Transverse Momentum Resummation for Z boson Plus Jet Production at the LHC

We study the transverse momentum resummation effects for the Z boson plus jet associated production at the LHC within the transverse momentum dependent (TMD) factorization formalism. The large logarithm ln (Q2/q⊥2) with Q ≫ q⊥ has been resumed to Next-to-Leading Logarithm (NLL) accuracy. We compare our numerical results to the CMS data by reweighting method. It shows that our prediction agree with the data very well.

Azimuthal Asymmetries of the Drell-Yan Process in pA Collisions

We discuss the azimuthal asymmetries of the Drell-Yan process in nucleon-nucleus collisions at the low transverse momentum of the lepton pair. Within the transverse-momentum-dependent (TMD) factorization formalism, the nuclear effects of these azimuthal asymmetries can be from the gauge link of the TMD quark distribution. We estimate all these nuclear effects within the assumption that all the TMD parton distributions or correlations are in Gaussian forms.

DOUBLE PARTON FRAGMENTATION FUNCTION AND ITS EVOLUTION IN QUARKONIUM PRODUCTION

We summarize the results of a recent study on a new perturbative QCD factorization formalism for the production of heavy quarkonia of large transverse momentum pT at collider energies. Such a new factorization formalism includes both the leading power (LP) and next-to-leading power (NLP) contributions to the cross section in the [Formula: see text] expansion for heavy quark mass mQ. For the NLP contribution, the so-called double parton fragmentation functions are involved, whose evolution equations have been derived. We estimate fragmentation functions in the non-relativistic QCD formalism, and found that their contribution reproduce the bulk of the large enhancement found in explicit NLO calculations in the color singlet model. Heavy quarkonia produced from NLP channels prefer longitudinal polarization, in contrast to the single parton fragmentation function. This might shed some light on the heavy quarkonium polarization puzzle.

NRQCD: Fundamentals and Applications to Quarkonium Decay and Production

I discuss NRQCD and, in particular, the NRQCD factorization formalism for quarkonium production and decay. I also summarize the current status of the comparison between the predictions of NRQCD factorization and experimental measurements.

QCD and Rescattering in Nuclear Targets

We review the extension of the factorization formalism of perturbative QCD to soft rescattering associated with hard processes in nuclei.

Production of the Bc Meson

The production of the Bc and [Formula: see text] mesons was studied in the framework of the factorization formalism and perturbative QCD. Predicted results implied that an observable number of Bc and [Formula: see text] events can be produced at LEP I and at Tevatron. The fragmentation approximation describes the production of the Bc and [Formula: see text] mesons very well in high energy e+ e- collisions. In hadronic collisions, it is valid when and only when the transverse momentum PT of the produced Bc and [Formula: see text] is much larger than the mass of the Bc meson.

Determining Color-Octet ψ-Production Matrix Elements from γp and ep Processes

We calculate, within the NRQCD factorization formalism, the leading color-octet contributions to ψ production in photon-nucleon and electron-nucleon collisions. The expressions we obtaine depend on the NRQCD matrix elements [Formula: see text] and [Formula: see text]. These matrix elements can be determined by fitting to experimental data. The color-octet contribution to ψ photoproduction is in the forward region of phase space, where there may be large corrections to the NRQCD result from higher twist terms. As to ψ leptoproduction we point out that the theoretical uncertainties plaguing the photoproduction calculation vanish in the large momentum transfer limit. In this region of phase space the NRQCD formalism should be valid, making ψ leptoproduction an ideal laboratory for testing the theory.