The challenge in searching for fundamental symmetry violation.Neutrinoless double-beta(0νββ)decay represents one of the most profound tests of fundamental symmetries in nature.This hypothetical nuclear process,in w...The challenge in searching for fundamental symmetry violation.Neutrinoless double-beta(0νββ)decay represents one of the most profound tests of fundamental symmetries in nature.This hypothetical nuclear process,in which two neutrons simultaneously decay into two protons with the emission of two electrons but no neutrinos,would demonstrate that lepton number is not conserved and confirm that neutrinos are their own antiparticles(Majorana particles).The observation of 0νββdecay would provide crucial insights into the absolute neutrino mass scale and could illuminate the origin of matter-antimatter asymmetry in the universe.展开更多
The tensor force changes the nuclear shell structure and thus may result in underlying influence of the collectivity and decay properties of the nucleus.We carefully examined the impact of the monopole and multipole e...The tensor force changes the nuclear shell structure and thus may result in underlying influence of the collectivity and decay properties of the nucleus.We carefully examined the impact of the monopole and multipole effects originating from the tensor force on both the collectivity and the matrix element for the neutrinoless double-β(0νββ)decay,using the generatorcoordinate method with an effective interaction.To analyze the effect of the tensor force,we employed an effective Hamiltonian associated with the monopole-based universal interaction that explicitly consists of the central,tensor,and spin-orbit coupling terms.The interferences among the shell structure,quadrupole collectivity,nucleon occupancy,and 0νββmatrix elements were analyzed in detail.A better understanding of the tensor force would be of great importance in reducing the theoretical uncertainty in 0νββnuclear matrix element calculations.展开更多
In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neu...In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neutrinos having a hierarchical mass structure:the lighter one is lighter enough than the typical Fermi-momentum scale of nuclei while the heavier one is sufficiently heavy to decouple from the neutrinoless double beta decay.Then,in the basis where the mass matrices of the charged leptons and right-handed neutrinos are diagonal,for some particular texture of the Dirac neutrino mass matrix M_(D),the neutrinoless double beta decay can be hidden.In this paper,on top of this specified model,we study the interesting scenario that M_(D)further obeys the TM1 symmetry orμ-τreflection symmetry which are well motivated by the experimental results for the neutrino mixing parameters.展开更多
We report the search for neutrinoless double-beta decay of 136Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target.The data reconstruction and the background modeling are optimized in the MeV energy ...We report the search for neutrinoless double-beta decay of 136Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target.The data reconstruction and the background modeling are optimized in the MeV energy region.A blind analysis is performed with data from the commissioning run and the first science run.No significant excess of signal over the background is observed.A lower limit on the half-life of 136Xe neutrinoless double-beta decay is established to be 211024 yr at the 90%confidence level,with a 136Xe exposure of 44.6 kg yr.Our result represents the most stringent constraint from a natural xenon detector to date.展开更多
The search for neutrinoless double-beta decay(0 b)represents one of the most compelling challenges in modern physics.Observ-ing this elusive nuclear process would not only confirm that neu-trinos are Majorana particle...The search for neutrinoless double-beta decay(0 b)represents one of the most compelling challenges in modern physics.Observ-ing this elusive nuclear process would not only confirm that neu-trinos are Majorana particles-their own antiparticles-but also provide definitive evidence of lepton number violation,offering critical insights into the matter-antimatter asymmetry of the universe.Despite decades of experimental efforts,no conclusive signal has been detected.A key obstacle lies in the persistent theoretical uncertainties surrounding predicted decay rates,which stem pri-marily from the calculation of nuclear matrix elements(NMEs)-the quantum-mechanical factors governing how the decay unfolds within complex nuclei.A major unresolved issue has been the missing short-range contribution,which arises from nucleon over-lap effects and cannot be deduced from long-range pion-exchange interactions alone.展开更多
