jan 28th, 2009colin jessop at notre dame an experiment to measure cp violation in b mesons colin...
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Jan 28th, 2009 Colin Jessop at Notre Dame
An experiment to measure CP An experiment to measure CP violation in B mesons violation in B mesons
Colin Jessop
University of Notre Dame
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Measuring a CP phase by InterferenceMeasuring a CP phase by Interference
Interference of two amplitudes is required
initial final
The two amplitudes must have a relative CP even phaseand relative CP odd phase
CP even phase:
CP odd phase: (the CP violating phase)
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
initial final
For the (antiparticle) process
Define an Asymmetry:
Acp=0 if =0 or =0
Measuring a CP violating Phase Measuring a CP violating Phase
:CP M M
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Real Amplitude + Complex: CP odd phase from Vub CP even phase from gluon
Strong Phase from non-perturbative QCD is not reliably predicted
Direct CP ViolationDirect CP Violation
CP even phase from strong interaction.
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
b
borsd
d
tcu ,,tcu ,,
W
W
00 BB
Use Mixing to Provide CP even PhaseUse Mixing to Provide CP even Phase
0B0B
Mixing parameters discovered to be favourable to such a measurement in 1980’sand these parameters are precisely measurable
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
fcp (e.g K0s)
CP eigenstates fcp accessible to B0 and B0 are rare ( < 1 in 3000 B decays)
Measuring CP odd phase in B MixingMeasuring CP odd phase in B Mixing
Need to produce millions of B meson decays
Need a way to identify if you started with B0 or B0
sin sincp mix cpA t
Need to measure time dependence of process sin 0mixt dt
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
A Confluence of Nature and TechnologyA Confluence of Nature and Technology
In the 1980’s we found that the parameters of B decays made this measurementpossible but not at existing facilities
Challenge Solution
Millions of B mesons
High Luminosity e+e- storage rings
Identifying B or B Produce BB pairs
Measuring time dependence
Development of silicon track detectors
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
An Asymmetric B meson “Factory”An Asymmetric B meson “Factory”
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Two B-Factories: USA and JapanTwo B-Factories: USA and Japan
BELLE at KEKB nr Tokyo, Japan
Both US and Japanese experimentsParralleled each other 1993-2004
After 2004 funding issues in US slowedBaBar down and lead to eventualtermination of experiment in 2007 (486 fb-1)
BELLE in Japan is still going strong(895 fb-1 so far)
At termination BaBar was running at seven times design luminosity.and had publishedover 300 papers
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
z ~ 260 m
0tagB
ee
4S
K
0recB
B-Flavor Tagging
cβγz/ΔtΔ
Exclusive B Meson
Reconstruction
0
SK
/J
0 0rec fl avB B (flavor eigenstates) lifetime, mixing analyses0 0
rec CPB B (CP eigenstates) CP analysis
Experimental Technique for B FactoriesExperimental Technique for B Factories
(4S) produces coherent B pair: t t
Time-integrated asymmetries are zero
0
0
( )
( )
tag
rec
B B t
B B t
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
BABAR CollaborationBABAR Collaboration
Gathering at SLAC, July 2002
9 Countries76 Institutions550 Physicists
July 2002
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Cerenkov Detector (DIRC)
1.5 T solenoid Electromagnetic Calorimeter
Drift Chamber
Instrumented Flux ReturnSilicon Vertex Tracker
e+ (3.1 GeV)
e- (9 GeV)
BABAR DetectorBABAR Detector
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Silicon Vertex Detector at BABARSilicon Vertex Detector at BABAR
• 5 Layer AC-coupled double-sided silicon detector
• Located in high radiation area – Radiation hard readout electronics (4-
5Mrad)
• 97% hit reconstruction efficiency
• Hit resolution ~15 μm at 90o
e- beam e+ beam
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Completed SVT DetectorCompleted SVT Detector
Beam pipe
Layer 1,2Layer 3
Layer 4Layer 5
B1 bending magnet
Readoutchips
rBP,IR = 25 mm 2 x Be walls = 0.83+0.53 mm
T1.5 mm H2O cooling gap
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
BABAR Drift ChamberBABAR Drift Chamber
• 40 layers of wires (7104 cells) in 1.5 Tesla magnetic field• Helium:Isobutane 80:20 gas, Al field wires, Beryllium inner wall, and all
readout electronics mounted on rear endplate• Particle identification from ionization loss (7% resolution)
16 axial, 24 stereo layers
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
An Innovative Detector for Seperating KAn Innovative Detector for Seperating K++//++
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Projection Screen Quartz bars
Cerenkov Detector Construction
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
KK++//+ + SeparationSeparation
KK++//+ + for tagging and CP eigenstate identifiction for tagging and CP eigenstate identifiction
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
High Resolution Electromagnetic CalorimeterHigh Resolution Electromagnetic Calorimeter
• 6580 CsI(Tl) crystals with photodiode readout
0 reconstruction for rare
CP eigenstates
= 5.0%
0
July30th, 2008 Bigi,Jessop,LoSecco at Notre Dame
Completed DetectorsCompleted Detectors
Completed Feb 1999First collisions May, 1999
First collisions May, 1999