PoS(FPCP2016)033 ). νββ http://pos.sissa.it/ ∗ [email protected] Measurements of this hypothetical decay could determine theand Dirac/Majorana possibly nature their of absolute neutrinos, mass. Thus far,current-generation only and limits on next-generation this experiments process is have reported, beentechniques with set. which an The can status emphasis be of on used the to diverse search for this rare process. Speaker. Here we review the status of experimental searches for neutrinoless double beta decay (0 ∗ Copyright owned by the author(s) under the terms of the Creative Commons c Flavor Physics and CP Violation, 6-9 June 2016 Caltech, Pasadena CA, USA Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). Author Indiana University E-mail: Joshua Albert Neutrinoless Double Beta Decay PoS(FPCP2016)033 , and µ , e Joshua Albert fermions which only 2 / 1 ], and all neutrinos appear 1 [ et al. decay spectra, but no measurement. Cos- β 1 . The other possibility is known as inverted ordering or inverted τ , and µ , decay measurements may be capable of measuring the small absolute mass. e β The third question is that of CP-violation. It is possible that neutrinos and anti-neutrinos may Neutrino helicity was first measured in 1958 by Goldhaber The first and the third of these questions can be answered using long-baseline neutrino oscil- If we ignore clearly Beyond Standard Model (BSM) phenomena (such as a fourth neutrino The second question is that of the absolute neutrino mass. There are upper limits on the While neutrinos have been a part of the Standard Model since the Model’s formulation, the , correspond to the three known charged leptons. oscillate differently, and thismatrix. difference is Finally, there parameterized is by theparticles, a question or the of cp-violating same whether phase particle, neutrinos with in and different anti-neutrinos the helicities. are mixing actually distinct lation experiments. The second and fourthprocess cannot. called neutrinoless However, if double neutrinos beta areand decay Majorana fourth must particles, questions exist, a would and, be if answered. it could be measured, the second τ which is sterile), there are fourthe major mass questions ordering. remaining The about neutrino how neutrinos massand behave. squared we differences The are know first known that is from there oscillationmass is experiments, splitting a is small between mass the splitting lighterwhich and two the a neutrinos lighter or large two the neutrinos mass have heavier splitting,normal the two but smaller hierarchy. is whether mass This unknown. the splitting "normal" The is small refers ordering known to in of as how the the this normal charged splitting ordering, leptons would or be similar to that of the masses mology experiments offer some model-dependentin estimates the and future, limits tritium on the neutrino mass, and, to be left-handed. Allmass energy anti-neutrinos is appear much as lesshighly right-handed. than relativistic), their their As kinetic helicity neutrinos energy andmaximally are in chirality CP-violating, very all are so light neutrino very left-handed detections, (their closely neutrinosand so coupled. right-handed would they anti-neutrinos only would The are only be weak always be allowedcharge allowed interaction to to is opens couple couple to the positrons. to possibility The electrons, different lack that of helicities. neutrino neutrinos Fundamentally and distinct anti-neutrinosparticles neutrinos where could and the be anti-neutrinos only are theModel distinction termed same Lagrangian “Dirac”, is particles in and spin different with are ways,mass and termed (the have lightness “Majorana”. different of possible which These is mechanisms puzzling fit to to acquire into theorists). neutrino the Standard absolute neutrino mass, set by careful measurement of hierarchy. interact via the weakobserved interaction anti-neutrinos are (and right-handed. gravity). From oscillationhave All a experiments, we small observed have but neutrinos learned non-zero that are mass,mixing they matrix, that left-handed, and there and that are all all 3 3 mass real and mixing flavor angles eigenstates, are non-zero. connected through The three a neutrino flavors, way in which they fit is not exactly clear. We know neutrinos are spin- Review of Neutrinoless Double Beta Decay 1. Introduction 1.1 The State of Neutrino Knowledge PoS(FPCP2016)033 and νββ νββ νββ 29 Joshua Albert resolution )spectrum ν (0 ββ (Q is the endpoint) e decays from background -axis is sum of electron kinetic 1.0 x 1.10 νββ /Q e years), experiments are typically 1.00 K ]. 2 decays could be a valid signal. To 25 ), there is also a theoretical process, ) is forbidden or highly suppressed, 0.8 e eexperiments,notablyGe,haveamuch 10 on kinetic energies K ν 0.90 , is that the entire Q-value of the decay 0
)decays(solidcurve).The 30 20 10
∼ νββ
+ x10 ν νββ -6 (0 − νββ e ββ 0.6 /Q + e (solid) spectra. The p K ) violates lepton number conservation, and so is 2 − e → . From reference [ 2 νββ n 0.4 spectrum can be clearly distinguished from the 0 + p νββ 2 ), which must exist if neutrinos are massive (we know they in the figure inset). All spectra are convolved with an energy νββ 6 → − 0.2 n (10 νββ 2 − (dotted) and 0 )normalizedto1(dottedcurve)and ν 0.0 νββ . (2 1 2.0 1.5 1.0 0.5 0.0 ββ ) could still be allowed, and in fact has been observed for several nuclei and e of 5%, representative ofbetter several energy resolution. experiments. However, som is normalized to 10 Figure 1: Illustration of the spectra of the sum of the electr Double Beta Decay for the ν 2 -axis is an arbitrary normalization. A 5% energy resolution has been convoluted in, and + y − e 2 + Illustration of the 2 p 2 is shown in Figure Due to the rarity of this decay (half lives of at least In addition to this two-neutrino double beta decay (2 Double beta decay is a second order weak interaction which occurs for certain even-even → n νββ the ratio of normalizations for these two curves is not to scale, though the upper right inset shows the 0 energies, and the spectrum at a more realistic scale relative to 2 designed to have very lowachieve backgrounds, this so requires just an a extremelythe few clean primary 0 (radiopure) background; detector, as anenergy radioactive underground resolution, decays laboratory, to are ensure to typically that reduceline; the and the 2 additional effect techniques, of beyond justprocesses. cosmic energy, Additionally, rays; to a large distinguish good quantity 0 ofenrichability, the candidate and isotope is Q-value required. of Thestands these cost, out availability, candidate as the isotopes obvious choice. vary considerably, and no single isotope Figure 1: zero-neutrino double beta decay (0 are) and Majorana. This process (2 is predicted in others. nuclei. In these cases, ordinary beta decay ( Review of Neutrinoless Double Beta Decay 1.2 Double Beta Decay typically because the daughter nucleus is(2 heavier than the initial one. However, double beta decay of particular interest, as nolepton other known number process of can zero, do some that.signature lepton-number of violating Assuming this process the process, universe must which began exist. distinguishesis with it The a carried from main 2 away experimental with the0 electrons. A plot of the sum of electron kinetic energies for 2 PoS(FPCP2016)033 for (1.1) (1.2) νββ ββ m , assuming Joshua Albert rays are well ββ , and a matrix γ ν m 0 G . Detailed measure- νββ ) is a function of the mixing ma- ββ 100 keV. Penetrating m , ∼ 2 ββ
