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
A new search for two-neutrino double-beta(2νββ)decay of^(136)Xe to the 0+1 excited state of 136Ba is performed with the full EXO-200 dataset.A deep learning-based convolutional neural network is used to discriminat...A new search for two-neutrino double-beta(2νββ)decay of^(136)Xe to the 0+1 excited state of 136Ba is performed with the full EXO-200 dataset.A deep learning-based convolutional neural network is used to discriminate signal from background events.Signal detection efficiency is increased relative to previous searches by EXO-200 by more than a factor of two.With the addition of the Phase II dataset taken with an upgraded detector,the median 90%confidence level half-life sensitivity of 2νββdecay to the 0+1 state of 136Ba is 2.9×10^(24)yr using a total^(136)Xe exposure of 234.1 kg yr.No statistically significant evidence for 2νββdecay to the 0^(+)_(1)state is observed,leading to a lower limit of T2ν1/2(0^(+)→0^(+)_(1))>1.4×10^(24)yr at 90%confidence level,improved by 70%relative to the current world's best constraint.展开更多
We report the first results on ^(76)Ge 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 994 g has been instal...We report the first results on ^(76)Ge 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 994 g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304 kg d has been analyzed over a wide spectral band from 500 keV to 3 MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039 MeV energy range. The half-life of ^(76)Ge neutrinoless double beta decay derived based on this result is T^(0ν)1/2>6.4×10^(22) yr(90% C.L.). An upper limit on the effective Majorana-neutrino mass of 5.0 eV 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
The double beta decay of ^(136)Xe to excited states of 136Ba(DBD-ES)has not yet been discovered experimentally.The experimental signature of such decays,one or two gamma rays following the beta signals,can be identifi...The double beta decay of ^(136)Xe to excited states of 136Ba(DBD-ES)has not yet been discovered experimentally.The experimental signature of such decays,one or two gamma rays following the beta signals,can be identified more effectively in a gaseous detector with the help of topological signatures.We have investigated key parameters of particle trajectories of DBD-ES with Monte Carlo simulation data of the proposed PandaX-III detector as an example.The background rates can be reduced by about one order of magnitude while keeping more than half of signals with topological analysis.The estimated half-life sensitivity of DBD-ES can be improved by 1.8 times to 4.1×10^(23) year(90%C.L.).Similarly,the half-life sensitivity of neutrinoless double beta decay of ^(136)Xe to excited states of 136Ba can be improved by a factor of 4.8 with topological signatures.展开更多
According to a new electron screening theory,we discuss the beta decay rates of nuclide 56Fe,56Co,56Ni,56Mn,56Cr and 56V with and without strong electron screening (SES).The results show that SES has only a slight e...According to a new electron screening theory,we discuss the beta decay rates of nuclide 56Fe,56Co,56Ni,56Mn,56Cr and 56V with and without strong electron screening (SES).The results show that SES has only a slight effect on the beta decay rates for ρ/μe 108 g/cm3.However the beta decay rates would be influenced greatly for ρ/μe 108 g/cm3.Due to SES,the maximum values of the C-factor (in %) on beta decay rates of 56Fe,56Co,56Ni,56Mn,56Cr and 56V is of the order of 95.03%,35.02%,98.05%,80.33%,98.30% and 98.71% at T9 = 4.0 and 98.83%,98.89%,99.65%,10.32%,4.10% and 40.21% at T9 = 7.0,respectively.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
Superallowed nuclear beta decay between 0^+analog states is a sensitive probe of the weak interaction, with the established strength – or F t value – of each such transition being a direct measure of the vector coup...Superallowed nuclear beta decay between 0^+analog states is a sensitive probe of the weak interaction, with the established strength – or F t value – of each such transition being a direct measure of the vector coupling constant, GV. Each transition's F t value depends on the half-life of the parent nucleus as well as on the Q-value and branching ratio for the transition of interest. It also depends on small(~1%) transition-dependent theoretical corrections, of which the most sensitive accounts for isospin symmetry breaking. We have recently published a new survey of world superallowed-decay data, which establishes the F t values of 14 separate superallowed transitions to a precision of order 0.1% or better.The results from this very robust data set yield the value of Vud, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa(CKM) matrix, and lead to the most demanding test available of CKM unitarity. The survey results and their outcome are described, as is the current direction of experiments that focus on testing the validity of the isospin-symmetry-breaking corrections.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
