Violation in Mixing

98 Strategy and Tools for Charmless Two-body � Decays Analysis
¯ 10.1 million events (���� fb ) ÙÙ, �� and ×× Monte Carlo
¯ 6.2 million events (���� fb ) Monte Carlo
¯ 4.0 million events (�� fb ) � � Monte Carlo
¯ 0.94 million events ( � fb ) generic � charmless Monte Carlo
¯ �k events of each signal Monte Carlo sample
The � � � � and � � £ � decays have also been analyzed for control sample studies. All cuts
are tuned using Monte Carlo simulation and off-resonance data samples together with the sidebands of the
on-resonance data. Cuts were defined before analyzing the signal band of the on-resonance data-set (blind
analysis).
4.2 Event selection
The preselection is done checking the value of a number of tagbits based on some event variables: each
event should pass the so called BGFMultiHadron selection which consists of requiring at least 3 charged
tracks and Ê � ��� (see Eq. (4.4) for the definition of this variable).
Then, a specific selector has been studied to set a tagbit (named TagTwoBody) for a very efficient exclusive
selection of charmless twobody B decays. It is designed to look separately for � � , � ¦ Ã Ë, � � ¦ ,
� � , � Ã Ë and Ã Ë Ã Ë , selected among the charged tracks and the Ã Ë candidates reconstructed with
loose criteria (see Sec. 3.1.1). For this selector we consider as a � every cluster in the �� (where a
cluster is a connected set of �� crystals with an energy deposit) with a raw (not calibrated) energy greater
than ����Î� . In order to take into account � ’s split in two clusters, we use also a list of pseudoclusters
created by every pair of clusters having their centroids closer than ÑÖ��. In order to reduce
combinatorics, we loop over charged candidate or neutral cluster lists without considering tracks (clusters)
with momentum (energy) less than ����� ��� .
A pair of candidate � � (� ¦ ÃË , ÃËÃË ) is accepted when both tracks (track and ÃË , both ÃË )havea
momentum between � and ����Î�1 , when the sum of their momenta (Ô £ � of the � candidate) is in the
range – ��� ��Î� , and when the angle � £ between the two tracks (track and à Ë, both à Ë) is such that
Ó× � £ � ��. All quantities (Ô £ and � £ ) are calculated in the center-of-mass (CM) rest-frame.
A pair of candidate � ¦ � (� Ã Ë ) is defined when the sum of the energies of a track and a cluster in the CM
rest-frame is between ��� and �����Îand the angle � £ between track direction and cluster centroid is such
that Ó× � £ � ��. A pair of candidate � � is defined when the sum of the energies of the two clusters in
the CM rest-frame is between �� and �����Î and the angle � £ between the cluster centroids is such that
Ó× � £ � ��.
1 we use � (� ) mass hypothesis for charged track (neutral cluster)
MARCELLA BONA