We report the first results on 76Ge neutrinoless double beta decay from stage one of the China dark-matter experiment （CDEX）. A p-type point-contact high-purity germanium detector with a mass of 994g has been instal...We report the first results on 76Ge neutrinoless double beta decay from stage one of the China dark-matter experiment （CDEX）. A p-type point-contact high-purity germanium detector with a mass of 994g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304kgd has been analyzed over a wide spectral band from 500keV to 3MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039MeV energy range. The half-life of76Ge neutrinoless double beta decay derived based on this result is 70v2〉6.4× 1022 yr （90%C.L.）. An upper limit on the effective Majorana-neutrino mass of 5.0eV has been achieved.展开更多
The scintillation properties of a CdMoO4 crystal have been investigated experimentally.The fluorescence yields and decay times measured from 22 K to 300 K demonstrate that CdMoO4 crystal is a good candidate for an abs...The scintillation properties of a CdMoO4 crystal have been investigated experimentally.The fluorescence yields and decay times measured from 22 K to 300 K demonstrate that CdMoO4 crystal is a good candidate for an absorber for a bolometer readout,for both heat and scintillation signals.The results from Monte Carlo studies,taking the backgrounds from 2ν2β of^100 42Mo ^116 48Cd） and internal trace nuclides ^214Bi and ^208Tl into account,show that the expected sensitivity of a CdMoO4 bolometer for neutrinoless double beta decay experiments with an exposure of 100kg·years is one order of magnitude higher than those of the current sets of the limT1/2^0νββ of ^100 42Mo and ^116 48Cd.展开更多
Searching for the neutrinoless double beta decay(NLDBD)is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments.Panda X-II...Searching for the neutrinoless double beta decay(NLDBD)is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments.Panda X-III(particle and astrophysical xenon experiment III)will search for the NLDBD of136Xe at the China Jin Ping Underground Laboratory(CJPL).In the first phase of the experiment,a high pressure gas Time Projection Chamber(TPC)will contain 200 kg,90%136Xe enriched gas operated at10 bar.Fine pitch micro-pattern gas detector(Microbulk Micromegas)will be used at both ends of the TPC for the charge readout with a cathode in the middle.Charge signals can be used to reconstruct the electron tracks of the NLDBD events and provide good energy and spatial resolution.The detector will be immersed in a large water tank to ensure～5 m of water shielding in all directions.The second phase,a ton-scale experiment,will consist of five TPCs in the same water tank,with improved energy resolution and better control over backgrounds.展开更多
We emphasize that it is extremely important for future neutrinoless double-beta(0νββ)decay experiments to reach the sensitivity to the effective neutrino mass|mββ|≈1 meV.With such a sensitivity,it is highly poss...We emphasize that it is extremely important for future neutrinoless double-beta(0νββ)decay experiments to reach the sensitivity to the effective neutrino mass|mββ|≈1 meV.With such a sensitivity,it is highly possible to discover the signals of 0νββ decays.If no signal is observed at this sensitivity level,then either neutrinos are Dirac particles or stringent constraints can be placed on their Majorana masses.In this paper,assuming the sensitivity of|mββ|≈1 meV for future 0νββ decay experiments and the precisions on neutrion oscillation parameters after the JUNO experiment,we fully explore the constrained regions of the lightest neutrino mass m1 and two Majorana-type CP-violating phases{ρ,σ}.Several important conclusions in the case of normal neutrino mass ordering can be made.First,the lightest neutrino mass is severely constrained to a narrow range m1∈[0.7,8]meV,which together with the precision measurements of neutrino mass-squared differences from oscillation experiments completely determines the neutrino mass spectrum m2∈[8.6,11.7]meV ing phases is limited to ρ∈[130°,230°],which cannot be obtained from any other realistic experiments.Third,the sum of three neutrino masses is found to beΣ≡m1+m2+m3∈[59.2,72.6]meV,while the effective neutrino mass for beta decays turns out to be mβ≡(|Ue1|2m1^2+|Ue2|2m2^2+|Ue3|2m3^2)1/2∈[8.9,12.6]meV.These observations clearly set up the roadmap for future non-oscillation neutrino experiments aiming to solve the fundamental problems in neutrino physics.展开更多
