T-2, Nuclear and Particle Physics, Astrophysics and Cosmology

Quarkonium production in jet physics

Yiannis Makris
Duke U.

In non-relativistic quantum chromodynamics (NRQCD) the fragmentation function of quarkonium states factorizes in short distance coefficients and long distance matrix elements (LDME). While the short distance coefficients are calculable in perturbation theory, LDMEs must be fitted to data. The extracted values of the J/ψ LDMEs from global fits to the world’s data predict polarization for J/ψ in disagreement with observations—the well know polarization puzzle. My research focuses on alternative approaches of extracting charmonium production LDMEs within the framework of soft and collinear effective theory (SCET) by studying jet observables in semi-inclusive processes. Factorization theorems in SCET are presented for dijet events in hadron colliders for various regions of phase-space. Transverse vetoes with rapidity constraints are considered for the out-of-jet soft radiation. These factorization approaches, alongside with the use of Fragmenting Jet Functions (FJFs), consist of a complete framework for the study of charmonium production in jets. Using this framework, the cross section is calculated for the production of J/ψ at NLL’ accuracy and showed that monte carlo simulations fail to reproduce the predicted energy ratio distribution of J/ψ. I will discuss this discrepancy and how simulation packages can be modified to include a realistic showering process for the quarkonium states.


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