Progress on Neutron-Target Multipoles above 1 GeV

We report a new extraction of nucleon resonance couplings using pi- photoproduction cross sections on the neutron. The world database for the process gn-->pi-p above 1 GeV has quadrupled with the addition of new differential cross sections from the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab in Hall B. Differential cross sections from CLAS have been improved with a new final-state interaction determination using a diagrammatic technique taking into account the SAID phenomenological NN and piN final-state interaction amplitudes. Resonance couplings have been extracted and compared to previous determinations. With the addition of these new cross sections, significant changes are seen in the high-energy behavior of the SAID cross sections and amplitudes.Comment: 4 pages, 3 figures, 1 table; talk given at 12th International Workshop on Meson Production, Properties and Interaction (MESON2012), 31 May - 5 June 2012, Krakow, Poland; will be published online in European Journal Web of Conference

Energy Calibration of the JLab Bremsstrahlung Tagging System

In this report, we present the energy calibration of the Hall B bremsstrahlung tagging system at the Thomas Jefferson National Accelerator Facility. The calibration was performed using a magnetic pair spectrometer. The tagged photon energy spectrum was measured in coincidence with $e^+e^-$ pairs as a function of the pair spectrometer magnetic field. Taking advantage of the internal linearity of the pair spectrometer, the energy of the tagging system was calibrated at the level of $\pm 0.1$. The absolute energy scale was determined using the $e^+e^-$ rate measurements close to the end-point of the photon spectrum. The energy variations across the full tagging range were found to be $<3$ MeV.Comment: 15 pages, 12 figure

DVCS on spinless nuclear targets in impulse approximation

Within the impulse approximation, we derive expressions for the amplitude of deeply virtual Compton scattering on spinless nuclei in terms of the generalized parton distributions of the nucleon. As an application, nuclear effects in the beam-charge and single-spin asymmetries are discussed.Comment: 13 pages, 2 figures, Late

The Heavy Photon Search beamline and its performance

The Heavy Photon Search (HPS) is an experiment to search for a hidden sector photon, aka a heavy photon or dark photon, in fixed target electroproduction at the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment searches for the e$^+$e$^-$ decay of the heavy photon with bump hunt and detached vertex strategies using a compact, large acceptance forward spectrometer, consisting of a silicon microstrip detector (SVT) for tracking and vertexing, and a PbWO$_4$ electromagnetic calorimeter for energy measurement and fast triggering. To achieve large acceptance and good vertexing resolution, the first layer of silicon detectors is placed just 10 cm downstream of the target with the sensor edges only 500 $\mu$m above and below the beam. Placing the SVT in such close proximity to the beam puts stringent requirements on the beam profile and beam position stability. As part of an approved engineering run, HPS took data in 2015 and 2016 at 1.05 GeV and 2.3 GeV beam energies, respectively. This paper describes the beam line and its performance during that data taking

How to measure the parity of the Θ+\Theta^+ in p⃗p⃗\vec p\vec p collisions

Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which observables can be used to determine the parity of the $\Theta^+$ from the reaction $\vec p\vec p \to \Sigma^+\Theta^+$ near its production threshold. In particular, we show that the sign of the spin correlation coefficient $A_{xx}$ for small excess energies yields the negative of the parity of the $\Theta^+$. The argument relies solely on the Pauli principle and parity conservation and is therefore model--independent.Comment: References completed, discussion on possible influence of background added; conclusions unchange

Exotic baryon multiplets at large number of colours

We generalize the usual octet, decuplet and exotic antidecuplet and higher baryon multiplets to any number of colours Nc. We show that the multiplets fall into a sequence of bands with O(1/Nc) splittings inside the band and O(1)splittings between the bands characterized by "exoticness", that is the number of extra quark-antiquark pairs needed to compose the multiplet. Each time one adds a pair the baryon mass is increased by the same constant which can be interpreted as a mass of a quark-antiquark pair. At the same time, we prove that masses of exotic rotational multiplets are reliably determined at large Nc from collective quantization of chiral solitons.Comment: 13 p., 5 figs. New section and references adde

Spectrum of the Y=2 Pentaquarks

By assuming a mass formula for the spectrum of the Y=2 pentaquarks, where the chromo-magnetic interaction plays a main role, and identifying the lightest state with the Theta^+(1540), we predict a spectrum in good agreement with the few I=0 and I=1 candidates proposed in the past.Comment: 12 pages, 4 figures, LaTe

The Chiral Soliton Model for Arbitrary Colors and Flavors

The quantum numbers of the chiral soliton are derived for an arbitrary number of colors and flavors

Probing the nucleon structure with CLAS

An overview of recent results with CLAS is presented with emphasis on nucleon resonance studies, nucleon spin structure, and generalized parton distributions.Comment: Plenary talk presented at NSTAR 2007, Bonn, German