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Triggering the LHCb experiment

Triggering the LHCb experiment. The LHCb detector LHCb trigger system High Level Trigger with muons: Specific selections Generic selections Hugo Ruiz. 4a Trobada de Nadal de Física Teòrica a la Universitat de Barcelona. Detector overview. Muon System. RICHES: PID: K,  separation.

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Triggering the LHCb experiment

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  1. Triggering the LHCb experiment The LHCb detector LHCb trigger system High Level Trigger with muons: Specific selections Generic selections Hugo Ruiz 4a Trobada de Nadal de Física Teòrica a la Universitat de Barcelona

  2. Detector overview Muon System RICHES: PID: K, separation VELO: primary vertex impact parameter displaced vertex PileUp System Interaction point Calorimeters: PID: e,, 0 Trigger Tracker: p for trigger Tracking Stations: p of charged particles

  3. LHCb environment • LHC: • 40 MHz crossing rate • 30 MHz with bunches from both directions at LHCb IP • Luminosity: 2·1032 cm-2 s-1 • 10 to 50 times lower than @ ATLAS, CMS • well under machine design! • Reason: single interaction preferred to identify secondary vertices from B mesons • Relevant rates: (for visible events  at least 2 tracks in acceptance) • Total rate (minimum bias): 10 MHz (60 mb out of 80 mb) • bb:100KHz • Whole decay of one B in acceptance: 15KHz • cc: 600KHz

  4. MC generation • PYTHIA 6.2 used • Minimum bias: hard QCD, single / double diffraction, elastic scattering • Signal: forcing B-mesons in a minimum bias event to decay into specific final state • Charged particle distributions tuned to data fors < 1.8 TeV • Predicted cross-sections: sinel = 79.2 mb, sbb=633 mb • Pileup (multiple interactions in single bunch crossing) simulated • GEANT4 for full simulation of all events (minimum bias, signal) • Additional backgrounds: • off-beam muons • low-energy background at muon chambers • Spilloversimulated in detector response • from two preceding and one following bunch crossings

  5. Trigger overview Pileup system VELO + Trigger tracker Calorimeters + Muon system new proposal: ~ 2 KHz 10 MHz On custom boards: LHCb trigger TDR September ‘03 L0:hight pT + not too busy • Synchronous 40 MHz, latency: 4ms PC farm ~1800 CPUs 1 MHz L1:IP + high pT • <latency>: 1 ms (max 50 ms) • Buffer: ~ 59k events 40 KHz HLT + reconstruction • Full detector: ~ 40 kb / evt 200 Hz

  6. Level 0 • Fast search for ‘high’ pT particles(calorimeters, muon syst) • Charged hadrons: HCAL (~ 3 GeV) • Electrons, photons, p0: ECAL (~ 3 GeV) • Muons: muon system (~ 1 GeV) • Cut on global variables: • Require minimum total ET in HCAL (calorimeters) • Reduces background from halo-muons • Rejection of multi-PV and busy events (Pileup system, SPD) : • Fake B signatures (lots of tracks with high IP) • Busy events spend trigger resources without being more signal-like • Better throw them early and use bandwidth to relax other cuts

  7. Level 0: calorimeter trigger ECAL HCAL SPD-PreShower FE Scintillator Pad Detector (SPD) • The LHCb calorimeter: • ECAL: 6000 cells, 8x8 to 24x24 cm2 • HCAL: 1500 cells, 26x26, 52x52 cm2 • Trigger strategy: look for high ET candidates: • In regions of 2x2 cells • Particle identification from • ECAL / HCAL energy • PS and SPD information • ET threshold ~ 3 GeV • Sent to L0 decision unit: • Highest ET candidate each type • Global variables: • Total calorimeter energy • SPD multiplicity ECAL HCAL Pre-Shower Detector Validation cards Selection crates g ETtot e± p0 hadr SPD mult

  8. Level 0: muon trigger • The LHCb muon system: • 5 stations • Variable segmentation • Projective geometry • Trigger strategy: • Straight line search in M2-M5 • Look for compatible hits in M1 • Momentum measurement • Sent to L0 decision unit: 2 highest pT candidates per quadrant threshold

  9. Level 0: Pile-up system Interaction region • Pileup system: • 2 silicon planes • Measure R coordinate • Backwards from interaction point  no tracks from signal B • Trigger strategy: veto multi-PV evts • From hits on two planes  produce a histogram of z on beam axis • Sent to L0 Decision Unit: height of two highest peaks + multiplicity

  10. Level 0: Decision • L0 decision unit: • OR of high ET candidates • Apply cuts on global properties • Thresholds and partial rates: (Trigger TDR, Sept 2003) • Composition:

