L1 Track Trigger for ATLAS at HL-LHC

1. RAL seminar, 18/05/2011 L1 Track Trigger for ATLAS at HL-LHC Nikos Konstantinidis (University College London)

2. Outline • High Luminosity LHC (HL-LHC) • Motivation, physics potential, timelines, parameters • ATLAS upgrades for HL-LHC • Overview, focus on Level-1 Trigger upgrade • The ATLAS L1Track R&D programme • Motivation, challenges, studies, plans • Conclusions – Outlook Track Trigger for ATLAS at HL-LHC

3. The HL-LHC project

4. HL-LHC idea • Upgrade the LHC to deliver O(3000fb-1) per experiment in the 2020s (x10 the LHC lumi) • O(250fb-1) per year, peak luminosity 5e34 • Motivation: • Increased discovery potential • multi-TeV region, corners of SUSY parameter space… • Detailed studies of discoveries made with 250fb-1 • e.g. Higgs couplings, SUSY properties etc • Probe the gauge structure of the SM • Vector Boson Fusion at 1TeV, triple gauge couplings… Track Trigger for ATLAS at HL-LHC

5. Timelines for HL-LHC • Current dates for “Long Shutdown 3”: 2021-22 • Dates driven by two factors: • Integrated lumi “saturation” • Radiation damage of accelerator components • Two other long shutdowns in this decade: • LS1 (2013-14): work to prepare for 14TeV & 1e34 • LHC will have delivered ~O(10fb-1) at 7TeV • LS2 (2017/18?): upgrades for peak lumi 2e3 • LHC will have delivered ~O(50fb-1) at 14TeV Track Trigger for ATLAS at HL-LHC

6. LHC int. luminosity evolution 50fb-1 250fb-1 10fb-1 If it takes many (>10) years to deliver integrated luminosity that halves statistical errors, then it is not cost-effective. Track Trigger for ATLAS at HL-LHC

7. LHC: Draft 10-year plan (03/2011) Track Trigger for ATLAS at HL-LHC

8. How to deliver 250fb-1/year • Upgrade the machine to deliver 10e34 (5e34 with luminosity leveling • Higher current per bunch • Higher field magnets for stronger focusing • Superconducting crab cavities for lumi leveling • Extreme collimation in the collision points • … • All these require a lot of R&D Track Trigger for ATLAS at HL-LHC

9. Lumi leveling with crab cavities qc • RF crab cavity deflects head and tail in opposite direction so that collision is effectively “head on” for luminosity and tune shift • bunch centroids still cross at an angle (easy separation) • First proposed in 1988, in operation at KEKB since 2007 →world record luminosity! Track Trigger for ATLAS at HL-LHC

10. Lumi profile with leveling • Much more manageable for the detectors • ~100 vs. ~200 pp collisions per bunch crossing • Also better for LHC • Reduced peak heat deposition in critical cold regions of the machine Track Trigger for ATLAS at HL-LHC

11. Example HL-LHC parameters Track Trigger for ATLAS at HL-LHC

12. ATLAS Upgrades for HL-LHC

13. ATLAS Upgrades this decade • At LS1 (2013-2014) • New Pixel barrel layer very close to the beam (+new beam pipe) • The existing innermost Pixel layer becomes inefficient above 1e34 • At LS2 (2017/18?) • New Muon inner endcap Wheels • Too high rate in existing chambers above 1e34 • New wheels will give sharper L1 muon thresholds in forward region • Trigger upgrades • L1 topological processor • Hardware track finder after L1 (FTK) Track Trigger for ATLAS at HL-LHC

14. ATLAS upgrades for 2021-22 • Upgrades are necessary to retain performance at 5e34 or to withstand irradiation up to ~3000fb-1 • New, all-silicon tracker (pixels + strips) • New calorimeter readout to provide higher granularity information for the L1 Calo trigger • Major redesign of the L1 Trigger hardware and other upgrades to Trigger-DAQ system • Changes in the very forward calorimeters • Present Calorimeters, Muon Chambers and Magnets don’t change Track Trigger for ATLAS at HL-LHC

15. Current TDAQ architecture • L1 uses only Calo/Muon • 40MHz L175kHz • Unlikely to change hugely, given material constraints • L2 accesses only ~10% of event data (in RoIs) • Rate to disk ~200Hz • Unlikely to change hugely, given increased event size Track Trigger for ATLAS at HL-LHC

16. L1 Trigger upgrade for 5e34 • Physics at HL-LHC will still require triggering on signatures at the electroweak scale (W/Z/H) • Raising the pT thresholds effectively cancels the benefits of upgrading the LHC luminosity! • L1 Trigger has to achieve 5x higher rejection in much more complex events • E.g. electron/muon isolation may be less effective • Reading out the tracker at ~500kHz not an option • Costly, wasteful and introduces a lot of material Track Trigger for ATLAS at HL-LHC

17. Options for ATLAS • Upgrade L1Calo • Use finer granularity information from Calorimeters • Upgrade L1Muon • Sharpen pT thresholds, reject more fake triggers • Use tracking info at L1 • Known to be a key element for rejection at L2 • A combination of all of the above Track Trigger for ATLAS at HL-LHC

18. L1Calo upgrades for 5e34 • Finer granularity info for L1Calo is the main physics driver for Calo readout upgrade • Currently 0.1x0.1 trigger towers • Studies ongoing to understand what info is most important for L1Calo • In depth or lateral shower profile • Which HLT Calo techniques can be ported to L1 • Strips of Dh=0.003 in 1stLAr sampling are essential for rejecting p0s ATLAS Trigger upgrade plans and activities

