Nucleon Structure and Generalized Parton Distributions

This paper discusses a selected part of the experimental program dedicated to the study of Generalized Parton Distributions, a recently introduced concept which provides a comprehensive framework for investigations of the partonic structure of the nucleon. Particular emphasis is put on the Deeply Virtual Compton Scattering program performed at the Jefferson Laboratory. The short and long term future of this program is also discussed in the context of the several experimental efforts aiming at a complete and exhaustive mapping of Generalized Parton Distributions.Comment: Proceedings of the XXVth International Workshop on Nuclear Theory, Rila (Bulgaria), June 26 - July 1 2006; 11 pages, 6 figure

Results and Prospects of Few-Body System Structure Studies

This paper presents a selected review of the (e,e'p) experimental program recently completed at the Jefferson Laboratory in the domain of high momentum transfer and high recoil momentum. Particular emphasis is put on the current understanding of the reaction mechanisms and of the large final state interaction effects. Their consequences on the study of the nuclear wave function and nucleon-nucleon correlations are addressed. The short and long term future of the (e,e'p) experimental program is also discussed in the perspective of the study of the quark and gluon structure of nucleons and nuclei.Comment: Proceedings of the XXIIIrd International Workshop on Nuclear Theory, Rila (Bulgaria), 14-19 June 2004; 21 pages, 12 figure

Lepton mass effects in the Bethe-Heitler process

We develop the full finite lepton mass formalism for the production of real photons via the Bethe-Heitler reaction of unpolarized leptons off unpolarized nucleons. Genuine lepton mass effects are described, in particular their dependence upon the lepton mass and the initial beam energy, as well as their sensitivity to the nucleon isospin. In the minimum momentum transfer region, these effects dominate the muon induced proton cross section and become significant for electron scattering at small $x_B$.Comment: Final version including errat

Monitoring of the calibration constants of the DVCS calorimeter

Radiation exposure of the DVCS calorimeter during data taking has degraded the optical properties of the cristals in a time dependent way. This note presents a method which allows to determine the effective gain of each single block all along data taking, relying on the two absolute elastic calibrations performed at the beginning and at the end of the experiment. Consideration of time dependent gain is shown to improve the missing mass resolution, allowing for a better identification of DVCS events

Characterization of the Analyzing Target of the PEPPo Experiment

On behalf of the PEPPo Collaboration - MOPWA079 - ISBN 978-3-95450-122-9International audienceVarious methods have been investigated over the past decades for the production of polarized positrons. The purpose of the PEPPo (Polarized Electrons for Polarized Positrons) experiment is to demonstrate, for the first time, the production of polarized positrons from a polarized electron beam. This two-step process involves the production of circularly polarized photons in a high Z target via the bremsstrahlung process followed, within the same target, by the conversion of polarized photons into polarized e+e- pairs through the pair creation process. The PEPPo experiment was performed in Spring 2012 at the injector of the Jefferson Laboratory using a highly spin-polarized (∼85%) 8.3 MeV/c electron beam. The positron polarization was measured by means of a Compton transmission polarimeter over the momentum range from 3.2 MeV/c to 6.2 MeV/c. This presentation will discuss the experimental set-up with a special emphasis on the analyzing magnet constituting the polarization filter of the experiment. The knowledge of the analyzing target polarization will be discussed on the basis of simulations and calibrated to experimental data

Lang's Conjecture and Sharp Height Estimates for the elliptic curves y2=x3+axy^{2}=x^{3}+ax

For elliptic curves given by the equation $E_{a}: y^{2}=x^{3}+ax$, we establish the best-possible version of Lang's conjecture on the lower bound of the canonical height of non-torsion points along with best-possible upper and lower bounds for the difference between the canonical and logarithmic height.Comment: published version. Lemmas 5.1 and 6.1 now precise (with resultant refinement to Theorem 1.2). Small corrections to

Generalized parton distributions, the hunt for quark orbital momenta

The Generalized Parton Distributions (GPDs) are the appropriate framework for a universal description of the partonic structure of the nucleon. They characterize the dynamics of quarks and gluons inside the nucleon and consequently contain information about the spin of the nucleon. The current experimental knowledge about GPDs is reviewed with the emphasis on the determination of E^q(Q^2,x,xi,t), the least known and constrained GPD, of particular importance in the nucleon spin puzzle. The perspectives of this experimental program are also addressed.Comment: 6 pages, 2 figures Proceedings of the XVIIIth Symposium on Spin Physics, Charlottesville (Virginia, USA), October 6-11,200

Tagger design optimization

This note presents the simulations and tests performed at LPSC Grenoble for the optimization of the DVCS tagger paddles. The choice of the wrapping material and the addition of a light guide with a specific triangular cut are discussed and confronted to experimental measurements. This study led to the final configuration of the DVCS tagger

Evaluation of a High-Power Target Design for Positron Production at CEBAF

A source for polarized positron beams at the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab is being designed. The Polarized Electrons for Polarized Positrons (PEPPo) concept is used to produce polarized e$^+$e$^-$-pairs from the bremsstrahlung radiation of a longitudinally polarized electron beam interacting within a high-$Z$ conversion target. The scheme under consideration includes a 4 mm thick tungsten target that absorbs 17 kW deposited by a 1 mA continuous-wave electron beam with an energy of 120 MeV. The concept of a rotating tungsten rim mounted on a water-cooled copper disk was explored. The results of ANSYS thermal and mechanical analyses are discussed together with FLUKA evaluations of the radiation damages.Comment: 14th International Particle Accelerator Conference (IPAC'23

Determination of the moments of the proton charge density

A global analysis of proton electric form factor experimental data from Rosenbluth separation and low squared four-momentum transfer experiments is discussed for the evaluation of the spatial moments of the proton charge density based on the recently published integral method \cite{Hob20}. Specific attention is paid to the evaluation of the systematic errors of the method, particularly the sensitivity to the choice of the mathematical expression of the form factor fitting function. Within this comprehensive analysis of proton electric form factor data, the moments of the proton charge density are determined for integer order moments, particularly: $\langle r^2 \rangle$=0.682(02)$_{Sta.}$(11)$_{Sys.}$~fm$^2$, $\langle r^3 \rangle$=0.797(10)$_{Sta.}$(58)$_{Sys.}$~fm$^3$, and $\langle r^4 \rangle$=1.02(05)$_{Sta.}$(31)$_{Sys.}$~fm$^4$. This analysis leads to the proton charge radius 0.8459(12)$_{Sta.}$(76)$_{Sys.}$~fm once relativistic effects are taken into account.Comment: 10 pages, 3 figure