Elliptic flow in proton–proton collisions at $\sqrt{s}=7$ TeV

Abstract

The angular correlations measured in proton–proton collisions at $\sqrt{s}=7$ TeV are decomposed into contributions from back to back emission and elliptic flow. Modeling the dominant term in the correlation functions as a momentum conservation effect or as an effect of the initial transverse velocity of the source, the remaining elliptic flow component can be estimated. The elliptic flow coefficient extracted from the CMS Collaboration data is 0.06–0.01. Part of the extracted elliptic flow is due to non-flow effects. The minimal elliptic flow necessary to explain the observed ridge structure in the data is 0.04–0.06, depending on the transverse momentum bin. This number could serve as an estimate of the amount of collective flow in proton–proton collisions, if it is assumed to be generated during the expansion of the dense fireball. No additional small-angle, ridge-like correlations are needed to explain the experimental data.