Simple analytic solution of fireball hydrodynamics

A new family of simple analytic solutions of hydrodynamics is found for non-relativistic, rotationally symmetric fireballs assuming an ideal gas equation of state. The solution features linear flow profile and a non-trivial transverse temperature profile. The radial temperature gradient vanishes only in the collisionless gas limit. The Zimanyi-Bondorf-Garpman solution and the Buda-Lund parameterization of expanding hydrodynamical sources are recovered as special cases. The results are applied to predict new features of proton-proton correlations and spectra data at 1.93 AGeV Ni + Ni reactions.Comment: Latex, Revte

Conference Summary of QNP2018

This report is the summary of the Eighth International Conference on Quarks and Nuclear Physics (QNP2018). Hadron and nuclear physics is the field to investigate high-density quantum many-body systems bound by strong interactions. It is intended to clarify matter generation of universe and properties of quark-hadron many-body systems. The QNP is an international conference which covers a wide range of hadron and nuclear physics, including quark and gluon structure of hadrons, hadron spectroscopy, hadron interactions and nuclear structure, hot and cold dense matter, and experimental facilities. First, I introduce the current status of the hadron and nuclear physics field related to this conference. Next, the organization of the conference is explained, and a brief overview of major recent developments is discussed by selecting topics from discussions at the plenary sessions. They include rapidly-developing field of gravitational waves and nuclear physics, hadron interactions and nuclear structure with strangeness, lattice QCD, hadron spectroscopy, nucleon structure, heavy-ion physics, hadrons in nuclear medium, and experimental facilities of EIC, GSI-FAIR, JLab, J-PARC, Super-KEKB, and others. Nuclear physics is at a fortunate time to push various projects at these facilities. However, we should note that the projects need to be developed together with related studies in other fields such as gravitational physics, astrophysics, condensed-matter physics, particle physics, and fundamental quantum physics.Comment: 10 pages, LaTeX, 1 style file, 3 figure files, Proceedings of Eighth International Conference on Quarks and Nuclear Physics (QNP2018), November 13-17, 2018, Tsukuba, Japa

Resonance decay effects on anisotropy parameters

We present the elliptic flow $v_2$ of pions produced from resonance decays. The transverse momentum $p_T$ spectra of the parent particles are taken from thermal model fits and their $v_2$ are fit under the assumption that they follow number-of-constituent-quark (NCQ) scaling expected from quark-coalescence models. The $v_2$ of pions from resonance particle decays is found to be similar to the measured pion $v_2$. We also propose the measurement of electron $v_2$ as a means to extract open-charm $v_2$ and investigate whether a thermalized system of quarks and gluons (a quark-gluon plasma) is created in collisions of Au nuclei at RHIC.Comment: 5 pages, 4 figure

Size of Fireballs Created in High Energy Lead-Lead Collisions as Inferred from Coulomb Distortions of Pion Spectra

We compute the Coulomb effects produced by an expanding, highly charged fireball on the momentum distribution of pions. We compare our results to data on Au+Au at 11.6 A GeV from E866 at the BNL AGS and to data on Pb+Pb at 158 A GeV from NA44 at the CERN SPS. We conclude that the distortion of the spectra at low transverse momentum and mid-rapidity can be explained in both experiments by the effect of the large amount of participating charge in the central rapidity region. By adjusting the fireball expansion velocity to match the average transverse momentum of protons, we find a best fit when the fireball radius is about 10 fm, as determined by the moment when the pions undergo their last scattering. This value is common to both the AGS and CERN experiments.Comment: Enlarged discussion, new references added, includes new analysis of pi-/pi+ at AGS energies. 12 pages 5 figures, uses LaTex and epsfi

Effect of Finite Granularity of Detectors on Anisotropy Coefficients

The coefficients that describe the anisotropy in the azimuthal distribution of particles are lower when the particles are recorded in a detector with finite granularity and measures only hits. This arises due to loss of information because of multiple hits in any channel. The magnitude of this loss of signal depends both on the occupancy and on the value of the coefficient. These correction factors are obtained for analysis methods differing in detail, and are found to be different.Comment: 11 pages including 2 figure

