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D Mixing Plots for Early Summer `98
The plots below are based on a fraction of the total
CLEO-II/SVX data that has been processed; around 3-4 1/fb of
integrated luminosity. The total sample now accumulated
is about 6 1/fb, and the ultimate CLEO-II/SVX sample should
be about 8-9 1/fb.
- K-pi+ Mass Plot (ps) (gif) (from David Asner)
for D*+ -> D0 pi+, D0 ->K-pi+, with D*+ momentum
greater than 1.5 GeV/c, for 3.7 1/fb of integrated luminosity.
The number of events
is about 11000, corresponding to a visible cross section
of about 3 picobarns. The resolution in mass is about 6.5 MeV,
which reflects improvements in CLEO track fitting due to
the Kalman-type algorithm, as well as the reduction in
multiple scattering from use of a Helium-Propane mixture in
the drift chamber.
These events are required to be within 2 standard deviations of the
nominal D*+ - D0 mass difference (see below).
No particle ID requirements, which in
CLEO would come from measurement of dE/dx in the drift chamber, or
from measurement of time-of-flight, have been made.
- D*+ - D0 Mass Difference Plot (ps)
(gif)
(from David Asner) for a sample selected in the manner above,
except now the events are within 2 standard deviations of
the nominal D0 mass.
The resolution in mass difference is about 260 KeV, which
reflects improvements in track reconstruction in the
coordinate parallel to the colliding beam axis. These
improvements were enabled by the CLEO silicon vertex detector.
- Proper Time (ps) (gif) (from David Asner) from the 3-dimensional flight distance of the
D0 from a reconstructed `primary' vertex to the `secondary' vertex where
the D0>K-pi+ decay takes place, for events that pass 2 sigma cuts in
both K-pi+ mass and D*-D mass difference. The gaussian core resolution
is about 1/3 of a lifetime; there are tails, which can be seen
on a logarithmic plot (ps)
(gif); the origin of these tails
is under study.
- Mass Plot (ps) (gif) (from Craig Prescott)
for the decay D0 -> phi K_short, which is a CP eigenstate,
(say CP = -1)
with CP opposite that of the K+K- or pi+pi- final states (which
would then have CP = 1).
These events are not required to originate from a D*+ decay,
but they are required to have momentum greater than 2.0 GeV/c.
There are about 1700 signal events, in an integrated luminosity
of 3.5 1/fb, which constitutes a visible cross section of about 0.5 picobarns.
The resolution in mass is about 3.8 MeV, which is smaller than
the 6.5 MeV measured for the decay D0 -> K-pi+; there are two
reasons for the resolution improvement: there are twice as many
charged particles in the final state here, and the energy release
Q in this decay is smaller than that in D0 -> K-pi+.
- Mass Plot (ps) (gif) (from Tony Hill)
for the decay D0 -> K+K-, which is a CP eigenstate, say CP=+1,
and is single-Cabibbo suppressed.
These events are required to originate from a D*+ decay,
and must have a D*+ - D0 mass difference within about
2.5 standard deviations of the nominal value; the D*+ is required
to have momentum greater than 2.0 GeV/c.
There are about 840 signal events, in an integrated luminosity
of 3.5 1/fb, which constitutes a visible cross section of about 0.24 picobarns.
Mixing through on-shell intermediate states would cause
the lifetime measured with these CP +1 K+K- final states to be shifted
relative to the CP -1 phi K_short final states.
- Mass Plot (ps) (gif) (from Tony Hill)
for the decay D0 -> pi+pi-, which is similar to the
K+K- decay described above. The principal difference
is that the branching ratio for D0 -> pi+pi- is two to three
times smaller than the branching ratio for D0 -> K+K-, and
so the number of signal events here is only 340.
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hnn@charm.physics.ucsb.edu 6/12/97
