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Measurement of sin2 b at B A B AR. Update B 0 (cc) K 0 Update B 0 D *+ D *- New B 0 f K 0 S New B 0 J / p 0. Douglas Wright Lawrence Livermore National Laboratory For the B A B AR Collaboration. 31st International Conference in High Energy Physics - PowerPoint PPT Presentation
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Measurement of sin2 at BABARDouglas Wright
Lawrence Livermore National LaboratoryFor the BBAABBARAR Collaboration
31st International Conference in High Energy Physics
Amsterdam, 24 July 2002
Update B 0(cc)K 0
Update B 0D*+D*-
New B 0 K0S
New B 0J/ 0
July 24, 2002 Doug Wright, ICHEP Amsterdam 2
1
2
3
Weak interaction of quarks in the Standard Model
CP violation will arise from complex component of Vub, Vtd
Unitarity TriangleCKM Matrix
July 24, 2002 Doug Wright, ICHEP Amsterdam 3
B0-B0 mixing introduces time-dependant CP violation
B0
B 0
fCP
BL ,H p B0 q B0 b
d
d
bu,c,t
u,c,t
top quark box introduces: Vtb Vtd*
f(t )e t /
41S f sin(mdt)C f cos(mdt)
md = mH - mL
W W
Cf 1 f
2
1 f2
Sf 2 Im f
1 f2
f qp
A(B0 fCP)
A(B0 fCP)
qp~
Vtd
Vtd*
f (B0 fCP)
f (B0 fCP)
Direct CP violation if multiple amplitudes with different phases
Sensitive to overall phase of
f even if no
Direct CP Violation
July 24, 2002 Doug Wright, ICHEP Amsterdam 4
Theoretically clean: Tree level dominates and CP only from B0-B0 mixing
Relatively large branching fractions
Clear experimental signatures
CP asymmetry in B0 (cc)K0
ACP (t) f+ f-f+ f-
f sin 2 sin(mdt)
f = f e-
i2f=±1
c
s
c
d
d
b
f qp
A(B0
fCP)A(B 0 fCP)
B0 K0
July 24, 2002 Doug Wright, ICHEP Amsterdam 5
+e-e
Boost: = 0.55
Start the Clock
Coherent BB pair
B0
B0
Experimental technique at the (4S) resonance
4S
e+e- (4S) B B
Exclusive B meson and vertex reconstruction
Exclusive B meson and vertex reconstruction
KS
z
t z c
Btag
Brec
K-
Flavor tag and vertex reconstructi
on
Flavor tag and vertex reconstructi
on
July 24, 2002 Doug Wright, ICHEP Amsterdam 6
PEP-II top luminosity: 4.60 x 1033cm-2s-1 (exceeded design goal 3.0 x 1033)
PEP-II delivered 99 fb-1
BaBar recorded 94 fb-1
In this analysisOn peak 81 fb-1
88M BB pairsOff peak 10 fb-1
PEP-II top luminosity: 4.60 x 1033cm-2s-1 (exceeded design goal 3.0 x 1033)
PEP-II delivered 99 fb-1
BaBar recorded 94 fb-1
In this analysisOn peak 81 fb-1
88M BB pairsOff peak 10 fb-1
SLAC B Factory performance
9 GeV e- on 3.1 GeV e+
Boost = 0.55
IP beam size 147 m x 5 m
July 24, 2002 Doug Wright, ICHEP Amsterdam 7
BABAR Detector
SVT: 97% efficiency, 15 m z hit resolution (inner layers, perp. tracks)SVT+DCH: (pT)/pT = 0.13 % pT + 0.45 %
DIRC: K- separation 4.2 @ 3.0 GeV/c 2.5 @ 4.0 GeV/c EMC: E/E = 2.3 %E-1/4 1.9 %
July 24, 2002 Doug Wright, ICHEP Amsterdam 8
Vertex and t Reconstruction
Reconstruct Brec vertex fromcharged Brec daughters
Determine BTag vertex from All charged tracks
not in Brec
Constrain with Brec vertex, beam spot, and (4S) momentum
Remove high 2 tracks (to reject charm decays)
High efficiency: 95% Average z resolution ~ 180 m (dominated
by BTag) (<|z|> ~ 260 m)
t resolution function measured from data
Beam spot
Interaction Point
BREC Vertex
BREC daughters
BREC direction
BTAG direction
TAG Vertex
TAG tracks, V0s
z
July 24, 2002 Doug Wright, ICHEP Amsterdam 9
B Flavor tagging method
Using tracks with or without particle identification, and kinematic variables, a multilevel neural network assigns each event to one of five mutually-exclusive categories:
Lepton tag: primary leptons from semileptonic decay Kaon1 tag: high quality kaons, correlated K- and +
s (from D*) Kaon2 tag: lower quality kaons, s from D*
Inclusive tag: unidentified leptons, low quality K, leptons No tag: event is not used for CP analysis
b sc
K-
New and improved tagging method
July 24, 2002 Doug Wright, ICHEP Amsterdam 10
BtagB0
perfect tagging & time resolution
Tagging errors and finite t resolution dilute the CP asymmetry
BtagB 0
BtagB0
typical mistagging & finite time
resolution
Need to know mistag fraction w and t resolution function R in order to measure CP asymmetry.
