J/ψPolarization at the Tevatron and the LHC: Nonrelativistic-QCD Factorization at the Crossroads

Abstract

We study the polarization observables of J/ψ hadroproduction at next-to-leading order within the factorization formalism of nonrelativistic quantum chromodynamics. We complete the present knowledge of the relativistic corrections by also providing the contribution due to the intermediate 3 P [8] J color-octet states at this order, which turns out to be quite significant. Exploiting the color-octet long-distance matrix elements previously extracted through a global fit to experimental data of unpolarized J/ψ production, we provide theoretical predictions in the helicity and Collins-Soper frames and compare them with data taken by CDF at Fermilab Tevatron I and II and by ALICE at CERN LHC. The notorious CDF J/ψ polarization anomaly familiar from leading-order analyses persists at the quantum level, while the situation looks promising for the LHC, which is bound to bring final clarification.

Measurement of Quarkonium Polarization to Probe QCD at the LHC

“…The ones relevant for this work can be found in Refs. [23,24,25,26,27,28,29]. CS channel (left), the dominating gluon fragmentation diagram for the 3 S [8] 1 CO channel (middle), and a LO diagram for the 1 S [8] 0 and 3 P [8] J CO channels (right).…”

“…Moreover, the experimental results of the analyses described in this thesis, together with other results in the quarkonium production sector from the LHC experiments, can be interpreted in a much more rigorous way than previously possible, due to the higher p T reach and the usage of more reliable experimental techniques for the estimation of the polarizations of the quarkonium states. Several state-of-the-art NLO NRQCD analyses can be found in the literature, affected by various problems leading to contradictory results for the estimated LDMEs [29,30,31,32,33,34,35]. The second core topic of this thesis is an attempt to clarify this situation by introducing an original phenomenological interpretation of the LHC results [36], characterized by a meticulously developed global fit framework, providing the possibility for a detailed study of the quarkonium production cross section and polarization observables, simultaneously and consistently treating these highly correlated measurements.…”

“…Besides this experimental progress in the understanding of quarkonium polarization, NRQCD calculations were extended from leading order (LO) in α s to next-to-leading order (NLO) [23,24,25,26,27,28,29], providing a more rigorous framework for the tests of NRQCD calculations. Moreover, the experimental results of the analyses described in this thesis, together with other results in the quarkonium production sector from the LHC experiments, can be interpreted in a much more rigorous way than previously possible, due to the higher p T reach and the usage of more reliable experimental techniques for the estimation of the polarizations of the quarkonium states.…”

“…[GeV] [29] for J/ψ production in pp collisions at √ s = 7 TeV at mid-rapidity, as a function of p T , showing the SDCs at NLO (top left), the ratio of the SDCs at NLO with respect to the LO calculations (top right) and the polarization parameter λ HX ϑ at NLO (bottom).…”

“…2.3. These calculations are made for |y| < 0.9, but the calculations [29] have shown that the SDCs and polarizations of the individual color channels change only marginally with rapidity.…”