Mon·Jul 4, 2011Monday·July 4, 2011

1. 01*

   Charged-particle multiplicity and transverse energy in Pb-Pb collisions at sqrt(snn) = 2.76 TeV with ALICE

   Constantin Loizides (for the ALICE collaboration)🇺🇸

   The measurements of charged-particle multiplicity and transverse energy at mid-rapidity in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV are reported as a function of centrality. The fraction of the inelastic cross section recorded by the ALICE detector is estimated using a Glauber model. The results scaled by the number of participating nucleons are compared with pp collisions at the same collision energy, to similar results obtained at significantly lower energies, and with models based on different mechanisms for particle production in nuclear collisions.

   nucl-exJ.Phys.G(2011)·20 citations
2. 02*

   Dihadron correlations in PbPb collisions at 2.76 TeV with CMS

   Jeremy Callner (for the CMS Collaboration)🇺🇸

   Measurements of charged dihadron DeltaEta-DeltaPhi correlations from the CMS collaboration are presented for PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair over a broad range of pseudorapidity and the full range of azimuthal angle. A significant correlated yield is observed for pairs of particles with small DeltaPhi but large longitudinal separation DeltaEta, commonly known as the "ridge". The ridge persists up to at least |DeltaEta| = 4 and the dependence of the ridge region shape and yield on collision centrality and transverse momentum has been measured. A Fourier analysis of the long-range two-particle correlation is presented and discussed in the context of higher order flow coefficients.

   nucl-exJ.Phys.G(2011)·0 citations
3. 03*

   Elliptic and triangular flow of identified particles at ALICE

   M.Krzewicki (for the ALICE Collaboration)🇳🇱

   We report on the first measurements of elliptic and triangular flow for charged pions, kaons and anti-protons in lead-lead collisions at 2.76 TeV measured with the ALICE detector at the LHC. We compare the observed mass splitting of differential elliptic flow at LHC energies to RHIC measurements at lower energies and theory predictions. We test the quark coalescence picture with the quark number scaling of elliptic and triangular flow.

   nucl-exJ.Phys.G(2011)·64 citations
4. 04*

   Observation of the antimatter helium-4 nucleus at RHIC

   Liang Xue🇨🇳

   We present the observation of the \Heebar nucleus, the heaviest antinucleus observed to date. In total, 18 \Heebar counts were detected at the STAR experiment at RHIC in 10${}^9$ recorded Au+Au collisions at beam energies of $\sqrt{s_{NN}}$ = 200 GeV and 62 GeV. The background has been estimated, and the misidentification probability is found to be lower than 10${}^{-11}$.

   nucl-exJ.Phys.G(2011)·9 citations
5. 05*

   Jet Reconstruction with Particle Flow in Heavy-Ion Collisions with CMS

   Matthew Nguyen (for the CMS collaboration)🇨🇭

   In the particle-flow approach information from all available sub-detector systems is combined to reconstruct all stable particles. The global event reconstruction has been shown to improve, in particular, the resolution of jet energy and missing transverse energy in pp collisions compared to purely calorimetric measurements. This improvement is achieved primarily by combining the precise momentum determination of charged hadrons in the silicon tracker with the associated energy depositions in the calorimeters. By resolving individual particles inside jets, particle flow reduces the sensitivity of the jet energy scale to the jet fragmentation pattern, which is known to be one of the largest sources of systematic uncertainty in jet reconstruction. Particle flow reconstruction is thus potentially well-suited for the study of potential modifications to jet fragmentation in heavy-ion collisions. The particle flow algorithm has been adapted to the heavy-ion environment. The performance of jet reconstruction from particle flow objects in PbPb collisions using the anti-kT jet reconstruction algorithm is presented.

