1. measuring the CP angle  at Babar
Status and future of
measuring the CP angle  at Babar
Jeroen van Hunen
(Babar plots: Max Baak , NIKHEF)

2. Some decay modes to access 
 sin(2+)
hep:ex/ (fully reconstructed) and (partially rec.)
 
Theoretically clean, but the 2 triangles of the 6 decay amplitudes
are squashed since is suppressed with respect to
 
Theoretical uncertainties: FSI, SU(3)-breaking corrections, etc.
and others……………
CERN B-Journal Club
October 3, 2003

3. No penguin pollution, theoretically clean
The decay mode
V*ud
Vcd
Vcb
V*ub
h = , , a1
 Interference between the mixing and the decay
Large BR, but:
 Interference is tiny
No penguin pollution, theoretically clean
CERN B-Journal Club
October 3, 2003

4. The angle 
mixing term
CERN B-Journal Club
October 3, 2003

5. The decay rates 4 decay rates, for example:
Fit the 4 decay rates with the data to obtain  and thus sin(2+) , but the value of r is unknown (not enough statistics to fit it together with ).
CERN B-Journal Club
October 3, 2003

6. The value for r Temporary solution:
With SU(3) symmetry relation determine r from the branching
fractions for This gives:
Add additional theoretical uncertainty of 30% on validity of SU(3) symmetry
In future (statistical errors on measurements reduced) improvement is needed:
theoretical models ~ 20% spread
other options? (no solution yet)
CERN B-Journal Club
October 3, 2003

7. The results for full reconstruction
CERN B-Journal Club
October 3, 2003

8. The t distribution
CERN B-Journal Club
October 3, 2003

9. The Measurements The results of the Babar fit : If become smaller
value of r is problem
CERN B-Journal Club
October 3, 2003

10. Interpretation : what is sin(2+)
Probabilistic interpretation: simulate (many) experiments with characteristics as data for many sin(2+) values, and count number of experiments where 2(sin(2+)- 2min is smaller then the data
68% CL : |sin(2+)|>0.69 (43<2+<137)
83% CL : |sin(2+)|>0 (at 98% CL for partial reco)
sin(2+) 1  sine not very dependent on 2+ (Bd : sin(2)  0.7 , but for Bs the phase s
very small (with BsDsK we measure s + )
CERN B-Journal Club
October 3, 2003

11. The Measurements
Full and partial reconstruction combined (roughly same precision)
If sin(2+)  0.94  continue setting lower limits
If sin(2+) < 0.75 (but excluded at 60% CL)  not good for SM
CERN B-Journal Club
October 3, 2003

12. The future No error on r included Thus: Current : 82fb-1
Summer : 500fb-1
Summer : 1000fb-1
Thus:
Summer 2007 : err*0.4
Summer 2009 : err*0.3
68% CL |sin(2+)|>0.92
(67 <2+<113)
CERN B-Journal Club
October 3, 2003

13. Some conclusions
now :
Full reco = at 68% CL |sin(2+)|> (43<2+<137)
Partial reco = at 90% CL |sin(2+)|>0.75
in 2009 :
full reco = at 68% CL |sin(2+)|>0.92 ? (67 <2+<113)
(but no error on r included!)
partial reco similar/better
Other modes will improve the results (how much?)
CERN B-Journal Club
October 3, 2003