η Photoproduction on the Proton for Photon Energies From 0.75 to 1.95 GeV

Differential cross sections for γp→ηp have been measured with tagged real photons for incident photon energies from 0.75 to 1.95 GeV. Mesons were identified by missing mass reconstruction using kinematical information for protons scattered in the production process. The data provide the first extensive angular distribution measurements for the process above W = 1.75  GeV. Comparison with preliminary results from a constituent quark model support the suggestion that a third S11 resonance with mass ∼1.8  GeV couples to the ηN channel

Exclusive Electroproduction of ᵠ Mesons at 4.2 GeV

We studied the exclusive reaction ep → e\u27 p\u27 ᵠ using the ᵠ →K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of ᵠ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c Δ t below 2 fm. At c Δ t = 0.6 fm, we measure bɸ = 2.27 ± 0.42 GeV-2. The cross section dependence on W as W0.2 ±0.1 at Q2, 1.3 GeV2 was determined by comparison with ɸ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction

Corrected Article: Exclusive Electroproduction of ᵠ Mesons at 4.2 GeV [Physical. Rev. C 63, 065205, (2001)]

We studied the exclusive reaction ep → e\u27 p\u27 ᵠ using the ᵠ →K+K- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility. Our experiment covers the range in Q2 from 0.7 to 2.2 GeV2and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of ᵠ production on the proton. Our measurement shows the expected decrease of the t slope with the vector-meson formation time c Δ t below 2 fm. At c Δ t = 0.6 fm, we measure bɸ = 2.27 ± 0.42 GeV-2. The cross section dependence on W as W0.2 ±0.1 at Q2, 1.3 GeV2 was determined by comparison with ɸ production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction

Electroproduction of the Λ(1520) Hyperon

The reaction e→pe′K+Λ(1520) with Λ(1520)→p′K− was studied at electron beam energies of 4.05, 4.25, and 4.46 GeV, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The cos θK+, φK+, Q2, and W dependencies of Λ(1520) electroproduction are presented for the kinematic region 0.9 \u3c Q2 \u3c 2.4 GeV2 and 1.95 \u3c W \u3c 2.65 GeV. Also, the Q2 dependence of the Λ(1520) decay angular distribution is presented for the first time. The cosθK+ angular distributions suggest t-channel diagrams dominate the production process. Fits to the Λ(1520) t-channel helicity frame decay angular distributions indicate the mz = ± ½ parentage accounts for about 60% of the total yield, which suggests this reaction has a significant contribution from t-channel processes with either K+ exchange or longitudinal coupling to an exchanged K*. The Q2 dependence of the Λ(1520) production cross section is the same as that observed for Λ(1116) photo- and electroproduction

First Measurement of Transferred Polarization in the Exclusive \u3csup\u3e→\u3c/sup\u3ee p → e\u27K\u3csup\u3e+ →\u3c/sup\u3eΛ

The first measurements of the transferred polarization for the exclusive →ep → e\u27K+ →Λ over right arrow reaction have been performed at Jefferson Laboratory using the CLAS spectrometer. A 2.567 GeV beam was used to measure the hyperon polarization over Q2 from 0.3 to 1.5 (GeV/c)2, W from 1.6 to 2.15 GeV, and over the full K+ center-of-mass angular range. Comparison with predictions of hadrodynamic models indicates strong sensitivity to the underlying resonance contributions. A nonrelativistic quark-model interpretation of our data suggests that the s -s quark pair is produced with spins predominantly antialigned. Implications for the validity of the most widely used quark-pair creation operator are discussed

ep → ep π⁰ Reaction Studied in the Δ(1232) Mass Region Using Polarization Asymmetries

Measurements of the angular distributions of target and double-spin asymmetries for the Δ+(1232) in the exclusive channel → p(→e,e\u27p)π0 obtained at the Jefferson Lab in the Q2 range from 0.5 to 1.5 GeV2/c2 are presented. Results of the asymmetries are compared with the unitary isobar model [D. Drechsel , Nucl. Phys. A645, 145 (1999)], dynamical models [T. Sato and T. S. Lee, Phys. Rev. C 54, 2660 (1996); S. S. Kamalov , Phys. Lett. B 27, 522 (2001)], and the effective Lagrangian theory [R. M. Davidson , Phys. Rev. D 43, 71 (1991)]. Sensitivity to the different models was observed, particularly in relation to the description of background terms on which the target asymmetry depends significantly

Measurement of Inclusive Spin Structure Functions of the Deuteron

We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer [Q2 = 0.27-1.3 (GeV/c)2] and final hadronic state mass in the nucleon resonance region (W=1.08-2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target (15ND3) and detected the scattered electrons with the CEBAF large acceptance spectrometer. From our data, we extract the longitudinal double spin asymmetry A∥ and the spin structure function g1d. Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function g1d and study its approach to both the deep inelastic limit at large Q2 and to the Gerasimov-Drell-Hearn sum rule at the real photon limit (Q2→ 0). We find that the first moment varies rapidly in the Q2 range of our experiment and crosses zero at Q2 between 0.5 and 0.8 (GeV/c)2, indicating the importance of the Delta resonance at these momentum transfers

Search for the Photoexcitation of Exotic Mesons in the π+π+π- System

A search for exotic mesons in the π+π+π− system photoproduced by the charge exchange reaction γp→π+π+π−(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 JPC=1−+ resonant state in the 1 to 2 GeV mass range. Our partial wave analysis shows production of the a2(1320) and the π2(1670) mesons, but no evidence for the a1(1260) , nor the π1(1600) exotic state at the expected levels. An upper limit of 13.5 nb is determined for the exotic π1(1600) cross section, less than 2% of the a2(1320) production