First measurement of $b$-jet mass with and without grooming

TL;DR

This paper reports the first measurement of $b$-jet mass with and without grooming at the LHCb, providing new insights into QCD and heavy-flavour production mechanisms at high energies.

Contribution

It introduces the first measurement of heavy-flavour jet mass with a clear flavour definition and uses jet grooming to enhance theoretical constraints.

Findings

Jet mass measurements for $B^$ hadrons with and without grooming.

Provides tests of quark flavour and mass dependence in QCD.

Establishes a baseline for heavy-flavour jet quenching studies.

Abstract

The LHCb collaboration presents a novel suite of heavy-flavour jet substructure measurements at forward rapidity in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 13$ TeV. The jet mass is a perturbatively calculable probe of the virtuality of hard-scattered quarks and gluons, connecting small-distance quantum chromodynamics (QCD) with long-distance experimental measurement. It becomes dominated by nonperturbative corrections at small values, presenting an excellent test of QCD across a broad range of energies. Measuring heavy-flavour jet mass with a theoretically unambiguous flavour definition for the first time probes the gluon splitting mechanism for heavy-flavour production and pushes tests of perturbative QCD to unprecedented theoretical precision. Utilising the soft drop jet-grooming technique to access the perturbative jet core further enhances constraints on first-principles theory. Measurements of the jet mass for jets containing fully reconstructed $B^\pm$ hadrons are reported with and without grooming. These results offer unparalleled tests of quark flavour and mass dependence in QCD and provide a baseline for future studies of heavy-flavour jet quenching in heavy-ion collisions.