1. Status of KLOE real data analysis by the AMADEUS group Oton Vázquez Doce, 4 Maggio 2007

2. Our firsts steps were with Monte Carlo... Production of dedicated KLOE Monte Carlo ntuples Estimation of fraction of K - stopped in the Drift Chambers volume of KLOE setup

3. K - “stopped” Monte Carlo Nuclear Interactions: K - + N 0.1% stopped inside the DC's | z | < 140 cm 40 < ρ < 150 cm ρ vs z (cm)

4. Since begginning of 2007 February 2007 accepted to use 2005 data up to a luminosity equivalent to the 2001/2002 year (400 pb -1 ) Production of KLOE real data ntuples with tag mechanisms 2BODY + DE/DX (50 pb -1 up to now) Start analysis tunning strategy

5. Strategy of search K - + 4 He -> n + (K - ppn) n ~ 510 MeV/c K - + 4 He -> p + (K - pnn) p ~ 550 MeV/c

6. Signature for ppnK - Decay decay:  + p + n p +  - 4 He + K -  ppnK - + n n n p p -- -- Many channels with Λ can be identified by their decay products: p+π - or n+π 0 Classical hadronic interactions of K - in 4 He producing also Λ (69%) P. A. Katz, et.al., Reactions of stopping K - in Helium, Phys. Rev. D1, 1267-1276, (1970)

7. Λ  p+π - search criteria: Vertex made of two opposite charge particles inside the Drift Chamber volume For the negative track (π - ) require energy deposit in the DC wires < 95 ADC counts For the positive track (proton) start looking for an associated cluster to in the extrapolation of the track to the calorimeter region

8. Protons identification Implementation of cuts to remove K- 3 body decay background ( K -  π - π - π + ) E (MeV) charge * p (MeV/c)

9. Protons identification Implementation of cuts to remove K- 3 body decay background ( K -  π - π - π + ) charge * p (MeV/c) E (MeV) proton p (MeV/c)pion p (MeV/c) Lambda inv. Mass (Mev/c 2 )Lambda p (Mev/c)

10. Protons identification (low energy) If no cluster associated, require: ▫last DC measurement for the track compatible with the particle reaching the calorimeter ▫Proton signature in the ADC values of DC wires ADC counts p (MeV/c)

11. Protons identification (low energy) If no cluster associated, require: ▫last DC measurement for the track compatible with the particle reaching the calorimeter ▫Proton signature in the ADC values of DC wires ADC counts p (MeV/c)

12. Final Selection: pionsprotons p (MeV/c) ADC

13. Final Selection: Λ invariant Mass (MeV/c 2 ) θ (deg) proton-pion p Λ (MeV/c) M pπ (MeV/c 2 ) σ~0.5 MeV/c 2

14. Final Selection: Λ invariant Mass (MeV/c 2 ) θ (deg) proton-pion p Λ (MeV/c) Cut in momentum in the Λ c.m.s. 91 < p p,π- < 111 (MeV/c)

15. Final Selection: Λ invariant Mass (MeV/c 2 ) θ (deg) proton-pion p Λ (MeV/c) Cut in Λ invariant mass 1114 < M Λ < 1115 (MeV/c)

16. Λ vertices ρ vs Z (cm) Z (cm)ρ (cm) x vs y (cm) ρ (cm) Interactions in the DC entrance wall (Carbon) 8500 events Interactions in 4 He 1500 events search for Σ(1385)  Λ π

17. Search for Λ “partners” Particles in the same vertex of the p and π - p (MeV/c)

18. Search for Λ “partners” Particles “near” to the Λ vertex ? π p Λ ADC charge * p (MeV/c) # negative tracks# positive tracks ADC charge * p (MeV/c)

19. Search for Λ “partners” Particles “near” to the Λ vertex ? π p Λ ADC charge * p (MeV/c) # negative tracks# positive tracks ADC charge * p (MeV/c) Invariant mass Λ d (MeV/c 2 ) angle Λ d (deg)

20. Next steps... Additional checks on Λ (low momentum, vertex reconstruction, efficiencies...) Increase statistics Study the underlying physics of Λ (formation mechanism, deeply bound?) Search for Λ  n+π 0 (started) Strategy for neutral particle search