BEAM-BEAM INTERACTION WITH A HORIZONTAL CROSSING ANGLE

We report measurements of the dependence of luminosity and beam-beam t une-shift parameter on horizontal crossing angle at a single interacti on point in the Cornell Electron Storage Ring. The report is based on data collected between September 1991 and January 1992 at CESR. For he ad-on collisions (zero crossing angle) the achieved tune-shift paramet er is xi(v) = 0.03 +/- 0.002 at 11 mA/bunch. For a crossing half-angle of theta(c) = +/- 2.4 mrad, we achieve xi(c) = 0.024 +/- 0.002 at sim ilar bunch currents. The data suggest some degradation of performance if the trajectory through the interaction region is distorted magnetic ally even while head-on collisions are preserved. Therefore at least s ome of the observed dependence of tune-shift parameter on crossing ang le may be due to the associated large displacement of the beam traject ories in the interaction region optics. Furthermore, with the introduc tion of the crossing angle, the algorithm for optimizing luminosity is significantly complicated due to linear optical errors and the soleno id compensation. We interpret the measured tune-shift parameter at the ta(c) = 2.4 mrad as a lower limit to what can ultimately be achieved.