Precision measurements of A1N in the deep inelastic regime

We have performed precision measurements of the double-spin virtual-photon asymmetry A1A1 on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized 3He target. Our data cover a wide kinematic range 0.277≤x≤0.5480.277≤x≤0.548 at an average Q2Q2 value of 3.078 (GeV/c)2, doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in the same kinematic range. Our data are consistent with a previous observation of anA1n zero crossing near x=0.5x=0.5. We find no evidence of a transition to a positive slope in(Δd+Δd¯)/(d+d¯) up to x=0.548x=0.548

ABSOLUTE ENERGY MEASUREMENT IN e

A technique based on the Compton scattering of linearly polarized visible light is proposed for measuring the absolute energy of an electron beam in a linear collider. In the vicinity of 90 degrees in the rest frame of the electron the ratio of the crosssection for different linear light polarizations depends strongly on the absolute energy of the beam. This is especially true when the backscattering rates with light polarized perpendicular to the scattering plane is compared with light polarized in the scattering plane. As a result, the absolute energy of the beam can be determined to a high degree of precision by measuring the ratio of two counting rates. Using a strong laser field (e.g. that in a Fabry-Perot resonant cavity), the measurement can be performed in a fraction of a second. Examples of possible practical arrangements are given. I. TECHNIQUES FOR MEASURING ENERGY The energy of a stored electron beam can be measured both elegantly and accuratly by depolarization. In lina..

Electroexcitation of the giant resonance of 17O

The 11 to 30 MeV excitation region of 17O has been investigated by means of inelastic electron scattering, with special emphasis placed on the giant resonance. The scattering angle employed was 75.1°, and the incident energies were 64.9, 83.3, 101.3, 113.6, and 124.0 MeV. These conditions correspond to momentum transfers in the range 0.33 to 0.77 fm-1. The data reveal a broad resonance centred at 22 - 23 MeV excitation, with strength extending down to 10 - 12 MeV excitation. Some fine structure is observed which correlates well with the positions of previously observed levels. A particle-hole model with harmonic oscillator wavefunctions and Kuo-Brown residual interaction is found to predict the strength distribution and q-dependence of the giant resonance form factor very well. However, a scale factor of 1.85 is required to achieve agreement in magnitude. A fit to the Helm model prediction for a C1 transition yields reasonable values for the skin thickness and transition radius parameters. No clear evidence is found for isospin splitting of the giant resonance. The particle-hole model predicts only a slight degree of splitting in the transverse (E1) component of the form factor, and none at all in the longitudinal (C1) component. A smaller structure between 17.5 and 19.6 MeV excitation is reported for the first time. The Helm model for a C2 transition using parameters determined by the fit to the giant resonance form factor is found to predict the form factor for this structure extremely well. Levels at 16.5 and 19.6 MeV excitation are also reported for the first time. The former is found to have a natural width of about 300 keV, while the latter appears to be considerably narrower

A compton backscattering polarimeter for measuring longitudinal electron polarization

Compton backscattering polarimetry provides a fast measurement of the polarization of an electron beam in a storage ring. Since the method is non-destructive, the polarization of the electrons can be monitored during internal target experiments. At NIKHEF a Compton polarimeter has been constructed to measure the polarization of the longitudinally polarized electrons stored in the AmPS ring. First results obtained with the polarimeter, the first Compton polarimeter to measure the polarization of a stored longitudinally polarized electron beam, are presented in this paper