Tue·Jul 5, 2016Tuesday·July 5, 2016

1. 01*

   Minimizing statistical and systematic bias in transverse momentum correlations for relativistic heavy-ion collisions

   Robert L. Ray🇺🇸 · Prabhat Bhattarai🇺🇸

   Two-particle correlation measurements and analysis are an important component of the relativistic heavy-ion physics program. In particular, particle pair-number correlations on two-dimensional transverse momentum ($p_t$) allow unique access to soft, semi-hard and hard-scattering processes in these collisions. Precise measurements of this type of correlation are essential for understanding the dynamics in heavy-ion collisions. However, transverse momentum correlation measurements are especially vulnerable to statistical and systematic biases. In this paper the origins of these large bias effects are explained and mathematical correlation forms are derived from mean-$p_t$ fluctuation quantities in the literature. Monte Carlo simulations are then used to determine the conditions, e.g. multiplicity and collision centrality bin widths, where each correlation form is minimally biased. The ranges of applicability for each correlation quantity are compared. Several are found to reproduce the assumed input correlations with reasonable fidelity over a wide range of conditions encountered in practical analysis of data.

   nucl-exPRC(2016)·3 citations
2. 02*

   Isobaric multiplet mass equation in the $A=31$ $T=3/2$ quartets

   M. B. Bennett🇺🇸 · C. Wrede🇺🇸 · B. A. Brown🇺🇸 · S. N. Liddick🇺🇸 · D. Pérez-Loureiro🇺🇸 · D. W. Bardayan🇺🇸 · A. A. Chen🇨🇦 · K. A. Chipps🇺🇸 · C. Fry🇺🇸 · B. E. Glassman🇺🇸 · C. Langer🇩🇪 · N. R. Larson🇺🇸 and 11 other authors

   The observed mass excesses of analog nuclear states with the same mass number $A$ and isospin $T$ can be used to test the isobaric multiplet mass equation (IMME), which has, in most cases, been validated to a high degree of precision. A recent measurement [Kankainen et al., Phys. Rev. C 93 041304(R) (2016)] of the ground-state mass of ${}^{31}$Cl led to a substantial breakdown of the IMME for the lowest $A=31,T=3/2$ quartet. The second-lowest $A=31,T=3/2$ quartet is not complete, due to uncertainties associated with the identity of the ${}^{31}$S member state. Using a fast ${}^{31}$Cl beam implanted into a plastic scintillator and a high-purity Ge $\gamma$-ray detection array, $\gamma$ rays from the ${}^{31}$Cl$(\beta \gamma )$${}^{31}$S sequence were measured. Shell-model calculations using USDB and the recently-developed USDE interactions were performed for comparison. Isospin mixing between the ${}^{31}$S isobaric analog state (IAS) at 6279.0(6) keV and a nearby state at 6390.2(7) keV was observed. The second $T=3/2$ state in ${}^{31}$S was observed at $E_x=7050.0(8)$ keV. Isospin mixing in ${}^{31}$S does not by itself explain the IMME breakdown in the lowest quartet, but it likely points to similar isospin mixing in the mirror nucleus ${}^{31}$P, which would result in a perturbation of the ${}^{31}$P IAS energy. USDB and USDE calculations both predict candidate ${}^{31}$P states responsible for the mixing in the energy region slightly above $E_x=6400$ keV. The second quartet has been completed thanks to the identification of the second ${}^{31}$S $T=3/2$ state, and the IMME is validated in this quartet.

   nucl-exPRC(2016)·12 citations
3. 03*

   Beam energy dependence and updated test of the Trojan horse nucleus invariance via the d(d,p)t measurement at ultra-low energies

   Chengbo Li · Qungang Wen · Yuanyong Fu · Jing Zhou · Shuhua Zhou · Qiuying Meng · C. Spitaleri · A. Tumino · R. G. Pizzone · L. Lamia

