The European Physical Journal C > 2019 > 79 > 4 > 1-17
Charged-particle pseudorapidity density at mid-rapidity in p–Pb collisions at $$\pmb {\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}}}$$ sNN = 8.16 TeV
Source
Abstract
The pseudorapidity density of charged particles, $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη , in p–Pb collisions has been measured at a centre-of-mass energy per nucleon–nucleon pair of $$\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}}$$ sNN = 8.16 TeV at mid-pseudorapidity for non-single-diffractive events. The results cover 3.6 units of pseudorapidity, $$|\eta |<1.8$$ |η|<1.8 . The $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη value is $$19.1\pm 0.7$$ 19.1±0.7 at $$|\eta |<0.5$$ |η|<0.5 . This quantity divided by $$\langle N_{\mathrm{part}} \rangle $$ ⟨Npart⟩ / 2 is $$4.73\pm 0.20$$ 4.73±0.20 , where $$\langle N_{\mathrm{part}} \rangle $$ ⟨Npart⟩ is the average number of participating nucleons, is 9.5% higher than the corresponding value for p–Pb collisions at $$\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}}$$ 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 $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ dNch/dη distribution. Saturation-based models reproduce the distributions well for $$\eta >-1.3$$ η>-1.3 . The $$\mathrm {d}N_{\mathrm{ch}}/\mathrm {d}\eta $$ 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.
Identifiers
journal ISSN : | 1434-6044 |
journal e-ISSN : | 1434-6052 |
DOI | 10.1140/epjc/s10052-019-6801-9 |