### Proceedings Series

#### Conference Strangeness in Quark Matter 2011

Open and Hidden Strangeness in Hadronic Systems

Acta Phys. Pol. B Proc. Suppl. 5, 201 (2012)

page 201 •

abstract

We investigate production of $\phi$ mesons and ${\mit \Xi }$ baryons in nucleus–nucleus collisions. Reactions on strange particles acting as a catalyser are proposed to interpret the high observed $\phi$ yields in HADES experiments as well as the energy dependence of the widths of $\phi$ rapidity spectra in collisions at the SPS energies. It is argued that the enhancement of ${\mit \Xi }^-$ yield observed by HADES is even higher than originally reported, if effects of the experimental centrality trigger are taken into account. Cross sections for new hadronic processes that could produce ${\mit \Xi }^-$ are reviewed.

What Collective Flow Observables Tell Us About the Expansion of the Plasma

Acta Phys. Pol. B Proc. Suppl. 5, 207 (2012)

page 207 •

abstract

The dynamics of partons, hadrons and strings in relativistic nucleus–nucleus collisions is analyzed within the novel Parton–Hadron–String Dynamics (PHSD) transport approach, which is based on a dynamical quasiparticle model for partons (DQPM) matched to reproduce recent lattice-QCD results — including the partonic equation of state — in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark–antiquark pairs or three quarks (antiquarks), respectively, obeying flavor current-conservation, color neutrality as well as energy-momentum conservation. The PHSD approach is applied to nucleus–nucleus collisions from low SIS to RHIC energies with particular emphasis on strange mesons, baryons and antibaryons as well as azimuthal asymmetries. The traces of partonic interactions are found in particular in the elliptic flow of hadrons with increasing bombarding energy.

Measurements of $K^0_{\rm S}$, ${\mit \Lambda }$ and ${\mit \Xi }$ from Au + Au Collisions at $\sqrt {s_{_{NN}}}=7.7$, 11.5 and 39 GeV in STAR

Acta Phys. Pol. B Proc. Suppl. 5, 213 (2012)

page 213 •

abstract

We report on the measurements of $K^0_{\rm S}$, ${\mit \Lambda }$ and ${\mit \Xi }$ spectra at mid-rapidity ($|y|\lt 0.5$) in the most central (0–5%) Au + Au collisions at $\sqrt {s_{_{NN}}}=7.7$, 11.5 and 39 GeV from the STAR experiment. The extracted yields are consistent with the corresponding data from Pb + Pb collisions measured by the NA49 and CERES experiments at SPS. The ${\mit \Lambda }$, $\overline {{\mit \Lambda }}$, ${\mit \Xi }^-$ and $\overline {{\mit \Xi }}^+$ to $\pi$ ratios agree well with the predictions of the statistical hadronization model at all three energies.

$K^{0}_{\rm {S}}$ and ${\mit \Lambda }$ Production in $pp$ and Pb–Pb Collisions with ALICE at LHC

Acta Phys. Pol. B Proc. Suppl. 5, 219 (2012)

page 219 •

abstract

We have studied the $K^{0}_{\rm {S}}$ and ${\mit \Lambda }$ particles production in $pp$ interactions at $\sqrt {s}=7$ TeV and Pb–Pb collisions at $\sqrt {s_{{NN}}}=2.76$ TeV. The $p_{\rm {T}}$ and centrality dependence of the ${\mit \Lambda }/K^{0}_{\rm {S}}$ ratio are presented and analyzed. Our results are compared with the previous results obtained in $\sqrt {s}=0.9$ TeV $pp$ collisions from ALICE experiment and with the Au–Au results from the STAR experiment at $\sqrt {s_{{NN}}}=0.2$ TeV.

Global Properties of Strange Particle Production in $pp$ and Pb–Pb Collisions with the ALICE Detector

Acta Phys. Pol. B Proc. Suppl. 5, 225 (2012)

page 225 •

abstract

The production of strange and identified hadrons was measured by the ALICE experiment in the new regime of LHC energies. ALICE’s unique particle identification capabilities are based on energy loss, Time of Flight, and decay topology. Thus transverse momentum spectra of pions, kaons, protons, ${\mit \Lambda }$s, ${\mit \Xi }$s, and ${\mit \Omega }$s were measured in $pp$ collisions at $\sqrt {s} = 900$ GeV and $\sqrt {s} = 7$ TeV, as well as in Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV. This allows the precise determination of integrated yields and mean transverse momenta. The results are discussed with respect to their dependence on $\sqrt {s}$ and to expectations from thermal models.

Production of Multi-strange Baryons in 7 TeV Proton–Proton Collisions with ALICE

Acta Phys. Pol. B Proc. Suppl. 5, 231 (2012)

page 231 •

abstract

In the perspective of comparisons between proton–proton and heavy-ion physics, understanding the production mechanisms (soft and hard) in $pp$ that lead to strange particles is of importance. Measurements of charged multi-strange (anti-)baryons (${\mit \Omega ^{\pm }}$ and ${\mit \Xi ^{\pm }}$) are presented for $pp$ collisions at $\sqrt {s} = 7$ TeV. This report is based on results obtained by ALICE (A Large Ion Collider Experiment) from the 2010 data-taking. Taking advantage of the characteristic cascade-decay topology, the identification of ${\mit \Xi ^{-}}$, $\overline {\mit \Xi }^{+}$, ${\mit \Omega }^{-}$ and $\overline {\mit \Omega }^{+}$ can be performed over a wide range of momenta (cf. from 0.6 to 8.5 GeV/$c$ for ${\mit \Xi ^{-}}$, with the present statistics analysed). The production at central rapidity ($\left |y \right | \lt 0.5$) as a function of transverse momentum, $d^{2}N/d{p_{\mathrm {t}}}\,dy$, is presented. These results are compared to PYTHIA Perugia 2011 predictions.

Multi-strange Baryon Production in Pb–Pb Collisions at $\sqrt {s_{NN}} = 2.76$ TeV with the ALICE Experiment at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 237 (2012)

page 237 •

abstract

Preliminary results by the ALICE Collaboration at the CERN Large Hadron Collider are presented for the multi-strange baryons in Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV. Mid-rapidity transverse momentum spectra of the charged ${\mit \Xi }$ and ${\mit \Omega }$ baryons are shown in 0–90% centrality as well as in four centrality classes. The enhancements with respect to $pp$ collisions at the same centre-of-mass energy have also been studied as a function of the mean number of participating nucleons and compared to existing measurements at SPS and RHIC.

Results on Strange Resonances in Pb–Pb Collisions at $\sqrt s_{NN}= 2.76$ TeV from the ALICE Experiment at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 243 (2012)

page 243 •

abstract

Short lived hadronic resonances are sensitive to the properties of the medium created in a heavy-ion collision, in particular to the temperature, density and expansion velocity. Resonances decaying into hadrons are used to estimate the hadronic lifetime and hadronic interaction cross section in the hadronic phase between chemical and kinetic freeze-out. The detection of early decoupled resonances aims at studying chiral symmetry restoration via their mass shift and width broadening. There are reported the first $K^{*}$(892) and $\phi$(1020) results from Pb–Pb collisions at the LHC using the ALICE detector, with excellent identification of the decay particles in a large momentum range.