  11. L1-HLT infrastructure Front-end Electronics FE FE FE FE FE FE FE FE FE FE FE FE TRM 126 links 44 kHz 5.5 GB/s Multiplexing Layer Switch Switch Switch Switch Switch 64 Links L1-Decision Readout Network Sorter 94 Links 7.1 GB/s 94 SFCs SFC SFC SFC SFC CPUFarm … ~1800 CPUs Switch Switch Switch Switch CPU CPU CPU CPU CPU CPU CPU CPU CPU CPU CPU CPU Gb Ethernet Level-1 Traffic HLT Traffic Mixed Traffic • L1 & HLT share infrastructure: • Ethernet network • Sub-farm controllers • Computing nodes • Provides flexibility, scalability • HLT & reconstruction run in background • L1 task has top priority • CPU share: ~ 55% L1, 25% HLT, 20% reconstruction

  12. Level 1  sensor R sensor 100 cm • Trigger strategy: • Find high IP tracks (tracking in VELO) • Confirm track / estimate pT from TT • Special treatment treatment for calorimeter and muon-matched objects • The LHCb VELO: • 21 stations (~ 100 cm) • Alternated R-f sensors • 40 μm to 100 μm pitch • Busy environment: • ~ 70 tracks/event after L0 • but low occupancy in VELO (~0.5%) Interaction region

  13. Level 1: IP at VELO • Fast-tracking strategy: • First in R-Z view (only R sensors) • Primary vertex σZ ~ 60 mm • Select tracks with IP in (0.15, 3) mm • about 8.5 / event • 3D tracking for those tracks • pT measurement using TT • Silicon, 2 layers, 200 mm pitch • Only 0.15 T.m between VELO and TT DpT / pT ~ 20-40% • Rejects most low momentum tracks, which can fake high IP

  14. Level 1 decision • ‘OR’ of 5 different streams: • Generic two high pt tracks with IP>0.15 mm • Electron or photon with high pT, together with two high PT & IP tracks • Single muon with high PT & IP • Dimuons • High mass, flight significance • Mass ~ mJ/y, no flight bias • Composition of triggered sample: Dimuon masses at L1

  15. Performance: L0 x L1 • Results from Trigger TDR (Sept 2003) • Efficiencies computed on offline selected events • Overall L0xL1 efficiency: • 30% for • hadronic channels • e/γ/π0 channels • 60-70% for di-muons • Software and hardware prototyped and working, within time budget • see Trigger TDR, Sept 2003 L0 efficiency L1 efficiency L0L1 efficiency

  16. HLT flow diagram D* ~300 Hz Flight-unbiased J/ys ~ 500 Hz B-generic (single m) ~1KHz Storage (more complicated access due to distribution on grid) Recent additions, effect on computing model 40 KHz (15% bb, 18% cc) Re-reconstruct L1-firing tracks (now using all tracking stations) and confirm calo/m objects Good m or calo object Rest Confirm generic L1 decision (p)/p ~ 0.6 % Apply loose pre-selection HLT no 10 KHz (45% bb, 20% cc) Reconstruct all tracks (RICH info?) HLT selection algorithms HLT no CP channels, large e, ~200 Hz Complete reco Hot !

  17. Status of HLT • Two milestones on summer 2005: • Trigger-DAQ Challenge: one complete sub-farm running continuously on MC data • Computing TDR • Status of HLT reconstruction: • All pieces are there • They ensure use of full detector at enough speed • Calo reconstruction, m id, tracking, L1 confirmation • Studying feasibility of using pId from RICH at HLT! • Effort is put in improving performance of tracking: • Efficiency: current losses of 3 to 15% per track depending channel, compared to offline reconstruction • reverts in > 8% selection inefficiencies! • Computation of errors in track parameters • Use of Kalman filter takes too long • Alternative method needs to be used, as such errors needed to compute c2 of vertices, significance of displacements from PV next 2 slides

  18. Status of HLT Tracking • Obtain track errors from a parameterization on 1/pT: 1. Fit s(IPx), s(IPx) vs 1/pT 2. Assume cylindrical errors and insert in covariance matrix sx sy observed 10 GeV 125 MeV 50 mm • Use the matrix to compute IP significances, vertex c2, flight significances 1 p0 45.2 ± 0.7 2 p1 12.2 ± 0.6 3 p2 1.8 ± 0.1

  19. Status of HLT Tracking • Advantage of the parameterization: • Fast • Direct control of track retention • Trigger can adjust rate by itself, no need of understanding errors of Kalman filter • Performance proven to be ~ the same • (Near) future improvement: • Make use of the fact that main component of the error is multiple scattering at VELO’s RF foil Flight significance computed using parameterized matrix: Dimuons from offline-selected B  J/y f All pairs of pions FS Hugo Ruiz

