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B-triggers at ATLAS & CMS

B-triggers at ATLAS & CMS. Julie Kirk Rutherford Appleton Laboratory On behalf of ATLAS and CMS. Outline. Introduction B physics at LHC B-triggering at LHC ATLAS Overview of trigger and B-strategy Specific triggers Di-muon trigger RoI guided triggers CMS

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B-triggers at ATLAS & CMS

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  1. B-triggers atATLAS & CMS Julie Kirk Rutherford Appleton Laboratory On behalf of ATLAS and CMS Julie Kirk

  2. Outline • Introduction • B physics at LHC • B-triggering at LHC • ATLAS • Overview of trigger and B-strategy • Specific triggers • Di-muon trigger • RoI guided triggers • CMS • Overview of trigger and B-strategy • Examples of specific channels – Bs→J/ψ • Plans for 900 GeV running • Summary Julie Kirk

  3. B physics at LHC • LHC: proton-proton collisions at √s = 14 TeV bunch crossing rate 40kHz • High bb production cross section: ~500 µb (~ 1 in 100 p-p collisions → bb pair). Must select those of interest. • Current luminosity plans: • Pilot-run in 2007, 900 GeV, ~1029 cm-2s-1 • low-luminosity: up to 2x1033 cm-2 s-1 (~10 fb-1 per year) • high-luminosity: 1034 cm-2s-1 (~100 fb-1 per year) • B-physics programme - plan to study: (covered by other talks) • CP violation (e.g. B→J/ψ(X), B→) • Bs oscillations (e.g. Bs→Dsπ, Bs→Dsa1) • Rare decays (e.g. B→(X), B→K*γ) Julie Kirk

  4. B trigger strategies • Limited bandwidth for B-triggers (ATLAS & CMS emphasis on high-pT physics) – need to be efficient and selective. • Factor ~2 drop in luminosity during a fill ( use some of spare capacity for B-physics?) • Many b-decays contain J/ψ(useful for calibration/understanding detector as well as B-physics) • B-trigger is based on single and di-muons • BR ~ 10 % but clean signature at early level in trigger and give flavour tag (needed in many analyses) • Different strategies in different lumi regimes : • High lumi (>2x1033 cm-2s-1) • LVL1 di-muon trigger → events with 2 muons • rare decays (B→(X)) & J/ψ→ • Lower lumi (< 2x1033 cm-2s-1) • Continue di-muon trigger • Add triggers using LVL1 single muon trigger. High Level Trigger (HLT) reconstruction in secondary Regions of Interest identified by LVL1. • Broad programme of B-physics in initial low luminosity period. • Continue with rare-decay searches at high luminosity Julie Kirk

  5. ATLAS (see talk by H.Burckhart) ➸ 46m Long, 22m Diameter, 7'000 Ton Detector Julie Kirk

  6. <2.5 ms ~1-2 kHz out ~10 ms HLT ~100 Hz out ~1 s Overview of ATLAS trigger • LEVEL 1 TRIGGER • Hardware based (FPGAs ASICs) • Uses coarse granularity calorimeter • and muon information • Identifies Regions Of Interest for • further processing B physics allowed ~5-10% of total trigger resources => it must be fast, efficient and selective. • LEVEL 2 TRIGGER • Full granularity • Confirm LVL1 trigger • Combine info from different • detectors in RoIs around LVL1 HLT: software based • EVENT FILTER • Refines LVL2 selection using • “offline-like” algorithms • Better alignment and • calibration data available Julie Kirk

  7. ATLAS B-trigger • High luminosity – di-muon trigger (pT > 6 GeV) • B →J/ψ() X • Rare decays with di-muon , e.g. B→, B→K0* • Low luminosity – add single muon trigger with additional JET/EM ROI information from LVL1. At LVL2 have 2 possible approaches: • Full reconstruction inside inner detector (time costly) • Use LVL1 Regions of Interest (RoI) to seed LVL2 reconstruction: • Jet RoI for hadronic final states (e.g. Bs→Ds(π)π) • EM RoIfor e/g final states (e.g. J/ψ→ee, K*γ, γ) • Muon RoIto recover di-muon final-states in which second muon was missed at LVL1. • New comparison of the 2 approaches using Jet RoI for Bs→Ds(π)π Julie Kirk

