Studies of azimuthal anisotropy harmonics in ultra-central PbPb collisions at sqrt(s[NN]) = 2.76 TeV
S. Chatrchyan
,
S. Baffioni
(1)
,
F. Beaudette
(1)
,
P. Busson
(1)
,
C. Charlot
(1)
,
N. Daci
(1)
,
T. Dahms
(1)
,
M. Dalchenko
(1)
,
L. Dobrzynski
(1)
,
A. Florent
(1)
,
R. Granier de Cassagnac
(1)
,
M. Haguenauer
(1)
,
P. Mine
(1)
,
C. Mironov
(1)
,
I.N. Naranjo
(1)
,
M. Nguyen
(1)
,
C. Ochando
(1)
,
P. Paganini
(1)
,
D. Sabes
(1)
,
R. Salerno
(1)
,
Y. Sirois
(1)
,
C. Veelken
(1)
,
Y. Yilmaz
(1)
,
A. Zabi
(1)
,
J.-L. Agram
(2)
,
J. Andrea
(2)
,
D. Bloch
(2)
,
J.-M. Brom
(2)
,
E.C. Chabert
(2)
,
C. Collard
(2)
,
E. Conte
(2)
,
F. Drouhin
(2)
,
J.-C. Fontaine
(2)
,
D. Gele
(2)
,
U. Goerlach
(2)
,
C. Goetzmann
(2)
,
P. Juillot
(2)
,
A.-C. Le Bihan
(2)
,
P. van Hove
(2)
,
S. Gadrat
(3)
,
S. Beauceron
(4)
,
N. Beaupere
(4)
,
G. Boudoul
(4)
,
S. Brochet
(4)
,
J. Chasserat
(4)
,
R. Chierici
(4)
,
D. Contardo
(4)
,
P. Depasse
(4)
,
H. El Mamouni
(4)
,
J. Fan
(4)
,
J. Fay
(4)
,
S. Gascon
(4)
,
M. Gouzevitch
(4)
,
B. Ille
(4)
,
T. Kurca
(4)
,
M. Lethuillier
(4)
,
L. Mirabito
(4)
,
S. Perries
(4)
,
J.D. Ruiz Alvarez
(4)
,
L. Sgandurra
(4)
,
V. Sordini
(4)
,
M. Vander Donckt
(4)
,
P. Verdier
(4)
,
S. Viret
(4)
,
H. Xiao
(4)
S. Chatrchyan
- Fonction : Auteur
P. Busson
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R. Granier de Cassagnac
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C. Mironov
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P. Paganini
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J.-L. Agram
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C. Collard
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E. Conte
- Fonction : Auteur
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P. van Hove
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M. Gouzevitch
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M. Lethuillier
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V. Sordini
- Fonction : Auteur
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P. Verdier
- Fonction : Auteur
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Résumé
Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at sqrt(s[NN]) = 2.76 TeV 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 inverse microbarns. 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 greater than or equal to 3). The pt-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.