Predictions for low-pTand high-pThadron spectra in nearly central Pb+Pb collisions at

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 dec are studied. Comparison with RHIC data at √ s NN = 130 and 200 GeV suggests a rather high value T 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+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 √ s 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.

Radiative jet energy loss in a three-dimensional hydrodynamical medium and highpTazimuthal asymmetry ofπ0suppression at mid and forward rapidity in

“…The index j represents one of the partonic species (j = q,q, g), and x j T = 2p j T / √ s N N , where √ s N N is the center of mass energy. The distribution dσ/dt is the leading order QCD differential cross section, and the Kfactor accounts for NLO effects and is taken to be constant in our calculation as it is almost p T independent [37,38,39]. The initial Cronin effect is neglected in our calculation since the nuclear modification factor of neutral pions from d+Au collisions measured by PHENIX is consistent with 1 within systematic errors [40].…”

“…The fragmentation function D h/j (z j , Q F ) gives the average multiplicity of the hadron h with the momentum fraction z j = p T /p j T produced from a jet j at a scale Q F , taken from KKP parametrization [44]. The fractorization scale Q = p j T and fragmentation scale Q F = p T are set as in [37] where the K-factor is found to be 2.8. We use these values throughout the present study.…”

What to expect when you're expecting: femtoscopy at the LHC

“…However, especially at the LHC, the large transverse flow generated by the intense pressure gradients cannot be ignored. Eskola and collaborators [22], estimate that the time required to cool from the maximum energy density (at r = 0 in Fig. 5 to the critical energy density (ε c = 1.93GeV / f m 3 ) would be 6 fm/c (20 fm/c) at RHIC (LHC), due to longitudinal expansion alone.…”

“…Recently, Eskola and collaborators [22] coupled a pQCD+saturation-based prediction for initial conditions at LHC to their 1 + 1-dimensional hydro calculation. The Equation-of-State featured a first-order phase transition between an ideal QGP at high temperature and a hadron resonance gas at low temperature.…”

Angular hadron correlations probing the early medium evolution

“…In [5] it was shown that there is about 50% uncertainty in the extraction of the medium quenching power (given by K) from R AA even for model evolutions which describe bulk soft matter properties; a 2+1d hydrodynamical evolution [6], a 3+1d hydrodynamical evolution [7] and a parametrized evolution [8]. Greater sensitivity to the medium density evolution can hence only be gained in more differential probes such as γ-hadron correlations [2], R AA for non-central collisions [5] or back-toback hadron correlations [4], here we focus on the latter.…”