Measurement of charm production at central rapidity in proton-proton collisions at s=2.76\sqrt{s} = 2.76 TeV

The $p_{\rm T}$-differential production cross sections of the prompt (B feed-down subtracted) charmed mesons D$^0$, D$^+$, and D$^{*+}$ in the rapidity range $|y|<0.5$, and for transverse momentum $1< p_{\rm T} <12$ GeV/$c$, were measured in proton-proton collisions at $\sqrt{s} = 2.76$ TeV with the ALICE detector at the Large Hadron Collider. The analysis exploited the hadronic decays D$^0 \rightarrow$K$\pi$, D$^+ \rightarrow$K$\pi\pi$, D$^{*+} \rightarrow$D$^0\pi$, and their charge conjugates, and was performed on a $L_{\rm int} = 1.1$ nb$^{-1}$ event sample collected in 2011 with a minimum-bias trigger. The total charm production cross section at $\sqrt{s} = 2.76$ TeV and at 7 TeV was evaluated by extrapolating to the full phase space the $p_{\rm T}$-differential production cross sections at $\sqrt{s} = 2.76$ TeV and our previous measurements at $\sqrt{s} = 7$ TeV. The results were compared to existing measurements and to perturbative-QCD calculations. The fraction of cdbar D mesons produced in a vector state was also determined.Comment: 20 pages, 5 captioned figures, 4 tables, authors from page 15, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/307

Particle-yield modification in jet-like azimuthal di-hadron correlations in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}} = 2.76 TeV

The yield of charged particles associated with high-$p_{\rm T}$ trigger particles ($8 < p_{\rm T} < 15$ GeV/$c$) is measured with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jet-like correlation peaks in azimuthal di-hadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta $p_{\rm T}> 3$ GeV/$c$ on the away-side drops to about 60% of that observed in pp collisions, while on the near-side a moderate enhancement of 20-30% is found.Comment: 15 pages, 2 captioned figures, 1 table, authors from page 10, published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/350

Centrality Dependence Of The Pseudorapidity Density Distribution For Charged Particles In Pb-pb Collisions At √snn=2.76tev

7264/Mai61062

Elliptic flow of identified hadrons in Pb-Pb collisions at 1asNN = 2.76 TeV

The elliptic flow coefficient (v2) of identified particles in Pb-Pb collisions at 1asNN = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle corre- lation technique, using a pseudo-rapidity gap of | 06\u3b7| > 0.9 between the identified hadron under study and the reference particles. The v2 is reported for \u3c0\ub1, K\ub1, K0S, p+p, \u3c6, \u39b+\u39b, \u39e 12+\u39e+ and \u3a9 12+\u3a9+ in several collision centralities. In the low transverse momentum (pT) region, pT 3 GeV/c

Charge correlations using the balance function in Pb-Pb collisions at √sNN=2.76 TeV

In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of such studies using the electric charge balance function in the relative pseudorapidity (d?) and azimuthal angle (df) in Pb-Pb collisions at sNN=2.76 TeV with the ALICE detector at the Large Hadron Collider. The width of the balance function decreases with growing centrality (i.e. for more central collisions) in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured correlations in df but fails to describe the correlations in d?. A thermal blast-wave model incorporating local charge conservation and tuned to describe the pTspectra and v2measurements reported by ALICE, is used to fit the centrality dependence of the width of the balance function and to extract the average separation of balancing charges at freeze-out. The comparison of our results with measurements at lower energies reveals an ordering with sNN: the balance functions become narrower with increasing energy for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also with the late stage creation scenario of balancing charges. However, the relative decrease of the balance function widths in d? and df with centrality from the highest SPS to the LHC energy exhibits only small differences. This observation cannot be interpreted solely within the framework where the majority of the charge is produced at a later stage in the evolution of the heavy-ion collision. © 2013 CERN

Rapidity and transverse momentum dependence of inclusive J/Ψ production in pp collisions at s=7 TeV

