Real Compton Scattering Research Articles

Proton scalar dipole polarizabilities from real Compton scattering data using fixed-t subtracted dispersion relations and the bootstrap method

We perform a fit of the real Compton scattering (RCS) data below pion-production threshold to extract the electric (αE1) and magnetic (βM1) static scalar dipole polarizabilities of the proton, using fixed-t subtracted dispersion relations and a bootstrap-based fitting technique. The bootstrap method provides a convenient tool for including the effects of the systematic errors on the best values of and , and for propagating the statistical errors of the model parameters fixed by other measurements. We also implement various statistical tests to investigate the consistency of the available RCS data sets below pion-production threshold, and conclude that there are not strong motivations to exclude any data point from the global set. Our analysis yields and , with p-value = 12%.

Scalar dipole dynamical polarizabilities from real Compton scattering data

We present an extraction of the scalar dipole dynamical polarizabilities from proton real Compton scattering (RCS) data below pion-production threshold. The theoretical approach relies on dispersion relations, and on the low-energy expansion and multipole expansion of the scattering amplitude. The statistical analysis is based on the parametric bootstrap technique, that revealed to be crucial to deal with problems inherent to both the low sensitivity of the RCS cross section to the energy dependence of the dynamical polarizabilities and the poor accuracy of the available data sets.

Probing saturation physics in the Real Compton Scattering at ultraperipheral pPb collisions

The Real Compton Scattering in ultraperipheral pPb collisions at RHIC and LHC energies is investigated and predictions for the squared transverse momentum (t) and rapidity (Y) distributions are presented. The scattering amplitude is assumed to be given by the sum of the Reggeon and Pomeron contributions and the Pomeron one is described by the Color Dipole formalism taking into account the non-linear (saturation) effects in the QCD dynamics. We demonstrate that the behavior of the cross sections at large-t and/or Y is dominated by the Pomeron contribution and is strongly affected by the non-linear effects present in the QCD dynamics. These results indicate that a future experimental analysis of this process can be useful to probe the QCD dynamics at high energies.

Investigating the proton structure through polarization transfers in real Compton scattering processes at JLAB

In the present work, preliminary results of the analysis of polarization transfers in real Compton scattering (RCS) performed in Hall-C at JLAB are presented, for data collected at large scattering angle (cm=70 o ) in the experiment E07-002. A previous experiment, E99-114, has already demonstrated a complete inconsistence of its results with a pQCD mechanism at JLAB energy regime. This kind of experiment, therefore, is of crucial importance for understanding the nature of the reaction mechanism for such a simple process, involving a real photon. Furthermore, RCS experiments allow the extraction of Compton form factors and Generalized Parton Distributions (GPDs), the latter connected to the total angular momentum of the nucleon. 1. Physics motivation and preliminary results Real Compton scattering (RCS) in the hard scattering limit is a powerful probe of the structure of the nucleon. With a real photon at wide angle regime (1), RCS provides access to the high-t transverse structure of the hadron, whereas deep virtual Compton scattering (DVCS) provides access mostly to the high-Q 2 low-t structure. For RCS on proton, the hard scale is reached when the Mandelstam variables s ,- t, and -u are larger than the proton mass. Under such conditions the transition amplitude is expected to factorize as Tif (s,t) = f ⊗ K(s,t) ⊗ i, where K(s,t) is the hard scattering amplitude, involving the coupling of the external photons to the active quarks, and the 's are the soft initial and final wave functions, describing the coupling of the active quarks to the proton. Two different approaches are usually taken as a reference in the interpretation of the results: the handbag mechanism (2, 3), which involves only one active constituent (Fig. 1 (left)), with the soft physics for the coupling of this active quark to the proton described in the Generalized Parton Distributions (GPD's) (4, 5), and the perturbative QCD (pQCD) mechanism (6), in which all three valence quarks are active participants in the hard subprocess, the latter effected by the exchange of two hard gluons (Fig. 1 (right)), with the soft physics contained in the valence quark distribution. In principle, both mechanisms contribute to

An electromagnetic calorimeter for the JLab real compton scattering experiment

A lead–glass hodoscope calorimeter that was constructed for use in the Jefferson Lab Real Compton Scattering experiment is described. The detector provides a measurement of the coordinates and the energy of scattered photons in the GeV energy range with resolutions of 5 mm and 6%/ E γ GeV . Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.

Virtual Compton scattering and neutral pion electroproduction in the resonance region up to the deep inelastic region at backward angles

We have made the first measurements of the virtual Compton scattering (VCS) process via the H$(e,e'p)\gamma$ exclusive reaction in the nucleon resonance region, at backward angles. Results are presented for the $W$-dependence at fixed $Q^2=1$ GeV$^2$, and for the $Q^2$-dependence at fixed $W$ near 1.5 GeV. The VCS data show resonant structures in the first and second resonance regions. The observed $Q^2$-dependence is smooth. The measured ratio of H$(e,e'p)\gamma$ to H$(e,e'p)\pi^0$ cross sections emphasizes the different sensitivity of these two reactions to the various nucleon resonances. Finally, when compared to Real Compton Scattering (RCS) at high energy and large angles, our VCS data at the highest $W$ (1.8-1.9 GeV) show a striking $Q^2$- independence, which may suggest a transition to a perturbative scattering mechanism at the quark level.

Beam normal spin asymmetry in the quasireal Compton scattering approximation

he two-photon exchange contribution to the single spin asymmetries with the spin orientation normal to the reaction plane is discussed for elastic electron-proton scattering in the equivalent photon approximation. In this case, the hadronic part of the two-photon exchange amplitude describes real Compton scattering (RCS). We show that in the case of the beam normal spin asymmetry this approximation selects only the photon helicity flip amplitudes of RCS. At low energies, we make use of unitarity and estimate the contribution of the piN multipoles to the photon helicity flip amplitudes. In the Regge regime, the quasi-RCS (QRCS) approximation allows for a contribution from two-pion exchange, and we provide an estimate of such contributions.

Real Compton Scattering on Proton at High Momentum Transfers

The E99-114 experiment was carried out to measure the cross sections for Real Compton Scattering (RCS) on the proton in the kinematic range s = 5 − 11 GeV 2 , − t = 2 − 7 GeV 2 . In addition, a measurement of longitudinal and transverse polarization transfers was made at s = 6.9 GeV 2 and − t = 4.0 GeV 2 . These measurements were done to test the existing theoretical mechanisms for this process and will possibly lead to the determination of RCS form factors which are related to the Generalized Parton Distributions (GPD). The experiment was conducted in Hall A of Thomas Jefferson National Accelerator Facility (Jefferson Lab). Final results of polarization transfer measurements are presented.

Virtual compton scattering and polarizabilities

Virtual Compton Scattering (VCS) off the proton below pion threshold allows access to generalized polarizabilities of the proton. These observables measure the response of the nucleon to low energy electromagnetic field perturbations. This paper presents a comparison with Real Compton Scattering and also results for the first dedicated VCS experiment performed at the Mainz Microtron MAMI with high resolution spectrometers at Q 2 = 0.33 GeV 2.

The first virtual compton scattering experiment at MAMI

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 results.

Virtual versus real nuclear Compton scattering in the Δ(1232) region

In this paper we calculate the cross section for Virtual Compton Scattering off nuclei in the delta resonance region. We also calculate the background for the process from Coherent Bremsstrahlung in nuclei and explore the regions where the Virtual Compton Scattering cross section dominates. The study also shows that it is possible to extract the cross section for Real Compton Scattering from the Virtual Compton one in a wide range of scattering angles.