Leptonic Decay of $\phi$(1020) Meson Measured with the STAR Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 249 (2012)

page 249 •

abstract

We present the measurement of the $\phi$(1020)$\rightarrow e^{+}e^{-}$ transverse momentum spectrum and yield for $0.3 \lt p_{\rm T} \lt 2.5$ GeV at mid-rapidity ($|\eta | \lt 1$) from the STAR experiment in Au+Au collisions at $\sqrt {s_{_{NN}}} = 200$ GeV and compare it to the yield and spectrum from the hadronic decays. We also compare the $\phi$(1020) mass and width obtained by fitting Breit–Wigner function to simulated distributions. Particle identification based on the newly installed STAR Time-of-Flight (TOF) detector in conjunction with energy-loss ($dE/dx$) based particle identification measurements from the Time Projection Chamber (TPC) are used for a clean electron and positron identification.

Strangeness Production in Au–Au Collisions at $\sqrt {s_{NN}}=62.4$ GeV

Acta Phys. Pol. B Proc. Suppl. 5, 255 (2012)

page 255 •

abstract

We obtain strangeness production as function of centrality in a statistical hadronization model analysis of all experimental hadron production data in Au–Au collisions at $\sqrt {s_{NN}}=62.4$ GeV. Our analysis describes successfully the yield of strange and multi-strange hadrons recently published. We explore condition of hadronization as a function of centrality and find universality for the case of chemical non-equilibrium in the hadron phase space corresponding to quark-gluon plasma (QGP) in chemical equilibrium.

Charged Particle Multiplicity, Centrality and the Glauber Model in Pb–Pb Collisions at $\sqrt {s_{NN}}=2.76$ TeV with ALICE

Acta Phys. Pol. B Proc. Suppl. 5, 263 (2012)

page 263 •

abstract

Charged particle multiplicity and transverse energy at midrapidity are key observables to characterize the properties of matter created in heavy-ion collisions. Their dependence on the heavy-ion collision centre-of-mass energy and the collision geometry are important for understanding the dominant particle production mechanisms and the relative contributions from hard scattering and soft processes. The Glauber model connects the geometry and multiplicity of heavy-ion collisions using the nucleon–nucleon cross section. This work will discuss the centrality definition and how it is obtained by ALICE via the Glauber model. The measurement of the inelastic proton–proton cross section and the fraction of the Pb–Pb inelastic cross section seen by the ALICE detector, will be outlined. Finally, the charged particle multiplicity $dN_{\rm ch}/d\eta$ and transverse energy $dE_{\rm T}/d\eta$ as a function of the centrality and energy of the colliding system will be presented.

Identified Primary Hadron Spectra in $pp$ and Pb–Pb Collisions with the ALICE Detector at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 271 (2012)

page 271 •

abstract

The ALICE experiment at the LHC collected $pp$ collisions at $\sqrt {s} = 0.9$, $2.76$ and $7.0$ TeV and Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV. ALICE has several detectors dedicated to Particle IDentification (PID), covering complementary transverse momentum ($p_{\rm T}$) ranges; this enables ALICE to reconstruct identified charged hadron spectra over a wide $p_{\rm T}$ range at mid-rapidity. After a brief review of the different ALICE identification techniques and performance, the $\pi /K/p$ spectra obtained in $pp$ ($\sqrt {s} = 0.9$ TeV and $7.0$ TeV) and Pb–Pb ($\sqrt {s_{NN}} = 2.76$ TeV) collisions will be presented. In addition, studies on the energy dependence of the spectral shape and transverse radial flow will be shown.

Resonance Results from the ALICE Detector in 7 TeV $pp$ Collisions at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 277 (2012)

page 277 •

abstract

The study of resonances in $\sqrt s=7$ TeV $pp$ collisions provides a test of QCD in a new energy domain as well as a baseline for heavy-ion collisions. The resonances $K^*(892)^0$, $\phi (1020)$, ${\mit \Lambda }(1520)$, ${\mit \Sigma }(1385)^{\pm }$, and ${\mit \Xi }(1530)^0$ are reconstructed at mid-rapidity from their hadronic decay using data collected by the ALICE detector. We compare the $\phi (1020)$ and ${\mit \Sigma }(1385)^{\pm }$ $p_{\rm T}$ spectra to perturbative QCD models such as PHOJET and different PYTHIA tunes. We also search for the ${\mit \Phi }(1860)$ pentaquark for which we find no evidence.

Single Electron Analysis of PHENIX Cu+Cu Collisions at Center-of-Mass Energy 200 GeV per Nucleon Pair

Acta Phys. Pol. B Proc. Suppl. 5, 285 (2012)

page 285 •

abstract

Analysis of single electrons created in $\sqrt {s_{NN}} = 200$ GeV Cu+Cu collisions at the PHENIX experiment at RHIC can reveal the influence of the medium on heavy flavor particles created in such collisions. Heavy flavor single electron spectra are presented after use of a cocktail background subtraction, as well as a cross-check using a converter to find photonic background. Comparisons of the nuclear modification factor to $d$+Au and Au+Au collisions of similar $N_{\rm coll}$ are done.

Electrons from Heavy-flavour Decays at Mid-rapidity Measured in $pp$ Collisions at $\sqrt {s}=$ 7 TeV and in Pb–Pb Collisions at $\sqrt {s_{NN}}=$ 2.76 TeV with ALICE at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 291 (2012)

page 291 •

abstract

We present the production cross section of electrons from heavy-flavour hadron decays measured at mid-rapidity ($|\eta |\lt 0.8$) with ALICE in proton–proton collisions at $\sqrt {s}=7$ TeV. The contribution from pure beauty decays is identified using the electron displacement from the interaction vertex. The results are compared to FONLL calculations and used as $pp$ reference for Pb–Pb collisions after scaling to the same centre-of-mass energy. In Pb–Pb collisions at $\sqrt {s_{NN}}=2.76$ TeV, the inclusive electron spectrum is measured at mid-rapidity for different centrality classes and compared to a cocktail of background electrons. The corresponding nuclear modification factor of cocktail-subtracted electrons indicates heavy-flavour suppression by a factor 1.5–5 at high $p_{\rm T}$ in most central Pb–Pb collisions.

Heavy Flavour Production in the Semi-muonic Channel in $pp$ and Pb–Pb Collisions Measured with the ALICE Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 297 (2012)

page 297 •

abstract

The inclusive production differential cross section of muons from heavy flavour decays measured with the ALICE experiment is presented. In $pp$ collisions at $\sqrt {s} = 7$ TeV, the heavy flavour muon production cross section, measured at forward rapidity ($2.5 \lt \eta \lt 4$), is compared to perturbative QCD predictions. A good agreement is found between the data and the model calculations. In Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV the ratio of inclusive muon yield in central to peripheral collisions ($R_{\mathrm {CP}}$) as a function of the collision centrality is reported. A suppression of the inclusive muon yield is observed.

