Single-spin asymmetries in $$p^\uparrow p \rightarrow J/\psi +X$$ within a TMD approach: role of the color octet mechanism

We calculate the transverse single-spin asymmetry (SSA) for $$J/\psi $$J/ψ production in proton-proton collisions, within non-relativistic QCD, employing the transverse momentum dependent, generalized parton model, which includes both spin and intrinsic motion effects. In particular, we study the role of the color octet mechanism in accessing the gluon Sivers function. In doing that, we also show, within this approach, how the singularities coming from color octet terms in the low-$$P_T$$PT region can be handled, leading to finite cross sections. Predictions for both unpolarized cross sections and SSAs are given and compared against PHENIX data. Estimates for LHCb in the fixed target mode are also presented.

HADRONIC DECAYS OF CHARMONIA FROM BESII

Recent results on charmonia decays at BESII/BEPC are reported, including the observation of [Formula: see text], ψ′→Vector Tensor and ψ′→Vector Pseudoscalar for the measurement of the relative phase between the strong and electromagnetic decays of ψ′ and a test of the pQCD "12% rule" between ψ′ and J/ψ decays; the test of the color-octet mechanism via [Formula: see text] and [Formula: see text]; the first observation of χc0→f0(980)f0(980); and a study of the ψ′ and χcJ decays with [Formula: see text] in the final states.

POWER SCALING RULES FOR CHARMONIA PRODUCTION AND HQEFT

We discuss the power scaling rules along the lines of a complete heavy quark effective field theory (HQEFT) for the description of heavy quarkonium production through a color-octet mechanism. To this end, we firstly derive a tree-level heavy quark effective Lagrangian keeping both particle–antiparticle mixed sectors allowing for heavy quark–antiquark pair annihilation and creation, but describing only low-energy modes around the heavy quark mass. Then we show the consistency of using HQEFT fields in constructing four-fermion local operators à la NRQCD, to be identified with standard color-octet matrix elements. We analyze some numerical values extracted from charmonia production by different authors and their hierarchy in the light of HQEFT.