PHOTON 2019 - International Conference on the Structure and the Interactions of the Photon. Satellite Workshop: Photon Physics and Simulation at Hadron Colliders.

The ${\gamma^* \gamma^* \to \eta_c (1S,2S)}$ transition form factor

4 Jun 2019, 12:45

20m

Bruno Touschek Auditorium (INFN-LNF, Italy)

Talk Gamma-Gamma Collisions Gamma-Gamma Collisions

Speakers

Izabela Babiarz (Institute of Nuclear Physics, Polish Academy of Sciences)Prof. Victor P. Goncalves (Instituto de Fisica e Matematica Universidade Federal de Pelotas (UFPel))Dr Roman Pasechnik (Department of Astronomy and Theoretical Physics, Lund University)Dr Wolgang Sch\"afer (nstitute of Nuclear Physics, Polish Academy of Sciences)Prof. Antoni Szczurek (Institute of Nuclear Physics, Krakow and Rzeszow University, Rzeszow)

Description

We discuss $\gamma^* \gamma^* \to \eta_c(1S)\, , \,\eta_c(2S)$ transition form factor for both virtual photons. The general formula is given. We use different models for the $c \bar c$ wave function (LFQM or the ones obtained from the solution of the Schr\"odinger equation for different $c \bar c$ potentials: harmonic oscillator, Cornell, logarithmic, power-law and Buchm\"uller-Tye).
We compare our results to the BaBar experimental data for $\eta_c(1S)$, for one real and one virtual photon. We discuss approaching of $Q_1^2 F(Q_1^2,0)$ or $Q_2^2 F(0,Q_2^2)$ to their asymptotic value $\frac{8}{3}f_{\eta_{c}}$
predicted by Brodsky and Lepage formalizm.We discuss applicability of the collinear and/or massless limit and delayed onset of asymptotic behaviour.
We present some examples of two-dimensional distributions for $F_{\gamma^* \gamma^* \to \eta_c}(Q_1^2,Q_2^2)$.
A factorization breaking measure is proposed and factorization breaking effects are quantified and shown to be almost model independent.

Presentation materials

Babiarz_photon2019.pdf