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Multiple PV at L1 - update

This update presents significant improvements in the treatment of multiple primary vertices (PVs) during L1 trigger decision-making, focusing on defining multiplicity, histogram criteria, and backward track requirements. Key conditions for accepting secondary and tertiary PVs are outlined, including minimum track multiplicity and distance criteria. The analysis reveals issues affecting L1 performance, notably edge effects and the interplay between L0 dimuon and pile-up veto. Optimizations are suggested to enhance signal efficiency, with a call for further systematic studies on the adjusted multiple PV reconstruction.

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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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