1. Vivek Sharma University of California, San Diego
BaBar Physics Status
Vivek Sharma
University of California, San Diego
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2. Outline of This Talk UCSD physics effort
BaBar physics infrastructure responsibilities
CP physics and B Mixing analyses
BaBar physics preparation : snapshots
First events and the  (4S) scan
Reminder: CP Asymmetry measurement checklist
Luminosity
B reconstruction
Flavor tagging
Delta Z measurement
Status of BaBar physics software
Tracking and vertex reconstruction
Particle identification and flavor tag
Charm and B meson reconstruction
Near future physics plans and requirements
Precision tracking and vertexing
Efficient and Accurate b quark flavor identification
Data access, Simulation and Computing
V.Sharma DOE Review

3. BaBar Physics Infrastructure Responsibilities
Charged Particle Reconstruction Coordinator
Gerhard Raven
BaBar MicroDST Data-Format Development
Riccardo Faccini
Vertexing and Particle Composition Tools : Development and Validation
Riccardo Faccini, Shahram Rahatlou, David MacFarlane and Vivek Sharma
Primary Vertex Reconstruction
Particle Identification (dE/dx) in DCH
Fergus Wilson
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4. Current UCSD Physics Analysis Activities
 (4S) Scan
Riccardo Faccini
B Reco in B  Charmonium X modes
Shahram Rahatlou, Carsten Hast, Riccardo Faccini and Vivek Sharma
B Reco in B  D/D* X Modes
Shahram Rahatlou, Fergus Wilson, David MacFarlane and Vivek Sharma
Time-dependent B0 Mixing
Gerhard Raven, David MacFarlane,Vivek Sharma and Shahram Rahatlou
Data Validation : UCSD group
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5. MicroDST Development For BaBar Physics Analyses
Objective : Fill a gaping hole in BaBar Data Analysis Concept
To speed up analysis time, create a OO Database of information for each reconstructed event which
Is fast to access
Possesses comprehensive info about all attributes of event for physics analysis
Is small in size ~ 3Kb/event
Interfaces with (comprehensive but rather bulky and slow ) BaBar reconstruction software OO environment
Implementation
Contains
lists of candidate charged tracks, calorimeter objects etc
variables describing each candidate in an event (e.g., momentum, energy, track error matrix, basic subsystem information etc )
Result
“Micro” is THE Database used by all BaBar physicists for physics analysis (e.g. LP99).
Designed and Implemented by R.Faccini
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6. First Data ! : 26 May 1999
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7. Energy Scan for (4S)
Next Step : Scan for the peak of (4S) and sit at the peak
Have sat on the peak mostly with modest off-Y(4s) running
Analysis and feedback done “on the fly” with micro DST: R.Faccini
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8. Time Dependent CP Asymmetry Measurement
Btag
Bcp
lepton
Kaon
Z 
Three Requirements
1. Large samples of reconstructed “CP-interesting” decays of B Mesons => Luminosity at (4s)
2. Ability to measure the Z between the tag B and the CP B  Precision tracking and Vertexing
3. Ability to tag flavor of the other B(tag) via leptons or Kaon => Particle Identification
Relatively quick consolidation on all three requirements achieved in early BaBar data
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9. The Interaction Region
First Determine average location of beam “ribbon” (run-by-run) X Y Z
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10. Primary Vertex X Vs Z position
Beams Are Tilted in Z
Primary Vertex X Vs Z position
Tilt ~ 20 mrad
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11. Impact Parameter Resolution : Trajectory near IP
Critical for time-dependent CP Asymmetry Measurement
B Decay IP
Very close to expected precision, will be better with SVT/DCH alignment resolution ( see Raven talk next )
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12. Ks Reconstruction and Lifetime
Clean Ks signal with high ~ 60% efficiency
Evidence for good estimate of tracking efficiency and errors
Ks lifetime consistent with PDG
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13. Specific Ionization In Drift Chamber
dE/dx resolution of 7.5% is close to design
Useful for low momentum particle ID
Expect final calibration in next few weeks
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14. DIRC Particle ID Performance
Critical for high momentum tracks where dE/dx can not separate /K
Factor of ~ 14 pion rejection
Efficiency ~ 67%
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15. Muon Identification
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16. Electron Identification and  Rejection
Compare E/P : energy deposited in EMC with momentum measured in DCH
Electrons
Pions
Needs Better Calibration of EMC
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17. Inclusive Electron Spectrum
Preliminary look at the lepton spectrum, shown in the Y(4s) rest frame
Identification efficiencies and fake rate under study. Shape of the spectrum agrees with MC prediction for lepton spectrum in B decays
Kinematic end point
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18. CP-Interesting B Meson Decays
“CP Interesting” B Decay Modes
Most B decay final states contain
J/, D* or Ks
Their efficient reconstruction is critical
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19. Identification
After EMC calibration, will be sensitive to very low energy (>50 MeV)
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20. Inclusive D* Reconstruction
D* and D masses and resolution consistent with expectations
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21. Inclusive D* Reconstruction
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22. Slow Pion From D* Fitted Thru The Interaction Point
D*-D mass resolution limited by slow pion momentum reconstruction ~ 0.8 MeV
Precision in low pion trajectory reconstruction limited due to large mult. coulomb scattering.
