The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

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The CEBAF large acceptance spectrometer (CLAS)

About 120 baryons and baryon resonances are known, from the abundant nucleon with $u$ and $d$ light-quark constituents up to the recently discovered $\Omega_b^-=bss$, and the $\Xi_b^-=bsd$ which contains one quark of each generation In spite of this impressively large number of states, the underlying mechanisms leading to the excitation spectrum are not yet understood Heavy-quark baryons suffer from a lack of known spin-parities In the light-quark sector, quark-model calculations have met with considerable success in explaining the low-mass excitations spectrum but some important aspects like the mass degeneracy of positive-parity and negative-parity baryon excitations are not yet satisfactorily understood At high masses, above 18 GeV, quark models predict a very high density of resonances per mass interval which is not observed In this review, issues are identified discriminating between different views of the resonance spectrum; prospects are discussed how open questions in baryon spectroscopy may find answers from photo- and electro-production experiments which are presently carried out in various laboratories

Baryon spectroscopy

Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.

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Properties of baryon resonances from a multichannel partial wave analysis

https://hadron.physics.fsu.edu/~skpark/document/arXiv_nucl-ex_0306023.pdf

Study of Non-Strange Baryon Resonances with Meson Photoproduction

Recent experimental and theoretical advances in investigating electromagnetic meson production reactions in the nucleon resonance region are reviewed. We give a description of current experimental facilities with electron and photon beams and present a unified derivation of most of the phenomenological approaches being used to extract the resonance parameters from the data. The analyses of π and η production data and the resulting transition form factors for the Δ(1232)P33, N(1535)S11, N(1440)P11, and N(1520)D13 resonances are discussed in detail. The status of our understanding of the reactions with production of two pions, kaons, and vector mesons is also reviewed.

Electromagnetic meson production in the nucleon resonance region

We present new Sigma beam asymmetry data for eta meson photoproduction on the proton, using a novel tagged, laser backscattered, linearly polarized photon beam up to 1.1 GeV. The data show large, positive asymmetries, at all incident photon energies. In addition to the S-11(1535) and D-13(1520) resonances necessary to reproduce the cross sections, P-13(1720) and D-15(1675) "four stars" resonances contribute to the Sigma observable, but cannot reproduce the strong forward asymmetries measured at energies higher than 900 MeV.

New Measurement of Σ Beam Asymmetry for η Meson Photoproduction on the Proton

The cross section for straight phi meson photoproduction on the proton has been measured for the first time up to a four-momentum transfer -t = 4 GeV2, using the CLAS detector at the Thomas Jefferson National Accelerator Facility. At low four-momentum transfer, the differential cross section is well described by Pomeron exchange. At large four-momentum transfer, above -t = 1.8 GeV2, the data support a model where the Pomeron is resolved into its simplest component, two gluons, which may couple to any quark in the proton and in the straight phi.

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Photoproduction of φ(1020) mesons on theproton at large momentum transfer

J. Ajaka,1 M. Anghinolfi,2 V. Bellini,3 G. Berrier,1 J. P. Bocquet,4 M. Breuer,5 P. M. Calvat,4 M. Capogni,5 L. E. Casano,5 M. Castoldi,2 L. Ciciani,5 P. Corvisiero,2 A. D’Angelo,5 J.-P. Didelez,1,* R. Di Salvo,1 Ch. Djalali,1 M. A. Duval,1 R. Frascaria,1 G. Gervino,6 F. Ghio,7 P. Girard,1 B. Girolami,7 E. Guinault,1 P. Hoffmann-Rothe,1 E. Hourany,1 I. Kilvington,8 V. Kouznetsov,9 A. Lapik,9 P. Levi Sandri,10 D. Moricciani,4 M. Morlet,1 V. Nedorezov,9 L. Nicoletti,5 C. Perrin,4 D. Rebreyend,4 F. Renard,4 M. Ripani,2 L. Rosier,1 P. Rossi,10 F. Roudot,5 T. Russew,4 M. Sanzone,2 C. Schaerf,5,† M. L. Sperduto,3 A. Sudov,9 M. Taiuti,2 A. Turinge,11 J. Van de Wiele,1 and A. Zucchiatti2 1IN2P3, Institut de Physique Nucleaire, 91406 Orsay, France 2INFN Genova and Universita di Genova, 16146, Italy 3 INFN Laboratori Nazionali del Sud and Universita di Catania, 95123, Italy 4IN2P3, Institut des Sciences Nucleaires, 38026 Grenoble, France 5INFN sezione di Roma 2 and Universita di Roma "Tor Vergata", 00133, Italy 6INFN sezione di Torino and Universita di Torino, 10125, Italy 7INFN sezione Sanita and Istituto Superiore di Sanita, Roma, 00161, Italy 8European Synchrotron Radiation Facility, 38026 Grenoble, France 9Institute for Nuclear Research, 117312 Moscow, Russia 10INFN Laboratori Nazionali di Frascati, 00044, Italy 11I. Kurchatov Institute of Atomic Energy, Moscow, Russia (Received 2 February 1998)

F. Roudot

Papers

New Measurement of Σ Beam Asymmetry for η Meson Photoproduction on the Proton

Photoproduction of φ(1020) mesons on theproton at large momentum transfer

New Measurement of S Beam Asymmetry for h Meson Photoproduction on the Proton