LHCb: a stroll from Trigger to Physics Eduardo Rodrigues NIKHEF Seminar at CPPM, Marseille, 4th May 2007

LHCb: a stroll from Trigger to Physics Contents LHCb: the must know Detector and simulation Trigger system Reconstruction and PID Analysis: tagging and event selection Physics sensitivity studies Disclaimer: no complete review of all aspects; emphasis put on personal work LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Jura Geneva 9 km diameter LHC CERN LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics I. LHCb: the must know LHCb Goal: B-physics studies CP violation rare B-decays Acceptance: 1.8 < h < 4.9 Luminosity: 21032 cm-2 s-1 Nr of B’s / year: 1012 How forward is LHCb? B hadrons mainly produced in forward region(s) both B’s tend to be correlated Unique forward spectrometer at high energy! Excellent tracking Excellent PID LHCb: a stroll from Trigger to Physics

LHC(b) environment LHC environment Cross sections pp collisions at ECM = 14 TeV tbunch = 25 ns  bunch crossing rate = 40 MHz <L> = 2x1032 cm-2 s-1 @ LHCb interaction region  10-50 times lower than for ATLAS/CMS Cross sections Physical quantity Value Event rate Yield / year s total ~ 100 mb s visible ~ 60 mb ~ 12 MHz s (c-cbar) ~ 3.5 mb ~ 700 kHz ~ 7x1012 pairs s (b-bbar) ~ 0.5 mb ~ 100 kHz ~ 1012 pairs Expected B-signal rates branching ratios ~ 10-9 – 10-4  10 – 106 events / year ? B-hadrons are heavy and long-lived ! LHCb: a stroll from Trigger to Physics

Ring Imaging Cherenkov LHCb: a stroll from Trigger to Physics II. LHCb detector Ring Imaging Cherenkov Calorimeters 250/300 mrad Acceptance 10 mrad pp collision (side view) Muon System « Tracking » detectors LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics LHCb cavern LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Simulation LHCb Monte Carlo simulation software: Pythia, EvtGen, GEANT4 and Gaudi-based reconstruction Detailed detector and material description (GEANT) Pattern recognition, trigger simulation and offline event selection Implements detector inefficiencies, noise hits, effects of events from the previous bunch crossings LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics III. The LHCb Trigger Trigger overview and strategy Level-0: first level trigger HLT: High Level Trigger LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Trigger overview pp collisions 12 MHz custom hardware high ET particles partial detector information Level-0 1 MHz CPU farm -> software trigger high ET / IP particles full detector information HLT ~2 kHz event size ~35 kb Storage LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Trigger Strategy Be alert ! Two-level Trigger L0 high ET / PT particles hardware trigger, sub-detector specific implementation pipelined operation, fixed latency of 4 ms (minimum bias) rate reduction ~12 MHz -> 1 MHz HLT: high ET/PT & high Impact Param. particles & displaced vertices & B-mass & … algorithms run on large PC farm with ~1800 nodes several trigger streams to exploit and refine L0 triggering information software reconstruction on part/all of the data  tracking / vertexing with accuracy close to offline selection and classification of interesting physics events  inclusive / exclusive streams rate reduction 1 MHz -> 2 kHz estimated event size ~ 30kb LHCb: a stroll from Trigger to Physics

Level-0 Trigger strategy LHCb: a stroll from Trigger to Physics select high ET / PT particles  hadrons / electrons / photons / p0’s / muons reject complex / busy events  more difficult to reconstruct in HLT  take longer to reconstruct in HLT reject empty events  uninteresting for future analysis L0 thresholds on ET / PT of candidates global event variables Pile-up system Calorimeter Muon system LHCb: a stroll from Trigger to Physics

