Wed·Mar 18, 2015Wednesday·March 18, 2015

1. 01*

   Total and partial cross sections of the ${}^{112}$Sn($\alpha ,\gamma$)${}^{116}$Te reaction measured via in-beam $\gamma$-ray spectroscopy

   L. Netterdon🇩🇪 · J. Mayer🇩🇪 · P. Scholz🇩🇪 · A. Zilges🇩🇪

   An extended database of experimental data is needed to address uncertainties of the nuclear-physics input parameters for Hauser-Feshbach calculations. Especially $\alpha$+nucleus optical model potentials at low energies are not well known. The in-beam technique with an array of high-purity germanium (HPGe) detectors was successfully applied to the measurement of absolute cross sections of an ($\alpha$,$\gamma$) reaction on a heavy nucleus at sub-Coulomb energies. The total and partial cross-section values were measured by means of in-beam $\gamma$-ray spectroscopy. Total and partial cross sections were measured at four different $\alpha$-particle energies from $E_{\alpha }=10.5$ MeV to $E_{\alpha }=12$ MeV. The measured total cross-section values are in excellent agreement with previous results obtained with the activation technique, which proves the validity of the applied method. The experimental data was compared to Hauser-Feshbach calculations using the nuclear reaction code TALYS. A modified version of the semi-microscopic $\alpha$+nucleus optical model potential OMP 3, as well as modified proton and $\gamma$ widths, are needed in order to obtain a good agreement between experimental data and theory. It is found, that a model using a local modification of the nuclear-physics input parameters simultaneously reproduces total cross sections of the ${}^{112}$Sn($\alpha$,$\gamma$) and ${}^{112}$Sn($\alpha$,p) reactions. The measurement of partial cross sections turns out to be very important in this case in order to apply the correct $\gamma$-ray strength function in the Hauser-Feshbach calculations. The model also reproduces cross-section values of $\alpha$-induced reactions on ${}^{106}$Cd, as well as of ($\alpha$,n) reactions on ${}^{115,116}$Sn, hinting at a more global character of the obtained nuclear-physics input.

   nucl-exPRC(2015)·20 citations
2. 02*

   Spallation Backgrounds in Super-Kamiokande Are Made in Muon-Induced Showers

   Shirley Weishi Li🇺🇸 · John F. Beacom (Ohio State University)🇺🇸

   Crucial questions about solar and supernova neutrinos remain unanswered. Super-Kamiokande has the exposure needed for progress, but detector backgrounds are a limiting factor. A leading component is the beta decays of isotopes produced by cosmic-ray muons and their secondaries, which initiate nuclear spallation reactions. Cuts of events after and surrounding muon tracks reduce this spallation decay background by $\simeq 90\%$ (at a cost of $\simeq 20\%$ deadtime), but its rate at 6--18 MeV is still dominant. A better way to cut this background was suggested in a Super-Kamiokande paper [Bays {\it et al.}, Phys.~Rev.~D {\bf 85}, 052007 (2012)] on a search for the diffuse supernova neutrino background. They found that spallation decays above 16 MeV were preceded near the same location by a peak in the apparent Cherenkov light profile from the muon; a more aggressive cut was applied to a limited section of the muon track, leading to decreased background without increased deadtime. We put their empirical discovery on a firm theoretical foundation. We show that almost all spallation decay isotopes are produced by muon-induced showers and that these showers are rare enough and energetic enough to be identifiable. This is the first such demonstration for any detector. We detail how the physics of showers explains the peak in the muon Cherenkov light profile and other Super-K observations. Our results provide a physical basis for practical improvements in background rejection that will benefit multiple studies. For solar neutrinos, in particular, it should be possible to dramatically reduce backgrounds at energies as low as 6 MeV.

   ↳ hep-phastro-ph.HEhep-exnucl-ex+1PRD(2015)·72 citations
3. 03*

   Interaction of neutrons with alpha particles: A tribute to Heinz Barschall

   B. Hoop (Walden University, Minneapolis, MN, USA)

   As a tribute to our teacher and mentor on the occasion of his centennial celebration, we provide a brief historical overview and a summary of sustained interest in the topic of interaction of neutrons with alpha particles.

   ↳ physics.hist-phnucl-ex1 citation
4. 04*

   A hybrid model for studying nuclear multifragmentation around Fermi energy domain: Case for central collision of Xe on Sn

   S. Mallik🇮🇳 · G. Chaudhuri🇮🇳 · S. Das Gupta

   Experimental data for central collisions of ${}^{129}$Xe on ${}^{119}$Sn at beam energies of (a) 32 MeV/nucleon, (b) 39 MeV/nucleon, (c) 45 MeV/nucleon and (d) 50 MeV/nucleon are compared with results calculated using a hybrid model. We use a transport model (BUU) to obtain the excitation energy per nucleon in the center of mass of the multifragmenting system. The canonical thermodynamic model is then used to determine the temperature which would lead to this excitation energy. With this temperature we use the canonical thermodynamic model to calculate various experimental data such as multiplicities of different composites, probability distribution of the largest cluster etc. Agreement with data establishes the validity of the model.

   ↳ nucl-thnucl-exPRC(2015)·21 citations
5. 05*

   Low Background Micromegas in CAST

   J. G. Garza · S. Aune · D. Calvet · J. F. Castel · F. E. Christensen · T. Dafni · M. Davenport · T. Decker · E. Ferrer-Ribas · J. Galán · J. A. García · I. Giomataris and 13 other authors

   Solar axions could be converted into x-rays inside the strong magnetic field of an axion helioscope, triggering the detection of this elusive particle. Low background x-ray detectors are an essential component for the sensitivity of these searches. We report on the latest developments of the Micromegas detectors for the CERN Axion Solar Telescope (CAST), including technological pathfinder activities for the future International Axion Observatory (IAXO). The use of low background techniques and the application of discrimination algorithms based on the high granularity of the readout have led to background levels below 10${}^{-6}$ counts/keV/cm${}^2$/s, more than a factor 100 lower than the first generation of Micromegas detectors. The best levels achieved at the Canfranc Underground Laboratory (LSC) are as low as 10${}^{-7}$ counts/keV/cm${}^2$/s, showing good prospects for the application of this technology in IAXO. The current background model, based on underground and surface measurements, is presented, as well as the strategies to further reduce the background level. Finally, we will describe the R&D paths to achieve sub-keV energy thresholds, which could broaden the physics case of axion helioscopes.

   ↳ physics.ins-detnucl-exJ.Phys.Conf.Ser.(2015)·7 citations
6. 06*

   ${\eta }_c$ production in photon - induced interactions at the AFTER@LHC experiment as a probe of the Odderon

   V. P. Goncalves🇧🇷 · W. K. Sauter🇧🇷

   One of the open questions of the strong interaction theory is the existence of the Odderon, which is an unambiguous prediction of Quantum Chromodynamics, but still not confirmed experimentally. An alternative to probe the Odderon is the exclusive ${\eta }_c$ photoproduction in hadronic collisions. As the Pomeron exchange cannot contribute to this process, its observation would indicate the existence of the Odderon. In this paper we estimate the ${\eta }_c$ production in photon - induced interactions in hadronic collisions at the AFTER@LHC experiment. We demonstrate that the experimental analysis of this process is feasible in the AFTER@LHC experiment and that the observation of the ${\eta }_c$ production in nuclear collisions is a unambiguous signature of the Odderon.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2015)·37 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.