Comparing Luminosity Scans and Profile Monitor Results The size of the overlap of the two beams can be calculated from the individual beam sizes using: A. Bevan, Queen Mary University of London, London, UK W. Kozanecki, CEA/Saclay, F91191 Gif-sur-Yvette, France B. Viaud, Université de Montréal, Québec, Canada, H3C 3J7 Y. Cai, A. Fisher, C. O’Grady, J. Thompson, M. Weaver SLAC, Stanford, CA 94309, USA The klystron gallery of the 2-mile long linear accelerator. (C) Peter Ginter (2002). The Silicon Vertex Detector from the BaBar Experiment. (C) Peter Ginter (2002). The High (e  ) and Low (e + ) energy rings of PEP-II. (C) Peter Ginter (2002). The BaBar Detector. (C) Peter Ginter (2002). The PEP-II Accelerator Collides 9 GeV e - (HER) on 3.1 GeV e + (LER) Designed for producing B-meson pairs at high luminosity at the interaction region within the BaBar detector Instrumented with beam profile monitors in both rings Two Synchrotron Light Monitors: SLM H, SLM L An X-ray monitor: SXM L BaBar Detector SXM L SLM H SLM L The BaBar Detector Designed for particle physics CP asymmetry measurements Precision tracking, particle identification, and calorimetry Located within a 1.5T solenoid field Clean reconstruction of e + e - → e + e - (γ), μ + μ - events DIRC  PID) 144 quartz bars PMs 1.5T solenoid EMC 6580 CsI(Tl) crystals Drift Chamber 40 layers Instrumented Flux Return iron / RPCs or LSTs (muon / neutral hadrons) Silicon Vertex Tracker 5 layers, double sided strips e + (3.1GeV) e - (9GeV) Beam Profile Monitors Beam transverse ellipse is measured by synchrotron light imaging devices Beam vertical size is also measured by interferometry devices Beam eigenmode emittances can be extracted from the measured sizes and tilt angles using previously measured lattice functions including x-y coupling and dispersion. The fringe pattern of the HER profile monitor, where the rectangle shows the region of the interference pattern fitted to extract the vertical beam size (  y ). BaBar Luminous Region Measurements The reconstruction of e + e - → e + e - (γ), μ + μ - event vertices and kinematics provide measures of beam parameters at the IP z-distribution of e + e - (γ), μ + μ - events, L (z) x- and y-spread of μ + μ - event vertices,, x’- and y’-spread of μ + μ - event momentum vector angles,, Calculate  y, and with the measured L SP, calculate  x Using  x calculate horizontal constraints Neglect x-y coupling and longitudinal waist offsets. LER and HER Profile Monitors 1212 Predict beam sizes at the IP,  x/y and L SP Eigen plane lattice functions from MIA data At high current, the model needs to account for beam-beam effects. Constraints from BaBar L(x,y,z) and p t of  +   pairs) Typical transverse profile for SXM L Typical transverse profile for SLM L Result of boost measurements ● e - ○ e + ● e - ○ e + Time of x-tune change towards ½-integer Combining Luminous Region x-measurements Luminosity Scans Beam overlap sizes can be measured directly by scanning transverse offsets between the beams x offset (μm) y offset (μm) L sp Σ minor Σ major ψ “Σx”“Σx” “Σy”“Σy” Towards a Combined Analysis Profile monitor measurements need to improve by accounting for beam-beam focusing Luminous region measurements need to incorporate a formal description of x-y coupling and dispersion Comparing results from both sets of measurements will further highlight systematic problems and possible solutions hourglass losses → β y *