| 41. |
- Aamodt, K., et al.
(författare)
-
Rapidity and transverse momentum dependence of inclusive J/psi production in pp collisions at root s=7 TeV
- 2011
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 704:5, s. 442-455
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied inclusive J/psi production at central and forward rapidities in pp collisions at root s = 7 TeV. In this Letter, we report on the first results obtained detecting the J/psi through the dilepton decay into e(+)e(-) and mu(+)mu(-) pairs in the rapidity ranges vertical bar y vertical bar < 0.9 and 2.5 < y < 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 L-int = 5.6 nb(-1) and the number of signal events is N-J/psi = 352 +/- 32 (stat.) +/- 28 (syst.): the corresponding figures in the dimuon channel are L-int = 15.6 nb(-1) and N-J/psi = 1924 +/- 77 (stat.) +/- 144 (syst.). The measured production cross sections are sigma(J/psi) (vertical bar y vertical bar < 0.9) = 10.7 +/- 1.0 (stat.) +/- 1.6 (syst.)(-2.3)(+1.6) (syst.pol.) mu b and sigma(J/psi) (2.5 < y < 4) = 6.31 +/- 0.25 (stat.) +/- 0.76 (syst.)(-1.96)(+0.95) (syst.pol.) mu b. The differential cross sections, in transverse momentum and rapidity, of the J/psi were also measured. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
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| 42. |
- Abelev, B., et al.
(författare)
-
Heavy flavour decay muon production at forward rapidity in proton-proton collisions at root s=7 TeV
- 2012
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 708:3-5, s. 265-275
-
Tidskriftsartikel (refereegranskat)abstract
- The production of muons from heavy flavour decays is measured at forward rapidity in proton-proton collisions at root s = 7 TeV collected with the ALICE experiment at the LHC. The analysis is carried out on a data sample corresponding to an integrated luminosity L-int = 16.5 nb(-1). The transverse momentum and rapidity differential production cross sections of muons from heavy flavour decays are measured in the rapidity range 2.5 < y <4, over the transverse momentum range 2 < p(t) < 12 GeV/c. The results are compared to predictions based on perturbative QCD calculations. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 43. |
- Abelev, B., et al.
(författare)
-
Inclusive J/psi production in pp collisions at root s=2.76 TeV
- 2012
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 718:2, s. 295-306
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration has measured inclusive J/psi production in pp collisions at a center-of-mass energy root s = 2.76 TeV at the LHC. The results presented in this Letter refer to the rapidity ranges vertical bar y vertical bar < 0.9 and 2.5 < y <4 and have been obtained by measuring the electron and muon pair decay channels, respectively. The integrated luminosities for the two channels are L-int(e) = 1.1 nb(-1) and L-int(mu) = 19.9 nb(-1), and the corresponding signal statistics are N-J/psi(e+e-) = 59 +/- 14 and N-J/psi(mu+mu-) = 1364 +/- 53. We present d sigma(J/psi)/dy for the two rapidity regions under study and, for the forward-y range, d(2)sigma(J/psi)/dydp(t) in the transverse momentum domain 0 < p(t) < 8 GeV/c. The results are compared with previously published results at root s = 7 TeV and with theoretical calculations. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 44. |
- Abelev, B., et al.
(författare)
-
J/psi Polarization in pp Collisions at root s=7 TeV
- 2012
-
Ingår i: Physical Review Letters. - 1079-7114. ; 108:8
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration has studied J/psi production in pp collisions at root s = 7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/psi polarization parameters lambda(theta) and lambda(phi) were obtained. The study was performed in the kinematic region 2: 5 < y < 4, 2 < p(t) < 8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.
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| 45. |
- Abelev, B., et al.
(författare)
-
J/psi Suppression at Forward Rapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
-
Ingår i: Physical Review Letters. - 1079-7114. ; 109:7
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment has measured the inclusive J/psi production in Pb-Pb collisions at root s(NN) = 2.76 TeV down to zero transverse momentum in the rapidity range 2.5 < y < 4. A suppression of the inclusive J/psi yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%-80% most central collisions, is 0.545 +/- 0.032(stat) +/- 0.083dsyst_ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/psi production from charm quarks in a deconfined partonic phase can describe our data.
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| 46. |
- Abelev, B., et al.
(författare)
-
Light vector meson production in pp collisions at root s=7 TeV ALICE Collaboration
- 2012
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 710:4-5, s. 557-568
-
Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment has measured low-mass dimuon production in pp collisions at root s = 7 TeV in the dimuon rapidity region 2.5 < y < 4. The observed dimuon mass spectrum is described as a superposition of resonance decays (eta, rho, omega, eta', phi) into muons and semi-leptonic decays of charmed mesons. The measured production cross sections for omega and phi are sigma(omega)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 5.28 +/- 0.54(stat) +/- 0.49(syst) mb and sigma(phi)(1 < p(t) < 5 GeV/c. 2.5 < y < 4) = 0.940 +/- 0.084(stat) +/- 0.076(syst) mb. The differential cross sections d(2)sigma/dy dp(t) are extracted as a function of p(t) for omega and phi. The ratio between the rho and omega cross section is obtained. Results for the phi are compared with other measurements at the same energy and with predictions by models. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 47. |
- Abelev, B., et al.
