Search

The current experiments searching for neutrinoless double-β (0νββ) decay also collect large statistics of Standard Model allowed two-neutrino double-β (2νββ) decay events. These can be used to search for Beyond Standard Model (BSM) physics via 2νββ decay spectral distortions. 100Mo has a natural advantage due to its relatively short half-life, allowing higher 2νββ decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a 100Mo exposure of 1.47 kg × years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on 0νββ decays with the emission of one or more Majorons, on 2νββ decay with Lorentz violation, and 2νββ decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the 2νββ decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of 2νββ decay events among the next-generation experiments.

Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of ^{100}Mo to the ground state of ^{100}Ru of [7.07±0.02(stat)±0.11(syst)]×10^{18}  yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in ^{100}Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ_{3,1}=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20Li2Mo100O4 (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-β decays of Mo100 to the first 0+ and 2+ excited states of Ru100 using the full CUPID-Mo exposure (2.71kgyr of LMO). We measure the half-life of 2νββ decay to the 01+ state as T1/22ν→01+=(7.5±0.8(stat.)-0.3+0.4(syst.))×1020yr. The bolometric technique enables measurement of the electron energies as well as the γ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 21+ state of T1/22ν→21+>4.4×1021yr(90% c.i.) and on the neutrinoless modes of T1/20ν→21+>2.1×1023yr(90% c.i.), T1/20ν→01+>1.2×1023yr(90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to make the first comparison of the single and higher state dominance 2νββ decay models for the 01+ excited state of Ru100.

CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation 0 νββ decay experiment, CUPID. It consisted of an array of 20 enriched Li 2100 MoO 4 bolometers and 20 Ge light detectors and has demonstrated that the technology of scintillating bolometers with particle identification capabilities is mature. Furthermore, CUPID-Mo can inform and validate the background prediction for CUPID. In this paper, we present a detailed model of the CUPID-Mo backgrounds. This model is able to describe well the features of the experimental data and enables studies of the 2 νββ decay and other processes with high precision. We also measure the radio-purity of the Li 2100 MoO 4 crystals which are found to be sufficient for the CUPID goals. Finally, we also obtain a background index in the region of interest of 3.7 -0.8+0.9 (stat) -0.7+1.5 (syst) ×10-3 counts/ Δ EFWHM/ mol iso/ year , the lowest in a bolometric 0 νββ decay experiment.

The CUPID-Mo experiment to search for 0$u\beta\beta$ decay in $^{100}$Mohas been recently completed after about 1.5 years of operation at LaboratoireSouterrain de Modane (France). It served as a demonstrator for CUPID, a nextgeneration 0$u\beta\beta$ decay experiment. CUPID-Mo was comprised of 20enriched Li$_2$$^{100}$MoO$_4$ scintillating calorimeters, each with a mass of$\sim$ 0.2 kg, operated at $\sim$20 mK. We present here the final analysis withthe full exposure of CUPID-Mo ($^{100}$Mo exposure of 1.47 kg$\times$yr) usedto search for lepton number violation via 0$u\beta\beta$ decay. We report onvarious analysis improvements since the previous result on a subset of data,reprocessing all data with these new techniques. We observe zero events in theregion of interest and set a new limit on the $^{100}$Mo 0$u\beta\beta$ decayhalf-life of $T^{0u}_{1/2} > 1.8 \times 10^{24}$ year (stat.+syst.) at 90%CI. Under the light Majorana neutrino exchange mechanism this corresponds to aneffective Majorana neutrino mass of $\left <(0.28$--$0.49)$ eV, dependent upon the nuclear matrix element utilized.

The CUPID-Mo experiment to search for 0νββ decay in 100Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0νββ decay experiment. CUPID-Mo was comprised of 20 enriched Li 2100MoO 4 scintillating calorimeters, each with a mass of ∼ 0.2 kg, operated at ∼ 20 mK. We present here the final analysis with the full exposure of CUPID-Mo (100Mo exposure of 1.47 kg × year) used to search for lepton number violation via 0νββ decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the 100Mo 0νββ decay half-life of T1/20ν> 1.8 × 10 24 year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of 〈 mββ〉

The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale bolometric 0νββ experiment. It consists of a 4.2 kg array of 20 enriched Li_{2}^{100}MoO_{4} scintillating bolometers to search for the lepton-number-violating process of 0νββ decay in ^{100}Mo. With more than one year of operation (^{100}Mo exposure of 1.17  kg×yr for physics data), no event in the region of interest and, hence, no evidence for 0νββ is observed. We report a new limit on the half-life of 0νββ decay in ^{100}Mo of T_{1/2}>1.5×10^{24}  yr at 90% C.I. The limit corresponds to an effective Majorana neutrino mass ⟨m_{ββ}⟩

