Eccentricity fluctuations make flow measurable in high multiplicity p-p collisions

TL;DR

The conditions under which elliptic flow becomes measurable in the samples of high-multiplicity (dN(ch)/dy > or = 50) p-p collisions, which will soon be collected at the LHC are delineated.

Abstract

Elliptic flow is a hallmark of collectivity in hadronic collisions. Its measurement relies on analysis techniques which require high event multiplicity and could be applied so far to heavy ion collisions only. Here, we delineate the conditions under which elliptic flow becomes measurable in the samples of high-multiplicity ($dN_{\rm ch}/dy \geq 50$) p-p collisions, which will soon be collected at the LHC. We observe that fluctuations in the p-p interaction region can result in a sizable spatial eccentricity even for the most central p-p collisions. Under relatively mild assumptions on the nature of such fluctuations and on the eccentricity scaling of elliptic flow, we find that the resulting elliptic flow signal in high-multiplicity p-p collisions at the LHC becomes measurable with standard techniques.

Figures (3)

• Figure 1: Schematic view of region of hadron production may be located in the transverse overlap region of a central proton-proton and central nucleus-nucleus collision respectively. Depending on the number and size of hadronically active regions, large eccentricities can result even in central collisions.
• Figure 2: Eccentricity distribution of central high multiplicity p-p collisions (central) for different number of interaction regions $N_s$ (top) of different size $r_0$ (bottom).
• Figure 3: The flow signal $v_2\{4\}$ as a function of multiplicity in most central p-p collisions, for models of $N_s = 3$ interaction regions of radius $r_0=0.1$ (top 3 curves), $r_0= 0.2$ (middle curves), and $r_0 = 0.3$ fm (bottom curves). Signals calculated for $\bar{\lambda}/K_0=0,\,5.8$ and $11.6\, {\rm fm}^{-2}$ are displayed by solid, dashed and dotted lines, respectively.