idea of the Majorana nature of the neutrino, which was associated with beta decays.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> Furry stated the transition probability to even be higher for neutrinoless double beta decay.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> It was the first idea proposed to search for the violation of lepton number conservation.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a> It has, since then, drawn attention to it for being useful to study the nature of neutrinos (see quote).

<blockquote>[T]he 0ν mode [...] which violates the lepton number and has been recognized since a long time as a powerful tool to test neutrino properties. — Oliviero Cremonesi<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a></blockquote>
<h2 id="physical-relevance">Physical relevance</h2>
<h3>Conventional double beta decay</h3>
Neutrinos are conventionally produced in weak decays.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> Weak beta decays normally produce one <a href="/facts/Electron/L0KBo5cW">electron</a> (or <a href="/facts/Positron/HgV4zBzA">positron</a>), emit an <a href="/facts/Neutrino/yGWVfSg2">antineutrino</a> (or neutrino) and increase (or decrease) the <a href="/facts/Atomic_nucleus/orpIm5Xl">nucleus</a>' <a href="/facts/Proton_number/bgAr581S">proton number</a> 
 
 
 
 Z
 
 
 {\displaystyle Z}
 
 by one. The nucleus' mass (i.e. <a href="/facts/Binding_energy/2Q3poXgg">binding energy</a>) is then lower and thus more favorable. There exist a number of elements that can decay into a nucleus of lower mass, but they cannot emit one electron only because the resulting nucleus is kinematically (that is, in terms of energy) not favorable (its energy would be higher).<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a> These nuclei can only decay by emitting two electrons (that is, via double beta decay). There are about a dozen confirmed cases of nuclei that can only decay via double beta decay.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a> The corresponding decay equation is:

(
 A
 ,
 Z
 )
 →
 (
 A
 ,
 Z
 +
 2
 )
 +
 2
 
 e
 
 −
 
 
 +
 2
 
 
 
 
 ν
 ¯
 
 
 
 
 e
 
 
 
 
 {\displaystyle (A,Z)\rightarrow (A,Z+2)+2e^{-}+2{\bar {\nu }}_{e}}
 
.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>
It is a weak process of second order.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> A simultaneous decay of two <a href="/facts/Nucleon/6fguU9Xk">nucleons</a> in the same nucleus is extremely unlikely. Thus, the experimentally observed lifetimes of such decay processes are in the range of 
 
 
 
 
 10
 
 18
 
 
 −
 
 10
 
 21
 
 
 
 
 {\displaystyle 10^{18}-10^{21}}
 
 years.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a> A number of <a href="/facts/Isotope/KD9B1y6o">isotopes</a> have been observed already to show this two-neutrino double beta decay.<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a>
This conventional double beta decay is allowed in the <a href="/facts/Standard_Model/LhVGf9ow">Standard Model</a> of <a href="/facts/Particle_physics/YgIuyj2t">particle physics</a>.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> It has thus both a theoretical and an experimental foundation.

<h3>Overview</h3>

If the nature of the neutrinos is Majorana, then they can be emitted and absorbed in the same process without showing up in the corresponding final state.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a> As <a href="/facts/Dirac_equation/DzFaXS4p">Dirac particles</a>, both the neutrinos produced by the decay of the <a href="/facts/W_boson/gAncY5XV">W bosons</a> would be emitted, and not absorbed after.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a>
Neutrinoless double beta decay can only occur if

<ul><li>the neutrino particle is Majorana,<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> and</li>
<li>there exists a right-handed component of the weak leptonic current or the neutrino can change its <a href="/facts/Handedness/wb7Urd7u">handedness</a> between emission and absorption (between the two W vertices), which is possible for a non-zero neutrino mass (for at least one of the neutrino species).<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a></li></ul>
The simplest decay process is known as the light neutrino exchange.<a class="footnote-ref" id="fnref:26" href="#fn:26">26</a> It features one neutrino emitted by one nucleon and absorbed by another nucleon (see figure to the right). In the final state, the only remaining parts are the nucleus (with its changed proton number 
 
 
 
 Z
 
 
 {\displaystyle Z}
 
) and two electrons:

(
 A
 ,
 Z
 )
 →
 (
 A
 ,
 Z
 +
 2
 )
 +
 2
 
 e
 
 −
 
 
 
 
 {\displaystyle (A,Z)\rightarrow (A,Z+2)+2e^{-}}
 
<a class="footnote-ref" id="fnref:27" href="#fn:27">27</a>
The two electrons are emitted quasi-simultaneously.<a class="footnote-ref" id="fnref:28" href="#fn:28">28</a>
The two resulting electrons are then the only emitted particles in the final state and must carry approximately the difference of the sums of the binding energies of the two nuclei before and after the process as their kinetic energy.<a class="footnote-ref" id="fnref:29" href="#fn:29">29</a> The heavy nuclei do not carry significant kinetic energy.
In that case, the <a href="/facts/Decay_rate/Ya6FVjt4">decay rate</a> can be calculated with

Γ
 
 β
 β
 
 
 0
 ν
 
 
 =
 
 
 1
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 
 
 =
 
 G
 
 0
 ν
 
 
 ⋅
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 2
 
 
 ⋅
 ⟨
 
 m
 
 β
 β
 
 
 
 ⟩
 
 2
 
 
 
 
 {\displaystyle \Gamma _{\beta \beta }^{0\nu }={\frac {1}{T_{\beta \beta }^{0\nu }}}=G^{0\nu }\cdot \left|M^{0\nu }\right|^{2}\cdot \langle m_{\beta \beta }\rangle ^{2}}
 
,
where 
 
 
 
 
 G
 
 0
 ν
 
 
 
 
 {\displaystyle G^{0\nu }}
 
 denotes the <a href="/facts/Phase_space/qPe4Fq57">phase space</a> factor, 
 
 
 
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 2
 
 
 
 
 {\displaystyle \left|M^{0\nu }\right|^{2}}
 
 the (squared) <a href="/facts/Matrix_element_(physics)/bA3793Ry">matrix element</a> of this nuclear decay process (according to the Feynman diagram), and 
 
 
 
 ⟨
 
 m
 
 β
 β
 
 
 
 ⟩
 
 2
 
 
 
 
 {\displaystyle \langle m_{\beta \beta }\rangle ^{2}}
 
 the square of the effective Majorana mass.<a class="footnote-ref" id="fnref:30" href="#fn:30">30</a>
First, the effective Majorana mass can be obtained by

⟨
 
 m
 
 β
 β
 
 
 ⟩
 =
 
 ∑
 
 i
 
 
 
 U
 
 e
 i
 
 
 2
 
 
 
 m
 
 i
 
 
 
 
 {\displaystyle \langle m_{\beta \beta }\rangle =\sum _{i}U_{ei}^{2}m_{i}}
 
,
where 
 
 
 
 
 m
 
 i
 
 
 
 
 {\displaystyle m_{i}}
 
 are the Majorana neutrino masses (three neutrinos 
 
 
 
 
 ν
 
 i
 
 
 
 
 {\displaystyle \nu _{i}}
 
) and 
 
 
 
 
 U
 
 e
 i
 
 
 
 
 {\displaystyle U_{ei}}
 
 the elements of the neutrino mixing matrix 
 
 
 
 U
 
 
 {\displaystyle U}
 
 (see <a href="/facts/PMNS_matrix/gCbWaCBE">PMNS matrix</a>).<a class="footnote-ref" id="fnref:31" href="#fn:31">31</a> Contemporary experiments to find neutrinoless double beta decays (see section on experiments) aim at both the proof of the Majorana nature of neutrinos and the measurement of this effective Majorana mass 
 
 
 
 ⟨
 
 m
 
 β
 β
 
 
 ⟩
 
 
 {\displaystyle \langle m_{\beta \beta }\rangle }
 
 (can only be done if the decay is actually generated by the neutrino masses).<a class="footnote-ref" id="fnref:32" href="#fn:32">32</a>
The nuclear matrix element (NME) 
 
 
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 
 {\displaystyle \left|M^{0\nu }\right|}
 
 cannot be measured independently;[why?] it must, but also can, be calculated.<a class="footnote-ref" id="fnref:33" href="#fn:33">33</a> The calculation itself relies on sophisticated nuclear many-body theories and there exist different methods to do this. The NME 
 
 
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 
 {\displaystyle \left|M^{0\nu }\right|}
 
 differs also from nucleus to nucleus (i.e. <a href="/facts/Chemical_element/0jducgWD">chemical element</a> to chemical element). Today, the calculation of the NME is a significant problem and it has been treated by different authors in different ways. One question is whether to treat the range of obtained values for 
 