   nucl-exJ.Phys.G(2011)·10 citations
6. 06*

   Charmonium production measured in PbPb and pp collisions by CMS

   Torsten Dahms (for the CMS Collaboration)🇫🇷

   The Compact Muon Solenoid (CMS) is fully equipped to measure hard probes in the di-muon decay channel in the high multiplicity environment of nucleus-nucleus collisions. Such probes are especially relevant for studying the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. CMS is able to distinguish non-prompt from prompt J/psi in pp and PbPb collisions. We report here the nuclear modification factor of prompt J/psi in PbPb as a function of transverse momentum, rapidity, and the number of nucleons participating in the collision.

   nucl-exJ.Phys.G(2011)·14 citations
7. 07*

   Triggered di-hadron correlations in Pb--Pb collisions from the ALICE experiment

   Andrew Adare🇺🇸

   Angular correlations between unidentified hadron trigger and associated particles are measured by the ALICE experiment for $0.5<p_T^{t,a}<15$ GeV, where $\text{ptt}\ge \text{pta}$. The pair correlation shapes are examined in a variety of centrality categories for pairs in $|\eta |<1.0$ where $|{\eta }^t-{\eta }^a|>0.8$. A series of two-particle Fourier components $V_{n\Delta }\equiv <\cos (n\Delta \varphi )>$ are extracted from the long-range azimuthal correlation functions. The sum of $n<6$ terms match the data. For each $n$, a fit is applied over all $p_T$ bins simultaneously to test the collectivity hypothesis $V_{n\Delta }\simeq v_n^t{v}_n^a$. The factorization holds at $p_T^{t,a}$ below approximately 4 GeV but breaks progressively at higher momenta. The divergence between the data and the global fit quantifies the onset of nonflow dominance in long-range correlations due to the away side jet. The $v_n$ values from the global fit are in close agreement with results from more established methods. At higher \pt where jet correlations dominate, the modification of conditional yields in central Pb--Pb collisions is measured with respect to $pp$ ($I_{AA}$) and with respect to peripheral events ($I_{CP}$). Significant suppression is observed on the side opposing the trigger, while a moderate enhancement is measured on the near side.

   nucl-exJ.Phys.G(2011)·9 citations
8. 08*

   The thermal model on the verge of the ultimate test: particle production in Pb-Pb collisions at the LHC

   A. Andronic🇩🇪 · P. Braun-Munzinger🇩🇪 · K. Redlich🇵🇱 · J. Stachel🇩🇪

   We investigate the production of hadrons in nuclear collisions within the framework of the thermal (or statistical hadronization) model. We discuss both the ligh-quark hadrons as well as charmonium and provide predictions for the LHC energy. Even as its exact magnitude is dependent on the charm production cross section, not yet measured in Pb-Pb collisions, we can confidently predict that at the LHC the nuclear modification factor of charmonium as a function of centrality is larger than that observed at RHIC and compare the experimental results to these predictions.

   ↳ nucl-thnucl-exJ.Phys.G(2011)·211 citations
9. 09*

   The QGP shear viscosity -- elusive goal or just around the corner?

   Chun Shen🇺🇸 · Steffen A Bass🇺🇸 · Tetsufumi Hirano🇯🇵 · Pasi Huovinen🇩🇪 · Zhi Qiu🇺🇸 · Huichao Song🇺🇸 · Ulrich W Heinz🇺🇸

   With the new viscous hydrodynamic + hadron cascade hybrid code VISHNU, a rather precise (O(25%)) extraction of the QGP shear viscosity (eta/s)_QGP from heavy-ion elliptic flow data is possible if the initial eccentricity of the collision fireball is known with <5% accuracy. At this point, eccentricities from initial state models differ by up to 20%, leading to an O(100%) uncertainty for (eta/s)_QGP. It is shown that a simultaneous comparison of elliptic and triangular flow, v_2 and v_3, puts strong constraints on initial state models and can largely eliminate the present uncertainty in (eta/s)_QGP. The variation of the differential elliptic flow v_2(p_T) for identified hadrons between RHIC and LHC energies provides additional tests of the evolution model.