Scintillator Pad Detector (SPD) Pre-Shower Detector (PS) Level-0 sub-systems L0 Pile-up system: 2 silicon planes upstream of nominal IP, part of the Vertex Locator (VELO) Identifies multi-PV events: - 2-interactions crossings identified with efficiency ~60% and purity ~95% Scintillator Pad Detector (SPD) Pre-Shower Detector (PS) ECAL HCAL L0 Calorimeter : Identify high-ET hadrons / e’s / g’s / p0’s Electromagnetic and hadronic calorimeters - large energy deposits  ET in 2x2 cells Scintillator Pad Detector (SPD) and Preshower (PS) - used for charged/electromagnetic nature of clusters, respectively L0 Muon System: M1 – M5 muon stations (4 quadrants each) σp/p ~ 20% for b-decays LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Level-0 Decision Unit Calorimeter total ET in HCAL SPD multiplicity highest- ET candidates: h, e, g, 2 p0‘s Muon system 2 m candidates per each of 4 quadrants Pile-up system total multiplicity # tracks in second vertex L0 Decision unit cuts on global event variables thresholds on the ET candidates 1 MHz L0DU report LHCb: a stroll from Trigger to Physics

Level-0 bandwidth division Overall optimization given benchmark channels Global event variables applied first … ~ 13 ~ 8.3 3 Tracks in 2nd vertex 112 hits Pile-up multiplicity 280 hits SPD multiplicity ~ 7 5.0 GeV S ET Rate (MHz) Cut Global event cuts Redundancy: Sub-triggers overlap … and then cuts on the ET / PT candidates Decision Unit Variables 130 2.6 Photon 110 4.5 po local 150 4.0 po global 280 100 2.8 Electron 700 3.6 Hadron 1.3 Di-muon 160 1.1 Muon Approx. rate (kHz) Threshold (GeV) Trigger Di-muon trigger is special - not subject to the global event selection - PTmm = PTm1 + PTm2 with PTm2 = 0 possible - “tags” clean B-signatures LHCb: a stroll from Trigger to Physics

Level-0 performance studies LHCb: a stroll from Trigger to Physics Typical Level-0 performance Dedicated sub-triggers most relevant for each « channel type » Bs → Ds p B → pp B → J/Y(mm) Ks B → K* mm B → K* g B → J/Y(ee) Ks N.B.: efficiencies with respect to events selected offline LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics High Level Trigger Strategy Independent alleys: Follow the L0 triggered candidate  Muon, Muon + Hadron, Hadron, ECal streams ~2 kHz Partial Reconstruction: A few tracks selected per alley (cuts e.g. on PT, Impact Parameter, mass) full reconstruction done at the end of the alleys Summary Information: decision, type of trigger fired, info on what triggered LHCb: a stroll from Trigger to Physics

Timing and Fast Control LHCb: a stroll from Trigger to Physics Trigger Farm FE FE FE Event Filter Farm with ~1800 nodes (estimated from 2005 Real-Time Trigger Challenge) Sub-divided in 50 sub-farms Readout from Level-0 at 1 MHz  50 Gb/s throughput Scalable design  possible upgrade L0 trigger Readout network Timing and Fast Control CPU CPU CPU CPU CPU permanent storage HLT algos CPU time tested on a real farn  will fit in the size of the farm foreseen LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Muon Alley - Strategy Muon PreTrigger Standalone m reconstruction: σp/p ~ 20% VELO tracks reconstruction Primary vertex reconstruction Match VELO tracks and muons: σp/p ~ 5% L0-m Entry ~200 kHz Muon Pre-trigger ~20 kHz Muon Trigger Tracking of VELO track candidates in the downstream T stations: σp/p ~ 1% Refine m identification: match long (VELO-T) tracks and muons Muon Trigger ~1.8 kHz LHCb: a stroll from Trigger to Physics

