Abstract
We present measurements of two-particle differential number correlation functions $R_{2}$ and transverse momentum correlation functions $P_{2}$, obtained from p-Pb collisions at 5.02 TeV and Pb-Pb collisions at 2.76 TeV. The results are obtained using charged particles in the pseudorapidity range $|\eta| <$ 1.0, and transverse momentum range $0.2 < p_{\rm T} < 2.0$ GeV/$c$ as a function of pair separation in pseudorapidity, $|\Delta\eta|$, azimuthal angle, $\Delta\varphi$, and for several charged-particle multiplicity classes. Measurements are carried out for like-sign and unlike-sign charged-particle pairs separately and combined to obtain charge-independent and charge-dependent correlation functions. We study the evolution of the width of the near-side peak of these correlation functions with collision centrality. Additionally, we study Fourier decompositions of the correlators in $\Delta\varphi$ as a function of the pair separation $|\Delta\eta|$. Significant differences in the dependence of their harmonic coefficients on multiplicity classes are found. These differences can be exploited, in theoretical models, to obtain further insight into charged-particle production and transport in heavy-ion collisions. Moreover, an upper limit of non-flow contributions to flow coefficients $v_{n}$ measured in Pb-Pb collisions based on the relative strength of Fourier coefficients measured in p-Pb interactions is estimated.
Highlights
Measurements carried out at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) during the last decade indicate that a strongly interacting quarkgluon plasma is produced in heavy nuclei collisions at high beam energies [1,2,3,4]
The varied track quality criteria included the minimal number of time projection chamber (TPC) space points per track, the maximum χ 2 per degree of freedom obtained in the momentum fit, as well as the maximum track distance of closest approach (DCA) to the primary vertex
The R2 and P2 correlation functions measured in Pb-Pb collisions are displayed in Figs. 2 and 3 for unlike- and like-sign pairs for three representative multiplicity classes corresponding to 70%–80%, 30%–40%, and 0%–5% fractions of the cross section
Summary
Measurements carried out at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) during the last decade indicate that a strongly interacting quarkgluon plasma (sQGP) is produced in heavy nuclei collisions at high beam energies [1,2,3,4]. Nonflow effects may arise from resonance decays or low-multiplicity hadronization processes associated with mini-jets, string fragmentation, or color tube breakup [30,31,32,33,34] It remains unclear how these different particle-production mechanisms influence the shape and strength of correlation functions and what their relative contributions might be. The width of the correlation functions, most their charge-dependent components R2(CD) and P2(CD), are sensitive to charged-particle creation mechanisms and time of origin [36,37,38,39], momentum conservation [40,41,42], as well as transport phenomena such as radial flow [43,44,45] and diffusion processes [46,47,48,49]. Fourier decompositions are studied as a function of pseudorapidity pair separation to obtain a detailed characterization of flow and nonflow contributions to these correlation functions.
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