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Vertex Efficiency Evaluation of Neutral Clusters in K Charged Event Selection

This document presents a methodology for selecting events where neutral cluster candidates align with a K± charged vertex. It outlines the use of electromagnetic cluster (EmC) information for vertex efficiency evaluation. The authors discuss the selection process, including momentum and impact parameter cuts for kaon tracks, and the assessment of vertex resolution through tagged events. Key objectives include measuring the K decay vertex and momentum, with the aim to distinguish between decay types while maintaining low contamination rates in selected events.

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Vertex Efficiency Evaluation of Neutral Clusters in K Charged Event Selection

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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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