1. Update on Track Efficiency Fitting using Kshorts 17. May 2010 Till Eifert, Grant Gorfine

2. where we stopped last time … Using MC truth to run on – All Kshorts that have both tracks reco’d – Works, can fit tracking efff pT turn-on (in eta-slices) Include V0Finder – Today Include resolution (track pT,eta, phi) Include background 5/6/102

3. V0Finder Orange circles: both pions reco’d Green triangles: conditional V0Finder eff., given both tracks are reco’d As function of track pT, eta, and V0 decay radius Conditional V0Finder eff. strongly depends on all three variables  – Not many cuts in the V0Finder that we used Pos-neg tracks pairs Ignore tracks associated to PV Chi2 < 15 (1 dof) 5/6/103

4. Modified V0Finder Re-run MinBias D3PD production for 5 mill. MC events – Include tracks associated to PV – Done on grid Conditional V0Finder eff. much flatter now, however – At the expense of much more background (!) – Flat at the few % level (if R 100 MeV) Structures – vs R : material layers no thickness in tracking-geo- description – Vs eta: maybe track err. do not fully scale with TRT hits 5/6/104

5. Why care at all (?) Angular (cosθ*, φ*) distribution not flat, because – ε trk (pT, eta) – ε V0 (trk1, trk2) – ε sel (trk1, trk2) In other words, the predicted shape is P = N ε trk (trk1) x ε trk (trk2) x ε V0 (trk1, trk2) x ε sel (trk1, trk2) If we aim for fitting ε trk with a precision of X%, then we also need to know the shape of ε V0 and ε sel with a precision of X%, both in data and MC (!) 5/6/105

6. Test Fit Run on MC Kshorts where both tracks are reco’d and found by V0Finder – No resolution, no background subtraction yet Black: ε trk from MC – efficiency to reconstruct tracks from truth pions from Kshort decays, with decay radius < 10mm Red: Angular fit results, incl. stat fit error – Can see some bias due to ε V0 – Correct results for remaining ε V0 shape (?) Apply same correction in data and MC (?) Likely to run into same issue with ε sel 5/6/106

7. summary Basic idea works Not ready yet, missing: – Procedure to deal with V0Finder and selection eff. Cuts to reduce bkg e.g. on inv. mass or pointing angle (flight vector vs pion tracks) depends on track variables  – Cope with background Ideas: – Run on all positive-negative track pairs (+) No (in)efficiencies beyond tracking (-) background – Understand and remove all V0Finder & selection eff. dependences on track variables Chi2 of badly-measured tracks propagates into vertex fit chi2 (?) 5/6/107