[en] In this note the author briefly outlines progress on the design of a ring imaging Cerenkov detector (RICH) utilizing a silica aerogel radiator for integration into the CLAS detector. This detector is used to augment particle identification in the CLAS detector when operating with higher energy electron beams. At increased JLAB energy there is a need for additional particle identification beyond the current CLAS capability. In particular, the separation of kaons from pions using ordinary time of flight becomes less useful for momenta much greater than 2 GeV/c, whereas for an incident energy of 10 GeV the momentum of produced kaons within the CLAS acceptance is greater than 6 GeV/c. In order to achieve this separation two types of Cerenkov techniques, threshold and ring imaging (RICH), have been commonly applied. Recently, there have been technological developments which have simplified the technology of RICH detectors and opened up the potential for their more common use. First, the quality of silica aerogel has been improved in the light transparency and index of refraction (n) variability so that they have been shown to be useful Cerenkov Radiators. Second, techniques for detecting the rings of Cerenkov light with good resolution are being developed

[en] Recently there hae been promising developments in bridging the high and low Q² extremes with a QCD quark-parton description of exclusive reactions. In this approach the perturbative hard part of the reaction, which is calculable, is isolated from the non-perturbative soft, physics which is parameterized in terms of off-forward parton distributions (OFPD), generically illustrated in a figure. An attractive aspect of this is that the same OFPD's are common to different exclusive reactions which involve the same set of hadrons. In the limit of forward scattering it is shown that the OFPD become the usual inclusive parton distribution functions, as illustrated for the case of virtual Compton scattering in a figure. A figure illustrates how they are related specifically to baryon elastic and transition form factors, which is the subject of this article

[en] A fundamental issue in hadron physics is which degrees of freedom are appropriate to describe exclusive reactions at experimentally accessible momentum transfers, and how are models at low, medium and high Q² related? Constituent quark models (CQM) appear to work well at the low Q² limit, and it is widely believed that valance pQCD will be valid in the limit of high Q². How far the validity of these models extend in Q² is still an open question. Many exclusive reactions exhibit constituent scaling behavior at moderate Q² ( few GeV²/c²) which is interpreted by some [1] as the onset of perturbative QCD. Others [2] argue that the observed scaling is not a manifestation of pQCD, and that at the experimentally accessible range of Q² exclusive reactions are explained primarily by soft Feynman mechanism. Recently[3][4], there have been promising developments in bridging the high and low Q² extremes for exclusive reactions in terms of a quark-parton description of exclusive reactions In this approach the perturbative hard part of the reaction, which is calculable, is isolated from the non-perturbative soft, physics which is parameterized in terms of non-forward parton distributions (NFPD). These NFPD's are generalizations of the usual parton non-spin and spin distribution functions obtained in unpolarized and polarized deep inelastic inclusive scattering, and in fact reduce to them in the limit of forward scattering. An attractive aspect of this approach is that the same NFPD can be carried over to a variety of exclusive reactions which involve the same set of hadrons, and can be constrained in a number of different experiments which are discussed in these proceedings

[en] In this note, I will briefly outline the rationale for a program of measurement of baryon transition form factors in Hall C as support for the construction of a new high quality spectrometer

[en] We review the current experimental situation of pentaquark searches, and second generation experiments, with emphasis on the Jefferson Lab program

[en] We review the latest results from experiments dedicated to pentaquark searches carried out at the Jefferson Lab with the CLAS detector

[en] Deeply virtual Compton scattering, cross sections and asymmetries for the pi⁰ and eta exclusive electroproduction in a very wide kinematic range of Q², t and x_B have been measured with CLAS (Jlab). Initial analyzes already are showing remarkable results. These data will help us to better understand the transition from soft to hard mechanisms

[en] We review the current experimental situation of pentaquark searches, and second generation experiments, with emphasis on the Jefferson Lab program

[en] 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 S₁₁(1535) via the reactions p(e,e^'p)pi⁰ and p(e,e^'p)eta respectively at Q² ∼ 2.8 and 4 GeV²/c² is described, and the state of analysis reported

[en] The reaction γp → π⁺ K^- K⁺n was studied at Jefferson Lab using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S = +1 and mass M = 1555 ± 10 MeV/c² was observed in the nK⁺ invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM = 26 MeV/c²), and its statistical significance is 7.8 ± 1.0 σ. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by a chiral soliton model for the Θ⁺ baryon. In addition, the pK⁺ invariant mass distribution was analyzed in the reaction γ p → K^- K⁺p with high statistics in search of doubly-charged exotic baryon states. No resonance structures were found in this spectrum