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

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics2/54 Contents I. LHCb: the must know II. Detector and simulation III. Trigger system IV. Reconstruction and PID V. Analysis: tagging and event selection VI. Physics sensitivity studies Disclaimer: no complete review of all aspects; emphasis put on personal work

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics3/54 9 km diameter Geneva Jura CERN

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics4/54 I. LHCb: the must know LHCb Goal: B-physics studies CP violation rare B-decays Acceptance: 1.8 <  < 4.9 Luminosity: 2  cm -2 s -1 Nr of B’s / year: How forward is LHCb? B hadrons mainly produced in forward region(s) B hadrons mainly produced in forward region(s) both B’s tend to be correlated both B’s tend to be correlated Unique forward spectrometer at high energy!  Excellent tracking  Excellent PID

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics5/54 B-hadronsheavylong-lived ! B-hadrons are heavy and long-lived ! LHC(b) environment LHC environment  pp collisions at E CM = 14 TeV  t bunch = 25 ns  bunch crossing rate = 40 MHz  = 2x10 32 cm -2 s LHCb interaction region  times lower than for ATLAS/CMS ~ 7x10 12 pairs~ 700 kHz~ 3.5 mb  (c-cbar) ~ 100 kHz ~ 12 MHz Event rate ~ 60 mb  visible ~ 0.5 mb ~ 100 mb Value ~ pairs  b-bbar)  total Yield / yearPhysical quantity Expected B-signal rates  branching ratios ~ –  10 – 10 6 events / year ?  10 – 10 6 events / year ? Cross sections

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics6/54 II. LHCb detector (side view) pp collision Acceptance 10 mrad 250/300 mrad « Tracking » detectors Muon System Calorimeters Ring Imaging Cherenkov

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics7/54 LHCb cavern

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics8/54 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 Simulation

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics9/54 III. The LHCb Trigger  Trigger overview and strategy  Level-0: first level trigger  HLT: High Level Trigger

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics10/54 HLT Level-0 custom hardware high E T particles partial detector information CPU farm -> software trigger high E T / IP particles full detector information Trigger overview Storage pp collisions 12 MHz 1 MHz~2 kHz event size ~35 kb

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics11/54 Two-level Trigger L0 L0 high E T / P T particles  hardware trigger, sub-detector specific implementation  pipelined operation, fixed latency of 4  s  (minimum bias) rate reduction ~12 MHz -> 1 MHz HLT: HLT: high E T /P T & 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 Trigger Strategy Be alert !

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics12/54  select high E T / P T particles  hadrons / electrons / photons /  0 ’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 E T / P T of candidates global event variables Level-0 Trigger strategy Pile-up system Calorimeter Muon system

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics13/54 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% L0 Calorimeter :  Identify high-E T hadrons / e’s /  ’s /  0 ’s  Electromagnetic and hadronic calorimeters - large energy deposits  E T 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)  σ p /p ~ 20% for b-decays Level-0 sub-systems Scintillator Pad Detector (SPD) Pre-Shower Detector (PS) ECALHCAL

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics14/54 Pile-up system  total multiplicity  # tracks in second vertex Muon system  2  candidates per each of 4 quadrants Calorimeter  total E T in HCAL  SPD multiplicity  highest- E T candidates: h, e, , 2  0 ‘s L0 Decision unit  cuts on global event variables  thresholds on the E T candidates L0DU report Level-0 Decision Unit 1 MHz

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics15/ Photon  o local  o global Electron Hadron Di-muon Muon Approx. rate (kHz)Threshold (GeV)Trigger ~ 13 ~ 8.3 3Tracks in 2 nd vertex 112 hitsPile-up multiplicity 280 hitsSPD multiplicity ~ GeV  E T Rate (MHz)CutGlobal event cuts E T / P T candidates … and then cuts on the E T / P T candidates Global event variables Global event variables applied first … Di-muon trigger is special - not subject to the global event selection - P T  = P T  1 + P T  2 with P T  2 = 0 possible - “tags” clean B-signatures Decision Unit Variables Redundancy: Sub-triggers overlap Level-0 bandwidth division Overall optimization given benchmark channels

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics16/54 Level-0 performance studies Dedicated sub-triggers most relevant for each « channel type » Dedicated sub-triggers most relevant for each « channel type » B s → D s  B →  B → J/  (  K s B → K*  B → K*  B → J/  (ee  K s Typical Level-0 performance N.B.: efficiencies with respect to events selected offline

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics17/54 Strategy Independent alleys: Follow the L0 triggered candidate  Muon, Muon + Hadron, Hadron, ECal streams ~2 kHz Summary Information: decision, type of trigger fired, info on what triggered Partial Reconstruction:  A few tracks selected per alley (cuts e.g. on P T, Impact Parameter, mass)  full reconstruction done at the end of the alleys High Level Trigger

