A measurement of the analysing power of aluminium for 490 MeV protons

Abstract

We report measurements of the analysing power A(O) for proton-aluminium scattering over the range 2 ° ¢o 20 ° laboratory angle, at a mean kinetic energy of 490 MeV. There was no discrimination against inelastic events, except where more than one track was observed in the optical spark chambers used. The measurements provided data for an experiment in which thick-plate aluminium spark chambers were used to analyse the proton polarization in a measurement of D(90 °) for p-p scattering near 1 GcV (1). A polarized proton beam was produced by scattering the internal beam of the 1 GeV Birmingham proton synchrotron, running at a reduced energy of 500 MeV, off a carbon target at an angle of (7.2 4-0.2) °. This beam was focussed by a ~ self-excited quadrupole >) (z) and collimated to approximately 10 mm width by 15 mm height (see Fig. 1). The energy selection of this arrangement due to the fringing field of the synchrotron was estimated from the tracking program TRAMP ¢o be ± 15 MeV; however, the inclusion of quasi-elastically scattered particles within this energy range has been shown to have negligible effect on the polarization (s). Three visual spark chambers, each with an active area of (100 × 100)mm 2 defined the tracks of the beam particles, incident on the second target consisting of a thickness of 30 mm of aluminium, representing an energy loss of 18 MeV. The paths of the scattered particles were determined by means of three spark chambers behind the target, each of (250 × 100)mm z active area. The chambers were triggered by a coincidence between the counter telescope in the beam and one of the two 13 mm thick scintillation counters placed on either side of the beam behind the large chambers (see Fig. 2). These counters were tapered in order to have an increasing acceptance for larger-angle scatters, and so to compensate somewhat for the falling differential cross-section. The angular range was covered in two overlapping segments