The LHCb Velo detector

1
The LHCb Velo detector

• A high precision silicon device for vertexing,
  tracking and triggering in LHCb.
• J.P. Palacios, University of Liverpool

2
Talk Overview

• The LHCb detector
• Physics reach
• General layout of components
• Velo Requirements
• Physics
• System and mechanical
• Velo Layout
• Silicon RD
• Outlook
• Conclusions

3
The LHCb Detector

• Physics where are the Bs?
• LHC 14TeV pp collisions
• For L 2x1032cm-2s-1 and ?bb500?b have 100K
  bb/s produced!
• O(1012) bb pairs/year at LHCb
• 0.5 of total inelastic cross section
• Cross sections forward peaked and correlater
• Opt for a small angle forward spectrometer

LHCb is a day one experiment! Full physics even
at LHC startup luminosity!
4
The LHCb Decector (2)

• Layout
• LHCb is a single arm small angle forward
  spectrometer

Muons
HCAL
ECAL
TT1
Velo
Rich1
Rich2
Tracker
5
Velo Requirements (1)

• Physics
• Primary vertex reconstruction
• Sensitive area as close to beam as possible
• Highest resolution close to beam line
• Coverage in forward and backward hemispheres
• Interaction point distributed in Z with s 5.3
  cm
• Secondary vertex reconstruction
• Interesting events show displaced vertices from B
  and Charm decays. Resolution on these crucial to
  sensitivity of LHCb measurements.
• Busy secondary vertices can point to multiple
  interactions
• Minimal material between vertex and first
  measured point

High resolution on first measurement
6
Requirements (2)

• Trigger
• FAST 2D (rz) and 3D (rzf) standalone tracking for
  L1 Trigger (see talk by Niels Tuning)
• Rejection of multiple interactions
• LHCb Tracking system (see talk by F. Lehner)
• Track reconstruction for B and Charm decays
• Match LHCb forward acceptance
• Sufficient hits/track at least 3 hits
• Single hit efficiency (give number)
• Good extrapolation of Velo tracks into rest of
  LHCb tracking system
• Minimize material seen by tracks going through
  Velo dealing with tracks of Energy O(GeV)

Implications on strip layout
Number of Si layers
7
Requirements (3)

• All this in an extreme radiation environment

Flux between 5x1012neqcm-2 /year and
1.3x1014neqcm-2 /year depending on r and z
Velo must be operational for at least 2 years
under these conditions
8
Requirements (4)

• System and Mechanical Requirements
• No material closer than 5mm from LHC beam (LHC
  machine constraint)
• During injection clearance from LHC beam is 25mm
• Velo must be able to retract by 30mm for
  injection
• Shield Velo system from beam-induced RF pickup
• Isolate system from LHC primary vacuum
• Protect vacuum from detector module outgasing

9
Velo Layout (1)

• Baseline Sensor Design
• Sensors 7mmgtRgt44mm
• (Active area 8mm to 43mm)
• 182o angular coverage

• R sensors
• Pitch 40mm to 92mm
• 45o inner, 90o outer sections
• f sensors
• Pitch 37mm to 40mm and 40mm to 118mm
• Stereo angle

10
Velo Layout (2)

• 21 stations with Si perpendicular to beamline
• Stations divided into oposing modules with an R
  and a f 182o Si strip sensor
• 2048 channels per sensor read out with 16 chips
• Hybrid readout electronics, thermal
  conductivity, mechanical support

11
Velo layout (3)

• Z range -17cm to 74cm
• Trade-off between hits/track and material

f detector
R detector
Beam direction
Pile-up R detectors (multiple interatction rejecti
on)
12
Velo Layout (4)

• RF shielding
• No beam pipe
• Shield Velo modules from RF pickup
• Shielding must be retractable
• Must have 1mm clearance from sensors
• Protect LHC vacuum
• Must withstand pressure differential of 15 mBar
  between primary and secondary vacua
• Guide the wakefields

13
Velo Layout (5)

• RF Shielding (2)
• All this complicated by physics performance
  reasons
• Minimise material between Velo halves and in LHCb
  acceptance
• Minimise material before first measured hit
  inner corrugations
• Silicon RD
• Ongoing program to determine the technology
  choice for first Velo and further iterations.

Picture of XZ cross section with stations?
First full size foil from NIKHEF!
14
Silicon RD Program

• Test before and after irradiation in beam and lab

Plus ALICE, GLAST detectors
Lab tests with IR laser and 40MHz
electonics. See talk by Gianluigi Casse
15
Silicon RD (2)

• Test beam experimental setup
• 120 GeV µ and p from CERN SPS
• Check R/F geometry satisfies LHCb Velo trigger
  and offline requirements
• Research best Silicon technology for Velo

16
Silicon RD (3)

• Results from DELPHI, PR01,PR02 show n-on-n has
  clear advantages over p-on-n in resolution and
  efficiency when operated underdepleted
• n-bulk becomes effective p after irradiation.
  Depletion evolves from n implant side

Irradiated DELPHI ds
Full efficiency at 0.6V dep !
Resolution robust Vs CCE!
17
Silicon RD (4)

• Double metal layer
• A concern we have lots!
• Charge pickup from double metal layer a problem,
  particularly for irradiated p-on-n

Effects on n-on-n currently under study. Expect
better performance vs. irradiation
See Bowcock et al. NIM 478 (2002) 291-295
18
Silicon RD (5)

• Non-uniform irradiation
• Depletion voltage varies across irradiated
  detector. n-on-n segmentation allows to operate
  underdepleted
• Detailed study on PR02 in LHCb-2001-053. See talk
  by G. Casse
• Future ideas
• Floating strips (see talk by Jim Libby)
• Data for non-irradiated n-on-n encouraging.
  Irradiated case to be tested
• High resistivity CZ substrate
• Test beam data of prototype undergoing analysis
• P-bulk detectors
• See talk by G. Casse and NIM A (2002) 465-470
• Thin detectors
• Produced 150mm n-on-n PR03. To test?

19
Silicon RD (6)

• Conclusions from silicon research
• n-in-n a clear choice for Velo
• All requirements for irradiated detectors met
• Operational below full depletion
• Floating strips remain an option for replacement
  of Velo if necessary
• R f geometry allows fast tracking (Trigger)
• Final R and F strip layout decision imminent
• Open to technology improvements for future Velo
  sensors (eg CERN RD50)

20
Outlook

• Silicon sensor design for Velo near completion.
• Hybrid prototype tested succesfully
• First Mechanical module being built
• Plan to have complete Velo in 2005 and place in
  test beam in 2006
• Startup in 2007

21
Conclusions

• The Velo is in an advanced stage of design.
  Prototyping is underway
• A range of issues regarding the choice of silicon
  technology have been investigated and a baseline
  design for the first Velo completed
• The performance of the system exceeds the physics
  and system requirements of LHCb

22
Backup Slides
23
Silicon RD

• Ongoing program to determine the technology
  choice for first Velo and further iterations.

• Tested in test beam and lab
• DELPHI ds XY 6cmX3.4cm
• P pitch 25 µm (readout 50 µm)
• n pitch 42 µm
• Hamamatsu R, F 300µm n-on-n, 72o (PR01)
• pitch 40-126 µm
• up to 2.51014 neq/cm2
• MICRON F 200 µm, p-on-n, 182o (PR02)
• pitch 24-124 µm
• irradiated up to 6.41014 neq/cm2
• ALICE, GLAST
• Micron R, 300 µm

Lab tests with IR laser and 40MHz
electonics. See talk by Gianluigi Casse
R/f geometry validation and test beam telescope