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.