Thu·Jan 4, 2018Thursday·January 4, 2018

1. 01*

   Direct Measurement of Astrophysically Important Resonances in ${}^{38}\mathrm{K}(p,\gamma ){}^{39}\mathrm{Ca}$

   G. Christian🇨🇦 · G. Lotay🇬🇧 · C. Ruiz🇨🇦 · C. Akers🇰🇷 · D. S. Burke · W. N. Catford🇬🇧 · A. A. Chen🇿🇦 · D. Connolly · B. Davids🇨🇦 · J. Fallis🇨🇦 · U. Hager · D. Hutcheon and 3 other authors

   According to sensitivity studies, the ${}^{38}\mathrm{K}\left(p,\gamma \right){}^{39}\mathrm{Ca}$ reaction has a significant influence on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ production in classical novae. In order to constrain the rate of this reaction, we have performed a direct measurement of the strengths of three candidate $\ell =0$ resonances within the Gamow window, at $386\pm 10\mathrm{keV}$, $515\pm 10\mathrm{keV}$, and $689\pm 10\mathrm{keV}$. The experiment was performed in inverse kinematics using a beam of unstable ${}^{38}\mathrm{K}$ impinged on a windowless ${\mathrm{H}}_2$ target. The ${}^{39}\mathrm{Ca}$ recoils and prompt $\gamma$ rays from ${}^{38}\mathrm{K}\left(p,\gamma \right){}^{39}\mathrm{Ca}$ reactions were detected in coincidence using a recoil mass separator and a BGO array, respectively. For the $689$ keV resonance, we observed a clear recoil-$\gamma$ coincidence signal and extracted resonance strength and energy values of $120_{-30}^{+50}{(stat.)}_{-60}^{+20}(sys.)\mathrm{meV}$ and $679_{-1}^{+2}(stat.)\pm 1(sys.)\mathrm{keV}$, respectively. We also performed a singles analysis, extracting a resonance strength of $120\pm 20(stat.)\pm 15(sys.)\mathrm{meV}$, consistent with the coincidence result. For the $386$ keV and $515$ keV resonances, we extract $90\%$ confidence level upper limits of $2.54$ meV and $18.4$ meV, respectively. We have established a new recommended ${}^{38}\mathrm{K}(p,\gamma ){}^{39}\mathrm{Ca}$ rate based on experimental information, which reduces overall uncertainties near the peak temperatures of nova burning by a factor of $\sim 250$. Using the rate obtained in this work in model calculations of the hottest oxygen-neon novae reduces overall uncertainties on $\mathrm{Ar}$, $\mathrm{K}$, and $\mathrm{Ca}$ synthesis to factors of $15$ or less in all cases.

   nucl-exastro-ph.SRPRC(2018)·9 citations
2. 02*

   Fission fragment mass distribution in ${}^{210}$Po and ${}^{213}$At

   A. Sen🇺🇸 · T. K. Ghosh🇮🇳 · S. Bhattacharya🇮🇳 · K. Banerjee🇮🇳 · C. Bhattacharya🇮🇳 · S. Kundu · G. Mukherjee🇮🇳 · A. Asgar · A. Dey · A. Dhal · Md. Moin Shaikh🇮🇳 · J.K. Meena🇮🇳 and 7 other authors

   Background: The influence of shell effect on the dynamics of the fusion fission process and it's evolution with excitation energy in the pre-actinide Hg-Pb region in general is a matter of intense research in recent years. In particular, a strong ambiguity remains for the neutron shell closed ${}^{210}$Po nucleus regarding the role of shell effect in fission around $\approx$ 30 - 40 MeV of excitation energy. Purpose: We have measured the fission fragment mass distribution of ${}^{210}$Po populated using fusion of ${}^4$He + ${}^{206}$Pb at different excitation energies and compare the result with recent theoretical predictions as well as with our previous measurement for the same nucleus populated through a different entrance channel. Mass distribution in the fission of the neighbouring nuclei ${}^{213}$At is also studied for comparison. Methods: Two large area Multi-wire Proportional Counters (MWPC) were used for complete kinematical measurement of the coincident fission fragments. The time of flight differences of the coincident fission fragments were used to directly extract the fission fragment mass distributions. Results: The measured fragment mass distribution for the reactions ${}^4$He + ${}^{206}$Pb and ${}^4$He + ${}^{209}$Bi were symmetric and the width of the mass distributions were found to increase monotonically with excitation energy above 36.7 MeV and 32.9 MeV, respectively, indicating the absence of shell effects at the saddle. However, in the fission of ${}^{210}$Po, we find minor deviation from symmetric mass distributions at the lowest excitation energy (30.8 MeV). Conclusion: Persistence of shell effect in fission fragment mass distribution of ${}^{210}$Po was observed at the excitation energy $\approx$ 31 MeV as predicted by the theory; at higher excitation energy, however, the present study reaffirms the absence of any shell correction in the fission of ${}^{210}$Po.

   nucl-exPRC(2017)·17 citations
3. 03*

   Two-particle correlations in azimuthal angle and pseudorapidity in Be+Be

   Bartosz Maksiak (for the NA61/SHINE Collaboration)🇵🇱

   The NA61/SHINE experiment aims to discover the critical point of strongly interacting matter and study the properties of the onset of deconfinement. These goals are to be achieved by performing a two dimensional phase diagram $(T-{\mu }_B)$ scan by measurements of hadron production properties in proton-proton, proton-nucleus and nucleus-nucleus interactions as a function of collision energy and system size. In this contribution, the results on two-particle correlations in pseudorapidity and azimuthal angle will be presented for the first time for Be+Be interactions at beam momenta: 20, 30, 40, 75 and 150 GeV/c per nucleon. The NA61/SHINE results will be compared with the already presented results of proton-proton collisions at similar beam momenta as well as to the EPOS model results

   nucl-exhep-exPoS(2018)·0 citations
4. 04*

   Detectors for Nuclear Physics

   T.K. Ghosh🇮🇳

   Progress in nuclear physics is driven by the experimental observation that requires state of the art detectors to measure various kinematic properties, such as energy, momentum, position etc. of the particles produced in a nuclear reaction. Advances in detector technology has enabled nuclear physicists to measure these quantities with better precision, and the reduced cost of the detection system has helped to have larger detection systems (array of detectors) to measure the rare processes with greater sensitivity. Several detection systems have been designed, developed and built in India over last few decades and are being used by the physicists. In this article, I will focus on such developments of detection systems at Variable Energy Cyclotron Centre (VECC), Kolkata.

   ↳ physics.ins-detnucl-exSpringer Proc.Phys.(2018)·1 citation
5. 05*

   Dark Matter Interpretation of the Neutron Decay Anomaly

   Bartosz Fornal🇺🇸 · Benjamin Grinstein🇺🇸

   There is a long-standing discrepancy between the neutron lifetime measured in beam and bottle experiments. We propose to explain this anomaly by a dark decay channel for the neutron, involving one or more dark sector particles in the final state. If any of these particles are stable, they can be the dark matter. We construct representative particle physics models consistent with all experimental constraints.

   ↳ hep-phnucl-exnucl-thPRL(2018)·262 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.