Violation in Mixing

3.3 Studies on data 91
0.508
0.506
0.504
0.502
0.5
0.498
0.496
0.494
observed Ks candidate masses
0.492
0 5 10 15 20 25 30 35 40
flight length (cm)
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Ks reconstruction efficiency
0
0 5 10 15 20 25 30 35 40
MC true flight length (cm)
Figure 3-11. Monte Carlo: Ã Ë invariant mass (left) and reconstruction efficiency (right) as function of
decay length from the Monte Carlo truth: the empty dots correspond to block 2 Monte Carlo sample, while
the black points are the block 1 Monte Carlo sample.
¯ on-resonance data corresponding to a luminosity of � �� pb and to a number of �� � �� ��� ¦
� ��� giving an average cross-section of � � ¦ � �(stat) ¦ � � (syst) nb
No further selection is applied apart from the hadronic selection which has been updated with respect to the
Run 1 selection (see Sec. 3.3.1). The new selection consists of:
¯ BGFMultiHadron tag bit set
¯ number of GoodTrackLoose 5 in the event �
¯ Ê � ��
¯ the sum of energy of charged tracks plus calorimeter clusters in the fiducial region � �����Î
¯ primary vertex within 0.5 cm of beam spot in x and y
¯ primary vertex within 6.0 cm of beam spot in z.
This results in a slightly looser selection with respect to the previous one. This selection is the one used for
B counting analysis: it is described and discussed in [45]. A first estimate of the efficiency of this hadronic
selection is shown in table 3-4: the Monte Carlo sample used is the Run 1 equivalent one so these are just
preliminary values to be checked with the appropriate Run 2 Monte Carlo.
As in the Run 1 analysis, no other selection is applyed: the number of observed Ã Ë and their average
invariant mass are evaluated from a fit to the invariant mass plot, using a double Gaussian with a linear
background. The resolution on the Ã Ë mass is evaluated using a single Gaussian and linear background fit.
The invariant mass fit on this Run 2 data sample gives � � ¦ � �(stat) number of reconstructed à Ë
(see Fig. 3-15).
5
GoodTrackLoose definition: more than 11 drift chamber hits, � within 1.5 cm, Þ within 10 cm and transverse momentum
greater than Å�Î.
Ã Ë RECONSTRUCTION AND EFFICIENCY STUDIES