Advances in the LHCb Vertex Locator: Current Status and Future Upgrades

1. LHCb Vertex Locator: present and future Martin van Beuzekom On behalf of the LHCb VELO group Liverpool University Outline: • Introduction to LHCb and VErtex LOcator (VELO) • Status of VELO • Beamtests • Upgrades • Summary 1

2. LHCb overview Large Hadron Collider pp collisions: √s = 14 TeV bunch crossing every 25 ns LHCb Studies physics of b-flavoured hadrons (CP violation) B-hadrons produced at small angles -> Single arm forward spectrometer 10 – 300 (250) mrad in bending plane (non bend.) Luminosity 2·1032 cm-2 s-1 interaction region 2

3. Vertex Locator • 2 retractable detector halves • Range 3 cm each • 23 silicon microstrip modules / side • Silicon modules in secondary vacuum (2 mm) • Modules separated from beam vacuum (10-9) by 300 mm Alu foil (RF box) • Maximum allowed diff. pressure 5 mbar • Shield against beam induced EMI • Innermost strip 8 mm from beam 3

4. Silicon sensor details R-measuring sensor (45 degree circular segments) • 300 mm thick sensors • n-on-n, DOFZ wafers • 42 mm radius • AC coupled, double metal • 2048 strips / sensor • Pitch from 40 to 100 mm • Produced by Micron Semiconductor 42 mm 8 mm F-measuring sensor (radial strips with a stereo angle) 4

5. Module construction Beetle • 4 layer kapton circuit • Heat transport with TPG • Readout with 16 Beetle chips • 128 channels, 25 ns shaping time, analog pipeline • 0.25 mm CMOS • no performance loss up to 40 Mrad • Yield > 80 % Kapton hybrid Carbon fibre Thermal Pyrolytic Graphite (TPG) 5

6. Silicon microstrip modules RF-foil VELO sensors PileUp sensors • 21 stations with R-F geometry • Fast R-Z tracking in trigger farm • Overlap of right and left det. halves • Total of 176k strips • 2 stations with R-sensor for PileUp trigger Carbon fibre base Fine pitch kapton cables 6

7. Pile Up (veto) trigger n = # pp interactions/crossing • PileUp system detects multiple interactions • Vetoes Level-0 trigger • Increases physics output • Multiple interactions complicate Level-1 trigger (CPU-farm) • Factor 3 reduction in #crossings with multiple interactions • 2 R-sensors, prompt binary readout • Combine 4 strips in 1 to reduce # inputs • 2048 “bits” @ 40 MHz = 80 Gbit/sec • Special hybrids (4 times #signals) LHCb luminosity 7

8. PileUp continued all combinations true tracks • Each vertex bin corresponds to a small wedge in the RA-RB correlation plot • Each “track” is represented by a point • Histogramming of Z-vertex • determine # vertices with FPGAs • find 1st peak, mask hits, find 2nd peak • Algorithm highly pipelined ( ~ 80 Bunch crossings) 2 vertices 8

9. LHCb status Installation progressing, first collisions expected in fall 2007 9

10. Status @ Interaction point • Vacuum vessel installed May 2006 • Vacuum controlled by PLC • Movement system controlled by PLC • Thin (2 mm) exit foil mounted in Aug 2006 • Vacuum qualification ongoing • Detector installation early 2007 10

11. CO2 cooling • 2 phase CO2 cooling system • Low mass • Radiation hard • Non toxic • Silicon modules in parallel • 1 mm Ø stainless steel capillaries • Pressure up to 70 bar • Large DT over TPG + interface • heat load max. 30W T=-30 ºC T ~ -5 ºC 11

12. Testbeam performance 2004: • Single sided module with 200 mm sensor • Characterized (final) sensor + (final) Beetle • S/N 16 • Spillover @25 ns < 25 % • Resolution ~4 mm Beetle Frontend pulseshape August 2006 • 3 double sided modules • Full electronics chain with final electronics • ADCs, Timing, Fast & Slow Control • Data taken for many sensor and chip settings • Analysis ongoing November 2006 • Aim for a complete detector half (21 mod.) • Module production in Liverpool at full speed • Delivery 4 modules per week • Major effort! 12

13. VELO Upgrades Why: • Limited lifetime of VELO due to high radiation dose • (1.3x1014 neq/cm2/year) • Improve (impact parameter) resolution • Displaced vertex trigger • Increase statistics • Readout of complete LHCb detector @ 40 MHz How: • Different sensor technology/geometry • Reduce material in VELO • Move closer to beam • Currently 8 mm, goal 5 mm (min. allowed by accelerator) • Up to 36% resolution improvement • Increase luminosity (not SLHC) • Level-1 computing power 13

14. Radiation environment Middle station Far station Radiation environment for current design • Strongly non-uniform • Dependence on radius and z-position • Max fluence 1.3x1014 neq/cm2/year Define as 1 LHCb-year • Expected (useful) lifetime ~3 years • assuming nominal luminosity • no accidents With upgrades • 5 mm strip radius -> 2.5x increase • Luminosity to 1x1033 -> 5x increase • Fluence 1.7x1015 neq/cm2/year Only possible with • Different sensor technology • and/or smaller strips or pixels (Syracuse group) 14

15. Radiation Hard Technologies Magnetic Czochralski • p-on-n MCz • Assume required CCE min. 60 % • Single sided processing • R&D by Glasgow group 5..6 LHCb-years 15

16. Radiation Hard Technologies- II n-on-p > 20 LHCb-years • High resistivity p-silicon • Single sided processing • Very high bias voltage • R&D by Liverpool group Presentation by Gian-Luigi Casse 16

17. Radiation Hard Technologies- III 3D - sensors Extremely radiation hard Low bias voltage Very promising Complex processing R&D by Glasgow group 17

18. Reduce material in VELO Radiation length of total VELO: 19 % X0 Largest contribution from RF-foil and sensors Thin sensors (200 mm) already tested extensively Thinner RF-foil is under investigation • BTeV planned sensors in primary vacuum • Beam (mirror) current via wires/strips • Cryo pumping against outgassing • Totem (@LHC) • 150 mm Inconel (Ni-Cr) foil 1 mm from beam 18

19. Summary • Construction of LHCb VErtex LOcator is well underway • Mechanics, vacuum, motion system installed • Cooling system steadily progressing • Silicon module production at full speed • Next deadline is half detector for November testbeam • Detector (sensors) installation early 2007 • Already starting to think about upgrades • Limited lifetime of VELO • More radiation hard sensors • Reduce material to improve performance 19