Appelshäuser, H.

Heckel, S.

GSI Repository

Monte Carlo studies on event-by-event mean pT fluctuations and comparisonwith results from the ALICE experiment∗S. Heckel1, H. Appelsha¨user1 for the ALICE Collaboration1Institut fu¨r Kernphysik, Goethe-Universita¨t, Frankfurt am Main, GermanyFor the study of event-by-event fluctuations in heavy-ioncollisions the understanding of effects seen in pp collisionsis of major importance. They serve as a baseline for theinterpretation of observations in heavy-ion collisions.In this analysis, non-statistical event-by-event fluctua-tions of the mean transverse momentumM(pT) of chargedparticles are studied as a function of the event multipli-city. A detailed comparison of results for pp collisions at√s = 7 TeV, obtained with the ALICE detector [1] at theLHC, with different Monte Carlo event generators is per-formed in 0.15 < pT < 2 GeV/c and |η| < 0.8.Full simulations including the implementation of the de-tector setup are computing expensive. To be able to com-pare the data to a larger set of generators and tunes, a fastsimulation method based on a simple pT-dependent effi-ciency filter is developed. The filter is shown for both ppand Pb–Pb collisions in figure 1.Tp0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Accepted / MC truth0.50.60.70.80.911.1Efficiency filter = 7 TeVspp:   = 2.76 TeVNNsPb-Pb:  | < 0.8η| < 2 GeV/cT0.15 < p07/17/2012Figure 1: Efficiency filter as a function of pT in pp colli-sions at√s = 7 TeV (solid line) and Pb–Pb collisions at√sNN = 2.76 TeV (dashed line).As a measure of dynamical fluctuations the two-particlecorrelator C = 〈ΔpT,i,ΔpT,j〉 [2] is analysed, withC =1Npsevnev∑k=1Nk∑i=1Nk∑j=i+1(pT,i −M(pT))(pT,j −M(pT)),where nev is the number of events, Nk the number of parti-cles and Npsk the number of particle pairs in event k and∗Work supported by GSI, BMBF, HGS-HIRe, and Helmholtz AllianceHA216/EMMI.Npsev =∑nevk=1Npsk . By construction, C equals zero inthe presence of only statistical fluctuations. The correlatoris calculated in bins of the event multiplicity Nacc, whereNacc is the number of tracks accepted by the analysis cuts.accN1 10m) T  /  M(pmC-110 = 7 TeVspp:  ALICEPythia6 Perugia-0 (full sim.)Phojet (full sim.)Pythia8.150 (fast sim.)Pythia6 Perugia-11 default (fast sim.)Pythia6 Perugia-11 NOCR (fast sim.)| < 0.8η| < 2 GeV/cT0.15 < pFigure 2:√Cm/M(pT)m as a function of Nacc in pp col-lisions at√s = 7 TeV and comparison to different MonteCarlo generators and tunes.The results for pp collisions at√s = 7 TeV are pre-sented in figure 2 in terms of the relative fluctuations√Cm/M(pT)m, where m indicates the given multipli-city class. The Monte Carlo simulations PHOJET [3],PYTHIA6 (Perugia-0 and -11) [4] and PYTHIA8 are ana-lysed. For Perugia-11, the default version is comparedto one without color reconnections (NOCR), which is ex-pected to show a steeper slope in figure 2. All PYTHIA6tunes show a good description of the data, though, Perugia-11 slightly better than Perugia-0. The good agreementof Perugia-11 NOCR rules out color reconnections as thereason for the slope being different from a simple super-position expectation. PYTHIA8 also shows the correctslope, but overestimates the data by about 10–15%, whilePHOJET shows only qualitative agreement.References[1] K. Aamodt et al [ALICE] 2008 JINST 3 S08002[2] S.A. Voloshin et al 1999 Phys. Rev. C 60 024901[3] R. Engel et al 1995 Phys. Rev. D 52 1459[4] P.Z. Skands 2010 Phys. Rev. D 82 074018GSI SCIENTIFIC REPORT 2012 PHN-NQM-EXP-6697

Monte Carlo studies on event-by-event mean p$_{T}$ fluctuations and comparison with results from the ALICE experiment

http://repository.gsi.de/record/52000/files/PHN-NQM-EXP-66.pdf

Monte Carlo studies on event-by-event mean p $_{T}$ fluctuations and comparison with results from the ALICE experiment

Abstract

Similar works

Full text

Available Versions

GSI Repository

Monte Carlo studies on event-by-event mean pT_{T}T​ fluctuations and comparison with results from the ALICE experiment

Abstract

Similar works

Full text

Available Versions

GSI Repository

Monte Carlo studies on event-by-event mean p $_{T}$ fluctuations and comparison with results from the ALICE experiment