Effect of Temperature-dependent $\eta /s$ on Flow Anisotropies

Acta Phys. Pol. B Proc. Suppl. 5, 305 (2012)

page 305 •

abstract

We investigate the effects of a temperature-dependent shear viscosity over entropy density ratio $\eta /s$ on the flow anisotropy coefficients $v_2$ and $v_4$ in ultrarelativistic heavy-ion collisions at RHIC and LHC. We find that $v_4$ is more sensitive to the viscosity at low temperatures than $v_2$. At RHIC $v_2$ is mostly affected by the viscosity around the phase transition, but the larger the collision energy, the more the quark-gluon plasma viscosity affects $v_2$.

The Elliptic Flow in Au + Au Collisions at $\sqrt {{s}_{_{NN}}}=7.7$, 11.5 and 39 GeV at STAR

Acta Phys. Pol. B Proc. Suppl. 5, 311 (2012)

page 311 •

abstract

We present elliptic flow, $v_2$, measurements for charged and identified particles at midrapidity in Au + Au collisions at $\sqrt {{s}_{_{NN}}}=7.7$, 11.5 and 39 GeV at STAR. We compare the inclusive charged hadron $v_2$ to those from high energies at RHIC ($\sqrt {{s}_{_{NN}}}=62.4$ and 200 GeV) and LHC ($\sqrt {{s}_{_{NN}}}=2.76$ TeV). A significant difference in $v_2$ between baryons and anti-baryons is observed and the difference increases with decreasing beam energy. The $v_2$ of $\phi$ meson is systematically lower than other particles in Au + Au collisions at $\sqrt {{s}_{_{NN}}}=11.5$ GeV.

Energy Dependence of Elliptic Flow of $\phi$-meson in STAR at RHIC

Acta Phys. Pol. B Proc. Suppl. 5, 317 (2012)

page 317 •

abstract

We present the measurement of elliptic flow ($v_{2}$) as a function of transverse momentum ($p_{\rm T}$) for the $\phi$-meson in Au + Au collisions at $\sqrt {s_{NN}} = 7.7$, 11.5 and 39 GeV. At low $p_{\rm T}$ $\phi$-meson $v_{2}$ decreases with decrease in beam energy. The number of constituent quark ($n_{\rm {cq}}$) scaled $v_{2}$ for $\phi$-meson versus ($m_{\rm T} - m_{0}$)/$n_{\rm {cq}}$ follows similar trend as other hadrons for $\sqrt {s_{NN}}= 39$ GeV, whereas the $n_{\rm {cq}}$ scaled $v_{2}$ for $\phi$-mesons follows a different trend compared to the other hadrons at $\sqrt {s_{NN}}= 11.5$ GeV.

Measurement of $J/\psi$ Elliptic Flow in Au + Au Collisions at $\sqrt {s_{NN}}=$ 200 GeV in STAR Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 323 (2012)

page 323 •

abstract

The measurement of $J/\psi$ elliptic flow is presented as a function of transverse momentum for 20%–60% central 200 GeV Au + Au collisions. Total number of reconstructed $J/\psi$ used for this measurement is 13,000, which is unprecedented in relativistic heavy ion collisions so far. Extracted value of elliptic flow is found to be consistent with no flow within errors for transverse momentum larger than 2 GeV/$c$. This suggests that either $J/\psi$ with high transverse momentum is dominantly produced by direct pQCD processes, or charm quarks are not fully thermalized in the medium.

Anisotropic Flow of Identified Particles Measured with the ALICE Detector in the First Year of Heavy Ion Program

Acta Phys. Pol. B Proc. Suppl. 5, 329 (2012)

page 329 •

abstract

The anisotropic flow of identified particles is an important observable to probe the parton nature of the system created in heavy-ion collisions. We report on the measurement of elliptic and triangular flow for charged pions, kaons and protons in lead–lead collisions at 2.76 TeV per nucleon pair center of mass energy, measured with the ALICE detector at the LHC in the first year of the heavy-ion programme. In addition, we focus on the anisotropic flow of particles with strangeness (i.e. ${K^0_{\rm s}}$ and ${\mit \Lambda }$) to reveal any dependence on the flavour of constituent quarks. For identified particles with intermediate transverse momenta we test the quark coalescence picture with $v_{2}$ and $v_{3}$ scaled by the number of constituent quarks as a function of scaled transverse mass $m_{\rm t}$. Comparisons with the RHIC measurements at lower energies and with predictions from models are also discussed.

Measurement of Elliptic Flow of $D^0$ in Pb–Pb Collisions at $\sqrt {s_{NN}}=2.76$ TeV with ALICE at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 335 (2012)

page 335 •

abstract

The study of particle azimuthal anisotropy in heavy-ion collisions provides insight on the collective hydrodynamic expansion of the system and on its equation of state. The measurement of the elliptic flow, $v_2$, of $D$ mesons compared to that of light hadrons is expected to be sensitive to the degree of thermalization of charm quarks within the quark-gluon plasma. The first measurement of $v_2$ of $D^0$ mesons with the ALICE detector at the LHC will be presented. The preliminary results obtained with the first Pb–Pb run at LHC show a hint of non-zero $v_2$ for transverse momenta obeying $2\lt p_{\rm T} \lt 5$ GeV/$c$.

Parton Energy Loss in Two-stream Plasma System

Acta Phys. Pol. B Proc. Suppl. 5, 343 (2012)

page 343 •

abstract

The energy loss of a fast parton scattering elastically in a weakly coupled quark-gluon plasma is formulated as an initial value problem. The approach is designed to study an unstable plasma, but it also reproduces the well known result of energy loss in an equilibrium plasma. A two-stream system, which is unstable due to longitudinal chromoelectric modes, is discussed here in some detail. In particular, a strong time and directional dependence of the energy loss is demonstrated.

Jets and Their Role in Modification of $v_4/v_2^2$ Ratio

Acta Phys. Pol. B Proc. Suppl. 5, 349 (2012)

page 349 •

abstract

Formation and evolution of the $v_2$ and $v_4$ flow pattern in Pb + Pb collisions at $\sqrt {s} = 2.76$ $A$TeV and in Au + Au collisions at $\sqrt {s} = 200$ $A$GeV are analyzed for charged hadrons within the framework of HYDJET++ Monte Carlo model. The model contains both hydrodynamic part and jets, thus allowing for a study of the interplay between the soft and hard processes. It is found that jets are terminating the rise of the elliptic flow with increasing transverse momentum. The final state interactions play a minor role in modification of the $v_4/(v_2)^2$ ratio. In contrast, jets increase this ratio. While jets together with the eccentricity fluctuations are sufficient to describe the RHIC data, the high value of the ratio at LHC is still underpredicted.