 
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 
 {\displaystyle \left|M^{0\nu }\right|}
 
 as the theoretical uncertainty and whether this is then to be understood as a statistical uncertainty.<a class="footnote-ref" id="fnref:34" href="#fn:34">34</a> Different approaches are being chosen here. The obtained values for 
 
 
 
 
 |
 
 M
 
 0
 ν
 
 
 |
 
 
 
 {\displaystyle \left|M^{0\nu }\right|}
 
 often vary by factors of 2 up to about 5. Typical values lie in the range of from about 0.9 to 14, depending on the decaying nucleus/element.<a class="footnote-ref" id="fnref:35" href="#fn:35">35</a>
Lastly, the phase-space factor 
 
 
 
 
 G
 
 0
 ν
 
 
 
 
 {\displaystyle G^{0\nu }}
 
 must also be calculated.<a class="footnote-ref" id="fnref:36" href="#fn:36">36</a> It depends on the total released kinetic energy (
 
 
 
 Q
 =
 
 M
 
 nucleus
 
 
 before
 
 
 −
 
 M
 
 nucleus
 
 
 after
 
 
 −
 2
 
 m
 
 electron
 
 
 
 
 {\displaystyle Q=M_{\text{nucleus}}^{\text{before}}-M_{\text{nucleus}}^{\text{after}}-2m_{\text{electron}}}
 
, i.e. "
 
 
 
 Q
 
 
 {\displaystyle Q}
 
-value") and the atomic number 
 
 
 
 Z
 
 
 {\displaystyle Z}
 
. Methods use <a href="/facts/Paul_Dirac/6bt5yRdk">Dirac</a> <a href="/facts/Wave_function/KgM5ykjY">wave functions</a>, finite nuclear sizes and electron screening.<a class="footnote-ref" id="fnref:37" href="#fn:37">37</a> There exist high-precision results for 
 
 
 
 
 G
 
 0
 ν
 
 
 
 
 {\displaystyle G^{0\nu }}
 
 for various nuclei, ranging from about 0.23 (for 
 
 
 
 
 
 
 
 52
 
 
 128
 
 
 T
 e
 
 →
 
 54
 
 
 128
 
 
 X
 e
 
 
 
 {\displaystyle \mathrm {^{128}_{52}Te\rightarrow _{54}^{128}Xe} }
 
), and 0.90 (
 
 
 
 
 
 
 
 32
 
 
 76
 
 
 G
 e
 
 →
 
 34
 
 
 76
 
 
 S
 e
 
 
 
 {\displaystyle \mathrm {^{76}_{32}Ge\rightarrow _{34}^{76}Se} }
 
) to about 24.14 (
 
 
 
 
 
 
 
 60
 
 
 150
 
 
 N
 d
 
 →
 
 62
 
 
 150
 
 
 S
 m
 
 
 
 {\displaystyle \mathrm {^{150}_{60}Nd\rightarrow _{62}^{150}Sm} }
 
).<a class="footnote-ref" id="fnref:38" href="#fn:38">38</a>
It is believed that, if neutrinoless double beta decay is found under certain conditions (decay rate compatible with predictions based on experimental knowledge about neutrino masses and mixing), this would indeed "likely" point at Majorana neutrinos as the main mediator (and not other sources of new physics).<a class="footnote-ref" id="fnref:39" href="#fn:39">39</a> There are 35 nuclei that can undergo neutrinoless double beta decay (according to the aforementioned decay conditions).<a class="footnote-ref" id="fnref:40" href="#fn:40">40</a>

<h2 id="experiments-and-results">Experiments and results</h2>
Nine different candidates of nuclei are being considered in experiments to confirm neutrinoless double beta-decay: 
 
 
 
 
 
 
 
 48
 
 
 C
 a
 
 ,
 
 76
 
 
 G
 e
 
 ,
 
 82
 
 
 S
 e
 
 ,
 
 96
 
 
 Z
 r
 
 ,
 
 100
 
 
 M
 o
 
 ,
 
 116
 
 
 C
 d
 
 ,
 
 130
 
 
 T
 e
 
 ,
 
 136
 
 
 X
 e
 
 ,
 
 150
 
 
 N
 d
 
 
 
 {\displaystyle \mathrm {^{48}Ca,^{76}Ge,^{82}Se,^{96}Zr,^{100}Mo,^{116}Cd,^{130}Te,^{136}Xe,^{150}Nd} }
 
.<a class="footnote-ref" id="fnref:41" href="#fn:41">41</a> They all have arguments for and against their use in an experiment. Factors to be included and revised are <a href="/facts/Natural_abundance/dGjaAwc9">natural abundance</a>, reasonably priced enrichment, and a well understood and controlled experimental technique.<a class="footnote-ref" id="fnref:42" href="#fn:42">42</a> The higher the 
 
 
 
 Q
 
 
 {\displaystyle Q}
 
-value, the better are the chances of a discovery, in principle. The phase-space factor 
 
 
 
 
 G
 
 0
 ν
 
 
 
 
 {\displaystyle G^{0\nu }}
 
, and thus the decay rate, grows with 
 
 
 
 
 Q
 
 5
 
 
 
 
 {\displaystyle Q^{5}}
 
.<a class="footnote-ref" id="fnref:43" href="#fn:43">43</a>
Experimentally of interest and thus measured is the sum of the kinetic energies of the two emitted electrons. It should equal the 
 
 
 
 Q
 
 
 {\displaystyle Q}
 
-value of the respective nucleus for neutrinoless double beta emission.<a class="footnote-ref" id="fnref:44" href="#fn:44">44</a>
The table shows a summary of the currently best limits on the lifetime of 0νββ. From this, it can be deduced that neutrinoless double beta decay is an extremely rare process, if it occurs at all.

