Measurement of \Sigma beam asymmetry in \pi^{0}_{} photoproduction off the neutron in the second and third resonances region⋆

The $ \Sigma$ beam asymmetry in the photoproduction of neutral pions from quasi-free nucleons in a deuteron target was measured for the first time between 0.60 and 1.50GeV, with the GRAAL polarized and tagged photon beam. The asymmetry values from the quasi-free proton were found equal to the ones extracted from a pure proton target. The asymmetries from quasi-free proton and quasi-free neutron were found equal up to 0.82GeV and substantially different at higher energies. The results are compared with recent partial-wave analyses.     

Study of the baryon resonances structure via η photoproduction

Within a quark model the process γp → ηp, for E_γ^lab < 1.2 GeV, is investigated. We find that the recent data from GRAAL on the polarized beam asymmetry require significant contributions from the resonances D₁₃(1520), F₁₅(1680), and to a lesser extent from P₁₃(1720) in addition to those from the dominant S₁₁(1535) resonance, implied by the Mainz differential cross-section data. The contributions from the resonances S₁₁(1650), D₁₃(1700) and D₁₅(1675) are found consistently small but sensitive to the polarized target asymmetry measured recently at ELSA. These results are shown to be consistent with the quark model predictions.     

Measurement of K β K /α values using proton beamvalues using proton beam

The Measurement of K _β K _/α intensity ratios are measured in some 3d shell elements by using a 2 MeV proton beam along with a high resolution Si(Li) detector. The present Measurement of K _β K _/α intensity ratios are in good agreement with Scofield modified theoretical values, thus supporting the basic assumptions in that theory. From the present Measurement of K _β K _/α intensity ratios, it is evident that due to chemical effects, the experimental Measurement of K _β K _/α intensity ratios will be increased while they will be decreased due to the presence of simultaneous M-shell vacancies which are produced due to proton excitation.     

Measurement of the η production in proton-proton collisions with the COSY time-of-flight spectrometer

The reaction pp → ppη was measured at excess energies of 15 and 41 MeV at an external target of the Jülich Cooler Synchrotron COSY with the time-of-flight spectrometer. About 25000 events were measured for the excess energy of 15 MeV and about 8000 for 41 MeV. Both protons of the process ppη were detected with an acceptance of nearly 100% and the η was reconstructed by the missing-mass technique. For both excess energies the angular distributions are found to be nearly isotropic. In the invariant-mass distributions strong deviations from the pure phase space distributions are seen. Received: 24 May 2002 / Accepted: 20 September 2002 / Published online: 17 January 2003 RID="a" ID="a"e-mail: e.roderburg@fz-juelich.de Communicated by M. Gar?on     

Exclusive photoproduction of \Phi on proton in the quark–diquark model

We present predictions for exclusive photoproduction of a meson on proton at large transfer, where we use a quark–diquark structure model for the proton. Extrapolation from our results to lower transfers is comparable in magnitude with available data in that range. This may support the diquark model in its ability to provide, for that process, an appropriate link between diffractive physics at low transfer and the standard semiperturbative approach of hard exclusive processes at very large transfer, in which the proton recovers its three-quark structure. Received: 5 November 1998 / Revised version: 13 July 1999 / Published online: 3 November 1999     

Off-shell effects in the coherent π0 photoproduction off nuclei

The strong sensitivity of coherent π⁰ photoproduction to the choice of the reaction energy ω in the elementary t_πγ (ω)-matrix is demonstrated. The best agreement of the DWIA results with the experimental data is achieved when ω is chosen as an eigenvalue of the free relativistic hamiltonian of the πN system. This is in agreement with the consequences of the relativistic potential theory.     

Measurement of the forward-backward asymmetry of μ+μ− pairs in CMS

The measurement of the forward-backward asymmetry A _FB and the effective weak mixing angle with the Drell-Yan process at the LHC is presented. The samples of 2011 collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5 fb^?1 and 1.1 fb^?1, were used. The results are consistent with the standard model expectations.     

Near threshold photoproduction of η mesons from 4 He

Photoproduction of - mesons from ⁴He has been measured for the first time. The experiment was performed at the Mainz Microtron (MAMI) using the TAPS photon spectrometer and the Glasgow/Mainz tagged photon facility. - mesons were identified in coincidence with recoil nucleons. Total and differential cross sections are presented in the photon energy range between threshold and 818 MeV. The exclusive data are used to determine the ratio of the elementary production cross sections on bound neutrons and protons, C_n/C_p = 0.68 - 0.02 - 0.09. In addition, upper limits for the total coherent cross section have been derived.     

Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance

The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.     

Capacitive beam position monitors for the low-β beam of the Chinese ADS proton linac

Beam Position Monitors(BPMs) for the low-β beam of the Chinese Accelerator Driven Subcritical system(CADS) Proton linac are of the capacitive pick-up type.They provide higher output signals than that of the inductive type.This paper will describe the design and tests of the capacitive BPM system for the low-β proton linac,including the pick-ups,the test bench and the read-out electronics.The tests done with an actual proton beam show a good agreement between the measurements and the simulations in the time domain.     

Measurement of the tensor analyzing power components in the coherent photoproduction of a π 0 meson on a deuteron

The components of the tensor analyzing powers, T ₂₀, T ₂₁, and T ₂₂, of the coherent photoproduction of a π₀ meson on a deuteron have been measured for photon energies of 250–450 MeV and pion emission angles of 90°–145°. The results are compared with the theoretical predictions.     

