Measurement of the angle between jet axes in pp collisions at $$ \sqrt{s} $$ = 5.02 TeV

Abstract

This article reports measurements of the angle between differently defined jet axes in pp collisions at $$ \sqrt{s} $$ s = 5.02 TeV carried out by the ALICE Collaboration. Charged particles at midrapidity are clustered into jets with resolution parameters R = 0.2 and 0.4. The jet axis, before and after Soft Drop grooming, is compared to the jet axis from the Winner-Takes-All (WTA) recombination scheme. The angle between these axes, ∆Raxis, probes a wide phase space of the jet formation and evolution, ranging from the initial high-momentum-transfer scattering to the hadronization process. The ∆Raxis observable is presented for 20 <$$ {p}_{\textrm{T}}^{\textrm{ch}\ \textrm{jet}} $$ p T ch jet < 100 GeV/c, and compared to predictions from the PYTHIA 8 and Herwig 7 event generators. The distributions can also be calculated analytically with a leading hadronization correction related to the non-perturbative component of the Collins-Soper-Sterman (CSS) evolution kernel. Comparisons to analytical predictions at next-to-leading-logarithmic accuracy with leading hadronization correction implemented from experimental extractions of the CSS kernel in Drell-Yan measurements are presented. The analytical predictions describe the measured data within 20% in the perturbative regime, with surprising agreement in the non-perturbative regime as well. These results are compatible with the universality of the CSS kernel in the context of jet substructure.

Measurements of HF-tagged jet substructure and energy-energy correlators with ALICE

“…Comparing Δ𝑅 WTA−D 0 distribution with Δ𝑅 WTA−STD of inclusive jets, reported in Ref. [8], D 0 mesons are more collinear with the jet axis than the hardest prong of inclusive jets, pointing towards a narrowing of the heavy-flavour jets with respect to inclusive jets. These studies serve as baseline for future measurements of heavy-flavour jet Δ𝑅 axis in Pb-Pb collisions, where crucial insights on the in-medium energy loss mechanism can be obtained.…”

“…has been studied [8]. The different definition used for the jet-axis determination allows us to differentially probe the sensitivity to the soft radiation in the parton shower.…”