Muon Alley – Performance LHCb: a stroll from Trigger to Physics Muon PreTrigger bμ ~11% Signal efficiency: ~88% ~20 kHz Muon Trigger Single muon PT> 3GeV and IPS> 3 Bm content 60% Dimuon mass >0.5GeV and IP>100mm J/y: mass>2.5GeV (no IP cut!) Signal efficiency: ~87% < 1s of LHCb J/Ψ ~1.8 kHz dimuon mass (MeV) LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Exclusive Selections Exclusive selections Use common available reconstructed and selected particles (Ds, D0, K*, Φ,..) Wide B-mass windows (typically ~ 500 MeV) Efficiency: e.g. ~90% for Bππ Bs→Dsp Bs→ DsK 4 tracks ~200 Hz Bs → fg f →KK p, K Bs → ff Ds→KKp Bs → Dsp Off-line B → pp On-line B → pp LHCb: a stroll from Trigger to Physics

IV. Reconstruction and PID LHCb: a stroll from Trigger to Physics Tracking: pattern recognition and fitting Vertexing RICH, Calo. and Muon reconstruction Particle Identification (PID) LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Tracking strategy |B| (T) A set of PR algorithms Multi-pass strategy A typical event: 26 long tracks  best quality for physics: good P & IP resolution 11 upstream tracks  lower p, worse p resol., but useful in the RICH1 pattern recognition 4 downtream tracks  improves Ks finding efficiency (good p resolution) 5 seed/T tracks  used in the RICH2 pattern recognition 26 VELO tracks  used in primary vertex reconstruction: good IP resolution B-field measured to ~ 0.03% precision! Z (cm) LHCb: a stroll from Trigger to Physics

Pattern recognition - strategy LHCb: a stroll from Trigger to Physics VELO tracking (VELO seeds) Seeding (T seeds) Matching (long tracks) VELO-TT (upstream tracks) Forward tracking (long tracks) Ks tracking (downstream tracks) Clone killing Set of “best” tracks LHCb: a stroll from Trigger to Physics

Pattern recognition - performance Performance on B-signal samples for “long” tracks: Efficiency ~ 95 % for p > 10 GeV Ghost rate ~16.7 % Dip due to beam-pipe material Efficiency Efficiency p (GeV) h LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Track fitting Tracks - pattern recognition attributes detector measurements to a track - modelled with straight-line segments, the (track) states Track fitting - determine the best track parameters and corresponding covariance matrix given the measurements on the track - take into account multiple scattering and energy losses in the detector material Description of a realistic detector with mis-alignments - introduction of trajectories to model “measurements” (concept adapted from BaBar) - trajectory = 3D curve in space (of arbitrary shape) - detector shapes locally described with trajectories - a track state (straight-line segment) can also be modeled as a trajectory - any trajectory can provide a parabolic approximation of its shape at any point along itself  closest approach track state – measurement becomes a general point-of-closest-approach problem! “banana-shaped” Outer Tracker modules LHCb: a stroll from Trigger to Physics

Track fitting « à la Kalman » LHCb: a stroll from Trigger to Physics LHCb uses the Kalman filter technique: Mathematically equivalent to least c2 method Adds measurements recursively starting from a initial track estimate Reconstructs tracks including multiple scattering and energy losses We use a “bi-directional” fit … Bi-directional fit direction of the filter direction of the reverse filter track prediction filtered track track prediction filtered track Filter in both directions … smoothed result = weighted mean of both filters LHCb: a stroll from Trigger to Physics

Fitting from a seed (track) state Measurements (hit & error) Seed State (position, direction & momentum) Prediction (adaptive 5th order Runge-Kutta method solves motion in the inhomogeneous B) Kalman Filtered (update prediction with Measurement info) LHCb: a stroll from Trigger to Physics

Fitter: prediction and Kalman filter Velo TT IT&OT LHCb: a stroll from Trigger to Physics

Fitter: Kalman smoother LHCb: a stroll from Trigger to Physics Velo TT IT&OT LHCb: a stroll from Trigger to Physics

Bi-directional fitting LHCb: a stroll from Trigger to Physics Velo TT filtered state weighted mean IT&OT LHCb: a stroll from Trigger to Physics

Track fitting performance Momentum resolution for “long” tracks dp/p = 0.35 – 0.55 % dp/p = 0.5% LHCb: a stroll from Trigger to Physics

