Izazov eksperimenata virtualnog Comptonovog raspršenja iznad 8 GeV

We discuss the experimental issues confronting measurements of the virtualCompton-scattering (VCS) reaction ep→epγ with electron beams of energy 6 – 30 GeV. We specifically address the kinematics of deeply-virtual-Comptonscattering (deep inelastic scattering, with coincident detection of the exclusive real photon nearly parallel to the virtual photon direction) and large transverse momentum VCS (high energy VCS of arbitrary Q2, and the recoil proton emitted with high-momentum transverse to the virtual photon direction). We discuss the experimental equipment necessary for these measurements. For the deeply virtual Compton scattering, we emphasize the importance of the Bethe-Heitler – Compton interference terms that can be measured with the electron-positron (beam charge) asymmetry, and the electron beam helicity asymmetryRaspravljamo teško´ce s kojima se sučeljavaju mjerenja reakcija virtualnog Comptonovog raspršenja (VCS) ep→epγ pri energijama elektrona od 6 do 30 GeV. Posebno se razmatra kinematika duboko virtualnog Comptonovog raspršenja i VCS s velikim prijenosom impulsa. Raspravljamo mjerne uređaje koji su potrebni za takva mjerenja. Za duboko virtualno Comptonovo raspršenje, naglašavamo važnost Bethe-Heitlerovih interferentnih članova koji se mogu mjeriti asimetrijom elektronpozitron (naboj snopa) i asimetrijom heliciteta elektronskog snopa

Izazov eksperimenata virtualnog Comptonovog raspršenja iznad 8 GeV

We discuss the experimental issues confronting measurements of the virtualCompton-scattering (VCS) reaction ep→epγ with electron beams of energy 6 – 30 GeV. We specifically address the kinematics of deeply-virtual-Comptonscattering (deep inelastic scattering, with coincident detection of the exclusive real photon nearly parallel to the virtual photon direction) and large transverse momentum VCS (high energy VCS of arbitrary Q2, and the recoil proton emitted with high-momentum transverse to the virtual photon direction). We discuss the experimental equipment necessary for these measurements. For the deeply virtual Compton scattering, we emphasize the importance of the Bethe-Heitler – Compton interference terms that can be measured with the electron-positron (beam charge) asymmetry, and the electron beam helicity asymmetryRaspravljamo teško´ce s kojima se sučeljavaju mjerenja reakcija virtualnog Comptonovog raspršenja (VCS) ep→epγ pri energijama elektrona od 6 do 30 GeV. Posebno se razmatra kinematika duboko virtualnog Comptonovog raspršenja i VCS s velikim prijenosom impulsa. Raspravljamo mjerne uređaje koji su potrebni za takva mjerenja. Za duboko virtualno Comptonovo raspršenje, naglašavamo važnost Bethe-Heitlerovih interferentnih članova koji se mogu mjeriti asimetrijom elektronpozitron (naboj snopa) i asimetrijom heliciteta elektronskog snopa

Hyperon Photoproduction in the Nucleon Resonance Region

High-statistics cross sections and recoil polarizations for the reactions γ+p → K++ Λ and γ+p→K++ Σ0 have been measured at CLAS for center-of-mass energies between 1.6 and 2.3 GeV. In the K+Λ channel we confirm a resonance-like structure near W = 1.9 GeV at backward kaon angles. Our data show more complex s- and u- channel behavior than previously seen, since structure is also present at forward angles, but not at central angles. The position and width change with angle, indicating that more than one resonance is playing a role. Large positive Λ polarization at backward angles, which is also energy dependent, is consistent with sizable s- or u-channel contributions. Presently available model calculations cannot explain these aspects of the data

η Photoproduction on the Proton for Photon Energies From 0.75 to 1.95 GeV

Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75  GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ∼1.8  GeV couples to the ηN channel

Measurement of Beam-Spin Asymmetries for π⁺ Electroproduction Above the Baryon Resonance Region

We report the first evidence for a nonzero beam-spin azimuthal asymmetry in the electroproduction of positive pions in the deep-inelastic kinematic region. Data for the reaction e→pe\u27π+X have been obtained using a polarized electron beam of 4.3 GeV with the CEBAF Large Acceptance Spectrometer at the Thomas Jefferson National Accelerator Facility. The amplitude of the sin ᵠ modulation increases with the momentum of the pion relative to the virtual photon, z. In the range z = 0.5-0.8 the average amplitude is 0.038 ± 0.005 ± 0.003 for a missing mass Mx \u3e 1.1 GeV and 0.037 ± 0.007 ± 0.004 for Mx \u3e1.4 GeV

Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering

We present the first measurements of the ep → epγ cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. The Q2 dependence (from 1.5 to 2.3 GeV2) of the helicity-dependent cross section indicates the twist-2 dominance of DVCS, proving that generalized parton distributions (GPDs) are accessible to experiment at moderate Q2. The helicity-independent cross section is also measured at Q2=2.3 GeV2. We present the first model-independent measurement of linear combinations of GPDs and GPD integrals up to the twist-3 approximation