The ALICE experiment at the LHC has studied inclusive J/Ψ production at central and forward rapidities in pp collisions at s=7 TeV. In this Letter, we report on the first results obtained detecting the J/Ψ through the dilepton decay into e+e- and μ+ μ- pairs in the rapidity ranges |y|&amp;lt;0.9 and 2.5&amp;lt;y&amp;lt;4, respectively, and with acceptance down to zero pT. In the dielectron channel the analysis was carried out on a data sample corresponding to an integrated luminosity Lint=5.6 nb- 1 and the number of signal events is NJ/Ψ=352±32(stat.)±28(syst.); the corresponding figures in the dimuon channel are Lint=15.6 nb-1 and NJ/Ψ=1924±77(stat.)±144(syst.). The measured production cross sections are σJ/Ψ(|y|&amp;lt;0.9)=10.7±1.0(stat.)±1.6(syst.)-2.3+1.6(syst.pol.)μb and σJ/Ψ(2.5&amp;lt;y&amp;lt;4)=6.31±0.25(stat.)±0.76(syst.)-1.96+0.95(syst.pol.)μb. The differential cross sections, in transverse momentum and rapidity, of the J/Ψ were also measured. © 2011 CERN

Production of K*(892)0 and ϕ(1020) in pp collisions at √s=7 TeV

The production of K*(892)0 and φ{symbol}(1020) in pp collisions at √s=7 TeV was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d2N/dydpT at midrapidity {pipe}y{pipe}&amp;lt;0. 5 in the range 0&amp;lt;pT&amp;lt;6 GeV/c for K*(892)0 and 0. 4&amp;lt;pT&amp;lt;6 GeV/c for φ{symbol}(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Ω baryons measured previously by ALICE at √s = 7 TeV, the ratios K*/K-, φ{symbol}/K*, φ{symbol}/K-, φ{symbol}/π-, and Ω + Ω)φ are presented. The values of the K*/K-, φ{symbol}/K* and φ{symbol}/K- ratios are similar to those found at lower centre-of-mass energies. In contrast, the φ{symbol}/π- ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The (Ω + \Ω)φ ratio in the pT range 1-5 GeV/c is found to be in good agreement with the prediction of the HIJING/BB̄ v2. 0 model with a strong colour field. © 2012 CERN for the benefit of the ALICE collaboration

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

Particle-yield modification in jetlike azimuthal dihadron correlations in Pb-Pb collisions at √sNN=2.76TeV

The yield of charged particles associated with high-pt trigger particles (8&amp;lt;pt&amp;lt;15GeV/c) is measured with the ALICE detector in Pb-Pb collisions at √sNN=2.76TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jetlike correlation peaks in azimuthal dihadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta pt&amp;gt;3GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%-30% is found. © 2012 American Physical Society

Harmonic decomposition of two particle angular correlations in Pb-Pb collisions at sNN=2.76TeV

Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb-Pb collisions at sNN=2.76TeV for transverse momenta 0.25&amp;lt;pTt,a&amp;lt;15GeV/c, where pTt&amp;gt;pTa. The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |η|&amp;lt;1.0. Distributions in relative azimuth δφ≡φt-φa are analyzed for |δη|≡|ηt-ηa|&amp;gt;0.8, and are referred to as &quot;long-range correlations&quot;. Fourier components Vnδ≡〈cos(nδφ)〉 are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy Vnδ(pTt,pTa) is fully described in terms of single-particle anisotropies vn(pT) as Vnδ(pTt,pTa)=vn(pTt)vn(pTa). This expectation is tested for 1≤n≤5 by applying a global fit of all Vnδ(pTt,pTa) to obtain the best values vn{GF}(pT). It is found that for 2≤n≤5, the fit agrees well with data up to pTa~3-4GeV/c, with a trend of increasing deviation as pTt and pTa are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full 0.25&amp;lt;pT&amp;lt;15GeV/c range using a single vn(pT) curve; such a description is however approximately possible for 2≤n≤5 when pTa&amp;lt;4GeV/c. For the n=1 harmonic, however, a single v1(pT) curve is not obtained even within the reduced range pTa&amp;lt;4GeV/c. © 2012 CERN