Abstract
Two-particle pseudorapidity correlations are measured in $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV Pb+Pb, $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV $p$+Pb, and $\sqrt{s}$ = 13 TeV $pp$ collisions at the LHC, with total integrated luminosities of approximately 7 $\mu\mathrm{b}^{-1}$, 28 $\mathrm{nb}^{-1}$, and 65 $\mathrm{nb}^{-1}$, respectively. The correlation function $C_{\rm N}(\eta_1,\eta_2)$ is measured as a function of event multiplicity using charged particles in the pseudorapidity range $|\eta|<2.4$. The correlation function contains a significant short-range component, which is estimated and subtracted. After removal of the short-range component, the shape of the correlation function is described approximately by $1+\langle{a_1^2}\rangle \eta_1\eta_2$ in all collision systems over the full multiplicity range. The values of $\sqrt{\langle{a_1^2}\rangle}$ are consistent between the opposite-charge pairs and same-charge pairs, and for the three collision systems at similar multiplicity. The values of $\sqrt{\langle{a_1^2}\rangle}$ and the magnitude of the short-range component both follow a power-law dependence on the event multiplicity. The $\eta$ distribution of the short-range component, after symmetrizing the proton and lead directions in $p$+Pb collisions, is found to be smaller than that in $pp$ collisions with comparable multiplicity.
Highlights
Heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) create hot, dense matter whose space-time evolution can be well described by relativistic viscous hydrodynamics [1,2]
The magnitude of the short-range correlations (SRC) in p + Pb is observed to be larger in the proton-going direction than in the lead-going direction, reflecting the fact that the particle multiplicity is smaller in the proton-going direction
The correlation function CN(η1,η2) is measured using charged particles in the pseudorapidity range |η| < 2.4 with transverse momentum pT > 0.2 GeV, and it is measured as a function of event multiplicity Nch defined by the total number of charged particles with |η| < 2.5 and pT > 0.4 GeV
Summary
Heavy-ion collisions at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) create hot, dense matter whose space-time evolution can be well described by relativistic viscous hydrodynamics [1,2]. Owing to strong event-by-event (EbyE) density fluctuations in the initial state, the space-time evolution of the produced matter in the final state fluctuates event to event These fluctuations may lead to correlations of particle multiplicity in momentum space in the transverse and longitudinal directions with respect to the collision axis. Longitudinal multiplicity correlations can be generated during the space-time evolution in the final state as resonance decays, single-jet fragmentation, and Bose-Einstein correlations These latter correlations are typically localized over a smaller range of η, and are commonly referred to as short-range correlations (SRC). Terms involving a0 reflect multiplicity fluctuations in the given event class, while the dynamical fluctuations between particles at different pseudorapidities in events of fixed multiplicity are captured by the terms in anam , n,m 1 It is the study of these dynamical fluctuations that is the goal of this analysis. A comparison is made between the pp data and QCD-inspired models
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