Overview of charm production at RHIC

In this presentation, I discussed a) the charm total cross-section and its comparisons to measurements at other beam energies and pQCD calculations; b) the semileptonic decay of charmed hadrons and the sensitivity of non-photonic leptons to charm quark collective flow and freeze-out; c) semileptonic decayed electron spectrum at high transverse momentum, its comparison to FONLL in p+p and d+Au collisions, and heavy-quark energy loss in Au+Au collisions.Comment: 8 pages, 4 figures, overview talk at SQM2006: Strangeness in Quark Matter Los Angeles, CA, Mar. 26-31, 2006; minor text changes and references adde

Evidence of early multi-strange hadron freeze-out in high energy nuclear collisions

Recently reported transverse momentum distributions of strange hadrons produced in Pb(158AGeV) on Pb collisions and corresponding results from the relativistic quantum molecular dynamics (RQMD) approach are examined. We argue that the experimental observations favor a scenario in which multi-strange hadrons are formed and decouple from the system rather early at large energy densities (around 1 GeV/fm$^3$). The systematics of the strange and non-strange particle spectra indicate that the observed transverse flow develops mainly in the late hadronic stages of these reactions.Comment: 4 pages, 4 figure

Low Freeze-out Temperature and High Collective Velocities in Relativistic Heavy-Ion Collisions

On the basis of a nine-parameter expanding source model that includes special relativity, quantum statistics, resonance decays, and freeze-out on a realistic hypersurface in spacetime, we analyze in detail invariant pi+, pi-, K+, and K- one-particle multiplicity distributions and pi+ and K+ two-particle correlations in nearly central collisions of Si + Au at a laboratory bombarding energy per nucleon of 14.6 GeV/c. By considering separately the one-particle data and the correlation data, we find that the central baryon density, nuclear temperature, transverse collective velocity, longitudinal collective velocity, and source velocity are determined primarily by one-particle multiplicity distributions and that the transverse radius, longitudinal proper time, width in proper time, and pion incoherence fraction are determined primarily by two-particle correlations. By considering separately the pion data and the kaon data, we find that although the pion freeze-out occurs somewhat later than the kaon freeze-out, the 99% confidence-level error bars associated with the two freeze-outs overlap. These and other detailed studies confirm our earlier conclusion based on the simultaneous consideration of the pion and kaon one-particle and correlation data that the freeze-out temperature is less than 100 MeV and that both the longitudinal and transverse collective velocities--which are anti-correlated with the temperature--are substantial. We also discuss the flaws in several previous analyses that yielded a much higher freeze-out temperature of approximately 140 MeV for both this reaction and other reactions involving heavier projectiles and/or higher bombarding energies.Comment: 14 pages. RevTeX 3.1. Submitted to Physical Review C. PostScript version available at http://t2.lanl.gov/publications/publications.html or at ftp://t2.lanl.gov/pub/publications/lf

Directed flow of antiprotons in Au+Au collisions at AGS

Directed flow of antiprotons is studied in Au+Au collisions at a beam momentum of 11.5A GeV/c. It is shown that antiproton directed flow is anti-correlated to proton flow. The measured transverse momentum dependence of the antiproton flow is compared with predictions of the RQMD event generator.Comment: 16 pages, 6 figure

Low-mass e+e- pair production in 158 A GeV Pb-Au collisions at the CERN SPS, its dependence on multiplicity and transverse momentum

We report a measurement of low-mass electron pairs observed in 158 GeV/nucleon Pb-Au collisions. The pair yield integrated over the range of invariant masses 0.2 < m < 2.0 GeV is enhanced by a factor of 3.5 +/- 0.4 (stat) +/- 0.9 (syst) over the expectation from neutral meson decays. As observed previously in S-Au collisions, the enhancement is most pronounced in the invariant-mass region 300-700 MeV. For Pb-Au we find evidence for a strong increase of the enhancement with centrality. In addition, we show that the enhancement covers a wide range in transverse momentum, but is largest at the lowest observed pt.Comment: 17 pages, 4 figures, submitted to Phys.Lett.