Can extract these from data with B0-B0 mixing events.
f(t) e t /
B
4B
1 f sin2(1 2w) sin(mdt)
R
BtagB 0
July 24, 2002 Doug Wright, ICHEP Amsterdam 11
Use self-tagged Bflav sample to measure w and R
Fully reconstruct self-tagged modes:
Bflav sample is x10 size of CP sample
fUnmixedMixed
(t) e t /
B
4 B
1(1 2w) cos(mdt)
R
Apply Btag to other side, fit for B0-B0 mixing
B0 D(*)-
a1
Ntagged=23618
Purity=84%
B0 J/K*0(KNtagged=1757
Purity=96%
July 24, 2002 Doug Wright, ICHEP Amsterdam 12
Tagging performance from Bflav sample
Category
Efficienc
y ()Mistag Fr. (w)
Q=(1-2w)2
Lepton 9.1 0.2 3.3 0.6 7.9 0.3
Kaon1 16.7 0.2 9.9 0.7 10.7 0.4
Kaon2 19.8 0.3 20.9 0.8
6.7 0.4
Inclusive
20.0 0.3 31.6 0.9
2.7 0.3
Total 65.6 0.5
28.1 0.7
This new tagging method increases Q by 7% compared to the method used in our previous result:PRL87 (Aug 01).
Amixing Nunmixed Nmixed
Nunmixed Nmixed
(1 2w) cos(mdt)~1-2w
(sin2) 1Q
July 24, 2002 Doug Wright, ICHEP Amsterdam 13
Recent addition:B0 c Ks
where c K+K-
0 or
K+Ks -
sin2 golden sample: (cc)KS (f = -1)
Sample NtaggedPurit
y
J/ Ks(+-) 974 97%
J/ Ks(00) 170 89%
(2S) Ks 150 97%
c1 Ks 80 95%
c Ks 132 73%
Total 1506 92%
Energy-substituted mass
J/Ks (+-)
J/Ks (00)
(2S)Ks
cKs
c1Ks
mES Ebeamcm 2 pB
cm 2
July 24, 2002 Doug Wright, ICHEP Amsterdam 14
sin2 samples: J/ KL and J/ K*0
J/ KL J/K*0(Ks0)
Signal
J/ Bkg
Fake J/ Bkg
• Data
Use mB constraint to determine pKL
J/ background shape estimated from Monte Carlo
Fake J/ background shape estimated from data sidebands
Vector-Vector mode: mixture of CP+ and CP-
Use angular analysis to determine CP- fraction
Treat CP- component as
dilution effective f
f = +0.65±0.07Ntagged = 147Purity = 81%
f = +1Ntagged = 988Purity = 55%
E Ebeamcm EKL
cm
July 24, 2002 Doug Wright, ICHEP Amsterdam 15
sin2 likelihood fit
Simultaneous unbinned maximum likelihood fit of CP and mixing samples
Fit Parameters 34 totalsin2 1 BCP
Mistag fractions w for B0 and B0 tags 8Bflav
Signal t resolution function R 8Bflav
Background properties 17BCP+Bflav
(mostly from mES sidebands in data)
B lifetime fixed (PDG 2002) B = 1.542 psMixing frequency fixed (PDG 2002) md = 0.489 ps-
1
July 24, 2002 Doug Wright, ICHEP Amsterdam 16
sin2 = 0.723 0.158 sin2 = 0.755 0.074
Fit results
f =-1 f =+1
sin2 = 0.741 0.067 (stat) 0.033 (sys)
July 24, 2002 Doug Wright, ICHEP Amsterdam 17
sin2 fit results by decay mode
Consistency of CP Channels: P(2) = 57%
July 24, 2002 Doug Wright, ICHEP Amsterdam 18
(cc)KS with lepton tag
Ntagged = 220
Purity = 98%
Mistag fraction 3.3%
