Unique Access to u-Channel Physics: Exclusive Backward-Angle Omega Meson Electroproduction

Abstract

Backward-angle meson electroproduction above the resonance region, which was previously ignored, is anticipated to offer unique access to the three quark plus sea component of the nucleon wave function. In this letter, we present the first complete separation of the four electromagnetic structure functions above the resonance region in exclusive ω electroproduction off the proton, ep → e ′ pω, at central Q 2 values of 1.60, 2.45 GeV 2 , at W = 2.21 GeV. The results of our pioneering −u ≈ −umin study demonstrate the existence of a unanticipated backward-angle cross section peak and the feasibility of full L/T/LT/TT separations in this never explored kinematic territory. At Q 2 =2.45 GeV 2 , the observed dominance of σT over σL, is qualitatively consistent with the collinear QCD description in the near-backward regime, in which the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes (TDAs): universal non-perturbative objects only accessible through backward angle kinematics.Deep exclusive reactions have recently gained much attention, as they provide direct access to the internal

Backward timelike Compton scattering to decipher the photon content of the nucleon

“…In conclusion, the study of the inner content of the nucleon already benefits much from the high luminosity experiments at medium energy electron facilities through the promising first results on the extraction of GPDs and transverse momentum dependent (TMDs) distributions. More is still to come and the TDA portal -both for nucleon-to-meson and nucleon-to-photon cases [25,26,[41][42][43] -opens completely new opportunities to access new hadronic matrix elements of quite fundamental quark trilocal operators on the light cone. occurring in the definition of nucleon-to-photon TDAs are listed below in Eqs.…”

“…[9]. This model has recently seen a success in the description of the nearbackward ω-meson electroproduction [25,26]. The VMDassumption (37) combined with the cross channel nucleon exchange model for V N TDAs results in great simplifications for the calculation of convolution of resulting γ N TDAs and nucleon DAs with hard scattering kernels.…”

“…(39) bring additional dependence on Q 2 and W 2 through the skewness variable ξ (5). Our model must be read as a very rough but plausible order of magnitude estimate 5 since the cross channel nucleon exchange model for ωN TDAs saw some success in the description of hard exclusive backward ω-production data [25]. We employ 6 the set of G V,T ωN N couplings Bonn 2000 [31].…”