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Status of L1 Pixel Trigger implications on ROC data rates

Status of L1 Pixel Trigger implications on ROC data rates. Fabrizio Palla (INFN Pisa and CERN) On behalf of the TTI group. Pixel Trigger framework. Two possible schemes depending on rates and latencies (two options under considerations: 10 and 20 µs)

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Status of L1 Pixel Trigger implications on ROC data rates

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  1. Status ofL1 Pixel Trigger implications on ROC data rates FabrizioPalla (INFN Pisa and CERN) On behalf of the TTI group

  2. Pixel Trigger framework • Two possible schemes depending on rates and latencies (two options under considerations: 10 and 20 µs) • “Push” architecture: pixel data readout at 40 MHz and provided to the L1 trigger • “Pull” architecture: Calorimeter/Muon L0-triggers (at a latency of <6 µs?) and/or L1-Tracks from outer tracker (at a latency of <10 µs?). See R. Horisberger talk at DESY CMS Upgrade week https://indico.cern.ch/getFile.py/access?contribId=5&resId=0&materialId=slides&confId=253700

  3. Introduction • Track Trigger Integration group is currently investigating the usage (and usefulness) of a L1-Trigger based on pixels • At the moment three use cases studied • Primary vertex reconstruction for jets • https://indico.cern.ch/getFile.py/access?contribId=11&resId=0&materialId=slides&confId=277737 • Tau → 3 prongs reconstruction • https://indico.cern.ch/getFile.py/access?contribId=7&resId=0&materialId=slides&confId=288250 • Electrons • https://indico.cern.ch/getFile.py/access?contribId=1&sessionId=3&resId=0&materialId=slides&confId=290480 • No data rate estimates yet • None of the above have (yet) demonstrated a compelling evidence about the necessity of a L1-pixel trigger • L1-Tracks with outer tracker have same rejections powers for similar (or better efficiencies). • However, have smaller precision on impact parameter (secondary vertices) or cannot reach pT<2 GeV(might result needed for isolation) • Other use cases being investigated (b-tagging, secondary vertex tagging)

  4. Jets primary vertex reconstruction A. Rizzi, S. Donato

  5. Jets primary vertex reconstruction • Algorithm uses pixel cluster information only from chips in the line-of-sight of jets • Two possible use cases • Make clusters on chip@40 MHz and read out reduced information to keep the data rate low • Read full pixel information for a subset of the detector (reduction x 5-10) only for Calo-jets with some threshold as L0-trigger (and if latency allows) • Performance depends on Jet ET. Typical reduction factors ~5 with ~90% efficiency. • CAVEAT: does not do better than L1 Tracks ~4 mm resolution (RMS) Similar resolution with L1-Tracks

  6. Data rate estimate Numbers will scale down depending on the L0 rate. E.g. for 500 kHz L0 rate they will be reduced by 80, but the complication will be to add extra latency. * At all effects a pT cut on tracks Data rates too large at 40 MHz: from 2.5 to 20 Gbps per chip (2.56x2.56 cm2). Rates could become affordable (a few hundred Mbps) at the expenses of a longer latency.

  7. Tau to 3 prongs • One “solution” using pixel-stand alone “tracking” at 40 MHz. (results presented here) • Another one is being investigated to use L1-track seeded regions (no results yet) M. T. Grippo, K. Androsov et al.

  8. Tau to 3 prongs • Identify triplets in a pixel chip of compatible cluster size in first two layers (using beam spot as a third point is in effect a pT cut) • Look for compatible triplets in the third layer and form all track combinations, requiring ≥2 GeV track pT. • Estimate tau decay vertex position in both R-Z and R-Phi planes. L1 rate 300 kHz and 75% efficiency with L1-tracks Or factor 4 reduction of L1 Calo Trigger at 40 GeV

  9. Data rate

  10. Electrons • Match a E/gamma cluster with pixel stand alone tracks To be compared with L1 track E/gamma rejection at 20 GeV ~6 with an efficiency of ~90% C.S. Moon, A. Savoy-Navarro et al.

  11. Conclusions • At the moment no clear “smoking gun” for the L1 pixel trigger • L1-Tracks Algorithms have similar (or better) performances than those tried with the pixels • Still a large phase space of investigations with pixels • “Pull” architecture seems more favorable in terms of data rates • Need however firm statements of what is needed from the Physics • Imply data to be available at ~few µs latency. • Isolation with low pT tracks (especially in taus) • Secondary vertex reconstruction/impact parameter • B-tagging (Higgs?) • B-hadron reconstruction (low pT for B-physics?)

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