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Multiple PV at L1 - update

Multiple PV at L1 - update. Update of talk on trigger meeting two weeks ago (13-10-2003). New. Better definition of PV multiplicity Histogram multiplicity : sum of 3 bins: pos-1, pos, pos+1) PV multiplicity: nr of tracks with weight>0.9 Backward tracks in PV

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Multiple PV at L1 - update

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  1. Multiple PV at L1 - update Update of talk on trigger meeting two weeks ago (13-10-2003) Mariusz Witek - Trigger

  2. New • Better definition of PV multiplicity • Histogram multiplicity: sum of 3 bins: pos-1, pos, pos+1) • PV multiplicity: nr of tracks with weight>0.9 • Backward tracks in PV • Require a minimum number of backward tracks if 2nd PV is close to 1st one • Smaller distance between PVs allowed without affecting signal efficiency • New conditions to accept 2nd and 3rd PV • Minimum multiplicity 10 tracks, minimum dz 5 mm • More than 5 backward tracks and total multiplicity > 20 if dz<10 mm • More than 3 backward tracks if dz<20 mm • L1 decision based onhighest multiplicity PV but all compatible with 2nd and 3rd PV discarded (IP<0.3 mm) Mariusz Witek - Trigger

  3. Resolutions (mbias L0L1 accept) 1st PV 2nd PV 3rd PV Mariusz Witek - Trigger

  4. Multiplicities (mbias L0L1 accept) 1st PV 2nd PV 3rd PV Mariusz Witek - Trigger

  5. Performance (mbias L0L1 accept) Resolutions are RMS of the histograms Mariusz Witek - Trigger

  6. L1 improvement Distance dz between 2nd and 1st PV • Two modifications: • 100 mm edge effect corrected (some time ago) • Multiple PV, discarding tracks with IP<0.3 mm to 2nd and 3rd PV => To be verified for offline selected signal events Mariusz Witek - Trigger

  7. Why multi PV treatment gives improvement? • The improvement comes from L1 no decision for events (accepted by previous L1 decision) having at least two primary vertices with relatively high multiplicity and relatively large distance. Should pile-up veto reject such events? • Pile-up veto is overwritten in case of L0 dimuon. Even if dimuon hypothesis is not confirmed by L1 a tiny fraction of events (with multiple PV) can cause a significant leak. • A consistency between L0 and L1 has to be kept to avoid mbias leaks. Mariusz Witek - Trigger

  8. Conclusions and outlook • Two mbias leaks affecting the L1 performance have been “discovered” since the trigger TDR • Edge effect of PV reconstruction at 100 mm (15 %) • L0 dimuon overwriting the pile-up veto (25 %) • Removal of both effects might increase the signal efficiency by a good few %. To be confirmed on off-line selected samples. • The multiple PV reconstruction has been adjusted but not really tuned. Needs further systematic study. • Possible improvement: on L0 accepted DsK, 5% of events has B-decay vertex attached to lower multiplicity PV (25 % of multiple PV events). Should one apply Level1 decision to second PV and make logical or? Mariusz Witek - Trigger

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