High $p_{\rm T}$ Suppression of ${\mit \Lambda }$ and $K^{0}_{\rm s}$ in Pb–Pb Collisions at $\sqrt {s_{NN}}=2.76$ TeV with ALICE

Acta Phys. Pol. B Proc. Suppl. 5, 355 (2012)

page 355 •

abstract

The nuclear modification factors $R_{AA}$ and $R_{\rm CP}$ of ${\mit \Lambda }$ and $K^{0}_{\rm s}$ in Pb–Pb collisions at $\sqrt {s_{NN}}=2.76$ TeV measured by the ALICE experiment at the LHC are presented. In central collisions a strong suppression at high $p_{\rm T}$ ($p_{\rm T} \sim 8$ GeV/$c$) with respect to $pp$ collisions is observed similar for ${\mit \Lambda }$ and $K^{0}_{\rm s}$. The $p_{\rm T}$ region below is dominated by an enhancement of ${\mit \Lambda }$ over the suppressed $K^{0}_{\rm s}$. The results are compared to those for charged particles and to ${\mit \Lambda }$ from lower collision energies.

Generalised Microcanonical Statistics and Fragmentation in Electron–Positron Collisions

Acta Phys. Pol. B Proc. Suppl. 5, 363 (2012)

page 363 •

abstract

A statistical fragmentation model based on the microcanonical ensemble and on a Koba–Nielsen–Olesen (KNO) type scaling of the multiplicity distribution of charged hadrons in electron–positron collisions is presented.

The Spectator-induced Electromagnetic Effect on Kaon Production in Heavy Ion Collisions

Acta Phys. Pol. B Proc. Suppl. 5, 369 (2012)

page 369 •

abstract

The effect of shape modification of charged meson spectra, induced by the presence of the spectator charge in nucleus–nucleus collisions, was studied experimentally and theoretically in our precedent works. The effect was found to cause very large modifications in spectra of light mesons produced in the forward direction. It was also found that due to its sensitivity to initial conditions imposed on final state particle emission, it can be used as a new source of information on the space-time evolution of the non-perturbative particle production process. In this paper, we present the first estimates of the spectator-induced electromagnetic effect on strange meson spectra. We discuss its sensitivity to the space-time evolution of strangeness production. Finally, we explore the possibility of using this effect as a new source of information on the evolution of strangeness in space and in time.

Finite Pressure Corrections to the Parton Structure of Baryon Inside a Nuclear Medium

Acta Phys. Pol. B Proc. Suppl. 5, 375 (2012)

page 375 •

abstract

Our model calculations performed in the frame of the Relativistic Mean Field (RMF) approach show how important are the modifications of a baryon Structure Function (SF) and a nucleon mass in Nuclear Matter (NM) above the saturation point. They originated from the conservation of a parton longitudinal momenta — essential in the explanation of the EMC effect at the saturation point of NM. For higher density the finite pressure corrections emerge from the Hugenholtz–van Hove theorem valid for NM. Here, we show that the course of Equation of State (EoS) in our modified Walecka model is very close to the phenomenlogical non-relativistic expansion of single particle energies in powers of Fermi momentum. The increasing pressure between nucleons starts to increase nucleon Fermi energies $e_{\rm F}$ in comparison to average nucleon energies $e_{\rm A}$, and consequently the Momentum Sum Rule (MSR) is broken by the factor $e_{\rm F}/e_{\rm A}$ in the RMF models. To compensate this factor which increases the longitudinal momentum for nuclear partons, the baryon SF in the nuclear medium and their masses have to be adjusted. We assume that, independently from nuclear density, quarks and gluons carry the same amount of a total longitudinal momenta — the similar assumption is used in the most nuclear models with parton degrees of freedom.

Planetary Impacts by Clustered Quark Matter Strangelets

Acta Phys. Pol. B Proc. Suppl. 5, 381 (2012)

page 381 •

abstract

We propose a model of clustered $u$-$d$-$s$ quark matter that leads to stable bulk strange quark matter. We discuss qualitatively consequences of impacts by sub-planetary mass strangelets on rocky solar system bodies.

Heavy Quark Production at Collider Energies: Some Selected Topics

Acta Phys. Pol. B Proc. Suppl. 5, 387 (2012)

page 387 •

abstract

We discuss production of charm quarks and mesons as well as nonphotonic electrons in $pp$ scattering at RHIC. The distributions in rapidity and transverse momentum are calculated in the $k_{\rm t}$-factorization approach. The hadronization of heavy quarks is done by means of phenomenological fragmentation functions. The semileptonic decay functions found by fitting semileptonic decay data are used. Good description of the inclusive data at large transverse momenta of electrons is obtained and a missing strength at small transverse momenta of electrons is found. We discuss kinematical correlations between charged leptons from semileptonic decays of open charm/bottom, leptons produced in the Drell–Yan mechanism as well as some other mechanisms not included so far in the literature. A good description of the dilepton invariant mass spectrum measured by the PHENIX Collaboration is achieved. Predictions for the dilepton pair transverse momentum distribution as well as distribution in azimuthal angle between electron and positron are presented.

Exclusive Open Strangeness Production in the $pp \to pp\,K^{+} K^{-}$ Reaction at High Energies and a Measurement of Scalar $\chi _{c0}$ Meson

Acta Phys. Pol. B Proc. Suppl. 5, 393 (2012)

page 393 •

abstract

We discuss the results of exclusive $p p \to p p \,K^{+} K^{-}$ reaction at high energies which constitutes an irreducible background to three-body processes $p p \to p p \,M$, where $M=\phi$, $f_{2}(1275)$, $f_{0}(1500)$, $f_{2}'(1525)$, $\chi _{c0}$. We consider central diffractive contribution mediated by Pomeron and Reggeon exchanges including absorption effects due to proton–proton interaction and kaon–kaon rescattering. We make predictions for future experiments at RHIC, Tevatron and LHC. Differential distributions in invariant two-kaon mass, kaon rapidities and transverse momenta of kaons are presented. We discuss a measurement of exclusive production of scalar $\chi _{c0}$ meson in the proton–(anti)proton collisions via $\chi _{c0} \to K^{+}K^{-}$ decay. The corresponding amplitude for exclusive central diffractive $\chi _{c0}$ meson production is calculated within the $k_{\rm t}$-factorization approach.

Results on Elliptic Flow and Higher-order Flow Harmonics in Pb + Pb Collisions from the ATLAS Detector at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 401 (2012)

page 401 •

abstract

The measurement of elliptic flow and higher-order flow harmonics of charged particles in $\sqrt {s_{NN}}=2.76$ TeV Pb + Pb collisions with the ATLAS detector is presented. Fourier harmonics $v_{2}$–$v_{6}$ were extracted with the event plane and two-particle correlation methods in a broad range of transverse momentum (0.5 GeV $\lt p_{\rm T}\lt 20$ GeV), pseudorapidity ($|\eta |\lt 2.5$) and collision centrality (0–80%). Results obtained with the two methods were found to be consistent. Elliptic flow shows rapid rise with $p_{\rm T}$ up to about 3 GeV followed by a decrease within range 3–8 GeV and then becomes weakly dependent at the highest $p_{\rm T}$. Similar trend is observed for higher-order harmonics. As a function of pseudorapidity a very weak dependence of all flow harmonics is measured.

