Tracking and Alignment in LHCb Florin MACIUC on behalf of LHCb collaboration florin.maciuc@mpi-hd.mpg.de Max-Planck Institute for Nuclear Physics Heidelberg Physics at LHC 2010 Hamburg – p. 1/22
LHCb and B-physics • LHCb - Large Hadron Collider beauty detector. • LHCb aims lay primary in the B-physics sector. • Nominal luminosity of about 2 × 10 32 cm − 2 s − 1 = ⇒ 10 12 b ¯ b per year. • The dominant channel behavior explains the single-arm forward spectrometer geometry chosen for LHCb. forward beaming of b ¯ Gluon fusion before fragmentation b in the LHCb frame Physics at LHC 2010 Hamburg – p. 2/22
y LHCb Detector z X x Primary Vertex (PV) y HCAL M5 ECAL M4 SPD/PS 5m M3 M2 Magnet RICH2 M1 T3 T2 T1 TT Vertex Locator z 5m 10m 15m 20m Physics at LHC 2010 Hamburg – p. 3/22
LHCb Detector pitch 38-102 µm , depth 300 µm VErtex LOcator (VELO): Silicon Detector y Tracker Turicensis (TT): Silicon Detector HCAL M5 ECAL pitch 183 µm , M4 SPD/PS 5m M3 M2 Magnet RICH2 depth 500 µm M1 T3 T2 T1 TT Vertex Locator pitch 198 µm , depth 320-410 µm z 5m 10m 15m 20m Inner Tracker (IT): Silicon Detector Physics at LHC 2010 Hamburg – p. 3/22
LHCb Detector Outer Tracker (OT): Straw Tube Detector y radius 2.45 mm hit resolution 200 µm HCAL M5 ECAL M4 SPD/PS 5m M3 M2 Magnet RICH2 M1 T3 T2 T1 TT Vertex Locator z 5m 10m 15m 20m Physics at LHC 2010 Hamburg – p. 3/22
LHCb Detector Warm Magnet : integrated magnetic field of 4 T · m y HCAL M5 ECAL M4 SPD/PS 5m M3 M2 Magnet RICH2 M1 T3 T2 T1 TT Vertex Locator z 5m 10m 15m 20m Physics at LHC 2010 Hamburg – p. 3/22
VErtex LOcator • Primary Vertex (PV) is inside VELO, towards middle; • VELO is a retractable detector, 2 VELO sides: ⋆ To protect from damage, VELO is in Open position before the beam is stable, and closed afterward. ⋆ Open VELO: sensors 30 mm further from the beam, ⋆ Closed VELO: sensors are about 8 mm from the beam line, VELO double-sensor modules: R+ φ Schematic: one side of VELO Physics at LHC 2010 Hamburg – p. 4/22
VErtex LOcator • Primary Vertex (PV) is inside VELO, towards middle; • VELO is a retractable detector, 2 VELO sides: ⋆ To protect from damage, VELO is in Open position before the beam is stable, and closed afterward. ⋆ Open VELO: sensors 30 mm further from the beam, ⋆ Closed VELO: sensors are about 8 mm from the beam line, Schematic VELO sensors in Open and Closed positions Physics at LHC 2010 Hamburg – p. 4/22
Primary Vertex Resolution • Primary Vertex (PV) is determined with VELO tracks. • Method: randomly split event track container in two, and MC Data reconstruct PV. ∆ x ( µm ) 11.5 15.8 • Results close to expected, ∆ y ( µm ) 11.3 15.2 ⋆ A residual ≈ 40 % difference - e.g. when using 25 tracks. ∆ z ( µm ) 57 91 ⋆ Improving. PV resolution vs track used, real data PV resolution vs track used, MC Physics at LHC 2010 Hamburg – p. 5/22
Impact Parameter Resolution • Impact parameter (IP) - Closest approach to PV of a track. • IP resolution is determined primarily by: ⋆ random scattering in VELO material, VELO misalignments and hit resolutions. • IP resolution for MC and data given. Impact Parameter resolution in X Impact Parameter resolution in Y IP Resolution Vs 1/p IP Resolution Vs 1/p X Y T T 0.09 VELO Closed LHCb VELO Preliminary 0.09 VELO Closed LHCb VELO Preliminary 2010 Data 2010 Data 0.08 0.08 Sim. 300 µ m Foil Sim. 300 µ m Foil Sim. 250 µ m Foil Sim. 250 µ m Foil 0.07 0.07 0.06 0.06 mm 0.05 mm 0.05 0.04 0.04 0.03 0.03 2010 Data: 16.2 + 24.6/p m µ 2010 Data: 15.7 + 24.4/p m µ 0.02 0.02 T T Sim. 300 µ m Foil: 11.2 + 21.0/p µ m Sim. 300 m Foil: 11.5 + 20.6/p m µ µ 0.01 0.01 T T Sim. 250 m Foil: 11.2 + 19.9/p m Sim. 250 m Foil: 11.9 + 19.3/p m µ µ µ µ T T 0 0 0 0.5 1 1.5 2 2.5 3 0 0.5 1 1.5 2 2.5 3 1/p (c/GeV) 1/p (c/GeV) T T Physics at LHC 2010 Hamburg – p. 6/22
Impact Parameter Resolution • Impact parameter (IP) - Closest approach to PV of a track. • IP resolution is determined primarily by: ⋆ random scattering in VELO material, VELO misalignments and hit resolutions. • IP resolution for MC and data given. • 15-40 % difference between MC and data. • Accounted for already. ⋆ Some disagreement in material description of MC. ⋆ Misalignment between VELO sides. • Remaining: - residual misalignments of sensors, � 4 . 4 µm , - too optimistic hit resolution in MC, - charge sharing. Physics at LHC 2010 Hamburg – p. 6/22
