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Consistency of Streak Camera Bunch Length Measurements with Luminous Size in BaBar Experiment

Investigating if streak camera measurements align with luminous size, considering prediction variations and calibration corrections in BaBar experiment data analysis.

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Consistency of Streak Camera Bunch Length Measurements with Luminous Size in BaBar Experiment

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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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