B-hadron cross-section measurement in pp collisions at $\sqrt{s}=14$ TeV with the ALICE muon spectrometer

ALICE (A Large Ion Collider Experiment) is the LHC detector designed to measure nucleus-nucleus (AA) collisions where the formation of the Quark Gluon Plasma is expected. The experiment will also study proton-proton (pp) collisions at 14 TeV. Amongst the relevant observables to be investigated in pp collisions, the B-hadron cross-section is particularly interesting since it provides benchmarks for theoretical models and it is mandatory for understanding heavy flavour production in AA collisions. The performances of the ALICE muon spectrometer to measure B-hadron cross-section in pp collisions at 14 TeV via single muons are presented.     

Study of QGP signatures with the ? → K+K– signal in Pb-Pb ALICE events

The ϕ → K ⁺ K ^– decay channel in Pb-Pb collisions at LHC is studied through a full simulation of the ALICE detector. The study focuses on possible signatures in this channel of quark-gluon plasma (QGP) formation. On a basis of 10⁶ collisions at high centrality some proposed QGP signatures are clearly visible both in K ⁺ K ^– invariant mass and transverse mass distributions. The high significance of this observation appears to reside heavily on the use of the TOF (Time Of Flight) system of ALICE in addition to its central tracking detectors. An erratum to this article is available at .     

Physics perspectives of the ALICE experiment at the large hadron collider

The large hadron collider (LHC) under construction at CERN will deliver ion beams up to centre of mass energies of the order of 5.5 TeV per nucleon, in case of lead. If compared to the available facilities for the study of nucleus-nucleus collisions (SpS and RHIC), this represents a huge step forward in terms of both volume and energy density that can be attained in nuclear interactions. ALICE (a large ion collider experiment) is the only detector specifically designed for the physics of nuclear collisions at LHC, even though it can also study high cross-section processes occurring in proton-proton collisions. The main goal of the experiment is to observe and study the phase transition from hadronic matter to deconfined partonic matter (quark gluon plasma —QGP). ALICE is conceived as a general-purpose detector and will address most of the phenomena related to the QGP formation at LHC energies: for this purpose, a large fraction of the hadrons, leptons and photons produced in each interaction will be measured and identified.     

Electroweak boson detection in the ALICE muon spectrometer

The ALICE capabilities for W and Z detection at LHC are discussed. The contributions to single muon transverse momentum distribution are evaluated. The expected performance of the muon spectrometer for detecting W and Z bosons via their muonic decay is presented. Possible application for the study of in-medium effects in ultrarelativistic heavy ion collisions is discussed.     

Low mass dimuon production in proton and ion induced interactions at the SPS

The low mass dimuon spectra collected in p-U collisions by the NA38 experiment significantly exceeds the total cross section expected from previous analysis, done by other experiments. The ‘excess’ events have a harder distribution than the muon pairs from and Dalitz decays, expected to dominate the mass window 0.4–0.65 GeV/. We conjecture that the excess events may be due to annihilations, negligible at low but made visible by the cut applied in the NA38 data. Taking this assumption to parametrise the p-U spectra, we proceed with the corresponding analysis of the S-Cu, S-U and Pb-Pb data, collected by the NA38 and NA50 experiments, comparing the measured low mass dimuon spectra with the ‘expected cocktail’. Received: 14 July 1999 / Revised version: 3 November 1999 / Published online: 27 January 2000     

Study of the quarkonium polarization in the muon channel at ALICE

The study of quarkonium polarization at hadron colliders represents an important test of the production models. Recent results, obtained at CDF, are in striking disagreement with NRQCD predictions, although such a model correctly reproduces the production cross sections. Furthermore, in nucleus-nucleus collisions, the observed degree of polarization may be related to the characteristics of deconfined matter. Because of these interesting features, quarkonium polarization will surely represent an interesting observable at LHC energies. In ALICE, the polarization of the Ω and Γ states can be measured in the dilepton channel, both in the central barrel and in the forward (2.5<y<4) muon arm. We present the results of a feasibility study, relative to the muon channel, concerning p-p and Pb-Pb collisions, showing the expected performance for the measurement of J/Ω and Γ polarization, both as a function of transverse momentum and centrality.     