Measurement of inelastic J/ψ photoproduction at HERA

We present a measurement of the inelastic, non diffractive J/ψ photoproduction cross section in the reaction e ⁺ p → e ⁺J/ψ X with the ZEUS detector at HERA. The J/ψ was identified using both the μ ⁺ μ ^- and e ⁺ e ^- decay channels and events were selected within the range 0.4 < z < 0.9 (0.5 < z < 0.9) for the muon (electron) decay mode, where z is the fraction of the photon energy carried by the J/ψ in the proton rest frame. The cross section, the p _T ² and the z distributions, after having subtracted the contributions from resolved photon and diffractive proton dissociative processes, are given for the photon-proton centre of mass energy range 50 < W < 180 GeV; p _T ² is the square of the J/ψ transverse momentum with respect to the incoming proton beam direction. In the kinematic range 0.4 < z < 0.9 and p _T ² > 1 GeV², NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data. The predictions of a specific leading order colour-octet model, as formulated to describe the CDF data on J/ψ hadroproduction, are not consistent with the data.     

Measurement of the η mass at KLOE<Superscript>⋆</Superscript>

In this report the measurement of the η mass is presented. The analysis has been performed on 450pb^-1 of data collected in the years 2001 and 2002. The measured value is m _η = (547.874±0.07_stat±0.029_syst) MeV. Original article based on material presented at HADRON 2007.     

A novel beam–spin asymmetry in double-hadron inclusive lepto-production

We show that a new beam–spin asymmetry appears in deep inelastic inclusive lepto-production at low transverse momenta when a hadron in the target fragmentation region is observed in association with another hadron in the current fragmentation region. The beam leptons are longitudinally polarized while the target nucleons are unpolarized. This asymmetry is a leading-twist effect generated by the correlation between the transverse momentum of quarks and the transverse momentum of the hadron emitted by the target. Experimental signatures of this effect are discussed.     

Measurement of velocity distribution in an atomic beam by means of Doppler resonance fluorescence

Introduction Measurement of velocity distribution in atomic beams is of significance to laser spec-troscopy and atomic physics.Previously,workers used to investigate atomic velocity distribu-tion by means of mechanic separators.Recently, spectroscopic methods of measuring veloc-ity distribution are developed,which find velocity distribution from detecting atomic fluo-rescence frequency distribution or from detecting atomic deflection due to radiation force.Un-fortunately,these methods can not realize real time measurement.In this paper we propose a     

Investigation of the anomaly in η-photoproduction off the neutron

Quasi-free photoproduction of η-mesons off the neutron and off the proton has been studied using a deuterium target and bremsstrahlung photons produced by MAMI-C with incident energies up to 1.5 GeV. The η-mesons were detected in coincidence with the recoil nucleons thus a fully exclusive measurement was performed. Preliminary results show a bump-like structure in the excitation function for the neutron close to W ≈ 1675 MeV which is not seen for the proton. Considering the experimental resolution and using a Breit-Wigner fit the width of this structure was approximated below 50 MeV.     

Measurement of the production cross section for charmed baryons in proton–nucleus interactions at 70 GeV

The results of an analysis of data from the SERP-Е-184 experiment devoted to studying mechanisms of the production of charmed particles in proton–nucleus interactions at 70 GeV and their decays are presented. The data in question were obtained upon irradiating the SVD-2 active target consisting of carbon, silicon, and lead plates with a beam of 70-GeV protons. A detailed simulation on the basis of the FRITIOF7.02 and GEANT3.21 code packages made it possible to optimize event-selection criteria and to calculate the detection efficiency for Λ_c⁺ baryons. After selecting a signal from the threebody decay of a Λ_c⁺ baryon, the inclusive cross section for its production at near-threshold energies, its lifetime, and the parameter of the A dependence of the cross section were found. The Λ_c⁺ -baryon yields are tabulated along with data from other experiments and theoretical predictions.     

Signature of the ηNN configurations in coherent πphotoproduction on the deuteron

The photoproduction of a neutral pion on the deuteron is considered in the energy region around the η threshold, where a bump-like structure was observed at very backward pion angles. Different dynamical aspects which may be responsible for this phenomenon are analysed within a theoretical frame which includes intermediate ηNN configurations. The results show, in particular, that a three-body treatment of the ηNN interaction is of special importance.     

Measurement of the total photoabsorption cross section on a proton in the energy range 600–1500 MeV at the GRAAL

The total photoabsorption cross section on a free proton was measured at the GRAAL facility in the energy range E _γ = 600−1500 MeV. The large-aperture LAGRANγE detector and a liquid hydrogen target were used in the experiment performed with a back-scattered Compton gamma beam. To improve the accuracy, two alternative methods were employed. First, a subtraction method of using empty-target measurements allowed the cross section σ _tot to be evaluated directly because of a low level of the electromagnetic background. Second, an algorithm for evaluating σ _tot on the basis of summing the dominating partial cross sections was developed. Experimental results obtained for σ _tot by the two methods are compared with existing data. The article was translated by the authors. Published in Russian in Yadernaya Fizika, 2008, Vol. 71, No. 1, pp. 76–83.