Abstract: | We address the possibility of accessing nucleon-to-pion ($pi N$) Transition
Distribution Amplitudes (TDAs) from $ar{p}p o e^+e^- pi^0$ 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 $q^2$, the amplitude of the
signal channel $ar{p}p o e^+e^- pi^0$ admits a QCD factorized description
in terms of $pi N$ 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 $ar{p}p
o e^+e^- pi^0$ 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.} $ar{p}p o pi^+pi^- pi^0$ 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 $5 < q^2 < 9$ GeV$^2$,
respectively, with a neutral pion scattered in the forward or backward cone $|
cos heta_{pi^0}| > 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 $10^8$ ($2cdot 10^7$) at low (high) $q^2$ 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 $pi N$ TDAs. |