Experimental limits (at least 90% <a href="/facts/Confidence_interval/NS8mG5UE">C.I.</a>)<a class="footnote-ref" id="fnref:45" href="#fn:45">45</a> on a collection of isotopes for 0νββ decay process mediated by the light neutrino mechanism, as shown in the Feynman diagram above.<table><tbody><tr><th>Isotope</th><th>Experiment</th><th>lifetime T β β 0 ν {\displaystyle T_{\beta \beta }^{0\nu }} [years]</th></tr><tr><td> 48 C a {\displaystyle \mathrm {^{48}Ca} } </td><td>ELEGANT-VI</td><td> > 1.4 ⋅ 10 22 {\displaystyle >1.4\cdot 10^{22}} </td></tr><tr><td> 76 G e {\displaystyle \mathrm {^{76}Ge} } </td><td><a href="/facts/Heidelberg-Moscow_experiment/7u36G9d4">Heidelberg-Moscow</a><a class="footnote-ref" id="fnref:46" href="#fn:46">46</a></td><td> > 1.9 ⋅ 10 25 {\displaystyle >1.9\cdot 10^{25}} <a class="footnote-ref" id="fnref:47" href="#fn:47">47</a></td></tr><tr><td> 76 G e {\displaystyle \mathrm {^{76}Ge} } </td><td><a href="/facts/Germanium_Detector_Array/IDaFW6zu">GERDA</a></td><td> > 1.8 ⋅ 10 26 {\displaystyle >1.8\cdot 10^{26}} <a class="footnote-ref" id="fnref:48" href="#fn:48">48</a></td></tr><tr><td> 76 G e {\displaystyle \mathrm {^{76}Ge} } </td><td><a href="/facts/MAJORANA/SbQDzWtT">MAJORANA</a></td><td> > 8.3 ⋅ 10 25 {\displaystyle >8.3\cdot 10^{25}} <a class="footnote-ref" id="fnref:49" href="#fn:49">49</a></td></tr><tr><td> 82 S e {\displaystyle \mathrm {^{82}Se} } </td><td><a href="/facts/Neutrino_Ettore_Majorana_Observatory/dLnMxhuf">NEMO</a>-3</td><td> > 1.0 ⋅ 10 23 {\displaystyle >1.0\cdot 10^{23}} </td></tr><tr><td> 82 S e {\displaystyle \mathrm {^{82}Se} } </td><td>CUPID-0</td><td> > 4.6 ⋅ 10 24 {\displaystyle >4.6\cdot 10^{24}} <a class="footnote-ref" id="fnref:50" href="#fn:50">50</a></td></tr><tr><td> 96 Z r {\displaystyle \mathrm {^{96}Zr} } </td><td>NEMO-3</td><td> > 9.2 ⋅ 10 21 {\displaystyle >9.2\cdot 10^{21}} </td></tr><tr><td> 100 M o {\displaystyle \mathrm {^{100}Mo} } </td><td>NEMO-3</td><td> > 2.1 ⋅ 10 25 {\displaystyle >2.1\cdot 10^{25}} </td></tr><tr><td> 116 C d {\displaystyle \mathrm {^{116}Cd} } </td><td>Solotvina</td><td> > 1.7 ⋅ 10 23 {\displaystyle >1.7\cdot 10^{23}} </td></tr><tr><td> 128 T e {\displaystyle \mathrm {^{128}Te} } </td><td><a href="/facts/CUORE/MDgmAGFR">CUORE</a></td><td> > 3.6 ⋅ 10 24 {\displaystyle >3.6\cdot 10^{24}} <a class="footnote-ref" id="fnref:51" href="#fn:51">51</a></td></tr><tr><td> 130 T e {\displaystyle \mathrm {^{130}Te} } </td><td>CUORE</td><td> > 2.2 ⋅ 10 25 {\displaystyle >2.2\cdot 10^{25}} </td></tr><tr><td> 136 X e {\displaystyle \mathrm {^{136}Xe} } </td><td>EXO</td><td> > 3.5 ⋅ 10 25 {\displaystyle >3.5\cdot 10^{25}} <a class="footnote-ref" id="fnref:52" href="#fn:52">52</a></td></tr><tr><td> 136 X e {\displaystyle \mathrm {^{136}Xe} } </td><td><a href="/facts/Kamioka_Liquid_Scintillator_Antineutrino_Detector/N98scgc7">KamLAND-Zen</a></td><td> > 2.3 ⋅ 10 26 {\displaystyle >2.3\cdot 10^{26}} <a class="footnote-ref" id="fnref:53" href="#fn:53">53</a></td></tr><tr><td> 150 N d {\displaystyle \mathrm {^{150}Nd} } </td><td>NEMO-3</td><td> > 2.1 ⋅ 10 25 {\displaystyle >2.1\cdot 10^{25}} </td></tr></tbody></table>
<h3>Heidelberg-Moscow collaboration</h3>
The so-called "Heidelberg-Moscow collaboration" (HDM; 1990–2003) of the German <a href="/facts/Max_Planck_Institute_for_Nuclear_Physics/4ehcz8eL">Max-Planck-Institut für Kernphysik</a> and the Russian science center <a href="/facts/Kurchatov_Institute/lSkWUomv">Kurchatov Institute</a> in Moscow famously claimed to have found "evidence for neutrinoless double beta decay" (<a href="/facts/Double_beta_decay/ILmpbfqS">Heidelberg-Moscow controversy</a>).<a class="footnote-ref" id="fnref:54" href="#fn:54">54</a><a class="footnote-ref" id="fnref:55" href="#fn:55">55</a> Initially, in 2001 the collaboration announced a 2.2σ, or a 3.1σ (depending on the used calculation method) evidence.<a class="footnote-ref" id="fnref:56" href="#fn:56">56</a> The decay rate was found to be around 
 
 
 
 2
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle 2\cdot 10^{25}}
 
 years.<a class="footnote-ref" id="fnref:57" href="#fn:57">57</a> This result has been topic of discussions between many scientists and authors.<a class="footnote-ref" id="fnref:58" href="#fn:58">58</a> To this day, no other experiment has ever confirmed or approved the result of the HDM group.<a class="footnote-ref" id="fnref:59" href="#fn:59">59</a> Instead, recent results from the GERDA experiment for the lifetime limit clearly disfavor and reject the values of the HDM collaboration.<a class="footnote-ref" id="fnref:60" href="#fn:60">60</a>
Neutrinoless double beta decay has not yet been found.<a class="footnote-ref" id="fnref:61" href="#fn:61">61</a>

<h3>GERDA (Germanium Detector Array) experiment</h3>
The <a href="/facts/Germanium_Detector_Array/IDaFW6zu">Germanium Detector Array</a> (GERDA) collaboration's result of phase I of the detector was a limit of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 2.1
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>2.1\cdot 10^{25}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:62" href="#fn:62">62</a> It used <a href="/facts/Germanium/wtoALHGs">germanium</a> both as source and detector material.<a class="footnote-ref" id="fnref:63" href="#fn:63">63</a> Liquid <a href="/facts/Argon/QX6NRH6d">argon</a> was used for <a href="/facts/Muon/BP2fLVIR">muon</a> vetoing and as a shielding from background radiation.<a class="footnote-ref" id="fnref:64" href="#fn:64">64</a> The 
 
 
 
 Q
 
 
 {\displaystyle Q}
 
-value of 76Ge for 0νββ decay is 2039 keV, but no excess of events in this region was found.<a class="footnote-ref" id="fnref:65" href="#fn:65">65</a> Phase II of the experiment started data-taking in 2015, and it used around 36 kg of germanium for the detectors.<a class="footnote-ref" id="fnref:66" href="#fn:66">66</a> The exposure analyzed until July 2020 was 10.8 kg yr. Again, no signal was found and thus a new limit was set to 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 5.3
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>5.3\cdot 10^{25}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:67" href="#fn:67">67</a> The detector has been decommissioned and published its final results in December 2020. No neutrinoless double beta decay was observed.<a class="footnote-ref" id="fnref:68" href="#fn:68">68</a> The successor experiment is LEGEND, which uses the same technology to achieve sensitivity to longer lifetimes.<a class="footnote-ref" id="fnref:69" href="#fn:69">69</a>

<h3><a href="/facts/Enriched_Xenon_Observatory/QKTChNvL">EXO</a> (Enriched Xenon Observatory) experiment</h3>
The Enriched Xenon Observatory-200 experiment uses <a href="/facts/Xenon/9E3XR69R">xenon</a> both as source and detector.<a class="footnote-ref" id="fnref:70" href="#fn:70">70</a> The experiment is located in New Mexico (US) and uses a <a href="/facts/Time-projection_chamber/4ysP0jL1">time-projection chamber</a> (TPC) for three-dimensional spatial and temporal resolution of the electron track depositions.<a class="footnote-ref" id="fnref:71" href="#fn:71">71</a> The EXO-200 experiment yielded a lifetime limit of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 3.5
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>3.5\cdot 10^{25}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:72" href="#fn:72">72</a> When translated to effective Majorana mass, this is a limit of the same order as that obtained by GERDA I and II.<a class="footnote-ref" id="fnref:73" href="#fn:73">73</a>

<h3>Currently data-taking experiments</h3>
<ul><li><a href="/facts/Cryogenic_Underground_Observatory_for_Rare_Events/MDgmAGFR">CUORE</a> (Cryogenic Underground Observatory for Rare Events) experiment:
<ul><li>The CUORE experiment consists of an array of 988 ultra-cold <a href="/facts/Tellurium_dioxide/yrILUsAM">TeO2</a> crystals (for a total mass of 206 kg of 
 
 
 
 
 
 
 
 130
 
 
 T
 e
 
 
 
 {\displaystyle \mathrm {^{130}Te} }
 
) used as bolometers to detect the emitted beta particles and as the source of the decay. CUORE is located underground at the <a href="/facts/Laboratori_Nazionali_del_Gran_Sasso/7psp5gt7">Laboratori Nazionali del Gran Sasso</a>, and it began its first physics data run in 2017.<a class="footnote-ref" id="fnref:74" href="#fn:74">74</a> CUORE published in 2020 results from the search for neutrinoless double-beta decay in 
 
 
 
 
 
 
 
 130
 
 
 T
 e
 
 
 
 {\displaystyle \mathrm {^{130}Te} }
 
 with a total exposure of 372.5 kg⋅yr, finding no evidence for 0νββ decay and setting a 90% CI Bayesian lower limit of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 3.2
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>3.2\cdot 10^{25}}
 
 years<a class="footnote-ref" id="fnref:75" href="#fn:75">75</a> and in April 2022 a new limit was set on 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 2.2
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>2.2\cdot 10^{25}}
 
 years at the same confidence level.<a class="footnote-ref" id="fnref:76" href="#fn:76">76</a><a class="footnote-ref" id="fnref:77" href="#fn:77">77</a> The experiment is steadily taking data, and it is expected to finalize its physics program by 2024.[needs update]</li></ul></li>
<li><a href="/facts/Kamioka_Liquid_Scintillator_Antineutrino_Detector/N98scgc7">KamLAND-Zen</a> (Kamioka Liquid Scintillator Antineutrino Detector-Zen) experiment:
<ul><li>The KamLAND-Zen experiment commenced using 13 tons of xenon as a source (enriched with about 320 kg of 
 
