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46 CHAPTER 4. DATA SAMPLE AND KL TAG
4.2.2 Dependence of the tagging efficiency with LK
KL → π 0 π 0 π 0 events are tagged by KS → π + π − events which satisfy the requirements
described in Sec. 4.2. The tagging efficiency has been evaluated by Monte
Carlo as a function of LK (KL decay vertex position) for the dominant KL decay
channels. For a KL decaying in a given channel at a given LK, the tagging efficiency
is defined as:
ε(tag, KL → i, LK) = N(tag, KL → i, LK)
N(KL → i, LK)
(4.11)
where N(tag, KL → i, LK) is the number of KL → i decay mode events retained
after the tagging procedure, and N(KL → i, LK) is the total number of KL → i
decay mode events. The results are shown in Fig. 4.3.
ε tag
0.8
0.75
0.7
0.65
0.6
0.55
0.5
96.39 / 69
P1 0.7033 0.1724E-03
P2 0.3423E-04 0.1681E-05
π 0 π 0 π 0
π + π - π 0
K e3
K μ3
0 25 50 75 100 125 150 175 200 225 250
K L decay length KINE (cm)
Figure 4.3: Tagging efficiency as a function of LK for main KL decay modes.
The difference in tagging efficiency among the modes is mainly due to the dependence
of the trigger efficiency on the KL behaviour (Ref. [42]). Only the calorimeter
trigger (Ref. [35]), which requires two local energy deposits above some threshold,
is used for the present analysis (see Sec. 3.3).
The reconstructed transverse radius distributions of the KL vertex with very
loose tagging requests have been studied on 2001-02 data sample (Ref. [42]). They
show a very good data - Monte Carlo agreement in the fiducial volume for charged
KL decays and KL → π 0 π 0 π 0 decay, respectively shown in fig. 4.4 left and right. The
slight disagreement in the first bins of the spectrum in the charged decays has been
further investigated in the quoted reference, to understand tracking inefficiencies,