Eperimental access to Transition Distribution Amplitudes with the PANDA experiment at FAIR

We address the possibility of accessing nucleon-to-pion (πN) Transition Distribution Amplitudes (TDAs) from p¯p→e+e−π0 reaction with the future \={P}ANDA detector at the FAIR facility. At high center of mass energy and high invariant mass of the lepton pair q2, the amplitude of the signal channel p¯p→e+e−π0 admits a QCD factorized description in terms of πN TDAs and nucleon Distribution Amplitudes (DAs) in the forward and backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring p¯p→e+e−π0 with the \={P}ANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, {\it i.e.} p¯p→π+π−π0 were performed for the center of mass energy squared s=5 GeV2 and s=10 GeV2, in the kinematic regions 3.0<q2<4.3 GeV2 and 5<q2<9 GeV2, respectively, with a neutral pion scattered in the forward or backward cone |cosθπ0|>0.5 in the proton-antiproton center of mass frame. Results of the simulation show that the particle identification capabilities of the \={P}ANDA detector will allow to achieve a background rejection factor at the level of 108 (2⋅107) at low (high) q2 while keeping the signal reconstruction efficiency at around 40% and that a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 fb−1 of integrated luminosity. The future measurement of the signal channel cross section with \={P}ANDA will provide a new test of perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing πN TDAs.