   ↳ nucl-thhep-phnucl-exJ.Phys.G(2011)·66 citations
10. 10*

    K0s-K0s correlations in 7 TeV pp collisions from the ALICE experiment at the LHC

    T. J. Humanic (for the ALICE Collaboration)🇺🇸

    Identical neutral kaon pair correlations are measured in 7 TeV pp collisions in the ALICE experiment. K0s-K0s correlation functions are formed in 3 multiplicity X 4 kT bins. The femtoscopic kaon source parameters Rinv and lambda are extracted from these correlation functions by fitting a (femtoscopy) X (PYTHIA) model to them, PYTHIA accounting for the non-flat baseline found in pp collisions. Source parameters are obtained from a fit which includes quantum statistics and final-state interactions of the a0/f0 resonance. K0s-K0s correlations show a systematic increase in Rinv for increasing multiplicity bin and decreasing Rinv for increasing kT bin as seen in pi-pi correlations in the pp system, as well as seen in heavy-ion collisions. Also, K0s-K0s correlations are observed to smoothly extend this pi-pi Rinv behavior for the pp system up to about three times higher kT than the kT range measured in pi-pi correlations.

    ↳ hep-exnucl-exJ.Phys.G(2011)·4 citations
11. 11*

    Isobaric yield ratios in heavy-ion reactions, and symmetry energy of neutron-rich nuclei at intermediate energies

    Chun-Wang Ma🇨🇳 · Fang Wang🇨🇳 · Yu-Gang Ma🇨🇳 · Chan Jin🇨🇳

    The isobaric yield ratios of the fragments produced in the neutron-rich 48Ca and 64Ni projectile fragmentation are analyzed in the framework of a modified Fisher model. The correlations between the isobaric yield ratios (R) and the energy coefficients in the Weiszäcker-Beth semiclassical mass formula (the symmetry-energy term asym, the Coulomb-energy term ac, and the pairing-energy term ap) and the difference between the chemical potentials of the neutron and proton ({\mu}n-{\mu}p) are investigated. Simple correlations between ({\mu}n-{\mu}p)/T, ac/T, asym/T, and ap/T (where T is the temperature), and lnR are obtained. It is suggested that ({\mu}n-{\mu}p)/T, ac/T, asym/T, and ap/T of neutron-rich nuclei can be extracted using isobaric yield ratios for heavy-ion collisions at intermediate energies.

    ↳ nucl-thnucl-exPRC(2011)·42 citations
12. 12*

    Heavy-flavor dynamics in nucleus-nucleus collisions: from RHIC to LHC

    M. Monteno (1)🇮🇹 · W.M. Alberico (2 and 1)🇮🇹 · A. Beraudo (3 and 4)🇮🇹 · A. De Pace (1)🇮🇹 · A. Molinari (2 and 1)🇮🇹 · M. Nardi (2)🇮🇹 · F. Prino (2) ((1) INFN, Sezione di Torino, (2) Dipartimento di Fisica Teorica, Università di Torino, (3) Centro Studi e Ricerche E. Fermi, Rome, (4) Theory Unit, CERN)🇮🇹

    The stochastic dynamics of c and b quarks in the fireball created in nucleus-nucleus collisions at RHIC and LHC is studied employing a relativistic Langevin equation, based on a picture of multiple uncorrelated random collisions with the medium. Heavy-quark transport coefficients are evaluated within a pQCD approach, with a proper HTL resummation of medium effects for soft scatterings. The Langevin equation is embedded in a multi-step setup developed to study heavy-flavor observables in pp and AA collisions, starting from a NLO pQCD calculation of initial heavy-quark yields, complemented in the nuclear case by shadowing corrections, k_T-broadening and nuclear geometry effects. Then, only for AA collisions, the Langevin equation is solved numerically in a background medium described by relativistic hydrodynamics. Finally, the propagated heavy quarks are made hadronize and decay into electrons. Results for the nuclear modification factor R_AA of heavy-flavor hadrons and electrons from their semi-leptonic decays are provided, both for RHIC and LHC beam energies.

    ↳ hep-phnucl-exnucl-thJ.Phys.G(2011)·54 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.