Design and performance of the LHCb Silicon Tracker

Design and performance of the LHCb Silicon Tracker Introduction Silicon Tracker project: design production Tracking strategy and performance Kim Vervink Ecole Polytechnique Fédérale de Lausanne Oct 4, 2005 TIME 05 - Zurich

A huge one arm spectrometer. Dipole Magnet Vertex Locator Tracking Systems ad r 250 m p p Rich 1 & 2 Oct 4, 2005 Precision 10 mrad Calorimeters Muon Chambers Kim Vervink and rare decays in the B sector 2 measurements of CP violation

Neighbouring detectors of the Silicon Tracker. The vertex locator R – f detector strip orientation 21 stations around the interaction point 1 m The other subdetector that uses silicon Half discs open during beam injection and close around the interaction point up until 8 mm Whole subdetector in vacuum Silicon thickness: 300 mm Oct 4, 2005 Kim Vervink 3

the outer tracker Outer Tracker 3 stations with 4 double planes 4, 7 m! OT Straw tubes 5 mm diameter Pitch 5, 25 mm Module production going to completion Oct 4, 2005 Kim Vervink 4

Silicon Tracker Project Some participants Involved institutes: M. I. P. – Heidelberg E. P. F. L. – Lausanne U. S. C. – Santiago de Compostela Uni. Zh – Zurich Oct 4, 2005 Kim Vervink 5

Challenges of the Silicon Tracker. 1. Large areas have to be covered in Silicon. The Silicon design is adapted in order: • to keep it affordable • not to become overloaded in readout channels Long readout strips More load capacitance which increases the noise Beetle chip front-end design Adapted sensor thickness Large distance between readout strips Decreases S/N between strips optimise width/pitch of the strips 2. Bunch crossings every 25 ns fast shaping time Increases noise Optimised front-end electronics 3. Momentum resolution is limited by multiple scattering minimization of material for the acceptance: Thin sensors Oct 4, 2005 Thinner Kim Vervink sensors make S/N go down Best compromise 6

Where is the Trigger Tracker? Located behind the Velo & Rich 1 Just in front of the Magnet: still in frindge field Active area of the detector covers full acceptance (cooling and electronics outside) VELO TT 2 half stations in one box with in total 4 detector planes (0°, 5°, -5°, 0° orientation) Oct 4, 2005 Kim Vervink 7

Trigger Tracker Staggered front-end readout hybrids Silicon sensors Pitch adaptor Interconnect cable Oct 4, 2005 Kim Vervink 8 Support rails

Where is the Inner Tracker? Inner Tracker consists out of 3 stations, surrounded by the Outer Tracker VELO 2 boxes with 2 Si-sensors modules TT 2 boxes with 1 Si-sensor modules Complete IT detector inside the acceptance (hybrids, pcb’s, cooling, cabling, …) Oct 4, 2005 Kim Vervink 1, 3 % of acceptance, 20% of tracks. 9

Si-sensor Pitch Adaptor + hybrid with Beetles. Kapton insulation Aluminium Mini-Balcony Airex foam Carbon Fiber support layer: helps the cooling flow to the sensors Ladders are attached via the mini-balcony on a cooling rod, through which runs a cooling liquid Þ detector is cooled (10°C) Þ in order to control thermal runaway Readout Cables, High and Low voltage cables Cooling System Oct 4, 2005 Kim Vervink 10

Silicon sensors for a fast and precise measurement. TT IT Type p+ microstrips on n type bulk Dimensions (active area) 94, 4 mm x 94, 6 mm (93, 9 mm x 91, 6 mm) 110 mm x 78 mm (108 mm x 76 mm) Readout channels 512 384 Implant width 0, 25 (w/p) Pitch 198 mm 183 mm Thickness 500 mm 320 mm or 410 mm Left strip Oct 4, 2005 Right strip Bond pads & DC readout! HV input to the backside of the sensor S/N value is above 12, taking into account the charge loss between strips. Kim Vervink 11

Production Status Trigger Tracker: 2 half stations with 280 (+15% spare) readout sectors have to be build Inner Tracker: 3 stations with 336 (+15% spare) modules are to be produced and tested A typical production trategy: Building of a module using jigs (parallel production) Metrology Electrical test using internal test pulses in order find broken or unbonded strips Schedual: Prototyping finished in August for both detectors Start of production All modules need to be fabricated by April 2006 Installation in the LHCb pit in June 2006 Oct 4, 2005 Kim Vervink Status: Inner Tracker has about 20 modules produced to Inner tracker testing box 12

A Trigger Tracker module and burn-in test setup A built TT module Cooling system Kapton readout cable 4 modules Burn-in box Sensor Oct 4, 2005 Hybrid TT burn-in test Kim Vervink 13

Support and IT modules are in the production phase… The 2 nd short ladder module that was made… Setup of the support frame Oct 4, 2005 Kim Vervink 14

Silicon project: essential part for the tracking of the LHCb detector Reconstruction is not a trivial task LHCb gets about 50 primary particles per event: check…. 30% radiation length between interaction point and Rich 2 Secondary particles Multiple scattering Degrades the momentum resolution Interaction every 25 ns Spillover from previous bunch crossings Oct 4, 2005 Kim Vervink 15

Tracking reconstruction Particles spread out by magnet. Bdl = 4 Tesla m Warm magnet Top view Multipass strategy • Long tracks • Ks after Velo • Only Velo and TT Oct 4, 2005 Kim Vervink 16

Tracking strategy First look for tracks that pass the whole tracking device (from Velo to T) Easiest to find Highest track resolution The most important ones for physics studies Start with a Velo Seed ( almost straight line: only position and direction known) Adding one T station measurement to a Velo track Use optical parameterisation to calculate where the track passed using z. Center and d. Slope Use the other measurements of the T stations to confirm hypothesis Fast algoritm: main tracking done in HLT Optical method parametrisation z. Center Oct 4, 2005 Kim Vervink d. Slope 17

Second pass of long track reconstruction: work backwards Seeding: Seeding in T stations using unused hits Three hits define an ”almost” straight line Collect more hits around “trial track” to confirm your hypothesis Also used to optimise Rich 2 performance Tracking: Transport the track seed to the Velo and compare with a Velo seed Look at the difference of track parameters Use c² criteria for matches This method adds about 3% to the overall long track finding efficiency Oct 4, 2005 Kim Vervink 18

Other track types Of the remaining hits, make tracks from particles that passed only in TT and IT/OT • • • Most are decay products of a Ks that decay outside Ve. Lo Look for unused seeds in the T stations and add hits in TT Use optical method again. Look amongst the remaining particles for hits in the Velo and TT stations alone. • • • Particles with low momentum: bent out by magnetic field Look for unused Velo tracks with hits in the TT detector Moderate efficiency (70%) and resolution (dp/p ~ 15%) but used to improve RICH 1 performance, kaon tagging and to find slow p from D* Oct 4, 2005 Kim Vervink 19

Tracking Performance on long tracks Cut out in physics analysis Momentum dependent: B particles have higher momentum Track finding efficiency ~95% Oct 4, 2005 Kim Vervink 20

Performance on the resolution of the momentum and the impact parameter (long tracks) Oct 4, 2005 Kim Vervink 21

Summary The design and prototyping of the Silicon Tracker subdetectors is finished. Production of both the Silicon Tracker has started and Installation in the LHCb pit is schedualed in June 2006. Tracking performances are highly dependent on the quality of the Silicon Tracker detector. A tracking strategy has been implemented, and its performance is satisfactory. Oct 4, 2005 Kim Vervink 22