Entropy production in pp and Pb-Pb collisions at the LHC


We use experimentally measured identified particle spectra and Hanbury Brown-Twiss radii to determine the entropy per unit rapidity dS/dy produced in $\sqrt{s}=7~\text{TeV}$ pp and $\sqrt{s_{NN}}=2.76~\text{TeV}$ Pb-Pb collisions. We find that $dS/dy=11335\pm1188$ in 0-10% Pb-Pb, $dS/dy=135.7\pm17.9$ in high-multiplicity pp, and $dS/dy=37.8\pm3.7$ in minimum bias pp collisions and compare the corresponding entropy per charged particle $(dS/dy)/(dN_\text{ch}/dy)$ to predictions of statistical models. Finally, we use the QCD kinetic theory pre-equilibrium and viscous hydrodynamics to model entropy production in the collision and reconstruct the average temperature profile at $\tau_0=1~\text{fm}/c$ for high multiplicity pp and Pb-Pb collisions.

Phys. Rev. C100