Mon·May 10, 2021Monday·May 10, 2021

1. 01*

   Measurement of ${}^{216}$Po half-life with the CUPID-0 experiment

   O. Azzolini🇮🇹 · J. W. Beeman🇺🇸 · F. Bellini🇮🇹 · M. Beretta🇮🇹 · M. Biassoni🇮🇹 · C. Brofferio🇮🇹 · C. Bucci🇮🇹 · S. Capelli🇮🇹 · L. Cardani🇮🇹 · P. Carniti🇮🇹 · V. Caracciolo🇮🇹 · N. Casali🇮🇹 and 35 other authors

   Rare event physics demands very detailed background control, high-performance detectors, and custom analysis strategies. Cryogenic calorimeters combine all these ingredients very effectively, representing a promising tool for next-generation experiments. CUPID-0 is one of the most advanced examples of such a technique, having demonstrated its potential with several results obtained with limited exposure. In this paper, we present a further application. Exploiting the analysis of delayed coincidence, we can identify the signals caused by the ${}^{220}$Rn-${}^{216}$Po decay sequence on an event-by-event basis. The analysis of these events allows us to extract the time differences between the two decays, leading to a new evaluation of ${}^{216}$ half-life, estimated as (143.3 $\pm$ 2.8) ms.

   nucl-exphysics.ins-detPLB(2021)·9 citations
2. 02*

   Drastic change in inelastic scattering depending on the development of dineutron correlation in ${}^{10}$Be

   T. Furumoto🇯🇵 · T. Suhara · N. Itagaki🇯🇵

   We investigated the development and breaking of the dineutron correlation in ${}^{10}$Be by analyzing the elastic and inelastic scatterings with a framework combing the microscopic structure and reaction models. For studying the structure, the ${}^{10}$Be nucleus was constructed under the assumption of a four-body ($\alpha +\alpha +n+n$) cluster model. In this work, we focused on the change in the inner structure for the 0${}_1^{+}$, 2${}_1^{+}$, and 2${}_2^{+}$ states when the strength of the spin-orbit interaction is varied. The inner structure, including various physical quantities such as energy, radius, and transition strength, is drastically influenced by the strength of the spin-orbit interaction. In particular, the development and breaking of the dineutron correlation is governed by the spin-orbit strength. The differences in the inner structure can be manifested by applying the obtained wave functions to elastic and inelastic scatterings with a proton target at $E/A=$ 59.4 and 200 MeV. Although the 0${}_1^{+}$ and 2${}_1^{+}$ states are significantly influenced by the spin-orbit strength of the nuclear structure calculation, the elastic and inelastic cross sections are not much affected. On the other hand, the inelastic cross section of the 2${}_2^{+}$ state depends greatly on the spin-orbit strength of the structure calculation. Thus, we discovered a way to measure the degree of the development of dineutron cluster structure based on its sensitivity to the inelastic cross section of the 2${}_2^{+}$ state of ${}^{10}$Be.

   ↳ nucl-thnucl-exPRC(2021)·6 citations
3. 03*

   Two-Orders-of-Magnitude Improvement in the Total Spin Angular Momentum of 131Xe Nuclei Using Spin Exchange Optical Pumping

   Michael J. Molway · Liana Bales-Shaffer · Kaili Ranta · Dustin Basler🇺🇸 · Megan Murphy · Bryce E. Kidd · Abdulbasit Tobi Gafar · Justin Porter · Kierstyn Albin · Boyd M. Goodson🇺🇸 · Eduard Y. Chekmenev · Matthew S. Rosen and 6 other authors

   We report on hyperpolarization of quadrupolar (I=3/2) 131Xe via spin-exchange optical pumping. Observations of the 131Xe polarization dynamics show that the effective alkali-metal/131Xe spin-exchange cross-sections are large enough to compete with 131Xe spin relaxation. 131Xe polarization up to 7.6 p/m 1.5 percent was achieved in ca. 8.5EE20 spins--a ca. 100-fold improvement in the total spin angular momentum--enabling applications including measurement of spin-dependent neutron-131Xe s-wave scattering and sensitive searches for time-reversal violation in neutron-131Xe interactions beyond the Standard Model.

