| 1. |
- Abelev, B., et al.
(författare)
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Multiplicity dependence of two-particle azimuthal correlations in pp collisions at the LHC
- 2013
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :9
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Tidskriftsartikel (refereegranskat)abstract
- We present the measurements of particle pair yields per trigger particle obtained from di-hadron azimuthal correlations in pp collisions at root s = 0.9, 2.76, and 7TeV recorded with the ALICE detector. The yields are studied as a function of the charged particle multiplicity. Taken together with the single particle yields the pair yields provide information about parton fragmentation at low transverse momenta, as well as on the contribution of multiple parton interactions to particle production. Data are compared to calculations using the PYTHIA6, PYTHIA8, and PHOJET event generators.
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| 2. |
- Abelev, B., et al.
(författare)
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Technical Design Report for the Upgrade of the ALICE Inner Tracking System
- 2014
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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Tidskriftsartikel (refereegranskat)abstract
- LICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. A key element of the ALICE upgrade is the construction of a new, ultra-light, high-resolution Inner Tracking System (ITS) based on monolithic CMOS pixel detectors. The primary focus of the ITS upgrade is on improving the performance for detection of heavy-flavour hadrons, and of thermal photons and low-mass di-electrons emitted by the QGP. With respect to the current detector, the new Inner Tracking System will significantly enhance the determination of the distance of closest approach to the primary vertex, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a 50 μm thick CMOS pixel sensor with a pixel pitch of about 30×30 μm2. This document, submitted to the LHCC (LHC experiments Committee) in September 2013, presents the design goals, a summary of the R&D activities, with focus on the technical implementation of the main detector components, and the projected detector and physics performance.
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| 3. |
- Abelev, B., et al.
(författare)
-
Upgrade of the ALICE Experiment Letter Of Intent
- 2014
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 41:8
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Tidskriftsartikel (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is studying the physics of strongly interacting matter, and in particular the properties of the Quark–Gluon Plasma (QGP), using proton–proton, proton–nucleus and nucleus–nucleus collisions at the CERN LHC (Large Hadron Collider). The ALICE Collaboration is preparing a major upgrade of the experimental apparatus, planned for installation in the second long LHC shutdown in the years 2018–2019. These plans are presented in the ALICE Upgrade Letter of Intent, submitted to the LHCC (LHC experiments Committee) in September 2012. In order to fully exploit the physics reach of the LHC in this field, high-precision measurements of the heavy-flavour production, quarkonia, direct real and virtual photons, and jets are necessary. This will be achieved by an increase of the LHC Pb–Pb instant luminosity up to 6×1027 cm−2s−1 and running the ALICE detector with the continuous readout at the 50 kHz event rate. The physics performance accessible with the upgraded detector, together with the main detector modifications, are presented.
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| 4. |
- Abelev, B, et al.
(författare)
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Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 111:23
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Tidskriftsartikel (refereegranskat)abstract
- The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta p_{T} between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even p_{T} shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.
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| 5. |
- Abelev, B., et al.
(författare)
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Measurement of charm production at central rapidity in proton-proton collisions at root s=7 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :1
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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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| 6. |
- Abelev, B., et al.
(författare)
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Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=7 TeV
- 2012
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Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 86:11
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Tidskriftsartikel (refereegranskat)abstract
- The differential production cross section of electrons from semileptonic heavy-flavor hadron decays has been measured at midrapidity (\y\ < 0.5) in proton-proton collisions at root s = 7 TeV with ALICE at the LHC. Electrons were measured in the transverse momentum range 0.5 < p(t) < 8 GeV/c. Predictions from a fixed-order perturbative QCD calculation with next-to-leading-log resummation agree with the data within the theoretical and experimental uncertainties. DOI: 10.1103/PhysRevD.86.112007
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| 7. |
- Abelev, B., et al.
(författare)
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Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at root s(NN)=2.76 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :3
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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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| 8. |
- Abelev, B., et al.
(författare)
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Multi-strange baryon production in pp collisions at root s=7 TeV with ALICE
- 2012
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 712:4-5, s. 309-318
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the multi-strange Xi(-) and Omega(-) baryons and their antiparticles by the ALICE experiment at the CERN Large Hadron Collider (LHC) is presented for inelastic proton-proton collisions at a centre-of-mass energy of 7 TeV. The transverse momentum (p(T)) distributions were studied at mid-rapidity (vertical bar y vertical bar < 0.5) in the range of 0.6 < p(T) < 8.5 GeV/c Xi(-) for and Xi(+) baryons, and in the range of 0.8 < P-T < 5 GeV/c for Omega(-) and<(Omega)over bar>(+). Baryons and antibaryons were measured as separate particles and we find that the baryon to antibaryon ratio of both particle species is consistent with unity over the entire range of the measurement. The statistical precision of the current data has allowed us to measure a difference between the mean p(T) of Xi(-) ((Xi) over bar)(+) and Omega(-) ((Omega) over bar (+)). Particle yields, mean pi, and the spectra in the intermediate pi range are not well described by the PYTHIA Perugia 2011 tune Monte Carlo event generator, which has been tuned to reproduce the early LHC data. The discrepancy is largest for Omega(-)((Omega) over bar (+)). This PYTHIA tune approaches the pi spectra of Xi(-) and Xi(+) baryons below p(T) <0.85 GeV/c and describes the Xi(-) and Xi(+) spectra above p(T) > 6.0 GeV/c. We also illustrate the difference between the experimental data and model by comparing the corresponding ratios of (Omega(-) +(Omega) over bar (+))/(Xi(-) + Xi(+)) as a function of transverse mass. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 9. |
- Abelev, B., et al.
(författare)
-
Net-Charge Fluctuations in Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2013
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Ingår i: Physical Review Letters. - 1079-7114. ; 110:15
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Tidskriftsartikel (refereegranskat)abstract
- We report the first measurement of the net-charge fluctuations in Pb-Pb collisions at root s(NN) = 2.76 TeV, measured with the ALICE detector at the CERN Large Hadron Collider. The dynamical fluctuations per unit entropy are observed to decrease when going from peripheral to central collisions. An additional reduction in the amount of fluctuations is seen in comparison to the results from lower energies. We examine the dependence of fluctuations on the pseudorapidity interval, which may account for the dilution of fluctuations during the evolution of the system. We find that the fluctuations at the LHC are smaller compared to the measurements at the BNL Relativistic Heavy Ion Collider, and as such, closer to what has been theoretically predicted for the formation of a quark-gluon plasma. DOI: 10.1103/PhysRevLett.110.152301
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| 10. |
- Abelev, B., et al.
(författare)
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Production of Muons from Heavy Flavor Decays at Forward Rapidity in pp and Pb-Pb Collisions at root s(NN)=2.76 TeV
- 2012
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Ingår i: Physical Review Letters. - 1079-7114. ; 109:11
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE Collaboration has measured the inclusive production of muons from heavy-flavor decays at forward rapidity, 2.5 < y < 4, in pp and Pb-Pb collisions at root s(NN) = 2.76 TeV. The p(t)-differential inclusive cross section of muons from heavy-flavor decays in pp collisions is compared to perturbative QCD calculations. The nuclear modification factor is studied as a function of p(t) and collision centrality. A weak suppression is measured in peripheral collisions. In the most central collisions, a suppression of a factor of about 3-4 is observed in 6 < p(t) < 10 GeV/c. The suppression shows no significant p(t) dependence.
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