scholarly journals Quasi-real photon contribution to $A_N$ in $\ell p^\uparrow \to \pi\, X$ within a TMD approach

2017 ◽  
Author(s):  
Umberto D'Alesio ◽  
Carlo Flore ◽  
Francesco Murgia
Keyword(s):  
Real Photon

scholarly journals Studying time-like electromagnetic baryonic transitions with HADES in pion induced reactions

2020 ◽  
Vol 241 ◽  
pp. 01012
Author(s):  
Béatrice Ramstein
Keyword(s):  
Center Of Mass ◽  
Quantitative Description ◽  
Form Factors ◽  
Resonance Region ◽  
Partial Wave Analysis ◽  
Real Photon ◽  
Pion Beam ◽  
Dalitz Decay ◽  
Covariant Model ◽  
Proton Induced Reactions

A dedicated programme aiming at studying electromagnetic baryonic transitions in the time-like region has started at GSI using the pion beam and the High Acceptance Di-Electron Spectrometer (HADES) set-up. A pioneering experiment has been carried out in the second resonance region, at a center-of-mass energy of 1.49 GeV, using carbon and polyethylene targets, allowing for an analysis of the inclusive e+e- production and of the exclusive quasi-free π-p → ne+e- reaction, in complement to hadronic channels. Predictions for the Dalitz decay of N(1520) and N(1535) based on real photon couplings strongly underestimate the e+e- yield at invariant masses larger than 300 MeV/c2, which signals effects of time-like baryon transition form factors, in qualitative agreement with the Vector Dominance Models (VDM). A quantitative description of the observed e+e- yield is achieved by taking into account the contribution from off-shell ρs. The latter was provided by the preliminary results of a Bonn-Gatchina Partial Wave Analysis of the two-pion production channels, which were measured simultaneously in our experiment. A good agreement is also obtained using a covariant model for the time-like electromagnetic form factors for the N-N(1520) transition. The angular distributions for the e+e- production contain additional selective information on the spin structure of the different transitions. The measurements with the pion beam will be extended in future in the third resonance region. Hyperon Dalitz decay studies in proton induced reactions are also foreseen.

scholarly journals Modern Technique for Real Photon Radiative Correction Calculations

2021 ◽  
Vol 24 (2) ◽  
pp. 184-191
Author(s):  
I. A. Shershan ◽  
T. V. Shishkina
Keyword(s):  
Gauge Boson ◽  
Cross Sections ◽  
Dimensional Regularization ◽  
Real Photon ◽  
Boson Production ◽  
Radiative Corrections ◽  
Hard Photon ◽  
Regularization Scheme ◽  
Modern Technique ◽  
Bremsstrahlung Contribution

The problem of the bremsstrahlung contribution calculation as a part of the radiative corrections in the case of single gauge boson production was discussed. It was shown that the hard photon bremsstrahlung contribution can be divided into the finite and divergent terms. The exact calculation of soft photon bremsstrahlung and infrared part of hard photon bremsstrahlung was presented in frame of the dimensional regularization scheme. Numerical analysis of radiative corrections to the cross sections of single gauge boson production was performed.

RECENT RESULTS FROM THE REAL PHOTON EXPERIMENT AT MAMI

2010 ◽  
Vol 19 (05n06) ◽  
pp. 1064-1075
Author(s):  
ANDREAS THOMAS
Keyword(s):  
High Intensity ◽  
Photon Beam ◽  
Real Photon ◽  
Final States ◽  
Detection Capability ◽  
Crystal Ball ◽  
The Real ◽  
The Future ◽  
Set Up

Experiments with real photons have been performed for many years at the Mainz accelerator MAMI with different detectors. The upgraded MAMI C accelerator recently delivered electrons with an energy of 1604MeV. The A2 collaboration performs experiments with energy tagged polarised real photons produced via 'Bremsstrahlung'. Linear and circular photon polarisation is possible. In the years 2005/2006 the Crystal Ball detector with its unique detection capability for multi photon final states was set up in Mainz. The Crystal Ball at MAMI setup offers an excellent possibility to study decays of the η and η′ mesons. Due to the high intensity photon beam the apparatus can be seen as an η-factory. Recent results from the Crystal Ball experiment at MAMI are presented. In the future we plan to use a longitudinal and transverse polarised frozen spin target to investigate the spin polarisibilities of the nucleons.

Radiative corrections to the scattering of electrons and positrons by electrons

1953 ◽  
Vol 220 (1141) ◽  
pp. 219-239 ◽  
Keyword(s):  
Cross Section ◽  
Ultra Violet ◽  
Laboratory Frame ◽  
Real Photon ◽  
Rest Energy ◽  
Electrons And Positrons ◽  
Charge Renormalization ◽  
The Cross ◽  
Maximum Bremsstrahlung Energy ◽  
Exact Calculations

The e 6 corrections to the Moller formula for the scattering of electrons by electrons and the Bhabha formula for the scattering of positrons by electrons, arising from the interaction of the particles with virtual photons, are formulated using the Feynman-Dyson techniques. After removing ultra-violet divergences by mass and charge renormalization the cross-section still suffers from a logarithmic infra-red divergence. This is cancelled by adding on the cross-section for the production of a single real photon of low energy during the collision. The result is evaluated assuming that the maximum bremsstrahlung energy radiated is small compared with the rest energy of the electron, as viewed from the laboratory frame. Non-relativistic and extreme relativistic approximations to the formulae are presented, together with the results of exact calculations for a laboratory energy of 20 mc 2 .

OVERVIEW OF EXPERIMENTAL RESULTS FROM HERMES

2012 ◽  
Vol 20 ◽  
pp. 19-28
Author(s):  
MARCO CONTALBRIGO
Keyword(s):  
Degrees Of Freedom ◽  
Distribution Functions ◽  
Real Photon ◽  
Final States ◽  
Spin Orbit ◽  
Parton Distribution Functions ◽  
Transverse Momentum Dependent ◽  
Hermes Experiment ◽  
Electrons And Positrons ◽  
Azimuthal Asymmetries

The investigation of the partonic degrees of freedom beyond collinear approximation (3D description) has been gained increasing interest in the last decade. At the HERMES experiment, azimuthal asymmetries in hard exclusive reactions and in semi-inclusive deep-inelastic scattering of electrons and positrons off a (polarized) hydrogen and deuterium target have been measured. Such asymmetries provide new insights on crucial aspects of the parton dynamics. By measuring various hadron types in the initial and final states, flavor sensitivity is achieved. Non zero signals are reported for azimuthal asymmetries with respect the transverse target polarization in real-photon exclusive-electroproduction, which are related (still in a model dependent way) to the elusive quark orbital motion. Evidence is reported of the poorly known transversity function and of naive-T-odd transverse-momentum-dependent parton distribution functions related to spin-orbit effects. Evidence of spin-orbit effects in quark fragmentation is also observed, which are opposite in sign for favored and disfavored processes.

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