Transcript A. Bevan, Queen Mary University of London, London, UK W. Kozanecki, CEA/Saclay, F91191 Gif-sur-Yvette, France B.

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 High (e) and Low (e+)
energy rings of PEP-II.
(C) Peter Ginter (2002).
The BaBar Detector.
(C) Peter Ginter (2002).
The Silicon Vertex Detector
from the BaBar Experiment.
(C) Peter Ginter (2002).
The klystron gallery of the
2-mile long linear accelerator.
(C) Peter Ginter (2002).
The BaBar Detector
The PEP-II Accelerator
• 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
• Collides 9 GeV e- (HER) on 3.1 GeV e+ (LER)
• Designed for producing B-meson pairs at high luminosity
e e  (4S )  BB
at the interaction region within the BaBar detector
• Instrumented with beam profile monitors in both rings
EMC
6580 CsI(Tl) crystals
1.5T
solenoid
• Two Synchrotron Light Monitors: SLMH, SLML
• An X-ray monitor: SXML
e+ (3.1GeV)
DIRC (PID)
144 quartz
bars
11000 PMs
SLML
BaBar Detector
Drift Chamber
40 layers
e- (9GeV)
Silicon Vertex Tracker
5 layers, double sided
strips
Instrumented Flux Return
iron / RPCs or LSTs (muon
/ neutral hadrons)
SXML
SLMH
BaBar Luminous Region Measurements
Beam Profile Monitors
• Beam transverse ellipse is measured by synchrotron
light imaging devices
Constraints from BaBar
L(x,y,z) and pt of + pairs)
LER and HER
Profile Monitors
Neglect x-y coupling and
longitudinal waist offsets.
 y'B
(
( z)  ( 
( z)  ( 
 xL
 
L ( z )   z ,  y*eff
Typical transverse profile for SXML
1
2
Typical transverse profile for SLML
• Beam vertical size is also measured by interferometry
devices
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).
• 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)
Calculate y, and
with the measured
LSP, calculate x
Eigen plane
lattice functions
from MIA data
Predict beam sizes
at the IP, x/y and LSP
At high current, the model
needs to account for
beam-beam effects.
Using x
calculate
horizontal
constraints
 yL


*eff
y
,
*eff
y
,  yH ,  yL
*
xH / L
eff
y
hourglass
losses
→ βy*

,  xH / L 
• x- and y-spread of μ+μ- event vertices,
*
 x ' B  (  xH /  xH

 xL
,
 yL (z )
 xL   x  x*
*
*

 xx ' B ( z )   xH ,  xL 
• Beam eigenmode emittances can be extracted from the
measured sizes and tilt angles using previously measured
lattice functions including x-y coupling and dispersion.
• Result of boost measurements
• x’- and y’-spread of μ+μ- event momentum vector angles,  x ,
B

x
 x*

y
 *y
  *y
Luminosity Scans
• Beam overlap sizes can be measured directly by scanning transverse offsets between the beams
• Combining Luminous Region x-measurements
Σminor
Lsp
“Σx”
x offset (μm)
Time of x-tune
change towards
½-integer
ψ
Lsp
“Σy”
Σmajor
● e○ e+
y offset (μm)
Towards a Combined Analysis
Comparing Luminosity Scans and Profile Monitor Results
• 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
• The size of the overlap of the two beams can be calculated from the individual beam sizes
using:
• Comparing results from both sets of measurements will
further highlight systematic problems and possible solutions
● e○ e+
 yB (z )