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics18/54 Trigger Farm  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 FE Readout network CPU FE L0 trigger Timing and Fast Control CPU permanent storage HLT algos CPU time tested on a real farn  will fit in the size of the farm foreseen

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics19/54 Muon Alley - Strategy L0-  Entry Muon Pre-trigger Muon Trigger ~200 kHz ~20 kHz ~1.8 kHz Muon PreTrigger  Standalone  reconstruction: σ p /p ~ 20%  VELO tracks reconstruction  Primary vertex reconstruction  Match VELO tracks and muons: σ p /p ~ 5% Muon Trigger  Tracking of VELO track candidates in the downstream T stations: σ p /p ~ 1%  Refine  identification: match long (VELO-T) tracks and muons

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics20/54 Muon Alley – Performance Muon PreTrigger  b  μ ~11%  Signal efficiency: ~88% Muon Trigger  Single muon P T > 3GeV and IPS> 3 B   content 60%  Dimuon mass >0.5GeV and IP>100  m J/  mass>2.5GeV (no IP cut!)  Signal efficiency: ~87% J/Ψ ~20 kHz ~1.8 kHz dimuon mass (MeV) dimuon mass (MeV) < 1s of LHCb

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics21/54 Exclusive Selections Bs→DsBs→Ds B s → D s K 4 tracks Exclusive selections –Use common available reconstructed and selected particles (D s, D 0, K*, Φ,..) –Wide B-mass windows (typically ~ 500 MeV) –Efficiency: e.g. ~90% for B  ππ ~200 Hz B s →  B s →  D s → KK   → KK , K B s → D s  Off-line B →  On-line B → 

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics22/54 IV. Reconstruction and PID  Tracking: pattern recognition and fitting  Vertexing  RICH, Calo. and Muon reconstruction  Particle Identification (PID)

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics23/54 Tracking 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 K s 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| (T) Z (cm) B-field measured to ~ 0.03% precision!  A set of PR algorithms  Multi-pass strategy

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics24/54 Pattern recognition - strategy VELO tracking (VELO seeds) Forward tracking (long tracks) Matching (long tracks) Seeding (T seeds) VELO-TT (upstream tracks) Clone killing Set of “best” tracks K s tracking (downstream tracks)

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics25/54 Pattern recognition - performance Efficiency p (GeV)  Performance on B-signal samples for “long” tracks: Efficiency ~ 95 % for p > 10 GeV Ghost rate ~16.7 % Dip due to beam-pipe material

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics26/54 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 “banana-shaped” Outer Tracker modules Track fitting 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!

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics27/54 LHCb uses the Kalman filter technique:  Mathematically equivalent to least  2 method  Adds measurements recursively starting from a initial track estimate  Reconstructs tracks including multiple scattering and energy losses  We use a “bi-directional” fit … Track fitting « à la Kalman » direction of the filter track prediction filtered track direction of the reverse filter track prediction filtered track Bi-directional fit Filter in both directions … smoothed result = weighted mean of both filters

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics28/54 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)

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics29/54 Fitter: prediction and Kalman filter Velo TT IT&OT

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics30/54 Fitter: Kalman smoother Velo TT IT&OT

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics31/54 Bi-directional fitting Velo TT IT&OT filtered state weighted mean filtered state

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics32/54 Track fitting performance  p/p = 0.5% Momentum resolution for “long” tracks  p/p = 0.35 – 0.55 %

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics33/54 Vertexing performance btbt BsBs KK KK  ,K   DsDs Primary vertex p p B s vertex resolution Typical resolutions  z,core = 168  m Primary vertex resolutions  x = 8  m  z = 47  m

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics34/54 RICH reconstruction 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 RICH1RICH2

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics35/54 RICH performace K      Particle Momentum (GeV/c) K  K or p   K or p   e,  or  K  e,  or  Particle Momentum (GeV/c)  identification K identification  Particle identification needed over momentum range GeV/c  Ex.: need to distinguish B d   from other similar topology 2-body decays

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics36/54 Calorimeter reconstruction (1/2) electrons:  Identification with  ~95% based on -  2 of match calo. cluster energy – position of extrapolated track - Energy deposited in the preshower detector - Energy deposited in the hadronic calorimeter - Bremsstrahlung correction ECAL Magnet E PS (MeV) True Electrons backgrounds example

