Exclusive Photoproduction of the Cascade (Xi) Hyperons

We report on the first measurement of exclusive Xi-(1321) hyperon photoproduction in gamma p --> K+ K+ Xi- for 3.2 < E(gamma) < 3.9 GeV. The final state is identified by the missing mass in p(gamma,K+ K+)X measured with the CLAS detector at Jefferson Laboratory. We have detected a significant number of the ground-state Xi-(1321)1/2+, and have estimated the total cross section for its production. We have also observed the first excited state Xi-(1530)3/2+. Photoproduction provides a copious source of Xi's. We discuss the possibilities of a search for the recently proposed Xi5-- and Xi5+ pentaquarks.Comment: submitted to Phys. Rev.

Survey of A_LT' Asymmetries in Semi-Exclusive Electron Scattering on 4He and 12C

Single spin azimuthal asymmetries A(LT') were measured at Jefferson Lab using 2.2 and 4.4 GeV longitudinally polarised electrons incident on He-4 and C-12 targets in the CLAS detector. ALT' is related to the imaginary part of the longitudinal-transverse interference and in quasifree nucleon knockout it provides an unambiguous signature for final state interactions (FSI). Experimental values of ALT' were found to be below 5 %, typically \A(LT')\ less than or equal to 3 % for data with good statistical precision. Optical model in eikonal approximation (OMEA) and relativistic multiple-scattering Glauber approximation (RMSGA) calculations are shown to be consistent with the measured asymmetries. (C) 2004 Elsevier B.V. All rights reserved

Exclusive Rho0 Meson Electroproduction from Hydrogen at CLAS

The longitudinal and transverse components of the cross section for the ep --> e' prho(0) reaction were measured in Hall B at Jefferson Laboratory using the CLAS detector. The data were taken with a 4.247 GeV electron beam and were analyzed in a range of x(B) from 0.2 to 0.6 and of Q(2) from 1.5 to 3.0 GeV2. The data are compared to a Regge model based on effective hadronic degrees of freedom and to a calculation based on Generalized Parton Distributions. It is found that, at our lowest x(B) values, the transverse part of the cross section is well described by the former approach while the longitudinal part can be reproduced by the latter

Onset of Asymptotic Scaling in Deuteron Photodisintegration

We investigate the transition from the nucleon-meson to the quark-gluon description of the strong interaction using the photon energy dependence of the d(gamma,p)n differential cross section for photon energies above 0.5 GeV and center-of-mass proton angles between 30degrees and 150degrees. A possible signature for this transition is the onset of cross-section s(-11) scaling with the total energy squared, s, at some proton transverse momentum P-T. The results show that the scaling has been reached for proton transverse momentum above about 1.1 GeV/c. This may indicate that the quark-gluon regime is reached above this momentum

Measurement of two- and three-nucleon short-range correlation probabilities in nuclei

The ratios of inclusive electron scattering cross sections of 4He, 12C, and 56Fe to 3He have been measured at 1 \u3c xB \u3c. At Q2 \u3e 1.4 GeV2, the ratios exhibit two separate plateaus, at 1.5 \u3c xB \u3c 2 and at xB \u3e 2.25. This pattern is predicted by models that include 2- and 3-nucleon short-range correlations (SRC). Relative to A = 3, the per-nucleon probabilities of 3-nucleon SRC are 2.3, 3.1, and 4.4 times larger for A = 4, 12, and 56. This is the first measurement of 3-nucleon SRC probabilities in nuclei

Measurement of semi-inclusive pi+ electroproduction off the proton

Semi-inclusive pi(+) electroproduction on protons has been measured with the CLAS detector at Jefferson Lab. The measurement was performed on a liquid-hydrogen target using a 5.75 GeV electron beam. The complete five-fold differential cross sections were measured over a wide kinematic range including the complete range of azimuthal angles between hadronic and leptonic planes, phi, enabling us to separate the phi-dependent terms. Our measurements of the phi-independent term of the cross section at low Bjorken x were found to be in fairly good agreement with pQCD calculations. Indeed, the conventional current fragmentation calculation can account for almost all of the observed cross section, even at small pi(+) momentum. The measured center-of-momentum spectra are in qualitative agreement with high-energy data, which suggests a surprising numerical similarity between the spectator diquark fragmentation in the present reaction and the antiquark fragmentation measured in e(+)e(-) collisions. We have observed that the two phi-dependent terms of the cross section are small. Within our precision the cos2 phi term is compatible with zero, except for the low-z region, and the measured cos phi term is much smaller in magnitude than the sum of the Cahn and Berger effects

SEPARATED STRUCTURE FUNCTIONS FOR THE EXCLUSIVE ELECTROPRODUCTION OF K+ LAMBDA AND K+ SIGMA0 FINAL STATES

We report measurements of the exclusive electroproduction of K+Lambda and K+Sigma(0) final states from a proton target using the Continuous Electron Beam Accelerator Facility (CEBAF) large-acceptance spectrometer (CLAS) detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions sigma(T),sigma(L),sigma(TT), and sigma(LT) were extracted from the Phi- and epsilon-dependent differential cross sections taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis represents the first sigma(L)/sigma(T) separation with the CLAS detector, and the first measurement of the kaon electroproduction structure functions away from parallel kinematics. The data span a broad range of momentum transfers from 0.5 <= Q(2) <= 2.8 GeV2 and invariant energy from 1.6 <= W <= 2.4 GeV, while spanning nearly the full center-of-mass angular range of the kaon. The separated structure functions reveal clear differences between the production dynamics for the Lambda and Sigma(0) hyperons. These results provide an unprecedented data sample with which to constrain current and future models for the associated production of strangeness, which will allow for a better understanding of the underlying resonant and nonresonant contributions to hyperon production