decays. Text for the blessed web page - CDF note 6391
decays. The CDF Collaboration
August 2, 2004
We present a measurement of the relative branching fractions 
and
and of the CP asymmetries in the decay of Cabibbo
suppressed decays, based on about 
of data
collected by the CDF experiment during the Feb. 2002 - May. 2003 data taking
period.
The relative branching fractions are found to be:
The direct CP asymmetries are found to be:
The sample is collected using the Two Track hadronic Trigger (SVT), specifically designed for the collection of heavy flavor decays.
The Silicon Vertex Tracker (SVT) is being used to trigger on hadronic
decays of charmed and bottom mesons. Using about of data collected
by CDF during the 2002/2003 data-taking, we measure the relative branching ratios
and
, and perform the first measurement of the
direct CP-violating decay rate asymmetries in CDF.
In the amplitude ratios many of the systematic associated with trigger and
reconstruction efficiency cancel to first order, thus allowing
very precise measurements.
, 
and 
candidates are reconstructed picking up two tracks pairs
of opposite charge. The track selection match offline tracks to SVT tracks in order
to select only candidate vertices that were firing the SVT multi-body trigger.
The latter require two opposite charged tracks with transverse momentum
greater than 
and impact parameter between 
and
.
The reconstructed candidates are then combined with a
soft pion track to reconstruct the
final 
candidates. The charge of the soft pion
is required to match the charge of the pion from the decay.
No particle identification has been used in this analysis.
About 180000 , 16000 and 7000 candidates (tagged with 
),
pass our selection cuts based on few simple quantities: impact parameter less
than 
, projected decay length of the meson 
,
inside a 
window (
)
around the expected value, and the product of the impact parameters of the
two tracks less or equal to zero.
We will determine the relative branching ratios as
where 
is the number of decaying in the appropriate mode in our data and
are the overall acceptance for each of the decay modes. This includes
both trigger efficiency and offline reconstruction
efficiency, and is estimated using a complete simulation of the CDF detector including
realistic emulation of the SVT trigger, the effects of the nuclear interactions and decay
in flight of kaons and pions and time dependent detector inefficiencies.
We use the same procedure to search for the direct CP asymmetries
where f can be 
or 
.
The charge of the slow pion from the decay serves as an unbiased
tag of the 
flavor.
We correct for the intrinsic charge asymmetry of the CDF detector studying this effect on samples of unbiased tracks as a function of the track transverse momentum, and testing any possible residual effect after the correction on independent samples of meson decays where CP-asymmetry is not expected.
This section summarizes the numbers which have been blessed for this analysis.
Number of events in the various modes:
Table 1: Number of events in the various modes.
Our largest sources of systematic error for the relative branching ratios come from
the model for the
background, the lifetime difference between the mass eigenstates and
the MC statistic.
Other sources of systematic uncertainty come from the
estimate of the relative acceptance and
contamination from non prompt production.
Dominant systematic for the direct CP asymmetry measurements come
from the correction for the charge asymmetry for low momentum tracks
in the CDF tracking system.
Other sources of systematic come from the MC Pt input spectrum, the effect on the relative acceptance due to the description of the Tevatron beam profile in Z, the uncertainties on the nuclear interactions for hadronic particles in GEANT.
Table 2 and 3 summarizes individual systematic
uncertainties, and the overall systematic we assign to our measurements
taken as the as the quadrature sum of the each contribution.
Table 2 refers to the relative branching fraction measurement,
the uncertainties are expressed as relative errors.
Table 3 refers to the CP asymmetries measurement,
the uncertainties are expressed as absolute errors.
Table 2: Relative systematic uncertainties for the relative
branching fraction measurements.
Table 3: Absolute systematic uncertainties for the CP
asymmetry measurements.
Relative branching fractions:
The direct CP asymmetries are found to be:
The following figures have been blessed for the mass difference measurement. More text can be found in CDF note 6391.
Figure 4: 
invariant mass distribution for 
Figure: invariant mass distribution for 
Figure: 
invariant mass distribution for 
Figure: invariant mass distribution for 
Figure 6: KK invariant mass distribution for 
Figure: KK invariant mass distribution for 
Figure 7: track charge asymmetry (defined as 
) in the CDF
detector as a function of the track transverse momentum, used to correct the
measured asymmetries.
Figure 8: 
asymmetry as a function of transverse momentum for the
decay 
. Black point show the measured
asymmetry w/o any correction applied, red point after correction for the acceptance,
and blue points after correction for the intrinsic charge asymmetry of the detector
response and tracking algorithms
Figure 9: transverse momentum spectrum in data and in the simulation (input spectrum
from the CDF charm x-section measurement) for
decays.
Figure 10: Same as previous figure but in logY scale
CP Asymmetries and Decay Rate Ratios of Cabibbo supressed decays.
Text for the blessed web page - CDF note 6391
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