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Update on Track Efficiency Fitting using Kshorts

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

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Update on Track Efficiency Fitting using Kshorts

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  1. Update onTrack 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

  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)

  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 < 25mm, pT > 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. Why care at all (?) • Angular (cosθ*, φ*) distribution not flat, because • εtrk(pT, eta) • εV0(trk1, trk2) • εsel(trk1, trk2) • In other words, the predicted shape is P = N εtrk(trk1) x εtrk(trk2) x εV0(trk1, trk2) x εsel(trk1, trk2) • If we aim for fitting εtrk with a precision of X%, then we also need to know the shape of εV0 and εsel with a precision of X%, both in data and MC (!)

  6. Test Fit • Run on MC Kshorts where both tracks are reco’d and found by V0Finder • No resolution, no background subtraction yet • Black: εtrk 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 εV0 • Correct results for remaining εV0 shape (?) • Apply same correction in data and MC (?) • Likely to run into same issue with εsel

  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 (?)

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