Alignment Status of Subdetectors • Optical alignment of VELO, OT, IT, TT : Survey. • Updated software alignment Aligned. • Monte Carlo results: black histograms. • R track − R hit , measurement residual distribution gauges the alignment quality. VELO R-sensor residuals OT residuals Physics at LHC 2010 Hamburg – p. 7/22
Alignment Status of Subdetectors • Optical alignment of VELO, OT, IT, TT : Survey. • Updated software alignment Aligned. • Monte Carlo results: black histograms. • R track − R hit , measurement residual distribution gauges the alignment quality. IT residuals TT residuals Physics at LHC 2010 Hamburg – p. 7/22
Silicon Trackers: Hit Resolution • 40-50% difference between Monte Carlo and Data for IT and TT. • IT and TT are single-sided silicon strip detectors. • One source of disagreement was found in the charge sharing between neighboring strips. ⋆ This effect was overestimated in MC. ⋆ After correction: an increase from 40 µm to 50 µm for IT hit resolution. • We expect residual misalignments to account for the rest. charge sharing between two strips larger cluster of strips improve measurement resolution Physics at LHC 2010 Hamburg – p. 8/22
Long Track Efficiency • Long track efficiency obtainable from K S candidates. • Method: ⋆ Finds VELO segment and the associated CALO cluster, ⋆ Gets Long tracks from reconstruction, ⋆ K S Candidates 1: VELO+CALO track and a Long track, ⋆ K S Candidates 2: 2 Long tracks. • The method supplies IT/OT/TT efficiency in tracking. • Results close to 100%, with MC and data agreement. Long-Long K S candidates, mass plot Efficiency as a function p T 25000 efficiency candidates / 2 MeV longtrack + velo-calo track 1 LHCb preliminary s = 7 TeV signal component longtrack + ( longtrack & velo-calo track ) 20000 signal component 0.8 LHCb preliminary s = 7 TeV 15000 0.6 10000 0.4 Data 5000 0.2 Monte Carlo 0 0 400 450 500 550 600 0 200 400 600 800 1000 p [MeV] m [MeV] π π T Physics at LHC 2010 Hamburg – p. 9/22
An Other Method for Track Efficiency • Method, phase 1: ⋆ For all VELO segments, finds a corresponding CALO cluster in the bending plane (x,z) ⋆ Checks in the non-bending ( z, y ) plane, ⋆ Fits track VELO+CALO, • Phase 2: ⋆ IT/OT/TT segments are matched to the found track. ⋆ the previous segments are provided by the various Pattern-Recognition algorithms. Physics at LHC 2010 Hamburg – p. 10/22
An Other Method for Track Efficiency • Method, phase 1: ⋆ For all VELO segments, finds a corresponding CALO cluster in the bending plane (x,z) ⋆ Checks in the non-bending ( z, y ) plane, ⋆ Fits track VELO+CALO, • Phase 2: ⋆ IT/OT/TT segments are matched to the found track. ⋆ the previous segments are provided by the various Pattern-Recognition algorithms. Difference in y for the track and CALO cluster includes only VELO+CALO tracks, which position, includes all VELO+CALO tracks have an associated Downstream segment ǫ eff = n 2 n 1 Physics at LHC 2010 Hamburg – p. 10/22
Particle Zoo • Mass values of several detected particle agree with the PDG values to per mil level. • Small signal widths , e.g. 2.8 MeV for Λ , 2.7 MeV Ξ − , 8.5 MeV D 0 , 2.5 MeV Ω , etc. K S Λ J/ψ Ξ − ) ) Events / ( 5 ) Events / ( 5 ) ) ) 2 2 25 25 2 2 250 250 Entries / (3 MeV/c Entries / (3 MeV/c LHCb LHCb Events / ( 4.75 MeV/c Events / ( 4.75 MeV/c 35 35 LHCb N = 1539 ± 46 N signal = N = 68.8 ± 11 51.9 ± 9.2 Signal Signal Preliminary Preliminary m Preliminary m = 1869.9 1.5 MeV = Mass µ = 1863.38 ± 0.27 MeV/c 2 ± 2286.1 ± 0.72 MeV 0 30 30 0 σ = σ 20 20 8.48 1.2 MeV = 3.73 0.79 MeV 200 200 s = 7 TeV Data ± ± Gauss Gauss Mass = 8.69 0.24 MeV/c 2 s = 7 TeV Data s = 7 TeV Data σ ± 25 25 150 150 15 15 20 20 15 15 100 100 10 10 10 10 50 50 5 5 5 5 0 0 0 0 0 0 1800 1800 1850 1850 1900 1900 1800 1800 1850 1850 1900 1900 1950 1950 2200 2200 2250 2250 2300 2300 2350 2350 2 2 m m (MeV/c (MeV/c 2 2 ) ) m m mass (MeV/c mass (MeV/c ) ) m m mass (MeV/c mass (MeV/c 2 2 ) ) K K π π K K π π pK pK π π S S D 0 D + Ω Λ c Plus many more other .... Physics at LHC 2010 Hamburg – p. 11/22
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