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Status of analysis

Status of analysis. The K ± → p 0 p 0 e ± n e decay. Allows the study of p - p scattering Selection rule D I = ½ Form factor F. PDG value : (2.2 ±0.4)·10 -5.

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Status of analysis

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  1. Status of analysis

  2. The K±→p0p0e±nedecay • Allows the study of p-pscattering • Selection rule DI = ½ • Form factor F PDG value: (2.2±0.4)·10-5

  3. 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

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

  5. 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

  6. Step 2:gg→p0association • Cut on c2 of the • association gg→p0 • Cut on • Dc2 =|c2best–c2near|

  7. Step 3: kinematic fit K00p3 hypotesis K00e4 hypotesis • 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

  8. Step 3: kinematic fit

  9. Step 4: Track to cluster association

  10. Background analysis: K±→p±p0p0

  11. Background analysis: K±→p±p0p0

  12. Background analysis: K±→p±p0p0 We require p/E < 3

  13. Energies constrained by a kinematic fit Background analysis: K±→p0e±ne(Ke3)

  14. Minimum tridimensional distance Splitted clusters in Ke3 background To reject Ke3 events with split clusters we cut on the minimum distance (in 3D) among each couple of clusters. Ke3 K00e4 cm

  15. Radiative Ke3 background We look at the minimum angle between the 4 photons and the secondary track. Ke3(g) K00e4 K00e4 K00e4

  16. We consider the events distribution in the (m2,p) plane. The measurement method K00e4 (blue region): -900 < m2 < 3500 (MeV2) 35 < p < 180 (MeV) K00p3 (violet region): m2 < -1000 (MeV2) 25 < p < 180 (MeV)

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

  18. Measure of the branching ratio

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

  20. Step 1: The neutral vertex method (2g) • 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

  21. Step 2: Track-to-cluster association -900 < m2 < 3500 Mev/c2

  22. Step 2: Track-to-cluster association (m2 cut)

  23. Step 3: Kpp0 event rejection p* < 150 Mev/c

  24. Step 3: Ke3 event rejection We look for two more neutral clusters in the calorimeter.

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

  26. Step 3: Ke3 rejection We require E2m-P2m < 104

  27. To be done • We have to inquire Ke3 events with two fake neutral clusters • (e.g. radiative + splitting). • Look to P/E variable to reject K00p3 event.

  28. 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.

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