  8. ATLAS LVL1 muon trigger Muon Trigger Chambers (TGC) Muon Trigger Chambers (RPC) • LVL1 muon trigger requires hits in different layers within coincidence window (3/4 hits for low pT muon). • Efficiency ~85% (inefficiency mostly due to geometrical reasons (feet and supports)) Muon Precision Chambers (MDT) Inner Detector pT>6 GeV pT>20 GeV RPC: Restive Plate Chambers TGC: Thin Gap Chambers MDT: Monitored Drift Tubes Julie Kirk

  9. pT of muons from different processes LVL1 muon trigger • Predict LVL1 rate from convolution of efficiency with predicted cross-section as a function of pT • Rate ~ 21kHz (pT>6GeV) • ~15% due to b events • Main background from π/K • Reduce rate at LVL2 by: • use precision muon chambers • extrapolate and match to inner detector tracks Julie Kirk

  10. Not normalized Bm+ m- B K* m+ m- Di-m Mass, (MeV) Di-muon trigger for rare decays LVL1:2m RoI pT (m) > 6GeV (~500 Hz @ L=1033cm-2s-1) LVL2: • Confirm each mRoI • In precision muon chambers • Combine m with Inner Detector track • Mass cut (>2GeV) EF:Refit ID tracks in Level-2 RoI Decay vertex reconstruction Transverse Decay length cut: Lxy > 500mm Angular Distribution cut Efficiency estimation after EF: • 70% of B m+m- • 60% of B K* m+ m- • Output rate < 10 Hz bbm+m- both m pT>6 GeV Found mass cut very sensitive for asymmetry study (B→K*) Re-analysis underway investigating vertex quality cuts Also used for J/ψ→ Julie Kirk

  11. LVL2 ROI guided approach RoI multiplicity bb→(6)X • Limits on cpu and bandwidth for B-triggers => need to be fast, efficient and selective. • Retrieve information for smaller region of detector => faster execution times • Speed depends on RoI size and mean LVL1 RoI multiplicity per event • RoI multiplicity required to be about 1-2 to keep resource needs reasonable => determines thresholds chosen • Higher Jet ET threshold → lower rate but reduced efficiency Jet RoI EM RoI Julie Kirk

  12. Bs→Ds(φπ)π – RoI guided Efficiency for B to be within LVL1 RoI • LVL1: 1μ (> 6GeV) + ≥1 Jet RoI • Efficiency for B to be within RoI is 78% (pT(B)>10 GeV, pT(K,K,π)>1.5GeV). Efficiency pT(Bs) (GeV) Mean = 1.020 GeV σ = 5 MeV Mean = 1.968 GeV σ = 18 MeV • LVL2: confirm muon • Reconstruct tracks in area around Jet RoI : ΔηxΔφ=1.5x1.5 • Search for pairs of opposite sign tracks with |M(KK) –M(φ)| < 3 σ • Add additional tracks to form Ds and apply mass cuts • |M(KKπ) –M(Ds)| < 3 σ True KK(π) combinations M(KK) (GeV) M(KKπ) (GeV) Julie Kirk

  13. Bs→Ds(π)π : RoI vs Full Scan • For fullscan method: • LVL1 muon confirmed at LVL2 • reconstruct tracks in whole inner detector and combine to form  and Ds • Lose less low pT B’s • LVL2 efficiencies : (pT(B)>10 GeV, pT(K,K,π)>1.5GeV) • RoI: 60% • Fullscan: 68% • Background rate (bb→X) ~175Hz (L=1x1033) Efficiency to select Ds after LVL2 • RoI guided • Fullscan Julie Kirk

