Observation of enhanced long-range elliptic anisotropies inside high-multiplicity jets in pp collisions at the LHC, with the CMS detector

by Austin Alan Baty (Rice University (US))

Tuesday 18 Jul 2023, 11:00 → 12:00 Europe/Zurich

zoom only (CERN)

It has been postulated that nonperturbative quantum chromodynamics (QCD) evolution of a single parton in the vacuum can develop long-range collective effects of a multiparton system, reminiscent of those observed in high-energy nuclear interactions from the formation of a quark-gluon plasma. For the first time, a search for such QCD collective effects is performed via correlation measurements of charged constituents inside jets produced in high-pileup proton-proton (pp) collisions. The data set used corresponds to the full LHC Run-2 sample, with an integrated luminosity of 138 fb${}^{-1}$ recorded by the CMS experiment at $\sqrt{s}=13$ TeV. For charged constituents within a reconstructed jet of cone radius 0.8, two-particle correlations as functions of relative azimuthal angle ($\mathrm{\Delta }{\varphi }^{\ast }$) and pseudorapidity ($\mathrm{\Delta }{\eta }^{\ast }$) are performed in a novel "jet frame'', where constituent kinematics are defined relative to the jet direction being the $z$ axis. The correlation functions are studied in classes of in-jet charged multiplicity up to nearly 100 for different ranges of transverse momentum in the jet frame. Anisotropy Fourier harmonics are extracted from long-range azimuthal correlation functions for $\left|\mathrm{\Delta }{\eta }^{\ast }\right|>2$. A striking rising trend for the long-range elliptic anisotropy harmonic is found to emerge at in-jet charged multiplicity above about 80 in the data but not reproduced by MC models. This observed enhancement might indicate new dynamics of the parton fragmentation process in the vacuum, and potentially opening up a new experimental direction for studying QCD emergent phenomena using high-luminosity pp data sets.

PLEASE NOTE THIS SEMINAR WILL BE VIA ZOOM ONLY

Baty_LHCSeminar_v4.pdf

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