3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 1 Tracking performance in LHCb Tracking Performance Jeroen van Tilburg NIKHEF On behalf of the LHCb collaboration IV INTERNATIONAL SYMPOSIUM ON LHC PHYSICS AND DETECTORS FermiLab, Chicago May Overview: LHCb setup Velo/ST/OT performance Track finding Track fitting

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 2 LHCb setup ~1.4  1.2 m 2 ~6  5 m 2 VELO 21 stations R and φ sensors

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 3 Vertex Locator Vertex Locator: 21 stations. R/φ sensors (single sided, 45º sectors). Pitch ranges from 37 μm to 103 μm. 220 μm thin silicon. Sensitive area starts at only 8 mm from beam axis.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 4 Silicon Tracker TT T1 T2 T3 IT OT Trigger Tracker: 4 layers arranged in 2 stations. 30 cm split. 400/500 μm thin silicon. Stereo views: 0°,+5°,-5°,0°. 198 μm readout pitch. 170k readout channels. Used in L1 trigger. The Silicon Tracker: Two parts: 1. IT (Inner Tracker) 2. TT (Trigger Tracker)

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 5 Inner Tracker 3 stations (T1-T3) with 4 layers each (0°,+5°,-5°,0°). 320 μm thin silicon. 198 μm readout pitch. 130 k readout channels. After clustering: ~65% ~30%

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 6 Outer Tracker OT double layer cross section 5mm straws Outer Tracker 3 stations (T1-T3) with 4 double layers (0°,+5°,-5°,0°). 5 mm straws. Fast drift gas (Ar(75)/CF 4 (15)/CO 2 (10)) → Signal collection < 50 ns. 25 ns beam crossing → spillover from previous and next spills. Straws are 4.7 m with readout on top and below (long modules). 50k readout channels. Short prototype module pitch 5.25 mm Track e-e- e-e- e-e- e-e- e-e-

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 7 Outer Tracker Resolution: Tails due to low momentum secondaries: Average occupancy in OT ~ 4 % (hottest region ~ 7 %) p > 2 GeV Cross shape determined by restricting the OT occupancy: Core σ = 200 μm

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 8 Geant3 LHCb event display Track finding Track finding challenges in LHCb High density of hits and tracks. Track pattern recognition must be fast (in trigger and offline). High track efficiency important (especially for many-prong decays).

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 9 Track finding Track finding challenges in LHCb High density of hits and tracks. Track pattern recognition must be fast (in trigger and offline). High track efficiency important (especially for many-prong decays). Zoom of OT station (hits in red)

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 10 Track finding algorithms Velo tracks Velo tracks: Find straight line segments in Velo. Start search for triplets in R-z projection. Then add φ hits and extend track to other sensors. Important for finding primary vertex. Efficiency ~ 97%, ghost rate < 5%.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 11 Track finding algorithms Forward tracks Velo tracks Forward tracks: Starts with Velo track and find continuations in TT and T1-T3. Uses optical model. Accurate measurement of momentum. Long track: important for most physics studies. B decay products. Efficiency ~ 90%. Afterwards the used hits are discarded for use in remaining algorithms.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 12 Track finding algorithms Velo tracks Forward tracks Seed tracks Seed tracks: Stand-alone track finding in stations T1-T3. Tracks almost straight lines (parameterized as parabola). First search for x-hits then add stereo hits. Improves RICH2 performance.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 13 Track finding algorithms Velo tracks Forward tracks Seed tracks Matched tracks Matched tracks: Try to match Seed tracks with Velo tracks. First, estimate momentum from deflection of Seed track. Then extrapolate Seed track to Velo. Match with Velo track. Finds remaining long tracks: additional to Forward tracks. Adds ~ 2% to efficiency for long tracks.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 14 Track finding algorithms Velo tracks Forward tracks Seed tracks Matched tracks VTT tracks Velo  TT (VTT): Finds tracks without hits after the magnet (momentum too low). Start with unused Velo tracks. Find a continuation of at least 3 hits in TT. Magnetic deflection before TT: moderate momentum estimate Δ p/p~20%. Improve RICH1 performance, slow pions, kaon tagging. Efficiency ~75%.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 15 Track finding algorithms Velo tracks Forward tracks Seed tracks Matched tracks VTT tracks T  TT tracks T  TT (or Upstream): Find tracks without hits in Velo. Start with unused Seed tracks and try to add hits in TT. Estimate momentum from deflection Seed track. Final momentum estimate Δp/p~0.4% Enhance K S finding. Pion efficiency ~74%.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 16 Track finding algorithms Finally apply clone killing algorithm. Select the best candidate among tracks that share many hits. Velo tracks Forward tracks Seed tracks Matched tracks VTT tracks T  TT tracks Many track types, many algorithms