  14. Timings for track reconstruction <Time/RoI> (RoI based) = 23ms <Time/event> = 44 ms <Time/event> (Fullscan) = 160ms Includes RoI multiplicity LVL2 muon confirmation reduces rate by factor ~4 (21 → 5kHz) Time available for track reconstruction x4 (10ms → 40ms) 400 ms 100 ms • RoI guided approach ~4 x faster than full scan. • Also EM and muon RoIs which will increase RoI guided time. • Fullscan looks possible for early running or if use a higher muon pT threshold (pT>8GeV => ~2x reduction in rate) Julie Kirk

  15. e+ e- EM RoI ATLAS EM RoI J/ψ->e+e- Bd J/y (e+e-)Ks(p+p-) • LVL1: 1 μ (> 6GeV) + ≥1 EM RoI • LVL2: • confirm LVL1 muon and EM cluster • reconstruct tracks in enlarged area around EM RoI • electron ID using calorimeter & TRT • combine pairs of tracks to form J/ψ, mass cuts • Efficiency after LVL2 ~ 68% (both e+/e- pT>5GeV) • background ~170 Hz EM Calorimeter TRT Rare radiative decays (e.g. Bd→K*γ, Bs→γ) Need large RoI (ΔηxΔ ~ 2x2) Trigger performance predicted using offline code, for 30fb-1 : 15000Bd K*0γ 4800Bsγ Now repeating analysis using trigger reconstruction code. Rate (EF): 0.6 Hz Bd  K*0γ 0.5 Hz Bs γ Δφ (γ - daughter) Julie Kirk Δη (γ - daughter)

  16. J/ψ→+- at low lumi(lowering 2nd muon threshold) Efficiency vs. Δη (RoI half-width) 1.1 • Add single muon at LVL1 (22kHz) • LVL2: • confirm muon (first in muon detector and then combined with ID) => rate ~ 5 kHz • Open region around muon RoI and search for J/ψ in inner detector. • Mass cut (M(+-)>2.8GeV) • Extrapolate tracks to muon system. • EF : Refit tracks in RoI • Vertex reconstruction 1 0.9 0.8 Efficiency 0.7 0.6 0.5 0.4 0.3 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Delta eta J/y  m+ m- efficiency vs. background rate 78 76 74 LVL2: Efficiency 68-77% (1st 6Gev,2nd 3GeV) Background 260-380 Hz J/psi Efficiency (%) 72 70 68 66 0.2 0.25 0.3 0.35 0.4 0.45 Use similar method to improve efficiency for other di-muon channels at low lumi Background rate, (kHz) Julie Kirk

  17. CALORIMETERS SUPERCONDUCTING COIL ECAL Scintillating PbWO4 HCAL Plastic scintillator Crystals brass sandwich Total weight : 12,500 t Overall diameter : 15 m Overall length : 21.6 m IRON YOKE Magnetic field : 4 Tesla TRACKERs MUON ENDCAPS MUON BARREL Silicon Microstrips Pixels Resistive Plate Cathode Strip Chambers (CSC) Drift Tube Resistive Plate Chambers (RPC) Chambers (RPC) Chambers (DT) CMS detector(see talk by O. Buchmuller) ➸ Tracking up toη~2.5 Julie Kirk

  18. Overview CMS trigger Two level trigger: • Level 1 based on muons and calorimeters (40 MHz → ~100 kHz) • High Level trigger (HLT) uses similar reconstruction to offline (100 kHz → ~150 Hz) For B-physics: • Level 1 : single or di- muon trigger • single muon pT>14 GeV (~3.2 kHz) • di-muon pT> 3GeV (~900 Hz) • HLT : • Inclusive b, c trigger through b-tagging: ~ 5 Hz (L1: high ET jet). Doesn’t trigger decays of interest for B-physics measurements. • Exclusive b trigger: reconstruct b-decays using partial reconstruction in region of interest around Level1 muon. Julie Kirk

  19. CMS trigger for B-physics • Benchmark channels: • B→ • LVL1: di-muon • HLT : reconstruct tracks around muons, vertex fit and mass cuts • Bs→Dsπ→KKππ • LVL1: single muon (pT>14GeV) or lower pT muon and low pT jet trigger • HLT: Partial track reconstruction, mass cuts and vertex fit, decay length cut • Bs→J/ψ→KK • LVL1: di-muon • HLT step 1: partial track reconstruction around muons, J/ψ search • HLT step 2:  and Bs search TDR results (2002) Recent update Julie Kirk

  20. Partial track reconstruction • Track parameter resolution asymptotic after only 5/6 hits. • Partial Reconstruction – stop track reconstruction once enough information is available to answer a specific question, e.g. momentum resolution is good enough. Resolutions as a function of the numberof hits used: (b-jets, 2.5<pT<5, |η|<0.9) pT resolution Transverse impact parameter resolution Julie Kirk (“0 hits” indicates full track reconstruction!)