 
 
 
 
 
 
 136
 
 
 X
 e
 
 
 
 {\displaystyle \mathrm {^{136}Xe} }
 
), contained in a nylon balloon that is surrounded by a liquid <a href="/facts/Scintillation_counter/DFB1gpJv">scintillator</a> outer balloon of 13 m diameter.<a class="footnote-ref" id="fnref:78" href="#fn:78">78</a> Starting in 2011, KamLAND-Zen Phase I started taking data, eventually leading to set a limit on the lifetime for neutrinoless double beta decay of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 1.9
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>1.9\cdot 10^{25}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:79" href="#fn:79">79</a> This limit could be improved by combining with Phase II data (data-taking started in December 2013) to 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 2.6
 ⋅
 
 10
 
 25
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>2.6\cdot 10^{25}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:80" href="#fn:80">80</a> For Phase II, the collaboration especially managed to reduce the decay of 
 
 
 
 
 
 
 
 110
 m
 
 
 A
 g
 
 
 
 {\displaystyle \mathrm {^{110m}Ag} }
 
, which disturbed the measurements in the region of interest for 0νββ decay of 
 
 
 
 
 
 
 
 136
 
 
 X
 e
 
 
 
 {\displaystyle \mathrm {^{136}Xe} }
 
.<a class="footnote-ref" id="fnref:81" href="#fn:81">81</a> In August 2016, KamLAND-Zen 800 was completed containing 800 kg of 
 
 
 
 
 
 
 
 136
 
 
 X
 e
 
 
 
 {\displaystyle \mathrm {^{136}Xe} }
 
,<a class="footnote-ref" id="fnref:82" href="#fn:82">82</a> reporting a limit of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 1.07
 ⋅
 
 10
 
 26
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>1.07\cdot 10^{26}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:83" href="#fn:83">83</a><a class="footnote-ref" id="fnref:84" href="#fn:84">84</a><a class="footnote-ref" id="fnref:85" href="#fn:85">85</a> In 2023 the limit was improved limit of 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 2.3
 ⋅
 
 10
 
 26
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>2.3\cdot 10^{26}}
 
 years (90% C.L.).<a class="footnote-ref" id="fnref:86" href="#fn:86">86</a><a class="footnote-ref" id="fnref:87" href="#fn:87">87</a></li></ul></li>
<li>LEGEND<a class="footnote-ref" id="fnref:88" href="#fn:88">88</a>
<ul><li>The LEGEND experiment consists of high-purity <a href="/facts/Semiconductor_detector/HzvpIobR">germanium detectors</a> enriched to ~90% 76Ge and immersed in a liquid argon cryostat, whose scintillation lights acts as a veto for external background events. The LEGEND experiment is the successor to the GERDA and MAJORANA DEMONSTRATOR<a class="footnote-ref" id="fnref:89" href="#fn:89">89</a> experiments.</li></ul></li></ul>
<h3>Proposed/future experiments</h3>
<ul><li><a href="/facts/Enriched_Xenon_Observatory/QKTChNvL">nEXO</a> experiment:
<ul><li>As EXO-200's successor, nEXO is planned to be a ton-scale experiment and part of the next generation of 0νββ experiments.<a class="footnote-ref" id="fnref:90" href="#fn:90">90</a> The detector material is planned to weigh about 5 t, serving a 1% energy resolution at the 
 
 
 
 Q
 
 
 {\displaystyle Q}
 
-value.<a class="footnote-ref" id="fnref:91" href="#fn:91">91</a> The experiment is planned to deliver a lifetime sensitivity of about 
 
 
 
 
 T
 
 β
 β
 
 
 0
 ν
 
 
 >
 1.35
 ⋅
 
 10
 
 28
 
 
 
 
 {\displaystyle T_{\beta \beta }^{0\nu }>1.35\cdot 10^{28}}
 
 years after 10 years of data-taking.<a class="footnote-ref" id="fnref:92" href="#fn:92">92</a></li></ul></li>
<li>SuperNEMO</li>
<li>NuDoubt++:
<ul><li>The NuDoubt⁺⁺ experiment aims at the measurement of two-neutrino and neutrinoless positive double weak decays (2β⁺/ECβ⁺).<a class="footnote-ref" id="fnref:93" href="#fn:93">93</a> It is based on a new detector concept combining hybrid and opaque scintillators paired with a novel light read-out technique.<a class="footnote-ref" id="fnref:94" href="#fn:94">94</a> The technology is particularly suitable detecting positrons (β⁺) signatures. In its first phase, NuDoubt⁺⁺ is going to operate under high-pressure loading of enriched Kr-78 gas. It expects to discover two-neutrino positive double weak decay modes of Kr-78 within 1 tonne-week exposure<a class="footnote-ref" id="fnref:95" href="#fn:95">95</a> and is able to probe neutrinoless positive double weak decay modes at several orders of magnitude improved significance compared to current experimental limits. After 1 ton-week exposure, a half-life sensitivity of 
 
 
 
 
 T
 
 β
 +
 β
 +
 
 
 0
 ν
 
 
 >
 
 10
 
 24
 
 
 
 
 {\displaystyle T_{\beta +\beta +}^{0\nu }>10^{24}}
 
 years (90% C.L.) is expected for Kr-78.<a class="footnote-ref" id="fnref:96" href="#fn:96">96</a> Later phases may involve searches for positive double weak decays in Xe-124 and Cd-106.</li></ul></li></ul>
<h2 id="neutrinoless-muon-conversion">Neutrinoless muon conversion</h2>
The muon decays as 
 
 
 
 
 μ
 
 +
 
 
 →
 
 e
 
 +
 
 
 +
 
 ν
 
 e
 
 
 +
 
 
 
 ν
 ¯
 
 
 
 μ
 
 
 
 
 {\displaystyle \mu ^{+}\to e^{+}+\nu _{e}+{\overline {\nu }}_{\mu }}
 
 and 
 
 
 
 
 μ
 
 −
 
 
 →
 
 e
 
 −
 
 
 +
 
 
 
 ν
 ¯
 
 
 
 e
 
 
 +
 
 ν
 
 μ
 
 
 
 
 {\displaystyle \mu ^{-}\to e^{-}+{\overline {\nu }}_{e}+\nu _{\mu }}
 
. Decays without neutrino emission, such as 
 
 
 
 
 μ
 
 +
 
 
 →
 
 e
 
 +
 
 
 +
 γ
 
 
 {\displaystyle \mu ^{+}\to e^{+}+\gamma }
 
, 
 
 
 
 
 μ
 
 −
 
 
 →
 
 e
 
 −
 
 
 +
 γ
 
 
 {\displaystyle \mu ^{-}\to e^{-}+\gamma }
 
, 
 
 
 
 
 μ
 
 +
 
 
 →
 
 e
 
 +
 
 
 +
 
 e
 
 −
 
 
 +
 
 e
 
 +
 
 
 
 
 {\displaystyle \mu ^{+}\to e^{+}+e^{-}+e^{+}}
 
 and 
 
 
 
 
 μ
 
 −
 
 
 →
 
 e
 
 −
 
 
 +
 
 e
 
 +
 
 
 +
 
 e
 
 −
 
 
 
 
 {\displaystyle \mu ^{-}\to e^{-}+e^{+}+e^{-}}
 
 are so unlikely that they are considered <a href="/facts/Muon/BP2fLVIR">prohibited</a> and their observation would be considered evidence of <a href="/facts/New_Physics/UX68py44">new physics</a>. A number of experiments are pursuing this path such as <a href="/facts/Mu_to_E_Gamma/gIp8Eowc">Mu to E Gamma</a>, <a href="/facts/Comet_(experiment)/w1M2F8Pz">Comet</a>, and <a href="/facts/Mu2e/ICcNQ7B1">Mu2e</a> for 
 
 
 
 
 μ
 
 +
 
 
 →
 
 e
 
 +
 
 
 γ
 
 
 {\displaystyle \mu ^{+}\to e^{+}\gamma }
 
 and <a href="/facts/Mu3e/zIoC8MA6">Mu3e</a> for 
 
 
 
 
 μ
 
 +
 
 
 →
 
 e
 
 +
 
 
 
 e
 
 −
 
 
 
 e
 
 +
 
 
 
 
 {\displaystyle \mu ^{+}\to e^{+}e^{-}e^{+}}
 
.
Neutrinoless tau conversion in the form 
 
 
 