Vertexing performance bt Bs K K ,K  Ds Primary vertex p Bs vertex resolution sz,core = 168 mm Primary vertex resolutions sx = 8 mm sz = 47 mm Typical resolutions LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics RICH reconstruction RICH1 RICH2 Algorithm: Input: all types of tracks available Search for hits assuming different hypotheses Global ring fit Cherenkov angle resolutions in the range 0.6 – 1.8 mrad LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics RICH performace Particle identification needed over momentum range 1-100 GeV/c Ex.: need to distinguish Bd pp from other similar topology 2-body decays K  p p  p Particle Momentum (GeV/c) K  K or p p  K or p 20 40 60 80 100 p  e, m or p K  e, m, or p p identification K identification LHCb: a stroll from Trigger to Physics

Calorimeter reconstruction (1/2) electrons: Identification with e~95% based on - c2 of match calo. cluster energy – position of extrapolated track - Energy deposited in the preshower detector - Energy deposited in the hadronic calorimeter - Bremsstrahlung correction EPS(MeV) True Electrons backgrounds ECAL Magnet example LHCb: a stroll from Trigger to Physics

Calorimeter reconstruction (2/2) Neutral pions: Resolved p0 : - reconstructed from isolated calo. photon clusters - mass resolution ~10 MeV, e~30% Merged p0 : - Several clustes merged into single (high energy) cluster - mass resolution ~15 MeV , e~20% all π0s Merged π0 π0 from B π0 mass (Mev/c²) Resolved π0 Bd→ π+π-π0 events Merged cluster Resolved cluster LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Muon reconstruction Extrapolate well-reconstructed tracks to the Muon system Look for compatible hits in a “field of interest” around the extrapolated tracks eff ~ 94 % misid ~ 1.0 % Typical performances for b  J/Y(mm) X  ~ 10 MeV/c² em m  ~ 94 % and ep  m  ~ 1.0 % for tracks in Muon detector acceptance LHCb: a stroll from Trigger to Physics

Particle Identification (PID) LHCb: a stroll from Trigger to Physics No PID Hadrons: RICH1 and RICH2 Electrons & neutrals: Calorimeter system Muons: Muon system  invariant mass  invariant mass K invariant mass With PID LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics V. Physics analysis Flavour tagging Event selection & background estimation - example of the decay Bs Ds h LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Flavour tagging (1/2) Purpose / need: Determination of flavour of B-mesons at production (at primary vertex) tagging gives (best estimate of) the flavour by examining the rest of the event time-dependent analyses require flavour tagging Quantifying the tagging performance : tagging efficiency wrong tag fraction CP asymmetries diluted with dilution factor LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Flavour tagging (2/2) Dz/bgc = Dt Bs0 rec t =0 b s u K+ Dt picoseconds after leaving the primary vertex, the reconstructed B decays. PV b-hadron l + (e+, m+) l - (e-, m-) K - Uses flavour conservation in the hadronization around the Brec eD2  1% (B0) , 3% (Bs) Same-side tag Assume: Opposite side tag eD2  5% LHCb: a stroll from Trigger to Physics

bt Event selection: example of Bs  Ds h (1/3) Bs → Ds- p + Bs -> Ds∓ K± bt Bs K K ,K  Ds Primary vertex Requirements Trigger on the B-decay of interest : high-PT tracks and displaced vertices efficient trigger Select the B-decay of interest while rejecting the background good mass resolution Tag the flavour of the B-decay efficient tagging and good tagging power (small mistag rate) Time-dependent measurements good decay-time resolution LHCb: a stroll from Trigger to Physics

Event selection: example of Bs  Ds h (2/3) Bs→DsK : Bs reconstructed mass signal and main background Bs→Dsπ : Bs reconstructed mass signal and main background Bs mass resolution ~14 MeV LHCb note 2007-017 LHCb: a stroll from Trigger to Physics