  21. Bs→J/ψ(μ+μ-)(K+K-): HLT step 1 • HLT split into 2 steps. First step – reconstruct J/ψ: • Regional, partial track reconstruction in cones around L1 muon candidates • Partial reconstruction up to 5 hits maximum • pTμ > 2.5 GeV/c (|η|<1.2) , pTμ > 2 GeV/c , pTJ/ψ> 4 GeV/c • Track pairs with opposite charge: |M(μμ) - M(J/ψ)| <150 MeV/c2 • Vertex Fit of track pairs: • χ2<20 • Transverse decay length significance > 3 • Cosine of angle (momentum/decay length) > 0.9 Signal *103 Inclusive b→J/ψ X Prompt J/ψ J/ψmass distribution (HLT) Mean = 3.098 GeV/c2 , = 51 MeV/c2 Transverse decay length significance Julie Kirk

  22. Bs→J/ψ(μ+μ-)(K+K-): HLT step 2 Level 3: Further reduction through full reconstruction –  and Bs search • Regional, partial track reconstruction in cones around J/ψcandidates • Partial reconstruction up to 5 hits maximum • pTK > 0.7 GeV/c, pT > 1.0 GeV/c, pTBs > 5.0 GeV/c • |M(KK) - M()| < 20 MeV/c2 • |M(KK)- M(Bs)| < 200 MeV/c2 • Vertex Fit on 4 tracks, similar requirements (Cosine of angle > 0.95)  mass distribution Mean = 1.019 GeV/c2, = 4.5 MeV/c2 Bs mass distribution Mean = 5.372 GeV/c2, = 65.4 MeV/c2 Julie Kirk

  23. Bs→J/ψ(μ+μ-)(K+K-) LVL2: Accept rate reduced to ~ 15 Hz 80% of J/ψ are from B decays After LVL3: Events/10fb-1: ~150'000 HLT accept rate < 0.1 Hz (L=2x1033) Efficiency w.r.t. generated sample (pT()>3(2)GeV, pT(K)>0.8GeV) Julie Kirk

  24. Plans for 900 GeV running 900 GeV • Cross-section for bb much lower w.r.t σtot => not much b-physics (O(1-10) bb→J/ψX) • For prompt J/ψ and  expect ~100 events (after 30 days @ 1029) • Use these to test mass reconstruction, etc. • Run loose triggers with single- or minimum-bias at LVL1. HLT in pass-through mode – i.e. record information about HLT reconstruction but don’t reject events on this information. Julie Kirk

  25. Summary • Demonstrated flexible B-physics trigger strategies • Various approaches for coping with increased luminosity (RoI guided track reconstruction/ partial reconstruction, eventually running only di-muon trigger at design luminosity) • Broad programme of B-physics during early running and rare decay searches continue at high luminosity. • Now preparing trigger menus to maximise B-physics potential of experiments. Look forward to first data. Julie Kirk

  26. Backup slides Julie Kirk

  27. ATLAS LVL1 muon rates Julie Kirk

  28. 900 GeV 1029cm-2s-1 rates, statistics Julie Kirk

  29. Level-1: Calorimeter Calorimeter Trigger looking for e/g + Jets + t objects Using trigger towers of Hadronic and Electromagnetic calorimeters The requirement for a trigger object: • The RoI cluster – local maximum • The most energetic cluster > ET • Total ET in EM isolation < EM Isolation Threshold • Total ET in Hadron < Hadronic isolation threshold Julie Kirk

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