Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at=2.76 TeV

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Abstract

Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at = 2.76TeV by the CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 mu b -aEuro parts per thousand 1. The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v (2) to v (6), are extracted as a function of particle transverse momentum. At higher transverse momentum, the v (2) harmonic becomes significantly smaller than the higher-order v (n) (n a parts per thousand yenaEuro parts per thousand 3). The p (T)-averaged v (2) and v (3) are found to be equal within 2%, while higher-order v (n) decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-by-event fluctuating initial conditions is also presented.

Autore Pugliese

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  • POMPILI A.;MARANGELLI B.;CALABRIA C.;SELVAGGI G.;SINGH G.;BARBONE L.;ABBRESCIA M.;DE PALMA M.;RADOGNA R.;VENDITTI R.;MY S.;NUZZO S.V.;CHHIBRA S.S

Titolo volume/Rivista

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Anno di pubblicazione

2014

ISSN

1029-8479

ISBN

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Numero di citazioni Wos

37

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Numero di citazioni Scopus

49

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Settori ERC

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