Search results for "Virtual"

Light-by-light scattering sum rules constraining meson transition form factors

2012

Relating the forward light-by-light scattering to energy weighted integrals of the \gamma* \gamma -fusion cross sections, with one real photon (\gamma) and one virtual photon (\gamma*), we find two new exact super-convergence relations. They complement the known super-convergence relation based on the extension of the GDH sum rule to the light-light system. We also find a set of sum rules for the low-energy photon-photon interaction. All of the new relations are verified here exactly at leading order in scalar and spinor QED. The super-convergence relations, applied to the \gamma* \gamma -production of mesons, lead to intricate relations between the \gamma \gamma -decay widths or the \gamma…

The first Virtual Compton Scattering experiment at MAMI

1999

Abstract Virtual Compton scattering, i.e. the exclusive reaction γ ∗ p → γ′p′ with γ ∗ denoting a virtual photon, provides new insights on the internal structure of the proton. Below π 0 production threshold, this experiment measures the generalized polarizabilities of the proton as defined by Guichon et al [1], [2] and Drechsel et al [3]. These new electromagnetic observables, functions of Q 2 , enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering ( Q 2 =0) [4]. The first VCS experiment [5] of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for Q 2 =0.33 GeV 2 and we present in this paper the preliminary resu…

Precise pion electroproduction in thep(e, e? ?+)n reaction at W=1125 MeV

1996

The reactione+p →> e+π ++n at c.m. energyW=1125MeV and momentum transfer Q2=0.117GeV2/c2 has been measured. The transverse and longitudinal structure functions have been separated by varying the polarization of the virtual photon (Rosenbluth plot) with a 3 to 4% error. In addition the longitudinal-transverse interference term has been determined measuring the right-left asymmetry with an accuracy of 3%. The experimental data are compared to model calculations, and the sensitivity of the results to the axial and pion formfactors is discussed.

Exchange currents in the deuteron

2008

The present status of exchange currents and their contribution to deuteron disintegration by real and virtual photons is reviewed. The importance of the Siegert theorem for electric transitions is stressed. Various experiments in photoabsorption, electron and photon scattering with respect to influences of exchange currents are discussed.

An experiment on the electroproduction of multi-hadron final states

1995

Abstract Electroproduction of final states including protons and pions was measured on 12C in close to 4π geometry using a BGO crystal ball at the 3-spectrometer facility at MAMI. The energy transfer regime studied at three incident electron energies ranged from the quasielastic proton knockout to the quasifree Δ excitation region. The 3-momentum of the virtual photon ranged from about 400 to 800 MeV/c. The performance of the experimental setup is discribed and missing energy distributions of the reactions 12C(e,e′p) and 12C(e,e′pp) are presented.

Virtual photons and electrodisintegration of the deuteron

1982

The validity of the virtual photon concept in the analysis of deuteron electrodisintegration for equivalent photon energies up to 300 MeV is investigated. The deuteron and the final state interaction are described by the consistent nonrelativistic calculation of Fabian and Arenhoevel neglecting the effects of meson exchange currents and isobar configurations. We find that in well defined kinematic domains the use of the virtual photon concept is justified in extracting photodisintegration cross sections.

Baryon transition form factors at the pole

2016

Electromagnetic resonance properties are uniquely defined at the pole and do not depend on the separation of the resonance from background or the decay channel. Photon-nucleon branching ratios are nowadays often quoted at the pole, and we generalize the considerations to the case of virtual photons. We derive and compare relations for nucleon to baryon transition form factors both for the Breit-Wigner and the pole positions. Using the MAID2007 and SAID SM08 partial wave analyses of pion electroproduction data, we compare the $G_M$, $G_E$, and $G_C$ form factors for the $\Delta(1232)$ resonance excitation at the Breit-Wigner resonance and pole positions up to $Q^2=5$ GeV$^2$. We also explore…

POLARIZED 3HE TARGETS FOR REAL AND VIRTUAL PHOTONS

2011

Radiative return at NLO and the measurement of the hadronic cross-section in electron–positron annihilation

2001

Electron-positron annihilation into hadrons plus an energetic photon from initial state radiation allows the hadronic cross-section to be measured over a wide range of energies. The full next-to-leading order QED corrections for the cross-section for e^+ e^- annihilation into a real tagged photon and a virtual photon converting into hadrons are calculated where the tagged photon is radiated off the initial electron or positron. This includes virtual and soft photon corrections to the process e^+ e^- \to \gamma +\gamma^* and the emission of two real hard photons: e^+ e^- \to \gamma + \gamma + \gamma^*. A Monte Carlo generator has been constructed, which incorporates these corrections and sim…

The pionic beta decay in chiral perturbation theory

2003

Within the framework of chiral perturbation theory with virtual photons and leptons, we present an updated analysis of the pionic beta decay including all electromagnetic contributions of order e**2 p**2. We discuss the extraction of the Cabibbo-Kobayashi-Maskawa matrix element |Vud| from experimental data. The method employed here is consistent with the analogous treatment of the Kl3 decays and the determination of |Vus|.