Testing hydrodynamic descriptions of p+p collisions at $$\sqrt{s}=7$$ TeV

Abstract

In high-energy collisions of heavy ions, experimental findings of collective flow are customarily associated with the presence of a thermalized medium expanding according to the laws of hydrodynamics. Recently, the ATLAS, CMS, and ALICE experiments found signals of the same type and magnitude in ultrarelativistic proton-proton collisions. In this study, the state-of-the-art hydrodynamic model SONIC is used to simulate the systems created in p+p collisions. By varying the size of the second-order transport coefficients, the range of applicability of hydrodynamics itself to the systems created in p+p collisions is quantified. It is found that hydrodynamics can give quantitatively reliable results for the particle spectra and the elliptic momentum anisotropy coefficient v 2 . Using a simple geometric model of the proton based on the elastic form factor leads to results of similar type and magnitude to those found in experiment when allowing for a small bulk viscosity coefficient.

Initial-state fluctuations in collisions between light and heavy ions

“…Recently similar flow-like features have also been observed in collisions between small and large nuclei (p+Au/Pb, d+Au, 3 He+Au [2][3][4][5][6][7][8][9][10][11][12][13]), and even in very high multiplicity p+p collisions at the LHC [9,[14][15][16][17][18]. While hydrodynamic models have been very successful in achieving a quantitatively accurate description of essentially all soft hadron data (momentum spectra and two-particle correlations of both unidentified charged and identified hadrons with transverse momenta below about 2 GeV) obtained from the collisions between heavy nuclei (Au+Au, Pb+Pb, Cu+Cu and Cu+Au), a similar convergence between theory and experiment has not yet been achieved in collisions involving small nuclei.…”

Relativistic hydrodynamic attractors with broken symmetries: non-conformal and non-homogeneous

“…Though not interpreted in this fashion, non-equilibrium equations of state are now routinely used (and indeed required!) to provide precision fits of hydrodynamic models of relativistic ion collisions to experimental data [33,34].…”

Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at s=5.02 and 13 TeV and pAaboud1, Bergeås2, Brenner3 et al. 2017Phys. Rev. C784780View full textAdd to dashboardCite

“…Indeed, an alternative explanation for the modulation using perturbative QCD and assuming saturated parton distributions in the lead nucleus is capable of reproducing many features of the p + Pb data [20][21][22][23][24][25][26][27][28][29]. Nonetheless, because of the many similarities between the p + Pb and Pb + Pb observations, extensive theoretical and experimental effort has been devoted to address the question of whether the strong-coupling physics understood to be responsible for the collective dynamics in A + A collisions may persist in smaller systems [30][31][32][33][34][35][36][37][38][39][40].…”