Higher Harmonic Anisotropic Flow Measurements of Charged Particles at $\sqrt {s_{_{NN}}} =$ 2.76 TeV with the ALICE Detector

Acta Phys. Pol. B Proc. Suppl. 5, 407 (2012)

page 407 •

abstract

We report the measurements of elliptic flow $v_{2}$, as well as higher harmonics triangular flow $v_{3}$ and quadrangular flow $v_{4}$, in $\sqrt {s_{_{NN}}}=2.76$ TeV Pb–Pb collisions, measured with the ALICE detector. We show that the measured elliptic and triangular flow can be understood from the initial spatial anisotropy and its event-by-event fluctuations. The resulting fluctuations of $v_{2}$ and $v_{3}$ are also discussed.

Non-photonic Electron and Charged Hadron Azimuthal Correlation in $p+p$ Collisions at $\sqrt {s}$ = 500 GeV in STAR

Acta Phys. Pol. B Proc. Suppl. 5, 413 (2012)

page 413 •

abstract

We present the STAR preliminary results of non-photonic electron and charged hadron azimuthal correlation at midrapidity at $6.5\lt p_{\rm T}^{\rm NPE}\lt 12.5$ GeV/$c$ in 500 GeV $p$+$p$ collisions. The correlation distributions are compared with PYTHIA simulations to extract the relative contribution of $B$ mesons to non-photonic electrons. Our measurements indicate that the extracted $B$ meson decay contribution is above 60% at $8.5\lt p_{\rm T}\lt 12.5$ GeV/$c$. By comparing the results between 200 and 500 GeV energies, we find that $e_B/(e_B+e_D)$ ratio is higher at 500 GeV than 200 GeV at $6.5\lt p_{\rm T}\lt 9.5$ GeV/$c$.

Bulk Observables, Long-range Correlations and Flow in $pp$ Collisions at LHC

Acta Phys. Pol. B Proc. Suppl. 5, 419 (2012)

page 419 •

abstract

Bulk observables like multiplicity, rapidity and transverse momentum distributions of hadrons produced both in inelastic and non-diffractive $pp$ collisions at energies from $\sqrt {s} = 200$ GeV to 7 TeV are described within the Monte Carlo quark-gluon string model. The short-range correlations of particles in the strings and interplay between the multi-string processes at ultra-relativistic energies lead to violation of Feynman scaling at midrapidity. Model predicts strong increase of the slope with energy in forward–backward multiplicity dependence $\langle n_{\rm F}(n_{\rm B}) \rangle$ due to long-range correlations between particles produced in the multi-string processes. The comparison of model results on pion–pion femtoscopic correlations with the experimental data favors significant decrease of particle formation time with rising collision energy. The possibility to produce anisotropic flow on the initial stages of $pp$ reactions, both directed $v_1$ and elliptic $v_2$, from the decay of the strings is discussed.

Investigating the Origin of the Long Range Pseudo Rapidity Correlation in 2d Dihadron Measurements from STAR

Acta Phys. Pol. B Proc. Suppl. 5, 425 (2012)

page 425 •

abstract

Angular dihadron correlations reveal novel structures in central Au+Au collisions at $\sqrt {S_{NN}} = 200$ GeV. One of them, known as the ridge, is elongated in pseudo rapidity and peaks on the near side ($\Delta \phi \approx 0$). Investigating the origin of the ridge structure helps to understand the hot dense matter that is created in ultra relativistic heavy ion collisions. Results showing the $\langle p_{\rm T}\rangle$ dependence of the ridge structure are presented. Evidence for possible jet and non-jet contributions to the ridge structure will be discussed.

Forward–Backward Rapidity Correlations in Relativistic Heavy Ion Collisions: Torqued Fireball

Acta Phys. Pol. B Proc. Suppl. 5, 433 (2012)

page 433 •

abstract

Statistical fluctuations in the transverse distribution of sources in relativistic heavy ion collisions and an asymmetric emission profile associated with the wounded nucleons lead to rapidity dependence of the reaction plane. The size of this effect is estimated for the gold–gold collisions at the highest RHIC energy ($\sqrt {s_{NN}}=200$ GeV) in the Glauber model using GLISSANDO. The hydrodynamical evolution of the resulting torqued fireball is carried out in 3+1 dimensions considering a perfect fluid. Hadronization is simulated using THERMINATOR including non-flow contribution coming from resonance decays. Some experimental measures that can be used to detect the torque effect are proposed.

Directed Flow of Identified Charged Particles from the RHIC Beam Energy Scan

Acta Phys. Pol. B Proc. Suppl. 5, 439 (2012)

page 439 •

abstract

We present the STAR measurements of directed flow, $v_1$, for $\pi ^\pm$, $K^\pm$, protons and antiprotons, as well as for all detected charged particles in Au + Au collisions at $\sqrt {s_{NN}} =$ 7.7, 11.5 and 39 GeV as a function of transverse momentum, rapidity and centrality. Results are compared to the predictions from transport models.

ALICE Measurement of Directed Flow of Hadrons in Pb–Pb Collisions

Acta Phys. Pol. B Proc. Suppl. 5, 445 (2012)

page 445 •

abstract

Directed flow is one of the key observables used for studying the properties of the hot and dense matter produced in relativistic heavy-ion collisions. Hereby we are reporting the recent results on the directed flow measurements performed by the ALICE Collaboration for Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV in a wide rapidity range, $|\eta |\lt 5.1$. Directed flow is studied as a function of pseudorapidity, $\eta$, transverse momentum, $p_{\rm t}$, and collision centrality. The results are compared with RHIC data and with the model predictions available for CERN LHC energies.

Strange and Non-strange Hadron Resonance Production by Quark Coalescence, Investigating Quark Number Scaling

Acta Phys. Pol. B Proc. Suppl. 5, 451 (2012)

page 451 •

abstract

RHIC data on light and strange hadron resonance production induced an extended discussion on hadron production mechanisms in heavy ion collisions. Resonance yields are far from the thermal expectations and standard coalescence models have also difficulties to reproduce these yields. We have developed the Resonance Coalescence Model (RCM) which contains the features of coalescence and quark scaling, and includes the width of the hadron resonances. It opens a way to handle resonances in the high mass region for all non-strange, strange and charm hadron resonances within the same description scheme. The talk focuses on the model structure, the question of quark scaling with resonances and predictions for strange and charm resonance ratios.

Flow Characteristics and Strangeness Production in the Framework of Highly-anisotropic and Strongly-dissipative Hydrodynamics

Acta Phys. Pol. B Proc. Suppl. 5, 457 (2012)

page 457 •

abstract

The recently formulated model of highly-anisotropic and strongly dissipative hydrodynamics is used in 3+1 dimensions to describe flow characteristics and strangeness production in Au+Au collisions at the highest RHIC beam energy. Our results show very weak dependence on the initial momentum anisotropy, provided the anisotropic phase lasts no longer than 1 fm/$c$.

