CP Violation Measuring matter/antimatter asymmetry with BaBar. Wouter Verkerke University of California, Santa Barbara. Outline of this talk. Introduction to CP violation A quick review of the fundamentals. CPviolating observables Experiment and analysis techniques
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Wouter Verkerke
University of California, Santa Barbara
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
s
b
u
c
t
The CabibboKobayashiMaskawa matrixMixes the lefthanded charge –1/3 quark mass eigenstates d,s,b to give
the weak eigenstates d’,s,b’.
l3
l
l
l2
l3
l2
l=cos(qc)=0.22
CP
The phase changes signunder CP.
Wouter Verkerke, UCSB
Transition amplitude violates CP if Vub ≠ Vub*, i.e. if Vub has a nonzero phase
s
b
u
c
t
The Unitarity Triangle – Visualizing CKM information from Bd decaysCKM phases
(in Wolfenstein convention)
Wouter Verkerke, UCSB
Bf
Observing CP violationBf
A=a1+a2
A=a1+a2
a2
A
+g
a1
a1
g
A
a2
A=A No observable CP asymmetry
Wouter Verkerke, UCSB
Bf
Observing CP violationBf
A=a1+a2
A=a1+a2
+g
d
d
A
g
a2
A
a2
a1
a1
AA Need also CPinvariant phase for observable CP violation
Wouter Verkerke, UCSB
f = b
CP violation: decay amplitudes vs. mixing amplitudesN(B0)N(B0)
N(B0)+N(B0)
2pDmd 2tB
Wouter Verkerke, UCSB
f = b
ACP(t) from interference between mixing+decay and decaymixing
decay
If only single real decay amplitude contributes
Wouter Verkerke, UCSB
bu
*In Wolfenstein phase convention.
td
B0 mixing + single bu decay
The distinction between a and gmeasurements is in the technique.
B0 mixing + single bc decay
Interfere bc and bu in B± decay.
Wouter Verkerke, UCSB
(4S)
BB threshold
Wouter Verkerke, UCSB
Beam currents of 12 amps!
Continuous ‘trickle’ injection
Reduces data taking interruption for ‘top offs’
High luminosity
6.6x1033 cm2s1
~7 BB pairs per second
~135 M BB pairs since day 1.
Daily delivered luminosity still increasing
Projected luminosity milestone
500M BB pairs by fall 2006.
The PEPII B factory – performanceWouter Verkerke, UCSB
Electromagnetic
Calorimeter (EMC)
1.5 T Solenoid
Detector for
Internally reflected
Cherenkov radiation
(DIRC)
SVT: 5 layers doublesided Si.
DCH: 40 layers in 10 super
layers, axial and stereo.
DIRC: Array of precisely
machined quartz bars. .
EMC: Crystal calorimeter (CsI(Tl))
Very good energy resolution.
Electron ID, p0 and g reco.
IFR: Layers of RPCs within iron.
Muon and neutral hadron (KL)
Drift chamber (DCH)
Instrumented
Flux Return (IFR)
Silicon Vertex
Detector (SVT)
Wouter Verkerke, UCSB
Readout
chips
Beam bending magnets
Beam pipe
Layer 1,2
Layer 3
Layer 4
Layer 5
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
DE
mes>5.27 GeV
N= 1506
Purity = 92%
mes
mes (GeV)
Selecting B decays for CP analysis(mES) 3 MeV
s(DE) 15 MeV
2
Wouter Verkerke, UCSB
Vertexing
Tagside vertexing
~95%
efficient
BFlavor Tagging
sz170 mm
sz70 mm
Dt=1.6 ps Dz 250 mm
Exclusive B Meson Reconstruction
Wouter Verkerke, UCSB
Dz/gbc
Determine flavor of Btag BCP(Dt=0)from partial decay products
Leptons : Cleanest tag. Correct >95%
Full tagging algorithm combines all in neural network
Four categories based on particle content and NN output.
Tagging performance
e
e+
W
W+
n
n
b
b
c
c
Kaons : Second best. Correct 8090%
efficiency
mistake rate
W
W+
c
c
K
s
s
b
K+
b
W
u
u
= 28%
W+
d
d
Wouter Verkerke, UCSB
B0(Dt)
B0(Dt)
ACP(Dt) = Ssin(DmdDt)+Ccos(DmdDt)
sin2b
Dsin2b
Putting it all together: sin(2b) from B0 J/y KSImperfect flavor tagging
Finite Dt resolution
Actual sin2b result on 88 fb1
Wouter Verkerke, UCSB
Dt
Dt
Vcb
c
b
J/Y
f = 0
W+
c
B0
Vcs
s
f = b
Ks
d
d
f = b
Bfactory ‘flagship’ measurement: sin2b from J/y KSDecay
B0 Mixing……followed by………Decay
d
Ks
s
Vcs
*
c
W+
J/Y
c
f = 0
Vcb
Wouter Verkerke, UCSB
Combined result (88 fb1, 2001)
sin2b = 0.741 0.067 0.034
l = 0.948 0.051 0.030
(stat)
(syst)
sin2b = 0.76 0.074
‘Golden’ measurement of sin2bB0 (cc) KS (CP=1)
No evidence for cos(DmDt) term
sin2b = 0.72 0.16
B0 (cc) KL (CP=+1)
Wouter Verkerke, UCSB
r = r(1l2/2)
h = h(1l2/2)
Standard Model interpretationConstraints on the apex of the Unitarity Triangle.
