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

Abstract

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 (πN ) TDAs frompp → e + e − π 0 reaction with the futurePANDA detector at the FAIR facility. At high centerof-mass energy and high invariant mass squared of the lepton pair q 2 , the amplitude of the signal channel pp → 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 measuringpp → e + e − π 0 with thePANDA detector. Detailed simulations on signal reconstruction efficiency as well as on rejection of the most severe background channel, i.e.pp → 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 < 9 GeV 2 , respectively, with a neutral pion scattered in the forward or backward cone | cos θ π 0 | > 0.5 in the proton-antiproton center-of-mass frame. Results of the simulation show that the particle identification capabilities of thePANDA 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%. At both energies, a clean lepton signal can be reconstructed with the expected statistics corresponding to 2 fb −1 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 withPANDA 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 πN TDAs.

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“…In particular, the predictions of the revised soft-pion-limit model (4) were recently employed in the first feasibility studies [11] for accessing πN TDAs withPANDA throughpp → γ * π 0 . Another simple model for πN TDAs suggested in Ref.…”

“…The characteristic features of the TDA-based description of (8) are the scaling behavior in 1/q 2 of the cross-section and the specific behavior in cos θ * (by θ * we denote the lepton polar angle defined in the CMS of the lepton pair) resulting from the leading twist dominance of the transverse polarization of the virtual time-like photon. A detailed feasibility study for accessing πN TDAs through p p → γ * π 0 → e + e − π 0 atPANDA was performed in [11]. As a phenomenological input, the predictions of the simple πN TDA model (4) were employed.…”

Baryon-to-Meson Transition Distribution Amplitudes: Formalism and Models

“…In particular, the predictions of the revised soft-pion-limit model (4) were recently employed in the first feasibility studies [11] for accessing π N TDAs withPANDA through…”

“…The characteristic features of the TDA-based description of (8) are the scaling behavior in 1/q 2 of the cross-section and the specific behavior in cos θ * (by θ * we denote the lepton polar angle defined in the CMS of the lepton pair) resulting from the leading twist dominance of the transverse polarization of the virtual time-like photon. A detailed feasibility study for accessing π N TDAs throughp p → γ * π 0 → e + e − π 0 atPANDA was performed in [11]. As a phenomenological input, the predictions of the simple π N TDA model (4) were employed.…”

“…Based on the cross-section estimates presented in Ref. [27] a detailed feasibility study for accessing pp → J/ψπ 0 atPANDA has been performed [11,28,29].…”