In this study,the possibility of observing a solar neutrino background in a future neutrinoless double beta decay experiment using a high-pressure gaseous ^(82)SeF_(6) TPC is investigated.Various contributions are sim...In this study,the possibility of observing a solar neutrino background in a future neutrinoless double beta decay experiment using a high-pressure gaseous ^(82)SeF_(6) TPC is investigated.Various contributions are simulated,and possible features that could be used for event classification are discussed;two types of backgrounds are identified.The rate of multi-site background events is approximately 0.63 events/(ton·yr)in a 30 keV ROI window.This background could be effectively reduced to less than 0.0001 events/(ton·yr)(95%C.L.)while maintaining a high signal efficiency of 93%by applying a selection based on the number of clusters and energy of the leading cluster.The rate of the single-electron background events is approximately 0.01 events/(ton·yr)in the ROI.Assuming a reduction factor of 10 for the single-electron background events obtained via the algorithms developed for radioactive background rejection,the total background induced by the solar neutrino would be 0.001 events/(ton·yr),which is sufficiently small for conducting ton-level experiments.展开更多
We operated a p-type point contact high purity germanium(PPCGe)detector(CDEX-1B,1.008 kg)in the China Jinping Underground Laboratory(CJPL)for 500.3 days to search for neutrinoless double beta(0νββ)decay of ^(76)Ge....We operated a p-type point contact high purity germanium(PPCGe)detector(CDEX-1B,1.008 kg)in the China Jinping Underground Laboratory(CJPL)for 500.3 days to search for neutrinoless double beta(0νββ)decay of ^(76)Ge.A total of 504.3 kg⋅day effective exposure data was accumulated.The anti-coincidence and the multi/single-site event(MSE/SSE)discrimination methods were used to suppress the background in the energy region of interest(ROI,1989–2089 keV for this work)with a factor of 23.A background level of 0.33 counts/(keV⋅kg⋅yr)was realized.The lower limit on the half life of^(76)Ge 0νββdecay was constrained as T_(1/2)^(0ν)>1.0×10^(23)yr(90%C.L.),corresponding to the upper limits on the effective Majorana neutrino mass:<mββ><3.2–7.5 eV.展开更多
Observing nuclear neutrinoless double beta (0vββ) decay would be a revolutionary result in particle physics.Observing such a decay would prove that the neutrinos are their own antiparticles,help to study the absolut...Observing nuclear neutrinoless double beta (0vββ) decay would be a revolutionary result in particle physics.Observing such a decay would prove that the neutrinos are their own antiparticles,help to study the absolute mass of neutrinos,explore the origin of their mass,and may explain the matter-antimatter asymmetry in our universe by lepton number violation.We propose developing a time projection chamber (TPC) using high-pressure ^(82)SeF_(6) gas and Topmetal silicon sensors for readout in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of82Se,called the NvDEx experiment.Besides being located at CJPL with the world’s thickest rock shielding,NvDEx combines the advantages of the high Qββ(2.996 MeV) of82Se and the TPC’s ability to distinguish signal and background events using their different topological characteristics.This makes NvDEx unique,with great potential for low-background and high-sensitivity 0 vββsearches.NvDEx-100,a NvDEx experiment phase with 100 kg of SeF_(6)gas,is being built,with plans to complete installation at CJPL by 2025.This report introduces 0 vββ physics,the NvDEx concept and its advantages,and the schematic design of NvDEx-100,its subsystems,and background and sensitivity estimation.展开更多
