Tue·Jan 10, 2017Tuesday·January 10, 2017

1. 01*

   Search for Possible Solar Influences in Ra-226 Decays

   Daniel D. Stancil · Sümeyra Balci Yegen · David A. Dickey · Chris R. Gould🇺🇸

   Measurements of Ra-226 activity from eight HPGe gamma ray detectors at the NC State University PULSTAR Reactor were analyzed for evidence of periodic variations, with particular attention to annual variations. All measurements were made using the same reference source, and data sets were of varying length taken over the time period from September 1996 through August 2014. Clear evidence of annual variations was observed in data from four of the detectors. Short time periodograms from the data sets suggest temporal variability of both the amplitude and frequency of these variations. The annual variations in two of the data sets show peak values near the first of February, while surprisingly, the annual variations in the other two are roughly out of phase with the first two. Three of the four detectors exhibited annual variations over approximately the same time period. A joint statistic constructed by combining spectra from these three shows peaks approximating the frequencies of solar r-mode oscillations with ${\nu }_R=11.74$ cpy, $m=1$, and $l=3,5,6.$ The fact that similar variations were not present in all detectors covering similar time periods rules out variations in activity as the cause, and points to differing sensitivities to unspecified environmental parameters instead. In addition to seasonal variations, the modulation of environmental parameters by solar processes remains a possible explanation of periodogram features, but without requiring new physics.

   nucl-exastro-ph.SRResults Phys.(2017)·3 citations
2. 02*

   Proton rms-radii from low-q power expansions?

   Ingo Sick🇨🇭 · Dirk Trautmann🇨🇭

   Several recent publications claim that the proton charge {\em rms}-radius resulting from the analysis of electron scattering data restricted to {\em low} momentum transfer agrees with the radius determined from muonic hydrogen, in contrast to the radius resulting from analyses of the full (e,e) data set which is $0.04fm$ larger. Here we show why these publications erroneously arrive at the low radii.

   nucl-exnucl-thPRC(2017)·26 citations
3. 03*

   Measurement of $D^0$ Meson Production and Azimuthal Anisotropy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 200 GeV

   Guannan Xie🇨🇳

   Due to the large masses, heavy-flavor quarks are dominantly produced in initial hard scattering processes and experience the whole evolution of the medium produced in heavy-ion collisions at RHIC energies. They are also expected to thermalize slower than light-flavor quarks. Thus the measurement of heavy quark production and azimuthal anisotropy can provide important insights into the medium properties through their interactions with the medium. In these proceedings, we report measurements of $D^0$ production and elliptic flow ($v_2$) via topological reconstruction using STAR's recently installed Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV confirms the strong suppression at high transverse momenta ($p_T$) reported in the previous publication with much improved precision. We also report the measurement of elliptic flow for $D^0$ mesons in a wide transverse momentum range in 0-80% minimum-bias Au+Au collisions. The $D^0$ elliptic flow is finite for $p_T$ $>$ 2 GeV/c and is systematically below that of light hadrons in the same centrality interval. Furthermore, several theoretical calculations are compared to both $R_{AA}$ and $v_2$ measurements, and the charm quark diffusion coefficient is inferred to be between 2 and $\sim$12.

   nucl-exhep-exNucl.Part.Phys.Proc.(2017)·4 citations
4. 04*

   Search for the QCD Critical Point with Fluctuations of Conserved Quantities in Relativistic Heavy-Ion Collisions at RHIC : An Overview

   Xiaofeng Luo🇨🇳 · Nu Xu🇨🇳

   Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in relativistic heavy-ion collisions to probe the QCD phase transition and search for the QCD critical point. In this paper, we review the experimental measurements of the cumulants (up to fourth order) of event-by-event net-proton (proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}}=7.7,11.5,14.5,19.6,27,39,62.4,200$ GeV from the first phase of beam energy scan program at the Relativistic Heavy-Ion Collider (RHIC). We also summarize the data analysis methods of suppressing the volume fluctuations, auto-correlations and the unified description of efficiency correction and error estimation. Based on theoretical and model calculations, we will discuss the characteristic signatures of critical point as well as backgrounds for the fluctuation observables in heavy-ion collisions. The physics implications and the future second phase of the beam energy scan (2019-2020) at RHIC will be also discussed.

   nucl-exhep-exhep-phnucl-thNucl.Sci.Tech.(2017)·550 citations
5. 05*

   Revisit of directed flow in relativistic heavy-ion collisions from a multiphase transport model

   Chong-Qiang Guo🇨🇳 · Chun-Jian Zhang🇨🇳 · Jun Xu🇨🇳

   We have revisited several interesting questions on how the rapidity-odd directed flow is developed in relativistic ${}^{197}$Au+${}^{197}$Au collisions at $\sqrt{s_{NN}}$ = 200 and 39 GeV based on a multiphase transport model. As the partonic phase evolves with time, the slope of the parton directed flow at midrapidity region changes from negative to positive as a result of the later dynamics at 200 GeV, while it remains negative at 39 GeV due to the shorter life time of the partonic phase. The directed flow splitting for various quark species due to their different initial eccentricities is observed at 39 GeV, while the splitting is very small at 200 GeV. From a dynamical coalescence algorithm with Wigner functions, we found that the directed flow of hadrons is a result of competition between the coalescence in momentum and coordinate space as well as further modifications by the hadronic rescatterings.

