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Title: Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at $$\sqrt{s_{NN}} =$$ 2.76 TeV

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. As a result, a comparison of the factorization data to hydrodynamic predictions with event-by-event fluctuating initial conditions is also presented.
  1. Yerevan Physics Inst. (YerPhI), Yerevan (Armenia). et al.
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1029-8479; arXiv eprint number arXiv:1312.1845
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of High Energy Physics (Online)
Additional Journal Information:
Journal Name: Journal of High Energy Physics (Online); Journal Volume: 2014; Journal Issue: 2; Journal ID: ISSN 1029-8479
Springer Berlin
Research Org:
Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
The CMS Collaboration
Country of Publication:
United States
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS relativistic heavy ion physics; heavy ions; harmonic flow