B-Physics Trigger Status

1. B-Physics Trigger Status John Baines B-trigger Working Group • Contents: • Introduction: • Di-muon triggers • Hadronic Final States • Muon-electron Final States • Program of work & Status

2. B-physics Trigger: Introduction • Flexible trigger strategy: • di-muon trigger at L> 2 x 1032 cm-2s-1 • Introducing other triggers at lower luminosities (lower lumi fills / later in beam-coast). • Two strategies for these other triggers: • Baseline: • Require >1 LVL1 JET or EM RoI in addition to muon pT > ~8 GeV • Perform track searches in RoI in SCT & Pixels (& TRT) • Make selections based on reconstructed tracks, e.g. J/y(ee), B(pp), Ds(fp) • Reconstruction in RoI => saving in time, provided RoI multiplicity is not too high • => Modest resources. • Fallback (if RoI multiplicity too high or efficiency too low): • Full-scan of SCT and pixels for events with muon pT > ~8 GeV • To save resources, no TRT reconstruction => no J/y(ee) trigger • Make selections based on reconstructed tracks, e.g. B(pp), Ds(fp) • => greater resources required, but better efficiency (lower pT threshold possible)

3. TDR B-physics single-muon all h b c all b h di-muon J/y c @1033cm-2s-1 • In all cases muon trigger initiates B-trigger • Cross-section for m from p an K falls more rapidly with pT than prompt m from b • e.g. pT > 8 GeV : • LVL1 rate 10 kHz for L = 1033 • LVL2 rate (muon & associated ID track) 2 kHz • about 1/3 of rate due to b -> m • Important not to raise muon threshold too high • Instead, reduce rate by requiring other triggers Cross section (nb) • Di-muon triggers: • Very effective trigger for e.g. • B->J/y(mm)K and B->mm(X) • LVL1 trigger efficient down to • pT ~3 GeV (barrel) • pT ~ 5 GeV (endcap) • For 6 GeV threshold, LVL1 rate: 600Hz at L = 2 x 1033 • Mostly m from heavy flavours, plus some double-counted m in endcaps (later removed at LVL2) • Muons confirmed at LVL2 using precision-m and ID • EF selections based on mass and decay length cuts.

4. Hadronic final states • Baseline : Use LVL1 jet clusters to define RoI for ID track reconstruction at LVL2 (SCT and Pixels, optionally TRT) • RoI ~ 10% of event => promises substantial saving of resources provided RoI multiplicities low. • Fallback: full-scan Event with muon pT > 6 GeV • Studied with : • Fast simulation including Longitudinal and transverse shower profiles, pulse history, digitisation and BCID • => Multiplicity ~2 for ET > 5 GeV • Full GEANT simulation, including noise, but without BCID. • => gives higher multiplicities (expected as no BCID) • => ET > 6 GeV gives efficiency of 80% for Bs-> Dsp events with Bs pT > 16 GeV • Final multiplicities expected to be closer to fast simulation results once BCID included Jet RoI Multiplicity Full Simul., No. BCID ET (GeV) • LVL2 selections for specific channels Based on ID tracks. • Tracks refit at EF inside LVL2 RoI including secondary vertex fit. Expect final multiplicities to be closer to Fast simul. results

5. Muon-electron final states • Used to select e.g.: • Bd -> J/y(ee)Ks with opposite side muon tag • Bd->J/y(mm)Ks with opposite sign e tag. Events with muon pT > 6 GeV • LVL1 low ET EM clusters define RoI at LVL2 • At LVL2, RoI confirmed as electrons in calorimeter • Inside RoI tracks reconstructed in SCT pixels and TRT • RoI small ~0.2 x ~0.2 => considerable saving in resources if RoI multiplicity not too high. Fast simulation results EM RoI Multiplicity • Studied with fast simulation: • Multiplicity ~1 for ET > 2 GeV • Efficiency ~80% to find both e from J/y(ee) in events with e pT > 3 GeV ET (GeV) • Tracks refit at EF, including vertex fit and cuts applied to decay length and vertex fit quality

