|
Résumé |
I will begin by reviewing the current status of quarkonium production theory
based on the non-relativistic QCD factorization formalism (NRCD). While this
theory provides a decent description of much of the world’s data on J/$\Psi$ and
Upsilon production, there are still outstanding problems, most notably the
polarization of quarkonia at large p_T in hadron colliders. I will introduce
nonperturbative functions which describe the distribution of hadrons
produced within jets, called fragmenting jet functions (FJFs). FJFs are
convolutions of fragmentation functions, evolved to the jet energy scale,
with perturbatively calculable matching coefficients. We show that the FJFs
for quarkonia can be calculated in NRQCD in terms of a few theory
parameters, so the dependence of the cross section on the energy fraction of
the heavy particle, z, is sensitive to the underlying production mechanism,
and hence can provide a new test of NRQCD. We apply this formalism to
two-jet events in e+e-; collisions with B mesons, and three-jet events with
J/$\Psi$. For B mesons, we use a phenomenological fragmentation function
extracted from e+e-; collisions at the scale 2mb, and find the dependence on
z and the angularity of the jet is consistent with predictions from Monte
Carlo event generators. In the case of quarkonia, the fragmentation
functions are calculable in Non-Relativistic QCD (NRQCD) and the z
dependence of the cross section can be used to perform an independent
extractions of NRQCD long-distance matrix elements. For J/$\Psi$ we find
reasonable agreement with Monte Carlo for the angularity distributions but
the z distributions differ significantly. Finally, we also define a boost
invariant generalization of the angularities and derive a boost invariant
soft function that is necessary for analytic calculations for jet cross
sections at the LHC with next-to-next-to leading log resummation. |
