Ch. de la Vaissiere, 7 octobre 1998

- Explore channels other than the rare J/psi channel of the book study
- Find channels which are also be well signed and pure
- Exploit kinematical+geometrical constraints to achieve accuracy on the vertex position of the reconstructed B and remove combinatorial background.

- 4000 Aslund B0-B0 events with one B0 decaying in J/psi K pi.
- This sample is used to develop prototype kinematical and geometrical fits algorithms.
- In this sample, there is only one useful B
_{0}per event - We attempt to reconstruct decay chains
B
_{0}--> D*^{+/-}+ pions - The D*
^{+/-}are looked in the D*^{+/-}--&gONT COLOR="#0000FF">D*^{+/-}--> D_{0}+ pi^{+/-}mode. - The D
_{0}are searched in 4 modes - K pi,
- K pi pi
_{0}, - K pi pi
_{0 }pi_{0 } - K pi pi pi
- Starting from D
_{0}candidates , we construct D*^{+/- }then B_{0}. - Kinematical(mass, Ebeam)+geometrical fits are performed at each step to purify the sample.

- Many candidates and important combinatorial background except for the K pi mode.
- Geometrical and kinematical fits (including pi0s) are performed
- Plots of D
_{0}fit probabilities fits are given in the following figure

- After a probability cut at 1% one finds :
- 2935 accepted, 414 true D0
- 0.103 D
_{0 }per B_{0}.B_{0}. - The average purity is only 14%

- After a classical cut on Delta-M between the D*
and D
_{0 }masses, one finds: - 499 accepted, 171 true D*
- 0.042 D* per B
_{0}. - The average D* purity is 35%
- One applies a fit with 2 kinematical constraints + 6(10) geometrical constraints, and 4 unknowns ; 4(8) n.d.o.f.
- Plots of D* fit probabilities fits are given in the following Figure
- After a probability cut at 1% one get
- 214 accepted, 168 true D*
- 0.042 D* per B
_{0}. - The average D* purity is 78%

- We add to the D* , 1,3 charged pions + 0, 1,2 pi0s
- Raw Selection ; M(D*
^{+/-}+ pions) ~ M(recoil) ~ M(B) - 38 accepted, 27 coil) ~ M(B)
- 38 accepted, 27 true B
_{0} - We perform a full fit of the decay chain
- Highly constrained fit ; <n.d.o.f> = 11
- 24 candidates accepted, all fully reconstructed B
_{0} - Accuracy on the vertex : < 60 microns> similar to golden Psi channels
- Plots of B
_{0 }fit probabilities fits and accuracies are given in the following Figure - Extrapolation of the 24 reconstructed B
_{0 }to 5M Upsilon(4S) events : 30 K B_{0} - Kinematical + geometrical fitting are efficient
to purify D*
and B
_{0 }. - NB: Background may be higher in ordinary B
_{0}B_{0 }events - ASLUND may be optimistic, but it is not the end of the road:
- In a near future addition ofIn a near future addition of
- channels with K0s
- extra D*
^{+/-}--> D^{+/-}+ pi_{0} - Reconstruct B
_{0 }with D^{+/-}+ pions. - Problem of
B
^{+/-}lifetimes : - B
^{+/-}love D*^{0}s but D*^{0}s decay in D_{0}+ pi_{0}or D_{0}+ gamma ; - There is no equivalent to the golden chain D
_{0}+ pi^{+/-}. - Measuring of the B
^{+/-}lifetimes with D* could be more difficult.