 τ
 →
 3
 μ
 
 
 {\displaystyle \tau \to 3\mu }
 
 has been searched for by the CMS experiment.<a class="footnote-ref" id="fnref:97" href="#fn:97">97</a><a class="footnote-ref" id="fnref:98" href="#fn:98">98</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Double_beta_decay/ILmpbfqS">Double beta decay</a></li>
<li><a href="/facts/Double_beta_decay/ILmpbfqS">Heidelberg-Moscow controversy</a></li>
<li><a href="/facts/Double_electron_capture/aQ1ElH3c">Neutrinoless double electron capture</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="978-0-85274-313-3" target="_blank">978-0-85274-313-3</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Oberauer, Lothar; Ianni, Aldo; Serenelli, Aldo (2020). Solar neutrino physics : the interplay between particle physics and astronomy. Wiley-VCH. pp. 120–127. ISBN 978-3-527-41274-7. <a href="978-3-527-41274-7" target="_blank">978-3-527-41274-7</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Oberauer, Lothar; Ianni, Aldo; Serenelli, Aldo (2020). Solar neutrino physics : the interplay between particle physics and astronomy. Wiley-VCH. pp. 120–127. ISBN 978-3-527-41274-7. <a href="978-3-527-41274-7" target="_blank">978-3-527-41274-7</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Deppisch, Frank F. (2019). A modern introduction to neutrino physics. Morgan & Claypool Publishers. ISBN 978-1-64327-679-3. <a href="978-1-64327-679-3" target="_blank">978-1-64327-679-3</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Patrignani et al. (Particle Data Group), C. (October 2016). "Review of Particle Physics". Chinese Physics C. 40 (10): 647. Bibcode:2016ChPhC..40j0001P. doi:10.1088/1674-1137/40/10/100001. hdl:10044/1/57200. S2CID 125766528. <a href="http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22" target="_blank">http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Majorana, Ettore (1937). "Teoria simmetrica dell'elettrone e del positrone". Il Nuovo Cimento. 14 (4): 171–184. Bibcode:1937NCim...14..171M. doi:10.1007/BF02961314. S2CID 18973190. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Majorana, Ettore (1937). "Teoria simmetrica dell'elettrone e del positrone". Il Nuovo Cimento. 14 (4): 171–184. Bibcode:1937NCim...14..171M. doi:10.1007/BF02961314. S2CID 18973190. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Furry, W. H. (15 December 1939). "On Transition Probabilities in Double Beta-Disintegration". Physical Review. 56 (12): 1184–1193. Bibcode:1939PhRv...56.1184F. doi:10.1103/PhysRev.56.1184. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Furry, W. H. (15 December 1939). "On Transition Probabilities in Double Beta-Disintegration". Physical Review. 56 (12): 1184–1193. Bibcode:1939PhRv...56.1184F. doi:10.1103/PhysRev.56.1184. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="978-0-85274-313-3" target="_blank">978-0-85274-313-3</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Cremonesi, Oliviero (April 2003). "Neutrinoless double beta decay: Present and future". Nuclear Physics B - Proceedings Supplements. 118: 287–296. arXiv:hep-ex/0210007. Bibcode:2003NuPhS.118..287C. doi:10.1016/S0920-5632(03)01331-8. S2CID 7298714. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Patrignani et al. (Particle Data Group), C. (October 2016). "Review of Particle Physics". Chinese Physics C. 40 (10): 647. Bibcode:2016ChPhC..40j0001P. doi:10.1088/1674-1137/40/10/100001. hdl:10044/1/57200. S2CID 125766528. <a href="http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22" target="_blank">http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Oberauer, Lothar; Ianni, Aldo; Serenelli, Aldo (2020). Solar neutrino physics : the interplay between particle physics and astronomy. Wiley-VCH. pp. 120–127. ISBN 978-3-527-41274-7. <a href="978-3-527-41274-7" target="_blank">978-3-527-41274-7</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Oberauer, Lothar; Ianni, Aldo; Serenelli, Aldo (2020). Solar neutrino physics : the interplay between particle physics and astronomy. Wiley-VCH. pp. 120–127. ISBN 978-3-527-41274-7. <a href="978-3-527-41274-7" target="_blank">978-3-527-41274-7</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="978-0-85274-313-3" target="_blank">978-0-85274-313-3</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">Oberauer, Lothar; Ianni, Aldo; Serenelli, Aldo (2020). Solar neutrino physics : the interplay between particle physics and astronomy. Wiley-VCH. pp. 120–127. ISBN 978-3-527-41274-7. <a href="978-3-527-41274-7" target="_blank">978-3-527-41274-7</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">Artusa, D. R.; Avignone, F. T.; Azzolini, O.; Balata, M.; Banks, T. I.; Bari, G.; Beeman, J.; Bellini, F.; Bersani, A.; Biassoni, M. (15 October 2014). "Exploring the neutrinoless double beta decay in the inverted neutrino hierarchy with bolometric detectors". The European Physical Journal C. 74 (10): 3096. arXiv:1404.4469. Bibcode:2014EPJC...74.3096A. doi:10.1140/epjc/s10052-014-3096-8. <a href="https://doi.org/10.1140%2Fepjc%2Fs10052-014-3096-8" target="_blank">https://doi.org/10.1140%2Fepjc%2Fs10052-014-3096-8</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">Schechter, J.; Valle, J. W. F. (1 June 1982). "Neutrinoless double-beta decay in SU(2)×U(1) theories". Physical Review D. 25 (11): 2951–2954. Bibcode:1982PhRvD..25.2951S. doi:10.1103/PhysRevD.25.2951. hdl:10550/47205. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="978-0-85274-313-3" target="_blank">978-0-85274-313-3</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
<li id="fn:26">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:26" class="footnote-back-ref">↩</a></li>
<li id="fn:27">Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="978-0-85274-313-3" target="_blank">978-0-85274-313-3</a> <a href="#fnref:27" class="footnote-back-ref">↩</a></li>