Can use IP coordinates as a constraint to better define slow pion  and 
Leads to much better resolution
D* -D Mass Diff(GeV)
Hope to refine technique to have ~180 KeV resolution, measure D* natural width if large
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23. Inclusive J/Psi Production
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24. Inclusive J/ Production
Signal/noise will improve with better electron/muon selection and better DCH-SVT alighnment
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25. DCH/SVT Misalignment and Impact on Mass Resolution
500  SVT-DCH Misalignment
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26. Fully Reconstructed B Mesons
Lepton Photon 99: first event fully reconstructed
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27.
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28. Fully Reconstructed B Decays
UCSD !
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29. B Meson Reconstruction
Shown today is a fraction of the decay modes that we plan to reconstruct
Reconstruction rate is comparable to CLEO, but we will do better after EMC and DIRC are calibrated  Better particle identification and resolution
Encouraging that within 3 months of beginning of data taking, we are cleanly reconstructing B mesons from data recorded so far
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30. Luminosity Projections
Expect ~ by Christmas 99. This is “CP engineering data”
Expect by July With this dataset we will start being sensitive to …(depending on its true value )
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31. Immediate Physics Goals
Align and fine-tune the tracking system for optimal tracking efficiency and impact parameter(vertex) resolution
IN PROGRESS (see Raven talk next)
Calibrate EMC, DIRC and optimize Muon ID efficiency in IFR. Optimize global particle Identification and b flavor tag
Crucial test of “CP-Readiness” will be precise measurements of
Time Dependent Mixing
B Lifetime
With the 1999 BaBar data
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32. UCSD Physics Goals
Continue fine-tuning BaBar charged particle tracking for CP studies
Build large samples of fully reconstructed B and Charm mesons
B  X,  ‘X and other Charmonium modes
B  D*X, DX etc
Use this sample for
Time-dependent mixing Studies
B lifetime is a by-product of Mixing studies
Expect first B-mixing results by Spring 2000
Concentrate on measurement of
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33. UCSD leading CP physics effort in BaBar
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34. Computing Challenges Ahead
The data taking and analysis experience of last few months has pointed to inadequacies in the current model of BaBar computing ( see MacFarlane talk later today)
Amongst other problems, access and analysis of processed data is quite painful and time-consuming
Turn around time for ~ is ~weeks already
will get worse with level data
BaBar has realized that this could be a show-stopper and is working towards a non-Objectivity based solution which still utilises existing software
Needs careful attention in the next months
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35. Summary and Conclusions
BaBar is off to a very good start
Tracking system has worked flawlessly from the beginning
Calibration and fine tuning of EMC, DIRC etc in progress
BaBar is able to reconstruct the intermediate states ( Ks, D*,  ) necessary for reconstructing “cp-interesting” B decays
B mixing is the first major goal towards CP violation searches
Can expect sensitivity to
By next year if the machine continues its excellent run towards high luminosity
V.Sharma DOE Review