Light Neutral Mesons Production in $p$–$A$ Collisions at $\sqrt {s} = 27.5$ GeV with the NA60 Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 465 (2012)

page 465 •

abstract

The NA60 experiment has studied low-mass muon pair production in proton–nucleus ($p$–$A$) collisions with a system of Be, Cu, In, W, Pb and U targets using a 400 GeV/$c$ proton beam at the CERN SPS. Thanks to the collected data sample of 180,000 low-mass muon pairs, the most precise measurement currently available was performed for the electromagnetic transition form factors of the $\eta$ and $\omega$ mesons. The $\rho$-line shape was quantitatively investigated, and its effective temperature measured for the first time in elementary collisions. The transverse momentum spectra for the $\rho /\omega$ and $\phi$ mesons have been studied in the full $p_{\rm T}$ range accessible, up to 2 GeV/$c$. The cross section ratios $\sigma _\rho /\sigma _\omega$ and $\sigma _\phi /\sigma _\omega$ have been considered in full $p_{\rm T}$ as a function of the size of the production target. The nuclear dependence of the production cross sections of the $\eta$, $\omega$ and $\phi$ mesons has finally been studied in terms of the power law $\sigma _{pA} \propto {A}^\alpha$, where the $\alpha$ parameter has been found to increase as a function of $p_{\rm T}$.

Dielectron Production in $p$ + $p$ and Au + Au Collisions at $\sqrt {s_{_{NN}}}=200$ from STAR

Acta Phys. Pol. B Proc. Suppl. 5, 471 (2012)

page 471 •

abstract

The dielectron spectra in the mass range $0\lt M_{ee}\lt 3.3$ GeV/$c^2$ are measured at midrapidity ($|y|\lt 1$) by the STAR experiment in $p$ + $p$ and Au + Au collisions at $\sqrt {s_{_{NN}}}=200$ GeV. The measured dilepton continuum is compared to hadronic cocktail simulations. The vector meson in-medium modification in the low mass region and the first result of dielectron elliptic flow are also presented. In addition, the $\omega$ yields via dileptonic decays are measured for $p$ + $p$ and Au + Au collisions.

Vector Meson Production in the Dimuon Channel in the ALICE Experiment at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 477 (2012)

page 477 •

abstract

The purpose of the ALICE experiment at the LHC is the study of the quark-gluon plasma (QGP) formed in ultra-relativistic heavy-ion collisions, a state of matter in which quarks and gluons are deconfined. The properties of this state of strongly-interacting matter can be accessed through the study of light vector mesons ($\rho$, $\omega$ and $\phi$). Indeed, the strange quark content ($s\bar {s}$) of the $\phi$ meson makes its study interesting in connection with the strangeness enhancement observed in heavy-ion collisions. Moreover, $\rho$ and $\omega$ spectral function studies give information on chiral symmetry restoration. Vector meson production in $pp$ collisions is important as a baseline for heavy-ion studies and for constraining hadronic models. We present results on light vector meson production obtained with the muon spectrometer of the ALICE experiment in pp collisions at $\sqrt {s}=7$ TeV. Production ratios, integrated and differential cross sections for $\phi$ and $\omega$ are presented. Those results are extracted for $p_{\rm T} \gt 1$ GeV/$c$ and $2.5 \lt y \lt 4$.

Mott–Hagedorn Resonance Gas and Lattice QCD Results

Acta Phys. Pol. B Proc. Suppl. 5, 485 (2012)

page 485 •

abstract

A combined effective model reproducing the equation of state of hadronic matter as obtained in recent lattice QCD simulations is presented.

System Size and Beam Energy Dependence of Hadronic Production and Freeze-out

Acta Phys. Pol. B Proc. Suppl. 5, 491 (2012)

page 491 •

abstract

We present results from STAR for Au + Au 19.6 GeV and Cu + Cu 22.4 GeV collisions from previous RHIC runs. Particle spectra for $\pi ^{\pm }$, $K^{\pm }$, $p$ and $\bar {p}$ are studied as a function of ${m_{\rm T}-m_{0}}$. We report on the $K/\pi$ and $p/\pi$ ratios from these collisions. Freeze-out parameters from both chemical freeze-out and kinetic freeze-out are extracted from the spectra. We make systematic comparisons with the data from 7.7, 11.5 and 39 GeV Au + Au collisions taken in 2010 during the RHIC Beam Energy Scan.

Search for the QCD Critical Point by Higher Moments of Net-proton Multiplicity Distributions at RHIC

Acta Phys. Pol. B Proc. Suppl. 5, 497 (2012)

page 497 •

abstract

Higher moments of net-proton multiplicity distributions are applied to search for the QCD critical point. In this paper, we will present measurements for kurtosis ($\kappa$), skewness ($S$) and variance ($\sigma ^2$) of net-proton multiplicity distributions at the mid-rapidity ($|y|\lt 0.5$) and transverse momentum range $0.4\lt p_{\rm T}\lt 0.8$ GeV/$c$ for Au+Au collisions at $\sqrt {s_{_{{NN}}}} = 7.7$, 11.5, 39, 62.4 and 200 GeV, Cu+Cu collisions at $\sqrt {s_{_{{NN}}}} = 22.4$, 62.4 and 200 GeV, and $p$+$p$ collisions at $\sqrt {s_{_{{NN}}}} = 62.4$ and 200 GeV. The moment products $\kappa \sigma ^2$ and $S \sigma$ of net-proton distributions, which are related to volume independent baryon number susceptibility ratios, are consistent with Lattice QCD and Hadron Resonance Gas (HRG) model calculations at high energies ($\sqrt {s_{_{{NN}}}} = 62.4$ and 200 GeV). Deviations of $\kappa \sigma ^2$ and $S\sigma$ for the Au+Au collisions at low energies ($\sqrt {s_{_{{NN}}}} = 7.7$, 11.5 and 39 GeV) from HRG model calculations are also observed.

Beam Energy Dependence of Event-by-Event Hadron Ratio Fluctuations from Au+Au Collisions at RHIC

Acta Phys. Pol. B Proc. Suppl. 5, 503 (2012)

page 503 •

abstract

We present measurements of event-by-event fluctuations on hadron multiplicity ratios ($K/\pi$, $p/\pi$, $K/p$) in Au+Au collisions at $\sqrt {s_{NN}} = 7.7$, 11.5, 19.6, 39 and 200 GeV using the STAR detector at RHIC. The magnitudes of dynamical fluctuations $\sigma _{\rm dyn}$ for $p/\pi$ and $K/p$ ratios change smoothly from a larger negative value at $\sqrt {s_{NN}} = 7.7$ GeV to a smaller negative value at 200 GeV while that for the $K/\pi$ ratios exhibits no significant beam energy dependence. We use a four-event mixing scheme as a reference to evaluate dynamical fluctuations related to pair production $\sigma ^{\rm pair}_{\rm dyn}$ for the $p/K$, $K/p$, $\bar {p}/p$ and $K^{-}/K^{+}$ ratios at $\sqrt {s_{NN}} = 200$ GeV. We find that these pair-related fluctuations all exhibit a maximum at the mid-central collisions and decrease at the most peripheral and most central collisions.