2 m ei 2 U
i ν m 0 1 3 2 MeV. Background reduction requires extensive M = ∑
i 3
ν ∼ 0 = G ββ = m 2 ν / 1 0 1 t experiment can be estimated with three metrics. First is sensitiv- model is mediated by light neutrino exchange, various BSM theories shielding is needed, but the shield must be effective against neutrons. is inversely related to the square of the neutrino mass by γ νββ νββ are often compared to searches for dark matter weakly interacting massive νββ rays, and extremely strict radiopurity requirements to avoid backgrounds from observation could be made. Discovery potential generally requires a stronger which includes a range between the extreme matrix elements from a variety νββ γ σ ββ m . This matrix element must be computed separately for each isotope, and there are or 5 ν 0 rate is zero. Second is discovery potential, which is a measure of the smallest σ M require Majorana neutrinos and lepton number non-conservation. νββ The potential of a 0 Searches for 0 The half life for 0 While the simplest 0 νββ ity (the most commonly cited), which is a measure of what limits can be set on 2. Experimental Searches ment of the angular distributions ofan the daughter extent, electrons but it may help would distinguish becontributions between very models difficult from to to supersymmetric rule particles. out these0 other Regardless mechanisms, of many of the which exact involve mechanism, all models of the 0 which a 3 background understanding (understanding the origin ofstraints all backgrounds on and them), having measured while con- Finally, sensitivity there is is usually the optimized issue by of minimizing cost backgrounds in and general. feasibility. This last one is difficult to quantify, but very may introduce other processes which, on the surface, look like standard 0 particles (WIMPs), as the detectors are similar, but with different optimizations. Searches for 0 of computational techniques. Comparisonstopes between are limits complicated by from this, experiments butadvances using these in systematic different computational uncertainties iso- nuclear should physics. decrease in the future with Review of Neutrinoless Double Beta Decay decays involve a focus on electronshielding recoils near against above this energy, so less The less stringent radiopurity requirements andexperiments lack can of isotopic iterate enrichment more means quickly thatmizations, from dark we one matter are generation not to yet at theexcel a next. in point both where Given types it these is of different economical searches. opti- to design a single experiment which can where defines the Majorana neutrino mass. This Majorana mass ( element considerable theoretical uncertainties on it.to Because of a this, limit half life on limits are typically converted primordial radionuclides. The signaltors of are WIMPs optimized would for be low thresholds, a with low a energy focus nuclear around recoil, so detec- trix terms, and, duemass to eigenstate. complex The phase other terms factors, in may the expression be include smaller a than phase space the factor actual lightest neutrino PoS(FPCP2016)033 to rays. νββ ββ 1.53% γ . It is m ∼ or β νββ Joshua Albert s at the 0 of the ionizing γ dx / ), and MS events are dE experiments. Emphasis νββ νββ Xe) to search for 0 5 : 1 rejection of 136 ∼ ]. 3 rays), they can be resolved individually, decays and depositions from γ α decays (mainly 2 β . All components located within the lead shield 2 4 experiments are being designed to have sensitivity to 1 cm. The energy of the events are reconstructed through a linear νββ ∼ 175 kg of enriched xenon (80% ∼ rays originating externally quite effectively. The TPC vessel was constructed Compton scatter events. This provides γ γ Signal/background discrimination is achieved in several ways, beyond simple calorimetry. The The EXO-200 (Enriched Xenon Observatory) experiment is a liquid xenon time projection The strengths of these programs lie in the detailed interaction information from the TPCs, as As a noble gas, xenon can be highly purified through the use of a heated getter, so the xenon What follows is an incomplete list of current and proposed 0 more likely from were screened by radioassay and selected for radiopurity [ particle, allowing for excellent discrimination between The multiplicity of charge depositions(MS) is events, used where to SS split events the are data more into likely single-site from (SS)Q-value, and and multi-site allows for better identification of background sources. Interaction positions are also ratio of the scintillation and ionization signals gives information about the chamber (TPC) utilizing well as the monolithic naturetric field of (374 the V/cm xenon for volume.through phase the I, xenon, The 2011-2014) they over TPC produce the prompt works scintillationtillation liquid by light light xenon. and putting is a When a immediately cloud charged of detected uniform particlesphotomultipliers freed (by move elec- electrons. (SiPMs) avalanche in The photodiodes scin- nEXO), (APDs) and in thethe EXO-200, freed detector by electrons anode silicon will where drift this tocollection ionization the signals signal crossed at will wireplanes the be at anode detected.position with of By the all combining time the charge for clusters induction thesitions and can ionization occur be cloud (as determined. to is drift common Additionally, to for if the Compton multiple scatters anode, separate from the charge 3D depo- volume is almost entirely free of radioactive contaminants.it shields The xenon itself is from a dense high-Zout material, so of copper (chosencopper for cryostat, its and radiopurity). a lead shield. Iton The is 4 clean room surrounded sides where by by thediagram a detector scintillating is of clean muon located the cryogenic veto is detector also panels fluid setup surrounded is to (HFE), shown identify a in and Figure reject cosmogenic backgrounds. A has been placed onprojected explaining sensitivities. the diverse design choices, and experimental results,2.1 rather than EXO-200/nEXO presently located underground atThe the experiment Waste has Isolation been taking Pilot data Plantwould since use (WIPP) 2011. 