Abstract
Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at sqrt(s_NN) = 2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 mb^-1. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle (phi), with the coefficients v_n denoting the magnitude of the anisotropy. Significant v_2-v_6 values are obtained as a function of transverse momentum (0.5<pT<20 GeV), pseudorapidity (|eta|<2.5) and centrality using an event plane method. The v_n values for n>=3 are found to vary weakly with both eta and centrality, and their pT dependencies are found to follow an approximate scaling relation, v_n^{1/n}(pT) \propto v_2^{1/2}(pT). A Fourier analysis of the charged particle pair distribution in relative azimuthal angle (Dphi=phi_a-phi_b) is performed to extract the coefficients v_{n,n}=<cos (n Dphi)>. For pairs of charged particles with a large pseudorapidity gap (|Deta=eta_a-eta_b|>2) and one particle with pT<3 GeV, the v_{2,2}-v_{6,6} values are found to factorize as v_{n,n}(pT^a,pT^b) ~ v_n(pT^a)v_n(pT^b) in central and mid-central events. Such factorization suggests that these values of v_{2,2}-v_{6,6} are primarily due to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v_{1,1}(pT^a,pT^b) data are consistent with the combined contributions from a rapidity-even v_1 and global momentum conservation. A two-component fit is used to extract the v_1 contribution. The extracted v_1 is observed to cross zero at pT\sim1.0 GeV, reaches a maximum at 4-5 GeV with a value comparable to that for v_3, and decreases at higher pT.
Highlights
The primary goal of high-energy heavy-ion physics is to understand the properties of the hot and dense matter created in nuclear collisions at facilities such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC)
This paper presents comprehensive results for v1–v6 over broad ranges of centrality, pseudorapidity, particles in lead-lead (Pb-Pb) collisions at a√nsdNpNT=fo2r .c7h6arTgeeVd with the ATLAS detector at the LHC
V2 varies strongly with centrality, reflecting an anisotropy mainly associated with a change in the average elliptic geometry with centrality
Summary
The primary goal of high-energy heavy-ion physics is to understand the properties of the hot and dense matter created in nuclear collisions at facilities such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). An important observable toward this goal is the azimuthal anisotropy of particle emission. At higher pT, this anisotropy is understood to result from the path-lengthdependent energy loss of jets as they traverse the matter, with more particles emitted in the direction of smallest path-length [2]. These directions of maximum emission are strongly correlated, and the observed azimuthal anisotropy is customarily expressed as a Fourier series in azimuthal angle φ [3,4]: d3N E dp d2N = 2πpT dpT d η ∞.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