   ↳ physics.atom-phnucl-ex2 citations
4. 04*

   Pairing and nonaxial-shape correlations in $N=150$ isotones

   Kenichi Yoshida🇯🇵

   Background: The $K^{\pi }=2^{-}$ excited band emerges systematically in $N=150$ isotones raging from Pu to No with even-$Z$ numbers, and a sharp drop in energies was observed in Cf. Purpose: I attempt to uncover the microscopic mechanism for the appearance of such a low-energy $2^{-}$ state in ${}^{248}$Cf. Furthermore, I investigate the possible occurrence of the low-energy $K^{\pi }=2^{+}$ state to elucidate the mechanism that prefers the simultaneous breaking of the reflection and axial symmetry to the breaking of the axial symmetry alone in this mass region. Method: I employ a nuclear EDF method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase approximation are used to describe the ground state and the transition to excited states. Results: The Skyrme-type SkM* and SLy4 functionals reproduce the fall in energy, but not the absolute value, of the $K^{\pi }=2^{-}$ state at $Z=98$, where the proton 2qp excitation $[633]7/2\otimes [521]3/2$ plays a decisive role for the peculiar isotonic dependence. I find interweaving roles by the pairing correlation of protons and the deformed shell closure at $Z=98$. The SkM* model predicts the $K^{\pi }=2^{-}$ state appears lower in energy in ${}^{246}$Cf than in ${}^{248}$Cf as the Fermi level of neutrons is located in between the $[622]5/2$ and $[734]9/2$ orbitals. Except for ${}^{250}$Fm in the SkM* calculation, the $K^{\pi }=2^{+}$ state is predicted to appear higher in energy than the $K^{\pi }=2^{-}$ state because the quasi-proton $[521]1/2$ orbital is located above the $[633]7/2$ orbital. Conclusions: A systematic study of low-lying collective states in heavy actinide nuclei provides a rigorous testing ground for microscopic nuclear models. The present study shows a need for improvements in the EDFs to describe pairing correlations and shell structures in heavy nuclei, that are indispensable in predicting the heaviest nuclei.

   ↳ nucl-thnucl-exPRC(2021)·5 citations
5. 05*

   Improving radioactive contaminant identification through the analysis of delayed coincidences with an $\alpha$-spectrometer

   G. Baccolo🇮🇹 · A. Barresi🇮🇹 · M. Beretta🇮🇹 · D. Chiesa🇮🇹 · M. Nastasi🇮🇹 · L. Pagnanini🇮🇹 · S. Pozzi🇮🇹 · E. Previtali🇮🇹 · M. Sisti🇮🇹 · G. Terragni🇮🇹

   In the framework of rare event searches, the identification of radioactive contaminants in ultra-pure samples is a challenging task, because the signal is often at the same level of the instrumental background. This is a rather common situation for $\alpha$-spectrometers and other detectors used for low-activity measurements. In order to obtain the target sensitivity without extending the data taking live-time, analysis strategies that highlight the presence of the signal sought should be developed. In this paper, we show how to improve the contaminant tagging capability relying on the time-correlation of radioactive decay sequences. We validate the proposed technique by measuring the impurity level of both contaminated and ultra-pure copper samples, demonstrating the potential of this analysis tool in disentangling different background sources and providing an effective way to mitigate their impact in rare event searches.

   ↳ physics.ins-detnucl-exEPJC(2021)·4 citations
6. 06*

   Vector-like Leptons in Light of the Cabibbo-Angle Anomaly

   Claudio Andrea Manzari🇨🇭

   The first row of the Cabibbo-Cobayashi-Maskawa (CKM) matrix shows a discrepancy of $\sim$$3\sigma$ with unitarity, known as the "Cabibbo Angle Anomaly" (CAA). This tension can be explained via modified $W$ couplings to leptons, but in order to consistently assess the validity of this solution, a global fit including the electroweak (EW) precision constraints and the low energy tests of lepton flavour universality (LFU) is necessary. Performing such a fit for gauge-invariant dimension-6 operators, we find that even when assuming LFU, including the CKM elements $V_{us}$ and $V_{ud}$ into the electroweak fit has a relevant impact, shifting the best fit point significantly. Vector-like leptons (VLLs) are prime candidates for a corresponding UV completion since they can affect the $W$ and $Z$ couplings to leptons already at tree-level. Studying each pattern of new physics (NP) given by the six possible representations of VLLs (under the SM gauge group) we find that any single representation describes experimental data at most slighlty better than the SM hypothesis. However, allowing for several representations of VLLs at the same time, we find a simple scenario consisting of a singlet, $N$, coupling to electrons and a triplet, ${\Sigma }_1$, coupling to muons which not only explains the CAA but also improves the electroweak fit in such a way that its best fit point is preferred by more than $4\sigma$ with respect to the SM.

   ↳ hep-phhep-exnucl-exnucl-th7 citations
7. 07*

   Background identification in cryogenic calorimeters through $\alpha -\alpha$ delayed coincidences

   O. Azzolini🇮🇹 · J. W. Beeman🇺🇸 · F. Bellini🇮🇹 · M. Beretta🇮🇹 · M. Biassoni🇮🇹 · C. Brofferio🇮🇹 · C. Bucci🇮🇹 · S. Capelli🇮🇹 · L. Cardani🇮🇹 · P. Carniti🇮🇹 · N. Casali🇮🇹 · D. Chiesa🇮🇹 and 33 other authors

   Localization and modeling of radioactive contaminations is a challenge that ultra-low background experiments are constantly facing. These are fundamental steps both to extract scientific results and to further reduce the background of the detectors. Here we present an innovative technique based on the analysis of $\alpha -\alpha$ delayed coincidences in ${}^{232}$Th and ${}^{238}$U decay chains, developed to investigate the contaminations of the ZnSe crystals in the CUPID-0 experiment. This method allows to disentangle surface and bulk contaminations of the detectors relying on the different probability to tag delayed coincidences as function of the $\alpha$ decay position.

   ↳ physics.ins-detnucl-exphysics.data-anEPJC(2021)·10 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.