Measurement of Beam-beam Tune-shift Parameter at Kekb

We have measured the coherent beam-beam tune shift at KEKB, an asymmetric double-ring electron/positron collider. The relationship between the tune shift and the beam-beam parameter is nonlinear, because the tunes are very close to a half integer. The estimated horizontal emittance is much larger than the calculated value, which is evidence of a dynamic effect due to the beam-beam interaction. The luminosity extrapolated from that of a single bunch, based on its vertical tune shift, is inconsistent with the luminosity measured for all bunches.