The exclusive omega electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q2) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross sections were measured up to large values of the four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the interference terms sigma_TT and sigma_TL to the cross sections, as well as an analysis of the omega spin density matrix, indicate that helicity is not conserved in this process. The t-channel pi0 exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction gamma* p -> omega p, even for Q2 as large as 5 GeV2. Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross sections is nearly Q2-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.
Differential cross sections DSIG/DT for Q**2 = 2.371 GeV**2 and W = 1.85 GeV.
The reactionsπ−p→K0(890) Λ,K0(890)Σ0 andK0(890)Σ0 are studied at an incident momentum of 3.95 GeV/c using data from a high statistics bubble chamber experiment corresponding to ∼90 events/μb. The differential cross sections, density matrix elements of the vector meson and hyperon polarizations are presented. A transversity amplitude analysis is performed for each of the reactions. The results are compared with those obtained for the SU(3) related processesK−p→ϕΔ, ϕΣ0, ϕΣ0(1385) andϱ−Σ+(1385) and with predictions of the additive quark model and SU(6) sum rules.
No description provided.
We have studied photoproduction using a 1 m streamer chamber at DESY and a tagged photon beam with an energy range of 1.6 GeV < E γ < 6.3 GeV. We analysed approximately 30 000 events and report topological, channel and resonance production cross sections for a large number of reactions with three and five outgoing charged particles.
QUASI TWO-BODY REACTIONS ARE NOT INCLUDED IN THE OTHER CORRESPONDING REACTIONS.
The photoproduction of ρ0-mesons and Δ-baryons at photon energies up to 2.6 GeV has been studied with the SAPHIR detector at the electron stretcher ELSA. Total and differential cross-sections were obt
Differential cross section for elastic RHO0 photoproduction.
The reactionsΣvp→π+n,K+Λ,K+∑0 andΣvn→π+n were studied at invariant hadronic masses around 2.2. GeV forQ2=0.06, 0.28, 0.70, and 1.35 GeV2. The main results are: At small |t| the π+ production is dominated by longitudinally polarized photons and can be described by one pion exchange. At low |t| the transverse (π+n) cross section drops steeply withQ2, but remains roughly constant forQ2≧0.5 GeV2. For |t⊢≧0.8 GeV2, (π+n/dt) is almost independent ofQ2. The integrated cross section (π+n) shows a similarQ2-dependence asσtot (γvp) forQ2≧0.28 GeV2. The ratioσ(π-p)/σ(π+n) atQ2=0.70 and 1.35 GeV2 for |t|≧0.6 GeV2 is smaller than in photoproduction and close to 1/4. The ratioσ(K+∑0 decreases steeply withQ2 following roughly the predictions of the quark-parton model.
No description provided.
The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The reduced diffractive cross sections obtained from the LPS data as a function of X(NAME=POMERON) for Q**2 = 3.9 GeV**2 and ABS(T) = 0.19 to 0.55 GeV**2 for M(X) values of 3, 7, 15 and 30 GeV.
The reduced diffractive cross sections obtained from the LRG data as a function of X(NAME=POMERON) for Q**2 = 22 GeV**2 and M(X) values of 3, 6, 11, 19 and 32 GeV.
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