Probe of the QCD Phase Diagram with $\phi$-meson Production in Relativistic Nuclear Collisions at STAR

Acta Phys. Pol. B Proc. Suppl. 5, 509 (2012)

page 509 •

abstract

We present $\phi$-meson transverse momentum distribution as well as its elliptic flow ($v_{2}$) measurements in Au + Au collisions at center-of-mass energy per nucleon pair $\sqrt {s_{NN}} =$ 7.7, 11.5 and 39 GeV with the data taken from STAR experiment at RHIC in the year 2010. We discuss the energy dependence of $\phi$-meson elliptic flow ($v_{2}$) and central-to-peripheral nuclear modification factors ($R_{\rm CP}$). The $v_2$ of $\phi$-mesons are compared to those from other hadron species. The implications on partonic-hadronic phase transition are discussed.

Charge Dependence and Scaling Properties of Dynamical $K/\pi$, $p/\pi$, and $K/p$ Fluctuations from the STAR Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 515 (2012)

page 515 •

abstract

Dynamical fluctuations in global conserved quantities such as baryon number, strangeness, or charge may be enhanced near a QCD critical point. Charge dependent results from new measurements of dynamical $K/\pi$, $p/\pi$, and $K/p$ ratio fluctuations are presented. The STAR experiment has performed a comprehensive study of the energy dependence of these dynamical fluctuations in Au+Au collisions at the energies $\sqrt {s_{NN}} = 7.7$–200 GeV using the observable, $\nu _{\rm dyn}$. These results are compared to previous measurements and to theoretical predictions. Various proposed scaling scenarios that attempt to remove the intrinsic volume dependence of $\nu _{\rm dyn}$ and to simplify comparisons between experimental measurements are also considered. Constructing an intensive quantity allows for a direct connection to thermodynamic predictions.

The QCD Critical End Point in the Context of the Polyakov–Nambu–Jona-Lasinio Model

Acta Phys. Pol. B Proc. Suppl. 5, 523 (2012)

page 523 •

abstract

We investigate the phase diagram of the so-called Polyakov–Nambu–Jona-Lasinio model at finite temperature and nonzero chemical potential with three quark flavors. Chiral and deconfinement phase transitions are discussed, and the relevant order parameters are analyzed. A special attention is payed to the critical end point (CEP): the influence of the strangeness on the location of the CEP is studied; also the strength of the flavor-mixing interaction alters the CEP location, since when it becomes weaker the CEP moves to low temperatures and can even disappear.

Fluctuations and Correlations in Polyakov Loop Extended Chiral Fluid Dynamics

Acta Phys. Pol. B Proc. Suppl. 5, 529 (2012)

page 529 •

abstract

We study nonequilibrium effects at the QCD phase transition within the framework of Polyakov loop extended chiral fluid dynamics. The quark degrees of freedom act as a locally equilibrated heat bath for the sigma field and a dynamical Polyakov loop. Their evolution is described by a Langevin equation with dissipation and noise. At a critical point we observe the formation of long-range correlations after equilibration. During a hydrodynamical expansion nonequilibrium fluctuations are enhanced at the first order phase transition compared to the critical point.

Strangeness in the Cores of Neutron Stars

Acta Phys. Pol. B Proc. Suppl. 5, 535 (2012)

page 535 •

abstract

The measurement of the mass $1.97\pm 0.04~M_\odot$ for PSR J1614-2230 provides a new constraint on the equation of state and composition of matter at high densities. In this contribution, we investigate the possibility that the dense cores of neutron stars could contain strange quarks either in a confined state (hyperonic matter) or in a deconfined one (strange quark matter) while fulfilling a set of constraints including the new maximum mass constraint. We account for the possible appearance of hyperons within an extended version of the density-dependent relativistic mean-field model, including the $\phi$ meson interaction channel. Deconfined quark matter is described by the color superconducting three-flavor NJL model.

Production of $J/\psi$ in Minimum-bias $p+p$ Collisions at $\sqrt {s}=$ 200 GeV in STAR

Acta Phys. Pol. B Proc. Suppl. 5, 543 (2012)

page 543 •

abstract

In this paper, the production of $J/\psi$ in minimum-bias $p+p$ collisions at $\sqrt {s}=200$ GeV in STAR is investigated. Low-$p_{\rm T}$ $J/\psi$ in $p+p$ collisions can provide information about the production mechanism and serve as a reference for $J/\psi$ production measurements in $A+A$ collisions. The invariant cross section is presented in the transverse momentum range of (0–3) GeV/$c$ and the $\langle p^{2}_{\rm T}\rangle$ has been calculated. The $J/\psi$ $p_{\rm T}$ spectrum is compared to Color Evaporation Model predictions and results from the PHENIX experiment at mid-rapidity. The results from STAR are consistent with Color Evaporation Model and PHENIX.

$J/\psi$ Polarization in $p$ + $p$ Collisions at $\sqrt {s} = 200$ GeV in STAR

Acta Phys. Pol. B Proc. Suppl. 5, 549 (2012)

page 549 •

abstract

In this paper, $J/\psi$ polarization at mid-rapidity in $p$ + $p$ collisions at $\sqrt {s}=200$ GeV measured in the STAR experiment at RHIC is reported. $J/\psi$ production is analyzed via the dielectron decay channel. $J/\psi$ polarization is extracted from the decay angular distribution in the helicity frame. The $J/\psi$ polarization is measured at transverse momentum range (2–6) GeV/$c$ and is found to be consistent with NLO$^+$ Color Singlet Model (NLO$^+$ CSM), Color Octet Model (COM) predictions and with no polarization within current uncertainties.

Open Heavy Flavor at RHIC and LHC in a Partonic Transport Model

Acta Phys. Pol. B Proc. Suppl. 5, 555 (2012)

page 555 •

abstract

Heavy quarks are a unique probe to study the medium produced in ultra-relativistic heavy ion collisions. Within the partonic transport model Boltzmann Approach to Multi-parton Scatterings (BAMPS) the production, energy loss and elliptic flow of heavy quarks are investigated in 3 + 1 dimensional simulations of the quark-gluon plasma evolution. With only binary interactions between heavy quarks and particles from the medium calculated within perturbative QCD, the results on elliptic flow and the nuclear modification factor are not compatible with experimental data from RHIC and LHC. However, if the binary cross section is multiplied with $K=4$ both the elliptic flow and the nuclear modification factor are simultaneously described at RHIC and also LHC. Furthermore, preliminary results are presented that the implementation of radiative processes leads to a stronger suppression which agrees well with the measured nuclear modification factor at RHIC without the need of any $K$ factor.

Inclusive $J/\psi$ Production in Proton–Proton Collisions at the ALICE Experiment

Acta Phys. Pol. B Proc. Suppl. 5, 561 (2012)

page 561 •

abstract

The ALICE experiment at the CERN Large Hadron Collider allows the study of $J/\psi$ production for various colliding systems at different energies. In particular, ALICE has studied $J/\psi$ production in proton–proton collisions at 2.76 and 7 TeV centre-of-mass energies, as well as in lead–lead collisions at 2.76 TeV per nucleon pair. In this paper, ALICE results on inclusive $J/\psi$ production in proton–proton collisions, measured in the rapidity region $|y| \lt 0.9$ for the dielectron channel and $2.5\lt y\lt 4$ for the dimuon one, are given. The integrated and differential inclusive cross sections, together with the charged particle multiplicity dependence are discussed. First preliminary results on non-prompt $J/\psi$ from $B$ mesons decays are also given.