In this paper,we take the B-L supersymmetric standard model(B-LSSM)and TeV scale left–right symmetric model(LRSM)as two representations of the two kinds of new physics models to study the nuclear neutrinoless double ...In this paper,we take the B-L supersymmetric standard model(B-LSSM)and TeV scale left–right symmetric model(LRSM)as two representations of the two kinds of new physics models to study the nuclear neutrinoless double beta decays(0ν2β)so as to see the senses onto these two kinds of models when the decays are taken into account additionally.Within the parameter spaces allowed by all the existing experimental data,the decay half-life of the nucleus^(76)Ge and^(136)Xe,T_(12)^(0ν)(^(76)Ge,^(136)Xe),is precisely calculated and the results are presented properly.Based on the numerical results,we conclude that there is greater room for LRSM type models than for B-LSSM type models in foreseeable future experimental observations on the decays.展开更多
The sensitivity of an experiment to detect the Majorana neutrino mass via neutrinoless double-beta decay(0νββ) strongly depends on the rate of background events that can mimic this decay. One major source of this b...The sensitivity of an experiment to detect the Majorana neutrino mass via neutrinoless double-beta decay(0νββ) strongly depends on the rate of background events that can mimic this decay. One major source of this background is the radioactive emissions from the laboratory environment. In our study, we focused on assessing the background contributions from environmental gamma rays, neutrons, and underground muons to the Jinping bolometric demonstration experiment. This experiment uses an array of lithium molybdate crystal bolometers to probe the potential 0νββ decay of the100Mo isotope at the China Jinping Underground Laboratory. We also evaluated the shielding effectiveness of the experimental setup through an attenuation study. Our simulations indicate that the combined background from environmental gamma rays, neutrons, and muons in the relevant100Mo 0νββ Q-value region can be reduced to approximately 0.003 cts/kg/keV/yr.展开更多
中国锦屏地下实验室是目前世界上岩石覆盖最深的深地实验室,对宇宙线μ子具有良好的屏蔽作用,具有极低的宇宙线通量,因此适用于开展对稀有物理事例的探测实验。目前,包括中国暗物质实验(China Dark matter EXperiment,CDEX)、粒子和天...中国锦屏地下实验室是目前世界上岩石覆盖最深的深地实验室,对宇宙线μ子具有良好的屏蔽作用,具有极低的宇宙线通量,因此适用于开展对稀有物理事例的探测实验。目前,包括中国暗物质实验(China Dark matter EXperiment,CDEX)、粒子和天体物理氙实验(Particle and Astrophysical Xenon Experiments,PandaX)、锦屏深地核天体物理实验装置(Jinping Underground Nuclear Astrophysics Experiment,JUNA)等实验组已经入驻锦屏实验室,对暗物质直接探测、无中微子双β衰变、天体核反应等一系列稀有物理事例进行实验探测,并给出了一系列国际先进水平的研究成果。本文总结了中国锦屏地下实验室自成立以来的发展过程和本底控制情况,并对实验室中各个实验组所开展实验的物理意义、实验原理、关键技术、物理成果等进行介绍,同时给出实验组接下来的实验计划。展开更多
文摘The challenge in searching for fundamental symmetry violation.Neutrinoless double-beta(0νββ)decay represents one of the most profound tests of fundamental symmetries in nature.This hypothetical nuclear process,in which two neutrons simultaneously decay into two protons with the emission of two electrons but no neutrinos,would demonstrate that lepton number is not conserved and confirm that neutrinos are their own antiparticles(Majorana particles).The observation of 0νββdecay would provide crucial insights into the absolute neutrino mass scale and could illuminate the origin of matter-antimatter asymmetry in the universe.
基金supported by the National Natural Science Foundation of China(No.12275369)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(No.22qntd3101)the Guangdong Major Project of Basic and Applied Basic Research(2021B0301030006)。
文摘The tensor force changes the nuclear shell structure and thus may result in underlying influence of the collectivity and decay properties of the nucleus.We carefully examined the impact of the monopole and multipole effects originating from the tensor force on both the collectivity and the matrix element for the neutrinoless double-β(0νββ)decay,using the generatorcoordinate method with an effective interaction.To analyze the effect of the tensor force,we employed an effective Hamiltonian associated with the monopole-based universal interaction that explicitly consists of the central,tensor,and spin-orbit coupling terms.The interferences among the shell structure,quadrupole collectivity,nucleon occupancy,and 0νββmatrix elements were analyzed in detail.A better understanding of the tensor force would be of great importance in reducing the theoretical uncertainty in 0νββnuclear matrix element calculations.
