Violation in Mixing

5.2 Ã Ë reconstruction 123
1
0.8
0.6
0.4
0.2
0
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
500
400
300
200
100
0
67.53 / 49
P1 5.699 0.2031
P2 1.869 0.2929E-03
P3 0.8193E-02 0.3343E-03
P4 -2047. 23.54
P5 2624. 13.82
P6 -773.9 6.745
1.8 1.82 1.84 1.86 1.88 1.9 1.92 1.94
D mass
Figure 5-2. Study to measure the efficiency of the Ã Ë mass using � � Ã Ë � control sample: efficiency
for a cut of Ò� on the Ã Ë mass in on-resonance � � Ã Ë � decays (left); a typical fit to the � ¦ mass
distribution (right).
is applied. Given the different Ã Ë mass resolution in Monte Carlo and data, a detailed study has been
performed to measure the efficiency of the mass window using real data.
The efficiency of the mass cut is determined using a data control sample of � � ÃË� decays on the
full Run1 data-set. We select � mesons from continuum events and we require Ô £ � �� ��Î�, where
Ô £ is the momentum of the � meson in the CM frame. For events with multiple candidates, we choose
the one with invariant � mass closest to the PDG value. A cut of � � ����� is applied to suppress
combinatorial background. Only high momentum (Ô � ����Î� ) ÃË candidates are considered and the
requirement ØÃË ��ÃË � � cut is applied in order to have a à Ë
sample compatible with the one from
charmless two-body analysis. Left plot in Fig. 5-2 shows efficiency as a function of the Ã Ë mass cut in this
sample. For each cut, the efficiency is defined by fitting the � mass distribution and dividing the yield
found by the one obtained when no cut is applied to the Ã Ë mass. Right plot in Fig. 5-2 shows a typical fit.
We find an efficiency of �� ¦ cutting at the default value of ���, where � � � Å�Î� . To evaluate
the error on this efficiency, we used the signal MC of all the two-body charmless modes involving Ã Ë :
the same invariant mass is applied and the efficiency of the cut is evaluated. The quoted error of is
the greatest difference between the efficiencies estimated from MC signal events and the value found from
� � Ã Ë � control sample.
The second cut used to reduce contamination from fake ÃË candidates is the lifetime significance one: left
plot in figure 5-5 shows the lifetime significance ØÃË��Ø , which is peaked at zero for fake Ã
ÃË
Ë and has a
flat distribution for true ÃË . The data-MC agreement for the distribution of this variable has been checked
on ÃË in �� events (see plots in [60]).
MEASUREMENT OF BRANCHING FRACTIONS FOR � ¦ � Ã � ¦ DECAYS