5 The in tonnes planned of New next-generation enriched Mexico, experiment, xenon nEXO, and USA. be located deeper underground, likely at SNOlab. for phase I data. with a position resolution of combination of the detected scintillation and ionization signals, with energy resolution of Review of Neutrinoless Double Beta Decay important. Most tonne-scale 0 cover all possible inverted hierarchy neutrinoand the masses, certainty but that the they will costs perform ofbetween as building designed, proposals. are these not experiments, yet known, and likely vary considerably PoS(FPCP2016)033 years), ]. 3 Q-value) 25 attenuation 10 Joshua Albert γ backgrounds. × νββ γ 9 . Xe 1 136 PANELS > window s VESSEL 2 years, corresponding to to virtually zero. VETO 2 νββ / ± ] in the Waste 0 1 LXe DOUBLE-WALLED CRYOSTAT 25 t analysis from EXO-200 is 6% at the SHIELDING 21 . yr (90% C.L.) in 1 10 Rn) chains. These are due to νββ 25 = LEAD × 10 47’34”W). 222 E νββ 1 / ⇥ . E 4 . 1 s 6 is defined by a > = U (also 2 nbb 2 nbb / 0 νββ 22’30”N 103 1 / T 0 1 238 t FOOT AND 5 Th and –5– JACK 232 ]) matrix element calculation. be beyond reach. 0 23 nbb ] (NSM [ 22 limit above corresponds to a 90% C.L. Majorana mass sensitivity of 109 meV 2 / AND 1 Cutaway view of the EXO-200 setup, with the primary subassemblies identified. Xe. The analysis set a limit of T 137 FILTER . Improved self-shielding, continued emphasis on radiopurity, deeper under- 5 PUMPS HV FEEDTHROUGH END Figure 2. . Based on the fit, the primary backgrounds (SS signals near the 0 3 The outermost shielding layer, outside the outer vessel of the cryostat, consists of 25 cm of A cosmic-ray veto counter made of plastic scintillators surrounds the cleanroom housing the A rendering of the EXO-200 detector and surrounding systems. From reference [ 2 year hiatus due to underground access issues, EXO-200 is now taking data again. and 450 meV. The limit is slightly worse than the sensitivity ( FRONT ELECTRONICS rays emitted from decays in the VACUUM 4 around the end-point and 40two background years. events This are estimate expected waswhile to made the accumulate using final in a detector fiducial such design mass asensitivity. has of window The 110 140 in kg kg (200 of kg active(135 with Xe, meV) 70% requiring using efficiency), a the longer QRPA [ time to reach the same lead. The low-noise front end electronics areto located outside the of the detector lead shielding through andsimplicity thin are and connected polyimide accessibility of cables. room temperature, This conventional construction choice electronics. trades somerest increased of the noise detector. for EXO-200 the Isolation is Pilot Plant located (WIPP) at near a Carlsbad, depth New of Mexico (32 1585 m2.2 water Design equivalent sensitivity [ and estimated backgrounds While the measured performance of EXO-200 utilizingdata substantial sets low-background will and calibration be the subjectparameters of for a the future detector paper, performance herevalidity and we of background. provide such Initial sensitivity parameters. data figures taking assumingend Using roughly design point, the confirms EXO-200 expected the was energy designed resolutiontwo to of years reach of a live sensitivity time, of should the 0 ∼ − γ 190 Figure 2: < After a The nEXO experiment will build on the strengths of EXO-200. It is being designed to have a The energy spectra after the fit to data from the most recent 0 ββ giant, monolithic active volume of pure xenon. The detector center will be at least 7 due to an upward fluctuation in background counts near the Q-value. Upgraded electronics, new analysis techniques,prove and the a physics radon reach reduction of systemresearch are EXO-200 and expected for design to this work im- is new ongoing run for (called nEXO. phase II). While this is proceeding, lengths from the TPC wall, making theSee center Figures of the detector nearly freeground of location, external improved energy andto spatial have resolution, sensitivity through and the larger inverted mass hierarchyare of should ongoing neutrino allow for masses. for barium Additionally, nEXO research tagging efforts daughter technology, which barium ions. would allow This is for not spectroscopicsuccessfully, strictly would identification part allow of of for the a nEXO reduction collaboration of plan, all but, backgrounds if except demonstrated 2 fit, discriminating between backgroundscorrelations originating between from signals can outside be the used to TPC identify and decay chains inside, and time shown in Figure come from Review of Neutrinoless Double Beta Decay contamination in the TPC vessel and indecay more of distant shielding. cosmogenic An additional 20% comes fromm beta PoS(FPCP2016)033 ]) has 5 Joshua Albert Xe dissolved in liquid scintillator. 136 would be a sharp peak in SS data at the Q-value νββ 6 Ag, an isotope released by the Fukushima nuclear accident in 2011. ] for more details. 4 m 110 Final fit to EXO-200 data with 477.6 days livetime. Single-site (SS) data is shown in the upper m thick IB. The KamLAND experiment (which successfully studied reactor neutrino oscillations [ KamLAND-Zen began data taking in 2011, though the initial data taking was hampered by µ contamination by an unexpected background,mined which the to KamLAND-Zen be collaboration decay has of deter- of 2458 keV. See reference [ 2.2 KamLAND-Zen been repurposed by adding a balloon toThe the xenon middle balloon containing (inner balloon,pure IB, scintillator 1.5 (6.5 m m radius), radius) which isthe is surrounded outside surrounded by of by a which a mineral the oil largerthrough buffer PMTs balloon volume vacuum are filled (9 distillation, mounted. m with radius) yielding The on a liquidactive very scintillator veto. large, has very been Within clean very the volume25 highly 6.5 which purified m can radius also scintillator serve as balloon, an the only non-scintillating region is the Figure 3: panel, and multi-site (MS) dataalso in shown. the The lower one. fitevent to position) The for data fitted SS was PDFs and performed for MS simultaneously signal data. in and The energy various signal backgrounds and for are standoff 0 distance (a function of Review of Neutrinoless Double Beta Decay PoS(FPCP2016)033 Q-value, Joshua Albert . Using a fit 6 νββ cm cm 46 U series) decays from the IB. Energy ] are shown in Figure 6 238 cm cm 7 130 Bi (from the was the leading background near the 0 214 Ag background had been significantly reduced by the pu- νββ m 110 years. Upper panels are SS events, and lower panels are MS events. Each column 27 C from muon spallation and 10 10 × Simulation of nEXO signal and backgrounds, corresponding to 5 years simulated data with Xe was performed. The Renderings of the EXO-200 TPC (right) and nEXO TPC (left), to scale. Note that the nEXO 6 . enr 6 = SS MS 2 νββ / 0 1 and event position data from the most recent publication [ Following a purification campaign, aof new 90% run with 534.5 daysrification of campaign, live-time and (phase decreased II) significantly andthe 380 over second kg the half course of of thefollowed by the phase II phase data, II 2 data taking. For corresponds to a listed xenon mass,ter where of the the data comes detector. from Thus, aof the cylindrical xenon right-most volume furthest of plot that from shows mass nearly anyidentifying in no and non-xenon the constraining backgrounds cen- masses. backgrounds, near while the This the Q-value demonstrates inner for xenon how the is the 500 nearly kg outer background-free. xenon is very useful for Figure 5: Figure 4: design removes the central cathode to increase the size of the monolithic xenon volume. Review of Neutrinoless Double Beta Decay t . - d 4 o w ± yr st- for Ag us- sin νββ νββ 25 1 m 0 0 − 165 . 10 8MeV 110 . Xe 4 × day) =2 · 2 136 . 2 9 Ag uniformly 165) meV ν / Bi background 2 signal indicates 1 – m > T
222
10
Xe is
− 10 10 10 We assess the systematic uncertainty of the FV Events/0.05MeV Events/0.05MeV Events/0.05MeV 10 0MeV . FIG. 2: (a) Energy spectrum of selected m-radius spherical volume inbackgrounds, Period-2 the drawn together with b limit for 3 cay rates for Period-1 and Period-2 are within the statistical uncertainties. The resolution tail and decays is an important background in the tial a3.0%systematicerroronFV radial-vertex-bias in the source calibration data. Otherof s systematic uncertainty such astor xenon energy mass scale (0.8%), (0.3%) detec- and efficiency (0.2%), and tail events are reproduced in on the study of uniformly distributed richment (0.09%), only have auncertainty small is contribution; the 3.1%. overa The measured assuming the Gaussian resolution, indicatingtion from that energy a reconstruction contri failures is negligible. result is consistent with ourdata, previous result based on Phase 136 65 (
8
Simulated Simulated Bi Event Rate (Events/Bin) Rate Event Bi -
2 < 214 = Bi re- experiment. For more information on this analysis, and )in dius 6 5 4 3 2 (c) τ . This is another example of how a large monolithic Bi is 214 , 10 1 10 10 10 10 10 ββ Po (b) ose the γ K Th 210 214 m strate the 40 experiments. The main weaknesses of the KamLAND- 97 yr oints) and . 232 νββ Uconcen- Bi+ νββ Kr+ U+ Ag 210 85 238 =2 Total + + 238 window), and window). The analysis. (b) An 110m Spallation τ νββ vertex distribution , ββν 3 window). The nor- γ νββ νββ νββ R 2 0 0 ( ( + νββ Xe 2 Cs (0.662 MeV 3 β 0 ). (c) Data 136 Spallation IB/External 0 137 years was set, with a sensitivity of Cs ( ) (the 7MeV 0MeV 2 . . 26 , position reconstruction allows for regions of low backgrounds to be 2 2 134 ,z < window. The curves show the best- (R/1.54m) (m 6 Cs to 2 (a) 2.3 < E < 2.7 MeV 2.3 < E (a) 10 134 +Y 7MeV 53 m . 2 . × νββ Visible Energy (MeV) Energy Visible 2 1 0 X
10 10 10
10 10
− −
4yr Bi in the region
There are presently two major experimental efforts, MAJORANA and GERDA, searching for The GERDA (GERmanium Detector Array) experiment is located underground at Gran Sasso As seen in Figure
. Background sources external to the Xe-LS are dominated Z (m) Z Events/0.05MeV Events/Bin tration in the nylon film is 0.16 ppb assuming secular equilib observed rate of adaughterof 43 from the Fukushima-I reactor accident in 2011 [8]. observed activity ratio of 214 the energy region by radioactive impurities on thefit IB to film. events reconstructed Based aroundthe oninant IB, a background we spectral find sources that are the dom- example of the energy spectrum in a volumeof bin candidate with events in high the fit background model components. background events around thegion lower in part (a) at of the IB film (shaded malization of thethick MC dashed event lines histogram indicate isspherical the volume, arbitrary. shape respectively. of Theshape The the solid of thin IB the dashed and equal-volume lines the2-m-radius spherical 1-m-ra illu spherical half-shells fiducial which volume comp for the FIG. 1: (a) Vertex distribution ofreproduced candidate events (black p togram) for νββ 0 National Laboratory (LGNS) incrystal Italy detectors. and The featuresperiment detectors 35 (2011-2013) are used kg the shielded argon of as within a instrumenteduses passive a shield enriched instrumented and liquid germanium for argon argon cooling, to though volume. phase serve II (ongoing) as Phase an I of active the veto. ex- The phase I analysis resulted in limits of 2.3 Germanium Experiments manium detectors are a matureprojects technology differ with in shielding excellent techniques energy and resolution some ( other design choices. poor energy resolution (4.5% at theruns Q-value with for KamLAND-Zen their most to recent useenergy data). a resolution There larger, with are cleaner higher plans balloon for quantumcones. with future efficiency more PMTs, An xenon, a imaging and new systemtarget to sensitivity liquid to improve for scintillator, provide this the and future multiplicity upgraded reflective discrimination detector (known is as also KamLAND2-Zen) is being developed. The Figure 6: between 2.3 and 2.7 MeV) area plotted color as scale. a function The ofdotted IB position. line. is Simulated Thin indicated dotted by lines thesecond indicate half solid position of black bins phase line, used II) in andreference events fitting. the within [ On the inner the inner 1 right, 1 m the m sphere energy radius is of are indicated period shown, 2 along by (the with a fitted thick backgrounds. From isolated, leading to stronger limitsactive on volume 0 can be valuableZen for approach 0 are the lack of multiplicity discrimination (to reject Review of Neutrinoless Double Beta Decay based on event position, energy,limit and of time, after significant cuts to remove spallation products, a corresponds to Majorana neutrino mass of the strongest limit on this mass of any 0 see reference [ t t l - e e d t- le o- en er. on on Po Co, han The -ray )that flight γ 60 214 decay s) de- µ + Xe with ,slightly Bi- ββ β 5day 136 . 214 =237 τ Bi and delayed of =5
Po rejection ef- (MeV) C, and -rays from
τ
E 214 γ 212 Po (
12
!
-rays from the cap-
/
γ Rn ( 01)%
Bi-
214
.
0
222
3%
212
Bi- .
