The LHCb VErtex LOcator Tracking, Vertexing and Triggering in a harsh radiation environment Doris Eckstein, CERN May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors The LHCb Experiment Dedicated to the study of CP violation in the B system LHC: -pp collisions @ 14TeV -full spectrum of B hadrons ( ) -high intensity: LHCb: -single arm spectrometer -15-300mrad angular acceptance -recently optimised to minimise material Vertex Locator May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors The requirements for the VELO ~1m Interaction region Downstream Reconstruction of pp interaction vertex wide spread of interaction region in z (sz=5.3cm) many stations around z=0 Reconstruction of b-hadron decay vertex short track extrapolation distances measure at smallest radii minimal multiple scattering minimise material between interaction and first measured point VELO is the tracker before the LHCb magnet Angular coverage of full downstream detector angular range 21 Silicon stations allowing to measure at least 3 hits/track 2 R- and 2 F-measuring sensors per station overlap (acceptance, alignment) May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors The VELO Design Mechanical design as consequence of these criteria VELO sensors as close as possible to beam no beam pipe, sensors ~7mm away from beam Injection: larger aperture required retraction by 30mm Protect sensors against RF pickup from the LHC beam Protect the LHC Vacuum from possible outgasing of detector modules Place sensors in a secondary vacuum: Roman pots May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Secondary Vacuum – RF Foil outer corrugations beam inner corrugations F sensors R sensors Made from 250mm thick Al Inner corrugations : Minimal material before the first sensor is hit Outer corrugations: allow for overlap of detector halves for full azimuthal coverage and for alignment Prototyping at NIKHEF method: Hotgas Forming full size foil vacuum tight and stiff May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors More requirements for the VELO Rejection of multiple interactions in L0 Trigger additional VETO stations upstream of interaction point Fast stand-alone tracking and vertexing for L1 Trigger motivates R-and F-measuring sensors Design allows to optimise resolution vs. number of channels Baseline design of sensors: Active area 8mm to 42 mm R measuring sensors: division into 45o sectors F measuring sensors: inner/outer region increasing pitch from inner towards outer radii 2nd metal layer to route signal to chips May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Second Level Vertex Trigger Forward flight direction of B: Rz impact parameter First step: 2D -build Triplets of clusters in R sensors -form tracks in Rz -fill z-vertex histogram -preselect large impact parameter tracks in Rz -match to m Second step: 3D -preselected (5-10) 2D tracks -add information from F sensors for 3D reconstruction -match to L0 and TT z-vertex histogram xy-vertex Example: 2D tracks in 45o sz~70mm sx,y~30mm May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Optimisation of VELO sensor design New 45o Old 90o 200mm sensor L1 Trigger: speed, number of ghost tracks sector division Clustering/tracking efficiency: Signal to Noise strip length Options of design studied (keeping constant number of strips) Different strip pitches Does impact parameter resolution suffer? max. 5% design chosen with gradual increase of pitch (40mm to 103mm) Resolution (mm) May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Even more requirements for the VELO This detector has to operate in an extreme radiation environment Middle station Far station Maximum irradiation per station: 5x1012 to 1.3x1014 neq/cm2/year Strongly non-uniform dependence on R and station (z) Maintain a good S/N performance for at least 2 years (replacement) Extensive R&D program to select Sensor and Front-End chip May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Prototype testing in Lab and Test beam Test beam: CERN SPS (120 GeV p and m) Irradiated Not irradiated Irradiated Not irradiated DELPHI-ds sensor Irradiated/Not irradiated PR03 sensors May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Tests of the p-on-n prototype Efficiency of cluster reconstruction close to track Box size ~ efficiency PR02 F-sensor: routing lines in outer region none in inner region More efficient in inner region Less efficient in irradiated region May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors P-on-n vs n-on-n P-on-n: -Fraction of charge in routing line reaches 20% in outer region -5% in inner region -Detector has undepleted and insulating layer after irradiation -Expected to be less for n-on-n Compare efficiency for p-on-n and n-on-n for different depletion depth P-on-n efficiency degrades fast N-on-n efficiency ~100% for only 60% depletion depth Chose n-on-n for VELO May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Front-End chip decision Two parallel developments: SCTA_VELO (DMILL) and Beetle (0.25mm CMOS) Features: 128 input channels 40MHz sampling (LHC clock) Hybrids equipped with 16 chips tested in test beam Decision taken at beginning of this year to use Beetle Performance equally good Availability, radiation hardness and usage in LHCb SCTA_VELO Beetle1.1 May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Beetle chip tests Currently Beetle1.2 under study Test set-up in Lab with one chip reading out a n-on-n 200mm thick prototype sensor Sensor close to final design Measure S/N with Sr source Prepare for test beam: Hybrid with 16 Beetle1.2 chips reading out a full sensor MPW submission of improved Beetle1.3 soon May 29, 2003 9th Pisa meeting on advanced detectors

9th Pisa meeting on advanced detectors Summary & Outlook VELO design is close to completion Important decisions: finalised sensor design choice of Front-End chip Successfully tested module prototypes consisting of Sensor, Hybrid and 16 chips Plan to have first module end of 2003 Complete VELO in 2006 May 29, 2003 9th Pisa meeting on advanced detectors