Understanding the roles of parton mass and Casimir colour factors in the quantum-chromodynamics parton shower represents an important step in characterising the emission properties of heavy quarks. ALICE has recently obtained the first direct experimental constraint on the charm-quark splitting function via the measurement of the splitting properties of charm jets, tagged by the presence of a fully reconstructed D0 meson in proton–proton collisions at 13 TeV. In this study, the shared momentum fraction, zg, and the opening angle, Rg, of the first splitting passing the Soft Drop grooming condition were measured in the interval of low jet transverse momentum of 15 < pTjet < 30 GeV/c. The total number of splittings per jet passing the Soft Drop condition were also reported. Comparisons to measurements of an inclusive-jet sample show a steeper splitting function for charm quarks compared to gluons and light quarks. Charm quarks also undergo fewer perturbative emissions in the parton shower, with a reduced probability of large-angle emissions.
The figure above shows the zg distribution (left) and distribution of the number of splittings passing the Soft Drop condition, nSD, (right) of jets tagged with prompt D0 mesons compared to that of inclusive jets and to PYTHIA simulations.
Further reading:
ALICE Collaboration, arXiv.2208.04857