7 ± 214 ∼ 95 . σ (99 ,confirmedwithhigh-Rndata.(iv) ’s [6] are discarded. (v) Poorly recon- s) decays which occur within a single γ µ events is less than 0.1%. Bi, a daughter of 3)% ± 214 ββ =0.4 Cs radioactive sources, τ Ag by more than a factor of 10. We report on the (95 137 ’s identified by a delayed coincidence of positrons m e Po ( ν 110 212 Bi- Po decay-events to be less than 1.9ms and 1.7m, respec- Following the end of Phase-II, we performed a detector We apply the following series of cuts to select Ge, and 200-ns-long data acquisition event window. Therefore, the Reactor ficiency is outer LS, which is correctedthe in non-linearities the for detector simulation, both whi theobserved LS energy regions resolution is are consistent. of the energy scale isnonlinear less energy than response 1.0%. dueCherenkov Uncertainties to from light scintillator the quenching production an tions. are The light constrained yield of by the Xe-LS the is 7% lower calibra- than that of the was introduced during the Xe-LSdata purification. indicate that The the calibrati reconstructed energy1.0% varies throughout by less the t Xe-LS volume, and the time variation ∼ cut is augmented with a double-pulseton identification in arrival the time ph distribution afterfrom subtracting the the time vertex of to each PMT. The 212 decays, where thecut, inefficiency and is the dominatedods uncertainty by with is the high estimated timing Rn from levels. analysis of The peri- same cut is not effective for ture of spallation neutrons on protons and cays are eliminated bythe a time and delayed distance coincidence between tag, the requiring prompt emissions from ter than 1.0 cm forter. events occurring within The 1 energy m of scale the was IB cen- studied using calibration campaign usingvarious radioactive sources positions deployed alongposition a the reconstruction central — determined axisphoton from of arrival the the times scintillati — IB.tions to reproduces The within the event 2.0 cm; known the source reconstruction posi- performance is be the whole Xe-LS volume. 214 tively. The cut removes LS was purified by vacuum distillationalso during purified each a cycle. mix We oftion recovered and and refining new Xe withXe through a was distilla- heated dissolved zirconium into the getter.started purified Finally, LS. the In th second December science 2013,tion we run of (Phase-II), and found a reduc structed events are rejected.avertex-time-chargediscriminatorwhichmeasureshowwel These eventsthe observed are PMT tagged time-charge distributions using expected agree based with on thos theinefficiency reconstructed for vertex [7]. The total cu analysis of the complete Phase-IIDecember data 11, set, 2013, collected betwe andtime is October 534.5 27, days after 2015.This muon corresponds spallation to The cuts, an total discussed exposure lat live- of 504kg-yr of 68 and neutron-capture worse relative to Phase-IPMTs. due to an increased number of dead after muons are rejected. (iii) events: (i)of The the reconstructed detector center. vertex must (ii) Muons be and within events 2.0m within 2 ms ]. Th 23 , 228 15 . t [ns] t [ns] 3 82000 82000 GERDA 13-06 surface (at ra- n+ 81800 81800 by itself is not a useful electrode event (bottom left) A/E p+ 81600 81600 ) only holes contribute to the signal 3 erent shapes since electrons and holes 81400 81400
PoS(FPCP2016)033↵ shows examples of current pulses from lo- Tl decay. The double escape peak (DEP, at 3 208 events close to the bore hole (at radius 6 mm) + 81200 81200 n MSE and the pulse asymmetry visible in Fig p+ erent methods have been investigated. The main one ]. ↵ - Th
> 23
di uses an artificial neuralevents; the network second to one identifydiscriminate relies single on between site a SSE likelihood likeevents; method events the to and third background A/E is based on the correlation between 2.3 Pulse shape calibration Common to allis methods the and use for oftest both calibration the data, detector performance taken types nition once and per programs – week, – in to calibration to case spectrum train of the contains patternfrom algorithm. the a recog- The peak1592.5 at keV) of 2614.5 this keV full line energy is peaks used (FEP, e.g. asescape at proxy 1620.7 peak keV) for (SEP, or at SSE the 2103.5The while single keV) are disadvantage dominantly of MSE. the DEP is that the distribution signal. Fig. calized energy depositions. These simulations haveperformed been using the software describedFor in energy Refs. [ depositions closedius 38 to mm the in Fig. and the current peaksface at the end.the In current contrast, peaks for earlier sur- inmon time. to BEGe This detectors. behavior Pulses is ina com- the bulk variety volume of show di contribute. Consequently, variable for coaxial detectors. Instead three significantly 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 γ a.u. a.u. a.u. a.u. , 228 15 2 . ] νββ t [ns] t [ns] t [ns] t [ns] / 3 0 1 22 has 100 1. t , A/E 82000 82000 82000 82000 ⇠ usion < GERDA 13-06 21 ↵ surface (at ra- , is ]. A/E 20 A Charge Current n+ 15 Joshua Albert 81800 81800 81800 81800 by itself is not a useful ]. The right panel 7 electrode event (bottom left) particles penetrat- A/E p+ 81600 81600 81600 81600 ]. 8 ]. The bottom right trace -like) and multi-site ( ) only holes contribute to the signal 19 3 β and and results in a low side erent shapes since electrons and holes ] and in liquid argon [ 81400 81400 81400 81400 ↵ A 16 shows examples of current pulses from lo- layer [ Tl decay. The double escape peak (DEP, at 3 Te. At very low temperatures, 208 distribution while events close to the n+ events close to the bore hole (at radius 6 mm) + + 81200 81200 n 81200 81200 p 130 SSE MSE and the pulse asymmetry visible in Fig p+ A/E erent methods have been investigated. The main one contact but the gradient is lower and hence in ↵ shows a candidate event.
