Physics with the ALICE experiment

ALICE experiment at LHC collects data in pp collisions at $\sqrt{s}$=0.9, 2.76 and 7 TeV and in PbPb collisions at 2.76 TeV. Highlights of the detector performance and an overview of experimental results measured with ALICE in pp and AA collisions are presented in this paper. Physics with proton-proton collisions is focused on hadron spectroscopy at low and moderate $p_T$. Measurements with lead-lead collisions are shown in comparison with those in pp collisions, and the properties of hot quark matter are discussed.Comment: Presented at the Conference of the Nuclear Physics Division of the Russian Academy of Science, 11-25.11.2011, ITEP, Moscow. 16 pages, 14 figure

Femtoscopy of Pb-Pb and pp collisions at the LHC with the ALICE experiment

We report on the results of femtoscopic analysis of Pb-Pb collisions at sqrt(s_NN)=2.76 TeV and pp collisions at sqrt(s)=0.9, 2.76 and 7 TeV with identical pions and kaons. Detailed femtoscopy studies in heavy-ion collisions at SPS and RHIC have shown that emission region sizes ("HBT radii") decrease with increasing pair transverse momentum k_T, which is understood as a manifestation of the collective behavior of matter. The trend was predicted to persist at the LHC. The data from Pb-Pb collisions confirm the existence of a flowing medium and provide strict constraints on the dynamical models. Similar analysis is carried out for pp collisions for pions and kaons and qualitative similarities to heavy-ion data are seen, especially in collisions producing large number of particles. The observed trends give insight into the soft particle production mechanism in pp collisions. 3D radii were also found to universally scale with event multiplicity in heavy-ion collisions. We extend the range of multiplicities both upwards with the Pb-Pb data and downwards with the pp data to test the scaling in new areas. In particular the high multiplicity pp collisions reach particle densities comparable to the ones measured in peripheral Cu-Cu and Au-Au collisions at RHIC. This allows for the first time to directly compare freeze-out sizes for systems with very different initial states.Comment: 8 pages, 5 figures, Proceedings of the Quark Matter 2011 plenary tal

Variation of jet quenching from RHIC to LHC and thermal suppression of QCD coupling constant

We perform a joint jet tomographic analysis of the data on the nuclear modification factor $R_{AA}$ from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of $R_{AA}$ from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC.Comment: 9 pages, 2 figure

Forward-Backward Correlations and Event Shapes as probes of Minimum-Bias Event Properties

Measurements of inclusive observables, such as particle multiplicities and momentum spectra, have already delivered important information on soft-inclusive ("minimum-bias") physics at the Large Hadron Collider. In order to gain a more complete understanding, however, it is necessary to include also observables that probe the structure of the studied events. We argue that forward-backward (FB) correlations and event-shape observables may be particulary useful first steps in this respect. We study the sensitivity of several different types of FB correlations and two event shape variables - transverse thrust and transverse thrust minor - to various sources of theoretical uncertainty: multiple parton interactions, parton showers, colour (re)connections, and hadronization. The power of each observable to furnish constraints on Monte Carlo models is illustrated by including comparisons between several recent, and qualitatively different, PYTHIA 6 tunes, for pp collisions at sqrt(s) = 900 GeV.Comment: 13 page

The First Year of the Large Hadron Collider: A Brief Review

The first year of LHC data taking provided an integrated luminosity of about 35/pb in proton-proton collisions at sqrt(s)=7 TeV. The accelerator and the experiments have demonstrated an excellent performance. The experiments have obtained important physics results in many areas, ranging from tests of the Standard Model to searches for new particles. Among other results the physics highlights have been the measurements of the W-, Z-boson and t t-bar production cross-sections, improved limits on supersymmetric and other hypothetical particles and the observation of jet-quenching, elliptical flow and J/Psi suppression in lead-lead collisions at sqrt(sNN) = 2.76 TeV.Comment: 11 pages, 9 figures, invited brief review for Mod. Phys. Lett.

Analyses of multiplicity distributions with \eta_c and Bose-Einstein correlations at LHC by means of generalized Glauber-Lachs formula

Using the negative binomial distribution (NBD) and the generalized Glauber-Lachs (GGL) formula, we analyze the data on charged multiplicity distributions with pseudo-rapidity cutoffs \eta_c at 0.9, 2.36, and 7 TeV by ALICE Collaboration and at 0.2, 0.54, and 0.9 TeV by UA5 Collaboration. We confirm that the KNO scaling holds among the multiplicity distributions with \eta_c = 0.5 at \sqrt{s} = 0.2\sim2.36 TeV and estimate the energy dependence of a parameter 1/k in NBD and parameters 1/k and \gamma (the ratio of the average value of the coherent hadrons to that of the chaotic hadrons) in the GGL formula. Using empirical formulae for the parameters 1/k and \gamma in the GGL formula, we predict the multiplicity distributions with \eta_c = 0.5 at 7 and 14 TeV. Data on the 2nd order Bose-Einstein correlations (BEC) at 0.9 TeV by ALICE Collaboration and 0.9 and 2.36 TeV by CMS Collaboration are also analyzed based on the GGL formula. Prediction for the 3rd order BEC at 0.9 and 2.36 TeV are presented. Moreover, the information entropy is discussed

Suppression of neutral pion production at large transverse momentum measured with the ALICE experiment in Pb-Pb collisions at sNN=2.76\sqrt{s_{NN}}=2.76 TeV

The ALICE collaboration at the LHC has measured the transverse momentum spectra of neutral pions via their two photon decay in pp and Pb$-$Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV over a broad transverse momentum range with different subsystems: with the electromagnetic calorimeters PHOS and EMCAL and with photon conversions in the inner material of the detectors using $e^{+}e^{-}$ pairs reconstructed with the Central Tracking System. In this report, neutral pions production is compared between pp and Pb$-$Pb collisions measured with conversion photons in terms of the nuclear modification factor, $R_{AA}$, for different centrality selections of the Pb$-$Pb data sample.Comment: 4 pages, 4 figures, proceedings of QM 201

Heavy Ions: Results from the Large Hadron Collider

On November 8, 2010 the Large Hadron Collider (LHC) at CERN collided first stable beams of heavy ions (Pb on Pb) at center-of-mass energy of 2.76 TeV/nucleon. The LHC worked exceedingly well during its one month of operation with heavy ions, delivering about 10 microbarn-inverse of data, with peak luminosity reaching to $L_{0} = 2 \times 10^{25}{\rm cm}^{-2}{\rm s}^{-1}$ towards the end of the run. Three experiments, ALICE, ATLAS and CMS, recorded their first heavy ion data, which were analyzed in a record time. The results of the multiplicity, flow, fluctuations, and Bose-Einstein correlations indicate that the fireball formed in nuclear collisions at the LHC is hotter, lives longer, and expands to a larger size at freeze-out as compared to lower energies. We give an overview of these as well as new results on quarkonia and heavy flavour suppression, and jet energy loss.Comment: Proceedings of Lepton-Photon 2011 Conference, to be published in Pramana, Journal of Physics. 15 page

Anomalous behavior of pion production in high energy particle collisions

A shape of invariant differential cross section for charged hadron production as function of transverse momentum measured in various collider experiments is analyzed. Contrary to the behavior of produced charged kaons, protons and antiprotons, the pion spectra require an anomalously high contribution of an exponential term to describe the shape.Comment: 4 pages, 6 figure

Grasshopper Control

This archival publication may not reflect current scientific knowledge or recommendations. Current information available from the University of Minnesota Extension: https://www.extension.umn.edu