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Multiple PV reconstruction at L1

Multiple PV reconstruction at L1. Improvement of L1 performance?. 2D PV reconstruction. PV reconstruction based on 2D VELO tracks Histogram of intersections with the beam ± 150 mm around z=0 Look for the highest bin and reconstruct base PV ( 1st ) New

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Multiple PV reconstruction at L1

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  1. Multiple PV reconstruction at L1 Improvement of L1 performance? Mariusz Witek

  2. 2D PV reconstruction • PV reconstruction based on 2D VELO tracks • Histogram of intersections with the beam ±150 mm around z=0 • Look for the highest bin and reconstruct base PV (1st) New • Reusing code of Ivan to reconstruct 2nd and 3rd PV • 2nd PV at least 10 mm away from 1st PV • Histogram multiplicity (sum of 3 bins: pos-1, pos, pos+1) at least 20 if dz<20 mm and at least 10 if dz>20 mm (to avoid treating B decay vertex as 2nd PV) • 3rd PV at least 10 mm away from 1st and 2nd PV • Same condition for multiplicity depending on distance to 1st PV Mariusz Witek

  3. Performance on L0&L1 accepted minimum bias σx 1st PV 2nd PV 3rd PV Mariusz Witek

  4. Performance on L0&L1 accepted minimum bias σz 1st PV 2nd PV 3rd PV Mariusz Witek

  5. Performance on L0&L1 accepted minimum bias events Resolutions are RMS of the histograms The numbers are derived from highly biased sample of L0&L1 accepted min. bias events (high multiplicity and multi PV) Mariusz Witek

  6. Possible improvements for L1 • Decision based on PV with highest multiplicity but … • discard high IP tracks which are compatible with either 2nd or 3rd PV (IP2nd,3rd<0.2 mm) • dz distribution z2nd-z1st (below) suggest that it might give an improvement Min. Bias L0&L1 B->DsK Mariusz Witek

  7. Expected performance improvements (preliminary) • Two modifications to PV reconstruction: • 100 mm bug corrected (some time ago) • Multiple PV (now) => To be verified for offline selected signal events Mariusz Witek

  8. Summary • New version of L1 PV reconstruction with a possibility of up to 3 PV is ready (reshufled code of Ivan) • Precision for 2nd PV and 3rd PV is reasonable • About 20% reduction of L0&L1 accepted min bias events possible without any real tuning (together with 100 mm bug fix gives 40% reduction). • Thus the performance of L1 can be probably improved by including information about 2nd and 3rd PV (to be confirmed on offline selected signals). Needs further study. • Further study to allow position of 2nd PV to be closer to 1st PV while keeping high signal efficiency (z of 2nd visible MC vertex peaks at position of 1st PV for min bias L0&L1 accepted) Mariusz Witek

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