Proton-proton physics with the ALICE muon spectrometer at the LHC

ALICE, the dedicated heavy-ion experiment at the LHC, has also an important proton-proton physics program. The ALICE muon spectrometer will be presented and the corresponding physics analysis will be reviewed. A particular emphasis will be placed on heavy-flavor measurement. (for the ALICE Collaboration) The text was submitted by the author in English.     

Measurement of(di)muons from heavy flavour decay in p-p collisions at 14 TeV with ALICE at the LHC

We present the performance of the ALICE muon spectrometer for measuring the charm and beauty inclusive pt differential production cross sections via single muons and unlike-sign dimuons in proton-proton collisions at(√s) = 14 TeV.     

Working group report: Quark gluon plasma

The 10th Workshop on High Energy Physics Phenomenology (WHEPP-10) was held at the Institute of Mathematical Sciences, Chennai during January 2–13, 2008. One of our working grops (WG) is QCD and QGP. The discussions of QGP WG include matter at high density, lattice QCD, charmonium states in QGP, viscous hydrodynamics and jet quenching, colour factor in heavy ion collisions and RHIC results on photons, dileptons and heavy quark. There were two plenary talks and several working group talks with intense discussions regarding the future activities that are going to be persued.      

The horn, kink and step, dale: from few GeV to few TeV

Rich experimental data have been collected in heavy-ion collisions at high energies to study the properties of strongly interacting matter. As the theory of strong interactions, QCD, predicts asymptotic freedom, the created matter at sufficiently high temperature and density will be dominated by a state of quasi-free quarks and gluons referred to as the Quark-Qluon Plasma (QGP). Experimental signals for the onset of the QGP creation (the onset of the deconfinement) have been predicted within the statistical model for the early stage of nucleus-nucleus collisions. In this model the existence of two different phases is assumed: confined mater and the QGP, as well as a first order phase transition between them. Until recently, these predictions were confirmed only by the NA49 experiment at the CERN SPS. In this report recent results from STAR at RHIC/BNL and from ALICE at LHC/CERN, related to the onset of deconfinement, will be compared to published results from NA49.     

φ meson production in NA60

NA60 is a fixed-target experiment at the CERN SPS which measured dimuon production in nucleus–nucleus and proton–nucleus collisions. The experiment collected muon pair samples of unprecedented quality in heavy-ion experiments. This paper presents a high quality measurement of the p_T distribution of the φ meson, covering a broad p_T window. The data were collected in 2003 in In-In collisions at 158 GeV per nucleon. The results, presented as a function of centrality, were studied against several possible sources of systematic effects and proved to be fairly stable. We show that the inverse m_T slope measured in In-In collisions, in the φ→μμ decay channel, depends significantly on the range used to perform the fit. When the fit is performed at low transverse momentum, the effective inverse slope increases from peripheral to central collisions, as measured by other experiments. We finally show that our measurement for In-In is compatible with the overall systematics of T slope versus mass, measured in different collision systems by the NA49 experiment PACS 25.75.Nq; 25.75.-q; 25.75.Dw; 14.40.Cs; 12.38.Mh     

Study of the ALICE performance for the measurement of beauty via the electron decay channel

We present a strategy for the detection of electrons coming from the semi-electronic decay of beauty particles generated in Pb–Pb and p–p collisions at LHC using the ALICE detector. The experiment’s performance for this measurement is evaluated in terms of accessible p_t range and expected uncertainties. PACS 25.75.-q, 12.38.Mh, 13.20.He     

Measuring beauty production in Pb-Pb collisions at the LHC via single electrons in ALICE

We present the expected ALICE performance for the measurement of the p _t-differential cross section of electrons from beauty decays in central Pb-Pb collisions at the LHC. for the ALICE Collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.     

Multiplicity studies and effective energy in ALICE at the LHC

In this work we explore the possibility to perform “effective energy” studies in very high energy collisions at the CERN large hadron collider (LHC). In particular, we focus on the possibility to measure in pp collisions the average charged multiplicity as a function of the effective energy with the ALICE experiment, using its capability to measure the energy of the leading baryons with the zero degree calorimeters. Analyses of this kind have been done at lower centre-of-mass energies and have shown that, once the appropriate kinematic variables are chosen, particle production is characterized by universal properties: no matter the nature of the interacting particles, the final states have identical features. Assuming that this universality picture can be extended to ion–ion collisions, as suggested by recent results from RHIC experiments, a novel approach based on the scaling hypothesis for limiting fragmentation has been used to derive the expected charged event multiplicity in AA interactions at LHC. This leads to scenarios where the multiplicity is significantly lower compared to most of the predictions from the models currently used to describe high energy AA collisions. A mean charged multiplicity of about 1000–2000 per rapidity unit (at η∼0) is expected for the most central Pb–Pb collisions at . In memory of A. Smirnitskiy     

