1. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 L1 Track Trigger for SuperCMS D. Newbold, J. Brooke, R. Frazier CMS Collaboration à CMS Upgrade for SLHC à L1 Trigger strategy at SLHC à Track trigger architecture n Work in progress! à Next steps

2. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 The CMS Detector à General-purpose detector à Outer muon tracking / 4T solenoid à High-performance calorimetry à Robust all-silicon tracker n Not currently used in L1 trigger decision

3. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Super LHC à Assume “SLHC” to be 14TeV, 10 35 /cm 2 /s, 20MHz n Base BX rate could still be 40Mhz in ‘high-low’ scheme à Estimate ~350 inelastic events per crossing n ~20000 charged tracks within CMS acceptance à The “Strait Plot” à 2015 timescale also driven by detector lifetime

4. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 “Super CMS” à The physics programme n Many scenarios where increased luminosity essential / desirable n New physics extend search; complement ILC n No new physics SLHC is the only game in town à Why upgrade the detector? n Inner tracking elements will be at end-of-life n Trigger and DAQ can take advantage of new tech development In the case of trigger, new algorithms are also required à What can be done? n Muon system should cope at SLHC n Calorimeters probably out of scope for upgrade (cost, time) n Inner tracking will be replaced n Trigger and DAQ - upgrade where necessary / feasible

5. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 L1 Trigger Performance à CMS L1 trigger strategy at LHC n Use of coarsified muon / calorimeter information only n Identification of prompt leptons / photons above threshold n Trigger on leptons in combination with jets, energy sums n Use inclusive signatures + (potentially) topological criteria at L1 à How to adapt for SLHC? n “Natural scale” for lepton thresholds set by W / Z mass Cannot simply raise thresholds for most physics channels n Control of rate via higher thresholds may not be robust n Increased use of ‘exclusive’ triggers is desirable Maintain acceptance for precise lower mass-scale physics à Track triggering n Use information from central tracker into L1 decision n Reinforce muon / calo trigger rejection power The same job currently done in first stage of software HLT n Add new information (precise p t, charge, z-vertex) to L1 candidates

6. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 L1 Trigger Performance à Muon L1 rate versus threshold (10 34, CMS DAQ TDR) à Limited rejection power at high p t without tracker information

7. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Track Trigger Requirements à What is needed / possible? n For muons: confirmation from tracker of isolated high-pt muon candidates + refinement of pt measurement with extra points For calo: increased rejection of fake e/  objects + refinement of isolation and  ID n Rejection of uncorrelated (different primary vertex) combinations à Do not require a stand-alone track trigger à Constraints Operate within few  s fixed L1 latency So cannot perform ‘selective readout’ of tracker, or iterative algos n Do not add substantially to tracker material / power budget n Reasonable bandwidth for readout n Reasonable processing density off-detector n Robust w.r.t background, inefficiency, alignment, etc n Interface to any non-upgraded elements of current L1 system Muon / calo trigger upgrade can provide enhanced space / p t resolution

8. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Technical Challenges à On-detector n Raw information from tracker is huge in size n Communication bandwidth likely to drive on-detector power budget n Tracker is a highly integrated electromechanical system Trigger functionality must be integral part of new design from the start à Off-detector: experience from existing L1 trigger n Communications density / data concentration is the key problem n In particular: dealing with overlaps / edges can be very hard n Processing density not a constraint; deep pipelining possible à Heavy on-detector data reduction is required n Communication between tracker layers is probably impractical n Require multiple stand-alone measurements of candidate tracks à Implementation of a track trigger will be challenging! n Focus on reduction of the key parameter: readout bandwidth

9. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Trigger Concept: On-Detector à Use ‘stacked layer’ concept: n Presented before in inner pixels context See talks of J. Jones et al n Use two space-points from sensors separated by some mm Correlate 2D hits for track stub position & slope in  /  Window cut in  excludes low-pt minbias tracks Also cuts down correlation logic  Modularity to match calo trigger towers (0.0875 in  /  ) n One trigger / readout ASIC per TT performs hit correlation n Output 4 candidate stubs ( 3GeV/c) n If >4 candidates, count and flag as possible jet activity Detailed information is not required, since isolation cut already failed

10. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Trigger Concept: On-Detector à Two specialised trigger planes in ‘outer tracker’ n Low occup. / long lever arm at large r allows coarse-resn sensors Reduced cost and power consumption compared to a true pixel layer n Outer (r=1.2m) plane allows correlation with muon / calo objects Inner (r=0.6m) plane gives b/g rejection, allows  / z measurement

11. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 On-Detector System Parameters à Design for track acceptance for p t > 4GeV/c Largely above minbias spectrum, still good acceptance for jet /  tracks Track curvature lies within ±1TT in  ; limits data-sharing requirements n Sensor doublet must cover all physical high-p t track trajectories à Hit resolution requirements Resolution in  dictated by practical limit of layer spacing Spacing upper limit from accidental coincidence reduction - to be tuned At 10mm spacing, resolution > 0.5mm n Resolution in z dictated by slope-matching + vertex z-resolution At 10mm spacing, resolution > 2mm is adequate (c.f. ~ 70mm) n Use full-precision 2D layers, also functioning as stereo layers? à Readout requirements n (4b+4b) position, (4b+4b) slope (with offset) will allow stub matching n Implies ~1200 x 10Gb/s readout fibres n Can reduce further (factor of 2?) using on-detector data compression Zero-suppression; p t sorting; variable-sized payload (asynchronous links)

12. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Trigger Concept: Off-Detector à Divide trigger processing regionally 36 regional subsystems each process a half-detector, 20 degrees in  n Each subsystem process muon, calo and track information n Data-sharing (~25% of data) covers track propagation between regions Simply a duplication of input data - passive optical splitting? à Track finding n Hold track segment info until muon / calo objects are available n Seed track building from candidates; define restricted ROI at inner layer Cuts down enormously on correlation logic n Outer stub eta directions used to identify + request inner layer stubs n A match in eta / phi slope (using beam constraint) flags physical track à Output to global trigger n Fixed number of muon / calo / jet candidates with p t / E t, charge, quality n Track-based jet tag for isolation purposes Also possibility of track-count  ID, etc etc.

13. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Processing Topology à Generic FPGA-based board for all subsystem functions?

14. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Technical Issues à Efficiency n There is no tracking redundancy in this scheme n What is the achievable hit efficiency for trigger sensors? n Are the geometric overlaps acceptable? Coping with dead channels? à Occupancy Simple simulations take no account of  conversions, noise, etc n In particular: simulate / measure calo backsplash at the outer radius à Alignment n Assume stacked layers will have adequate mechanical alignment n Is this true for the alignment between the two layers? à Endcaps n Work so far concentrates on the barrel portion of CMS n Endcaps can follow the same scheme in principle But data-sharing topology will be more complex Resolution requirements will be different - possibly less demanding n The ‘overlap region’ is yet to considered

15. Dave.Newbold@cern.chTWEPP 2007, 4/9/07 Summary / Next Steps à SuperCMS at the SuperLHC n An programme of upgrade R&D has begun n L1 triggering a key area; current approach cannot work at SLHC à Track trigger concept n First look at ‘system architecture’ seems challenging, but promising n No obvious show stoppers at the architecture level n Correlator ASIC design & tracker integration are the key questions à Next steps n A programme of more realistic simulation is now required Performance simulation on realistic full events is a quid pro quo n Details of on-detector implementation to be evaluated by experts n Proof-of-concept algorithm / processor design to be generated à Hope to work soon with expert collaborators to push this forward