Violation in Mixing

88 Ã Ë reconstruction and efficiency studies
x 10 2
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0.46 0.48 0.5 0.52 0.54
Ks mass
Figure 3-8. Invariant mass distribution of true Monte Carlo à Ë.
3.3.4 Correction for the Monte Carlo efficiencies
To evaluate the Ã Ë efficiency in data with respect to the Monte Carlo estimate, a set of corrections is
produced with the inclusive analysis described above. The corrections are given in � bins of the already
defined -dimensional flight length: and they are simply the bin-by-bin ratios between the Ã Ë efficiency in
the on-resonance data over the Ã Ë efficiency in the MC samples. This ratio does not depend on luminosity
of the two samples. A correction ¦ is assigned in case there are no reconstructed Ã Ë in the �Ö bin in
data or in MC (i.e. high flight length values). They are also normalized to the first bin: that means that in
principle one could get the same correction values from the ratio between the number of reconstructed à Ë
in the on-resonance data over the number of reconstructed Ã Ë in the MC samples. The normalization to the
first bin is due to the fact that Ã Ë reconstruction has to be correlated to the tracking efficiency. Since the
Ã Ë daughter candidates are selected from the list of all the charged tracks, the overall correction should take
into account also the differences of the charged track reconstruction in data and in Monte Carlo.
This tracking correction is studied in different control samples and these analyses provide the correction
value and the associated systematic error. For the ChargedTracks list (no selection cuts at all), it has been
found that no correction is necessary but a systematic error of per track has to be included into the
efficiency calculations. This leads to a systematic of per Ã Ë candidate.
Thus, since the normalization is done to the first bin, one should scale the pure Ã Ë correction for the tracking
efficiency correction that has to be applied within cm of flight length.
The bin-by-bin number of reconstructed Ã Ë candidates is obtained with the usual double Gaussian fit
with linear background to bin-by-bin invariant mass distributions: some examples of these fits are given
in Fig. 3-13.
Two sets of corrections are provided for each period (block 1 and block 2): the first set comes from ÃË reconstruction with no cuts except for the hadronic selection on the events, while the second set has an
additional momentum cut (ÔÃË � ��Î� ). This method is used in order to provide corrections which are
independent from the momentum range of the ÃË candidates taken into account in the specific analyses.
MARCELLA BONA