Dijet invariant mass of charged-particle jets in pp and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

TL;DR

This paper reports the first measurement of charged-particle dijet invariant mass spectra in pp and p-Pb collisions at 5.02 TeV, finding no significant nuclear modification but indicating potential sensitivity to nuclear parton distribution effects.

Contribution

It provides the first experimental dijet invariant mass spectra in p-Pb collisions at this energy, offering insights into nuclear effects on parton densities.

Findings

Nuclear modification factor $R_{pA}$ is consistent with unity.

Low-mass region sensitive to anti-shadowing effects.

Comparison with simulations suggests subtle nuclear effects.

Abstract

The ALICE collaboration presents the first measurement of the dijet invariant mass spectra of charged-particle jets in pp and p-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV. Charged particles in the mid-pseudorapidity region, $|\eta| < 0.9$, are clustered into jets using the anti-$k_{\rm T}$ algorithm with a resolution parameter $R = 0.4$. The leading and subleading jets are required to have a transverse momentum $p_{\rm T} > 20$ GeV$/c$ and to be contained within $\left|\eta_{\rm jet}\right| < 0.5$. The dijet invariant mass spectrum and the nuclear modification factor $R_{\rm pA}$ are presented in the low-mass region of 75 to 150 GeV/$c^2$. The nuclear modification factor for charged-particle dijet invariant mass is consistent with unity. This is in line with previous small-system jet studies. Comparisons with Monte Carlo simulations suggest that the low-mass region is sensitive to anti-shadowing effects on parton densities in the nucleus, however, the expected signal is subtle and below the present experimental sensitivity.