Harmonic decomposition of two particle angular correlations in Pb Pb collisions at s_NN = 2.76 TeV

Journal Article · Sun Jan 01 04:00:00 EST 2012 · Physics Letters B

DOI:https://doi.org/10.1016/j.physletb.2012.01.060· OSTI ID:1043960

Aamodt, K. ^[1]; Awes, Terry C ^[2]; Read, Kenneth F ^[3]; Silvermyr, David O ^[2]

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1. University of Oslo, Norway
2. ORNL
3. University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)

Angular correlations between unidentified charged trigger (t) and associated (a) particles are measured by the ALICE experiment in Pb-Pb collisions at {radical}s{sub NN} = 2.76 TeV for transverse momenta 0.25 < p{sub T}{sup t,a} < 15 GeV/c, where p{sub T}{sup t} > p{sub T}{sup a}. The shapes of the pair correlation distributions are studied in a variety of collision centrality classes between 0 and 50% of the total hadronic cross section for particles in the pseudorapidity interval |{eta}| < 1.0. Distributions in relative azimuth {Delta}{phi}{triple_bond}{phi}t-{phi}a are analyzed for |{Delta}{eta}|{triple_bond}|{eta}t-{eta}a| > 0.8, and are referred to as 'long-range correlations'. Fourier components Vn{Delta} {triple_bond} <cos(n{Delta}{phi})> are extracted from the long-range azimuthal correlation functions. If particle pairs are correlated to one another through their individual correlation to a common symmetry plane, then the pair anisotropy V{sub n{Delta}}(p{sub T}{sup t},p{sub T}{sup a}) is fully described in terms of single-particle anisotropies vn(pT) as V{sub n{Delta}}(p{sub T}{sup t},p{sub T}{sup a}) = v{sub n}(p{sub T}{sup t})v{sub n}(p{sub T}{sup a}). This expectation is tested for 1 {le} n {le} 5 by applying a global fit of all V{sub n{Delta}}(p{sub T}{sup t},p{sub T}{sup a}) to obtain the best values vn{l_brace}GF{r_brace}(p{sub T}). It is found that for 2 {le} n {le} 5, the fit agrees well with data up to p{sub T}{sup a} {approx} 3-4 GeV/c, with a trend of increasing deviation as p{sub T}{sup t} and p{sub T}{sup a} are increased or as collisions become more peripheral. This suggests that no pair correlation harmonic can be described over the full 0.25 < pT < 15 GeV/c range using a single vn(pT) curve; such a description is however approximately possible for 2 {le} n {le} 5 when p{sub T}{sup a} < 4 GeV/c. For the n = 1 harmonic, however, a single v{sub 1}(pT) curve is not obtained even within the reduced range p{sub T}{sup a} < 4 GeV/c.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1043960
• Journal Information: Physics Letters B, Journal Name: Physics Letters B Journal Issue: 3-5 Vol. 708; ISSN PYLBAJ; ISSN 0370-2693
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANGULAR CORRELATION
ANISOTROPY
CORRELATION FUNCTIONS
CROSS SECTIONS
HARMONICS
SYMMETRY