ϒ(3S) and χb(3P) production and polarization in the NRQCD with kT–factorization

Nizami Abdulov,Artem Lipatov

doi:10.1051/epjconf/201922203013

Abstract

The ϒ(3S) production and polarization at high energies is studied in the framework of kT–factorization approach. Our consideration is based on the non-relativistic QCD formalism for bound states formation and off-shell production amplitudes for hard partonic subprocesses. The transverse momentum dependent (TMD, or unintegrated) gluon densities in a proton were derived from the CiafaloniCatani-Fiorani-Marchesini (CCFM) evolution equation as well as from the Kimber–Martin–Ryskin (KMR) prescription. Treating the nonperturbative color octet transitions in terms of the mulitpole radiation theory and taking into account feed-down contributions from radiative χb(3P) decays, we extract the corresponding non-perturbative matrix elements for ϒ(3S) and χb(3P) mesons from a combined fit to ϒ(3S) transverse momenta distributions measured by the CMS and ATLAS Collaborations at the LHC energies √s = 7 and 13 TeV and central rapidities. Then we apply the extracted values to investigate the polarization parameters λθ, λφ and λθφ, which determine the ϒ(3S) spindensity matrix. Our predictions have a good agreement with the currently available data within the theoretical and experimental uncertainties.

Highlights

In recent years, the production processes of quarkonia J/ψ and Υ(nS) have been actively studied after the discovery of a strong discrepancy between theoretical predictions within the framework of the color singlet model (CS) and the data obtained at the Tevatron
We have included in the fitting procedure the Υ(3S) transverse momentum√ distributions measured by the CMS [12, 13] and ATLAS [14] Collaborations at s = 7 and 13 TeV
We have excluded from our fit low pT region and consider only the data at pT > pcTut = 10 GeV, where the non-relativistic QCD (NRQCD) formalism is believed to be most reliable

Summary

Introduction

The production processes of quarkonia J/ψ and Υ(nS) have been actively studied after the discovery of a strong discrepancy between theoretical predictions within the framework of the color singlet model (CS) and the data obtained at the Tevatron. This formalism implies a separation of perturbatively calculated short-distance cross-sections for the production of QQpair in an intermediate Fock state 2S+1L(Ja) and long-distance non-perturbative matrix elements (NMEs), which describe the transition of that intermediate QQstate into a physical quarkonium via soft gluon radiation. They are assumed to be universal (process- and energy-independent), not dependent on the quarkonium momentum and obeying certain hierarchy in powers of the relative heavy quark velocity υQ ∼ log−1 mQ/ΛQCD [3]. None of the fits can simultaneously describe data on the polarization and the quarkonia production

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Results

Conclusion