Charged-particle pseudorapidity density at mid-rapidity in p–Pb collisions at $$\pmb {\sqrt{s_{\scriptscriptstyle {\mathrm{NN}}}}}$$ sNN = 8.16 TeV

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, $$|\eta |-1.3$$ 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.