t 20% better than other tag categories
sin2 = 0.79 0.11
Dramatic effect in golden modes with lepton tag
July 24, 2002 Doug Wright, ICHEP Amsterdam 19
Cross-check on data control samples
Observed no asymmetry as expected
July 24, 2002 Doug Wright, ICHEP Amsterdam 20
Sources of Systematic Error
sin2Description of background events 0.017
CP content of background componentsBackground shape uncertainties
Composition and content of J/ KL background 0.015
t resolution and detector effects 0.017Silicon detector alignment uncertaintyt resolution model
Mistag differences between BCP and Bflav samples 0.012
Fit bias correction 0.010Fixed lifetime and oscillation frequency 0.005TOTAL 0.033
Steadily reducing systematic error: July 2002 = 0.033July 2001 = 0.05
July 24, 2002 Doug Wright, ICHEP Amsterdam 21
Standard Model comparison
One solution for is in excellent
agreement with measurements of unitarity triangle
apex
Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001
= (1-2/2)
= (1-2/2)
July 24, 2002 Doug Wright, ICHEP Amsterdam 22
Consistent with the Standard Model expectation of |f |=1 and nominal fit sin2 = 0.755 0.074 for (cc)Ks modes alone.
If another amplitude (new physics) contributes a different phase, then
In the Standard Model |f | = 1 (which we assume in the nominal sin2 fit)
Sf - f sin2 Cf 0 Fit |f| and Sf using the clean (cc)Ks modes
(f =-1, Ntagged = 1506, Purity = 92%):
Search for non-Standard Model effects in (cc)KS
| f | = 0.948 0.051 (stat) 0.017
(syst)
Sf = 0.759 0.074 (stat) 0.032 (syst)
ACP (t) S f sin(mdt) C f cos(mdt)
Cf 1
f
2
1 f
2
Sf 2 Im
f
1 f
2
July 24, 2002 Doug Wright, ICHEP Amsterdam 23
Cabbibo-suppressed mode with tree level weak phase same as b ccs
Penguin contribution uncertain, expected to be small < 0.1 Tree
Not a CP eigenstate, mixture of CP even (L=0,2) and CP odd (L=1) Resolve using angular analysis (in
transversity basis)
(b ccd) mode B0 D*+D*-
Ntagged= 102
Purity = 82%Reconstruct D*+ D0+
or D+0 , but not both to 0 mode
B0
D* -
D* +
B0
D* -
D* +
Vcd
July 24, 2002 Doug Wright, ICHEP Amsterdam 24
CP composition of B0 D*+D*-
We measure CP odd fraction (corrected for acceptance) to be small:
R = 0.07 0.06 (stat) 0.03 (syst)
ddcos tr
34
1 R sin2 tr 32
R cos2 tr
July 24, 2002 Doug Wright, ICHEP Amsterdam 25
CP asymmetry fit B0 D*+D*-
|+| = 0.98 0.25 (stat) 0.09 (syst)
Im(+) = 0.31 0.43 (stat) 0.10 (syst)
If penguins are negligible, then
Im(+) = - sin2
Im(+) measurement ~2.7 from BaBar sin2 in charmonium, assuming no penguins.
