High Level Triggers at CMS with the Tracker

1. Tommaso Boccali SNS and INFN Pisa Vertex 2002 Kailua-Kona, Hawaii 3-8 November 2002 High Level Triggers at CMS with the Tracker

2. Lot of b’s and tau’s from interesting Physics Supersymmetry Higgs decays Top, B physics Large QCD backgrounds (factor ~1000 or more) The Challenge L1: 40 MHz input L1:100 KHz output Write to offline:100 Hz The Challenge High Level Triggers at CMS with the Tracker

3. CMS HLT functionality depends on data rate and CPU resources available How to select events? • General idea: we would like to benefit from full offline analyses to discriminate events. • Since all the data is available after Lvl-1, we would need “only” ~infinite CPU power. • What can be done with a reasonable number of commercial CPUs? Traditional L2 functionality is the most challenging parameter. Does not benefits of full-granularity High Level Triggers at CMS with the Tracker

4. Timings? • We have ~100 kHz of input rate • We realistically can have a few thousands of (2007) CPUs • This means ~50 ms per decision • Use Moore’s Law: • 50 ms in 2007 ~ 500 ms on a 1 GHz CPU today • Timing for a 1 GHz CPU today ~500 ms High Level Triggers at CMS with the Tracker

5. What about the Tk? • The Tracker is the most precise subsystem, but is (thought to be) slow  not used at all for Lvl-1 • Extensive studies have be performed to answer the question: what can we do in ~500 ms? • The CMS Tracker has been already described by S. Schael (mStrips) and L. Cremaldi (Pixels) 6,136 Thin 300 mm (1 sensor) 9,096 Thick 500 mm (2 sensors) 9x106 strips Occupancy ~10-2 14192 chips 39x106pixels Occupancy ~10-4 High Level Triggers at CMS with the Tracker

6. Baseline TK Outer disks (TEC) TK Outer Barrel (TOB) pixels TK Inner Barrel (TIB) TK Inner Disk (TID) One charged track traversing the CMS Tracker interacts with a maximum of ~14 hits in the silicon (+3 in the Pixels) High Level Triggers at CMS with the Tracker

7. General recipes • Do something only when needed! • reconstruction on demand: never do anything until it is requested • Usually, one is not really interested in reconstructing “the event” in the trigger decision, a smaller region is sufficient • regional tracking • How close we have to be to full offline performance? • conditional tracking • In many cases, it is simple enough to recognize the trigger event from the pile-ups • pixel reconstruction High Level Triggers at CMS with the Tracker

8. Regional tracking • Reconstruct only clusters and tracks in a certain region of the Tracker (i.e., around a jet) • In principle, complexity (time!) scales with (W/4p)K • The region searched for is defined in terms of R typical cases DR~0.4 region around a Lvl-1calo jet -2.5<h<2.5; 0<f<2p High Level Triggers at CMS with the Tracker

9. Conditional tracking After the complete solution of the combinatorial problem, the time spent for each track is proportional to the number of hits. What about performances? if at least 7 hits are used, efficiencies and fake rates are close to optimal; 5 hits are enough if we can accept a higher ghost rate. @ 2x10 33 lumi High Level Triggers at CMS with the Tracker

10. Conditional tracking Not only eff/fake rates are fine, but also resolutions Full reconstruction Good resolution even with only 5 hits High Level Triggers at CMS with the Tracker

11. Pixels @ HLT @ 2x1033, at LHC we have ~3.5 minimum bias events per bunch crossing, @1034, ~17.5 moreover, we integrate signals from bunch crossings [-5,+3]. we have up to 200 events contribute; it is essential to isolate the trigger primary vertex and the tracks associated to it. Using only the Pixels: fast ~ 50 ms/1GHz CPU good resolution~ 30mmin z efficient ~100% s = 26 mm Pixel Resolution in z (cm) High Level Triggers at CMS with the Tracker

12. Physics @ HLT • With these ingredients, we can do • inclusive t tagging • inclusive b tagging • exclusive b tagging • Moreover, we must take care about detector configuration: we (yet) don’t know what will be available at the startup, particularly about pixel configuration: • 2 or 3 barrel layers? • 1 or two forward disks? • All combinations checked! !! High Level Triggers at CMS with the Tracker

13. t tagging Regional Tracking: Look only in Jet-track matching cone Loose Primary Vertex association a region DR=0.5 around the calo jet is searched Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. Reject event if no “leading track” found Regional Tracking: Look only inside Isolation cone Loose Primary Vertex association Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. Reject event as soon as additional track found High Level Triggers at CMS with the Tracker

14. t tagging A0/H02t2t-jetselection with Tracker:various configurations studied; heavy use of conditional tracking (6 hits) and regional tracking Efficiency in various situations and two different Higgs masses. The working point is chosen at a QCD background rejection of ~103 @ 2x1033 sec The time spent to reject QCD background is ~300 ms @ low lumi and less than 400 ms @ high lumi High Level Triggers at CMS with the Tracker

15. inclusive b tagging Regional Tracking: Look only in Jet-track matching cone Loose Primary Vertex association Conditional Tracking: Stop track as soon as Pixel seed found (PXL) / 6 hits found (Trk) If Pt<1 GeV with high C.L. bb uu Performance of HLT tagging close to offline! timings: ~300ms low lumi ~1s high lumi High Level Triggers at CMS with the Tracker

16. exclusive b tagging 900 Hz pT>3 GeV @ 95% 2 Lvl-1 m Specific decay channels: we have too many b’s in non interesting decay channels! Use dilepton triggers to start the selection, and apply tracker selection on invariant masses Use large tail in Lvl-1 resolution: we are mostly interested in muons with low pT wrongly selected (Lvl-1 thresholds are 95%) Most important: low rates on QCD backgrounds to tape. Primary vertex to associate tracks Reg & Cond tracking around the two jets (only tracks pT>2 GeV, max 5 hits) Hard cuts on mass peaks <2 Hz bkg eff ~ 10% Tape High Level Triggers at CMS with the Tracker

17. exclusive b tagging eff~10%rejection~100 CDF RunIIa 0 CDF RunIIb maybe Exclusive b-tagging:Use Level 1 events with 2 muons, together with regional/conditional tracking • BSmm • BSJ/YfmmKK • bm+BSpDS f(KK)p Offline HLT BSmm BSJ/YfmmKK CDF RunIIa~ 14 for now Everything feasible in HLT These are events in year 1 (~10 fb-1) High Level Triggers at CMS with the Tracker

18. Conclusions The CMS Tracker can be used in HLT on the full Lvl-1 output (100 kHz) with nearly offline performance now (startup –5y) b and t inclusive physics in good shape and ready for discovery b exclusive physics possible in parasitic mode These results are solid even if the detector will be staged, at and both 2x1033 and 1034 Lumi High Level Triggers at CMS with the Tracker