   The ${}^2\mathrm{H}(d,p){}^3\mathrm{H}$ bare nucleus astrophysical S(E) factor has been measured indirectly at energies from about 500 keV down to several keV by means of the Trojan-horse method applied to the quasi-free process ${}^2\mathrm{H}({}^6\mathrm{Li},pt){}^4\mathrm{He}$ induced at the lithium beam energy of 11 and 9.5 MeV, which makes the virtual binary process incident energy ${\mathrm{E}}_{dd}^{qf}$ go much closer to the zero-quasi-free-energy point than that in the previous similar experiment. The obtained results are compared with direct data as well as with previous indirect investigation of the same binary reactions. It shows that the precision of S(E) data in low energy range extracted via the same Trojan horse nucleus (${}^6\mathrm{Li}=(d\oplus \alpha )$ ) becomes better when the incident energy decreases from high value down to the zero-quasi-free-energy point. The very good agreement between data extracted from different Trojan horse nucleus (${}^6\mathrm{Li}=(d\oplus \alpha )$ vs. ${}^3\mathrm{He}=(d\oplus p)$) gives a strong updated test for the independence of the binary indirect cross section on the chosen Trojan horse nucleus at low energies.

   nucl-exPRC(2017)·12 citations
4. 04*

   Late Time Emission of Prompt Fission Gamma Rays

   P. Talou🇺🇸 · T. Kawano🇺🇸 · I. Stetcu🇺🇸 · J. P. Lestone · E. McKigney · M. B. Chadwick

   The emission of prompt fission $\gamma$ rays within a few nanoseconds to a few microseconds following the scission point is studied in the Hauser-Feshbach formalism applied to the deexcitation of primary excited fission fragments. Neutron and $\gamma$-ray evaporations from fully accelerated fission fragments are calculated in competition at each stage of the decay, and the role of isomers in the fission products, before $\beta$-decay, is analyzed. The time evolution of the average total $\gamma$-ray energy, average total $\gamma$-ray multiplicity, and fragment-specific $\gamma$-ray spectra, is presented in the case of neutron-induced fission reactions of ${}^{235}$U and ${}^{239}$Pu, as well as spontaneous fission of ${}^{252}$Cf. The production of specific isomeric states is calculated and compared to available experimental data. About 7% of all prompt fission $\gamma$ rays are predicted to be emitted between 10 nsec and 5 $\mu$sec following fission, in the case of ${}^{235}$U and ${}^{239}$Pu $(n_{\mathrm{th}},f)$ reactions, and up to 3% in the case of ${}^{252}$Cf spontaneous fission. The cumulative average total $\gamma$-ray energy increases by 2 to 5% in the same time interval. Finally, those results are shown to be robust against significant changes in the model input parameters.

   ↳ nucl-thnucl-exPRC(2016)·32 citations
5. 05*

   Electromagnetic effects on meson production: a new tool for studying the space-time evolution of heavy ion collisions

   Andrzej Rybicki🇵🇱 · Antoni Szczurek🇵🇱 · Mariola Klusek-Gawenda🇵🇱 · Nikolaos Davis🇵🇱 · Vitalii Ozvenchuk🇵🇱 · Miroslaw Kielbowicz🇵🇱

   We review our studies of spectator-induced electromagnetic (EM) effects on the emission of charged mesons in the final state of ultrarelativistic heavy ion collisions. We argue that these effects offer sensitivity to the distance $d_E$ between the charged meson formation zone at freeze-out and the spectator system. As such, they can serve as an independent, new tool to probe the space-time and longitudinal evolution of the system created in the collision. As a phenomenological application for this tool in the context of resonance production and decay, we obtain a first estimate of the time of pion emission from EM effects. This we compare to existing HBT data.

   ↳ nucl-thnucl-exEPJ Web Conf.(2016)·4 citations
6. 06*

   Towards laboratory detection of topological vortices in superfluid phases of QCD

   Arpan Das🇮🇳 · Shreyansh S. Dave🇮🇳 · Somnath De🇮🇳 · Ajit M. Srivastava🇮🇳

   Topological defects arise in a variety of systems, e.g. vortices in superfluid helium to cosmic strings in the early universe. There is an indirect evidence of neutron superfluid vortices from glitches in pulsars. One also expects that topological defects may arise in various high baryon density phases of quantum chromodynamics (QCD), e.g. superfluid topological vortices in the color flavor locked (CFL) phase. Though vastly different in energy/length scales, there are universal features, e.g. in the formation of all these defects. Utilizing this universality, we investigate the possibility of detecting these topological superfluid vortices in laboratory experiments, namely heavy-ion collisions. Using hydrodynamic simulations, we show that vortices can qualitatively affect the power spectrum of flow fluctuations. This can give unambiguous signal for superfluid transition resulting in vortices, allowing for check of defect formation theories in a relativistic quantum field theory system, and the detection of superfluid phases of QCD. Detection of nucleonic superfluid vortices in low energy heavy-ion collisions will give opportunity for laboratory controlled study of their properties, providing crucial inputs for the physics of pulsars.