基金supported in part by the National Natural Science Foundation of China under Grant Nos.11605081,12142507 and 12147214the Natural Science Foundation of the Liaoning Scientific Committee under grant NO.2022-MS-314。
文摘In Asaka et al(2021 Phys.Rev.D 103,015014),Asaka,Ishida and Tanaka put forward an interesting possibility that the neutrinoless double beta decay can be hidden in the minimal seesaw model with the two right-handed neutrinos having a hierarchical mass structure:the lighter one is lighter enough than the typical Fermi-momentum scale of nuclei while the heavier one is sufficiently heavy to decouple from the neutrinoless double beta decay.Then,in the basis where the mass matrices of the charged leptons and right-handed neutrinos are diagonal,for some particular texture of the Dirac neutrino mass matrix M_(D),the neutrinoless double beta decay can be hidden.In this paper,on top of this specified model,we study the interesting scenario that M_(D)further obeys the TM1 symmetry orμ-τreflection symmetry which are well motivated by the experimental results for the neutrino mixing parameters.
基金supported by the National Key R&D Program of China(2023YFA1606200 and 2023YFA1606202)the National Natural Science Foundation of China(12090060,12090062,and U23B2070)+6 种基金the Office of Science and Technology,Shanghai Municipal Government(21TQ1400218,22JC1410100,23JC1410200,and ZJ2023-ZD-003)the support by the Fundamental Research Funds for the Central Universitiesthe sponsorship from the Chinese Academy of Sciences Center for Excellence in Particle Physics(CCEPP)Hongwen Foundation in Hong KongNew Cornerstone Science FoundationTencent Foundation in ChinaYangyang Development Fund。
文摘We report the search for neutrinoless double-beta decay of 136Xe from the PandaX-4T experiment with a 3.7-tonne natural xenon target.The data reconstruction and the background modeling are optimized in the MeV energy region.A blind analysis is performed with data from the commissioning run and the first science run.No significant excess of signal over the background is observed.A lower limit on the half-life of 136Xe neutrinoless double-beta decay is established to be 211024 yr at the 90%confidence level,with a 136Xe exposure of 44.6 kg yr.Our result represents the most stringent constraint from a natural xenon detector to date.
文摘The search for neutrinoless double-beta decay(0 b)represents one of the most compelling challenges in modern physics.Observ-ing this elusive nuclear process would not only confirm that neu-trinos are Majorana particles-their own antiparticles-but also provide definitive evidence of lepton number violation,offering critical insights into the matter-antimatter asymmetry of the universe.Despite decades of experimental efforts,no conclusive signal has been detected.A key obstacle lies in the persistent theoretical uncertainties surrounding predicted decay rates,which stem pri-marily from the calculation of nuclear matrix elements(NMEs)-the quantum-mechanical factors governing how the decay unfolds within complex nuclei.A major unresolved issue has been the missing short-range contribution,which arises from nucleon over-lap effects and cannot be deduced from long-range pion-exchange interactions alone.
基金supported by the National Natural Science Foundation of China(Grant Nos.11275107,11475117,11475099,and 11675088)the National Key Basic Research Program of China(Grant No.2010CB833006)
文摘We report the first results on 76Ge neutrinoless double beta decay from stage one of the China dark-matter experiment （CDEX）. A p-type point-contact high-purity germanium detector with a mass of 994g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304kgd has been analyzed over a wide spectral band from 500keV to 3MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039MeV energy range. The half-life of76Ge neutrinoless double beta decay derived based on this result is 70v2〉6.4× 1022 yr （90%C.L.）. An upper limit on the effective Majorana-neutrino mass of 5.0eV has been achieved.
基金Supported by National Natural Science Foundation of China(11275199)
文摘The scintillation properties of a CdMoO4 crystal have been investigated experimentally.The fluorescence yields and decay times measured from 22 K to 300 K demonstrate that CdMoO4 crystal is a good candidate for an absorber for a bolometer readout,for both heat and scintillation signals.The results from Monte Carlo studies,taking the backgrounds from 2ν2β of^100 42Mo ^116 48Cd） and internal trace nuclides ^214Bi and ^208Tl into account,show that the expected sensitivity of a CdMoO4 bolometer for neutrinoless double beta decay experiments with an exposure of 100kg·years is one order of magnitude higher than those of the current sets of the limT1/2^0νββ of ^100 42Mo and ^116 48Cd.