The CUPID-Mo experiment at the Laboratoire Souterrain de Modane (France) is a demonstrator for CUPID, the next-generation ton-scale bolometric 0νββ experiment. It consists of a 4.2 kg array of 20 enriched Li_{2}^{100}MoO_{4} scintillating bolometers to search for the lepton-number-violating process of 0νββ decay in ^{100}Mo. With more than one year of operation (^{100}Mo exposure of 1.17  kg×yr for physics data), no event in the region of interest and, hence, no evidence for 0νββ is observed. We report a new limit on the half-life of 0νββ decay in ^{100}Mo of T_{1/2}>1.5×10^{24}  yr at 90% C.I. The limit corresponds to an effective Majorana neutrino mass ⟨m_{ββ}⟩

CUPID-Mo is a cryogenic detector array designed to search for neutrinoless double-beta decay (0νββ) of 100Mo. It uses 20 scintillating 100Mo-enriched Li2MoO4 bolometers instrumented with Ge light detectors to perform active suppression of α backgrounds, drastically reducing the expected background in the 0νββ signal region. As a result, pileup events and small detector instabilities that mimic normal signals become non-negligible potential backgrounds. These types of events can in principle be eliminated based on their signal shapes, which are different from those of regular bolometric pulses. We show that a purely data-driven principal component analysis based approach is able to filter out these anomalous events, without the aid of detector response simulations.

Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of ^{100}Mo to the ground state of ^{100}Ru of [7.07±0.02(stat)±0.11(syst)]×10^{18}  yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in ^{100}Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ&#95;{3,1}=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.

We report on the development of scintillating bolometers based on lithium molybdate crystals that contain molybdenum that has depleted into the double-β active isotope 100Mo (Li2100deplMoO4). We used two Li2100deplMoO4 cubic samples, each of which consisted of 45-millimeter sides and had a mass of 0.28 kg; these samples were produced following the purification and crystallization protocols developed for double-β search experiments with 100Mo-enriched Li2MoO4 crystals. Bolometric Ge detectors were utilized to register the scintillation photons that were emitted by the Li2100deplMoO4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc Underground Laboratory (Spain). We observed that the Li2100deplMoO4 scintillating bolometers were characterized by an excellent spectrometric performance (∼3-6 keV of FWHM at 0.24-2.6 MeV γs), moderate scintillation signal (∼0.3-0.6 keV/MeV scintillation-to-heat energy ratio, depending on the light collection conditions), and high radiopurity (228Th and 226Ra activities are below a few µBq/kg), which is comparable with the best reported results of low-temperature detectors that are based on Li2MoO4 using natural or 100Mo-enriched molybdenum content. The prospects of Li2100deplMoO4 bolometers for use in rare-event search experiments are briefly discussed.

Giant resonances are collective excitation modes for many-body systems of fermions governed by a mean field, such as the atomic nuclei. The microscopic origin of such modes is the coherence among elementary particle-hole excitations, where a particle is promoted from an occupied state below the Fermi level (hole) to an empty one above the Fermi level (particle). The same coherence is also predicted for the particle-particle and the hole-hole excitations, because of the basic quantum symmetry between particles and holes. In nuclear physics, the giant modes have been widely reported for the particle-hole sector but, despite several attempts, there is no precedent in the particle-particle and hole-hole ones, thus making questionable the aforementioned symmetry assumption. Here we provide experimental indications of the Giant Pairing Vibration, which is the leading particle-particle giant mode. An immediate implication of it is the validation of the particle-hole symmetry.

Energies and spectroscopic factors of the first 7/2-, 3/2-, 1/2-, and 5/2- states in the (35)Si21 nucleus were determined by means of the (d, p) transfer reaction in inverse kinematics at GANIL using the MUST2 and EXOGAM detectors. By comparing the spectroscopic information on the Si35 and S37 isotones, a reduction of the p3/2-p1/2 spin-orbit splitting by about 25% is proposed, while the f7/2-f5/2 spin-orbit splitting seems to remain constant. These features, derived after having unfolded nuclear correlations using shell model calculations, have been attributed to the properties of the two-body spin-orbit interaction, the amplitude of which is derived for the first time in an atomic nucleus. The present results, remarkably well reproduced by using several realistic nucleon-nucleon forces, provide a unique touchstone for the modeling of the spin-orbit interaction in atomic nuclei.

