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Status Report on K L --> gg. Work done since June-02 (Memo 272 ) Code and procedures revised to run on the DSTs K L --> gg : Cuts for background reduction simplified and studied Background shape controlled Signal obtained including different background levels - PowerPoint PPT Presentation
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Status Report on KL-->
Work done since June-02 (Memo 272) Code and procedures revised to run on the DSTs
KL--> Cuts for background reduction simplified and studied
Background shape controlledSignal obtained including different background levels
KL--> : Cluster Recovery Splitting avoided
Track veto efficiency controlled
2002 Data Sample : 150 pb-1 filtered
Status Report Memo by November, followed by the paper draft
C.Bloise, F.Ceradini 10-Oct-02 1
Pre-selection
Requirements: Kl tag
KL-->
2 clusters, with E > 100 MeV geometrical Etot > 350 MeV projected) > 160o signal vs cut under
study L< 4signal vs cut studied
KL--> :
at least 3 clusters connected to 1 neutral vertex within an enlarged fiducial volume
C.Bloise, F.Ceradini 10-Oct-02 2
0.03%
Signal vs efficiency Pre-filter cut on Lk
0.976 0.990
KL--> Selection
C.Bloise, F.Ceradini 10-Oct-02 4
Cuts studied and included in the present analysis:
| Etot
- | < 4 arc(cos < 15o
Etot
= mk/2 * ( 1/a
1 + 1/a
2 ) ; a
i = ( 1- p
k* r
i) E
i = m
k/2a
1
cos = (E1
r1 + E
2 r
2) * p
k / | (E
1 r1 + E
2 r
2) |
The efficiency has been measured with data selecting the signal (~4000 events used)
= 0.918 0.004 0.004
The systematics have been controlled changing the cuts, measuring the signal at each cut
Signal vs efficiency Cut on Signal cutting also on
0.3%
0.820 0.980
0.2%
Signal vs efficiency Cut on E* Signal cutting only on
0.4%
0.3%
0.950 0.995
Signal vs efficiency Cut on E* Signal cutting also on
0.3%
0.2%
0.900 0.930
Background shape
C.Bloise, F.Ceradini 10-Oct-02 8
The invariant mass of the photon system Mk
for the background has been compared with
Monte Carlo prediction, selecting events with:
| Etot
- | > 5 arc(cos >10o
At 280 MeV/c2 < Mk< 400 MeV/c2 maximum discrepancy on the cumulative
distribution was 0.04
The background content on the signal window has been changed by an arbitrary amount between 16% . The effect on the signal was ~10 times smaller.
A systematic error ~0.4% on the signal comes from the background shape predicted by the
Monte Carlo simulation.
Background shape study I
Background shape study II
Maximum distanceon the cumulative distributions0.04
KL--> Counting
C.Bloise, F.Ceradini 10-Oct-02 11
The Signal has been obtained by fitting the Mk distribution assuming the knowledge of the
shapes by Monte Carlo simulation:
151 pb-1 : KL--> 9141 ± 116
Background : 3596 ± 104 F
| Etot
- | < 4 arc(cos < 15o
For comparison, maintaing only the first cut, it has been obtained:
KL--> 9697 ± 116
Background : 9578 ± 178 F
| Etot
- | < 4
KL--> Selection
C.Bloise, F.Ceradini 10-Oct-02 14
Neutral vertices with 3 clusters enter the statistics (10% of the entire sample used) :
Additional Requirements: 3 cluster events QCAL hit, track veto , kinematic cut 4 cluster events track veto , kinematic cut
3 clust 4 clust 5 clust 151 pb-1 : K
L--> 1044 + 14894 + 382165
Background : 12.5 % 6.95 % -130 (20) -1035(200) -300 (40)
Dalitz Pairs to add : 2600 (1000)
Track Veto efficiency measured with Data - 6 events analyzed (~230,000)
TV = 0.775 ± 0.001
QCAL
= 0.61 ± 0.04 (± 0.50 )
Kine
= 0.996 ±0.001
Measurement 404300 ± 620 ± 1300 10% of the entire sample
Br(KL--> ) / Br(K
L--> ) Measurement
C.Bloise, F.Ceradini 10-Oct-02 15
Current Result :
Br(KL--> ) / Br(K
L--> ) = ( 2.79 ± 0.04
stat ± 0.02
syst) 10-3
3 measurements at 2% level have been compared ( ~ 50 pb-1 each ):
( 2.82 ± 0.06 stat
) 10-3 June - Aug
( 2.74 ± 0.06 stat
) 10-3 Sept - Oct
( 2.80 ± 0.06 stat
) 10-3 Nov - Dec
Conclusions
C.Bloise, F.Ceradini 10-Oct-02 16
The details of the measurement of the ratio Br(KL--> ) / Br(K
L--> ) have been
studied. The current result
Br(KL--> ) / Br(K
L--> ) = ( 2.80 ± 0.04
stat ± 0.02
syst) 10-3
is in our opinion well established
The Br(KL--> ) measurement is dominated by the current error (1.3%) on
Br(KL--> )
The status report will be circulated by beginning of November.
An increased Monte Carlo statistics for the background can improve the fit quality.
Further 150 pb-1 taken in 2002 have been filtered to be included in the paper.