Proton-anti-Proton Photoproduction at CLAS

The photoproduction of a state “X” which decays into a proton-anti-proton pair has been studied previously, partially because its production mechanism is to this day largely unknown. This X state is studied generally by looking for narrow resonances in the invariant mass distribution of the proton-anti-proton pair, but results have shown little evidence for it, in part because of the limited statistics that previous analysis had.

This work, which takes a dataset from the CLAS detector at Jefferson Lab, investigates the reaction of a photon being incident to a proton target at rest and producing two protons and an antiproton. This dataset provides with around 200,000 events for γ p → p p antip collected by CLAS in a beam energy 3.95-5.45 GeV. It is remarkable that in the final state of the reaction under the scope there are two indistinguishable protons; to obtain any information on the X intermediate state it is necessary to identify which of the protons is a decay product of X. To overcome this issue, this work uses a novel combinatorial approach that aims to address this ambiguity, therefore extracting the information for the resonant p antip pair. This method has been checked to work correctly under certain assumptions by Monte Carlo simulations performed by this analysis.

We will present simulation results as well as preliminary distributions of various kinematic variables for the possible intermediate mesons (such as transferred momentum, polar angular distribution, and invariant masses) after acceptance correction and background subtraction.