A detailed investigation of different decay modes,namely alpha decay,beta decay,cluster decay including heavy particle emission(Z_(c)>28),and spontaneous fission,was carried out,leading to the identification of new...A detailed investigation of different decay modes,namely alpha decay,beta decay,cluster decay including heavy particle emission(Z_(c)>28),and spontaneous fission,was carried out,leading to the identification of new cluster and beta-plus emitters in superheavy nucle with 104≤Z≤126.For the first time,we identified around20 beta-plus emitters in superheavy nuclei.Heavy-particle radioactivity was observed in superheavy elements of atomic number in the range 116≤Z≤126.^(292-293)Og were identified as ^(86)Kr emitters,and ^(298)122 and ^(300)122 were identified as ^(94)Zr emitters,whereas heavy-particle radioactivity from ^(91)Y was also observed in ^(299)123.Furthermore,the nuclei ^(300)124 and ^(306)126 exhibit ^(96)Mo radioactivity.The reported regions of beta-plus and heavyparticle radioactivity for superheavy nuclei are stronger than those for alpha decay.The identified decay modes for superheavy nuclei are presented in a chart.This study is intended to serve as a reference for identifying possible decay modes in the superheavy region.展开更多
Recent measurements of the two neutrino double beta decay high precision electron spectra,combined with charge exchange orβ-decay experimental data,have revealed severe constraints across current nuclear many body ca...Recent measurements of the two neutrino double beta decay high precision electron spectra,combined with charge exchange orβ-decay experimental data,have revealed severe constraints across current nuclear many body calculations.Our calculations show that the quasi-particle random phase approximation(QRPA)approach can adequately reproduce the measured spectra for the two open shell nuclei,^(82)Se and ^(100)Mo.For the closed shell nucleus ^(136)Xe,QRPA can also reproduce the spectra with proper treatments.Considering the high-lying state reduction,we also find that the nuclear shell model can also adequately reproduce the spectra and Gamow-Teller transition strength under a unique quenched axial-vector coupling constant gA.For ^(136)Xe,we find that flipping the sign for the decay strength causes the spectra to go beyond the so-called high-lying state dominance hypothesis.These results call for future high precision measurements of charge-exchange reactions.展开更多
In the past few decades,numerous searches have been made for the neutrinoless double-beta decay(0νββ) process,aiming to establish whether neutrinos are their own antiparticles(Majorana neutrinos),but no 0νββ...In the past few decades,numerous searches have been made for the neutrinoless double-beta decay(0νββ) process,aiming to establish whether neutrinos are their own antiparticles(Majorana neutrinos),but no 0νββdecay signal has yet been observed.A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass.We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory(JUNO) to improve the sensitivity to 0νββ up to a few me V,a major step forward with respect to the experiments currently being planned.JUNO is a 20 kton low-background liquid scintillator(LS) detector with 3%/(E(MeV))1/2 energy resolution,now under construction.It is feasible to build a balloon filled with enriched xenon gas(with136Xe up to 80%) dissolved in LS,inserted into the central region of the JUNO LS.The energy resolution is 1.9% at the Q-value of 136Xe 0νββ decay.Ultra-low background is the key for 0νββ decay searches.Detailed studies of background rates from intrinsic 2νββ and 8B solar neutrinos,natural radioactivity,and cosmogenic radionuclides(including light isotopes and 137Xe) were performed and several muon veto schemes were developed.We find that JUNO has the potential to reach a sensitivity(at 90% C.L.) to T1/20νββof 1.8×1028yr(5.6×1027yr) with 50 tons(5 tons) of fiducial136 Xe and 5 years exposure,while in the 50-ton case the corresponding sensitivity to the effective neutrino mass,mββ,could reach(5–12) meV,covering completely the allowed region of inverted neutrino mass ordering.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