escape peak (SEP, at 2103.5The keV) are disadvantage dominantly of MSE. the DEP is that the distribution signal. Fig. calized energy depositions. These simulations haveperformed been using the software describedFor in energy Refs. [ depositions closedius 38 to mm the in Fig. and the current peaksface at the end.the In current contrast, peaks for earlier sur- inmon time. to BEGe This detectors. behavior Pulses is ina com- the bulk variety volume of show di contribute. Consequently, variable for coaxial detectors. Instead threedi significantly uses an artificial neuralevents; the network second to one identifydiscriminate relies single on between site a SSE likelihood likeevents; method events the to and third background A/E is based on the correlation between 2.3 Pulse shape calibration Common to allis methods the and use for oftest both calibration the data, detector performance taken types nition once and per programs – week, – in to calibration to case spectrum train of the contains patternfrom algorithm. the a recog- The peak1592.5 at keV) of 2614.5 this keV full line energy is peaks used (FEP, e.g. as at proxy 1620.7 keV) for or SSE the while single Candidate pulse traces taken from BEGe data for a SSE (top left), MSE (top right), 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 a.u. a.u. 1.0 0.8 0.6 0.4 0.2 0.0 1.0 a.u. 0.8 0.6 0.4 0.2 0.0 a.u. a.u. a.u. a.u. surface event (bottom right). The maximal charge pulse amplitudes are set equal to one for normalization and current 2 p+ electrode cause a tail on the high side. Thus the n+ A pulse shape discrimination based on For double beta decay events, bremsstrahlung of ] t [ns] t [ns] , νββ 4 4 22 . has 100 yr 1. , 2.2 Semi-coaxial detectors For semi-coaxial detectors, the weighting field alsoat peaks the a larger part of the volume is relevant for the current Fig. 2 and pulses have equal integrals. The current pulses are interpolated. comes high enough to resulttion in probability. Due a to significant the recombina- compared slow nature to of the the charge di ume, carrier the drift rise in timeregion the of is active signals increased. vol- fromin This interactions the causes in energy a reconstruction. this ther ballistic The reduced deficit by latter recombination loss mightouter of be surface. free fur- The charges pulse near integrationtimes the time shorter for than thestronger one ballistic for deficit energy andratio. causing leading This an to is a even reduced utilizeding to through the identify of Fig. been developed in preparation forhere Phase and II. has It been is applied testedperimental extensively measurements before both through with ex- detectorsin operated vacuum cryostats [ as well as through pulse-shape simulations [ electrons can reduce tail of the p+ PSD survival probability of double beta decay is 4
Ge
yr. A/E Ge
1 82000 82000
⇠ usion < 2060
Bi 2204 keV 2204 Bi and 21
↵ 25 214 , 76 Q is enr ± 25 ]. E A/E 20 10 GERDA 13-07 A Charge Current Ge underground with at the Homestake mine in · 9
15 . 10
years (blue solid). From reference [ 2200 1 2190 keV 2190 2 9 . · signal are shown corresponding to half lives of 81800 81800 enr 2055 ± 4 25 energy [keV] . 4 eV. In addition to excellent energy resolution, the =2 ) (3) . 10 = . . The toolkit particles penetrat- 2 0 decay in 1 ⌫ L / νββ . × 0 1 2150 E − 81600 81600 1 T 2050 . yr O is proportional to the temperature to the third power, so 2 2 ]. The bottom right trace . 2 ⌫ 0 19 24 > and and results in a low side ] and in liquid argon [ 2100 ciencies of Table I, the = 0, namely no excess 81400 81400 < 5 counts. The system- 2045 . A 2 16 from Ref. [11], 5 ⌫ 3 νββ layer [ / 0 = 0 and the 90 % credible 0 1 ββ t 2
yr (with folded systematic
⌫ < ⌫ β β /
distribution while events close to the N n+ m background interpolation Q 0 yr (90 % C O crystals to measure these temperature changes, and in doing so, 0 1 + 81200 81200 ⌫ 2 p Te Q-value).
T 2050 25
2040 SSE 0 N 2039 keV 2039 25 A/E contact but the gradient is lower and hence 10 N 130 10 shows a candidate event. ·
·
Candidate pulse traces taken from BEGe data for a SSE (top left), MSE (top right), 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 1.0 a.u. a.u. a.u. a.u. surface event (bottom right). The maximal charge pulse amplitudes are set equal to one for normalization and current 2 p+ 9 DISCUSSION is superimposed with the expectations 1 ]. A major difference between MJD and GERDA is the choice of shielding. . . 2035 . 2000 electrode cause a tail on the high side. Thus the n+ 1 9 A pulse shape discrimination based on For double beta decay events, bremsstrahlung of 2 7 O crystal bolometer to search for 0 yr (red dashed) and with the 90% upper years and between 0 and 10 yr. 2 > > electrons can reduce tail of the p+ PSD survival probability of double beta decay is 2.2 Semi-coaxial detectors For semi-coaxial detectors, the weighting field alsoat peaks the a larger part of the volume is relevant for the current region is increased.in This the causes energy a reconstruction.ther ballistic The reduced deficit by latter recombination loss mightouter of be surface. free fur- The charges pulse near integrationtimes the time shorter for than thestronger one ballistic for deficit energy andratio. causing leading This an to is a even reduced utilizeding to through the identify of Fig. been developed in preparation forhere Phase and II. has It been is applied testedperimental extensively measurements before both through with ex- detectorsin operated vacuum cryostats [ as well as through pulse-shape simulations [ Fig. 2 and pulses have equal integrals. The current pulses are interpolated. comes high enough to resulttion in probability. Due a to significant the recombina- compared slow nature to of the the charge di ume, carrier the drift rise in time the of active signals vol- from interactions in this 4 Q 2 data show no indication of a peak at 25 ⌫ 2 25 / 2 25 ⌫ 0 / ⌫ 1 /
0 1
0 2030 10 1 1930 keV 1930 1950 10 10 · T T /T · × 0 19 after marginalization over all nuisance parame- . . years (red dashed) and 1 2 3 background events after the PSD cuts, as shown Gerda . 2 Plots of GERDA phase I data. On the left is the energy spectrum. Upper panel is zoomed in near . ⌫ 2025 / 2 25 0 0 1 > 1900 =1 T
2 ± 10
2 >
1 ⌫
0 3 2 ⌫ 4 2 0 8 6 The A Bayesian calculation [24] was also performed with / / counts/(2 keV) keV) counts/(2 counts/keV counts/keV 0 0 0 The MAJORANA collaboration has an experiment, the MAJORANA Demonstrator (MJD), The two collaborations plan to merge for the next-generation detector, and will use the best CUORE (Cryogenic Underground Observatory for Rare Events) is an experiment which will 1 1 . × i.e. the claim foris the not observation supported. of 0 decays Taking are expected (see2 note [26]) in in Fig. 1. This can be compared with three events de- limit derived in this work,(blue corresponding solid). to count. The bestof fit signal value events is abovehalf-life the is background. The limit on the including the systematichalf-life uncertainty. corresponds The to limitatic uncertainties on weaken the the limit bythe about background 1.5 %. levels and Given median the sensitivity e for the 90 % C.L. limit isthe 2 same fit describedtaken above. for A 1 flat priorBAT distribution [25] is isthe used data to sets performfor and the to combined analysis extractters. on the The posterior best fit distribution interval is is again uncertainties). The correspondingT median sensitivity is FIG. 1.detectors without (with)histogram. PSD The is combined The shownbackground energy lower by interpolation. spectrum panel the open shows fromtrum the (filled) zoomed all In to region(with the used PSD upper for selection) the basedT panel, on the the central spec- value of Ref. [11], 2 19 νββ / . 0 1 the heat capacity of crystals suchnear as absolute Te zero (CUORE isproduce designed a to large operate change below in 10thermistors temperature. mK), affixed a to CUORE small utilizes the energy neutron Te can deposition transmission make can doped a germanium calorimetric measurementresolution of (0.085% total at the energy deposited in a decay with excellent energy South Dakota, USA [ which is presently taking data with with 30 kg shows candidate pulse traces for single-site and multi-site events. From reference [ MJD uses ultra-pure copper, electroformed underground,the for experiment its will innermost be shielding. released Results in from the future. features of each detector in the designcrystals for will the not tonne scale change, future but experiment. theto The mass size those will of used be germanium scaled in up GERDA by and adding MJD. more modules of crystals similar 2.4 CUORE use a cryogenic Te Figure 7: the Q-value. The filled (open)cuts. histogram On represents the upper events panel, passing expectations (failing) for the1 the pulse 0 shape discrimination Review of Neutrinoless Double Beta Decay shape of the signal pulses can belike) used events. to discriminate The between phase single-site ( Iare GERDA shown energy in spectrum Figure and an example of pulse shape discrimination t 1 1 1 0 E 5 keV ciency, )cts 3 25 22 5keV. † 8 9 14 ± +4 ± ± +10 +11 +16 ± 5keV 5 expected .
