1. BaBar Physics Results and UCSD Contributions
Vivek Sharma
University of California, San Diego
4/23/2019
V.Sharma DOE Review 2000

2. BaBar Physics Highlights
Measurement of Sin2b with 9 fb-1 (Osaka)
Precise measurements of time-dependent B0 Oscillations with
inclusive dilepton
Exclusive fully reconstructed B Samples
Precise measurement of B0 and B- Meson lifetime
Measurement of B0 -> p+ p- and B0 -> K+ p- Rates
Measurement of B -> K*g
Search for B (K, K*)l+l-
B Meson Reconstruction and measurement of Branching Fractions
Time dependent Measurements
Future CP Physics
4/23/2019
V.Sharma DOE Review 2000

3. BaBar Physics Talks Today
Soeren Prell will describe time-dependent B Mixing analysis (headed to be the world’s best measurement) and measurement of mistag fractions for CP measurements
Riccardo Faccini will describe the Sin2b Measurement
I will summarize
Highlights of Babar Physics results
B reconstruction Effort and Physics with it
Future physics directions and timeline for publications
4/23/2019
V.Sharma DOE Review 2000

4. Observation of B0pp & Kp
Sensitive to angles
Sin2a via time dep. CP asymmetry
B0 -> K+pi- Vs B- -> K0Pi- possibly sensitive to g
Require excellent Pi Vs K discrimination (DIRC)
Precursor to other quasi-two body, three-body and four-body charmless B decay analysis needed for Sin2a
N() = 25+-8
N(K) = 26+-8
N(KK) = 1+-4
Cut-based analysis using kaon selector
4/23/2019
V.Sharma DOE Review 2000

5. Likelihood analysis Good News for Sin2a ?
Global likelihood fit using mES, E, event topology and energy flow based discriminant, and track Cherenkov angle
Mode Ns
Stat. Sig. (s)
BaBar
B (10-6)
CLEO
p+p-
5.7
K+p-
6.7
K+K-
2.1
<6.6
<1.9
Good News for Sin2a ?
4/23/2019
V.Sharma DOE Review 2000

6. Br(B0 -> K*0g) = (5.42 +- 0.82(stat) +-0.47(sys)) x 10-5
Electroweak Penguins
Vital for measurements of
V_td/V_ts
Direct CP violation searches
First step : Measurement of Exclusive mode B –K*g g t w
S/d
signal = events
BaBar (8.6 x 106 BB)
Br(B0 -> K*0g) = ( (stat) (sys)) x 10-5
4/23/2019
V.Sharma DOE Review 2000

7. Search for B (K, K*)l+l-
B K e+e-
B K m+m-
B K* e+e-
B K* m+m-
e+e- K+
e+e- K*0 2
m+m- K+
m+m- K*0 1
Mode
# obs. evts
Total 3
# bkg. evts
0.25
0.50
0.33
1.3
0.20
90% C.L. limit
< 12.8 x 10 -6
< 24.7 x 10 -6
< 25.2 x 10 -6
< 8.3 x 10 -6
3.15 fb-1
4/23/2019
V.Sharma DOE Review 2000

8. B Meson Lifetimes B0/B0 7.4 fb-1 B+/B-
B0 =  (stat)  (syst) ps
B+ =  (stat)  (syst) ps
B+/ B0 =  (stat)  (syst)
4/23/2019
V.Sharma DOE Review 2000

9. B0 Mixing with Dilepton Sample
POCA
B20
Lepton 1
True B1
vertex
True U(4s)
Estimated
Y(4S) vertex
(4S)
<z> = 250 µm B0 l+ l-
Dmd = (0.507 ± 0.015(stat) ± (syst))  ps-1
4/23/2019
V.Sharma DOE Review 2000

10. B Meson Reconstruction
A variety of measurements are done best with a large fully reconstructed sample of B mesons
B Oscillation
B lifetime
Study of Flavor tagging calibration (for CP)
Null CP measurements (calibration check for sin2beta)
With rising accumulated luminosity, a large sample of fully reconstructed events will change the way we do many key measurements in B physics
B decays with missing neutrino
b-> Tau nu and b -> s nu nubar
B-> u l nu inclusive and exclusive rates (Vub)
Reconstructing large B samples are non-trivial
Individual branching ratios are small (~0.2%)
Many “drops in the bucket”
Large multiplicity in B decay requires good particle reconstruction efficiency and background control (PID)
Requires good software coordination (~40-60 decay modes need to be reconstructed)
Babar has the largest sample of fully reconstructed B mesons
Reconstructed and analyses within weeks of data taking
4/23/2019
V.Sharma DOE Review 2000

