Publication Date:
2020-07-01
Description:
While the prompt $$mathrm{J}/psi $$J/ψ cross section and polarization have been measured with good precision as a function of transverse momentum, $$p_mathrm{T}$$pT, those of the directly produced $$mathrm{J}/psi $$J/ψ are practically unknown, given that the cross sections and polarizations of the $$chi _{{c}1} $$χc1 and $$chi _{{c}2} $$χc2 mesons, large indirect contributors to $$mathrm{J}/psi $$J/ψ production, are only known with rather poor accuracy. The lack of precise measurements of the $$chi _{{c}J} $$χcJ polarizations induces large uncertainties in the level of their feed-down contributions to the prompt $$mathrm{J}/psi $$J/ψ yield, because of the polarization-dependent acceptance corrections. The experimental panorama of charmonium production can be significantly improved through a consistent and model-independent global analysis of existing measurements of $$mathrm{J}/psi $$J/ψ, $$psi mathrm{(2S)}$$ψ(2S) and $$chi _{c}$$χc cross sections and polarizations, faithfully respecting all the correlations and uncertainties. In particular, it is seen that the $$chi _{{c}J} $$χcJ polarizations and feed-down fractions to $$mathrm{J}/psi $$J/ψ production have a negligible dependence on the $$mathrm{J}/psi $$J/ψ$$p_mathrm{T}$$pT, with average values $$lambda _vartheta ^{chi _{{c}1}} = 0.55 pm 0.23$$λϑχc1=0.55±0.23, $$lambda _vartheta ^{chi _{{c}2}} = -0.39 pm 0.22$$λϑχc2=-0.39±0.22, $$R^{chi _{{c}1}} = (18.8 pm 1.4)\%$$Rχc1=(18.8±1.4)% and $$R^{chi _{{c}2}} = (6.5 pm 0.5)\%$$Rχc2=(6.5±0.5)%. The analysis also shows that $$(67.2 pm 1.9)$$(67.2±1.9)% of the prompt $$mathrm{J}/psi $$J/ψ yield is due to directly-produced mesons, of polarization constrained to remarkably small values, $$lambda _vartheta ^{mathrm{J}/psi } = 0.04 pm 0.06$$λϑJ/ψ=0.04±0.06.
Print ISSN:
1434-6044
Electronic ISSN:
1434-6052
Topics:
Physics
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