Resonances as Probes of Heavy-Ion Collisions at ALICE

Hadronic resonances serve as unique probes in the study of the hot and dense nuclear matter produced in heavy-ion collisions. Properties of the hadronic phase of the collision can be extracted from measurements of the suppression of resonance yields. A comparison of the transverse-momentum spectra of the phi(1020) meson and the proton (which have similar masses) can be used to study particle production mechanisms. Resonance measurements in pp collisions provide input for tuning QCD-inspired particle production models and serve as reference measurements for other collision systems. Measurements of resonances in p-Pb collisions allow nuclear effects in the absence of a hot and dense final state to be studied. The ALICE Collaboration has measured resonances in pp, p-Pb, and Pb-Pb collisions. These measurements will be discussed and compared to results from other experiments and to theoretical models.Comment: 4 Pages, 1 figure, Proceedings of Hot Quarks 2014, Las Negras, Spain, 21-28 September 2014, to be published in Journal of Physics: Conference Serie

Hadronic resonance production in Pb-Pb collisions at the ALICE experiment

Measurements of the yields of hadronic resonances (relative to non-resonances) in high-energy heavy-ion collisions allow the chemical freeze-out temperature and the time between chemical and thermal freeze-out of the collision system to be studied, while modifications to resonance masses and widths could be a signature of chiral symmetry restoration. The spectra (for pT < 5 GeV/c), total integrated yields, ratios to non-resonances (phi/pi and phi/K), mass, and width of the phi(1020) meson and the uncorrected yields, mass, and width of the K*(892)0 and anti-K*(892)0 mesons have been measured using the ALICE detector for Pb-Pb collisions at 2.76 TeV. These measurements will be compared to results from other collision systems and energies. Angular correlations between leading trigger hadrons and phi(1020) mesons have been measured in Pb-Pb and pp collisions; the mass and width of the phi(1020) meson as a function of the correlation angle will be presented.Comment: 10 pages, 9 figures; Proceedings for Nucleus-Nucleus 2012, 21 May-1 June 2012, San Antonio, Texas, USA; Submitted for publication in J. Phys.: Conference Serie

Recent hadronic resonance measurements at ALICE

In heavy-ion physics, measurements of short-lived hadronic resonances allow the properties of the hadronic phase of the collision to be studied. In addition, resonances can be used along with stable hadrons to study parton energy loss in the quark-gluon plasma and the mechanisms that shape hadron pT spectra at intermediate transverse momenta. Resonance measurements in small systems serve as a reference for heavy-ion collisions and contribute to searches for collective effects. An overview of recent results on hadronic resonance production measured in ALICE is presented. These results include the pT spectra and yields of the rho(770)0, K*(892)0, and phi(1020) mesons in pp, p-Pb, and Pb-Pb collisions at different energies as well as the Sigma(1385)+/- and Xi(1530)0 baryons in pp and p-Pb collisions.Comment: 4 pages, 3 figures, Proceedings of the 16th International Conference on Strangeness in Quark Matter (SQM 2016), Berkeley, California, USA, 27 June-1 July 2016, to be published in Journal of Physics: Conference Serie

Hadronic resonances in heavy-ion collisions at ALICE (Strangeness in Quark Matter 2013)

Properties of the hadronic phase of high-energy heavy-ion collisions can be studied by measuring the ratios of hadronic resonance yields to the yields of longer-lived particles. These ratios can be used to study the strength of re-scattering effects, the chemical freeze-out temperature, and the lifetime between chemical and kinetic freeze-out. The restoration of chiral symmetry during the early hadronic phase or near the phase transition may lead to shifts in the masses and increases in the widths of hadronic resonances. The ALICE collaboration has measured the spectra, masses, and widths of the K*(892)0 and phi(1020) resonances in Pb-Pb collisions at 2.76 TeV. These results, including RAA and the ratios of the integrated resonance yields to stable hadron yields, are presented and compared to results from other collision systems and to theoretical predictions.Comment: 4 pages, 3 figures, Proceedings of Strangeness in Quark Matter conference, 21-27 July 2013, Birmingham, U

The ALICE electromagnetic calorimeter high level triggers

The ALICE (A Large Ion Collider Experiment) detector yields a huge sample of data from different sub-detectors. On-line data processing is applied to select and reduce the volume of the stored data. ALICE applies a multi-level hardware trigger scheme where fast detectors are used to feed a three-level (L0, L1, and L2) deep chain. The High-Level Trigger (HLT) is a fourth filtering stage sitting logically between the L2 trigger and the data acquisition event building. The EMCal detector comprises a large area electromagnetic calorimeter that extends the momentum measurement of photons and neutral mesons up to $p_T=250$ GeV/c, which improves the ALICE capability to perform jet reconstruction with measurement of the neutral energy component of jets. An online reconstruction and trigger chain has been developed within the HLT framework to sharpen the EMCal hardware triggers, by combining the central barrel tracking information with the shower reconstruction (clusters) in the calorimeter. In the present report the status and the functionality of the software components developed for the EMCal HLT online reconstruction and trigger chain will be discussed, as well as preliminary results from their commissioning performed during the 2011 LHC running period.Comment: Proceeding for the CHEP 2012 Conferenc

Nonphotonic electrons at RHIC within ktk_t-factorization approach and with experimental semileptonic decay functions

We discuss production of nonphotonic electrons in proton-proton scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the $k_t$-factorization approach. We use different unintegrated gluon distributions from the literature. The hadronization of heavy quarks is done by means of Peterson and Braaten et al. fragmentation functions. The semileptonic decay functions are found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations. We get good description of the data at large transverse momenta of electrons and find a missing strength concentrated at small transverse momenta of electrons. Plausible missing mechanisms are discussed.Comment: 16 pages, 11 figure

An empirical test for cellular automaton models of traffic flow

Based on a detailed microscopic test scenario motivated by recent empirical studies of single-vehicle data, several cellular automaton models for traffic flow are compared. We find three levels of agreement with the empirical data: 1) models that do not reproduce even qualitatively the most important empirical observations, 2) models that are on a macroscopic level in reasonable agreement with the empirics, and 3) models that reproduce the empirical data on a microscopic level as well. Our results are not only relevant for applications, but also shed new light on the relevant interactions in traffic flow.Comment: 28 pages, 36 figures, accepted for publication in PR

Single-vehicle data of highway traffic - a statistical analysis

In the present paper single-vehicle data of highway traffic are analyzed in great detail. By using the single-vehicle data directly empirical time-headway distributions and speed-distance relations can be established. Both quantities yield relevant information about the microscopic states. Several fundamental diagrams are also presented, which are based on time-averaged quantities and compared with earlier empirical investigations. In the remaining part time-series analyses of the averaged as well as the single-vehicle data are carried out. The results will be used in order to propose objective criteria for an identification of the different traffic states, e.g. synchronized traffic.Comment: 12 pages, 19 figures, RevTe

Excitation and relaxation in atom-cluster collisions

Electronic and vibrational degrees of freedom in atom-cluster collisions are treated simultaneously and self-consistently by combining time-dependent density functional theory with classical molecular dynamics. The gradual change of the excitation mechanisms (electronic and vibrational) as well as the related relaxation phenomena (phase transitions and fragmentation) are studied in a common framework as a function of the impact energy (eV...MeV). Cluster "transparency" characterized by practically undisturbed atom-cluster penetration is predicted to be an important reaction mechanism within a particular window of impact energies.Comment: RevTeX (4 pages, 4 figures included with epsf