1. For the BaBar Collaboration
Measurement of the Amplitude Ratio of B0  J/ K*0 to B0  J/ K*0 (K+-) decays
Max Baak
NIKHEF, Amsterdam
For the BaBar Collaboration
APS Meeting
Philadelphia, 8 April 2003
Max Baak

2. Two simple concepts ? 1 2 Wrong-flavor decay Right-flavor decay
B0  J/ K * 0
( )
Right-flavor decay
B0  J/ K * 0
( ) 1
( )
To tag a K*, use charge of kaon and pion 2
Max Baak

3. Can sin2ßS and sin2ßL be different?
Time-dependent asymmetry for B0  J/ KS,L normally given by -
sin2ßS = sin2ßL
Can sin2ßS and sin2ßL be different?
- SM corrections: (sin2ßS - sin2ßL) ~ 0.01
- Experimental limit: 0.02 ± 0.17
How to find wrong-flavor decays if K0 and K0 mix into CP states?
 Use B0 J/ K*0 sample! Same quark-level process. Tag with K*0 K+-.
BaBar data
Grossman, Ligeti, Kagan
Phys.Lett.B538:327
Observed asymmetry
sin2S =  0.067
For different sin2ßS and sin2ßL, need non-zero wrong-flavor decay amplitudes (New Physics)
sin2L =  0.158
Max Baak

4. B  J/ K*0 time dependent analysis
a) unmixed
B0(t)
J/K*0 B0
Initial state
Flavor eigenstate
b) mixed B0
With wrong- flavor decays
No wrong- flavor decays
B0(t) B0
Initial state
Flavor eigenstate
J/K*0 b) a) b) a)
Standard Model
Wrong-flavor
For final state J/ K*0
replace C  -C , S  -S .
J/K*0
Extract wrong-flavor to right-flavor
amplitude-ratios  and  from
time-dependent fit to
B0/B0  J/ K*0 and B0/B0  J/ K*0
=0  C=1, S=0 (standard B0B0 mixing)
Max Baak

5. BaBar Detector e+ (3.1 GeV) e- (9 GeV) z
Electromagnetic Calorimeter
6580 CsI(Tl) crystals
1.5 T solenoid
e+ (3.1 GeV)
Cerenkov Detector (DIRC)
144 quartz bars
11000 PMs
e- (9 GeV)
Drift Chamber
40 stereo layers z
Silicon Vertex Tracker
5 layers, double sided strips
SVT: % efficiency, 15 mm z hit resolution (inner layers, perp. tracks)
SVT+DCH: (pT)/pT = 0.13 %  pT %
DIRC: K- separation GeV/c  GeV/c
EMC: E/E = 2.3 %E-1/4  1.9 %
Max Baak

6. K-p separation with Cerenkov Detector (DIRC)
Good kaon-pion separation essential to distinguish between K*0K+- and K*0 K-+
BaBar uses DIRC: Čerenkov light in quartz  angle qc handle on particle ID
>9s
K/p separation
s(qc)  2.2 mrad
Momentum range of K and  from K* < 3 GeV
Max Baak

7. Analysis Technique sz ~ 110 mm sz ~ 65 mm U(4s) bg = 0.55 Dt @ Dz/gbc
At time of BTAG decay,
the 2 B’s are in opposite
flavor states K+
Tag B
sz ~ 110 mm
J/Y
Reco B
sz ~ 65 mm z
U(4s) Dz
K*0
bg = 0.55
Dz/gbc
260 mm
Determine flavor of other B meson BTAG (“tagging”)
Fully reconstruct B meson in state J/Y K*0 or J/Y K*0
Reconstruct vertex of BTAG and compute proper time difference Dt
Max Baak

8. Dt distribution of mixed and unmixed events
realistic
mis-tagging & finite time resolution w
J/Y K* pdf (similar for J/Y K*)
perfect
flavor tagging & time resolution
Bflav Mixing pdf
D(*) , , a1 sample (Bflav) determines mistag fraction w and resolution function
Res w
Max Baak

