Photon distribution amplitudes and light-cone wave functions in chiral quark models

The leading- and higher-twist distribution amplitudes and light-cone wave functions of real and virtual photons are analyzed in chiral quark models. The calculations are performed in the nonlocal quark model based on the instanton picture of QCD vacuum, as well as in the spectral quark model and the Nambu--Jona-Lasinio model with the Pauli-Villars regulator, which both treat interaction of quarks with external fields locally. We find that in all considered models the leading-twist distribution amplitudes of the real photon defined at the quark-model momentum scale are constant or remarkably close to the constant in the $x$ variable, thus are far from the asymptotic limit form. The QCD evolution to higher momentum scales is necessary and we carry it out at the leading order of the perturbative theory for the leading-twist amplitudes. We provide estimates for the magnetic susceptibility of the quark condensate $\chi_m$ and the coupling $f_{3\gamma}$, which in the nonlocal model turn out to be close to the estimates from QCD sum rules. We find the higher-twist distribution amplitudes at the quark model scale and compare them to the Wandzura-Wilczek estimates. In addition, in the spectral model we evaluate the distribution amplitudes and light-cone wave functions of the $\rho$-meson.Comment: 24 pages, 15 figure

Measurement of the Deuteron Structure Function F₂ in the Resonance Region and Evaluation of its Moments

Inclusive electron scattering off the deuteron has been measured to extract the deuteron structure function F2 with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. The measurement covers the entire resonance region from the quasielastic peak up to the invariant mass of the final-state hadronic system W similar or equal to 2.7 GeV with four-momentum transfers Q2 from 0.4 to 6 (GeV/c)2. These data are complementary to previous measurements of the proton structure function F2 and cover a similar two-dimensional region of Q2 and Bjorken variable x. Determination of the deuteron F2 over a large x interval including the quasielastic peak as a function of Q2, together with the other world data, permit a direct evaluation of the structure function moments for the first time. By fitting the Q2 evolution of these moments with an OPE-based twist expansion we have obtained a separation of the leading twist and higher twist terms. The observed Q2 behavior of the higher twist contribution suggests a partial cancelation of different higher twists entering into the expansion with opposite signs. This cancelation, found also in the proton moments, is a manifestation of the duality phenomenon in the F2 structure function

First Measurement of Target And Double Spin Asymmetries for ep → epπ° in the Nucleon Resonance Region Above the Δ (1232)

The exclusive channel polarized proton(polarized e,e\u27 p)π0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the π0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A 1/2 and S 1/2 for the Roper resonance N (1400) P11, and the N(1535)S11 and N(1520)D13 states

Measurement of Deeply Virtual Compton Scattering Beam-Spin Asymmetries

The beam-spin asymmetries in the hard exclusive electroproduction of photons on the proton (→ep→epγ ) were measured over a wide kinematic range and with high statistical accuracy. These asymmetries result from the interference of the Bethe-Heitler process and of deeply virtual Compton scattering. Over the whole kinematic range (xB from 0.11 to 0.58, Q2 from 1 to 4.8  GeV2, −t from 0.09 to 1.8  GeV2), the azimuthal dependence of the asymmetries is compatible with expectations from leading-twist dominance, A ≃ asinϕ/(1+ccosϕ). This extensive set of data can thus be used to constrain significantly the generalized parton distributions of the nucleon in the valence quark sector

Measurement of Coherent ɸ-Meson Photoproduction from the Deuteron at Low Energies

The cross section and decay angular distributions for the coherent ɸ-meson photoproduction on the deuteron have been measured for the first time up to a squared four-momentum transfer t = (pᵧ - pɸ)2 =-2 GeV2/c2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cross sections are compared with predictions from a rescattering model. In a framework of vector meson dominance, the data are consistent with the total ɸ-N cross section σɸN at about 10 mb. If vector meson dominance is violated, a larger σɸN is possible by introducing a larger t slope for the ɸN → ɸN process than that for the γN → ɸN process. The decay angular distributions of the phi are consistent with helicity conservation

Exclusive Photoproduction of the Cascade Ξ Hyperons

We report on the first measurement of exclusive Ξ-(1321) hyperon photoproduction in p → K+K+Ξ- for 3.2 \u3c E \u3c 3.9 GeV. The final state is identified by the missing mass in p(,K+K+)X measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground state Ξ-(1321)1/2+ and have estimated the total cross section for its production. We also have strong evidence for the first excited state Ξ-(1530)3/2+. Photoproduction provides a copious source of Ξ\u27s. We discuss the possibilities of a search for the recently proposed Ξ5- and Ξ5+ pentaquarks

Differential Cross Sections for + p → K⁺ + Y for Λ and Σ⁰ Hyperons

High-statistics cross sections for the reactions + p → K⁺ + Λ and + p → K⁺ + Σ⁰ have been measured using CLAS at Jefferson Lab for center-of-mass energies W between 1.6 and 2.53 GeV, and for -0.85 \u3c cos θ Kc.m. \u3c +0.95. In the K⁺ + Λ channel we confirm a resonance-like structure near W=1.9 GeV at backward kaon angles. The position and width of this structure change with angle, indicating that more than one resonance is likely playing a role. The K⁺ + Λ channel at forward angles and all energies is well described by a t-channel scaling characteristic of Regge exchange, whereas the same scaling applied to the K⁺ + Σ⁰ channel is less successful. Several existing theoretical models are compared to the data, but none provide a good representation of the results

Assessment of the quality of life of patients with achalasia of the cardia after videoendoscopic Heller cardiomyotomy with Dor fundoplication

Background. The leading symptom of achalasia of cardia (AC) is dysphagia, along with other symptoms significantly affecting the quality of life of patients.The aim. Based on the results of questioning patients using special and general questionnaires and using special methods for studying the closing function of the cardia, to evaluate the quality of life of patients with stages 2–4 of AC after video-laparoscopic esophagocardiomyotomy according to Heller with anterior hemiasophagofundoplication according to Dor.Materials and methods. The basis of the work was the analysis of the results of esophagocardiomyotomy according to Heller with anterior hemiesophagofundoplication according to Dor in 106 patients with stages 2–4 of AC. The postoperative follow-up period averaged 2 ± 0.4 years. In the pre- and postoperative periods, the results of fluoroscopy of the esophagus and stomach, manometry of the esophagus and the esophageal-gastric junction were studied, and three questionnaires were used (Eckhardt scale, GIQLI questionnaire and SF-36).Results. Analysis of the data obtained showed that the clinical manifestations of the disease in the postoperative period decreased in all patients with stages 2–4 of AC, the results in patients with stage 2 were better than in patients with stages 3 and 4 (p < 0.05). The results of fluoroscopy of the esophagus and stomach, manometry of the esophagus and the esophagogastric junction showed improvement in the postoperative period in patients at all stages of the disease, the results of patients with stage 4 were worse compared with stages 2 and 3 (p < 0.05).Conclusion. Videoendoscopic esophagomyotomy according to Heller with anterior fundoplication according to Dor significantly reduces the severity of clinical manifestations of AC and improves the quality of life in patients with stages 2–4 of AC, as a result of which surgery should be recommended to patients already at stage 2 and organ-preserving surgery at stage 4 of the disease

Precise Measurement of the Neutron Magnetic Form Factor GnM in the Few-GeV² Region

The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q2 = 1.0–4.8  GeV2 with the CLAS detector at Jefferson Lab. High precision was achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the dat