Plan for absolute BR measurements of

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Plan for absolute BR measurements of  D
semileptonic decays Bo Xin and Ian.Shipsey
Studies with Generic Monte Carlo samples
Introduction
Semileptonic decays provide direct measurements
of the Cabibbo-Kobayashi-Maskawa (CKM) Matrix
elements, which are fundamental parameters
describing the weak-current coupling of quarks
but are not predicted within the Standard Model.
However, semileptonic branching ratios are still
not well known.
Here we are using only one D tag mode The figure
on the right shows a fit to the Beam Constrain
Mass
The constraint on the CKM matrix in summer 2004
Assuming three generations, the 90 confidence
limits on the magnitudes of the elements are
distribution for
and ,
This is beginning to change with the start of
CLEO-c program
The signal for a semileptonic decay can be seen
at zero.
The CLEO detector
A typical event from our data

• State of Art Detector
• Drift Chamber Tracking (1 Tesla)
• RICH Particle ID
• Crystal EM Calorimetry
• 93 of solid angle
• Only small changes from CLEO III
• B field 1.5 ? 1 T
• Silicon ? ZD

Analysis Technique
Candidate events are selected by reconstructing a
D, called a tag, in several decay modes in which
there is a good signal to noise ratio. Then we
probe the system recoiling from the tag. The
absolute branching ratio can be determined as
, where is the
efficiency of finding a signal in the presence of
a tag D.

• Particle ID
• dE/dx RICH combined
• Electron ID
• A likelihood function
• constructed from E/p, dE/dx
• and RICH information
• Selection of pi0s
• The two photon combination with an invariant
  mass closest to the known pi0 mass.

Summary
Using 280 collected at the
resonance with the CLEO-c detector at the Cornell
Electron Storage Ring, we will present improved
measurements of the absolute branching ratios of
D semileptonic decays. Some preliminary studies
have been performed. Detailed studies will be
available soon. These measurements will
contribute greatly to the determination of CKM
matrix elements, and hence are of profound
importance to our understanding of the mixing of
flavors and generations induced by weak
interactions.