Event selection: example of Bs  Ds h (3/3) Event yields for 2fb-1 (defined as 1 year) Bs→Ds- π+ 140k ± 0.67k (stat.) ± 40k (syst.) Bs→DsŦ K± 6.2k ± 0.03k (stat.) ± 2.4k (syst.) Results for B/S ratios, no trigger applied Channel B/S at 90% CL (bb combinatorial) (bb specific) Bs→Ds-π+ [0.014,0.05] C.V 0.027±0.008 [0.08,0.4] C.V 0.21±0.06 Bs→DsŦ K± [0,0.18] C.V 0.0 [0.08,3] C.V 0.7±0.3 (central values used for sensitivity studies) LHCb note 2007-017 LHCb: a stroll from Trigger to Physics

VI. Physics sensitivity studies The example of Bs  Ds h Motivations Sensitivity studies with RooFit LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Motivations (1/2) B-decay channels Bs→Ds-π+ and Bs→DsŦK± Topology is very similar Physics is different: Bs→Ds-π+ can be used to measure Δms , ΔGs CDF measurement Δms = 17.77 ± 0.1(stat.) ± 0.07(syst.) ps-1 Bs→DsŦK± can be used to extract the CP angle g +fs Standard Model prediction g ≈ 60° LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Motivations (2/2) Bs  Ds p mode: Flavour-specific decay (2 decay amplitudes only) Bs  Ds K mode: 4 decay amplitudes of interest: Bs, Bs -> Ds+K-, Ds-K+ -> 2 time-dependent asymmetries for the 2 possible final states Ratio of amplitudes of order 1 -> large interference and asymmetry expected Bs → Ds- p + Bs -> Ds∓ K± LHCb: a stroll from Trigger to Physics

Physics sensitivity studies LHCb: a stroll from Trigger to Physics LHCb Sensitivity studies Measurement of g+fs with combined Bs  Ds p and Bs  Ds K samples Complete fit allows to obtain Dms, mistag rate, etc. RooFit implementation for Toy MC: Simultaneous Bs  Ds p and Bs  Ds K fit: correlations taken into account All decay rate equations included (see next page) Using latest 2004 data challenge selection results (LHCb-note 2007-017) Toy in propertime and mass includes: propertime acceptance function (after trigger & selection) per-event propertime error smearing due to mis-tagging background (rough estimate/description) Fit with tagged events, and also with untagged Bs  Ds K events LHCb: a stroll from Trigger to Physics

Decay rates with RooFit LHCb: a stroll from Trigger to Physics Final state f : Ds-π+ or Ds-K+ For charge conjugate final states: B → B , f → f , λf → λf , Af → Af p/q → q/p LHCb: a stroll from Trigger to Physics

Description in propertime LHCb: a stroll from Trigger to Physics Proper time per-event error distribution Acceptance function (after trigger & sel.) mean value 33fs most probable value 30fs Combined sample, tagged events, 5-year statistics LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Description in mass Signal & background, 5-year statistics LHCb: a stroll from Trigger to Physics

Results with untagged events LHCb: a stroll from Trigger to Physics 2 Dsπ equations, 4 DsK equations, simultaneous fit. DC04 input, collected data from 400 “experiments” of 5y tagged data, scaled results to 1y Fit a Gaussian to the fitted values distribution, pull distribution Parameter Δms (ps)-1 ω Arg(λf) rad Arg(λ f ) rad |λf| g+fs ° ΔT1/T2 ° input value 17.5 0.328 1.047 -1.047 0.37 60 fitted value 1.06 -1.04 60.14 0.28 resolution 5y 0.003 0.001 0.17 0.14 0.03 5.47 5.37 resolution 1y 0.007 0.26 0.32 0.06 12.2 12.0 Sensitivity to g Error on g + fs (scaled to 1 year) ~ 12° LHCb: a stroll from Trigger to Physics

LHCb: a stroll from Trigger to Physics Thank you LHCb: a stroll from Trigger to Physics