   ↳ hep-phcond-mat.supr-connucl-exnucl-thMod.Phys.Lett.A(2017)·5 citations
7. 07*

   Event patterns (particle scatter plots) extracted from charged particle spectra in $pp$ and Pb-Pb collisions at 2.76 TeV

   Ya-Hui Chen🇨🇳 · Fu-Hu Liu🇨🇳 · Sakina Fakhraddin🇸🇦 · Magda A. Rahim🇸🇦 · Mai-Ying Duan🇨🇳

   The transverse momentum ($p_T$) and pseudorapidity ($\eta$) spectra of charged particles produced in proton-proton ($pp$) and lead-lead (Pb-Pb) collisions at the large hadron collider (LHC) are described by a hybrid model. In the model, the $p_T$ spectrum is described by a two-component distribution which contains an inverse power-law suggested by the QCD (Quantum Chromodynamic) calculus and an Erlang distribution resulted from a multisource thermal model. The $\eta$ spectrum is described by a Gaussian rapidity ($y$) distribution resulted from the Landau hydrodynamic model and the two-component $p_T$ distribution, where the conversion between $y$ and $\eta$ is accurately considered. The modelling results are in agreement with the experimental data measured by the ATLAS Collaboration in $pp$ collisions at center-of-mass energy $\sqrt{s}=2.76$ TeV and in Pb-Pb collisions at center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=2.76$ TeV. Based on the parameter values extracted from $p_T$ and $\eta$ or $y$ spectra, the event patterns or particle scatter plots in three-dimensional velocity and momentum spaces are obtained.

   ↳ hep-phhep-exnucl-exnucl-thJ.Phys.G(2017)·5 citations
8. 08*

   Excitation functions of parameters extracted from three-source (net-)proton rapidity distributions in Au-Au and Pb-Pb collisions over an energy range from AGS to RHIC

   Li-Na Gao🇨🇳 · Fu-Hu Liu🇨🇳 · Yan Sun🇨🇳 · Zhu Sun🇨🇳 · Roy A. Lacey🇺🇸

   Experimental results of the rapidity spectra of protons and net-protons (protons minus antiprotons) emitted in gold-gold (Au-Au) and lead-lead (Pb-Pb) collisions, measured by a few collaborations at the alternating gradient synchrotron (AGS), super proton synchrotron (SPS), and relativistic heavy ion collider (RHIC), are described by a three-source distribution. The values of the distribution width ${\sigma }_C$ and contribution ratio (relative contribution) $k_C$ of the central rapidity region, and the distribution width ${\sigma }_F$ and rapidity shift $\Delta y$ of the forward/backward rapidity regions, are then obtained. The excitation function of ${\sigma }_C$ increases generally with increase of the center-of-mass energy per nucleon pair $\sqrt{s_{NN}}$. The excitation function of ${\sigma }_F$ shows a saturation at $\sqrt{s_{NN}}=8.8$ GeV. The excitation function of $k_C$ shows a minimum at $\sqrt{s_{NN}}=8.8$ GeV and a saturation at $\sqrt{s_{NN}}\approx 17$ GeV. The excitation function of $\Delta y$ increase monotonously with $\ln \sqrt{s_{NN}}$ in the considered energy range.

   ↳ hep-phhep-exnucl-exnucl-thEPJA(2017)·6 citations
9. 09*

   Has the QCD critical point been observed at RHIC?

   N.G. Antoniou🇬🇷 · N. Davis🇬🇷 · F.K. Diakonos🇬🇷

   The experimental search for the location of the QCD critical point in the phase diagram is of primary importance. In a recent publication it is claimed that measurements at RHIC lead not only to the location of the critical point (${\mu }_{cep}=95$ MeV, $T_{cep}=165$ MeV) but also to the verification of its universality class ($3d$ Ising system) by extracting the values of the critical exponents ($\gamma =1.2$, $\nu =0.66$). We argue that this claim is based on an erroneous treatment of scaling relations near the critical point. As a result, the correct interpretation of the measurements cannot be linked to the QCD critical point.

   ↳ nucl-thnucl-ex5 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.