In this paper,the β^(−)decay rates in the magnetic field of a neutron star are investigated under different conditions of electron density,temperature,and decay energy.By considering the influence of magnetic field o...In this paper,the β^(−)decay rates in the magnetic field of a neutron star are investigated under different conditions of electron density,temperature,and decay energy.By considering the influence of magnetic field on the electron spectrum,we improve the Takahashi-Yokoi model and perform the calculations of β^(−)decay rates for the nickel(Ni)isotopes,which are the typical neutron-rich nuclei participating in the rapid neutron-capture process(r-process).It is found that the β^(−)decay rates are increased significantly in the extremely strong magnetic field(B>10^(15)G).Furthermore,we find oscillation of β^(−)decay rates with the increase of magnetic field strength,implying that the magnitude of β^(−)decay rates is closely related to not only the decay energy but also the environmental electron density.In contrast,the impact of temperature on the β^(−)decay rates is found to be negligible in the range of 10^(7)K<T<10^(10)K.展开更多
In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are present...In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are presented for the half-lives,nuclear matrix elements(NMEs),phase space factors(G2ν),and convergence of the NMEs.The theoretical results agree well with the experimental data.In addition,we predict the half-lives of 2νββ decays for four nuclei.We focus on the convergence of the NMEs by analyzing the number of contributing intermediate 1+states(NC)for the nuclei of interest.We assume that NC is safely determined when the accumulated NMEs saturate 99.7%of the final calculated magnitude.From the calculations of the involved nuclei,we discover a connection between NC and the total number of intermediate 1+states(NT).According to the least squares fit,we conclude that the correlation is NC=(10.8±1.2)×N(0.29±0.02)T.展开更多
Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn...Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn nuclear force,we analyze the dependence of the nuclear matrix elements on the isovector and isoscalar parts of proton–neutron particle–particle interactions.The dependence on the different nuclear matrix elements is observed,and the results are explained.We also provide the phase space factors using numerical electron wavefunctions and properly chosen excitation energies.Finally,we present our results for the half-lives of this decay mode for different nuclei.展开更多
A precise background evaluation model is coincidence method, which is widely used in reactor proposed to address the complex data structure of the delayed electron-antineutrino oscillation experiments. In this model, ...A precise background evaluation model is coincidence method, which is widely used in reactor proposed to address the complex data structure of the delayed electron-antineutrino oscillation experiments. In this model, effects from the muon veto, uncorrelated random background, and background are all studied analytically, simplifying the estimation of the systematic uncertainties of signal efficiency and accidental background rate. The results of the calculations are validated numerically with a number of simulation studies and also applied and validated in the recent Daya Bay hydrogen-capture based oscillation measurement.展开更多
The preference of the normal neutrino mass ordering from the recent cosmological constraint and the global fit of neutrino oscillation experiments does not seem like a wise choice at first glance since it obscures the...The preference of the normal neutrino mass ordering from the recent cosmological constraint and the global fit of neutrino oscillation experiments does not seem like a wise choice at first glance since it obscures the neutrinoless double beta decay and hence the Majorana nature of neutrinos.Contrary to this naive expectation,we point out that the actual situation is the opposite.The normal neutrino mass ordering opens the possibility of excluding the higher solar octant and simultaneously measuring the two Majorana CP phases in future 0ν2βexperiments.Especially,the funnel region will completely disappear if the solar mixing angle takes the higher octant.The combined precision measurement by the JUNO and Daya Bay experiments can significantly reduce the uncertainty in excluding the higher octant.With a typical O(meV)sensitivity on the effective mass|mee|,the neutrinoless double beta decay experiment can tell if the funnel region really exists and hence exclude the higher solar octant.With the sensitivity further improved to sub-meV,the two Majorana CP phases can be simultaneously determined.Thus,the normal neutrino mass ordering clearly shows phenomenological advantages over the inverted one.展开更多
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.