基金supported by the National Key Programme for Research and Development (NKPRD) (Grant No. 2016YFA0400300)Shanghai Jiao Tong University (SJTU) for their financial and technical support+1 种基金technical and administrative assistance from China Jin Ping Underground Laboratory (CJPL)the European Research Council (Grant No. ERC-2009-St G-240054)
文摘Searching for the neutrinoless double beta decay(NLDBD)is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments.Panda X-III(particle and astrophysical xenon experiment III)will search for the NLDBD of136Xe at the China Jin Ping Underground Laboratory(CJPL).In the first phase of the experiment,a high pressure gas Time Projection Chamber(TPC)will contain 200 kg,90%136Xe enriched gas operated at10 bar.Fine pitch micro-pattern gas detector(Microbulk Micromegas)will be used at both ends of the TPC for the charge readout with a cathode in the middle.Charge signals can be used to reconstruct the electron tracks of the NLDBD events and provide good energy and spatial resolution.The detector will be immersed in a large water tank to ensure～5 m of water shielding in all directions.The second phase,a ton-scale experiment,will consist of five TPCs in the same water tank,with improved energy resolution and better control over backgrounds.
基金supported in part by the National Key R&D Program of China(2018YFA0404100)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA10010100)+1 种基金the National Natural Science Foundation of China(11605081,11775231,11775232,11835013,11820101005)the CAS Center for Excellence in Particle Physics
文摘We emphasize that it is extremely important for future neutrinoless double-beta(0νββ)decay experiments to reach the sensitivity to the effective neutrino mass|mββ|≈1 meV.With such a sensitivity,it is highly possible to discover the signals of 0νββ decays.If no signal is observed at this sensitivity level,then either neutrinos are Dirac particles or stringent constraints can be placed on their Majorana masses.In this paper,assuming the sensitivity of|mββ|≈1 meV for future 0νββ decay experiments and the precisions on neutrion oscillation parameters after the JUNO experiment,we fully explore the constrained regions of the lightest neutrino mass m1 and two Majorana-type CP-violating phases{ρ,σ}.Several important conclusions in the case of normal neutrino mass ordering can be made.First,the lightest neutrino mass is severely constrained to a narrow range m1∈[0.7,8]meV,which together with the precision measurements of neutrino mass-squared differences from oscillation experiments completely determines the neutrino mass spectrum m2∈[8.6,11.7]meV ing phases is limited to ρ∈[130°,230°],which cannot be obtained from any other realistic experiments.Third,the sum of three neutrino masses is found to beΣ≡m1+m2+m3∈[59.2,72.6]meV,while the effective neutrino mass for beta decays turns out to be mβ≡(|Ue1|2m1^2+|Ue2|2m2^2+|Ue3|2m3^2)1/2∈[8.9,12.6]meV.These observations clearly set up the roadmap for future non-oscillation neutrino experiments aiming to solve the fundamental problems in neutrino physics.
基金the National Natural Science Foundation of China(12105110)National Key Research and Development Program of China(2022YFA1604703)。
文摘In this study,the possibility of observing a solar neutrino background in a future neutrinoless double beta decay experiment using a high-pressure gaseous ^(82)SeF_(6) TPC is investigated.Various contributions are simulated,and possible features that could be used for event classification are discussed;two types of backgrounds are identified.The rate of multi-site background events is approximately 0.63 events/(ton·yr)in a 30 keV ROI window.This background could be effectively reduced to less than 0.0001 events/(ton·yr)(95%C.L.)while maintaining a high signal efficiency of 93%by applying a selection based on the number of clusters and energy of the leading cluster.The rate of the single-electron background events is approximately 0.01 events/(ton·yr)in the ROI.Assuming a reduction factor of 10 for the single-electron background events obtained via the algorithms developed for radioactive background rejection,the total background induced by the solar neutrino would be 0.001 events/(ton·yr),which is sufficiently small for conducting ton-level experiments.
