Photoproduction Of Lepton Pairs Research Articles

New ways to access the transverse spin content of the nucleon

We first describe a new way to access the chiral odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. We also show how the chiral-odd transversity generalized parton distributions (GPDs) of the nucleon can be accessed experimentally through the exclusive electro - or photoproduction process of a meson pair with a large invariant mass and when the final nucleon has a small transverse momentum. We calculate perturbatively the scattering amplitude at leading order, both in the high energy domain which may be accessed in electron-ion colliders and in the medium energy range. Estimated rates are encouraging.

Probing the Nucleon’s Transversity and the Photon’s Distribution Amplitude in Lepton Pair Photoproduction

We describe a new way to access the chiral-odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. A promising phenomenology of single and double spin observables emerges from the unusual features of this amplitude.

Photoproduction of electron–positron pairs on the proton in the resonance region

Production of lepton pairs in the gamma p-->e(-)e(+)p reaction is studied at photon energies up to 1 GeV. We show that even if lepton charge is not measured there are extensive kinematical regimes where the nuclear process dominates over the Bethe-Heitler contribution. The decomposition is performed of the unpolarized cross section for virtual Compton scattering in terms of response functions. These are expressed in terms of a polarization density matrix of the virtual photon and are shown to be sensitive to the properties of baryon resonances in the first and the second resonance regions. In the analysis a unitary K-matrix model is used, based on an effective Lagrangian including nucleon, mesons, and baryon resonances with masses up to 1.7 GeV. Results of the model are compared with data for real-photon Compton scattering and predictions are given for observables in photoproduction of lepton pairs.

Photoproduction of electron-positron pairs on the proton in the resonance region

Production of lepton pairs in the $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{p}{e}^{\ensuremath{-}}{e}^{+}p$ reaction is studied at photon energies up to 1 GeV. We show that even if lepton charge is not measured there are extensive kinematical regimes where the nuclear process dominates over the Bethe-Heitler contribution. The decomposition is performed of the unpolarized cross section for virtual Compton scattering in terms of response functions. These are expressed in terms of a polarization density matrix of the virtual photon and are shown to be sensitive to the properties of baryon resonances in the first and the second resonance regions. In the analysis a unitary K-matrix model is used, based on an effective Lagrangian including nucleon, mesons, and baryon resonances with masses up to 1.7 GeV. Results of the model are compared with data for real-photon Compton scattering and predictions are given for observables in photoproduction of lepton pairs.

Deep-inelastic photoproduction of lepton pairs and verification of colour symmetry

Considers in detail the effects of the broken colour symmetry in the deep-inelastic photoproduction of lepton pairs. The processes with both low and high invariant mass of the lepton pairs are studied. Crucial characteristics for the definition of quark charges are given. The role of Higgs bosons is also analysed.

Note on Parity-Violating Asymmetry in Inclusive Photoproduction of Lepton Pairs

The parity-violating asymmetry in the lepton pair production with circularly polarizer! photons is investigated. The neutral-current effects are of order 10- 5 in the process where only the detail of the lepton is observed, for the incident photon energy of 20GeV in the Wcinberg-Salam model. The parity-violating asymmetry of lepton pairs Produced by the right- and left-hand­ ed photons was investigated both in the inclusive and exclusive reactions in pre­ vious papersY ·2 ) In this short note, we present further results of the calculations for the parity-violating effects in the inclusive lepton pair production; r + N -e>l+ +l- +anything. This note is an ad­ dendum to our papers,ll in which we presented the numerical calculations of the asymmetry as a function of the lepton energy for the fixed energy of the anti­ lepton. In such configurations, the anti­ lepton energy as well as the lepton energy must be measured precisely in the experi­ ment. It will, however, be more feasible to observe the detail of the lepton (or antilepton) only. In this note, we further sum up all the final states of the antilep­ ton and define the asymmetry as [ dCJ

Parity-Violating Asymmetry in Exclusive Photoproduction of Lepton Pairs from Protons

Parity-Violating Asymmetry in Exclusive Photoproduction of Lepton Pairs from Protons

Weak neutral currents and photoproduction of lepton pairs

We have explored the consequences of weak neutral currents in the photoproduction of lepton pairs at high energies. Specifically, we have calculated the effects of the parity nonconserving interference between the weak amplitude and the purely electromagnetic Bethe-Heitler amplitude. This interference contributes to an asymmetry between the lepton pairs and, in addition, the leptons acquire a longitudinal polarization. Numerical results are presented for the Weinberg-Salam model and are typically a few percent in magnitude.

ρ−ωInterference and theω−φMixing Angle

The $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing angle of $\mathrm{SU}(3)$ is usually assumed to be positive, but only its magnitude is actually determined by various models of $\mathrm{SU}(3)$ breaking. The effect of this ambiguity of the relative sign of the $\mathrm{SU}(3)$ prediction of the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\rho}$ and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\omega}$ coupling constants on $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ interference is investigated. The interference can be "constructive" or "destructive." In photoproduction of lepton pairs, destructive interference causes the effect of $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ interference to be smaller than that of previous calculations. Two new models of $\ensuremath{\rho}\ensuremath{-}\ensuremath{\omega}$ interference in the colliding-beam reaction ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+{\ensuremath{\pi}}^{\ensuremath{-}}$ are discussed. A measurement of the cross section for the latter reaction would make possible a determination of the sign of the $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing angle.