Session Q10: Relativistic Heavy Ions II

Strangeness Signature of Quark Gluon Plasma at LHC

The Alice experiment at LHC has reported kaon and multistrange particle $\overline\Xi, \Xi, \overline\Omega, \Omega$ production multiplicity $dN/dy$ at central rapidity, which we interpret in terms of the statistical hadronization particle production model. This allows the determination of the total strangeness per entropy yield as well as the prediction of not yet reported yields of particles such as single strange $\overline\Lambda, \Lambda$ and the multiply strange $\phi$. We perform this analysis as function of collision centrality and show that for several most central triggers our analysis produces an outcome that is extraordinarily similar. We than use this insight to combine the pertinent data in order to determine the bulk properties of the fireball particle source with unprecedented precision. This helps to establish the hadronization pressure and hadronization energy density of the bulk. We further compare the volume of the fireball source $dV/dy$ with that reported by HBT analysis in order to demonstrate that the LHC generated bulk matter must be expanding more violently, and that it breaks apart at a lower $T$ than is the case at RHIC.   

Measurement of $\phi$ meson production in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV from PHOBOS

Due to a combination of its long lifetime and a small hadronic scattering cross-section, the $\phi$ meson is a valuable probe of the early evolution of matter created in heavy ion collisions. In this talk, we present our measurement of $\phi$ meson production in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV using the $\phi \to K^+K^-$ decay channel. A comparison to the corresponding measurements from PHENIX and STAR will be made. The centrality evolution of $\phi$ meson $dN/dy$ values will be discussed. A motivation for a measurement of $\phi$ meson production at $\sqrt{s_{NN}}\simeq$20 GeV will be given. We also discuss the implications of an absence of any observed in-medium modifications of the mean or the width of the $\phi$ meson.   

A study of lambda baryon production in $\sqrt{s_{NN}}$=200 GeV Au+Au and $p$+$p$ collisions at PHENIX

The lambda baryon is particularly useful in our study of the properties of the quark-gluon plasma (QGP). As a baryon, the lambda will allow us to refine our understanding of hadronization mechanisms. Additionally, the strangeness content of the lambda baryon makes it an excellent probe of the relative differences in strange quark production observed in Au+Au and $p$+$p$ collisions. We present the lambda baryon spectra as a function of transverse momentum $p_T$ and centrality class for $\sqrt{s_{NN}}$=200 GeV Au+Au collisions and for $\sqrt{s_{NN}}$=200 GeV $p$+$p$ collisions, as well as how they relate to one another. In Au+Au collisions we report spectra for 1~GeV/c~$ [Preview Abstract]

Strangeness Enhancement in Heavy Ion Collision

At the LHC energy the strangeness enhancement is expected to saturate leading to fireball of matter expanding and breaking apart, which in turn would provide a very high abundance of strange hadrons. The interaction cross section of kaon with B$_c$ would thus be useful in calculating the production rate of B$_c$ in relativistic heavy ion collision. Accordingly, the cross sections of B$_c$ absorption by kaons are presented, which are calculated using meson exchange model based on hadronic Lagrangian having SU(5) symmetry. The cross sections range from 0.2 to 12 mb for various processes. This scale of variation is comparable to that of pions.   

Higher order flow harmonics from 2.76 TeV PbPb collisions measured by CMS

Collective flow is an important probe of the earliest stages in the expansion of the hot and dense matter created in relativistic heavy-ion collisions. Higher harmonics of the azimuthal distribution of emitted particles, in particular v3 and v4, complement v2 measurements in elucidating the dynamical evolution of the bulk medium and providing constraints on its transport properties. With its large acceptance and broad rapidity coverage, the CMS detector is ideally suited to provide detailed analyses of higher order harmonic flow at the LHC. Measurements of vn (n = 2 to n = 6) in PbPb collisions at $\sqrt{s_{NN}} = 2.76$ TeV using the event-plane, cumulant, and Lee-Yang zeros methods will be presented as a function of p$_{\hbox{T}}$ and centrality. The scaling of the higher order flow harmonics with initial participant eccentricity will be examined.   

Elliptic flow results from 2.76 GeV PbPb collisions measured by CMS

We report on the CMS measurements of the unidentified charged hadron anisotropy parameter, v2, using four different methods: the event-plane, two- or four particle cumulants, and Lee-Yang zeros. Consistent results are found for the different methods after considering their respective sensitivities to non-flow correlations and event-by-event fluctuations in the initial conditions. The anisotropy is studied as a function of transverse momentum, pseudorapidity and centrality in a broad kinematic range: 0.3 $<$ pT $<$ 20 GeV/c, $|\eta|$ $<$ 2.4, and in 12 centrality classes in the range 0-80\%. The CMS results are compared to results obtained at lower center-of-mass energies and various scaling behaviors are examined. The eccentricity-scaled v2 is found to obey a universal scaling with the transverse particle density in different collisions systems and center-of-mass energies. These results are obtained from a large sample of over 22 million events, representing a nearly ten fold statistical increase over previously reported CMS results.   

HBT Measurements for charged pions in Au+Au collisions at $\sqrt{s_{NN}}$=39, 62.4 and 200 GeV

We present Hanbury Brown-Twiss interferometry (HBT) measurements for charged pion pairs obtained in Au+Au collisions using the PHENIX detector during the RHIC run-10 Beam Energy Scan for $\sqrt{s_{NN}}$=39, 62.4 and 200 GeV beam energies. This program is designed to search for the QCD critical point using a variety of observables. One such observable is the space-time extent of the emitting source, obtained through HBT measurements. The space-time extent, which is influenced by the source lifetime and its expansion dynamics, is expected to be sensitive to the location of the critical point. PHENIX measurements will be presented and discussed, as well as compared to recent results reported by the ALICE collaboration for $\sqrt{s_{NN}}$=2.6 TeV Pb+Pb collisions at the LHC and other results obtained at RHIC.