Improved fitting strategy since winter conferences: Parameterize in terms of CP even
(+) and odd () components, include angular information from partial-wave analysis
Fix CP odd component to =1, Im( ) = -0.741
July 24, 2002 Doug Wright, ICHEP Amsterdam 26
B0
B0
D*+
D _
D*+
D _
D+
D* _
D+
D* _
CPconjugation
strongphase
(b ccd) mode B0 D*+D-
D*D 56 fb-1
Ntagged= 85Purity = 52%
S+- = -0.43 1.41 0.20
C+- = 0.53 0.74 0.13
S-+ = 0.38 0.88 0.05
C-+= 0.30 0.50 0.08
Update to full data set in progress
D*D not CP eigenstate Possible strong phase
contribution (and still have penguins)
Different (but related) decay time distributions forB0 D*+D- B0 D*- D+
July 24, 2002 Doug Wright, ICHEP Amsterdam 27
(bccd) mode B0 J/ 0
Cabibbo and color-suppressed mode with comparable tree and penguin contributions
Ntagged= 49Purity = 59%
f = + 1
Vcd
Tree: ~VcbVcd* ~ O(3)
same weak phase as bccs
Penguin:~VcbVcd* + VubVud
* ~ O(3) adds additional weak phase
July 24, 2002 Doug Wright, ICHEP Amsterdam 28
CP asymmetry fit for B0 J/ 0
In absence of penguins C=0, S = -
sin2
f = + 1
July 24, 2002 Doug Wright, ICHEP Amsterdam 29
Charmless decay dominated by (b sss) gluonic penguins Weak phase same as b ccs, but sensitive to new physics in
loops
sin2 from penguin mode B0 KS
Ntagged = 66 Purity = 50%f = - 1
Small branching fraction O(10-5)
Significant background from qq continuum
Using only K+K-
July 24, 2002 Doug Wright, ICHEP Amsterdam 30
CP asymmetry fit for B0 KS
Fix |K| = 1, fit: SK = -0.19 (stat) 0.09
(syst)
+0.52- 0.50
Cross check on B+ K +
SK = 0.26 0.27
If no new physics, SK = sin2
Analysis of B0 ’ KS in progress
t (ps)
July 24, 2002 Doug Wright, ICHEP Amsterdam 31
Begun to probe the same CP-violating phase and possibly new physics via penguin modes:B 0 K0
S
B 0J/ 0
and open charm modes:B 0D*+D*-
B 0D*+D-
Conclusion
New measurement of sin2 from charmonium modes (88 x106 BB)
Submitted to PRL July 17, 2002(hep-ex/0207042)
Results have been improving by more than just luminosity gain
The Standard Model remains unscathed, but the high statistics future of BaBar will provide further opportunities to challenge the theory.
(First BaBar results)
Million BB pairs
July 00
Feb 01
July 01Mar 02
July 02
sin2sin2 = 0.741 ± 0.067 (stat) ± 0.033 (syst) = 0.741 ± 0.067 (stat) ± 0.033 (syst)
July 24, 2002 Doug Wright, ICHEP Amsterdam 32
July 24, 2002 Doug Wright, ICHEP Amsterdam 33
sin2 in subsamples
July 24, 2002 Doug Wright, ICHEP Amsterdam 34
Tagging performance
Category Efficiency () Mistag Fr. () Mistag Q=(1-2)2
Lepton 9.1 0.2 3.3 0.6 -1.4 1.1 7.9 0.3
KPiorK 16.7 0.2 9.9 0.7 -1.1 1.1 10.7 0.4
KorPi 19.8 0.3 20.9 0.8 -4.2 1.1 6.7 0.4
Inclusive 20.0 0.3 31.6 0.9 -2.0 1.2 2.7 0.3
Total 65.6 0.5 28.1 0.7
July 24, 2002 Doug Wright, ICHEP Amsterdam 35
Monte Carlo correction
We evaluated the size of any potential bias on sin2 by fitting the full MC in two ways: Fitting data-sized signal MC samples with mistag fractions and t
resolution fixed to the MC truth values (see plot).Average bias = +0.012 0.005.
Same as above except mistag fractions and t resolution from Breco MC.
Average bias = +0.014 0.005.
One possible source of bias comes from neglecting the known correlation between the mistag fractions (or dilutions) and sigma t. Estimates from toy and full MC inticate a bias at the level of +0.004.
We correct the fitted sin2 by subtracting 0.014 and assign a systematic error of 0.010 to this correction.