14 research outputs found
Measurement of charged jet production cross sections and nuclear modification in p-Pb collisions at \sqrt{s_\rm{NN}} = 5.02 TeV
No full textCharged jet production cross sections in p-Pb collisions at TeV measured with the ALICE detector at the LHC are presented. Using the anti- algorithm, jets have been reconstructed in the central rapidity region from charged particles with resolution parameters and , The reconstructed jets have been corrected for detector effects and the underlying event background. To calculate the nuclear modification factor, , of charged jets in p-Pb collisions, a pp reference was constructed by scaling previously measured charged jet spectra at TeV. In the transverse momentum range GeV/, is found to be consistent with unity, indicating the absence of strong nuclear matter effects on jet production. Major modifications to the radial jet structure are probed via the ratio of jet production cross sections reconstructed with the two different resolution parameters. This ratio is found to be similar to the measurement in pp collisions at TeV and to the expectations from PYTHIA pp simulations and NLO pQCD calculations at TeV
3ΛH and 3Λ¯H‾ production in Pb–Pb collisions at √sNN = 2.76 TeV
No full textThe production of the hypertriton nuclei 3
H and 3
¯ H has been measured for the first time in Pb–Pb
collisions at √sNN = 2.76 TeV with the ALICE experiment at LHC. The pT-integrated 3
H yield in one
unity of rapidity, dN/dy × B.R.
3
H→3He,π− = (3.86 ± 0.77(stat.) ± 0.68(syst.)) × 10−5 in the 0–10% most
central collisions, is consistent with the predictions from a statistical thermal model using the same
temperature as for the light hadrons. The coalescence parameter B3 shows a dependence on the
transverse momentum, similar to the B2 of deuterons and the B3 of 3He nuclei. The ratio of yields
S3 = 3
H/(3He×/p) was measured to be S3 = 0.60±0.13(stat.)±0.21(syst.) in 0–10% centrality events;
this value is compared to different theoretical models. The measured S3 is compatible with thermal
model predictions. The measured 3
H lifetime, τ = 181+54
−39(stat.) ± 33(syst.) ps is in agreement within 1σ
with the world average value.peerReviewe
Elliptic flow of muons from heavy-flavour hadron decays at forward rapidity in Pb-Pb collisions at root s(NN)=2.76TeV
No full textThe elliptic flow, v(2), of muons from heavy-flavour hadron decays at forward rapidity (2.5 <y <4) is measured in Pb-Pb collisions at root s(NN)= 2.76TeVwith the ALICE detector at the LHC. The scalar product, two- and four-particle Q cumulants and Lee-Yang zeros methods are used. The dependence of the v(2) of muons from heavy-flavour hadron decays on the collision centrality, in the range 0-40%, and on transverse momentum, p(T), is studied in the interval 3 <p(T)<10 GeV/c. A positive v(2) is observed with the scalar product and two-particle Q cumulants in semi-central collisions (10-20% and 20-40% centrality classes) for the p(T) interval from 3 to about 5GeV/c with a significance larger than 3 sigma, based on the combination of statistical and systematic uncertainties. The v(2) magnitude tends to decrease towards more central collisions and with increasing pT. It becomes compatible with zero in the interval 6 <p(T)<10 GeV/c. The results are compared to models describing the interaction of heavy quarks and open heavy-flavour hadrons with the high-density medium formed in high-energy heavy-ion collisions. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B.V.Peer reviewe
Coherent rho(0) photoproduction in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV
No full textWe report the first measurement at the LHC of coherent photoproduction of rho(0) mesons in ultra-peripheral Pb-Pb collisions. The invariant mass and transverse momentum distributions for rho(0) production are studied in the pi(+)pi(-) decay channel at mid-rapidity. The production cross section in the rapidity range vertical bar y vertical bar <0.5 is found to be d sigma/dy = 425 +/- 10 (stat.) (+42)(-50) (sys.) mb. Coherent rho(0) production is studied with and without requirement of nuclear breakup, and the fractional yields for various breakup scenarios are presented. The results are compared with those from lower energies and with model predictions.Peer reviewe
Measurement of dijet in \pPb{} collisions at TeV
No full textSee paper for full list of authors – 17 pages, 3 captioned figures, 1 table, authors from page 12, submitted to PLB, figures at http://aliceinfo.cern.ch/ArtSubmission/node/1542International audienceA measurement of dijet correlations in p-Pb collisions at TeV with the ALICE detector is presented. Jets are reconstructed from charged particles measured in the central tracking detectors and neutral energy deposited in the electromagnetic calorimeter. The transverse momentum of the full jet (clustered from charged and neutral constituents) and charged jet (clustered from charged particles only) is corrected event-by-event for the contribution of the underlying event, while corrections for underlying event fluctuations and finite detector resolution are applied on an inclusive basis. A projection of the dijet transverse momentum, k_{\rm Ty} = p_\rm{T,jet}^\rm{ch+ne} \; \rm{sin}(\Delta\varphi_{\rm{dijet}}) with the azimuthal angle between a full and charged jet and p_\rm{T,jet}^\rm{ch+ne} the transverse momentum of the full jet, is used to study nuclear matter effects in p-Pb collisions. This observable is sensitive to the acoplanarity of dijet production and its potential modification in p-Pb collisions with respect to pp collisions. Measurements of the dijet as a function of the transverse momentum of the full and recoil charged jet, and the event multiplicity are presented. No significant modification of due to nuclear matter effects in p-Pb collisions with respect to the event multiplicity or a PYTHIA8 reference is observed
