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K S  0

K S  0. F. Bossi, S. Miscetti, M. Moulson, M. Palutan, T. Spadaro, P. Valente. KLOE GM, Frascati Sept. 25, 2001. MOTIVATION. K S  3 0 : Purely CP Violating Decay. Expected B.R   –9. Present limit : 1.4 × 10 –5 ( SND 99 ).

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K S  0

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  1. KS 0 F. Bossi, S. Miscetti, M. Moulson, M. Palutan, T. Spadaro, P. Valente KLOE GM, Frascati Sept. 25, 2001

  2. MOTIVATION KS 30 : Purely CP Violating Decay Expected B.R  –9 Present limit : 1.4 × 10–5 ( SND 99 ) KLOE year 2000 : ~ 4 x 106tagged KS

  3. STRATEGY 1) KS tagging : KCRASH, known well understood 2) Photon counting : known, small system. @ low energy 3) Backg. rejection : mainly KS  20 + splitting/accidentals MC SIGNAL MC 20 6   44%

  4. Event preselection Photon “promptness” : tmax = 3 ns Photon energy cut : E  20 MeV Ask for KCRASH +  6 prompt  186 candidates in year 2000 ( 17 pb–1 ) Ask for NO tracks close to the I.P. 99 events survive

  5. Photon pairing Photons coupled and pairs ordered wrt 0 mass Mass of 3rd best pair M3 reasonably good discriminating variable MC SIGNAL DATA M3 (MeV) M3 (MeV)

  6. Splitting rejection Cut on ’s energy and mutual distance to remove splitting MC 2 DATA 6  4  MC 2 5  EMIN(ij) vs R(ij)

  7. After this cut 49 events survive in DATA, 4 predicted by STANDARD MC 20 Accidentals need to be taken into account: Using Miscetti prescription 139 MC 2 events survive 89 after splitting removal M3(MeV)

  8. THE FINAL SAMPLE Define MK invariant mass of best 2 0s Plot MK vs M3for surviving events Green : MC signal Blue : MC 20 MK (MeV) Red : DATA M3 (MeV)

  9. A SIMPLE EXCERCISE Cut in MK–M3 plane. Normalize result to known 20 yield (P.S.V.) to cancel out trigger and tagging efficiency Assume MK 400 MeV, M3= |M3 – M| M (MeV) Exp. Bck Obs. Ev. SIG (%) BR 90%CL 35 2 0 21.2 2.5 x 10–6 45 5 1 25.3 2.5 x 10–6 55 7 2 27.8 2.5 x 10–6

  10. WHAT NEXT Analysis cuts need to be optimized. Efficiencies have to be better investigated Some more understanding of mutual role of splittings and accidentals necessary HOWEVER: It seems we are very close to a nice publishable result!

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