Deep Virtual Compton Scattering Research Articles

COMPASS measurement of hard exclusive π0 muoproduction cross-section

One of the goals of the COMPASS experimental program is the measurement of exclusive processes. The exclusive processes, such as Deep Virtual Compton Scattering (DVCS) or Hard Exclusive Meson Production, are important inputs for constraining the General Parton Distributions (GPDs). Exclusive π0 production is the main source of background for DVCS process, while it provides important information on chiral-odd GPDs. The dedicated GPD program started with a one month pilot run in 2012, followed by two full years of data taking in 2016-2017, using 160 GeV/c positive and negative muon beams, a liquid hydrogen target and new detectors such as a recoil proton detector and a large-angle electromagnetic calorimeter. Our results of the exclusive π0 production from the 2012 pilot run, recently submitted to publication, are presented. Using average of both μ+ and μ− data, the γ*p cross section is extracted as a function of the squared four-momentum transfer t, and of the azimuthal angle ϕ between the scattering plane and the π0 production plane. The average kinematics of the measurement are ⟨Q2⟩ = 2.0 (GeV/c)2, ⟨ν⟩ = 12.8 GeV, ⟨xB⟩ = 0.093, and ⟨−t⟩ = 0.256 (GeV/c)2. A comparison of our results with the phenomenological Goloskokov-Kroll model are shown. Prospect are given on upcoming results of the 2016/17 measurement.

Tomographic image of the proton

We determine, based on the latest experimental Deep Virtual Compton Scattering experimental data, the dependence of the spatial size of the proton on the quark's longitudinal momentum. This results in a three-dimensional momentum-space image and tomography of the proton.

Searching saturation effects in inclusive and exclusiveeAprocesses

The searching of saturation effects in inclusive and exclusive eA collisions is reviewed. In particular, we present a comparison between the linear and non-linear predictions for the nuclear structure functions as well as for the Deep Virtual Compton Scattering and vector meson production in future eA colliders.

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

The COMPASS future: COMPASS II

Up to now the COMPASS experiment of Abbon et al. (2007) [8] contributed with the muon beam to precise measurements of the nucleon longitudinal momentum structure. A more complete nucleon description beyond collinear approximation includes the quark intrinsic momentum distributions which are described by the Transverse Momentum Dependent (TMD) Parton Distribution Functions (PDFs) and by Generalised Parton Distributions (GPDs). The next phase COMPASS Coll., (2010) [6] approved in December 2010 focuses on GPDs measurements through Deep Virtual Compton Scattering (DVCS) and Deep Virtual Meson Production (DVMP), in TMDs with Drell–Yan process and on Primakoff measurements. The latter shed light on the hadron structure through the hadron deformation in an external electromagnetic field described by the polarisabilities.

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.

Generalized parton distributions from deep virtual compton scattering at CLAS

We have analyzed the beam spin asymmetry and the longitudinally polarized target spin asymmetry of the Deep Virtual Compton Scattering process, recently measured by the Jefferson Lab CLAS collaboration. Our aim is to extract information about the Generalized Parton Distributions of the proton. By fitting these data, in a largely model-independent procedure, we are able to extract numerical values for the two Compton Form Factors HIm and H˜Im with uncertainties, in average, of the order of 30%.

Generalized Parton Distributions

We give a short theoretical and pedagogical introduction to the field of Generalized Parton Distributions and briefly review the first Deep Virtual Compton Scattering data.

A fitter code for Deep Virtual Compton Scattering and Generalized Parton Distributions

A fitter code for Deep Virtual Compton Scattering and Generalized Parton Distributions

Discussion on the recent proton-DVCS results of Jefferson Lab

We present the recent data issued from the Halls A and B of Jefferson Laboratory for the Deep Virtual Compton Scattering Process on the proton. An important set of data for beam spin asymmetries, unpolarized cross sections and differences of polarized cross sections have been obtained. We modestly attempt a first “global” analysis of these three observables at a single <xB>, <Q2> and <−t> kinematic point. We find that it is extremely challenging to describe simultaneously these data in the framework of a few Generalized Parton Distributions models.

Recent experimental results on Deep Virtual Compton Scattering and Generalized Parton Distributions

We review and discuss briefly the recent experimental results on Deep Virtual Compton Scattering on the proton. With the variety of independent observables beginning to be available and, in some instances, some very high precision data, some first global analysis for this process can be started, based on dedicated fitter codes, aiming at revealing the Generalized Parton Distributions content of the nucleon.

A fitter code for Deep Virtual Compton Scattering and Generalized Parton Distributions

We have developed a fitting code based on the leading-twist handbag Deep Virtual Compton Scattering (DVCS) amplitude in order to extract Generalized Parton Distribution (GPD) information from DVCS observables in the valence region. In a first stage, with simulations and pseudo-data, we show that the full GPD information can be recovered from experimental data if enough observables are measured. If only some of these observables are measured, valuable information can still be extracted, with certain observables being particularly sensitive to certain GPDs. In a second stage, we make a practical application of this code to the recent DVCS Jefferson Lab Hall-A data from which we can extract numerical constraints for the two H GPD Compton form factors.

Generalized Parton Distributions and deep virtual Compton scattering

We give a pedagogical introduction to the field of Generalized Parton Distributions and review shortly the experimental situation and perspective for Deep Virtual Compton Scattering.

Deep Virtual Compton Scattering and the Nucleon Generalized Parton Distributions

In the following, the subject of Deep Virtual Compton Scattering on the nucleon and its relation to the recently introduced concept of Generalized Parton Distributions are briefly reviewed. The general theoretical framework and the links between theory and experiment will be outlined and the recently published data which look promising for the development of this field will be discussed. Finally, the experimental prospectives of the domain will be presented.