Tue·Dec 25, 2018Tuesday·December 25, 2018

1. 01*

   Measurements of open charm hadron production in Au+Au Collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV at STAR

   Guannan Xie (for the STAR Collaboration)🇺🇸

   We report on the measurements of production of various charmed hadrons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV (including $D^0(\overline{D^0})$ and ${\Lambda }_c^{\pm }$) obtained via topological reconstruction, utilizing the Heavy Flavor Tracker at STAR. Precise results on the $D^0$ yields from the 2014 data are reported for a wide transverse momentum range down to 0 in various centrality bins. With the high-statistics data collected in 2014 and 2016, and the usage of a supervised machine learning algorithm for signal-to-background separation, the first measurement of the centrality and transverse momentum dependences of ${\Lambda }_c^{\pm }$ production is shown. Finally, the total charm quark cross section extracted from these measurements in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV is presented.

   nucl-exhep-exPoS(2018)·4 citations
2. 02*

   PHENIX measurements of low momentum direct photon radiation from large and small systems in (ultra)relativistic heavy ion collisions: direct photon scaling

   Vladimir Khachatryan (for the PHENIX Collaboration)🇺🇸

   The PHENIX collaboration has measured low momentum direct photon radiation in Au+Au collisions at 200 GeV, 62.4 GeV and 39 GeV, in Cu+Cu at 200 GeV as well as in p+p, p+Au and d+Au at $\sqrt{s_{NN}}=$ 200 GeV. In these measurements PHENIX has discovered a large excess over the scaled p+p yield of direct photons in A+A collisions, and a non-zero excess, observed within systematic uncertainties, over the scaled p+p yield in central p+A collisions. Another finding is that at low-$p_T$ the integrated yield of direct photons, $d{N}_{\gamma }/dy$, from large systems shows a behavior of universal scaling as a function of the charged-particle multiplicity, $(d{N}_{ch}/d\eta {)}^{\alpha }$, with $\alpha =1.25$, which means that the photon production yield increases faster than the charged-particle multiplicity.

   nucl-ex2 citations
3. 03*

   Direct-photon and heavy-flavour production in proton-proton collisions at $\sqrt{s}=7$ TeV with ALICE

   Horst Sebastian Scheid (for the ALICE Collaboration)🇩🇪

   Low-mass dielectron measurements play an essential role in the study of the Quark-Gluon Plasma (QGP) created in ultra-relativistic heavy-ion collisions. They are produced in all stages of the collision and are not affected by final-state interactions. Thus, they provide a penetrating probe of the created medium. In the dielectron intermediate-mass region a measurement of the thermal radiation from the QGP gives information on the medium temperature. However, in this region the main component of the dielectron continuum stems from correlated semi-leptonic decays of charm and beauty hadrons. Therefore, it is crucial to understand the heavy-flavour (HF) production in vacuum and to find a way to separate this contribution from the thermal dielectron signal of the QGP. In this paper we will present the production of correlated ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pairs in pp collisions at $\sqrt{s}=7$ TeV with the expectations from known hadronic sources as a function of $m_{\mathrm{ee}}$, $p_{\mathrm{T},\mathrm{ee}}$, and the pair distance of closest approach to the primary vertex $\mathrm{DC}{\mathrm{A}}_{\mathrm{ee}}$. The extraction of the ratio of inclusive photons to decay photons and the charm and beauty cross sections from a fit of the data with different Monte-Carlo generators are presented, providing insight into the mechanisms of heavy-flavour production. In particular, we demonstrate how the $\mathrm{DC}{\mathrm{A}}_{\mathrm{ee}}$ variable will allow prompt and non-prompt dielectron pairs to be separated and thus help to disentangle the contribution of thermal radiation from the contribution of charm and beauty. Finally, we present the prospect of extending this analysis to proton-lead collisions.

   nucl-exPoS(2019)·0 citations
4. 04*

   The Interaction of Neutrons With 7Be: Lack of Standard Nuclear Physics Solution to the "Primordial 7Li Problem"

   Moshe Gai🇺🇸

   The destruction of 7Be with neutrons represents the last possible standard avenue to reduce the predicted abundance of the primordial 7Li and in this way to attempt to solve the Cosmological 7Li problem. We discuss the results of an experiment performed at the Soreq Applied Research Accelerator Facility (SARAF) in Israel where we measured the Maxwellian Averaged Cross Sections (MACS) of the 7Be(n,p), 7Be(n,a), and 7Be(n,ga) reactions. Our MACS measured at 49.5 keV in the window of the Big Bang Nucleosynthesis (BBN), indicate the lack of standard nuclear physics solution to the "Primordial 7Li Problem".

   nucl-ex5 citations
5. 05*

   Time Projection Chamber (TPC) Detectors for Nuclear Astrophysics Studies With Gamma Beams

   M. Gai🇺🇸 · D. Schweitzer🇺🇸 · S.R. Stern🇺🇸 · A.H. Young🇺🇸 · R. Smith🇺🇸 · M. Cwiok🇵🇱 · J.S. Bihalowicz🇵🇱 · H. Czyrkowski🇵🇱 · R. Dabrowski🇵🇱 · W. Dominik🇵🇱 · A. Fijalkowska🇵🇱 · Z. Janas🇵🇱 and 24 other authors

   Gamma-Beams at the HIgS facility in the USA and anticipated at the ELI-NP facility, now constructed in Romania, present unique new opportunities to advance research in nuclear astrophysics; not the least of which is resolving open questions in oxygen formation during stellar helium burning via a precise measurement of the 12C(a,g) reaction. Time projection chamber (TPC) detectors operating with low pressure gas (as an active target) are ideally suited for such studies. We review the progress of the current research program and plans for the future at the HI{\gamma}S facility with the optical readout TPC (O-TPC) and the development of an electronic readout TPC for the ELI-NP facility (ELITPC).

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2020)·12 citations
6. 06*

   A meta-analysis of neutron lifetime measurements

   Ashwani Rajan🇮🇳 · Shantanu Desai🇮🇳

   We calculated the median as well as weighted mean central estimates for the neutron lifetime, from a subset of measurements compiled in the 2019 update of the Particle Data Group (PDG). We then reconstruct the error distributions for the residuals using three different central estimates and then check for consistency with a Gaussian distribution. We find that although the error distributions using the weighted mean as well as median estimate are consistent with a Gaussian distribution, the Student's $t$ and Cauchy distribution provide a better fit. This median statistic estimate of the neutron lifetime from these measurements is given by $881.5\pm 0.47$ seconds. This can be used as an alternate estimate of the neutron lifetime. We also note that the discrepancy between beam and bottle-based measurements using median statistics of the neutron lifetime persists with a significance between 4-8$\sigma$, depending on which combination of measurements is used.

   ↳ hep-phastro-ph.COhep-exnucl-ex+1PTEP(2020)·13 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.