Study of $J/\psi$ Production in Pb–Pb Collisions at 2.76 TeV with the ALICE Experiment at the LHC

Acta Phys. Pol. B Proc. Suppl. 5, 567 (2012)

page 567 •

abstract

We present the measurement of $J/\psi$ nuclear modification factor in Pb–Pb collisions at $\sqrt {s_{NN}}=2.76$ TeV at both mid- and forward rapidity, from data collected in 2010 by the ALICE experiment. Results are compared to RHIC data and results from other experiments at LHC, as well as with existing models. The current status of two ongoing analyses on $J/\psi$ production in ultra-peripheral collisions and $J/\psi$ elliptic flow is also discussed.

Charmonium Suppression in the UrQMD Transport Model

Acta Phys. Pol. B Proc. Suppl. 5, 573 (2012)

page 573 •

abstract

We study charmonium physics in heavy-ion collisions within the framework of the non-equilibrium transport model UrQMD. Using this model we compute the nuclear modification factor $R_{AA}$ at SPS, RHIC and LHC energies. For this purpose we test a scenario for charmonium dissociation and charmonium recombination containing charmonium melting, a prehadronic phase and a final hadronic phase. Our UrQMD approach includes explicitly the interactions of the charmed particles with the surrounding medium. We show that we are able to describe the charmonium suppression at different collision energies within this approach.

$D$ Meson Production at Central Rapidity in $pp$ Collisions at 7 TeV with the ALICE Detector

Acta Phys. Pol. B Proc. Suppl. 5, 579 (2012)

page 579 •

abstract

Heavy quark production is a powerful tool to test pQCD calculations in $pp$ collisions in the new energy regime of the LHC. In addition, the measurement of the $D$ meson $p_{\rm t}$ differential cross section provides a reference for the study of QCD matter effects on charm quarks in Pb–Pb collisions. Thanks to its excellent tracking system and particle identification capabilities, the ALICE detector allows charmed hadron measurements in the mid-rapidity region down to low momentum. We will present preliminary results for the $p_{\rm t}$ differential cross sections of $D^{0}$, $D^{*+}$ and $D^{+}$ in $pp$ collisions at 7 TeV measured via their hadronic decay channels. The status of the $D^{+}_{s}$ and ${\mit \Lambda }_{c}$ analyses will also be presented.

$D$ Meson Nuclear Modification Factors in Pb–Pb Collisions at $\sqrt {s_{NN}} = 2.76$ TeV Measured with the ALICE Detector at the CERN–LHC

Acta Phys. Pol. B Proc. Suppl. 5, 585 (2012)

page 585 •

abstract

The properties of the hot and dense QCD medium formed in ultra-relativistic heavy ion collisions, as well as the mechanism of in-medium partonic energy loss, can be accessed via the study of the $D$ mesons nuclear modification factor. The ALICE experiment has measured $D$ meson production in $pp$ and Pb–Pb collisions at the LHC at $\sqrt {s} =7$ and 2.76 TeV and at $\sqrt {s_{NN}} = 2.76$ TeV, respectively, via the exclusive reconstruction of hadronic decay channels. $D$ mesons are selected by exploiting the high-resolution tracking performance and the hadron identification capabilities of the ALICE detectors. In this contribution, we report on the analyses of the $D^0\rightarrow K^-\pi ^+$, the $D^+ \rightarrow K^- \pi ^+ \pi ^+$ and the $D^{*+}\rightarrow D^0 \pi ^+$ channels. The preliminary results on $D$ mesons nuclear modification factors are presented.

Study of Hyperon–Hyperon Correlations and Search for $H$-dibaryon Using STAR Detector at RHIC

Acta Phys. Pol. B Proc. Suppl. 5, 593 (2012)

page 593 •

abstract

High yield of strange particle production per central collision in nucleus–nucleus collisions at RHIC and high statistics data set from STAR experiment allow us to measure ${\mit \Lambda \Lambda }$ correlations. The ${\mit \Lambda \Lambda }$ correlation measurement is also closely related to a possible six-quark state $H$-dibaryon, which is yet to be observed experimentally. The first measurement of ${\mit \Lambda \Lambda }$ correlations in Au + Au collisions for $\sqrt {s_{NN}}= 39$, 62.4 and 200 GeV and search for $H$-dibaryon with its weak decay ${\mit \Lambda } p\pi$ in Au + Au collisions for $\sqrt {s_{NN}}= 200$ GeV using the STAR experiment at RHIC are presented here.

Light Hypernuclei Production in Pb–Pb Collisions at $\sqrt {s_{NN}}=2.76$ TeV with ALICE at LHC

Acta Phys. Pol. B Proc. Suppl. 5, 599 (2012)

page 599 •

abstract

Relativistic heavy-ion collisions offer a method to produce strangeness, hyperons, and also hyperon–baryon bound systems called hypernuclei. Thanks to its excellent performance for the reconstruction and identification of low $p_{\rm t}$ particles and light ions, the ALICE detector is ideally suited for this kind of measurements. In this paper, preliminary results of hypertriton production in Pb–Pb collisions at $\sqrt {s_{NN}} = 2.76$ TeV will be reported using the data sample collected by the ALICE experiment during the first LHC heavy-ion run at the end of 2010. The ${}^{3}_{\mit \Lambda }{\rm H}~({}^{3}_{\overline {\mit \Lambda }}\overline {\rm H}$) signal is extracted from the study of its mesonic decay ${}^{3}_{\mit \Lambda }{\rm H}\rightarrow {}^{3}{\rm He}+\pi ^{-} ({}^{3}_{\overline {\mit \Lambda }}\overline {\rm H} \rightarrow {}^{3}\overline {\rm He} + \pi ^{+}$). Different background evaluation methods will be discussed.

Light Nuclei and Anti-nuclei Production in $pp$ and Pb–Pb Collisions with ALICE

Acta Phys. Pol. B Proc. Suppl. 5, 605 (2012)

page 605 •

abstract

The production of nuclei and anti-nuclei in $pp$ collisions at $\sqrt {s}=7$ TeV and Pb–Pb collisions at $\sqrt {s_{NN}}=2.76$ TeV has been studied using the $\textrm {ALICE}$ experiment. These particles are identified using their specific energy loss ($dE/dx$) measurement in the Time Projection Chamber. The Inner Tracking System gives a precise determination of the event vertex, which helps to distinguish primary from secondary particles. The high statistics of over 380 million events for $pp$ collisions and 17 million events for Pb–Pb collisions provides a significant number of light nuclei and anti-nuclei (Pb–Pb collisions: $\sim 700$ anti-$^{3}$He and $\sim 4 \overline {\alpha }$). In this paper, we report on light nuclei and anti-nuclei production at the LHC.

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