基金Supported by the National Key Research and Development Program of China(2017YFA0402201,2022YFA1604701,2022YFA1605000)the National Natural Science Foundation of China(12322511,12175112,12005111,11725522)。
文摘We operated a p-type point contact high purity germanium(PPCGe)detector(CDEX-1B,1.008 kg)in the China Jinping Underground Laboratory(CJPL)for 500.3 days to search for neutrinoless double beta(0νββ)decay of ^(76)Ge.A total of 504.3 kg⋅day effective exposure data was accumulated.The anti-coincidence and the multi/single-site event(MSE/SSE)discrimination methods were used to suppress the background in the energy region of interest(ROI,1989–2089 keV for this work)with a factor of 23.A background level of 0.33 counts/(keV⋅kg⋅yr)was realized.The lower limit on the half life of^(76)Ge 0νββdecay was constrained as T_(1/2)^(0ν)>1.0×10^(23)yr(90%C.L.),corresponding to the upper limits on the effective Majorana neutrino mass:<mββ><3.2–7.5 eV.
基金This work was supported by the National Key Research and Development Program of China(Nos.2021YFA1601300 and 2022YFA1604703)From-0-to-1 Original Innovation Program of Chinese Academy of Sciences(No.ZDBS-LY-SLH014)+1 种基金International Partner Program of Chinese Academy of Sciences(No.GJHZ2067)National Natural Science Foundation of China Youth Science Fund Project(No.12105110).
文摘Observing nuclear neutrinoless double beta (0vββ) decay would be a revolutionary result in particle physics.Observing such a decay would prove that the neutrinos are their own antiparticles,help to study the absolute mass of neutrinos,explore the origin of their mass,and may explain the matter-antimatter asymmetry in our universe by lepton number violation.We propose developing a time projection chamber (TPC) using high-pressure ^(82)SeF_(6) gas and Topmetal silicon sensors for readout in the China Jinping Underground Laboratory (CJPL) to search for neutrinoless double beta decay of82Se,called the NvDEx experiment.Besides being located at CJPL with the world’s thickest rock shielding,NvDEx combines the advantages of the high Qββ(2.996 MeV) of82Se and the TPC’s ability to distinguish signal and background events using their different topological characteristics.This makes NvDEx unique,with great potential for low-background and high-sensitivity 0 vββsearches.NvDEx-100,a NvDEx experiment phase with 100 kg of SeF_(6)gas,is being built,with plans to complete installation at CJPL by 2025.This report introduces 0 vββ physics,the NvDEx concept and its advantages,and the schematic design of NvDEx-100,its subsystems,and background and sensitivity estimation.
基金supported in part by the National Natural Science Foundation of China(NNSFC)under Grants No.11821505 No.12047503,No.12075301 and No.11705045supported in part by the Key Research Program of Frontier Sciences,CAS,Grant No.QYZDY-SSW-SYS006。
文摘In this paper,we take the B-L supersymmetric standard model(B-LSSM)and TeV scale left–right symmetric model(LRSM)as two representations of the two kinds of new physics models to study the nuclear neutrinoless double beta decays(0ν2β)so as to see the senses onto these two kinds of models when the decays are taken into account additionally.Within the parameter spaces allowed by all the existing experimental data,the decay half-life of the nucleus^(76)Ge and^(136)Xe,T_(12)^(0ν)(^(76)Ge,^(136)Xe),is precisely calculated and the results are presented properly.Based on the numerical results,we conclude that there is greater room for LRSM type models than for B-LSSM type models in foreseeable future experimental observations on the decays.
基金supported in part by the State Key Research Development Program in China(Nos.2022YFA1604702 and 2022YFA1604900)the National Natural Science Foundation of China(No.12025501)Strategic Priority Research Program of Chinese Academy of Science(No.XDB34030200).
文摘The sensitivity of an experiment to detect the Majorana neutrino mass via neutrinoless double-beta decay(0νββ) strongly depends on the rate of background events that can mimic this decay. One major source of this background is the radioactive emissions from the laboratory environment. In our study, we focused on assessing the background contributions from environmental gamma rays, neutrons, and underground muons to the Jinping bolometric demonstration experiment. This experiment uses an array of lithium molybdate crystal bolometers to probe the potential 0νββ decay of the100Mo isotope at the China Jinping Underground Laboratory. We also evaluated the shielding effectiveness of the experimental setup through an attenuation study. Our simulations indicate that the combined background from environmental gamma rays, neutrons, and muons in the relevant100Mo 0νββ Q-value region can be reduced to approximately 0.003 cts/kg/keV/yr.
