559 research outputs found
A fitter code for Deep Virtual Compton Scattering and Generalized Parton Distributions
We have developped a fitting code based on the leading-twist handbag Deep
Virtual Compton Scattering (DVCS) amplitude in order to extract the Generalized
Parton Distributions (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 part of these observables are measured,
valuable information can still be extracted, 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 GPD Compton Form
Factors.Comment: 15 pages, 8 figure
Understanding 6He induced reactions at energies around the Coulomb barrier
Recent developments aimed to understand the observed features arising in the scattering
of the Borromean nucleus 6He on heavy targets are discussed and compared with recent data for
6He+208Pb measured at the RIB facility at Louvain-la-Neuve at energies around the Coulomb barrier.
The analysis of the elastic scattering data in terms of the optical model, reveals the presence of
a long range absorption mechanism, that manifests in the form of a large value of the imaginary diffuseness
parameter. The elastic data have been also compared with threeâbody CDCC calculations,
based on a di-neutron model of 6He, and fourâbody CDCC calculations, based on a more realistic
three-body model of this nucleus. Finally, the angular and energy distribution of a particles emitted
at backward angles are discussed and compared with different theoretical approaches.We find that
these a particles are produced mainly by a two-neutron transfer mechanism to very excited states
in the residual nucleus
A Search for Sigma^0_5, N^0_5 and Theta^++ Pentaquark States
A high-resolution (sigma_instr. = 1.5 MeV) search for narrow states (Gamma <
10 MeV) with masses of M_x approx 1500-1850 MeV in ep -> e'K^+ X, e'K^- X and
e' pi^+ X electroproduction at small angles and low Q^2 was performed. These
states would be candidate partner states of the reported Theta^+(1540)
pentaquark. No statistically significant signal was observed in any of the
channels at 90% C.L. Upper limits on forward production were determined to be
between 0.7% and 4.2% of the Lambda(1520) production cross section, depending
on the channel and the assumed mass and width of the state.Comment: 5 pages, 5 figures, to appear in Phys. Rev. C, update with responses
to referee suggestion
Production of highly-polarized positrons using polarized electrons at MeV energies
The Polarized Electrons for Polarized Positrons experiment at the injector of
the Continuous Electron Beam Accelerator Facility has demonstrated for the
first time the efficient transfer of polarization from electrons to positrons
produced by the polarized bremsstrahlung radiation induced by a polarized
electron beam in a high- target. Positron polarization up to 82\% have been
measured for an initial electron beam momentum of 8.19~MeV/, limited only by
the electron beam polarization. This technique extends polarized positron
capabilities from GeV to MeV electron beams, and opens access to polarized
positron beam physics to a wide community.Comment: 5 pages, 4 figure
Dynamic studies of 11Li and its core 9Li on 208Pb near the Coulomb barrier
We measured the scattering of the halo nucleus 11Li and its core 9Li on the lead target at TRIUMF at energies below and around to the Coulomb barrier. We report here on our preliminary analysis of the inclusive breakup reaction
Deeply Virtual Compton Scattering off the neutron
The present experiment exploits the interference between the Deeply Virtual
Compton Scattering (DVCS) and the Bethe-Heitler processes to extract the
imaginary part of DVCS amplitudes on the neutron and on the deuteron from the
helicity-dependent D cross section measured at =1.9
GeV and =0.36. We extract a linear combination of generalized parton
distributions (GPDs) particularly sensitive to , the least constrained
GPD. A model dependent constraint on the contribution of the up and down quarks
to the nucleon spin is deduced.Comment: Published in Phys. Rev. Let
The E00-110 experiment in Jefferson Lab's Hall A: Deeply Virtual Compton Scattering off the Proton at 6 GeV
We present final results on the photon electroproduction
() cross section in the deeply virtual Compton
scattering (DVCS) regime and the valence quark region from Jefferson Lab
experiment E00-110. Results from an analysis of a subset of these data were
published before, but the analysis has been improved which is described here at
length, together with details on the experimental setup. Furthermore,
additional data have been analyzed resulting in photon electroproduction cross
sections at new kinematic settings, for a total of 588 experimental bins.
Results of the - and -dependences of both the helicity-dependent and
helicity-independent cross sections are discussed. The -dependence
illustrates the dominance of the twist-2 handbag amplitude in the kinematics of
the experiment, as previously noted. Thanks to the excellent accuracy of this
high luminosity experiment, it becomes clear that the unpolarized cross section
shows a significant deviation from the Bethe-Heitler process in our kinematics,
compatible with a large contribution from the leading twist-2 DVCS term to
the photon electroproduction cross section. The necessity to include
higher-twist corrections in order to fully reproduce the shape of the data is
also discussed. The DVCS cross sections in this paper represent the final set
of experimental results from E00-110, superseding the previous publication.Comment: 48 pages, 32 figure
Scattering of 11 Be around the Coulomb barrier
Preliminary results on the 11Be+120Sn quasielastic scattering as well as the 11Be â 10Be +
n breakup channel are presented in this work. The angular distributions of these channels were
measured at REX-ISOLDE-CERN. The accuracy and angular range of the presented results provide
stronger constrains to the theoretical interpretation than existing published results. We compare
these new data with coupled-channel (CC) and continuum-discretized coupled-channel (CDCC)
calculations. The role played by transfer and breakup channels in the elastic scattering is discussed.CICYT FPA2007- 62170MEC FINURA (FPA2007-63074) CPAN (CSD 2007-00042)DGICYT FPA2006-13807-c02-01 CSD-2007-0004
- âŠ