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