210 research outputs found
Timelike Compton scattering: exclusive photoproduction of lepton pairs
We investigate the exclusive photoproduction of a heavy timelike photon which
decays into a lepton pair, gamma p -> l+ l- p. This can be seen as the analog
of deeply virtual Compton scattering, and we argue that the two processes are
complementary for studying generalized parton distributions in the nucleon. In
an unpolarized experiment the angular distribution of the leptons readily
provides access to the real part of the Compton amplitude. We estimate the
possible size of this effect in kinematics where the Compton process should be
dominated by quark exchange.Comment: 31 pages, 17 figure
Hard Pomeron in exclusive meson production at ILC
We calculate the exclusive process gamma* gamma* ->rho rho at high energy.
The Born order estimate and the leading (LLA) and next to leading order (NLLA)
BFKL resummation effects show the feasibility of experimental detection in a
quite large range of Q2 values at future high energy e+e- linear colliders.Comment: 4 pages, Presented at Photon2005, International Conference on the
Structure and Interactions of the Photon, Warsaw 31.08-04.09.2005, by Samuel
Wallo
Revealing transversity GPDs through the photoproduction of a photon and a meson
Photoproduction of a pair of particles with large invariant mass is a natural
extension of collinear QCD factorization theorems which have been much studied
for deeply virtual Compton scattering and deeply virtual meson production. We
discuss the production of a photon and a meson, where the wide angle Compton
scattering on a meson subprocess factorizes from generalized parton
distribution. We calculate at dominant twist and leading order in ,
the production cross-section of a transversely polarized meson which is
sensitive to chiral-odd GPDs, and show that it may be measurable in near future
JLab experiments.Comment: 6 pages, 3 figures. Contribution to the proceedings of the 6th
International Conference on Physics Opportunities at an Electron-Ion Collider
(POETIC6), September 7-11, 2015, Palaiseau, France. The numerical plot
(fig.3) has been corrected. arXiv admin note: text overlap with
arXiv:1511.0437
Transversity GPD in photo- and electroproduction of two vector mesons
The chiral-odd generalized parton distribution (GPD), or transversity GPD, of
the nucleon can be accessed experimentally through the photo- or
electroproduction of two vector mesons on a polarized nucleon target,
\gamma^(*) N --> \rho_1 \rho_2 N', where \rho_1 is produced at large transverse
momentum, \rho_2 is transversely polarized, and the mesons are separated by a
large rapidity gap. We predict the cross section for this process for both
transverse and longitudinal \rho_{2} production. To this end we propose a model
for the transversity GPD H_T(x,\xi,t), and give an estimate of the relative
sizes of the transverse and longitudinal \rho_{2} cross sections. We show that
a dedicated experiment at high energy should be able to measure the
transversity content of the proton.Comment: 15 pages, 9 figures. Extended discussion of experimental prospects in
the conclusions. Version to appear in EPJ
Off-Forward Parton Distributions in 1+1 Dimensional QCD
We use two-dimensional QCD as a toy laboratory to study off-forward parton
distributions (OFPDs) in a covariant field theory. Exact expressions (to
leading order in ) are presented for OFPDs in this model and are
evaluated for some specific numerical examples. Special emphasis is put on
comparing the and regimes as well as on analyzing the
implications for the light-cone description of form factors.Comment: Revtex, 6 pages, 4 figure
Hadron Helicity Violation in Exclusive Processes: Quantitative Calculations in Leading Order QCD
We study a new mechanism for hadronic helicity flip in high energy hard
exclusive reactions. The mechanism proceeds in the limit of perfect chiral
symmetry, namely without any need to flip a quark helicity. The fundamental
feature of the new mechanism is the breaking of rotational symmetry of the hard
collision by a scattering plane in processes involving independent quark
scattering. We show that in the impulse approximation there is no evidence for
of the helicity violating process as the energy or momentum transfer is
increased over the region 1 GeV^2 < Q^2 < 100 GeV^2. In the asymptotic region
Q^2> 1000 GeV^2, a saddle point approximation with doubly logarithmic accuracy
yields suppression by a fraction of power of Q^2. ``Chirally--odd" exclusive
wave functions which carry non--zero orbital angular momentum and yet are
leading order in the high energy limit, play an important role.Comment: uuencoded LaTeX file (21 pages) and PostScript figure
The Proton Electromagnetic Form Factor and Quark Orbital Angular Momentum
We analyze the proton electromagnetic form factor ratio
as a function of momentum transfer
within perturbative QCD. We find that the prediction for at large
momentum transfer depends on the exclusive quark wave functions, which are
unknown. For a wide range of wave functions we find that $ QF_2/F_1 \sim\
const$ at large momentum transfer, in agreement with recent JLAB data.Comment: 8 pages, 2 figures. To appear in Proceedings of the Workshop QCD
2002, IIT Kanpur, 18-22 November (2002
Indication of asymptotic scaling in the reactions H, He and
It is shown that the differential cross sections of the reactions and measured at c.m.s.scattering angle
in the interval of the deuteron beam energy 0.5 - 1.2 GeV demonstrate the
scaling behaviour,, which follows from constituent
quark counting rules. It is found also that the differential cross section of
the elastic scattering at follows
the scaling regime at beam energies 0.5 - 5 GeV. These data are
parameterized here using the Reggeon exchange.Comment: 6 pages, Latex, 2 eps figures; final version accepted by Pis'ma v
ZHETF, corrected and completed reference
Femto-Photography of Protons to Nuclei with Deeply Virtual Compton Scattering
Developments in deeply virtual Compton scattering allow the direct
measurements of scattering amplitudes for exchange of a highly virtual photon
with fine spatial resolution. Real-space images of the target can be obtained
from this information. Spatial resolution is determined by the momentum
transfer rather than the wavelength of the detected photon. Quantum photographs
of the proton, nuclei, and other elementary particles with resolution on the
scale of a fraction of a femtometer is feasible with existing experimental
technology.Comment: To be published in Physical Review D. Replaces previous version with
minor changes in presentatio
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