h
r
Wouter Verkerke, UCSB
Method as in Höcker et al, Eur.Phys.J.C21:225259,2001
4fold ambiguity because we measure sin(2b), not b
One solution for b is very consistent with the other constraints.
2
1
Latest results including the Belle experiment.
h
3
There is still room for improvement:
measurement is statistics dominated
Summer ’04 data 23 x 88fb1
4
r
Wouter Verkerke, UCSB
Method as in Höcker et al, Eur.Phys.J.C21:225259,2001
f=0
f=0
f=???
f=???
Wouter Verkerke, UCSB
u/
u/
Standard model expectation for sin(2b) from bs penguinsI
Experimentally best modes:
B0fK0
B0h’K0
B0p0K0
(I, II & III)
(II & III)
f = g / 0
(I)
II
f = g / 0
these limits
will improve
with additional
data
f = g
III
*Grossman, Ligeti, Nir, Quinn. PRD 68, 015004 (2003) and Gronau, Grossman, Rosner hepph/0310020
B0 fKS
B0 KSp0
B0 h’KS
Wouter Verkerke, UCSB
h’Ks
BaBar 0.02 0.34 0.03
fKs
BaBar 0.45 0.43 0.07
p0Ks
BaBar 0.48 (+0.38) 0.11
–0.47
bs penguin average
Babar 0.27 0.22
Wouter Verkerke, UCSB
sin2b from B0 (cc) KS
(My naïve averages)
h’Ks
BaBar 0.02 0.34 0.03
Belle 0.43 0.27 0.05
Ave 0.27 0.21
fKs
BaBar 0.45 0.43 0.07
Belle –0.96 0.50 (+0.09)
Ave –0.14 0.33
–0.11
p0Ks
Babar 0.48 (+0.38) 0.11
–0.47
K+KKs nonresonant
Belle 0.51 0.26 0.05 (+0.18)
–0.00
bs penguin average
Babar and Belle 0.27 0.15
Wouter Verkerke, UCSB
sin2b from B0 (cc) KS
S = 0.27 ± 0.15 (~3s below J/yKs S = 0.74 ± 0.05).
C = 0.10 ± 0.09
Wouter Verkerke, UCSB
f = b
The angle a from B ppACP(t)=sin(2a)sin(DmdDt).
B0 Mixing
bu decay
Vub
f = g
sin2a
Wouter Verkerke, UCSB
tree decay
penguin decay
s
Vtd/Vts
/ K+
Vub
f = 0
f = 0
f = g
Ratio of amplitudes P/Tand strong phase difference dcan not be reliably calculated
Unknown phase shift
Wouter Verkerke, UCSB
2k

Wouter Verkerke, UCSB
‘~105’
‘~106’
Wouter Verkerke, UCSB
Plots are after cut on signal probability ratio not including variable shown, optimized with S/sqrt(S+B) .
[BELLE: (1.7±0.6±0.2)x106, 3.4s]
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
*As predicted by G.Kramer, W.F.Palmer, PRD 45, 193 (1992). R.Aleksan et al., PLB 356, 95 (1995).
(BaBar)
(Belle)
(assuming full longitudinal polarization)
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
f=g
color
suppression
f=0
Ru is the left side of the Unitarity Triangle (~0.4).
FCS is (color) suppression factor([0.20.5], naively1/3)
Wouter Verkerke, UCSB
Branching fractionssmall (0.1%1%)
CKM favored
Doubly Cabibbo suppressed (by factor O(100))
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
GLW method: large BF, small ACP
D0p
background
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
MC yield prediction with BF=7x105: 12 evts
ADS method: small BF, large ACP
Yield in 115 fb1 of data:1.1 3.0 evts
No assumptions: rb < 0.22 (90% C.L.)
(95% C.I. region)
Wouter Verkerke, UCSB
g=75o, db=30o, dd=15o
Dc2
rb=0.3
3s
2s
GLW
1s
g
Wouter Verkerke, UCSB
g=75o, db=30o, dd=15o
Dc2
rb=0.3
3s
GLW+ADS+CLEOc
GLW+ADS
2s
11o
GLW
1s
g
Wouter Verkerke, UCSB
g=75o, db=30o, dd=15o
3s
rb=0.1
2s
67o
1s
3s
rb=0.2
2s
D2
1s
23o
3s
rb=0.3
2s
11o
1s
g
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB
Wouter Verkerke, UCSB