1. Sabino Meola Kloe meeting 10 March 2005 Status of analysis

2. Sabino Meola Kloe meeting 10 March 2005 The K ±      e ± e decay Allow the study of  -  scattering Selection rule  I = ½ Form factor F

3. Sabino Meola Kloe meeting 10 March 2005 at KLOE  high  production cross section  possibility of  -e discrimination  low efficiency for low momentum tracks  high backgrounds  and Ke3 

4. Sabino Meola Kloe meeting 10 March 2005 Aim is to measure a relative branching ratio normalized to events

5. Sabino Meola Kloe meeting 10 March 2005 Selection step 1: The neutral vertex method Allow the selection of events with 2  0 in the final state  ±      X ± The neutral vertex must satisfy the following requests: 4 neutral clusters on time (t - r/c)  = (t - r/c)   = (t - r/c)  = (t - r/c)  consistency with Kaon time of flight

6. Sabino Meola Kloe meeting 10 March 2005 Charged vertex efficiency

7. Sabino Meola Kloe meeting 10 March 2005 Step 2:    0 associations Cut on   of the association     Cut on   =|   best –   near |

8. Sabino Meola Kloe meeting 10 March 2005 Step 3: kinematic fit 4-momentum conservation    invariant mass cluster on time consistency with Kaon time of flight missing 4-momentum having zero mass   invariant mass cluster on time consistency with Kaon time of flight  3 ipotesys K°°e4 ipotesys

9. Sabino Meola Kloe meeting 10 March 2005 Step 3: kinematic fit

10. Sabino Meola Kloe meeting 10 March 2005 Track to cluster association

11. Sabino Meola Kloe meeting 10 March 2005 Background analysis: K ±   ±     We require p/E < 3

12. Sabino Meola Kloe meeting 10 March 2005 Track to cluster association

13. Sabino Meola Kloe meeting 10 March 2005 Background analisys: K ±    e ± e (Ke3)

14. Sabino Meola Kloe meeting 10 March 2005 Geant cluster (no accidental) no accidental 1 accidental Accidental clusters in Ke3 background Geant mother (no accidental)

15. Sabino Meola Kloe meeting 10 March 2005 Splitted clusters in Ke3 background Tridimensional clusters distance

16. Sabino Meola Kloe meeting 10 March 2005 Radiative Ke3 background The idea is to look at the minimun angle between the 4 photons and the secondary track.

17. Sabino Meola Kloe meeting 10 March 2005 The measurement method We consider the events distribution in the (m 2,p) plane. K°° e4 (blue region): -900 < m 2 < 3500 (MeV 2 ) 35 < p < 180 (MeV)  3 (violet region): m 2 < -1000 (MeV 2 ) 25 < p < 180 (MeV)

18. Sabino Meola Kloe meeting 10 March 2005 Measure of the branching ratio The contribution of  background on data is:

19. Sabino Meola Kloe meeting 10 March 2005 Measure of the branching ratio

20. Sabino Meola Kloe meeting 10 March 2005 Accidental clusters in  background no accidental 1 accidental

21. Sabino Meola Kloe meeting 10 March 2005 Conclusions The measurement method allow to estimate the K°°  3 background contribution directly from data. Normalization to  3 events guarantees a cancellation of the systematics effects. Still Ke3 background must be better evaluated on data. Probably need K  0 tag to increase statistics. Will benefit much from 2 fb -1 collection.