(författare)
-
Measurement of charm production at central rapidity in proton-proton collisions at root s=7 TeV
- 2012
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :1
-
Tidskriftsartikel (refereegranskat)abstract
- The p(t)-differential inclusive production cross sections of the prompt charmed mesons D-0, D+, and D*(+) in the rapidity range vertical bar y vertical bar < 0.5 were measured in proton-proton collisions at root s = 7 TeV at the LHC using the ALICE detector. Reconstructing the decays D-0 -> K-pi(+), D+ -> K-pi(+)pi(+), D*(+) -> D-0 pi(+), and their charge conjugates, about 8,400 D-0, 2,900 D+, and 2,600 D*(+) mesons with 1 < p(t) < 24 GeV/c were counted, after selection cuts, in a data sample of 3.14 x 10(8) events collected with a minimum-bias trigger (integrated luminosity L-int = 5 nb(-1)). The results are described within uncertainties by predictions based on perturbative QCD.
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| 48. |
- Abelev, B., et al.
(författare)
-
Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2012
-
Ingår i: Journal of High Energy Physics. - 1029-8479. ; :3
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of event background fluctuations on charged particle jet reconstruction in Pb-Pb collisions at root s(NN) = 2.76 TeV has been measured with the ALICE experiment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high p(t) particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-k(t) jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum track p(t) between 0.15 GeV/c and 2 GeV/c. For embedded jets reconstructed from charged particles with p(t) > 0.15 GeV/c, the uncertainty in the reconstructed jet transverse momentum due to the heavy-ion background is measured to be 11.3 GeV/c (standard deviation) for the 10% most central Pb-Pb collisions, slightly larger than the value of 11.0 GeV/c measured using the unbiased method. For a higher particle transverse momentum threshold of 2 GeV/c, which will generate a stronger bias towards hard fragmentation in the jet finding process, the standard deviation of the fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0 GeV/c for the 10% most central events. A non-Gaussian tail of the momentum uncertainty is observed and its impact on the reconstructed jet spectrum is evaluated for varying particle momentum thresholds, by folding the measured fluctuations with steeply falling spectra.
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| 49. |
- Abelev, B., et al.
(författare)
-
Production of charged pions, kaons and protons at large transverse momenta in pp and Pb-Pb collisions at root s(NN)=2.76 TeV
- 2014
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 736, s. 196-207
-
Tidskriftsartikel (refereegranskat)abstract
- Transverse momentum spectra of pi(+/-), K-+/- and p((p) over bar) up to p(T) = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at v root s(NN) = 2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pionratios both show a distinct peak at p(T) approximate to 3 GeV/c in central Pb-Pb collisions. Below the peak, p(T) < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For p(T) > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for pi(+/-), K-+/- and p((p) over bar) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
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| 50. |
- Aamodt, K., et al.
(författare)
-
Harmonic decomposition of two particle angular correlations in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2012
-
Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 708:3-5, s. 249-264
-
Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb-Pb collisions at root s(NN) = 2.76 TeV for transverse momenta 0.25 < p(T)(t,a) < 15 GeV/c, where p(T)(t) > p(T)(a). 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 |eta| < 1.0. Distributions in relative azimuth Delta phi equivalent to phi(t) - phi(a) are analyzed for |Delta eta| equivalent to |eta(t) - eta(a)| > 0.8, and are referred to as "long-range correlations". Fourier components V-n Delta equivalent to < cos(n Delta phi)> 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 V-n Delta (p(T)(t), p(T)(a)) is fully described in terms of single-particle anisotropies v(n)(p(T)) as V-n Delta(p(T)(t), p(T)(a)) = v(n)(p(T)(t))v(n)(p(T)(a)). This expectation is tested for 1 <= n <= 5 by applying a global fit of all V-n Delta(p(T)(t), p(T)(a)) to obtain the best values v(n){GF}(p(T)). It is found that for 2 <= n <= 5, the fit agrees well with data up to p(T)(a) similar to 3-4 GeV/c, with a trend of increasing deviation as p(T)(t) and p(T)(a) are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full 0.25 < p(T) < 15 GeV/c range using a single v(n)(p(T)) curve: such a description is however approximately possible for 2 <= n <= 5 when p(T)(a) < 4 GeV/c. For the n = 1 harmonic, however, a single v(1)(p(T)) curve is not obtained even within the reduced range p(T)(a) < 4 GeV/c. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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