Estimates of hadron azimuthal anisotropy from multiparton interactions in proton-proton collisions at sqrt(s) = 14 TeV

TL;DR

The study tests whether proton-proton collisions at the LHC can display collective elliptic flow by transferring heavy-ion v2 scaling to p-p geometry. A Glauber eikonal framework is used to compute eccentricity, overlap area, and midrapidity multiplicity for several proton transverse density profiles. Applying an incomplete-thermalization v2 scaling yields integrated v2 values typically below 3%, with profiles like hard-sphere or exponential giving extreme results. The work suggests that measuring a small but finite v2 could constrain the proton’s transverse structure, though disentangling flow from non-flow correlations will be challenging.

Abstract

We estimate the amount of collective "elliptic flow" expected at mid-rapidity in proton-proton (p-p) collisions at the CERN Large Hadron Collider (LHC), assuming that any possible azimuthal anisotropy of the produced hadrons with respect to the plane of the reaction follows the same overlap-eccentricity and particle-density scalings as found in high-energy heavy ion collisions. Using a Glauber eikonal model, we compute the p-p eccentricities, transverse areas and particle-multiplicities for various phenomenological parametrisations of the proton spatial density. For realistic proton transverse profiles, we find integrated elliptic flow v2 parameters below 3% in p-p collisions at sqrt(s) = 14 TeV.

Figures (9)

• Figure 1: Number of binary parton-parton collisions in $p\hbox{-}p$ collisions at $\sqrt{s}$ = 14 TeV as a function of scaled impact parameter $b/2R$ (left) and centrality $C$ (right) for the different proton density distributions considered in this work (Table \ref{['tab:1']}). For comparison, the results for $Au\hbox{-}Au$ at RHIC energies are shown as a dotted line.
• Figure 2: Probability density (normalised to unity) of inelastic parton scatterings in $p\hbox{-}p$ collisions at $\sqrt{s}$ = 14 TeV as a function of scaled impact parameter $b/2R$ (left) and centrality $C$ (right) for the different proton density distributions considered in this work (Table \ref{['tab:1']}). For comparison, the results for $Au\hbox{-}Au$ at RHIC energies are shown as a dotted line.
• Figure 3: Eccentricity $\varepsilon$ in $p\hbox{-}p$ collisions at $\sqrt{s}$ = 14 TeV as a function of scaled impact parameter $b/2R$ (left) and centrality $C$ (right) for the different proton density distributions considered in this work (Table \ref{['tab:1']}). For comparison, the results for $Au\hbox{-}Au$ at RHIC energies are shown as a dotted line.
• Figure 4: Effective overlap area $A_\perp$ in $p\hbox{-}p$ collisions at $\sqrt{s}$ = 14 TeV as a function of scaled impact parameter $b/2R$ for the different proton density distributions considered in this work (Table \ref{['tab:1']}). For comparison, the results for $Au\hbox{-}Au$ at RHIC energies are shown as a dotted line. The left plot shows the absolute value of $A_\perp$ (for clarity, the Fermi-II and $Au\hbox{-}Au$ curves are scaled by factors of 1/4 and 1/100 respectively). The right plot shows the area normalised to the value for central collisions, $A_{\perp}(b)/A_\perp(b=0\hbox{fm})$.
• Figure 5: Absolute (left) and normalised (right) particle multiplicity at midrapidity as a function of centrality $C$ in $p\hbox{-}p$ collisions at $\sqrt{s}$ = 14 TeV for the different proton density distributions considered in this work (Table \ref{['tab:1']}). For comparison, the results for $Au\hbox{-}Au$ at RHIC energies are shown as a dotted line.