An excited state in the proton-rich unbound nucleus 12O was identified at 1.8(4) MeV via missing-mass spectroscopy with the 14O(p,t) reaction at 51 AMeV. The spin-parity of the state was determined to be 0+ or 2+ by comparing the measured differential cross sections with distorted-wave calculations. The lowered location of the excited state in 12O indicates the breakdown of the major shell closure at Z=8 near the proton drip line. This demonstrates the persistence of mirror symmetry in the disappearance of the magic number 8 between 12O and its mirror partner 12Be.

Coulomb excitation of the exotic neutron-rich nucleus (26)Ne on a (208)Pb target was measured at 58 MeV/u in order to search for low-lying E1 strength above the neutron emission threshold. This radioactive beam experiment was carried out at the RIKEN Accelerator Research Facility. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV excitation energy. By performing a multipole decomposition of the differential cross section, a reduced dipole transition probability of B(E1)=0.49+/-0.16e(2) fm(2) is deduced, corresponding to 4.9+/-1.6% of the Thomas-Reiche-Kuhn sum rule. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is measured. The extracted decay pattern is not consistent with several mean-field theory descriptions of the pygmy states.

Angular distributions for 1n and 2n transfer are reported for the 6He+65Cu system at E&#95;{lab}=22.6 MeV. For the first time, triple coincidences between alpha particles, neutrons, and characteristic gamma rays from the targetlike residues were used to separate the contributions arising from 1n and 2n transfer. The differential cross sections for these channels, elastic scattering, and fusion were analyzed using a coupled reaction channels approach. The large measured ratio of the 2n-to-1n cross section and the strong influence of 2n transfer on other channels indicate that the dineutron configuration of 6He plays a dominant role in the reaction mechanism.

The isoscalar giant monopole resonance (GMR) and giant quadrupole resonance (GQR) have been measured in the 56Ni unstable nucleus by inducing the 56Ni(d,d') reaction at 50A MeV in the Maya active target at the GANIL facility. The GMR and GQR centroids are measured at 19.3+/-0.5 MeV and 16.2+/-0.5 MeV, respectively. The corresponding angular distributions are extracted from 3 degrees to 7 degrees . A multipole decomposition analysis using distorted wave Born approximation with random phase approximation transition densities shows that both the GMR and the GQR exhaust a large fraction of the energy-weighted sum rule. The demonstration of this new method opens a broad range of giant resonance studies at intermediate-energy radioactive beam facilities.

Inelastic scattering of 40Ca on 40Ca at 50 MeV/A has been measured in coincidence with protons at the GANIL facility. The SPEG spectrometer was associated with 240 CsI(Tl) scintillators of the INDRA 4pi array, allowing for the measurement of complete decay events. The missing energy method was applied to these events. For events with excitation energy between 42 and 55 MeV, a direct decay branch by three protons towards the low energy states of 37Cl gives the first evidence for a 3-phonon state built with giant resonances.

The N = 28 shell closure has been investigated via the 46Ar(d,p)47Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p(3/2), p(1/2), and f(5/2) states in 47Ar were determined and compared to those of the 49Ca isotone. We deduced a reduction of the N = 28 gap by 330(90) keV and spin-orbit weakenings of approximately 10(2) and 45(10)% for the f and p states, respectively. Such large variations for the f and p spin-orbit splittings could be accounted for by the proton-neutron tensor force and by the density dependence of the spin-orbit interaction, respectively. This contrasts with the picture of the spin-orbit interaction as a surface term only.

To investigate the behavior of the N = 14 neutron gap far from stability with a neutron-sensitive probe, proton elastic and 2(1)+ inelastic scattering angular distributions for the neutron-rich nucleus 22O were measured using the MUr à STrip detector array at the Grand Accélérateur National d'Ions Lourds facility. A deformation parameter beta(p,p') = 0.26 +/- 0.04 is obtained for the 2(1)+ state, much lower than in 20O, showing a weak neutron contribution to this state. A microscopic analysis was performed using matter and transition densities generated by continuum Skyrme-Hartree-Fock-Bogoliubov and quasiparticle random phase approximation calculations, respectively. The ratio of neutron to proton contributions to the 2(1)+ state is found close to the N/Z ratio, demonstrating a strong N = 14 shell closure in the vicinity of the neutron drip line.

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.

The energetic proton emission has been investigated as a function of the reaction centrality for the system (58)Ni + (58)Ni at 30A MeV. Extremely energetic protons (E(NN)(p) > or = 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.