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Estimate of Bunch Lengths from dL/dz Fits L NNdz e x y z z 2 2 3 2 2 2 2 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)
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Example Fit Norm Z c z Z w y 2 Z (mm) L (ee, events)
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, mm bucket RF transient has not been corrected, but it’s only a small change before V RF after
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RF Transient History z, mm bucket Apr 1 Apr 27 May 31 May 17
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z, mm BaBar Run since May 28 V RF zz
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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.
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y * (mm) BaBar Run since May 28
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Z (mm) L (ee, events) Z (mm) L (ee, events) z, mm BaBar Run since May 28 Some of this may not be statistical
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V RF
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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
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