Predictions for low-pTand high-pThadron spectra in nearly central Pb+Pb collisions atsNN=5.5TeV tested atsNN=130and 200 GeV

Abstract

We study the hadron spectra in nearly central $A+A$ collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) in a broad transverse momentum range. We cover the low-${p}_{T}$ spectra using longitudinally boost-invariant hydrodynamics with initial energy and net-baryon number densities from the perturbative QCD (pQCD)+saturation model. Buildup of the transverse flow and sensitivity of the spectra to a single decoupling temperature ${T}_{\mathrm{dec}}$ are studied. Comparison with RHIC data at $\sqrt{{s}_{\mathit{NN}}}=130$ and 200 GeV suggests a rather high value ${T}_{\mathrm{dec}}=150$ MeV. The high-${p}_{T}$ spectra are computed using factorized pQCD cross sections, nuclear parton distributions, fragmentation functions, and describing partonic energy loss in the quark-gluon plasma by quenching weights. Overall normalization is fixed on the basis of $p+\overline{p}(p)$ data and the strength of energy loss is determined from RHIC Au+Au data. Uncertainties are discussed. With constraints from RHIC data, we predict the ${p}_{T}$ spectra of hadrons in 5% most central Pb+Pb collisions at the LHC energy $\sqrt{{s}_{\mathit{NN}}}=5500$ GeV. Because of the closed framework for primary production, we can also predict the net-baryon number at midrapidity, as well as the strength of partonic energy losses at the LHC. Both at the LHC and RHIC, we recognize a rather narrow crossover region in the ${p}_{T}$ spectra, where the hydrodynamic and pQCD fragmentation components become of equal size. We argue that in this crossover region the two contributions are to a good approximation mutually independent. In particular, our results suggest a wider ${p}_{T}$ region of applicability for hydrodynamical models at the LHC than at RHIC.