19. L1Muon rates at 5e34 Rates for muons from b/c/W can be extracted by convoluting pT resolution with physics x-section pT resolution drives the physics rates: >50kHz for MU20, >25kHz for MU40 The above estimates do not include cavern background nor charged p/K decays in flight, hence they give a lower bound Track Trigger for ATLAS at HL-LHC

20. L1Muon upgrades for 5e34 All L1 Triggers Endcaps L1 Triggers with offline muon Endcaps • New Small Wheels (to be installed at LS2) will provide in forward region • significant reduction of fake triggers • sharper pT thresholds • Barrel L1Muon is harder to improve, but less sensitive to fakes • Ongoing studies • Possible L1Mu barrel improvements • to characterize fully the L1Muon performance in MC and project from data to higher luminosities Track Trigger for ATLAS at HL-LHC

21. The ATLAS L1Track R&D

22. Why tracking at L1 • Tracking is key for rate reduction at L2, so it would enhance the purity of the L1-accepted events • For electrons, muons, taus (high-pT tracks) • For double/multi-object triggers (ensure that they come from the same pp collision) • Will provide additional flexibility, redundancy & robustness to the L1 trigger in the harsh and uncertain conditions of HL-LHC • Otherwise we’ll have to rely exclusively on pT thresholds for controlling the L1 rates Track Trigger for ATLAS at HL-LHC

23. Track Trigger for ATLAS at HL-LHC

24. Possible L1Track designs Cannot readout the whole tracker at 40MHz • Self-seeded L1Track: use closely-spaced (few mm) Si layers electrically connected and instrumented with coincidence logic that is satisfied only by high-pT tracks (the CMS idea) • Coincidences have to be sent off-detector at 40MHz and combined in a further step • The L0/L1 idea (or RoI-based L1Track) • L1Calo/L1Muon reduce the rate from 40MHz to ~500kHz and identify Regions of Interest (Level-0) • Tracker data from these RoIs are readout and processed by L1Track; L1Track info is added to the L1Calo/L1Muon info to form global L1 decision Track Trigger for ATLAS at HL-LHC

25. The RoI-based L1Track • L0 is a synchronous pipelined trigger with latency ~3.2us (pretty much like current ATLAS L1 trigger) • Subsystems (e.g. Muons, Calorimeters) can either readout at the full L0 rate (~500kHz), ignoring L1, or have additional buffers (e.g. tracker) in their front-ends where L0-Accapted events are kept until the L1 decision arrives • L0 RoI information is converted into Regional Readout Requests that target specific modules in the tracker • From L0 to L1, the system is asynchronous; makes overall design more flexible • Depending on the size of the additional buffers, the L1 decision can take up to O(100us) Track Trigger for ATLAS at HL-LHC

26. Example: strips readout chip design Track Trigger for ATLAS at HL-LHC

27. Advantages of RoI-based L1Track • No impact on the tracker layout • Can be optimized for offline tracking performance • Full tracking information available (in principle) • For larger L1 latency, L1 rate can be significantly below 100kHz • Implications for the tracker’s material budget Track Trigger for ATLAS at HL-LHC

28. ATLAS vs. CMS L1 upgrades • Conclusions depend on initial conditions • At least ~2 years ago, CMS had the constrain for L1 6.4us/100kHz (no change of ECAL electronics) • ATLAS has more options for improving L1Calo and L1Muon • High granularity of LAr calorimeter is an advantage • Muon Small Wheels • Of course, with more options it is harder to converge Track Trigger for ATLAS at HL-LHC

29. Jet e/γ Tracks ID Tracks μ ET A possible architecture: L0/L1 Calorimeters Muon detectors Inner detector (Digitisation) 40MHz Level-0 Calo Level-0 Muon R3 25 ns per pipeline step Pre-Trigger Processor ~500kHz? Level-1 MDT Level-1 Track = 3.2 μs Central Topology Processor L1A L0A Trigger & Timing distribution <100kHz? = < 256 - 3.2 μs Track Trigger for ATLAS at HL-LHC L0A, L1A

30. RoI-based L1Track parameters • Key parameters for the design of L1Track are • L0 rate • L1 rate • could be <100kHz if enough rejection is achieved • Number/size of RoIs • hence the fraction of the tracker to readout at L0 rate • Number of tracker layers to readout • not necessarily all • Ongoing simulation studies to determine these parameters Track Trigger for ATLAS at HL-LHC

31. Regional Readout studies RoI: Df=0.2, Dh=0.2 at CaloDz=40cm at beamline PIXEL Module number in Z STRIPS Frequency (in %) inside an RoI Track Trigger studies

32. RoI-based L1Track – issues • All ATLAS sub-detector should either be able to readout at the L0 rate (~500kHz) or change their readout electronics • Not an issue for tracker (new), Calorimeters (new electronics) and other small sub-detectors • BUT: potential problem with Muon system: max readout rate 100kHz (max latency 3.2us) and replacing all electronics is a very long operation – unlikely to fit in a 2-year shutdown • Alternatives are under investigation • Unlikely that any L1Track scheme can fit within 3.2us/100kHz Track Trigger for ATLAS at HL-LHC

33. Conclusions – Outlook The HL-LHC will dominate the high energy discovery frontier in the 2020s Major upgrades of the detectors will be required to cope with the high-lumi environment (up to 200 pp collisions / bunch crossing) ATLAS is evaluating a number of alternatives for the upgrades of L1Calo and L1Muon, as well as the use of tracking information at L1 An RoI-based L1Track appears to be an attractive solution for ATLAS, but more studies are needed to converge to the optimal L1 architecture Track Trigger for ATLAS at HL-LHC