<li id="fn:28">Artusa, D. R.; Avignone, F. T.; Azzolini, O.; Balata, M.; Banks, T. I.; Bari, G.; Beeman, J.; Bellini, F.; Bersani, A.; Biassoni, M. (15 October 2014). "Exploring the neutrinoless double beta decay in the inverted neutrino hierarchy with bolometric detectors". The European Physical Journal C. 74 (10): 3096. arXiv:1404.4469. Bibcode:2014EPJC...74.3096A. doi:10.1140/epjc/s10052-014-3096-8. <a href="https://doi.org/10.1140%2Fepjc%2Fs10052-014-3096-8" target="_blank">https://doi.org/10.1140%2Fepjc%2Fs10052-014-3096-8</a> <a href="#fnref:28" class="footnote-back-ref">↩</a></li>
<li id="fn:29">Grotz & Klapdor 1990, p. 86. - Grotz, K.; Klapdor, H. V. (1990). The weak interaction in nuclear, particle, and astrophysics. Hilger. ISBN 978-0-85274-313-3. <a href="#fnref:29" class="footnote-back-ref">↩</a></li>
<li id="fn:30">Patrignani et al. (Particle Data Group), C. (October 2016). "Review of Particle Physics". Chinese Physics C. 40 (10): 647. Bibcode:2016ChPhC..40j0001P. doi:10.1088/1674-1137/40/10/100001. hdl:10044/1/57200. S2CID 125766528. <a href="http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22" target="_blank">http://bib-pubdb1.desy.de/search?p=id:%22PUBDB-2016-04859%22</a> <a href="#fnref:30" class="footnote-back-ref">↩</a></li>
<li id="fn:31">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:31" class="footnote-back-ref">↩</a></li>
<li id="fn:32">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:32" class="footnote-back-ref">↩</a></li>
<li id="fn:33">Bilenky, S.M; Grifols, J.A (December 2002). "The possible test of the calculations of nuclear matrix elements of the (ββ)0ν-decay". Physics Letters B. 550 (3–4): 154–159. arXiv:hep-ph/0211101. Bibcode:2002PhLB..550..154B. doi:10.1016/S0370-2693(02)02978-7. <a href="https://doi.org/10.1016%2FS0370-2693%2802%2902978-7" target="_blank">https://doi.org/10.1016%2FS0370-2693%2802%2902978-7</a> <a href="#fnref:33" class="footnote-back-ref">↩</a></li>
<li id="fn:34">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:34" class="footnote-back-ref">↩</a></li>
<li id="fn:35">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:35" class="footnote-back-ref">↩</a></li>
<li id="fn:36">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:36" class="footnote-back-ref">↩</a></li>
<li id="fn:37">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:37" class="footnote-back-ref">↩</a></li>
<li id="fn:38">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:38" class="footnote-back-ref">↩</a></li>
<li id="fn:39">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:39" class="footnote-back-ref">↩</a></li>
<li id="fn:40">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:40" class="footnote-back-ref">↩</a></li>
<li id="fn:41">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:41" class="footnote-back-ref">↩</a></li>
<li id="fn:42">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:42" class="footnote-back-ref">↩</a></li>
<li id="fn:43">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:43" class="footnote-back-ref">↩</a></li>
<li id="fn:44">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:44" class="footnote-back-ref">↩</a></li>
<li id="fn:45">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:45" class="footnote-back-ref">↩</a></li>
<li id="fn:46">"The Heidelberg-Moscow Experiment with enriched 76Ge". Prof.Dr.H.V.Klapdor-Kleingrothaus. Retrieved 16 July 2020. <a href="http://www.klapdor-k.de/Theory%20of%20Experiments/HDMDBD/HeiMos.htm#:~:text=The%20HEIDELBERG%2DMOSCOW%2DExperiment%20is,beta%20transitions%20in%20one%20nucleus." target="_blank">http://www.klapdor-k.de/Theory%20of%20Experiments/HDMDBD/HeiMos.htm#:~:text=The%20HEIDELBERG%2DMOSCOW%2DExperiment%20is,beta%20transitions%20in%20one%20nucleus.</a> <a href="#fnref:46" class="footnote-back-ref">↩</a></li>
<li id="fn:47">"The Heidelberg-Moscow Experiment with enriched 76Ge". Prof.Dr.H.V.Klapdor-Kleingrothaus. Retrieved 16 July 2020. <a href="http://www.klapdor-k.de/Theory%20of%20Experiments/HDMDBD/HeiMos.htm#:~:text=The%20HEIDELBERG%2DMOSCOW%2DExperiment%20is,beta%20transitions%20in%20one%20nucleus." target="_blank">http://www.klapdor-k.de/Theory%20of%20Experiments/HDMDBD/HeiMos.htm#:~:text=The%20HEIDELBERG%2DMOSCOW%2DExperiment%20is,beta%20transitions%20in%20one%20nucleus.</a> <a href="#fnref:47" class="footnote-back-ref">↩</a></li>
<li id="fn:48">GERDA Collaboration; Agostini, M.; Araujo, G. R.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Baudis, L.; Bauer, C.; Bellotti, E. (2020-12-17), "Final Results of GERDA on the Search for Neutrinoless Double-$\ensuremath{\beta}$ Decay", Physical Review Letters, 125 (25): 252502, arXiv:2009.06079, doi:10.1103/PhysRevLett.125.252502, PMID 33416389, S2CID 221655689 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:48" class="footnote-back-ref">↩</a></li>
<li id="fn:49">Majorana Collaboration; Arnquist, I. J.; Avignone, F. T.; Barabash, A. S.; Barton, C. J.; Barton, P. J.; Bhimani, K. H.; Blalock, E.; Bos, B.; Busch, M.; Buuck, M.; Caldwell, T. S.; Chan, Y-D.; Christofferson, C. D.; Chu, P.-H. (2023-02-10). "Final Result of the Majorana Demonstrator's Search for Neutrinoless Double-$\ensuremath{\beta}$ Decay in $^{76}\mathrm{Ge}$". Physical Review Letters. 130 (6): 062501. arXiv:2207.07638. doi:10.1103/PhysRevLett.130.062501. PMID 36827565. S2CID 256805278. <a href="https://link.aps.org/doi/10.1103/PhysRevLett.130.062501" target="_blank">https://link.aps.org/doi/10.1103/PhysRevLett.130.062501</a> <a href="#fnref:49" class="footnote-back-ref">↩</a></li>
<li id="fn:50">Azzolini, O. and Beeman, J. W. and Bellini, F. and Beretta, M. and Biassoni, M. and Brofferio, C. and Bucci, C. and Capelli, S. and Caracciolo, V. and Cardani, L. and Carniti, P. and Casali, N. and Chiesa, D. and Clemenza, M. and Colantoni, I. and Cremonesi, O. and Cruciani, A. and D'Addabbo, A. and Dafinei, I. and De Dominicis, F. and Di Domizio, S. and Ferroni, F. and Gironi, L. and Giuliani, A. and Gorla, P. and Gotti, C. and Keppel, G. and Martinez, M. and Nagorny, S. and Nastasi, M. and Nisi, S. and Nones, C. and Orlandi, D. and Pagnanini, L. and Pallavicini, M. and Pattavina, L. and Pavan, M. and Pessina, G. and Pettinacci, V. and Pirro, S. and Pozzi, S. and Previtali, E. and Puiu, A. and Rusconi, C. and Sch\"affner, K. and Tomei, C. and Vignati, M. and Zolotarova, A. S. (2022-09-06), "Final Result on the Neutrinoless Double Beta Decay of 
 