Study of vector mesons in dimuon production in a large kinematic region in p-W and S-W interactions at 200 GeV/c/nucleon

Results are presented on and production in p–W and S–W interactions at 200 GeV/c/nucleon measured via the dimuon decay in a large kinematic region. The data are normalized to the charged particle multiplicity in the same rapidity interval. They have been collected using the HELIOS/3 muon spectrometer at the CERN SPS. The ratio , where is the relevant resonance branching fraction, increases between proton and sulphur projectiles, and is somewhat enhanced going from peripheral to central S–W interactions. This results from an increase in the number of produced 's per charged particle. The ratio is measured in different intervals of p and rapidity. It is not clearly dependent on p, but is larger at higher rapidities. production, likewise normalized to charged multiplicity, is significantly lower in S–W compared to p–W interactions. Received: 27 October 1997 / Revised version: 5 March 1998 / Published online: 13 July 1998     

Strange prospects for LHC energies

Strange quark and hadron production will be studied at the large hadron collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb–Pb and pp data will be available. PACS 25.75.-q; 25.75.Dw     

High-p t and jet physics from RHIC to LHC

The observation of the strong suppression of high-p t hadrons in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) at BNL has motivated a large experimental program using hard probes to characterize the deconfined medium created. However, what can be denoted as “leading particle” physics accessible at RHIC presents some limitations which motivate at higher energy the study of much more penetrating objects: jets. The gain in center-of-mass energy expected at the Large Hadron Collider (LHC) at CERN will definitively improve our understanding on how the energy is lost in the system, opening a major new window of study: the physics of jets on an event-by-event basis. We will concentrate on the expected performance for jet reconstruction in ALICE using the EMCal calorimeter. (for the ALICE Collaboration) The text was submitted by the author in English.     

T-matrix approach to heavy quark diffusion in the QGP

We assess transport properties of heavy quarks in the quark–gluon plasma (QGP) using static heavy-quark (HQ) potentials from lattice-QCD calculations in a Brueckner many-body T-matrix approach to evaluate elastic heavy-quark–light-quark scattering amplitudes. In the attractive meson and diquark channels, resonance states are formed for temperatures up to ∼1.5T _c, increasing pertinent drag and diffusion coefficients for heavy-quark rescattering in the QGP beyond the expectations from perturbative-QCD calculations. We use these transport coefficients, complemented with perturbative elastic HQ gluon scattering, in a relativistic Langevin simulation to obtain HQ p _t distributions and elliptic flow (v ₂) under conditions relevant for the hot and dense medium created in ultrarelativistic heavy-ion collisions. The heavy quarks are hadronized to open-charm and -bottom mesons within a combined quark-coalescence fragmentation scheme. The resulting single-electron spectra from their semileptonic decays are confronted with recent data on “non-photonic electrons” in 200 A GeV Au–Au collisions at the Relativistic Heavy-Ion Collider (RHIC).     

Evidence for the production of thermal muon pairs with masses above 1 GeV/c 2 in 158 A GeV indium-indium collisions

The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c ² produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c ², rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c ² to be of largely partonic origin, when radial flow has not yet built up.     

Heavy ion collisions at CMS and quark-gluon plasma

One of the most actual goals in high energy physics is reaching the state of deconfinement of hadronic matter and studying the properties of resultant quark-gluon plasma (QGP). Jet production, as well as other hard processes, is considered to be an efficient probe for formation of QGP in future experiments on heavy ion collisions at LHC.The Compact Muon Solenoid (CMS) is the general purpose detector designed to run at the LHC and optimized mainly for the search of the Higgs boson in proton-proton collisions. However, a good muon system and electromagnetic and hadron calorimeters with fine granularity gives the possibility to cover several important aspects of the heavy ion physics. The production of heavy quarkonia Γ, Γ′, Γ″ through their muon decay channel and the energy loss of hard jets, are valuable processes for studying the phase transition from the hadronic matter to the plasma of deconfined quarks and gluons.