9. Data Sample [1999-2002]: 82 fb-1 on U(4s) Resonance
3s cut on
DE applied
signal region
E [MeV]
Sample
Ntagged
Purity
J/Y K*0
860
96%
856
‘tight’ kaon selection
mES [GeV/c2]
Max Baak

10. Fit Parameters Likelihood Fit
Combined unbinned maximum likelihood fit to Dt spectra of B-flavor and J/Y K*0 and J/Y K*0 samples.
Analysis performed blind.
Fit Parameters
C,S,C,S
Mistag fractions for B0 and B0 tags 12
Signal resolution function 8
Empirical description of background Dt 24
B lifetime fixed (PDG 2002 value) tB = ps
Mixing Frequency fixed (PDG) Dmd = ps-1
tagged J/Y K*
tagged flavor sample
48 total free parameters
All Dt parameters extracted from data
Correct estimate of the error and correlations
Max Baak

11. WARNING! Fake wrong-flavor decays! Need to minimize this effect
K- swapping
Doubly mis-IDing both K+ and - for each other fakes a K*0 for a K*0
- From MC: double mis-ID rate wrec = 0.3 %
WARNING! Fake wrong-flavor decays! Need to minimize this effect
Effect of K- swapping on time-dependent decay distributions?
To lowest order sine terms not affected, but cosine terms are.
(assuming C, C and S, S are of equal size)
mixed up
on wrec occasions
Determined using MC
Coefficient C S
Syst. Error
 0.004
 0.001
 0.003
Max Baak

12. Result C = 1.045 ± 0.058 (stat) ± 0.034 (syst)
S = ± (stat) ± (syst)
C = ± (stat) ± (syst)
S = ± (stat) ± (syst)
a) unmixed
Entries / 0.6 ps
b) mixed
Source
Error C/C
Error S/S
Background description
0.019
0.017
t resolution and detector effects
0.016
0.021
Signal mistag fractions
0.013
0.000
md and B (PDG 2002)
0.004
0.006
Monte Carlo statistics
0.015
K swapping
0.001
Tag-side DCKM decays
Total
0.034
0.039
c) asymmetry
Asymmetry
See my next talk!
t (ps)
Max Baak

13. Conclusion To be submitted to PRL.
No sign for wrong-flavor decays B0 J/ K*0 and B0 J/ K*0
Using the relations:
Measured values Standard Model 1 2 3
Assuming common wrong-flavor decay
amplitudes for B0 J/ K*0 and B0 J/ K*0
To be submitted to PRL.
Max Baak

14. Backup Slides
Max Baak

15. Cerenkov Particle Identification System (DIRC)
Good kaon-pion separation essential to distinguish between K*0K+- and K*0 K-+
DIRC: Čerenkov light in quartz
K- separation > 4 
for this analysis
Transmitted by internal reflection
Rings projected in standoff box
Detected by PMTs
Essential for Kaon ID >2 GeV
Max Baak

16. B Flavor Tagging Methods
In BaBar tagging is handled with Neural Nets
Information used:
Primary lepton
Secondary lepton
Kaon(s)
Soft pions from D* decays
Fast charged tracks
Mistag fraction w determined with flavor eigen-states sample Bflav (23.7k events, purity 82%)
Smallest mistag fraction
Tagging category
Fraction of tagged events e (%)
Wrong tag fraction w (%)
Q =
e (1-2w)2 (%)
Lepton
9.1  0.2
3.3  0.6
7.9  0.3
Kaon+Kpi
16.7  0.2
9.9  0.7
10.7  0.4
Kaon+Spi
19.8  0.3
20.9  0.8
6.7  0.4
Inclusive
20.0  0.3
31.6  0.9
0.9  0.2
ALL
65.6  0.5
28.1  0.7
The errors on C,S,C,S
scale with quality Q
Max Baak