Paper |
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MOPLS026 |
Monitoring of Interaction-point Parameters using the 3-dimensional Luminosity Distribution Measured at PEP-II
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598 |
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- B.F. Viaud
Montreal University, Montreal, Quebec
- W. Kozanecki
CEA, Gif-sur-Yvette
- C. O'Grady, J.M. Thompson, M. Weaver
SLAC, Menlo Park, California
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The 3-D luminosity distribution at the IP of the SLAC B-Factory is monitored using e+ e- -> e+ e-, mu+ mu- events reconstructed online in the BaBar detector. The transverse centroid and spatial orientation of the luminosity ellipsoid provide a reliable monitor of IP orbit drifts. The longitudinal centroid is sensitive to small variations in the average relative RF phase of the beams and provides a detailed measurement of the phase transient along the bunch train. Relative variations in horizontal luminous size are detectable at the micron level. The longitudinal luminosity distribution depends on the e± overlap bunch length and the vertical IP beta-function beta*y. In addition to continuous online monitoring of all the IP parameters above, we performed detailed studies of their variation along the bunch train to investigate a temporary luminosity degradation. We also used controlled variations in RF voltage and beam current to extract separate measurements of the e+ and e- bunch lengths. The time-history of the beta*y measurements, collected over a year of routine high-luminosity operation, are compared with HER & LER phase-advance data periodically recorded in single-bunch mode.
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MOPLS050 |
Combined Phase Space Characterization at the PEP-II IP using Single-beam and Luminous-region Measurements
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655 |
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- A.J. Bevan
Queen Mary University of London, London
- Y. Cai, A.S. Fisher, C. O'Grady, J.M. Thompson, M. Weaver
SLAC, Menlo Park, California
- W. Kozanecki
CEA, Gif-sur-Yvette
- B.F. Viaud
Montreal University, Montreal, Quebec
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We present a novel method to characterize the e ± phase space at the IP of the SLAC B-factory, that combines single-beam measurements with a detailed mapping of luminous-region observables. Transverse spot sizes are determined in the two rings with synchrotron-light monitors & extrapolated to the IP using measured lattice functions. The 3-D luminosity distribution, as well as the spatial dependence of the transverse-boost distribution of the colliding beams, are measured using e+ e- > mu+ mu- events reconstructed in the BaBar tracking detectors; they provide information on the luminous spot size, the e- angular divergence & the vertical emittance. The specific luminosity, which is proportional to the inverse product of the overlap IP beam sizes, is continuously monitored using Bhabha-scattering events. The combination of these measurements provide constraints on the horizontal & vertical spot sizes, angular divergences, emittances & beta functions of both beams at the IP during routine high-luminosity operation. Preliminary results of this combined-spot size analysis are confronted with measurements of IP beta-functions & overlap IP beam sizes at low beam current.
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