Violation in Mixing

108 Strategy and Tools for Charmless Two-body � Decays Analysis
Cut
�¡Å � ��� ��Î� � � �¡Å
�Å Ã� Ñ � � � � � �
Ô £ � � ����Î�
Ó× � £ à � ��
��� �Ô� ���� ��Î� or ��� �Ôà ���� ��Î�
Table 4-3. Cuts used to select a control sample of � £ � Ã � � decays.
candidate). Candidates in � mass side-band regions are used for background subtraction. The resulting
sample is used to parameterize the � distributions for pions and kaons.
A simple set of cuts were used to select a very clean sample of � £ decays in which either the à or � track
from the � decay has a momentum in the range ��� �� � ��� , covering � of the momentum range
of the daughters of the charmless two-body decays. The cuts are summarized in Table 4-3. The loose goodtrack
2 definition is used for selecting � daughter tracks and a very-loose good-track 3 definition is used
for the slow pion from the � £ decay. ¡Å is the measured mass difference between the � £ candidate
and the � candidate, �¡Å is the measured resolution on this quantity, Å Ã� is the reconstructed �
mass and �� is the resolution on Å Ã� . The mass resolutions are measured to be ��Å�Î� for �¡Å
and �Å�Î� for �� . The quantity Ó× � £ à is the cosine of the angle of the kaon track with respect to the
� flight direction, measured in the � center-of-mass system. For signal decays, this distribution is flat,
whereas the combinatorial background is peaked in the forward and backward directions.
The same set of cuts is used to select a sample of � £ in the Monte Carlo simulated data. The �
parameterizations obtained from this sample are used in constructing the PDFs for fits to Monte Carlo
events. This sample is also used to check that the Monte Carlo accurately simulates the efficiency of the
PID cuts. This is demonstrated in Figs. 4-6 which display the efficiencies of the PID � � cut used in the
� � � � analysis for kaons and pions, respectively, for both the data and Monte Carlo control samples.
There is good agreement between the two samples. Figs. 4-7 compare the efficiencies obtained from the
Monte Carlo � £ control sample to those obtained directly from Monte Carlo � � � � decays.
Good agreement is observed between the efficiency of the PID cuts in Monte Carlo simulated events and
that obtained from this control sample. Thus, the PID efficiencies obtained from Monte Carlo signal events
are used without any corrections.
2 see Sec. 4.2.2
3 The very loose good track selection does not include the ÔÌ and Æ ��Àhits cuts with respect to the loose good track one in
Sec. 4.2.2.
MARCELLA BONA