25 research outputs found
Diffractive charged meson pair production
We investigate the possibility to measure the nonforward gluon distribution
function by means of diffractively produced \pi^+\pi^- and K^+K^- pairs in
polarized lepton nucleon scattering. The resulting cross sections are small and
are dominated by the gluonic contribution. We find relatively large spin
asymmetries, both for \pi^+\pi^- and for K^+K^- pairs.Comment: 15 pages, version with changed kinematical cuts, to be pubished in
Phys.Lett.
pair hard electroproduction and exotic hybrid mesons
We show that hard electroproduction is a promising way to study exotic hybrid
mesons, in particular through the hybrid decay channel . We
discuss the generalized distribution amplitude, calculate the
production amplitude and propose a forward-backward asymmetry as a signal for
the hybrid meson production.Comment: 4 pages, 1 figure, presented by I.V. Anikin at Xth International
Conference "BARYONS'04", Palaiseau, Franc
Neutrino induced hard exclusive D_s production
Motivated by the possibility to use high intensity neutrino beams for
neutrino-nucleon scattering experiments we analyze charged current induced
exclusive meson production within the framework of generalized parton
distributions. The cross section for hard exclusive D_s production is estimated
in this formalism to leading order in QCD. The integrated cross section proves
to be sizable. It is shown that the considered process is well suited to
provide novel information on the gluon structure of nucleons, which is
contained in the generalized gluon parton distribution.Comment: 7 pages; modified plots in Fig. 3; accepted for publication in Phys.
Lett.
Hunting the QCD-Odderon in hard diffractive electroproduction of two pions
Charge asymmetries in diffractive electroproduction of two mesons are
proportional to the interference of Pomeron and Odderon exchange amplitudes. We
calculate in the framework of QCD and in the Born approximation a
forward-backward charge asymmetry which turns out to be sizable in a
kinematical domain accessible to HERA experiments. We predict a distinctive
dependence of this asymmetry on the invariant mass of the two pions. Testing
this prediction is a crucial step in the discovery of the QCD-Odderon.Comment: 13 pages LATEX, 6 .eps figures, numerical error corrected, new
figures,main conclusions not change
Probing generalized parton distributions in pi N -> l+ l- N
We study the exclusive reactions pi- p -> l+ l- n and pi+ n -> l+ l- p$ in
view of possible future experiments with high-intensity pion beams. For large
invariant mass of the lepton pair l+ l- and small squared momentum transfer to
the nucleon these are hard-scattering processes providing access to generalized
parton distributions. We estimate the cross section for these reactions,
explore their connection with the pion form factor, and discuss the role they
can play in improving our understanding of the relevant reaction mechanisms.Comment: 13 pages, 5 figure
Physics at the front-end of a neutrino factory: a quantitative appraisal
We present a quantitative appraisal of the physics potential for neutrino
experiments at the front-end of a muon storage ring. We estimate the forseeable
accuracy in the determination of several interesting observables, and explore
the consequences of these measurements. We discuss the extraction of individual
quark and antiquark densities from polarized and unpolarized deep-inelastic
scattering. In particular we study the implications for the undertanding of the
nucleon spin structure. We assess the determination of alpha_s from scaling
violation of structure functions, and from sum rules, and the determination of
sin^2(theta_W) from elastic nu-e and deep-inelastic nu-p scattering. We then
consider the production of charmed hadrons, and the measurement of their
absolute branching ratios. We study the polarization of Lambda baryons produced
in the current and target fragmentation regions. Finally, we discuss the
sensitivity to physics beyond the Standard Model.Comment: 73+1 pages, 33 figs. Report of the nuDIS Working Group for the
ECFA-CERN Neutrino-Factory study, M.L. Mangano (convener
Partonic structure of pi and rho mesons from data on hard (semi)exclusive production of two pions off nucleon
We fitted the pi-pi mass distribution in the range 0.5 < mpipi < 1.1 GeV
measured in hard exclusive positron-proton reactions at HERA by the form
dictated by QCD at leading twist level. Extracted parameters are related to
valence quark distribution in the pion, and to the pion and rho meson
distribution amplitudes. We obtain, for the first time, a measurement of the
second Gegenbauer coefficient of the rho meson distribution amplitude:
for a photon virtuality of =21.2 GeV^2.Comment: 12 pages, two figures. References and discussion are adde
Current in the light-front Bethe-Salpeter formalism II: Applications
We pursue applications of the light-front reduction of current matrix
elements in the Bethe-Salpeter formalism. The normalization of the reduced wave
function is derived from the covariant framework and related to non-valence
probabilities using familiar Fock space projection operators. Using a simple
model, we obtain expressions for generalized parton distributions that are
continuous. The non-vanishing of these distributions at the crossover between
kinematic regimes (where the plus component of the struck quark's momentum is
equal to the plus component of the momentum transfer) is tied to higher Fock
components. Moreover continuity holds due to relations between Fock components
at vanishing plus momentum. Lastly we apply the light-front reduction to
time-like form factors and derive expressions for the generalized distribution
amplitudes in this model.Comment: 12 pages, 6 figures, RevTex