Abstract
Two-particle angular correlations between unidentified charged trigger and associated particles are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum range 0.7<pT,assoc<pT,trig<5.0 GeV/c is examined, to include correlations induced by jets originating from low momentum-transfer scatterings (minijets). The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |η|<0.9. The near-side long-range pseudorapidity correlations observed in high-multiplicity p–Pb collisions are subtracted from both near-side short-range and away-side correlations in order to remove the non-jet-like components. The yields in the jet-like peaks are found to be invariant with event multiplicity with the exception of events with low multiplicity. This invariance is consistent with the particles being produced via the incoherent fragmentation of multiple parton–parton scatterings, while the yield related to the previously observed ridge structures is not jet-related. The number of uncorrelated sources of particle production is found to increase linearly with multiplicity, suggesting no saturation of the number of multi-parton interactions even in the highest multiplicity p–Pb collisions. Further, the number scales only in the intermediate multiplicity region with the number of binary nucleon–nucleon collisions estimated with a Glauber Monte-Carlo simulation.
Highlights
Data from p–Pb collisions at the LHC have resulted in several surprising measurements with observations which are typically found in collisions of heavy ions and are understood to be due to a collective expansion of the hot and dense medium
-called ridge structures which span over a large range in pseudorapidity (η) have been observed in two-particle correlations [1,2,3]
Long-range pseudorapidity correlations have been subtracted from the per-trigger yields in order to study the jet-like correlation peaks
Summary
Data from p–Pb collisions at the LHC have resulted in several surprising measurements with observations which are typically found in collisions of heavy ions and are understood to be due to a collective expansion of the hot and dense medium (hydrodynamic flow). -called ridge structures which span over a large range in pseudorapidity (η) have been observed in two-particle correlations [1,2,3] Their modulation in azimuth is described by Fourier coefficients and is dominated by those of second (v2) and third (v3) order [2,3,4]. Evidence for the existence of a common flow velocity field has been further corroborated by particle-identification measurements of the same observables [6] They revealed that the v2 of pions, kaons and protons as a function of pT shows a characteristic mass ordering as well as a crossing of pion and proton v2 at about 2.5 GeV/c which is reminiscent of measurements in Pb–Pb collisions [7].
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