Speaker
Description
The gluon radius of the proton is expected to increase at small gluon momentum fractions x, an effect which has hitherto not been considered in the dipole model framework. We investigate the energy dependence of exclusive J/ψ, φ, and ρ production by introducing three models for x dependence of the gluon thickness function. We allow the transverse width of the proton to increase as x decreases, using novel parametrisations in the spherical proton and the hotspot model. We compare these with a model in which the number of hotspots increases as x decreases and confront the models with HERA data. The models exhibit clear differences in the slope of the t-spectra as well as in the cross section ratios between coherent and incoherent events. The data shows a preference for models in which the proton’s size increases as x decreases. Time allowing the analysis will be extended to heavy ion geometries in UPC.
| Submitted on behalf of a Collaboration? | No |
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