The LHC collider in Geneva LHCb p-p collisions with 7 TeV + 7 TeV 14 Million collisions per second 1 in 160 collisions is B physics

LHCb Tracking Bs K K ,K  Ds

~1.41.2 m2 ~65 m2 21 stations R and φ sensors LHCb setup VELO

Vertex Detector Made @ NIKHEF Pile-Up Stations Interaction Region s=5.3 cm

Vertex detector Silicon stations y x z R Vertex has standalone track and vertex reconstruction (Projection in R-z plane) Second metal layer As explained the silicon stations have full phi coverage, the red area is the overlap between two stations. Schematically the detectors are arranged as show in the cross-section AA. The acceptance is shown as well as the interaction region of about 5 cm. The two Pile – Up stations are outside the acceptance. The silicon stations are using strip detectors with R phi geometry. The choice for strip detectors directly follow from the occupancy which is low enough because of the reduced luminosity and the selection of events with a low number of pp interactions. The minimum active radius is 8 mm and the outside radius is 42. The thickness is 220 mum. The R detectors are divided in 45 degree segments. The hits in those 45 degree segments can be projected on the R-z plane and then be used for the standalone track and vertex reconstruction. The blue line was successfully identified as a high pt displaced track, which is the key ingredient for the level-1 trigger. I will continue with some details about the silicon. The signal is read out over a double metal layer, allowing the chips to be outside the acceptance region. The pitch ranges from 40 to 103 mum for the R stations and the highest x-y resolution is naturally closest to the interaction region because of the phi strips. The phi strips have stereo angles of -20 degrees to 10 degrees. The detectors are maintained at a temperature of -5 degrees C and a CO2 cooling system is installed to do just that.

The detector apparatus Velo Detector The detector apparatus 21 stations

Simulated Event ,K Bs K Outer Tracker K Ds  Velo Particle momentum

Outer Tracker Track OT double layer cross section pitch 5.25 mm e-

Outer Tracker

Outer Tracker Simulation Geant3 LHCb event display Measurement simulation: OT double layer cross section 5mm straws pitch 5.25 mm Track e-

Track Finding Zoom of OT station (hits in red) OT double layer cross section e- e- e- pitch 5.25 mm e- e-

Track finding strategy T track Upstream track VELO seeds Long track (forward) Long track (matched) VELO track T seeds Downstream track Long tracks  highest quality for physics (good IP & p resolution) Downstream tracks  needed for efficient KS finding (good p resolution) Upstream tracks  lower p, worse p resolution, but useful for RICH1 pattern recognition T tracks  useful for RICH2 pattern recognition VELO tracks  useful for primary vertex reconstruction (good IP resolution)

Result of track finding On average: 26 long tracks 11 upstream tracks 4 downstream tracks 5 T tracks 26 VELO tracks Result of track finding T3 T2 T1 Typical event display: Red = measurements (hits) Blue = all reconstructed tracks TT VELO 2050 hits assigned to a long track: 98.7% correctly assigned Efficiency vs p : Ghost rate vs pT : Ghost rate = 3% (for pT > 0.5 GeV) Eff = 94% (p > 10 GeV) Ghosts: Negligible effect on b decay reconstruction

Experimental Resolution Momentum resolution Impact parameter resolution sIP= 14m + 35 m/pT dp/p = 0.35% – 0.55% 1/pT spectrum B tracks p spectrum B tracks

Mass resolution: ~ 14 MeV: B Reconstruction Mass resolution: ~ 14 MeV: p Bs K K ,K  Ds d B Decay time Distribution: t=md/cp

event