0 ± Q Q
after PSD. All ±
930
230 keV). “cts” is
1
E Q
45 11 .
and a frequentist
bkg BI ⌫
E· ±
0 N 031031 76018 19 18 23 63 42 022 3 5 Q . . . . 070 070 044 044 and standard deviation 0 0 0 0 yr). . . . . · 0 0 ± ± ± ± +0 +0 kg · Q i 688 688 720 619 619 663 ...... ✏ [keV] passed 0. It was verified that the method h > 2 cts/(keV ⌫ / 0 1 3 yr] 1.3 0 1.32.4 0 0 2.4 0 · cient coverage. The systematic uncertain- T 17.9 0 17.9 0 [kg E , which relates to the peak integral by Eq. 1. RG2GD32BRG1 2036.6 2041.3ANG3 28-Dec-2012 16-Dec-201200:09 09:50RG1 2035.5 2037.4 29-Jan-201303:35 yes no 02-Mar-201308:08 2041.7 27-Apr-201322:21 no yes no ANG 5ANG 5 2041.8 2036.9 18-Nov-2011 22:52 23-Jun-2012 23:02 no yes 2 ⌫ / 0 1 /T TABLE II. List of all events within To derive the signal strength Seven events are observed in the range silver silver BEGe BEGe golden golden )inunitsof10 golden silver golden BEGe golden golden golden dataset detector energy date PSD data set without PSD with PSD stant term for thethe background signal and with mean aaccording at Gaussian to peak the for free expected parameters: resolution. theand backgrounds The 1 of fit the has threeThe data four likelihood sets ratio isallowed region only evaluated forhas the always su physically ties due to theenergy detector resolution parameters, and selectionMonte energy e Carlo scale approach are which folded takes in correlations with into a ac- shape analysis. Ofdetectors, the three six are classified eventswith as from SSE the the by ANN, semi-coaxial expectation. consistent same classification Five by ofThe at the event least in six one thecut. events BEGe other have No data PSD the events set method.results remain is quoted within rejected in by the the following A/E are obtained withcoverage PSD. interval, a profile likelihoodsets fit is of the performed. three The data fitted function consists of a con- † before the PSD,background to counts. be No comparedpected excess to background of 5 is events observed beyondsets. in the any ex- This of interpretation the is three data strengthened by the pulse TABLE I. Parameters forout the the three pulse data shapeber sets discrimination with of (PSD). and “bkg” events with- background is in the index, the num- calculated 230the as keV observed bkg/( window number of and events BI in the the respective interval PoS(FPCP2016)033 .A νββ using ]. νββ 11 Compton νββ γ Te is 34%. Joshua Albert 130 ], arranged in 19 ] is a high-pressure 10 760 meV [ 14 − Te) [ Se. If the demonstrator is 270 130 82 < is a lack of a second detection with several isotopes, and the Se. ββ 82 5 kg m ∼ νββ νββ decays. There is now a research cam- O (206 kg β 2 100 kg ] is a project to search for 0 Te masses at modest cost. The detector ∼ 12 and 130 years and α 24 10 10 × 0 . 4 > 2 νββ / 0 isotopes with Q-values above 2615 keV (the highest prominent 1 0.4%) and longer particle tracks. This can make it possible to t , providing a strong topological discriminator against ∼ β νββ 5%) will be poor relative to most competing technologies, but future . 4 ∼ . Scaling up to large masses while maintaining low backgrounds will be a 8 decay, and most other backgrounds. An example of this from MC simulation β ] is a repurposing of the Sudbury Neutrino Observatory (SNO) detector for 0 O crystals do not require enrichment, as the natural abundance of 13 2 search. Crystals using 0 candidate isotopes. Many other projects are underway exploring other isotopes or techniques Neutrino Ettore Majorana Observatory (NEMO) [ Neutrino Experiment with a Xenon Time projection chamber (NEXT) [ This review has only covered experiments running or soon-to-run with large quantities of The Te The biggest challenge for future bolometric searches for 0 SNO+ [ line from primordial radioisotopes) are of particular interest. νββ νββ on smaller scales, and other large projects exist in the early conceptual stages. The field of 0 challenge. The NEXT collaboration100 kg is detector presently to follow. working on a 10 kg detector,3. with Conclusions plans for a 0 paign called Cuore Upgrade with PIDa (CUPID) investigating usable different Cherenkov crystals or which scintillation may produce signalnew in crystal addition technology to could the be phonons.0 used If with successfully the developed, a existingγ CUORE cryostat for an improved future 2.5 Other Experiments SuperNEMO demonstrator is currently in commissioning with is presently preparing forscintillator. a water fill, to be followed by a(15 fill bar) with gas TPC scintillator, experiment and beingare then developed. improved The loaded energy big resolution advantages ( ofobserve a the gas Bragg TPC peak over of a each liquid one upgrades, similar to those planned for KamLAND-Zen,enrichment, may help. it As should tellurium can be be possible used without to scale up to large channel which could be used to discriminate between foils of source materials andgood magnetized background tracking discrimination, volumes and on manydetector, either different but side. isotopes the can use The be of trackingas easily foils can other tested means give experiments. with that the the NEMO-3 same detector produced size measurements is of quite 2 largesuccessful, for a full-scale the SuperNEMO same may source be built, mass with central acrylic tank in the SNOThe detector energy will be resolution filled ( with liquid scintillator loaded with tellurium. scatters, single is shown in Figure Review of Neutrinoless Double Beta Decay CUORE has been proceeding intinuing a to staged CUORE-0 program, (2013-2015) starting and withto leading CUORICINO start to (2003-2008), taking con- the data full in CUOREtowers 2016. of experiment, 52 which CUORE crystals is will each expected haveand (CUORE-0 740 CUORE utilized kg results a yield Te single limits such of tower). The combined CUORICINO PoS(FPCP2016)033 ]). Bi 7 Ge , 214 76 6 . Tl. 5 ] Xe TPC Joshua Albert 208 decay, and the rise of the 136 2 (1958) 1015. Decay of /v νββ β . 