Violation in Mixing

122 Measurement of Branching Fractions for � ¦ � Ã � ¦ decays
delta E (GeV)
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5.18 5.2 5.22 5.24 5.26 5.28 5.3 5.32
beam-energy substituted mass (GeV)
Figure 5-1. Left plot: definition of the grand side-band, the Ñ �Ë and ¡� side-bands and signal box.
Signal Box � � ¡� � �� Å�Î
¡� upper side-band �� � ¡� � �� Å�Î
¡� lower side-band � � ¡� � � Å�Î�
where all the three ¡� band have the same � Å�Î width. The Ñ�Ë side-band and signal box are defined
in a mode independent way (see Sec. 4.2.2):
5.2 Ã Ë reconstruction
Ñ�Ë side-band �� �Ñ�Ë � �� � ��Î� �
Details of Ã Ë reconstruction can be found in Chapter 3. Candidate Ã Ë mesons are constructed using a
¬
preliminary loose cut ¬ Å � � Å Ã ¬ Ë � � � ��Î� . The ÃË candidates are then vertexed and
the daughter momenta are recalculated at the best-fit ÃË decay vertex.
To select ÃË we use two cuts: a cut on the invariant mass cut and a cut on the lifetime significance which is
is its error.
defined as ØÃË��Ø , where Ø
ÃË
ÃË is the measured 2-dimensional decay time and �Ø
ÃË
Figure 5-3 shows the invariant mass distribution of the Ã Ë candidates for � � Ã Ë � Monte Carlo, while
Fig. 5-4 shows the same variable in continuum Monte Carlo and off-resonance data. All distributions are
fitted with a double Gaussian on a linear background. The resolution is � �� in signal Monte Carlo
and �� Å�Î� in data. To reduce contamination from fake Ã Ë candidates, the cut
MARCELLA BONA
�ÑÃË ÑÈ��� � � Å�Î