Analytic and Monte Carlo Studies of Jets with Heavy Mesons and Quarkonia

TL;DR

This paper develops a theoretical framework combining analytic and Monte Carlo methods to study jets with heavy mesons and quarkonia, focusing on angularities and energy fractions, and compares predictions with simulations.

Contribution

It extends fragmenting jet functions to angularities, providing resummed calculations and applying them to B mesons and J/ production in jets, with comparisons to Monte Carlo simulations.

Findings

NLL' calculations agree with Monte Carlo for B mesons

Discrepancies found in J/ z distributions between theory and simulations

Merged PYTHIA with NRQCD FFs to improve agreement

Abstract

We study jets with identified hadrons in which a family of jet-shape variables called angularities are measured, extending the concept of fragmenting jet functions (FJFs) to these observables. FJFs determine the fraction of energy, z, carried by an identified hadron in a jet with angularity, \tau_a. The FJFs are convolutions of fragmentation functions (FFs), evolved to the jet energy scale, with perturbatively calculable matching coefficients. Renormalization group equations are used to provide resummed calculations with next-to-leading logarithm prime (NLL') accuracy. We apply this formalism to two-jet events in e^+ e^- collisions with B mesons in the jets, and three-jet events in which a J/\psi is produced in the gluon jet. In the case of B mesons, we use a phenomenological FF extracted from e^+ e^- collisions at the Z^0 pole evaluated at the scale \mu = m_b. For events with J/\psi, the FF can be evaluated in terms of Non-Relativistic QCD (NRQCD) matrix elements at the scale \mu =2 m_c. The z and \tau_a distributions from our NLL' calculations are compared with predictions from monte carlo event generators. While we find consistency between the predictions for B mesons and the J/\psi distributions in \tau_a, we find the z distributions for J/\psi differ significantly. We describe an attempt to merge PYTHIA showers with NRQCD FFs that gives good agreement with NLL' calculations of the z distributions.