Estimate of Bunch Lengths from dL/dz Fits   L NNdz e x y z z         xxHxL 222 ,,  yyHyL 222 ,,  zzHzL 222 ,, X-spot sizesY-spot sizes hourglass factor (1+z 2 /  y * 2 ) Bunch lengths  zH 2 , Fit L(z) for  z and  y before and after HER V RF change Use V RF dependence to extract bunch lengths (done several times by Chris O’Grady and Benoit Viaud)

Example Fit Norm Z c  z Z w  y 2 Z (mm) L (ee,  events)

, mm bucket RF transient has not been corrected, but it’s only a small change before  V RF after

RF Transient History z, mm bucket Apr 1 Apr 27 May 31 May 17

 z, mm BaBar Run since May 28  V RF zz

 z 2 = 9.7 mm 2 \pm 1.3 mm 2 zH , 10.5 mm 10.0 mm 11.1 mm \pm 0.7 mm zL , \pm 0.7 mm Results Uncertainty is large. Consider constraining  y * in fits.

 y * (mm) BaBar Run since May 28

Z (mm) L (ee,  events) Z (mm) L (ee,  events)  z, mm BaBar Run since May 28 Some of this may not be statistical

 V RF

 z 2 = 9.7 mm 2 \pm 1.3 mm 2 zH , 10.5 mm 10.0 mm 11.1 mm \pm 0.7 mm zL , \pm 0.7 mm Results  y * unconstrained  z 2 = 10.3 mm 2 \pm 0.4 mm 2 zH , 10.9 mm 10.4 mm 10.8 mm \pm 0.2 mm zL , \pm 0.2 mm  y * = 13mm Underestimated errors