Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at sNN−−−−√ =2.76 TeV
Issue Date
2014-02Author
CMS Collaboration
Bean, Alice
Publisher
Springer Verlag
Type
Article
Article Version
Scholarly/refereed, publisher version
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Show full item recordAbstract
Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at sNN−−−−√ = 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 μb − 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 ≥ 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.
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Citation
CMS Collaboration. "Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at sNN−−−−√ =2.76 TeV." Journal of High Energy Physics. February, 2014: v5 n2. http://dx.doi.org/10.1007/JHEP02(2014)088
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