Status of analysis

1. Status of analysis

2. Two normalization samples:- to events in order to obtain a cancellation of the systematic errors.- to events in order to keep under control the track-to-cluster association efficiency. The aim is to measure two relative branching ratios

3. K00e4 VSK00p3 • The measurement strategy is articulated in 5 steps: • Neutral vertex (4g). • gg→ p0 association. • Kinematic fit. • Track to cluster association. • Background rejection.

4. Step 1: The neutral vertex method (4g) • Allows the selection of events with 2 p0 • in the final state • K±→ p0p0X± • The neutral vertex must satisfy the • following requests: • 4 neutral clusters on time • (t - r/c)g1 = (t - r/c)g2= (t - r/c)g3= (t - r/c)g4 • consistency with Kaon time of flight Signal PDG value: (2.2±0.4)·10-5 K00p3 PDG value: (1.757±0.024)·10-2 Ke3 PDG value: (4.98±0.07)·10-2 S/B ratio after: ~ 8·10-2

5. Step 2:gg→p0association • Cut on c2 of the • association gg→p0 • Cut on • Dc2 =|c2best–c2near| S/B ratio after: ~ 7.5·10-2

6. Step 3: kinematic fit K00p3 hypothesis K00e4 hypothesis • 4-momentum conservation • p0invariant mass • clusters on time • consistency with Kaon time of flight • missing 4-momentum • having zero mass • p0 invariant mass • clusters on time • consistency with Kaon time of flight

7. Step 3: kinematic fit S/B ratio after: ~ 4·10-2

8. We consider the events distribution in the (m2,p) plane. The measurement method

9. The measurement method K00e4 (blue region): -900 < m2 < 3500 (MeV2) 35 < p < 180 (MeV) K00p3 (violet region): m2 < -1000 (MeV2) 25 < p < 180 (MeV)

10. Measure of the branching ratio The contribution of K00p3 background on data is:

11. Step 4: Track to cluster association S/B ratio after: ~ 0.4

12. Background analysis K00p3 Is due to photon’s clusters wrongly associated to the secondary track. Cut on P/E. Ke3 Is due to Ke3 radiative events. • Cut on minimum angle between the • 4 photons and the secondary track • Cut on Emiss

13. Background rejection S/B ratio after background rejection cuts: ~ 0.7

14. Measure of the branching ratio Relative error ~ 17%

15. K00e4 VS Ke3 • The measurement strategy is articulated in 3 steps: • Neutral vertex (2g). • Track to cluster association. • Background rejection.

16. Step 1: The neutral vertex method (2g) Signal PDG value: (2.2±0.4)·10-5 K00p3 PDG value: (1.757±0.024)·10-2 Ke3 PDG value: (4.98±0.07)·10-2 • Allows the selection of events with 1 p0 • in the final state • K±→ p0X± • The neutral vertex must satisfy the • following requests: • 2 neutral clusters on time • (t - r/c)g1 = (t - r/c)g2 • consistency with Kaon time of flight • p0 invariant mass S/B ratio after: ~ 4·10-3

17. Step 2: Track-to-cluster association -900 < m2 < 3500 Mev/c2 S/B ratio after: ~ 2.5·10-3

18. Step 3: Ke3 event rejection We perform a kinematic fit to constrain the photons 4-momentum. We consider the E2miss-P2miss variable

19. Step 3: Ke3 rejection We require E2m-P2m < 2·104

20. Background rejection • We require two more neutral clusters in the calorimeter. • Cut on p* to reject K±→p0p± events. • Cut on P/E in order to reject events with a charged pion in the final state. S/B ratio after background rejection cuts: ~ 0.2

21. To be done • Ke3 normalization method: • Implement a kinematic fit in Ke3 hypothesis (almost done). • For both measurement strategy: • Tracking efficiency (already done). • TCA efficiency (almost done). • Trigger efficiency (almost done). • Tag Bias. • Systematic checks.

22. Conclusions • The measurement method allowsto estimate the K00p3 background contribution directly from data. • Normalization to K00p3 events guarantees a cancellation of the systematic effects. • A second measurement method with normalization to Ke3 events would allow to keep under control the track-to-cluster association efficiency. • Will benefit of 2 fb-1 statistics.