21 research outputs found
Photoproduction of a \pi \rho Pair and Transversity GPDs
We demonstrate that the chiral-odd transversity generalized parton
distributions (GPDs) of the nucleon can be accessed through the exclusive
photoproduction process gamma + N -> pi + rho + N', in the kinematics where the
meson pair has a large invariant mass and the final nucleon has a small
transverse momentum, provided the vector meson is produced in a transversely
polarized state. We calculate perturbatively the scattering amplitude at
leading order in alpha_s: We build a simple model for the dominant transversity
GPD HT (x; chi; t) based on the concept of double distribution. Counting rates
estimates show that the experiment looks feasible with the real photon beam
characteristics expected at JLab@12 GeV, in low Q2 leptoproduction at Jlab@12
GeV and in the COMPASS experiment.Comment: Latex, 7 pages, 4 .eps figs, Invited talk at the 4th Workshop on
Exclusive Reactions at High Momentum Transfer May 18-21, 2010 Thomas
Jefferson National Accelerator Facility, Newport News, Virginia US
On chiral-odd Generalized Parton Distributions
While the chiral-even content of the nucleon is better and better studied,
the chiral-odd transversity generalized parton distributions (GPDs) remain
almost unknown. These GPDs can be accessed experimentally through the exclusive
photoproduction process gamma + N -> pi + rho + N', in the kinematics where the
meson pair has a large invariant mass and the final nucleon has a small
transverse momentum, provided the vector meson is produced in a transversally
polarized state. We calculate perturbatively the scattering amplitude at
leading order in alpha_s. We build a simple model for the dominant transversity
GPD H_T(x,xi,t) based on the concept of double distribution. We estimate the
unpolarized differential cross section for this process in the kinematics of
the Jlab and COMPASS experiments. Counting rates show that the experiment looks
feasible with the real and quasi real photon beam characteristics expected at
JLab@12 GeV, and with the quasi real photon beam in the COMPASS experiment.Comment: 5 pages, to appear in the proceedings of 35th International
Conference on High Energy Physics, (ICHEP 2010), Paris, France, July 22-28,
201
Chiral-odd transversity GPDs from a leading twist hard amplitude
The chiral-odd transversity generalized parton distributions (GPDs) of the
nucleon can be accessed experimentally through the exclusive photoproduction
process gamma + N -> pi + rho + N', in the kinematics where the meson pair has
a large invariant mass and the final nucleon has a small transverse momentum,
provided the vector meson is produced in a transversally polarized state. We
calculate perturbatively the scattering amplitude at leading order in alpha_s.
We build a simple model for the dominant transversity GPD H_T(x,xi,t) based on
the concept of double distribution. We estimate the unpolarized differential
cross section for this process in the kinematics of the Jlab and COMPASS
experiments. Counting rates show that the experiment looks feasible with the
real photon beam characteristics expected at JLab@12 GeV, and with the quasi
real photon beam in the COMPASS experiment.Comment: 5 pages, to appear in the proceedings of 18th International Workshop
on Deep-Inelastic Scattering and Related Subjects (DIS 2010), Florence,
Italy, 19-23 Apr 201
Probing photon structure in DVCS on a photon target
The factorization of the amplitude for the deeply virtual Compton scattering
(DVCS) process gamma*(Q) gamma -> gamma gamma at high Q2 is demonstrated in two
distinct kinematical domains, allowing to define the photon generalized parton
distributions and the diphoton generalized distribution amplitudes. Both these
quantities exhibit an anomalous scaling behaviour and obey new inhomogeneous
QCD evolution equations.Comment: 3 pages, 1 figure, to be published in the proceedings of the PANIC
2008 conference, Eilat (Israel), November 200
New ways to access the transverse spin content of the nucleon
We first describe a new way to access the chiral odd transversity parton
distribution in the proton through the photoproduction of lepton pairs. The
basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan
amplitudes with the amplitude of a process, where the photon couples to quarks
through its chiral-odd distribution amplitude, which is normalized to the
magnetic susceptibility of the QCD vacuum. We also show how the chiral-odd
transversity generalized parton distributions (GPDs) of the nucleon can be
accessed experimentally through the exclusive electro - or photoproduction
process of a meson pair with a large invariant mass and when the final nucleon
has a small transverse momentum. We calculate perturbatively the scattering
amplitude at leading order, both in the high energy domain which may be
accessed in electron-ion colliders and in the medium energy range. Estimated
rates are encouraging.Comment: 6 pages, Proceedings of Spin 2010, 19th International Spin Physics
Symposium September 27 - October 2, 2010, J\"ulich, German
Diphoton Generalized Distribution Amplitudes
We calculate the leading order diphoton generalized distribution amplitude by
calculating the amplitude of the process gamma* gamma -> gamma gamma in the low
energy and high photon virtuality region at the Born order and in the leading
logarithmic approximation. As in the case of the anomalous photon structure
functions, the gamma gamma generalized distribution amplitude exhibits a
characteristic \ln Q^2 behaviour and obeys inhomogeneous evolution equations.Comment: 15 pages, 5 figure
Two Photon Distribution Amplitudes
The factorization of the amplitude of the process gamma* gamma -> gamma gamma
in the low energy and high photon virtuality region is demonstrated at the Born
order and in the leading logarithmic approximation. The leading order two
photon (generalized) distribution amplitudes exhibit a characteristic ln Q2
behaviour and obey new inhomogeneous evolution equations.Comment: to be published in the proceedings of the workshop HLPW08, Spa, March
6-8, 2008, AIP conference proceedings serie
Generalized Parton Distributions of the Photon
We present a first calculation of the generalized parton distributions of the
photon(both polarized and unpolarized) using overlaps of light-front wave
functions at leading order in \alpha and zeroth order in \alpha_s; for non-zero
transverse momentum transfer and zero skewness. We present the novel parton
content of the photon in transverse position space.Comment: Numerical analysis repeated at a higher scale, discussions slightly
modifie
Tensor form factors of nucleon in QCD
We extract the isovector tensor nucleon form factors, which play an important
role in understanding the transverse spin structure of the nucleon when related
to the quark helicity-flip generalized parton distributions via their first
moments. We employ the light-cone QCD sum rules to leading order in QCD and
include distribution amplitudes up to twist 6 in order to calculate the three
tensor form factors , and . Our results agree well with
those from other approaches in the low and high momentum-transfer regions.Comment: 8 pages, 1 figure; minor changes, matches journal versio