Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sNN=2.76\sqrt{s_{\rm NN}} = 2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at $\sqrt{s_{_{\rm NN}}}$ = 2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in $|\eta|<0.8$ and $0.3 < p_T < 20$ GeV/$c$ are compared to the expectation in pp collisions at the same $\sqrt{s_{\rm NN}}$, scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor $R_{\rm AA}$. The result indicates only weak medium effects ($R_{\rm AA} \approx$ 0.7) in peripheral collisions. In central collisions, $R_{\rm AA}$ reaches a minimum of about 0.14 at $p_{\rm T}=6$-7GeV/$c$ and increases significantly at larger $p_{\rm T}$. The measured suppression of high-$p_{\rm T}$ particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC.Comment: 15 pages, 5 captioned figures, 3 tables, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/98

Two-pion Bose-Einstein correlations in central Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV at the Large Hadron Collider is presented. We observe a growing trend with energy now not only for the longitudinal and the outward but also for the sideward pion source radius. The pion homogeneity volume and the decoupling time are significantly larger than those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/388

J/psi production as a function of charged-particle pseudorapidity density in p-Pb collisions at root s(NN)=5.02 TeV

We report measurements of the inclusive J/ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density dNch/dη in p–Pb collisions at sNN=5.02TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ψ yield with normalised dNch/dη, measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity

A Very High Momentum Particle Identification Detector

A new detector concept has been investigated to extend the capabilities of heavy-ion collider experiments, represented here through the ALICE detector, in the high transverse momentum (pT region. The resulting Very High Momentum Particle Identification Detector (VHMPID) performs charged hadron identification on a track-by-track basis in the 5 GeV/c &lt; p &lt; 25 GeV/c momentum range and provides heavy-ion experiments with new opportunities to study parton-medium interactions at RHIC and LHC energies, where the creation of deconfined quark-gluon matter has been established. The detector is based on novel advances to the pressurized gaseous ring imaging Cherenkov (RICH) concept, which yield a very compact, high resolution addition to existing heavy-ion experiments. We conclude that in order for the device to yield statistically significant results not only for single particle measurements, but also for di-hadron and jet-tagged correlation studies, it has to cover contiguously up to 30% of a central barrel detector in radial direction. This will allow, for the first time, identified charged hadron measurements in jets. In this paper we summarize the physics motivations for such a device, as well as its conceptual design, layout, and integration into ALICE.1295DE-FG02-07ER41521; DOE; National Research Foundation of Korea; NRF; National Research Foundation of Korea; NSF-PHY-0968903; NSF; National Research Foundation of Korea; NSF-PHY-1305280; NSF; National Research Foundation of Korea(2006) J. Phys. G, 32, p. 1295Sapeta, S., Wiedemann, U.A., (2008) Eur. Phys. J. C, 55, p. 293Liu, W., Fries, R., (2008) Phys. Rev. C, 77, p. 054902Hwa, R.C., Yang, C.B., (2006) Phys. Rev. Lett., 97, p. 042301Lévai, P., Berényi, D., Pásztor, A., Skokov, V.V., (2011) J. 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Suppression of charged particle production at large transverse momentum in central Pb-Pb collisions at sNN=2.76 TeV

Inclusive transverse momentum spectra of primary charged particles in Pb-Pb collisions at sNN=2.76 TeV have been measured by the ALICE Collaboration at the LHC. The data are presented for central and peripheral collisions, corresponding to 0-5% and 70-80% of the hadronic Pb-Pb cross section. The measured charged particle spectra in |n|&lt;0.8 and 0.3&lt;pT&lt;20 GeV/c are compared to the expectation in pp collisions at the same sNN, scaled by the number of underlying nucleon-nucleon collisions. The comparison is expressed in terms of the nuclear modification factor RAA. The result indicates only weak medium effects (RAA≈0.7) in peripheral collisions. In central collisions, RAA reaches a minimum of about 0.14 at pT=6-7 GeV/c and increases significantly at larger pT. The measured suppression of high- pT particles is stronger than that observed at lower collision energies, indicating that a very dense medium is formed in central Pb-Pb collisions at the LHC. © 2010 CERN

Strange particle production in proton–proton collisions at √s = 0.9 TeV with ALICE at the LHC

The production of mesons containing strange quarks (K0 S, ϕ) and both singly and doubly strange baryons (⋀, ⊼, and Ξ− +Ξ+) are measured at mid-rapidity in pp collisions at √s = 0.9 TeV with the ALICE experiment at the LHC. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (dN/dy) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields (〈dN/dy〉) of 0.184 ± 0.002(stat.) ± 0.006(syst.) for K0 S and 0.021 ± 0.004(stat.) ± 0.003(syst.) for ϕ. For baryons, we find 〈dN/dy〉 = 0.048 ± 0.001(stat.) ± 0.004(syst.) for ⋀, 0.047 ± 0.002(stat.) ± 0.005(syst.) for ⊼ and 0.0101 ± 0.0020(stat.) ± 0.0009(syst.) for Ξ− +Ξ+. The results are also compared with predictions for identified particle spectra from QCD-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions. © CERN for the benefit of the ALICE collaboration 2011

Centrality Dependence Of The Charged-particle Multiplicity Density At Midrapidity In Pb-pb Collisions At √snn=2.76tev

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