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Status Report on K L --> gg

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

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Status Report on K L --> gg

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  1. Status Report on KL--> gg Work done since June-02 (Memo 272) Code and procedures revised to run on the DSTs KL--> gg : Cuts for background reduction simplified and studied Background shape controlled Signal obtained including different background levels KL--> p0p0p0 : 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

  2. Pre-selection Requirements: Kl tag KL--> gg : 2 clusters, with E > 100 MeV e = (92.60 0.10)% (0.936 geometrical) Etot > 350 MeV e = (99.88 0.02)% Y(projected) > 160o e = (97.48  0.08) %signal vs cut under study DLg < 4s e = (98.41 0.07  0.03) % signal vs cut studied e = (88.70  0.15 0.10) % KL--> p0p0p0 : at least 3 clusters connected to 1 neutral vertex within an enlarged fiducial volume C.Bloise, F.Ceradini 10-Oct-02 2

  3. Signal vs efficiency Pre-filter cut on DLk 0.03% 0.976 0.990

  4. KL--> gg Selection Cuts studied and included in the present analysis: | Etot - m | < 4 s arc(cosa) < 15o Etot = mk/2 * ( 1/a1 + 1/a2 ) ; ai = gk( 1- b pk* ri) Ei = mk/2a1 cosa = (E1 r1 + E2 r 2) *pk / | (E1 r1 + E2 r 2) | The efficiency has been measured with data selecting the signal (~4000 events used) e = 0.918± 0.004 ± 0.004 The systematics have been controlled changing the cuts, measuring the signal at each cut C.Bloise, F.Ceradini 10-Oct-02 4

  5. Signal vs efficiency Cut on a Signal cutting also on E* 0.2% 0.3% 0.820 0.980

  6. Signal vs efficiency Cut on E* Signal cutting only on E* 0.3% 0.4% 0.950 0.995

  7. Signal vs efficiency Cut on E* Signal cutting also on a 0.2% 0.3% 0.930 0.900

  8. Background shape The invariant mass of the photon system Mk for the background has been compared with Monte Carlo prediction, selecting events with: | Etot - m | > 5 s arc(cosa) >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. C.Bloise, F.Ceradini 10-Oct-02 8

  9. Background shape study I

  10. Background shape study II Maximum distance on the cumulative distributions 0.04

  11. KL--> gg Counting The Signal has been obtained by fitting the Mk distribution assuming the knowledge of the shapes by Monte Carlo simulation: 151 pb-1 : KL--> gg : 9141 ± 116 Background : 3596 ± 104 C2FIT = 143/100 | Etot - m | < 4 s arc(cosa) < 15oe = (91.8  0.4 0.4) % For comparison, maintaing only the first cut, it has been obtained: KL--> gg : 9697 ± 116 Background : 9578 ± 178C2FIT = 142/100 | Etot - m | < 4 se = (97.3  0.3 0.3) % C.Bloise, F.Ceradini 10-Oct-02 11

  12. KL--> p0p0p0Selection Neutral vertices with ³ 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 ³ 5 clust 151 pb-1 : KL--> p0p0p0: 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 g events analyzed (~230,000) eTV= 0.775 ± 0.001 eQCAL = 0.61 ± 0.04 (± 0.50 ) eKine = 0.996 ±0.001 Measurement 404300 ± 620 ± 130010% of the entire sample C.Bloise, F.Ceradini 10-Oct-02 14

  13. Br(KL--> gg) / Br(KL--> p0p0p0) Measurement Current Result : Br(KL--> gg) / Br(KL--> p0p0p0) = ( 2.79 ± 0.04stat ± 0.02syst) 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 ) 10-3Sept - Oct ( 2.80 ± 0.06 stat ) 10-3Nov - Dec C.Bloise, F.Ceradini 10-Oct-02 15

  14. Conclusions The details of the measurement of the ratio Br(KL--> gg) / Br(KL--> p0p0p0) have beenstudied. The current result Br(KL--> gg) / Br(KL--> p0p0p0) = ( 2.80 ± 0.04stat ± 0.02syst) 10-3 is in our opinion well established TheBr(KL--> gg) measurement is dominated by the current error (1.3%) on Br(KL--> p0p0p0) 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. C.Bloise, F.Ceradini 10-Oct-02 16

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