   ↳ nucl-thhep-exnucl-exEPJA(2017)·15 citations
6. 06*

   Analytical coalescence formula for particle production in relativistic heavy-ion collisions

   Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳

   Based on a covariant coalescence model with a blast-wave-like parametrization for the phase-space configuration of constituent particles at freeze-out, we derive an approximate analytical formula for the yields of clusters produced in relativistic heavy-ion collisions. Compared to previous existing formulae, the present work additionally considers the contributions from the longitudinal dimension in momentum space, the relativistic corrections and the finite size effects of the produced clusters relative to the spatial distribution of constituent particles at freeze-out. The new analytical coalescence formula provides a useful tool to evaluate the yield of produced clusters, such as light nuclei from nucleon coalescence and hadrons from quark coalescence, in heavy-ion collisions. As a first application of the new analytical formula, we explore the strangeness population factor $S_3{=}_{\Lambda }^3$H/(${}^3$He$\times \Lambda /$p) based on nucleon/$\Lambda$ coalescence as well as the production of exotic hadrons based on quark coalescence, in central Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV. The results are compared with the predictions from other models.

   ↳ nucl-thastro-ph.HEhep-phnucl-exPRC(2017)·58 citations
7. 07*

   Spin-dependent sum rules connecting real and virtual Compton scattering verified

   Vadim Lensky🇩🇪 · Vladimir Pascalutsa🇩🇪 · Marc Vanderhaeghen🇩🇪 · Chung Wen Kao🇹🇼

   We present a detailed derivation of the two sum rules relating the spin polarizabilities measured in real, virtual, and doubly-virtual Compton scattering. For example, the polarizability ${\delta }_{LT}$, accessed in inclusive electron scattering, is related to the spin polarizability ${\gamma }_{E1E1}$ and the slope of generalized polarizabilities $P^{(M1,M1)1}-P^{(L1,L1)1}$, measured in, respectively, the real and the virtual Compton scattering. We verify these sum rules in different variants of chiral perturbation theory, discuss their empirical verification for the proton, and prospect their use in studies of the nucleon spin structure.

   ↳ hep-phnucl-exnucl-thPRD(2017)·14 citations
8. 08*

   Observables for longitudinal flow correlations in heavy-ion collisions

   Jiangyong Jia🇺🇸 · Peng Huo🇺🇸 · Guoliang Ma🇨🇳 · Maowu Nie🇨🇳

   We propose several new observables/correlators, based on correlations between two or more subevents separated in pseudorapidity $\eta$, to study the longitudinal flow fluctuations. We show that these observables are sensitive to the event-by-event fluctuations, as a function of $\eta$, of the initial condition as well as the non-linear mode-mixing effects. Experimental measurement of these observables shall provide important new constraints on the boost-variant event-by-event initial conditions required by all 3+1-dimensional viscous hydrodynamics models.

   ↳ nucl-thnucl-exJ.Phys.G(2017)·33 citations
9. 09*

   Statistical model analysis of $\alpha$-induced reaction cross sections of ${}^{64}$Zn at low energies

   P. Mohr · Gy. Gyürky🇭🇺 · Zs. Fülöp

   Background $\alpha$-nucleus potentials play an essential role for the calculation of $\alpha$-induced reaction cross sections at low energies in the statistical model. Uncertainties of these calculations are related to ambiguities in the adjustment of the potential parameters to experimental elastic scattering angular distributions (typically at higher energies) and to the energy dependence of the effective $\alpha$-nucleus potentials. Purpose The present work studies cross sections of $\alpha$-induced reactions for ${}^{64}$Zn at low energies and their dependence on the chosen input parameters of the statistical model calculations. The new experimental data from the recent Atomki experiments allow for a ${\chi }^2$-based estimate of the uncertainties of calculated cross sections at very low energies. Method The recent data for the ($\alpha$,$\gamma$), ($\alpha$,$n$), and ($\alpha$,$p$) reactions on ${}^{64}$Zn are compared to calculations in the statistical model. A survey of the parameter space of the widely used computer code TALYS is given, and the properties of the obtained ${\chi }^2$ landscape are discussed. Results The best fit to the experimental data at low energies shows ${\chi }^2/F\approx 7.7$ per data point which corresponds to an average deviation of about 30% between the best fit and the experimental data. Several combinations of the various ingredients of the statistical model are able to reach a reasonably small ${\chi }^2/F$, not exceeding the best-fit result by more than a factor of 2. Conclusions The present experimental data for ${}^{64}$Zn in combination with the statistical model calculations allow to constrain the astrophysical reaction rate within about a factor of 2. However, the significant excess of ${\chi }^2/F$ of the best-fit from unity asks for further improvement of the statistical model calculations and in particular the $\alpha$-nucleus potential.

   ↳ nucl-thnucl-exPRC(2017)·16 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.