 
 
 
 
 
 
 82
 
 
 S
 e
 
 
 
 {\displaystyle \mathrm {^{82}Se} }
 
", Physical Review Letters, 129 (11): 111801, arXiv:2206.05130, doi:10.1103/PhysRevLett.129.111801, hdl:11573/1658118, PMID 36154394, S2CID 252154054, retrieved 2022-09-11{{citation}}: CS1 maint: multiple names: authors list (link) <a href="https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.111801" target="_blank">https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.111801</a> <a href="#fnref:50" class="footnote-back-ref">↩</a></li>
<li id="fn:51">CUORE Collaboration; Adams, D. Q.; Alduino, C.; Alfonso, K.; Avignone, F. T.; Azzolini, O.; Bari, G.; Bellini, F.; Benato, G.; Beretta, M.; Biassoni, M.; Branca, A.; Brofferio, C.; Bucci, C.; Camilleri, J. (2022-11-23). "New Direct Limit on Neutrinoless Double Beta Decay Half-Life of $^{128}\mathrm{Te}$ with CUORE". Physical Review Letters. 129 (22): 222501. arXiv:2205.03132. doi:10.1103/PhysRevLett.129.222501. OSTI 1924468. PMID 36493444. S2CID 253876939. <a href="https://link.aps.org/doi/10.1103/PhysRevLett.129.222501" target="_blank">https://link.aps.org/doi/10.1103/PhysRevLett.129.222501</a> <a href="#fnref:51" class="footnote-back-ref">↩</a></li>
<li id="fn:52">Anton, G.; Badhrees, I.; Barbeau, P. S.; Beck, D.; Belov, V.; Bhatta, T.; Breidenbach, M.; Brunner, T.; Cao, G. F.; Cen, W. R.; Chambers, C.; Cleveland, B.; Coon, M.; Craycraft, A.; Daniels, T. (2019-10-18). "Search for Neutrinoless Double- β Decay with the Complete EXO-200 Dataset". Physical Review Letters. 123 (16): 161802. arXiv:1906.02723. Bibcode:2019PhRvL.123p1802A. doi:10.1103/PhysRevLett.123.161802. ISSN 0031-9007. PMID 31702371. S2CID 174803277. <a href="https://doi.org/10.1103%2FPhysRevLett.123.161802" target="_blank">https://doi.org/10.1103%2FPhysRevLett.123.161802</a> <a href="#fnref:52" class="footnote-back-ref">↩</a></li>
<li id="fn:53">KamLAND-Zen Collaboration; Abe, S.; Asami, S.; Eizuka, M.; Futagi, S.; Gando, A.; Gando, Y.; Gima, T.; Goto, A.; Hachiya, T.; Hata, K.; Hayashida, S.; Hosokawa, K.; Ichimura, K.; Ieki, S. (2023-01-30). "Search for the Majorana Nature of Neutrinos in the Inverted Mass Ordering Region with KamLAND-Zen". Physical Review Letters. 130 (5): 051801. arXiv:2203.02139. Bibcode:2023PhRvL.130e1801A. doi:10.1103/PhysRevLett.130.051801. PMID 36800472. S2CID 247244665. <a href="https://link.aps.org/doi/10.1103/PhysRevLett.130.051801" target="_blank">https://link.aps.org/doi/10.1103/PhysRevLett.130.051801</a> <a href="#fnref:53" class="footnote-back-ref">↩</a></li>
<li id="fn:54">Klapdor-Kleingrothaus, H. V.; Dietz, A.; Harney, H. L.; Krivosheina, I. V. (21 November 2011). "Evidence for neutrinoless double beta decay". Modern Physics Letters A. 16 (37): 2409–2420. arXiv:hep-ph/0201231. Bibcode:2001MPLA...16.2409K. doi:10.1142/S0217732301005825. S2CID 18771906. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:54" class="footnote-back-ref">↩</a></li>
<li id="fn:55">Klapdor-Kleingrothaus H.V.; et al. (2004). "Search for neutrinoless double beta decay with enriched 76Ge in Gran Sasso 1990-2003". Physics Letters B. 586 (3–4): 198–212. arXiv:hep-ph/0404088. Bibcode:2004PhLB..586..198K. doi:10.1016/j.physletb.2004.02.025. <a href="https://doi.org/10.1016%2Fj.physletb.2004.02.025" target="_blank">https://doi.org/10.1016%2Fj.physletb.2004.02.025</a> <a href="#fnref:55" class="footnote-back-ref">↩</a></li>
<li id="fn:56">Klapdor-Kleingrothaus, H. V.; Dietz, A.; Harney, H. L.; Krivosheina, I. V. (21 November 2011). "Evidence for neutrinoless double beta decay". Modern Physics Letters A. 16 (37): 2409–2420. arXiv:hep-ph/0201231. Bibcode:2001MPLA...16.2409K. doi:10.1142/S0217732301005825. S2CID 18771906. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:56" class="footnote-back-ref">↩</a></li>
<li id="fn:57">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:57" class="footnote-back-ref">↩</a></li>
<li id="fn:58">Rodejohann, Werner (2 May 2012). "Neutrino-less double beta decay and particle physics". International Journal of Modern Physics E. 20 (9): 1833–1930. arXiv:1106.1334. doi:10.1142/S0218301311020186. S2CID 119102859. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:58" class="footnote-back-ref">↩</a></li>
<li id="fn:59">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:59" class="footnote-back-ref">↩</a></li>
<li id="fn:60">Bilenky, S. M.; Giunti, C. (11 February 2015). "Neutrinoless double-beta decay: A probe of physics beyond the Standard Model". International Journal of Modern Physics A. 30 (4n05): 1530001. arXiv:1411.4791. Bibcode:2015IJMPA..3030001B. doi:10.1142/S0217751X1530001X. S2CID 53459820. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:60" class="footnote-back-ref">↩</a></li>
<li id="fn:61">Deppisch, Frank F. (2019). A modern introduction to neutrino physics. Morgan & Claypool Publishers. ISBN 978-1-64327-679-3. <a href="978-1-64327-679-3" target="_blank">978-1-64327-679-3</a> <a href="#fnref:61" class="footnote-back-ref">↩</a></li>
<li id="fn:62">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:62" class="footnote-back-ref">↩</a></li>
<li id="fn:63">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:63" class="footnote-back-ref">↩</a></li>
<li id="fn:64">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:64" class="footnote-back-ref">↩</a></li>
<li id="fn:65">Agostini, M.; Allardt, M.; Andreotti, E.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Barnabé Heider, M.; Barros, N.; Baudis, L.; Bauer, C. (19 September 2013). "Results on Neutrinoless Double-Beta Decay of 76Ge from Phase I of the GERDA Experiment". Physical Review Letters. 111 (12): 122503. arXiv:1307.4720. doi:10.1103/PhysRevLett.111.122503. PMID 24093254. S2CID 53469782. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:65" class="footnote-back-ref">↩</a></li>
<li id="fn:66">Agostini, M.; Allardt, M.; Andreotti, E.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Barnabé Heider, M.; Barros, N.; Baudis, L.; Bauer, C. (19 September 2013). "Results on Neutrinoless Double-Beta Decay of 76Ge from Phase I of the GERDA Experiment". Physical Review Letters. 111 (12): 122503. arXiv:1307.4720. doi:10.1103/PhysRevLett.111.122503. PMID 24093254. S2CID 53469782. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:66" class="footnote-back-ref">↩</a></li>
<li id="fn:67">Agostini, M; Allardt, M; Bakalyarov, A M; Balata, M; Barabanov, I; Baudis, L; Bauer, C; Bellotti, E; Belogurov, S; Belyaev, S T; Benato, G (September 2017). "First results from GERDA Phase II". Journal of Physics: Conference Series. 888 (1): 012030. Bibcode:2017JPhCS.888a2030A. doi:10.1088/1742-6596/888/1/012030. hdl:2434/557457. <a href="https://doi.org/10.1088%2F1742-6596%2F888%2F1%2F012030" target="_blank">https://doi.org/10.1088%2F1742-6596%2F888%2F1%2F012030</a> <a href="#fnref:67" class="footnote-back-ref">↩</a></li>
<li id="fn:68">GERDA Collaboration; Agostini, M.; Araujo, G. R.; Bakalyarov, A. M.; Balata, M.; Barabanov, I.; Baudis, L.; Bauer, C.; Bellotti, E. (2020-12-17), "Final Results of GERDA on the Search for Neutrinoless Double-$\ensuremath{\beta}$ Decay", Physical Review Letters, 125 (25): 252502, arXiv:2009.06079, doi:10.1103/PhysRevLett.125.252502, PMID 33416389, S2CID 221655689 <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:68" class="footnote-back-ref">↩</a></li>
<li id="fn:69">"Home | Legend". legend-exp.org. Retrieved 2025-03-08. <a href="https://legend-exp.org/" target="_blank">https://legend-exp.org/</a> <a href="#fnref:69" class="footnote-back-ref">↩</a></li>
<li id="fn:70">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:70" class="footnote-back-ref">↩</a></li>
<li id="fn:71">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:71" class="footnote-back-ref">↩</a></li>
<li id="fn:72">Anton, G.; Badhrees, I.; Barbeau, P. S.; Beck, D.; Belov, V.; Bhatta, T.; Breidenbach, M.; Brunner, T.; Cao, G. F.; Cen, W. R.; Chambers, C.; Cleveland, B.; Coon, M.; Craycraft, A.; Daniels, T. (2019-10-18). "Search for Neutrinoless Double- β Decay with the Complete EXO-200 Dataset". Physical Review Letters. 123 (16): 161802. arXiv:1906.02723. Bibcode:2019PhRvL.123p1802A. doi:10.1103/PhysRevLett.123.161802. ISSN 0031-9007. PMID 31702371. S2CID 174803277. <a href="https://doi.org/10.1103%2FPhysRevLett.123.161802" target="_blank">https://doi.org/10.1103%2FPhysRevLett.123.161802</a> <a href="#fnref:72" class="footnote-back-ref">↩</a></li>
<li id="fn:73">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:73" class="footnote-back-ref">↩</a></li>
