engleski

Charged-particle pseudorapidity density at mid- rapidity in p–Pb collisions at √sNN = 8.16 TeV

The pseudorapidity density of charged particles, dNch/dη , in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon pair of √sNN = 8.16 TeV at mid- pseudorapidity for non- single- diffractive events. The results cover 3.6 units of pseudorapidity, |η|<1.8 . The dNch/dη value is 19.1±0.7 at |η|<0.5 . This quantity divided by ⟨Npart⟩ / 2 is 4.73±0.20 , where ⟨Npart⟩ is the average number of participating nucleons, is 9.5% higher than the corresponding value for p– Pb collisions at √sNN = 5.02 TeV. Measurements are compared with models based on different mechanisms for particle production. All models agree within uncertainties with data in the Pb- going side, while HIJING overestimates, showing a symmetric behaviour, and EPOS underestimates the p-going side of the dNch/dη distribution. Saturation-based models reproduce the distributions well for η>−1.3 . The dNch/dη is also measured for different centrality estimators, based both on the charged- particle multiplicity and on the energy deposited in the Zero- Degree Calorimeters. A study of the implications of the large multiplicity fluctuations due to the small number of participants for systems like p–Pb in the centrality calculation for multiplicity-based estimators is discussed, demonstrating the advantages of determining the centrality with energy deposited near beam rapidity.

rapidity density ; charged particle rapidity ; charged particle: multiplicity ; charged particle: density ; multiplicity: fluctuation ; calorimeter: forward spectrometer ; p nucleus: scattering ; p p: scattering ; nucleon nucleon: scattering ; experimental results ; quark gluon: plasma ; quantum chromodynamics perturbation theory ; 8160 GeV-cms/nucleon

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