Enhanced Deuteron Coalescence Probability in Jets

The transverse-momentum (pT) spectra and coalescence parameters B-2 of (anti)deuterons are measured ffiffiin p-p collisions at vs = 13 TeV for the first time in and out of jets. In this measurement, the direction of the leading particle with the highest pT in the event (p(T)(lead) > 5 GeV/c) is used as an approximation for the jet axis. The event is consequently divided into three azimuthal regions, and the jet signal is obtained as the difference between the toward region, that contains jet fragmentation products in addition to the underlying event (UE), and the transverse region, which is dominated by the UE. The coalescence parameter in the jet is found to be approximately a factor of 10 larger than that in the underlying event. This experimental observation is consistent with the coalescence picture and can be attributed to the smaller average phase -space distance between nucleons in the jet cone as compared with the underlying event. The results presented in this Letter are compared to predictions from a simple nucleon coalescence model, where the phase-space distributions of nucleons are generated using PYTHIA8 with the Monash 2013 tuning, and to predictions from a deuteron production model based on ordinary nuclear reactions with parametrized energy-dependent cross sections tuned on data. The latter model is implemented in PYTHIA8.3. Both models reproduce the observed large difference between in-jet and out-of-jet coalescence parameters, although the almost flat trend of the B-Jet (2) is not reproduced by the models, which instead give a decreasing trend.

Automated summary

The transverse-momentum spectra and coalescence parameters of (anti)deuterons in p-p collisions at 13 TeV have been measured for the first time. The results show that the coalescence parameter in the jet is approximately 10 times larger than that in the underlying event. This observation is consistent with the coalescence picture and can be attributed to the smaller phase-space distance between nucleons in the jet cone. Both a nucleon coalescence model and a deuteron production model reproduce the observed difference between in-jet and out-of-jet coalescence parameters.