Abstract
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 (pi N) TDAs from (p) over barp -> e(+)e(-)pi(0) reaction with the future PANDA 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 (p) over barp -> e(+)e(-)pi(0) admits a QCD factorized description in terms of pi N TDAs and nucleon Distribution Amplitudes (DAs) in the forward aid backward kinematic regimes. Assuming the validity of this factorized description, we perform feasibility studies for measuring (p) over barp -> e(+)e(-)pi(0) with the PANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e. (p) over barp -> pi(+)pi(-)pi(0) were performed for the center-of-mass energy squared s = 5 GeV2 and s = 10 GeV2, in the kinematic regions 3.0 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of the PANDA detector will allow to achieve a background rejection factor of 5 . 10(7) (1 . 10(7)) at low (high) q(2) for s = 5 GeV2, and of 1 . 10(8) (6 . 10(6)) at low (high) q(2) for s = 10 GeV2, while keeping the signal reconstruction efficiency at around 40%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 of integrated luminosity. The cross sections obtained from the simulations are used to show that a test of QCD collinear factorization can be done at the lowest order by measuring scaling laws and angular distributions. The future measurement of the signal channel cross section with PANDA will provide a new test of the perturbative QCD description of a novel class of hard exclusive reactions and will open the possibility of experimentally accessing pi N TDAs.
Highlights
Studies of hard exclusive reactions, such as Deeply Virtual Compton Scattering (DVCS) and Hard Exclusive Meson Electroproduction, within the collinear factorization approach, allow to challenge a QCD-based description of hadron structure
In the framework of the PANDA@FAIR experiment, cross section measurements of nucleon-antinucleon annihilation into a highly virtual lepton pair in association with a pion emitted in the forward or the backward region will represent a novel test of the QCD collinear factorization approach of hard exclusive reactions providing experimental access to the πN Transition Distribution Amplitudes (TDAs)
In this paper we address the feasibility of measuring pp → e+e−π0 with the PANDA detector for the center-ofmass energy squared s = 5 GeV2 and s = 10 GeV2 for the kinematic regimes in which the factorized description of the process in terms of πN TDAs and proton distribution amplitudes (DAs) can be assumed
Summary
Studies of hard exclusive reactions, such as Deeply Virtual Compton Scattering (DVCS) and Hard Exclusive Meson Electroproduction, within the collinear factorization approach, allow to challenge a QCD-based description of hadron structure (for a review see e.g. [1]). Bringing evidence for the validity of QCD factorization for ppannihilation into e+e−π0 in terms of πN TDAs will suffer from the same difficulties as the above-mentioned analysis of hard electroproduction of pions at JLab. Assuming the validity of the leading order factorized description for the signal reaction and adopting a particular normalization for πN TDAs, we show the feasibility of measuring of pp → e+e−π0 with the PANDA detector in the kinematic region where factorization is expected to hold. The kinematic region of the measurement ensures that, at each (q2, cos θπ0 ) point of the phase space, the appropiate momentum transfer squared (t or u for the forward and backward pion production, respectively) remains below 10% of the q2 value This is the definition adopted in this analysis of |t| q2 and |u| q2, needed to preserve the applicability of the QCD collinear factorization description. On the basis of a full Monte Carlo simulation, the reconstruction efficiency measured in a given bin of a
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