Electroproduction of theS11(1535)resonance at high momentum transfer

Abstract

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-ofmass energies encompassing the S11(1535) resonance. The latter point is the highest-Q 2 exclusive measurement of this process to date. The resonance width and the helicity-1/2 transition amplitude are extracted from the data, and evidence for the possible onset of scaling in this reaction is shown. A lower bound of ≈ 0.45 is placed on the S11(1535) → p η branching fraction.

Near Threshold electroproduction of the Omega Meson at Momentum Transfer Q²=0.5 (GeV/c)²

“…Armstrong Ph.D. thesis (Armstrong, 1998) that relied on the results of Wasson et al extensively discussed in papers (Makins, 1994;Wasson, Ent, Makins et al, 1998). There are two aspects of introducing radiative processes in the Monte Carlo simulation apart from the approach adopted in calculating their effects.…”

“…The uncertainty due the random subtraction was estimated by comparing results for different coincidence time cuts used in determining the fraction of the accidentals in the data sample. The uncertainty steming from the correction for the radiative effects was determined by studying the dependence of the data to Monte Carlo yield ratio on the W cut on the elastic peak (Armstrong, 1998). The global systematic errors are listed in the Table while bin dependent errors were added Variation of the cross section with the change of the momentum and geometrical acceptance cuts used in the analysis was also investigated.…”

“…For the duration of the experiments the position of the beam at the target was stable to within ±1.0mm, beam current -Beam Current Monitors -(BCMs) and Unser Monitor -the former, resonant cavities, provided the continuous measurement of the beam current during the data taking while the latter, a parametric current transformer, was used to perform an absolute current calibration (see (Armstrong, 1998)). Using this information the integrated beam charge was evaluated and recorded, beam energy -superharps and dipoles -allowed for non-concurrent measurements of the beam energy.…”

“…For proper operation the timeof-flight software had to be recalibrated (Niculescu, 1998;Armstrong, 1998) whenever any changes were made which affected the timing (changing the central momentum setting, for instance). Histograms in the diagnostic histogram file had to be carefully monitored to ensure quality of the TOF data.…”

Inclusive Electron Scattering from Nuclei in the Quasielastic Region at Large Momentum Transfer

“…A more detailed and complete description of both the BCM and Unser monitors can be found in C.S. Armstrong's thesis [68].…”