1. Status of vertex efficiency evaluation Fabio Ambrosino, Patrizia de Simone, Paolo Massarotti, Vincenzo Patera the idea is to look for events where the neutral clusters candidates to come from a   are in time with a “K  charged” vertex so the selection of the sample is done using only EmC info K charged meeting - 2 february 2004 – P. de Simone

2. sample preselection K charged meeting - 2 february 2004 – P. de Simone triggering  tag on one side a “good kaon” track is selected on the sample side, with standard cuts on momentum and I.P. distance the kaon track of the 2 body decay that tags the K + K - event is used as “handle” to clean the sample of the “good kaon” tracks, using the minimun distance  r  see the kaon track efficiency !! good K track Handle: K track with tagged decay K extrapolated rr 3 or more clusters are required on the sample side with Eclu > 50 MeV T  + 6ns < Tclu < T  + 55 ns

3. sample selection 00 E ,t ,x  ±± E ,x ,t  K  tag tt pKpK pKpK t0t0 lKlK xKxK E ,t ,x  starting from the first hit of the “good kaon track” we step along the path imposing that the “   “ neutral clusters are in time with the “kaon vertex position” (T  1 + T  2 )/2 = T  + ToF(K) about 11% of the  tagged events are selected, with a negligible contamination 0.1% (MC evaluated) K charged meeting - 2 february 2004 – P. de Simone vertex resolution tested on double tagged events  vx   vy  5.5 cm  vz  2.5 cm  r  7 cm …  global vertex efficiency evaluation

4. kinematical fit K charged meeting - 2 february 2004 – P. de Simone the “neutral” K    vertecies have been selected with a poor resolution  but (E, t, x) of  clusters, (p first_hit, x first_hit ) of the “good kaon track”, and his decay length are good starting point for a kinematical fit … imposing the kinematics of the 2 body decay K  the goals are measure the K decay vertex measure the  momentum measure the K momentum to distinguish the 3 body decay We are close to obtain  l K  1 cm … work in progress !!!

5. nota bene … !!! K charged meeting - 2 february 2004 – P. de Simone once that we have selected the “neutral” K    vertex we look for the charged K    vertex reconstructed by the DC … we look for a vertex with a total charge +2 or –2 … theta p son (MeV) correct charge assignment wrong charge assignment about 15% of the recon vtx has a wrong charge assignment …

6. vertex efficiency vs K decay lenght K charged meeting - 2 february 2004 – P. de Simone cm MC data

7. vertex efficiency vs K decay lenght K charged meeting - 2 february 2004 – P. de Simone cm MC data Vtx global   73.0% Vtx global   70.4%

8. … just for fun … !!! K charged meeting - 2 february 2004 – P. de Simone ns K ToF distribution in the kaon reference system  = 1/Slope  12.3 ns