文摘A new search for two-neutrino double-beta(2νββ)decay of^(136)Xe to the 0+1 excited state of 136Ba is performed with the full EXO-200 dataset.A deep learning-based convolutional neural network is used to discriminate signal from background events.Signal detection efficiency is increased relative to previous searches by EXO-200 by more than a factor of two.With the addition of the Phase II dataset taken with an upgraded detector,the median 90%confidence level half-life sensitivity of 2νββdecay to the 0+1 state of 136Ba is 2.9×10^(24)yr using a total^(136)Xe exposure of 234.1 kg yr.No statistically significant evidence for 2νββdecay to the 0^(+)_(1)state is observed,leading to a lower limit of T2ν1/2(0^(+)→0^(+)_(1))>1.4×10^(24)yr at 90%confidence level,improved by 70%relative to the current world's best constraint.
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 ^(76)Ge 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 994 g has been installed to detect neutrinoless double beta decay events, as well as to directly detect dark matter particles. An exposure of 304 kg d has been analyzed over a wide spectral band from 500 keV to 3 MeV. The average event rate obtained was about 0.012 counts per keV per kg per day over the 2.039 MeV energy range. The half-life of ^(76)Ge neutrinoless double beta decay derived based on this result is T^(0ν)1/2>6.4×10^(22) yr(90% C.L.). An upper limit on the effective Majorana-neutrino mass of 5.0 eV 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 R&D Program of China(Grant No.2016YFA0400300)the National Natural Science Foundation of China(Grant Nos.11775142,and 11905127)the Chinese Academy of Sciences Center for Excellence in Particle Physics(CCEPP)。
文摘The double beta decay of ^(136)Xe to excited states of 136Ba(DBD-ES)has not yet been discovered experimentally.The experimental signature of such decays,one or two gamma rays following the beta signals,can be identified more effectively in a gaseous detector with the help of topological signatures.We have investigated key parameters of particle trajectories of DBD-ES with Monte Carlo simulation data of the proposed PandaX-III detector as an example.The background rates can be reduced by about one order of magnitude while keeping more than half of signals with topological analysis.The estimated half-life sensitivity of DBD-ES can be improved by 1.8 times to 4.1×10^(23) year(90%C.L.).Similarly,the half-life sensitivity of neutrinoless double beta decay of ^(136)Xe to excited states of 136Ba can be improved by a factor of 4.8 with topological signatures.
基金Supported by Natural Science Foundation of Hainan Province (109004)Institution of Higher Education Scientific Research and Foundation of Hainan Provincial Education Department (Hjkj 2010–42)Institution of Higher Education Special Foundation of Sanya (YD09047)
文摘According to a new electron screening theory,we discuss the beta decay rates of nuclide 56Fe,56Co,56Ni,56Mn,56Cr and 56V with and without strong electron screening (SES).The results show that SES has only a slight effect on the beta decay rates for ρ/μe 108 g/cm3.However the beta decay rates would be influenced greatly for ρ/μe 108 g/cm3.Due to SES,the maximum values of the C-factor (in %) on beta decay rates of 56Fe,56Co,56Ni,56Mn,56Cr and 56V is of the order of 95.03%,35.02%,98.05%,80.33%,98.30% and 98.71% at T9 = 4.0 and 98.83%,98.89%,99.65%,10.32%,4.10% and 40.21% at T9 = 7.0,respectively.
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U.S.Department of Energy,Office of Science,Office of Nuclear Physics(DE-FG03-93ER40773)Welch Foundation(A-1397)
文摘Superallowed nuclear beta decay between 0^+analog states is a sensitive probe of the weak interaction, with the established strength – or F t value – of each such transition being a direct measure of the vector coupling constant, GV. Each transition's F t value depends on the half-life of the parent nucleus as well as on the Q-value and branching ratio for the transition of interest. It also depends on small(~1%) transition-dependent theoretical corrections, of which the most sensitive accounts for isospin symmetry breaking. We have recently published a new survey of world superallowed-decay data, which establishes the F t values of 14 separate superallowed transitions to a precision of order 0.1% or better.The results from this very robust data set yield the value of Vud, the up-down quark mixing element of the Cabibbo-Kobayashi-Maskawa(CKM) matrix, and lead to the most demanding test available of CKM unitarity. The survey results and their outcome are described, as is the current direction of experiments that focus on testing the validity of the isospin-symmetry-breaking corrections.
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.