11. B0 Meson Reconstruction
B0  D(*) -p+
 D(*) -r+
 D(*) -a1+
 J/Y K*0
2577±59 B0
4/23/2019
V.Sharma DOE Review 2000

12. B- Meson Reconstruction
B -D0 p +
B -D*0 p +
2636±56 B±
4/23/2019
V.Sharma DOE Review 2000

13. Fully Reconstructed (4S)p- K- p+ m+ m-
B0 y(2S)K0s
( )
B0D*+p-
D*+D0p+
y(2S)  m+ m-
K0s p+ p-
D0K-p+
4/23/2019
V.Sharma DOE Review 2000

14. B0  D* -l+ nl D*-  D0 - D0  K-p+ , D0  K-p+ p0 , D0  K-p+ p- p+
7517104
4/23/2019
V.Sharma DOE Review 2000

15. Fully Reconstructed B Decays at DOE Review last year
From 18 to Reconstructed B Mesons in 1 year
4/23/2019
V.Sharma DOE Review 2000

16. UCSD Contributions to Sin2b Measurement
4/23/2019
V.Sharma DOE Review 2000

17. Time Dependent CP Asymmetry Measurement
Btag
Bcp
lepton
Kaon
Z 
Four Requirements
Large samples of reconstructed “CP-interesting” decays of B Mesons
2. Measure the Z between the tag B and the CP B  Precision tracking and Vertexing
3. Tag flavor of the other B(tag) and measure “mistag” rates from data  Time-dependent Mixing with “non-CP” B decay modes
4. “null” CP measurements using non-CP B samples
UCSD group has played an important role in each of these issues
4/23/2019
V.Sharma DOE Review 2000

18. UCSD Role in Babar Physics
Riccardo Faccini :
Sin2b Technical Coordinator
Responsible for integrating all aspects of physics necessary for CP Asymmetry measurement
Convenor, Charmonium Group
Micro-DST database design and implementation for Physics analysis, New Data Model Taskforce
Gerhard Raven
Babar Tracking Coordinator (till ~June 2000)
Vertex Reconstruction
Data Delivery Model
Soeren Prell
Fitting algorithm (tFit) for Sin2b, time-dependent mixing and Lifetime (BaBar Standard)
Babar Statistics task force
Shahram Rahatlou
Author of analysis packages for B reconstruction (Babar Standard)
Thesis on Sin2b Measurement
David MacFarlane
Chair, Publication Board
B Reconstruction
Vivek Sharma
Convenor, B reconstruction (BRECO) Group
B Mixing and Sin2b
4/23/2019
V.Sharma DOE Review 2000

19. UCSD Role In Babar Physics Infrastructure
Developed and maintained Micro-DST for physics analysis used by all Babar analyses
Author of first (and only) B meson reconstruction and analysis packages: CharmUser, BrecoUser and DstarlnuUser heavily used in Babar
Copied for other analyses with technical input from UCSD
Author of CPFramework : Data-mining and delivery
Algorithm to “tune” MC with data performance to study systematic errors
Charged Particle tracking
Particle Identification : Leptons & Kaon
Taskforce to develop new Computing/analysis model for data analysis with ever-increasing data samples
tFIT: Framework for time-dependent CP asymmetry, B mixing and lifetime analysis is a Babar Standard
B & D meson vertex reconstruction and error evaluation :
Is 1 m measured by Babar the same as the standard
Critical for all time-dependent measurements
Critical Role in facilitating BaBar Physics
4/23/2019
V.Sharma DOE Review 2000

20. Publications on 2000 Data
First publication based on 2000 data targeted for spring 2001
Sin2b measurement targeted for BCP4 and Moriond
And validation (time-dependent) measurements which exercise relevant algorithms
B mixing with fully reconstructed B sample
B lifetime with fully reconstructed B samples
Expected to be the World’s best measurements
Expect a flurry of publication between spring and fall2001
4/23/2019
V.Sharma DOE Review 2000

21. Data Sample Accumulated and Projected
Osaka Data
20 fb-1
Future Luminosity Projections
Year  fb-1
Year  +40 fb-1
Year  +80 fb-1
Year  fb-1
Expect very precise test of Sin2b end 2001 and significant measure of Sin2a
4/23/2019
V.Sharma DOE Review 2000

22. UCSD Physics Goals
Continue with successful & singular focus on Sin2b and B0 mixing measurements
Develop CP fitting to include more decay modes with their specific physics issues
Transversity (angular) analysis for PsiK*, D*D*
Sin2a
Continue to build large samples of fully reconstructed B Mesons
B- -> Tau nu
B-> X_u l nu Final states
4/23/2019
V.Sharma DOE Review 2000