# Exploring the D* way

Ch. de la Vaissiere, 7 octobre 1998

# Objectives

• 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.

# Sample and description of the analysis:

• 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 B0 per event
• We attempt to reconstruct decay chains B0 --> D* +/- + pions
• The D* +/- are looked in the D* +/- --&gONT COLOR="#0000FF">D* +/- --> D0 + pi+/- mode.
• The D0 are searched in 4 modes
• K pi,
• K pi pi0,
• K pi pi0 pi0
• K pi pi pi
• Starting from D0 candidates , we construct D* +/- then B0.
• Kinematical(mass, Ebeam)+geometrical fits are performed at each step to purify the sample.

# Results on D0fits

• Many candidates and important combinatorial background except for the K pi mode.
• Geometrical and kinematical fits (including pi0s) are performed
• Plots of D0 fit probabilities fits are given in the following figure • After a probability cut at 1% one finds :
• 2935 accepted, 414 true D0
• 0.103 D0 per B0 .B0 .
• The average purity is only 14%

## Results on D* +/- --> D0 + pi+/- selection

• After a classical cut on Delta-M between the D* and D0 masses, one finds:
• 499 accepted, 171 true D*
• 0.042 D* per B0 .
• 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 B0 .
• The average D* purity is 78%

## Results on the reconstruction of B0 --> D* +/- + pions.

• 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 B0
• We perform a full fit of the decay chain
• Highly constrained fit ; <n.d.o.f> = 11
• 24 candidates accepted, all fully reconstructed B0
• Accuracy on the vertex : < 60 microns> similar to golden Psi channels
• Plots of B0 fit probabilities fits and accuracies are given in the following Figure # Preliminary conclusions

• Extrapolation of the 24 reconstructed B0 to 5M Upsilon(4S) events : 30 K B0
• Kinematical + geometrical fitting are efficient to purify D* and B0 .
• NB: Background may be higher in ordinary B0B0 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+/-+ pi0
• Reconstruct B0 with D+/- + pions.
• Problem of B+/- lifetimes :
• B+/- love D*0s but D*0s decay in D0 + pi0 or D0 + gamma ;
• There is no equivalent to the golden chain D0 + pi+/-.
• Measuring of the B+/- lifetimes with D* could be more difficult.
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