Contributor info: Prof. Wolfgang Schäfer

Izabela Babiarz, Roman Pasechnik, Wolfgang Schäfer, Antoni Szczurek

SciPost Phys. Proc. 8, 118 (2022) · published 13 July 2022 | Toggle abstract · pdf

We study the exclusive production of $J^{PC}=0^{++}, 0^{--}$ charmonium states in proton-proton collisions at the LHC energies. The amplitudes for $g^*g^*→\chi_{c0}$ as well as for$ gg→\eta_c$ mechanisms are derived in the kT-factorization approach. The $pp \to pp\eta_c$ reaction is discussed for the first time. We observe a substantial contribution from the nonperturbative domain of gluon virtualities, especially for $\eta_c$ production. To model the nonperturbative region better, we utilize models of the unintegrated gluon distribution based on parametrizations of the color dipole cross-section.

Agnieszka Łuszczak, Wolfgang Schäfer

SciPost Phys. Proc. 8, 109 (2022) · published 13 July 2022 | Toggle abstract · pdf

We discuss the role of $c \bar c g$-Fock states in the diffractive photoproduction of $J/\psi$-mesons. We build on our earlier description of the process in the color-dipole approach, where we took into account the rescattering of $c \bar c$ pairs using a Glauber-Gribov form of the dipole-nucleus amplitude. We compare the results of our calculations to recent data on the photoproduction of $J/\psi$ by the ALICE and LHCb collaborations.

Wolfgang Schäfer, Izabela Babiarz, Roman Pasechnik, Antoni Szczurek

SciPost Phys. Proc. 8, 032 (2022) · published 11 July 2022 | Toggle abstract · pdf

We present a new approach for the prompt production of quarkonia which is based on the $k_T$-factorization method. The production of even C-parity quarkonia proceeds via the fusion of two (off-shell) gluons. Especially in the kinematics of the LHCb experiment these processes are thus expected to be a sensitive probe of the small-x gluon distribution. We calculate the relevant off-shell matrix elements in terms of the light-front wave functions of the quarkonium states. We present our results for scalar and pseudoscalar charmonia and discuss photon transition form factors as well as cross sections for prompt hadroproduction. We compare our results for the $\eta_c$ to recent LHCb data.