Mon·Aug 17, 2020Monday·August 17, 2020

1. 01*

   Measurements of ${\pi }^{-}$ production in ${}^7$Be+${}^9$Be collisions at beam momenta from 19$A$ to 150$A$GeV/$c$ in the NA61/SHINE experiment at the CERN SPS

   NA61/SHINE Collaboration: A. Acharya🇵🇱 · H. Adhikary🇵🇱 · A. Aduszkiewicz🇵🇱 · K.K. Allison🇺🇸 · E.V. Andronov🇷🇺 · T. Antićić🇭🇷 · V. Babkin🇷🇺 · M. Baszczyk🇵🇱 · S. Bhosale🇵🇱 · A. Blondel🇫🇷 · M. Bogomilov🇧🇬 · A. Brandin🇷🇺 and 129 other authors

   The NA61/SHINE collaboration studies at the CERN Super Proton Synchrotron (SPS) the onset of deconfinement in hadronic matter by the measurement of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra and mean multiplicities of ${\pi }^{-}$ mesons produced in the 5\% most \textit{central} ${}^7$Be+${}^9$Be collisions at beam momenta of 19$A$, 30$A$, 40$A$, 75$A$ and 150$A$ GeV/$c$ obtained by the so-called $h^{-}$ method which does not require any particle identification. The shape of the transverse mass spectra differs from the shapes measured in central Pb+Pb collisions and inelastic p+p interactions. The normalized width of the rapidity distribution decreases with increasing collision energy and is in between the results for inelastic nucleon-nucleon and central Pb+Pb collisions. The mean multiplicity of pions per wounded nucleon in \textit{central} ${}^7$Be+${}^9$Be collisions is close to that in central Pb+Pb collisions up to 75$A$GeV/$c$. However, at the top SPS energy the result is close to the one for inelastic nucleon-nucleon interactions. The results are discussed in the context of predictions for the onset of deconfinement at the CERN SPS collision energies.

   nucl-exhep-exEPJC(2020)·21 citations
2. 02*

   Double Beta Decay Experiments at Canfranc Underground Laboratory

   Susana Cebrian🇪🇸

   The first activities of the Canfranc Underground Laboratory ("Laboratorio Subterráneo de Canfranc", LSC) started in the mid-eighties in a railway tunnel located under the Spanish Pyrenees; since then, it has become an international multidisciplinary facility equipped with different services for underground science. The research activity at LSC is about Astroparticle Physics, dark matter searches and neutrino Physics; but also activities in Nuclear Astrophysics, Geophysics, and Biology are carried out. The investigation of the neutrinoless double beta decay has been one of the main research lines of LSC since the beginning. Many unknowns remain in the characterization of the basic neutrino properties and the study of this rare decay process requiring Physics beyond the Standard Model of Particle Physics can shed light on the lepton number conservation, the nature of the neutrinos as Dirac or Majorana particles and the absolute scale and ordering of the masses of the three generations. Here, the double beta decay searches performed at LSC for different emitters and following very different experimental approaches will be reviewed: from the very first experiments in the laboratory including the successful IGEX for ${}^{76}$Ge, which released very stringent limits to the effective neutrino mass at the time, to the present NEXT experiment for ${}^{136}$Xe and future project CROSS ("Cryogenic Rare-event Observatory with Surface Sensitivity") for ${}^{130}$Te and ${}^{100}$Mo, both implementing innovative detector technologies to discriminate backgrounds. For the neutrinoless double beta decay channel and at 90% C.L., IGEX derived a limit to the half-life of ${}^{76}$Ge of $T_{1/2}^{0\nu }>1.57\times 10^{25}$ y while the corresponding expected limits are $T_{1/2}^{0\nu }>1.0\times 10^{26}$ y for ${}^{136}$Xe from NEXT-100 (for an exposure of 500 kg.y) and $T_{1/2}^{0\nu }>2.8\times 10^{25}$ y for ${}^{100}$Mo from CROSS (for 5 y and 4.7 kg of isotope). Activities related to double beta decays searches carried out in other underground laboratories have also been developed at LSC and will be presented too, like the operation of the BiPo-3 detector for radiopurity measurements of thin sheets with very high sensitivity. For each one of these experiments, the concept, the experimental set-ups and relevant results will be discussed.

   nucl-exhep-exphysics.ins-detPPNP(2020)·6 citations
3. 03*

   Statistical interpretation of sterile neutrino oscillation searches at reactors

   Pilar Coloma🇪🇸 · Patrick Huber🇺🇸 · Thomas Schwetz🇩🇪

   A considerable experimental effort is currently under way to test the persistent hints for oscillations due to an eV-scale sterile neutrino in the data of various reactor neutrino experiments. The assessment of the statistical significance of these hints is usually based on Wilks' theorem, whereby the assumption is made that the log-likelihood is ${\chi }^2$-distributed. However, it is well known that the preconditions for the validity of Wilks' theorem are not fulfilled for neutrino oscillation experiments. In this work we derive a simple asymptotic form of the actual distribution of the log-likelihood based on reinterpreting the problem as fitting white Gaussian noise. From this formalism we show that, even in the absence of a sterile neutrino, the expectation value for the maximum likelihood estimate of the mixing angle remains non-zero with attendant large values of the log-likelihood. Our analytical results are then confirmed by numerical simulations of a toy reactor experiment. Finally, we apply this framework to the data of the Neutrino-4 experiment and show that the null hypothesis of no-oscillation is rejected at the 2.6\,$\sigma$ level, compared to 3.2\,$\sigma$ obtained under the assumption that Wilks' theorem applies.

   ↳ hep-phhep-exnucl-exnucl-thEPJC(2021)·38 citations
4. 04*

   The energy response of the Oslo Scintillator Array OSCAR

   F. Zeiser🇳🇴 · G.M. Tveten🇳🇴 · F.L. Bello Garrote🇳🇴 · M. Guttormsen🇳🇴 · A.C. Larsen🇳🇴 · V.W. Ingeberg🇳🇴 · A. Görgen🇳🇴 · S. Siem🇳🇴

   The new Oslo Scintillator Array (OSCAR) has been commissioned at the Oslo Cyclotron Laboratory (OCL). It consists of 30 large volume (diameter 3.5 x 8 inches) LaBr${}_3$(Ce) detectors that are used for $\gamma$-ray spectroscopy. The response functions for incident $\gamma$-rays up to 20 MeV are simulated with $\text{Geant4}$. In addition, the resolution, and the total and full-energy peak efficiencies are extracted. The results are in very good agreement with measurements from calibration sources and experimentally obtained mono-energetic in-beam $\gamma$-ray spectra.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·24 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.