1. Barbara Sciascia July,29 th - LNF 1 Barbara Sciascia K  semileptonic decays Charged Kaon Meeting July, 29 th - LNF Single photon efficiency in KPM events (towards  0 efficiency) Status of the art

2. Barbara Sciascia July,29 th - LNF 2 On the way towards  0 efficiency-4 E  min (MeV) p  0 kine (MeV) Kl3 (MC) K  0 (MC) The low component of the  0 momentum spectrum for Kl3 events span a region of E  min which is fully contained in the E  min range of K  decays. Plenty of statistics to minimize contribution to efficiency error. Single-photon efficiency measured with K  2 events.

3. Barbara Sciascia July,29 th - LNF 3 Single photon efficiency-1 Select events with K  2 or K  2 tag. Unbias for the trigger: require Emc-trigger to  - or  0 -clusters, following the tag. Ask for a K  2 selection (p* cut) in the signal side. Get   0 from the missing momentum at vertex. Look for a  0 -photon from the vertex, excluding clusters already used by the tag or connected to a track.

4. Barbara Sciascia July,29 th - LNF 4 Single photon efficiency-2 Starting with K  2+  selection, estimate the energy and the position of the “other photon”. Look for a cluster close to the other photon. “Close to” criteria: 1- distance between cluster and estimated position. 2- opening angle between estimated and cluster direction from the vertex.

5. Barbara Sciascia July,29 th - LNF 5 Single photon efficiency-3 Measurement o the single photon efficiency as a function of estimated energy ot the photon, separately for different tags (K  2 or K  2) and charges. The efficiency behaviour at high energy (similar to the K L      0 measurement) indicate a not correct acceptance definition.

6. Barbara Sciascia July,29 th - LNF 6 Single photon efficiency-4 40 pb -1 of 2002 Data and 2002 MC all_phys have been used. Data and MC have different resolutions in p* and in cluster selection variables.

7. Barbara Sciascia July,29 th - LNF 7 Measuring BR(K  l3) BR(Kl3) = N(Kl3)  (  TAG (i) BR(i) ) 1 N TAG  TAG (Kl3)  SELE Fit results Tag bias correction [  (KAON+VTX+TRK)   TCA)   0 ) ] DATA 3 samples [  (KAON+VTX+TRK)   TCA)   0 ) ] MC  SELE =  SELE_MC CC Cosmic veto/T3 correction

8. Barbara Sciascia July,29 th - LNF 8 Measuring BR(K  l3) - cont’d 3 Tag samples: K  2 +  0 -trigger K  2 +  -trigger K  2 + Global_Emc-trigger Tag bias: trigger and kine stability checked Cosmic veto correction Selection efficiencies: Tracking: global, from P.M.; syst. at 0.3% level Track-to-Cluster: from neutral kaons  0 : from single photon efficiency (work is in progress) Counting Kl3 from fit The errors on Kl3 BR measurements are at now 2% level (dominated by MC; new MC prod. just started)

9. Barbara Sciascia July,29 th - LNF 9 Conclusions A method to measure the single photon efficiency in KPM events has been implemented. Preliminary results for the efficiency have been presented. Working is in progress to study the acceptance and the resolutions implied in the method. Status of the art for the measurement of BR(Kl3) has been presented.

10. Barbara Sciascia July,29 th - LNF 10 Spare slides

11. Barbara Sciascia July,29 th - LNF 11 On the way towards  0 efficiency-3 Agreement within the errors between the Ke3, K  3 and K  2 samples. Large errors for Ke3 and K  3 samples. The secondary track momentum is “anti- correlated” to the  0 momentum. Next step: single-photon efficiency ratio plugged in the MC. P(MeV) Ke3 K3K3 K2K2  DATA /  MC

12. Barbara Sciascia July,29 th - LNF 12 Single photon efficiency-5

13. Barbara Sciascia July,29 th - LNF 13 The errors on Kl3 BR measurements are at 2% level. They are dominated by the Kpm MC statistics As an example: BR(K + e3) = (4.8xx  0.110)% with: 0.110 %  (0.033  0.102  0.025)% A note on Kpm MC statistics The just started Kpm-MC campaign with 1/1 MC statistics wrt to Data will lower the MC sample contribution to the error from  2% to  0.5% [  (KAON+VTX+TRK)   TCA)   0 ) ] DATA [  (KAON+VTX+TRK)   TCA)   0 ) ] MC  SELE =  SELE_MC From the fit

14. Barbara Sciascia July,29 th - LNF 14 A first glance at the fit