1.5 kg of natural 109 Na gammas and ]. ⇠ 22 Xe 0 (2002) 115-151 ]. scatter. Identification of the 136 52 γ ]. and the results obtained Phys. Rev. 14 3 , Xe at a pressure of 5 atm. hep-ex/0801.4589 ], using a gaseous 8 136 (2013) 122503 111 hep-ex/1605.02889 Search for Majorana Neutrinos Near the nucl-ex/1402.6956 , ). The use of this topological signature to (2008) 221803 [ Search for Majorana Neutrinos with the First Two Results on Neutrinoless Double- right Helicity of Neutrinos - Ann. Rev. Nucl. Part. Sci. 11 Precision Measurement of Neutrino Oscillation –3– 1 , 100 The EXO-200 Detector, Part I: Detector Design and Phys. Rev. Lett. . The paper ends with the conclusion in Sec. , 4 physics.ins-det/1202.2192 (2014) 229-234 [ experiments was pioneered by the Caltech-Neuchˆatel-PSI 510 ⌫ 0 Phys. Rev. Lett. , ]. Double Beta Decay Nature . The data analysis is described in Sec. , 2 is the speed of the particle) leads to a significant energy deposition (2012) 05010 [ ]. 7 v event (left) and a single electron background event from a 2.44 MeV can be a powerful discriminator. From reference [ ⌫ (The GERDA Collaboration), (The EXO-200 Collaboration), 0 β ). Background events from single electrons, however, typically leave a single (The EXO Collaboration), (The KamLAND-Zen Collaboration), JINST , (The KamLAND Collaboration), et al. left et al. - 1 et al. et al. .A et al. Simulated data for a NEXT-like gas TPC. The left panel shows a The paper is organized as follows. The topological signal and reconstruction algorithms The use of a topological particle identification based on the expected signature of a nucl-ex/1307.4720 hep-ph/0202264 [ from Phase I of the GERDA Experiment Inverted Mass Hierarchy Region with KamLAND-Zen Parameters with KamLAND [ Construction Years of EXO-200 Data in a compact region,in which double will beta be decay events referredend appear to (Fig. as as a a singlecontinuous ‘blob’. continuous track trajectory with The with only two a oneeliminate electrons blob blob background produced at (Fig. in each Collaboration in the Gotthard Underground Laboratory [ 2 Topological signature inElectrons NEXT (and positrons) moving throughrate xenon until they gas become lose energy non-relativistic.energy at loss At an (where the approximately end fixed of the trajectory the 1 single electron tracks originating fromdouble the electron photoelectric tracks interaction from of the pair production of theare 2.614 described MeV in gamma Sec. from are presented and discussed in Sec. double electron (signal) event comparedby to the that interaction of a ofsimulation single of high electron the energy (background) NEXT-DEMO produced gammasdemonstration prototype of is the and presented power data here. of taken the method with Using has NEXT-DEMO the been a made. Monte first Carlo This involved the comparison of gamma (right) in Monte Carlo simulation (both events simulated at deSubterr´aneo 15 Canfranc. bar gas The pressure). principlenecessary know-how of has operation been of developedoperated NEXT-100 using at NEXT-DEMO, and the a NEW Instituto large and de scale Corpuscular F´ısica the prototype in which Valencia (Spain) with Figure 1 xenon at a pressure of 10 bar (for a detailed description of the prototype, see Refs. [ with multiwire read-out, with a fiducial mass of 3.3 kg of [2] S. R. Elliott and P. Vogel, [1] M. Goldhaber, L. Grodzins, and A. W. Sunyar, [3] M. Auger [6] A. Gando [7] M. Agostini [4] J. B. Albert [5] S. Abe right panel shows a single electronBragg background peak event from of each similar energy from a Figure 8: Review of Neutrinoless Double Beta Decay searches will be changing asgrow experimental to costs the for point next generationthat where these tonne-scale only experiments experiments may a will result few inbe such proof that limited experiments neutrinos (by will are direct Majorana, be or, measurementexclusion supported if or of the globally. determination neutrino Majorana mass that It neutrinos. can the isoutcome, hierarchy It possible multiple is also experiments inverted), possible will may that bebackground result only techniques needed in will limits to be will verify made be along results, the set. and way. impressive Regardless advances of in the low References PoS(FPCP2016)033 Te 130 ]. JHEP , Joshua Albert ]. (2016) 1719-1725 ]. 273-275 Latest Results from NEMO-3 and , Status Update of the MAJORANA ]. (2015) 67-69. physics.ins-det/1508.05759 nucl-ex/1504.02454 Pulse Shape Discrimination for GERDA Phase I Search for Neutrinoless Double-Beta Decay of Nucl. Part. Phys. Proc. 265-266 12 Current Status and Future Prospects of the SNO+ , First Proof of Topological Signature in the High Status of the CUORE and Results from the CUORE-0 . ]. physics.ins-det/1307.2610 (2016) 6194250 [ (2015) 102502 [ 115 (The MAJORANA Collaboration), (2013) 2583 [ Nucl. Part. Phys. Proc. et al. , C73 (The GERDA Collaboration), (The SNO+ Collaboration), physics.ins-det/1507.05902 (The CUORE Collaboration), (The NEMO-3 and SuperNEMO Collaborations), (The NEXT Collaboration), Phys. Rev. Lett. , (The CUORE Collaboration), Adv. High Energy Phys. et al. et al. et al. et al. , et al. et al. Eur. Phys. J. (2016) 104 [ , physics.ins-det/1502.03653 DEMONSTRATOR Neutrinoless Double Beta Decay Experiment physics.ins-det/1511.00395v1 Neutrinoless Double Beta Decay Experiments Data [ with CUORE-0 Status of SuperNEMO Experiment 1601 Pressure Xenon Gas TPC with Electroluminescence Amplification for the NEXT Experiment [9] J. Gruszko, N. Abgrall [8] M. Agostini [10] M. Sisti Review of Neutrinoless Double Beta Decay [12] A. Remoto [11] K. Alfonso [13] S. Andringa [14] P. Ferrario