The charged-particle pseudorapidity density measured over four units of pseudorapidity in nonsingle-diffractive $p+\mathrm{Pb}$ collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=5.02\mathrm{TeV}$ is presented. The average value at midrapidity is measured to be $16.81\pm 0.71(\mathrm{syst})$, which corresponds to $2.14\pm 0.17(\mathrm{syst})$ per participating nucleon, calculated with the Glauber model. This is 16% lower than in nonsingle-diffractive $pp$ collisions interpolated to the same collision energy and 84% higher than in $d+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=0.2\mathrm{TeV}$. The measured pseudorapidity density in $p+\mathrm{Pb}$ collisions is compared to model predictions and provides new constraints on the description of particle production in high-energy nuclear collisions.

• Received 18 October 2012

DOI:https://doi.org/10.1103/PhysRevLett.110.032301

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© 2013 CERN, for the ALICE Collaboration