Systematic study for particle transverse momentum asymmetry in minimum bias pp collisions at LHC energies

TL;DR

This study modifies PYTHIA6.4 to better simulate particle transverse momentum asymmetry in proton-proton collisions at LHC energies, successfully reproducing experimental data and predicting measurable elliptic flow signals.

Contribution

The paper introduces a novel modification to PYTHIA6.4 that accounts for elliptical transverse momentum distributions, enabling more accurate modeling of azimuthal anisotropies in pp collisions.

Findings

Modified PYTHIA6.4 reproduces ALICE data on transverse sphericity.

Predicted charged particle v2 upper limit is ~0.12 at 7 TeV.

Systematic measurements of sphericity, eccentricity, and elliptic flow are suggested.

Abstract

In PYTHIA6 (PYTHIA8) once the transverse momentum $p_T$ of a generated particle is randomly sampled, $p_x$ and $p_y$ are set on the circle with radius of $p_T$ randomly. This may largely suppress the development of the final hadronic state transverse momentum anisotropy from the initial state spatial asymmetry. We modify PYTHIA6.4 by randomly setting $p_x$ and $p_y$ on the circumference of an ellipse with the half major and minor axes being $p_T(1+\delta_p)$ and $p_T(1-\delta_p)$, respectively. The modified PYTHIA6.4 is then employed to systematically study the charged particle transverse momentum asymmetry in the minimum bias pp collisions at $\sqrt s$=0.9, 7, and 14 TeV. The ALICE data on the transverse sphericity as a function of charged multiplicity, $<S_T>(N_{ch})$, are well reproduced with the modified PYTHIA6.4. It is found that the predicted charged particle $v_2$ upper limit is a measurable value, $\sim 0.12$, in the minimum bias pp collisions at $\sqrt s$=7 TeV. We suggest a systematic measurement for the particle transverse momentum sphericity, eccentricity (ellipticity), and elliptic flow parameter.