Experimental access to Transition Distribution Amplitudes with the P̄ANDA experiment at FAIR

Baryon-to-meson Transition Distribution Amplitudes (TDAs) encoding valuable new information on hadron structure appear as building blocks in the collinear factorized description for several types of hard exclusive reactions. In this paper, we address the possibility of accessing nucleon-to-pion ( πN ) TDAs from p̅p → e^ + e^ - π ^0 reaction with the future P̄ANDA detector at the FAIR facility. At high center-of-mass energy and high invariant mass squared of the lepton pair q 2 , the amplitude of the signal channel p̅p → e^ + e^ - π ^0 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 p̅p → e^ + e^ - π ^0 with the P̄ANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. p̅p →π ^ + π ^ - π ^0 were performed for the center-of-mass energy squared s = 5 GeV 2 and s = 10 GeV 2 , in the kinematic regions 3.0 < q 2 < 4.3 GeV 2 and 5 < q 2 GeV 2 , respectively, with a neutral pion scattered in the forward or backward cone | cosθ _π ^0 | > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the P̄ANDA detector will allow to achieve a background rejection factor of 5 · 10 7 (1 · 10 7 ) at low (high) q 2 for s = 5 GeV 2 , and of 1 · 10 8 (6 · 10 6 ) at low (high) q 2 for s = 10 GeV 2 , while keeping the signal reconstruction efficiency at around 40