Abstract
We analyze joint LHC data on the production of chi _{c1} and chi _{c2} mesons together with the polarization data obtained very recently by the CMS Collaboration at sqrt{s} = 8 TeV. Our consideration is based on the k_T-factorization approach and nonrelativistic QCD formalism for the formation of bound states. The observed polar anisotropy of chi _{c1} and chi _{c2} decays can be described as a combined effect of the color-singlet and color-octet contributions. We extract the corresponding long-distance matrix elements from the fits. Our fits point to unequal color singlet wave functions for chi _{c1} and chi _{c2} states.
Highlights
The NRQCD calculations at next-to-leading order (NLO) successfully describe the charmonia J/ψ, ψ , χcJ [7,8,9,10,11,12,13,14] and bottomonia Υ(nS), χbJ (m P) [15,16,17,18,19] transverse momenta distributions and agree well with the first CMS data [1] on the χcJ polarization at the LHC
Very recently, the CMS Collaboration reported on the first measurement [1] of the polarization of prompt√χc1 and χc2 mesons produced in pp collisions at the energy s = 8 TeV
This result contrasts with the unpolarized scenario observed for direct S-wave charmonia (J/ψ, ψ ) and bottomonia Υ(nS) at the LHC over a wide transverse momentum range
Summary
The NRQCD calculations at next-to-leading order (NLO) successfully describe the charmonia J/ψ, ψ , χcJ [7,8,9,10,11,12,13,14] and bottomonia Υ(nS), χbJ (m P) [15,16,17,18,19] transverse momenta distributions and agree well with the first CMS data [1] on the χcJ polarization at the LHC. Thanks to the initial gluon transverse momentum kT , the final state pT spectrum becomes harder, and so, less color-octet contribution is needed to fit the data.
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