Abstract
We present the results of an improved Monte Carlo Glauber (MCG) model of relevance for collisions involving nuclei at center-of-mass energies of the BNL Relativistic Heavy Ion Collider ($\sqrt{{s}_{\mathit{NN}}}=0.2$ TeV), CERN Large Hadron Collider (LHC) ($\sqrt{{s}_{\mathit{NN}}}=2.76--8.8\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$), and proposed future hadron colliders ($\sqrt{{s}_{\mathit{NN}}}\ensuremath{\approx}10--63$ TeV). The inelastic $pp$ cross sections as a function of $\sqrt{{s}_{\mathit{NN}}}$ are obtained from a precise data-driven parametrization that exploits the many available measurements at LHC collision energies. We describe the nuclear density of a lead nucleus with two separated two-parameter Fermi distributions for protons and neutrons to account for their different densities close to the nuclear periphery. Furthermore, we model the nucleon degrees of freedom inside the nucleus through a lattice with a minimum nodal separation, combined with a ``recentering and reweighting'' procedure, that overcomes some limitations of previous MCG approaches. The nuclear overlap function, number of participant nucleons and binary nucleon-nucleon collisions, participant eccentricity and triangularity, overlap area, and average path length are presented in intervals of percentile centrality for lead-lead (PbPb) and proton-lead ($p\mathrm{Pb}$) collisions at all collision energies. We demonstrate for collisions at $\sqrt{{s}_{\mathit{NN}}}=5.02\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$ that the central values of the Glauber quantities change by up to 7% in a few bins of reaction centrality, due to the improvements implemented, though typically they remain within the previously assigned systematic uncertainties, while their new associated uncertainties are generally smaller (mostly below 5%) at all centralities than for earlier calculations. Tables for all quantities versus centrality at present and foreseen collision energies involving Pb nuclei, as well as for collisions of XeXe at $\sqrt{{s}_{\mathit{NN}}}=5.44\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$, and AuAu and CuCu at $\sqrt{{s}_{\mathit{NN}}}=0.2\phantom{\rule{0.16em}{0ex}}\mathrm{TeV}$, are provided. The source code for the improved Monte Carlo Glauber model is made publicly available.
Highlights
The interpretation of many results measured in high-energy heavy-ion collisions relies on the use of a model of the initial matter distribution resulting from the overlap of the two colliding nuclei at a given impact parameter b. Quantities such as (i) the centrality dependence, expressed by the number of participating nucleons in the collision, number of participants (Npart)(b), of any observable, (ii) the nuclear overlap function TAA(b) or the number of binary nucleon-nucleon collisions, nucleonnucleon collisions (Ncoll)(b), used to derive the nuclear modification factor (RAA) from the ratio of AA over pp spectra, (iii) the elliptic and triangular flow parameters v2 and v3 normalized by the eccentricity ε2(b) and triangularity ε3(b) of the overlap region, and the average (iv) surface area AT(b) and (v) path length L(b) of the interaction region all depend on a realistic model of the collision geometry [1]
In the Monte Carlo Glauber (MCG) models (e.g., Refs. [5,6,7,8,9,10]), individual nucleons are sampled event-by-event from the underlying 2pF distributions and the collision properties are calculated by averaging over multiple events
We have presented the results of an improved Monte Carlo
Summary
The interpretation of many results measured in high-energy heavy-ion collisions relies on the use of a model of the initial matter distribution resulting from the overlap of the two colliding nuclei at a given impact parameter b. Ncoll(b), Npart(b), TAA(b), and ε2(b) change due to the inclusion of the separated proton and neutron transverse distributions, but typically remain within the previously assigned systematic uncertainties Their new associated uncertainties are generally smaller than for earlier calculations except for mid-peripheral events where they are slightly larger in some cases. Appendix D provides tables with calculated quantities for aXCluleXCreueleccvooallnlliitssiciooonnlslsisaaitot√n√seNsnNNeNr=g=ie0s5.2.i4nT4veoTVlev.VingasPbwenlul calesi,AiunAcluudainngd
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