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Are streak-camera bunch length measurements consistent with the observed luminous size?

Are streak-camera bunch length measurements consistent with the observed luminous size?. Principle: compare longitudinal luminosity distribution L(z) measured by Babar L(z) prediction using measured b * x, y (phase advance data in LER & HER) assumed e x,y (highly insensitive)

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Are streak-camera bunch length measurements consistent with the observed luminous size?

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  1. Are streak-camera bunch length measurements consistent with the observed luminous size? • Principle: compare • longitudinal luminosity distribution L(z) measured by Babar • L(z) prediction using • measured b*x, y (phase advance data in LER & HER) • assumed ex,y (highly insensitive) • LER & HER bunch lengths measured using the streak camera • Data sets • streak-camera MD (A. Fisher + R. Holtzapple, June 04) • BaBar luminous-region data (BaBar ODF group) W. Kozanecki & B. Viaud

  2. LER 4.5 MV HER 16 MV Streak-camera bunch length measurements (as presented by AF on 16 Jul 04) LER 3.8 MV

  3. Babar luminous-region data 3.8 MV 3.2 MV Note Data not corrected for phase transient (z-centroid variation along bunch train)  reported width of luminous region is overestimated

  4. Parameters used in prediction Note that the data are systematically narrower than the prediction, even before correcting for the z-centroid variation along the bunch train. 3.8 MV (LER) sz+, - = strk cam. Data L(z)/Lmax (arb. units) Prediction zvtx (mm)

  5. Nominal streak-camera calibration L(z)/Lmax L(z)/Lmax 3.2 MV (LER) sz+, - = strk cam. 3.8 MV (LER) sz+, - = strk cam. arb. units Data arb. units Data Prediction Prediction zvtx (mm) zvtx (mm)

  6. Streak-camera calibration lowered by 15 % (both beams) L(z)/Lmax L(z)/Lmax 3.2 MV (LER) Assume sz+, - = strk cam./1.15 3.8 MV (LER) Assume sz+, - = strk cam./1.15 arb. units Data arb. units Data Prediction Prediction zvtx (mm) zvtx (mm) If one assumes that the streak camera calibration overestimates both bunch lengths by 15%, the data appear systematically wider than the prediction. Correcting for the z-centroid variation along the bunch train, would improve the agreement.

  7. Summary • The raw longitudinal luminosity distribution was compared to the theoretical distribution, using phase-advance measurements for the b functions, and streak-camera data for the bunch lengths. • If one takes the streak-camera measurements at face value, the data are systematically narrower than the prediction, even before correcting for the z-centroid variation along the bunch train. • If one assumes that the streak camera calibration overestimates both bunch lengths by 15%, the data appear systematically wider than the prediction. Correcting for the z-centroid variation along the bunch train, would improve the agreement. This suggests the actual bunch lengths lie somewhere between these two extremes. • If one assumes that the streak camera correctly measures the ratio (but not the absolute scale) of the LER & HER bunch lengths, this provides an additional constraint to extract individual bunch lengths from the longitudinal luminosity distribution. • A better understanding of the SVT acceptance & z-resolution are required to improve the agreement between measured & predicted luminosity distributions.

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