Event-shape engineering for inclusive spectra and elliptic flow in Pb-Pb collisions at √sNN = 2.76 TeV
No full textWe report on results obtained with the event-shape engineering technique applied to Pb-Pb collisions at
√sNN = 2.76 TeV. By selecting events in the same centrality interval, but with very different average flow,
different initial-state conditions can be studied. We find the effect of the event-shape selection on the elliptic
flow coefficient v2 to be almost independent of transverse momentum pT, which is as expected if this effect
is attributable to fluctuations in the initial geometry of the system. Charged-hadron, -pion, -kaon, and -proton
transverse momentum distributions are found to be harder in events with higher-than-average elliptic flow,
indicating an interplay between radial and elliptic flow.peerReviewe
Rapidity and transverse-momentum dependence of the inclusive J/psi nuclear modification factor in p-Pb collisions at root s(NN)=5.02 TeV
No full textAbstract: We have studied the transverse-momentum (pT) dependence of the inclusive J/ψ production in p-Pb collisions at √sNN = 5.02TeV, in three center-of-mass rapidity (ycms) regions, down to zero pT. Results in the forward and backward rapidity ranges (2.03 < ycms < 3.53 and −4.46 < ycms < −2.96) are obtained by studying the J/ψ decay to μ+μ−, while the mid-rapidity region (−1.37 < ycms < 0.43) is investigated by measuring the e+e− decay channel. The pT dependence of the J/ψ production cross section and nuclear modification factor are presented for each of the rapidity intervals, as well as the J/ψ mean pT values. Forward and mid-rapidity results show a suppression of the J/ψ yield, with respect to pp collisions, which decreases with increasing pT. At backward rapidity no significant J/ψ suppression is observed. Theoretical models including a combination of cold nuclear matter effects such as shadowing and partonic energy loss, are in fair agreement with the data, except at forward rapidity and low transverse momentum. The implications of the p-Pb results for the evaluation of cold nuclear matter effects on J/ψ production in Pb-Pb collisions are also discussed
Forward-central two-particle correlations in p-Pb collisions at root s(NN)=5.02 TeV
No full textTwo-particle angular correlations between trigger particles in the forward pseudorapidity range (2.5 2GeV/c. (C) 2015 CERN for the benefit of the ALICE Collaboration. Published by Elsevier B. V.Peer reviewe
Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at √sNN = 2.76 TeV
No full textTransverse momentum (pT) spectra of pions, kaons, and protons up to pT = 20 GeV/c have been measured
in Pb-Pb collisions at √sNN = 2.76 TeV using the ALICE detector for six different centrality classes covering
0%–80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central
Pb-Pb collisions that decreases for more peripheral collisions. For pT > 10 GeV/c, the nuclear modification factor
is found to be the same for all three particle species in each centrality interval within systematic uncertainties
of 10%–20%. This suggests there is no direct interplay between the energy loss in the medium and the particle
species composition in the hard core of the quenched jet. For pT < 10 GeV/c, the data provide important
constraints for models aimed at describing the transition from soft to hard physics.peerReviewe
Centrality dependence of pion freeze-out radii in Pb-Pb collisions at √sNN = 2.76 TeV
No full textWe report on the measurement of freeze-out radii for pairs of identical-charge pions measured in Pb-Pb
collisions at √sNN = 2.76 TeV as a function of collision centrality and the average transverse momentum
of the pair kT. Three-dimensional sizes of the system (femtoscopic radii), as well as direction-averaged onedimensional
radii are extracted. The radii decrease with kT, following a power-law behavior. This is qualitatively
consistent with expectations from a collectively expanding system, produced in hydrodynamic calculations. The
radii also scale linearly with dNch/dη 1/3. This behavior is compared to world data on femtoscopic radii in
heavy-ion collisions. While the dependence is qualitatively similar to results at smaller √sNN, a decrease in
the ratio Rout/Rside is seen, which is in qualitative agreement with a specific prediction from hydrodynamic
models: a change from inside-out to outside-in freeze-out configuration. The results provide further evidence
for the production of a collective, strongly coupled system in heavy-ion collisions at the CERN Large Hadron Collider.peerReviewe