  20. Status of HLT Specific selections Reconstruct all tracks (RICH info?) HLT selection algorithms HLT no D* ~300 Hz Flight-unbiased J/ys ~ 500 Hz B-generic (single m) ~1KHz CP channels, large e, ~200 Hz Complete reco Storage Hot ! • Chosen 10 benchmark channels representing the spectrum of interesting channels • Proved that they can be selected with enough sidebands with a rate of some tenths of Hz • Caveats: • Currently some inefficiency due to tracking • Some other tenths of channels to be included • Example: channels with di-muons: • Bs  J/(+-) • B  J/(+-) KS • Bs +- • B K*+- Bd->Jpsi(mm)K* Bs->Jpsi(mm)eta(gg) Bs->Jpsi(mm)phi Bs->Jpsi(mm)eta'(rhog) Bs->Jpsi(mm)eta(pipipi) Bs->Jpsi(mm)eta'(etapipi) Bc->Jpsi(mm)pi Bu->Jpsi(mm)K+ Bu->K+mumu Bu->smumu Bs->phimumu D0->mumu Benchmark Hugo Ruiz

  21. Statatus of HLT Specific selections with ms • BUT: • Expected ~ 100% (modulus tracking inefficiency), via J/y line • Ideally, the HOT dimuon trigger would be: • Based only on muon tracks (robustness) • As inclusive as possible • ex: all J/y channels at once  J/y with displacement • avoids explosion of # of selections • Performance: • HOT: • 90Hz with efficiency of ~ 85% on all J/y channels • 50 Hz of true J/y ! • To get ~ 85% on B K*+-, use of K* is needed Reconstruct all tracks (RICH info?) HLT selection algorithms HLT no D* ~300 Hz Flight-unbiased J/ys ~ 500 Hz B-generic (single m) ~1KHz CP channels, large e, ~200 Hz Complete reco Storage Hot ! Hugo Ruiz

  22. Status of HLT The high rate flows • Inclusive J/  (+ higher mass ): ~ 600 Hz • 150–200 Hz of J/  signal • Detailed calibration of tracking resolution • Unbiased b  J/ X (lifetimes) • Inclusive D*: ~ 300 Hz • Charm physics • PID calibration: D*+ D0( K-p+) p+,d(mD*-mD0) = 146 MeV (dmD* = 1865 MeV) • Inclusive bX: ~ 2 kHz • ~800 Hz of unbiased b-hadrons with good tagging • Data mining: effective number of generic B’s / year ~ B factories 2014! • Study acceptance and trigger biases Reconstruct all tracks (RICH info?) HLT selection algorithms HLT no D* ~300 Hz Flight-unbiased J/ys ~ 500 Hz B-generic (single m) ~1KHz CP channels, large e, ~200 Hz Complete reco Storage Hot ! m (always there!) tagging B X signal B BR(B X) ~ 10% Hugo Ruiz

  23. Inclusive J/y: CDF experience • Dimuon trigger: pTm > 1.5 GeV • ~ 2 million J/y • 80% prompt • 20% from B • Used to set absolute mass scale better than 1 MeV: • Needed for spectroscopy of B, D and quarkonium states • Understanding of trigger acceptance: • Compare acceptance vs pT, IP between MC and high statistics of J/y data

  24. Inclusive J/y: LHCb • After 0.5 seconds of LHC running (hopefully): -50 MeV +50 MeV sm = 36 MeV Offline 9 MeV • ~ 1.5·109 J/ys per year

  25. Inclusive J/y • As a function of flight significance:  Total rate True Jpsi * True J/y & bb

  26. Inclusive b  X For cut in pT of 1,2,3,4 GeV 50 % 100 % • Purity of the triggered sample

  27. Inclusive b  X • Comparison with specific selection (ex: Bd p+p-, using offline selected events) ex(1-2w)2 Very robust against online reco inefficiencies!

  28. Conclusions • L0&L1 of LHCb trigger are mature and ready • Of course, expect proposals for upgrades! • Lot of activity in developing HLT • Reconstruction still need some work • Most of specific selection algorithms there • High-rate flows in HLT are promising • Open doors to new physics • Allow study systematics from data instead of MC • Safer • And… negligible economic impact, as less MC needs to be produced! Hugo Ruiz

  29. BACKUP SLIDES

  30. L1

  31. Expected event yield • Taking into account efficiency from: • L0xL1 • Offline selection

  32. Close-up comparison of effective # evts Hugo Ruiz

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