Observation of Enhanced Long-Range Elliptic Anisotropies Inside High-Multiplicity Jets in pp Collisions at √s=13 TeV

Abstract

A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 138 fb(-1). Jets are reconstructed with the anti-kT algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550 GeV and pseudorapidity vertical bar eta(jet)vertical bar 2. For low-N-ch(j) jets, the long-range elliptic anisotropic harmonic, v(2)*, is observed to decrease with N-ch(j). This trend is well described by Monte Carlo event generators. However, a rising trend for v(2)* emerges at N-ch(j) greater than or similar to 80, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum.