D.W. Braben

Measurements of threshold π+ electroproduction at low momentum transfer

Abstract The reaction e− + p → e− + π+ + n has been studied near threshold at momentum transfer |k2| of 0.078, 0.155, 0.233 and 0.311 (GeV/c)2. The slope of the total cross section evaluated at threshold has been compared with models based on PCAC and current algebra to deduce the axial vector form factor of the nucleon, GA(k2). In the dipole parametrisation GA(k2)/GA(0) = (1 + |k2|/MA2)−2 we find that the models give values of MA ranging between 1.0 and 1.2 GeV. The π+n angular distributions are compared with fixed t dispersion relations and with a pseudovector Born approximation and are found to be in good agreement.

Efficiency and spatial resolution measurements of a modular neutron detector in the kinetic energy range 15–120 MeV

Abstract The detection efficiency of a 3 × 3 matrix of NE 110 scintillator blocks, 153 × 153 × 270 mm long, has been measured in the neutron kinetic energy range 15–120 MeV for several thresholds, ranging from 2.80 to 15.75 MeV equivalent electron energy, and for various thicknesses of lead shielding in front of the counter. The probabilities of detecting a neutron in a block different from the one struck by the beam (‘mixing’) and in more than one block (‘multifiring’) have also been measured as a function of threshold and shielding. Comparisons have been made with a Monte Carlo program which accounts for the modular structure of the counter. The efficiency and the spatial resolution of a very large matrix have been obtained, using both experimental and Monte Carlo results.

The total cross section for π+ electroproduction on hydrogen near threshold

Abstract The total cross section for the reaction ep → enπ+ at momentum transfers |k2| between 0.08 and 0.32 ( GeV c )2 and for centre of mass energies between threshold, at W = 1.078 GeV, and W = 1.106 GeV has been measured by detecting the electron and neutron in coincidence. Comparisons are made with both current algebra and dispersion relation theoretical models.

A Large Aperture Neutron Time-Of-Flight Spectrometer

Abstract We describe a large aperture 2 m × 2 m neutron time-of-flight spectrometer, consisting of 145 plastic scintillator blocks, each 270 mm deep and 153 × 153 mm 2 in area. We present details of the design, the construction and the on-line data acquisition and monitoring system. We briefly summarise its performance: detection efficiency ≳20%, time-of-flight and spatial resolution (standard deviation) ∼1.1 ns and ∼ 0.9 blocks respectively. The counter operated successfully for four years in conjuction with a high resolution electron spectrometer to measure electroproduction processes with a nucleon in the final state. Although it was designed for the detection of neutrons of kinetic energy between 30 and 500 MeV, it was well suited also for the detection of high energy protons.

Elastic electron-proton scattering between 0.05 and 0.30 (GeV/c)2

Abstract Elastic electron proton scattering has been used to check the validity of the dipole fit of the proton form factors at momentum transfer between 0.05 and 0.30 (GeV/ c ) 2 . The general behaviour of the cross sections is in agreement with previous measurements and is close to the dipole predictions but there is the suggestion of some small amplitude deviations. It is speculated that these deviations may be related to similar effects in the proton formfactor derived from the ISR pp elastic scattering data via a Chou-Yang model.

Inclusive neutron spectra in electroproduction above the resonance region

Abstract In electroproduction on hydrogen at momentum transfers −0.3, −0.6, −0.9 (GeV/ c ) 2 and W = 2.3 GeV we have measured, over a range of backward centre-of-mass angles, the yield of neutrons with momenta between 0.4 and 1.2 GeV/ c , and in addition, protons over a limited range with momenta greater than 0.8 GeV/ c . We compare the neutron yields with those of the protons and also with previous experiments. We find that the yield of neutrons is significantly greater than that of protons.