Physics

... CT 06824 18 Florida State University, Tallahassee, Florida 32306 19 Rice University, Houston, Texas 77005-1892 20 Edinburgh University, Edinburgh EH9 3JZ, United Kingdom 21 Universidad Te´cnica Federico Santa Mar´ıa, Casilla 110-V, Valpara´ıso, Chile 22 University of ...

The differential cross section for the process p(e,e ′ p)η has been measured at Q 2 =2.4 and 3.6 (GeV/c) 2 at center-of-mass energies encompassing the S 11 (1535) resonance. The latter point is the highest-Q 2 exclusive measurement of this process to date. The resonance ...

We studied the electroproduction of the Δ(1232) resonance via the reaction p(e,e ′ p)π 0 at four-momentum transfers Q 2 = 2.8 and 4.0 GeV 2 . This is the highest Q 2 for which exclusive resonance electroproduction has ever been observed. Decay angular distributions for ...

A search for exotic mesons in the pi;{+}pi;{+}pi;{-} system photoproduced by the charge exchange reaction gammap-->pi;{+}pi;{+}pi;{-}(n) was carried out by the CLAS Collaboration at Jefferson Lab. A tagged-photon beam with energies in the 4.8 to 5.4 GeV range, produced through bremsstrahlung from a 5.744 GeV electron beam, was incident on a liquid-hydrogen target. A partial wave analysis was performed on a sample of 83 000 events, the highest such statistics to date in this reaction at these energies. The main objective of this study was to look for the photoproduction of an exotic J;{PC}=1;{-+} resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a_{2}(1320) and the pi_{2}(1670) mesons, but no evidence for the a_{1}(1260), nor the pi_{1}(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic pi_{1}(1600) cross section, less than 2% of the a_{2}(1320) production.

We have measured the 3He(e,e' pp)n reaction at an incident energy of 4.7 GeV over a wide kinematic range. We identified spectator correlated pp and pn nucleon pairs by using kinematic cuts and measured their relative and total momentum distributions. This is the first measurement of the ratio of pp to pn pairs as a function of pair total momentum p(tot). For pair relative momenta between 0.3 and 0.5  GeV/c, the ratio is very small at low p(tot) and rises to approximately 0.5 at large p(tot). This shows the dominance of tensor over central correlations at this relative momentum.

The reaction gammap --> pK+K- was studied at Jefferson Lab with photon energies from 1.8 to 3.8 GeV using a tagged photon beam. The goal was to search for a Theta++ pentaquark, a narrow, doubly charged baryon state having strangeness S=+1 and isospin I=1, in the pK+ invariant mass spectrum. No statistically significant evidence of a Theta++ was found. Upper limits on the total and differential cross section for the reaction gammap --> K-Theta++ were obtained in the mass range from 1.5 to 2.0 GeV/c2, with an upper limit for a narrow resonance with a mass M(Theta++) = 1.54 GeV/c2 of about 0.15 nb, 95% C.L.. This result places a stringent upper limit on the Theta++ width Gamma(Theta++) <0.1 MeV/c2.

The role of resonance electroproduction at high Q² is discussed in the context of exclusive reactions, as well as the alternative theoretical models which are proposed to treat exclusive reactions in the few GeV²/c² region of momentum transfer. Jefferson Lab experiment 94-014, which measured the excitation of the Delta (1232) and Sââ(1535) via the reactions p(e,e{sup '}p)pi° and p(e,e{sup '}p)eta

The first measurements of the differential cross section from d(gamma,p)n up to 4.0 GeV were performed at the Thomas Jefferson National Accelerator Facility (TJNAF, formerly CEBAF). Bremsstrahlung photons from electron beam impinging on a copper radiator and a liquid deuterium target were employed for this experiment. The experiment was performed in Hall C where the photoprotons at forward angles in

... Jackson, С. Keppel, К. Kino, L, Kramer, D. Koltenuk, S. Кох, T. Leone, G. Lolos, AF Lung, D. Mack, M. Maeda, R. Madey, С J. Mart off. S. Majewski, D. Meekins, A. Mihul, H. Mkrtchyan, RM Mohriug, S. Mtingwa, G. Niculescu, I. Niculescu, S. Ole, R. Ferrino, D. Potterveld. ...

We report measurements of cross sections for the reaction {sup 1}H(e,e{prime} K{sup +})Y, for both the {Lambda} and {Sigma}{sup 0} hyperon states, at an invariant mass of W = 1.84 GeV and four-momentum transfers 0.5 < Q{sup 2} < 2 (GeV/c){sup 2}. Data were taken for three ...

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels gamma[over -->]p-->pi(+)pi(0)n, gamma[over -->]p-->pi(0)pi(0)p, and gamma[over -->]p-->pi(+)pi(-)p. The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of pi(0) mesons were detected in a 4pi electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.

The A(e,eK+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q² approx. 0.35 GeV² at a beam energy of 3.245 GeV for 1H,3He and 4He targets. Evidence for Lambda-hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed.

The first measurements of differential cross sections for deuteron photo-disintegration at photon energies up to 4 GeV were performed at the Thomas Jefferson National Accelerator Facility early in 1996. Cross section results for at proton center of mass angle of 35°, 53° and 90° will ...