文摘A detailed investigation of different decay modes,namely alpha decay,beta decay,cluster decay including heavy particle emission(Z_(c)>28),and spontaneous fission,was carried out,leading to the identification of new cluster and beta-plus emitters in superheavy nucle with 104≤Z≤126.For the first time,we identified around20 beta-plus emitters in superheavy nuclei.Heavy-particle radioactivity was observed in superheavy elements of atomic number in the range 116≤Z≤126.^(292-293)Og were identified as ^(86)Kr emitters,and ^(298)122 and ^(300)122 were identified as ^(94)Zr emitters,whereas heavy-particle radioactivity from ^(91)Y was also observed in ^(299)123.Furthermore,the nuclei ^(300)124 and ^(306)126 exhibit ^(96)Mo radioactivity.The reported regions of beta-plus and heavyparticle radioactivity for superheavy nuclei are stronger than those for alpha decay.The identified decay modes for superheavy nuclei are presented in a chart.This study is intended to serve as a reference for identifying possible decay modes in the superheavy region.
基金Supported by the National Key Research and Development Program of China (2021YFA1601300)。
文摘Recent measurements of the two neutrino double beta decay high precision electron spectra,combined with charge exchange orβ-decay experimental data,have revealed severe constraints across current nuclear many body calculations.Our calculations show that the quasi-particle random phase approximation(QRPA)approach can adequately reproduce the measured spectra for the two open shell nuclei,^(82)Se and ^(100)Mo.For the closed shell nucleus ^(136)Xe,QRPA can also reproduce the spectra with proper treatments.Considering the high-lying state reduction,we also find that the nuclear shell model can also adequately reproduce the spectra and Gamow-Teller transition strength under a unique quenched axial-vector coupling constant gA.For ^(136)Xe,we find that flipping the sign for the decay strength causes the spectra to go beyond the so-called high-lying state dominance hypothesis.These results call for future high precision measurements of charge-exchange reactions.
基金Supported by Strategic Priority Research Program of Chinese Academy of Sciences(XDA10010900)CAS Center for Excellence in Particle Physics(CCEPP)+1 种基金Postdoctoral Science Foundation of China and Chinese Academy of Sciences(2015IHEPBSH101)Program of International S&T Cooperation of Mo ST(2015DFG02000)
文摘In the past few decades,numerous searches have been made for the neutrinoless double-beta decay(0νββ) process,aiming to establish whether neutrinos are their own antiparticles(Majorana neutrinos),but no 0νββdecay signal has yet been observed.A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass.We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory(JUNO) to improve the sensitivity to 0νββ up to a few me V,a major step forward with respect to the experiments currently being planned.JUNO is a 20 kton low-background liquid scintillator(LS) detector with 3%/(E(MeV))1/2 energy resolution,now under construction.It is feasible to build a balloon filled with enriched xenon gas(with136Xe up to 80%) dissolved in LS,inserted into the central region of the JUNO LS.The energy resolution is 1.9% at the Q-value of 136Xe 0νββ decay.Ultra-low background is the key for 0νββ decay searches.Detailed studies of background rates from intrinsic 2νββ and 8B solar neutrinos,natural radioactivity,and cosmogenic radionuclides(including light isotopes and 137Xe) were performed and several muon veto schemes were developed.We find that JUNO has the potential to reach a sensitivity(at 90% C.L.) to T1/20νββof 1.8×1028yr(5.6×1027yr) with 50 tons(5 tons) of fiducial136 Xe and 5 years exposure,while in the 50-ton case the corresponding sensitivity to the effective neutrino mass,mββ,could reach(5–12) meV,covering completely the allowed region of inverted neutrino mass ordering.
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 by the National Natural Science Foundation of China (11822503)the Fundamental Research Funds for the Central Universities (Nanjing University)
文摘In this paper,the β^(−)decay rates in the magnetic field of a neutron star are investigated under different conditions of electron density,temperature,and decay energy.By considering the influence of magnetic field on the electron spectrum,we improve the Takahashi-Yokoi model and perform the calculations of β^(−)decay rates for the nickel(Ni)isotopes,which are the typical neutron-rich nuclei participating in the rapid neutron-capture process(r-process).It is found that the β^(−)decay rates are increased significantly in the extremely strong magnetic field(B>10^(15)G).Furthermore,we find oscillation of β^(−)decay rates with the increase of magnetic field strength,implying that the magnitude of β^(−)decay rates is closely related to not only the decay energy but also the environmental electron density.In contrast,the impact of temperature on the β^(−)decay rates is found to be negligible in the range of 10^(7)K<T<10^(10)K.
