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Status of vertex efficiency evaluation

the idea is to look for events where the neutral clusters candidates to come from a p  are in time with a “ K  charged” vertex so the selection of the sample is done using only EmC info. Status of vertex efficiency evaluation.

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Status of vertex efficiency evaluation

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

  2. Handle: K track with tagged decay good K track Dr K extrapolated • sample preselection • triggering mntag 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 Dr see the kaon track efficiency !! • 3 or more clusters are required on the sample side with Eclu > 50 MeV Tf + 6ns < Tclu < Tf + 55 ns K charged meeting - 2 february 2004 – P. de Simone

  3. Ep,xp,tp Eg,tg,xg p± xK pK lK Kmn tag tm t0 pK p0 Eg,tg,xg • sample selection starting from the first hit of the “good kaon track” we step along the path imposing that the “p “ neutral clusters are in time with the “kaon vertex position” (Tg1 + Tg2)/2 = Tf + ToF(K) about 11% of the mn tagged events are selected, with a negligible contamination 0.1% (MC evaluated) vertex resolution tested on double tagged events svxsvy 5.5 cm svz 2.5 cm Dr  7 cm …  global vertex efficiency evaluation K charged meeting - 2 february 2004 – P. de Simone

  4. kinematical fit the “neutral”Kpvertecies have been selected with a poor resolution  but (E, t, x) of g 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 pmomentum • measure the K momentum • to distinguish the 3 body decay We are close to obtain dlK 1 cm … work in progress !!! K charged meeting - 2 february 2004 – P. de Simone

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

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

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

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

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