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics37/54 Calorimeter reconstruction (2/2) Neutral pions:  Resolved  0 : - reconstructed from isolated calo. photon clusters - mass resolution ~10 MeV,  ~30%  Merged  0 : - Several clustes merged into single (high energy) cluster - mass resolution ~15 MeV,  ~20% all π 0 s Merged π 0 π 0 from B π 0 mass (Mev/c²) Resolved π 0 all π 0 s π 0 from B B d → π + π - π 0 events π 0 mass (Mev/c²) Merged cluster Resolved cluster

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics38/54 Muon reconstruction     ~ 94 % and      ~ 1.0 % for tracks in Muon detector acceptance  ~ 10 MeV/c² Typical performances for b  J/  (  ) X  eff ~ 94 %  misid ~ 1.0 %  Extrapolate well-reconstructed tracks to the Muon system  Look for compatible hits in a “field of interest” around the extrapolated tracks

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics39/54 Particle Identification (PID)  invariant massK  invariant mass With PID  invariant mass No PID Hadrons:  RICH1 and RICH2 Electrons & neutrals:  Calorimeter system Muons:  Muon system

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics40/54 V. Physics analysis  Flavour tagging  Event selection & background estimation - example of the decay B s  D s h - example of the decay B s  D s h

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics41/54 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 with dilution factor Flavour tagging (1/2)

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics42/54 Flavour tagging (2/2) b b s s u u t =0 Bs0Bs0 PV  z/  c =  t rec  t picoseconds after leaving the primary vertex, the reconstructed B decays. K+K+ l  (e +,   ) l  (e ,   ) K  Uses flavour conservation in the hadronization around the B rec  D 2  1% (B 0 ), 3% (B s ) Same-side tag Assume: Opposite side tag  D 2  5% b-hadron

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics43/54 Event selection: example of B s  D s h (1/3) btbt BsBs KK KK  ,K   DsDs Primary vertex B s → D s -   B s -> D s ∓ K ± Requirements  Trigger on the B-decay of interest : high-P T 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

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics44/54 Event selection: example of B s  D s h (2/3) B s →D s K : B s reconstructed mass signal and main background B s →D s π : B s reconstructed mass signal and main background B s mass resolution ~14 MeV LHCb note

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics45/54 Event selection: example of B s  D s h (3/3) Event yields for 2fb -1 (defined as 1 year) B s →D s - π + 140k ± 0.67k (stat.) ± 40k (syst.) B s →D s Ŧ K ± 6.2k ± 0.03k (stat.) ± 2.4k (syst.) Results for B/S ratios, no trigger applied ChannelB/S at 90% CL (bb combinatorial) B/S at 90% CL (bb specific) Bs→Ds-π+Bs→Ds-π+ [0.014,0.05] C.V 0.027±0.008 [0.08,0.4] C.V 0.21±0.06 B s →D s Ŧ 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

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics46/54 VI. Physics sensitivity studies The example of B s  D s h  Motivations  Sensitivity studies with RooFit

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics47/54 Motivations (1/2) B-decay channels B s →D s - π + and B s →D s Ŧ K ± Topology is very similar Physics is different: –B s →D s - π + can be used to measure Δm s, Δ  s CDF measurement Δm s = ± 0.1(stat.) ± 0.07(syst.) ps -1 –B s →D s Ŧ K ± can be used to extract the CP angle  +  s Standard Model prediction  ≈ 60°

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics48/54 Motivations (2/2) B s  D s  mode:  Flavour-specific decay (2 decay amplitudes only) B s  D s 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 B s -> D s ∓ K ± B s → D s -  

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics49/54 Physics sensitivity studies LHCb Sensitivity studies  Measurement of  +  s with combined B s  D s  and Bs  D s K samples  Complete fit allows to obtain  m s, mistag rate, etc. RooFit implementation for Toy MC:  Simultaneous B s  D s  and Bs  D s K fit: correlations taken into account  All decay rate equations included (see next page)  Using latest 2004 data challenge selection results (LHCb-note )  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  D s K events

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics50/54 Decay rates with RooFit  Final state f : D s - π + or D s - K +  For charge conjugate final states: B → B, f → f, λ f → λ f, A f → A f p/q → q/p

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics51/54 Description in propertime Acceptance function (after trigger & sel.) Combined sample, tagged events, 5-year statistics Proper time per-event error distribution mean value 33fs most probable value 30fs

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics52/54 Description in mass Signal & background, 5-year statistics

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics53/54 Results with untagged events Sensitivity to  Error on  +  s (scaled to 1 year) ~ 12° 2 D s π equations, 4 D s K 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 ParameterΔm s (ps) -1 ω Arg(λ f ) rad |λf||λf| +s °+s ° Δ T1/T2 ° input value fitted value resolution 5y resolution 1y

Eduardo RodriguesCPPM, 4 th May 2007 LHCb: a stroll from Trigger to Physics54/54 Thank you