基金Supported by National Natural Science Foundation of China(11647086,11647085)Shanxi Province Science Foundation for Youths(201901D211252)+1 种基金Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2019L0554,2019L0505)the Natural Science Research Fund of North University of China(XJJ201811)。
文摘In this work,the characteristics of 2νββ decays for six nuclei(36Ar,46Ca,48Ca,50Cr,70Zn,and 136Xe)in a mass range from A=36 to A=136 are studied within the nuclear shell model(NSM)framework.Calculations are presented for the half-lives,nuclear matrix elements(NMEs),phase space factors(G2ν),and convergence of the NMEs.The theoretical results agree well with the experimental data.In addition,we predict the half-lives of 2νββ decays for four nuclei.We focus on the convergence of the NMEs by analyzing the number of contributing intermediate 1+states(NC)for the nuclei of interest.We assume that NC is safely determined when the accumulated NMEs saturate 99.7%of the final calculated magnitude.From the calculations of the involved nuclei,we discover a connection between NC and the total number of intermediate 1+states(NT).According to the least squares fit,we conclude that the correlation is NC=(10.8±1.2)×N(0.29±0.02)T.
基金Supported by National Natural Science Foundation of China(11505078,1164730)“Light of West China”Program and key research program(XDPB09-2)from Chinese Academy of Sciences。
文摘Using partially restored isospin symmetry,we calculate the nuclear matrix elements for a special decay mode of a two-neutrino double beta decay–the decay to the first 2+excited states.Employing the realistic CD–Bonn nuclear force,we analyze the dependence of the nuclear matrix elements on the isovector and isoscalar parts of proton–neutron particle–particle interactions.The dependence on the different nuclear matrix elements is observed,and the results are explained.We also provide the phase space factors using numerical electron wavefunctions and properly chosen excitation energies.Finally,we present our results for the half-lives of this decay mode for different nuclei.
基金Supported by Ministry of Science and Technology of China(2013CB834302)National Natural Science Foundation of China(11235006,11475093)+1 种基金Tsinghua University Initiative Scientific Research Program(2012Z02161)Key Laboratory of Particle&Radiation Imaging(Tsinghua University),Ministry of Education
文摘A precise background evaluation model is coincidence method, which is widely used in reactor proposed to address the complex data structure of the delayed electron-antineutrino oscillation experiments. In this model, effects from the muon veto, uncorrelated random background, and background are all studied analytically, simplifying the estimation of the systematic uncertainties of signal efficiency and accidental background rate. The results of the calculations are validated numerically with a number of simulation studies and also applied and validated in the recent Daya Bay hydrogen-capture based oscillation measurement.
基金supported by JSPS KAKENHI(JP18K13536)the Double First Class start-up fund(WF220442604)provided by Shanghai Jiao Tong Universitysupported by the National Natural Science Foundation of China(11275101,11835005)。
文摘The preference of the normal neutrino mass ordering from the recent cosmological constraint and the global fit of neutrino oscillation experiments does not seem like a wise choice at first glance since it obscures the neutrinoless double beta decay and hence the Majorana nature of neutrinos.Contrary to this naive expectation,we point out that the actual situation is the opposite.The normal neutrino mass ordering opens the possibility of excluding the higher solar octant and simultaneously measuring the two Majorana CP phases in future 0ν2βexperiments.Especially,the funnel region will completely disappear if the solar mixing angle takes the higher octant.The combined precision measurement by the JUNO and Daya Bay experiments can significantly reduce the uncertainty in excluding the higher octant.With a typical O(meV)sensitivity on the effective mass|mee|,the neutrinoless double beta decay experiment can tell if the funnel region really exists and hence exclude the higher solar octant.With the sensitivity further improved to sub-meV,the two Majorana CP phases can be simultaneously determined.Thus,the normal neutrino mass ordering clearly shows phenomenological advantages over the inverted one.