NLO production and decay of quarkonium

Abstract

We present a calculation of next-to-leading-order (NLO) QCD corrections to total hadronic production cross sections and to light-hadron-decay rates of heavy quarkonium states. Both colour-singlet and colour-octet contributions are included. We discuss in detail the use of covariant projectors in dimensional regularization, the structure of soft-gluon emission and the overall finiteness of radiative corrections. We compare our approach with the NLO version of the threshold-expansion technique recently introduced by Braaten and Chen. Most of the results presented here are new. Others represent the first independent reevaluation of calculations already known in the literature. In this case a comparison with previous findings is reported.

Next-to-next-to-leading-order QCD corrections to χc0,2→γγ

“…Among them, the electromagnetic decay χ c0,2 → γγ provide a particularly interesting, and, rich testing ground of QCD [3,4]. In the past decades, these decay channels have been extensively studied from various theoretical angles, such as nonrelativistic potential model [5,6], relativistic quark model [7][8][9], Bethe-Salpeter approach [10], nonrelativistic QCD (NRQCD) factorization [11,12], as well as lattice QCD [13]. On the experimental side, they were previously measured by .…”

Soft-gluon resummation in heavy quarkonium physics

“…[4] the results are instead written in terms of ρ-distributions defined by [4]. Finally, µ and µ F are respectively the renormalization and factorization scales.…”

“…Such soft limits, derived in [4], read, for the gluon-gluon channel and for colour-singlet and -octet production respectively, col,pol…”

“…When the emitted gluon becomes soft, the ensuing singularity can only be cancelled by adding the corresponding qq → S-state process, in full accordance with the general NRQCD factorization formula (1.1) (see also section 6 of ref. [4] for more details). In this case we find indeed that the soft limit of the qq → P -state +g process amplitude does not factorize onto qq → P -state and no gluons, this cross section being actually zero, but rather onto the matrix element squared for qq → Sstate.…”

Reduced branching ratio for H → AA → 4 τ from A − η b mixing

“…The states η b (nS) (before mixing) would decay nearly exclusively into hadrons (like the states η c (nS)). Using the formalism in [42], the widths of the states η b (nS) can be estimated…”