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 17 Event with average occupancy: Event display Red: measurements (hits) Average number of tracks per event: 27 Long (Forward + Matched), 23 Velo, 10 VTT, 10 T  TT 4 Seed tracks + Total74 Average efficiency = 92 % Efficiency for B daughters ~ 95% Blue: reconstructed tracks

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 18 Tracking performance Long tracks 95% 8% Long tracks 8% Average efficiency = 92 % Efficiency for p>5GeV > 95% Total ghost rate = 16% Ghost rate p T >0.5 GeV ~ 8%. Large event to event fluctuations. Efficiency vs pGhost rate vs p cut Ghost rate vs p Tcut

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 19 Robustness tests Tracking is also robust against: Lower hit efficiencies, Decreased hit resolutions, More noise hits. Tracking is robust against number of interactions Note: Luminosity adjusted to have the maximum number of single interactions. Pile-up veto trigger (L0) rejects multiple interaction events. N interactions

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 20 Track fit The Kalman Fit properties: Adds measurements recursively. Mathematically equivalent to least χ 2 method. Needs as input initial track estimate. Multiple scattering and energy loss are naturally included. The tracks are fitted using the Kalman Filter. The Kalman Fit: 1.The prediction step. 2.The filter step. Adds measurements one-by-one. 3.The smoother step. direction of the filter track prediction filtered track

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 21 Track fit resolution LHCb provides an excellent momentum estimate at the vertex. Δp/p Momentum resolution core σ = 0.35% 2nd σ = 1.0% (fraction 0.1) Note: Fitted with single Gaussian in each bin. percent

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 22 Mass and vertex resolutions 4-prong prompt decay  all long tracks. Total tracking efficiency 84.6±0.5 % (= 95.6 % per track) Good resolutions: Good tracking performance essential input for physics analysis: Decay channel: B s  D s - (  KKπ) π +

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 23 K s reconstruction Example: B  J/ψ K s Combine oppositely charged T  TT tracks. p T > 250 MeV. Common vertex. Tracking efficiency for K s : 54% (74% per track). Where does the K s decay? ~25 % in Velo  Long tracks ~50 % between Velo and TT  T  TT tracks ~25 % after TT  Lost Reconstruction of K s (  π + π - ) challenging : Long decay lengths (~ 1 m); many decay outside Velo. Tracks don’t point to interaction point. Leave less hits in detector. π + π - mass of selected B  J/ψ K s σ=10.9±0.6 MeV/c 2

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 24 Conclusions Tracking system provides good spatial and momentum resolutions.: Vertex IP resolution (17+32/p T ) μm, Cluster resolutions 45 μm (ST), 200 μm (OT), Momentum resolution 0.35%. Many algorithms developed for finding tracks in optimised setup. Tracking efficiency ~ 95% for B-daughters, For pions from K s ~ 74%. (~54% both tracks), Ghost rate ~ 8% (for p T >0.5GeV). Tracking is robust against worse conditions. Provides excellent input for physics analysis: e.g. B s  D s - π + :Mass resolution 13 MeV/c 2 Proper time resolution 42 fs.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 25

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 26 BACKUP SLIDES

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 27 Event display Event with average occupancy: Red: measurements (hits) Blue: reconstructed tracks Average number of tracks per event: 27 Long (Forward + Matched), 23 Velo, 10 VTT, 10 T  TT 4 Seed tracks + Total74 Average efficiency = 90.6 % Efficiency for B daughters ~ 95%

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 28 Tracking performance Mean momentum 13 GeV On average 37 measurements (Velo, IT, OT) Long tracks:

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 29 Efficiency definition Efficiencies are normalised to a sample of “reconstructable” particles: in VELO at least 3 r and 3 φ hits, in T stations at least 1 x and 1 stereo hit in each station T1-T3. Long tracks must be reconstructable in VELO and T. VTT tracks must be reconstructable VELO and at least 3 TT hits. TTT tracks must be reconstructable in T and have at least 1 hit in TT. Successfully reconstructed track: at least 70% of hits from one MC particle. Long tracks must be successfully reconstructed in VELO and T, VTT tracks must be successfully reconstructed in VELO and have at least correct 1 hit in TT, TTT tracks must be successfully reconstructed in T and have at least 1 correct hit in TT.

3 May 2003, LHC2003 Symposium, FermiLab Tracking Performance in LHCb, Jeroen van Tilburg 30 LHCb classic setupLHCb light setup VELO