<li id="fn:74">Nutini, I. (24 February 2020). "The CUORE Detector and Results". Low Temp Phys. 199 (1–2): 519. Bibcode:2020JLTP..199..519N. doi:10.1007/s10909-020-02402-9. hdl:11573/1410485. S2CID 213239782. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:74" class="footnote-back-ref">↩</a></li>
<li id="fn:75">Adams, D.Q. (26 March 2020). "Improved Limit on Neutrinoless Double-Beta Decay in 130Te with CUORE". Physical Review Letters. 124 (12): 122501. arXiv:1912.10966. Bibcode:2020PhRvL.124l2501A. doi:10.1103/PhysRevLett.124.122501. PMID 32281829. S2CID 209444235. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:75" class="footnote-back-ref">↩</a></li>
<li id="fn:76">Adams, D. Q.; Alduino, C.; Alfonso, K.; Avignone, F. T.; Azzolini, O.; Bari, G.; Bellini, F.; Benato, G.; Beretta, M.; Biassoni, M.; Branca, A. (April 2022). "Search for Majorana neutrinos exploiting millikelvin cryogenics with CUORE". Nature. 604 (7904): 53–58. Bibcode:2022Natur.604...53C. doi:10.1038/s41586-022-04497-4. ISSN 1476-4687. PMC 8986534. PMID 35388194. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8986534" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8986534</a> <a href="#fnref:76" class="footnote-back-ref">↩</a></li>
<li id="fn:77">Becker, Adam (2022-04-06). "CUORE team places new limits on the bizarre behavior of neutrinos". News Center. Retrieved 2022-04-08. <a href="https://newscenter.lbl.gov/2022/04/06/cuore-team-places-new-limits-on-the-bizarre-behavior-of-neutrinos/" target="_blank">https://newscenter.lbl.gov/2022/04/06/cuore-team-places-new-limits-on-the-bizarre-behavior-of-neutrinos/</a> <a href="#fnref:77" class="footnote-back-ref">↩</a></li>
<li id="fn:78">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:78" class="footnote-back-ref">↩</a></li>
<li id="fn:79">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:79" class="footnote-back-ref">↩</a></li>
<li id="fn:80">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:80" class="footnote-back-ref">↩</a></li>
<li id="fn:81">Tornow, Werner (1 December 2014). "Search for Neutrinoless Double-Beta Decay". arXiv:1412.0734 [nucl-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:81" class="footnote-back-ref">↩</a></li>
<li id="fn:82">"KamLAND-ZEN". Kavli IPMU-カブリ数物連携宇宙研究機構. 16 May 2014. Retrieved 17 July 2020. <a href="https://www.ipmu.jp/en/research-activities/research-program/kamland" target="_blank">https://www.ipmu.jp/en/research-activities/research-program/kamland</a> <a href="#fnref:82" class="footnote-back-ref">↩</a></li>
<li id="fn:83">Gando, A.; Gando, Y.; Hachiya, T.; Hayashi, A.; Hayashida, S.; Ikeda, H.; Inoue, K.; Ishidoshiro, K.; Karino, Y.; Koga, M.; Matsuda, S.; Mitsui, T.; Nakamura, K.; Obara, S.; Oura, T. (2016-08-16). "Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen". Physical Review Letters. 117 (8): 082503. arXiv:1605.02889. Bibcode:2016PhRvL.117h2503G. doi:10.1103/PhysRevLett.117.082503. ISSN 0031-9007. PMID 27588852. S2CID 204937469. <a href="https://doi.org/10.1103%2FPhysRevLett.117.082503" target="_blank">https://doi.org/10.1103%2FPhysRevLett.117.082503</a> <a href="#fnref:83" class="footnote-back-ref">↩</a></li>
<li id="fn:84">"KamLAND-ZEN". Kavli IPMU-カブリ数物連携宇宙研究機構. 16 May 2014. Retrieved 17 July 2020. <a href="https://www.ipmu.jp/en/research-activities/research-program/kamland" target="_blank">https://www.ipmu.jp/en/research-activities/research-program/kamland</a> <a href="#fnref:84" class="footnote-back-ref">↩</a></li>
<li id="fn:85">"Investigating the Neutrino Mass Scale with the ultra-low background KamLAND-Zen detector". phys.org. Retrieved 17 July 2020. <a href="https://phys.org/news/2016-08-neutrino-mass-scale-ultra-low-background.html" target="_blank">https://phys.org/news/2016-08-neutrino-mass-scale-ultra-low-background.html</a> <a href="#fnref:85" class="footnote-back-ref">↩</a></li>
<li id="fn:86">KamLAND-Zen Collaboration; Abe, S.; Asami, S.; Eizuka, M.; Futagi, S.; Gando, A.; Gando, Y.; Gima, T.; Goto, A.; Hachiya, T.; Hata, K.; Hayashida, S.; Hosokawa, K.; Ichimura, K.; Ieki, S. (2023-01-30). "Search for the Majorana Nature of Neutrinos in the Inverted Mass Ordering Region with KamLAND-Zen". Physical Review Letters. 130 (5): 051801. arXiv:2203.02139. Bibcode:2023PhRvL.130e1801A. doi:10.1103/PhysRevLett.130.051801. PMID 36800472. S2CID 247244665. <a href="https://link.aps.org/doi/10.1103/PhysRevLett.130.051801" target="_blank">https://link.aps.org/doi/10.1103/PhysRevLett.130.051801</a> <a href="#fnref:86" class="footnote-back-ref">↩</a></li>
<li id="fn:87">Baudis, Laura (2023-01-30). "Probing Majorana Neutrinos". Physics. 16 (5): 13. arXiv:2203.02139. Bibcode:2023PhRvL.130e1801A. doi:10.1103/PhysRevLett.130.051801. PMID 36800472. S2CID 247244665. <a href="https://physics.aps.org/articles/v16/13" target="_blank">https://physics.aps.org/articles/v16/13</a> <a href="#fnref:87" class="footnote-back-ref">↩</a></li>
<li id="fn:88">"Home | Legend". legend-exp.org. Retrieved 2025-03-08. <a href="https://legend-exp.org/" target="_blank">https://legend-exp.org/</a> <a href="#fnref:88" class="footnote-back-ref">↩</a></li>
<li id="fn:89">"The MAJORANA Neutrinoless Double-beta Decay Experiment | MAJORANA". www.npl.washington.edu. Retrieved 2025-03-08. <a href="https://www.npl.washington.edu/majorana/majorana-experiment" target="_blank">https://www.npl.washington.edu/majorana/majorana-experiment</a> <a href="#fnref:89" class="footnote-back-ref">↩</a></li>
<li id="fn:90">Licciardi, Caio (2017). "Recent Results and Status of EXO-200 and the nEXO Experiment". Proceedings of 38th International Conference on High Energy Physics — PoS(ICHEP2016). Vol. 282. p. 494. doi:10.22323/1.282.0494. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:90" class="footnote-back-ref">↩</a></li>
<li id="fn:91">Licciardi, Caio (2017). "Recent Results and Status of EXO-200 and the nEXO Experiment". Proceedings of 38th International Conference on High Energy Physics — PoS(ICHEP2016). Vol. 282. p. 494. doi:10.22323/1.282.0494. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:91" class="footnote-back-ref">↩</a></li>
<li id="fn:92">Adhikari, G; Al Kharusi, S; Angelico, E; Anton, G; Arnquist, I J; Badhrees, I; Bane, J; Belov, V; Bernard, E P; Bhatta, T; Bolotnikov, A; Breur, P A; Brodsky, J P; Brown, E; Brunner, T (2022-01-01). "nEXO: neutrinoless double beta decay search beyond 10 28 year half-life sensitivity". Journal of Physics G: Nuclear and Particle Physics. 49 (1): 015104. arXiv:2106.16243. Bibcode:2022JPhG...49a5104A. doi:10.1088/1361-6471/ac3631. ISSN 0954-3899. S2CID 235683381. <a href="https://iopscience.iop.org/article/10.1088/1361-6471/ac3631" target="_blank">https://iopscience.iop.org/article/10.1088/1361-6471/ac3631</a> <a href="#fnref:92" class="footnote-back-ref">↩</a></li>
<li id="fn:93">"NuDoubt++ Experiment". NuDoubt++. 1 August 2024. Retrieved 1 October 2024. <a href="https://nudoubt.uni-mainz.de" target="_blank">https://nudoubt.uni-mainz.de</a> <a href="#fnref:93" class="footnote-back-ref">↩</a></li>
<li id="fn:94">Böhles, M.; et al. (NuDoubt++ Collaboration) (2024). "Combining Hybrid and Opaque Scintillator Techniques in the Search for Double Beta Plus Decays". arXiv:2407.05999 [hep-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:94" class="footnote-back-ref">↩</a></li>
<li id="fn:95">Böhles, M.; et al. (NuDoubt++ Collaboration) (2024). "Combining Hybrid and Opaque Scintillator Techniques in the Search for Double Beta Plus Decays". arXiv:2407.05999 [hep-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:95" class="footnote-back-ref">↩</a></li>
<li id="fn:96">Böhles, M.; et al. (NuDoubt++ Collaboration) (2024). "Combining Hybrid and Opaque Scintillator Techniques in the Search for Double Beta Plus Decays". arXiv:2407.05999 [hep-ex]. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:96" class="footnote-back-ref">↩</a></li>
<li id="fn:97">"CMS-PAS-BPH-21-005". cms-results.web.cern.ch. Retrieved 2023-07-20. <a href="https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/BPH-21-005/index.html" target="_blank">https://cms-results.web.cern.ch/cms-results/public-results/preliminary-results/BPH-21-005/index.html</a> <a href="#fnref:97" class="footnote-back-ref">↩</a></li>
<li id="fn:98">"Flavoured Mysteries: searching for the tau lepton's 3 muon decay | CMS Experiment". cms.cern. Retrieved 2023-07-20. <a href="https://cms.cern/news/flavoured-mysteries-searching-tau-leptons-3-muon-decay" target="_blank">https://cms.cern/news/flavoured-mysteries-searching-tau-leptons-3-muon-decay</a> <a href="#fnref:98" class="footnote-back-ref">↩</a></li>
</ol>

Neutrinoless double beta decay open-in-new

Neutrinoless double beta decay