6. Rates (Hz)

7. Work Programme - 1 • TDR back-up note finished (Innsbruck + Alan Watson): • ATL-COM-DAQ-2003-036. A study of the use of Low ET calorimeter RoI in the ATLAS B-Trigger • ATLAS note on muon and di-muon cross-sections and rates in progress (Maria Smizanska) • Measurement of LVL1 multiplicities and efficiencies based on full trigger simulation including trigger towers and BCID (Innsbruck + Alan Watson): • Trigger code in place (Alan Watson) • Currently waiting for help from LAr and Tile experts : • Minor issues for Tile, • Serious problems with LAr – noise too high, calibration stage missing • time-scale unknown since experts busy working on test-beam s/w. • => This is a major concern as it is currently impossible to get meaningful multiplicities • Include LVL2 ID algorithms running in LVL1 RoI & generate NTuples (John, Nikos, Sergey) : • Similar to e/g slice for J/y(e,e) trigger, but with B-physics datasets and initial layout • Need to verify all components for initial layout • Currently waiting for RegionSelector to be implemented for initial layout (Steve, Aline) • in the mean time, to enable analysis work to start, generate NTuples using 6.0.4 and data produced with DC1 layout

8. Resource Issues – The Challenge Need to demonstrate a viable B-trigger within planned resources. Planning for intial system based on 8 GHz processor: LVL2 latency of 10ms @ 25kHz max. rate => 250 cpu (1000 for final system) EF latency of 1s @ 3.2kHz (?) => 3200 cpu TestBed gives : T2Calo 5 ms on 2.6Ghz PC MuFast 8ms => both ~2ms for 8GHz PC Given current uncertainties in timings & overheads, how to compare resources? Compare B-trigger with EM25I trigger (50% of LVL1 rate) e/gamma trigger @ 2x1033 B –trigger @ 1033 8kHz EM25i x 2ms T2Calo = 16 cpu 10 kHz MU8I x 2ms MuFast = 20 cpu 2kHz em25i x t(ID FEX in 0.2x0.2 RoI) = 2Tid 4 kHz mu8i x t(ID Fex in muon RoI) ~ 4Tid Mult(jet) x 2kHz x t(ID FEX in 1x1 RoI) ~ 2Mjet x 5? Tid Mult(em) x 2kHz x t(ID FEX in 0.2x0.2 RoI) ~ 2Mem x Tid e/gamma = 16 + 2Tid cpu B-trigger (RoI) = 20 + (4 + 10? Mjet + 2 Mem) Tid ~ 20 +23 Tid B-trigger (full-scan) = 20 + 80? Tid Average no. SCT + Pixel RoB in 0.2x0.2 RoI : Total no. SCT & Pixel RoB :

9. Work Programme • Develop & compare strategies for J/y(e,e) trigger, e.g.: • LVL1: muon RoI + 2 EM RoI • LVL2: 2 calo e tags + vertex, decay length + J/y(e,e) mass • LVL1: muon RoI + 1 jet RoI + 1 (2ndary) EM RoI • LVL2: 1 calo e tag + J/y(e,e) mass (e + other track pT>5) + vertex + decay length • LVL1 : muon RoI + 1 jet RoI • LVL2 : 2 TRT e-tags, vertex, decay length + J/psi(e,e) mass • LVL1: muon RoI + jet RoI • LVL2: J/psi(e,e) mass (tracks pT>5) + vertex + decay length • Measure Efficiencies for LVL2 RoI-based selections for J/y(e,e) and Ds(f(KK),p) • Measure rates for B->mX • Measure speed-up obtained for xKalman/iPatRec running at EF inside LVL2 RoI c.f. full event reconstruction: • Requires xKalman and iPatRec running on data selected by RegionSelector. • Make timing measurements & update resource estimates • Include muon trigger simulation: • Needs work on combined muon & ID tracks at LVL2 (muon trigger group) • Need LVL1 di-muon trigger (muon trigger group) • => ATLAS note on B-Trigger strategy planned for end 2003/early 2004

10. Available Effort • Some improvement to available effort: • Aras Papadelis (Lund Diploma Student) • Bill Scott (RAL ex. OPAL) • Effort still very tight, especially people experienced with running Athena. • Problem : expert knowledge still required to use ATLAS software • Continue to try to help with this by providing recipes on web pages. Will work on J/y trigger

11. Summary • Work going on on LVL1 RoI multiplicities & efficiencies • Note on muon rates and cross-sections in progress • Making progress with tools • Major part of work still on hold awaiting missing infrastructure: • RegionSelector for initial layout • LAr calibration • Aim for note on B-trigger strategy for end of year, but now looking very tight. Probably move to early 2004. • Making progress, but still a lot to do • Concerns over code stability during Autumn