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The LHCb VELO Upgrade. Jianchun Wang Syracuse University For the LHCb VELO Group VERTEX 2009 Workshop,Veluwe, Netherlands, Sept 13-18, 2009. The LHCb Environment. b. doesn’t occur. b. b. b. b. b. A dedicated b-physics experiment.

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the lhcb velo upgrade

The LHCb VELO Upgrade

Jianchun Wang

Syracuse University

For the LHCb VELO Group

VERTEX 2009 Workshop,Veluwe, Netherlands, Sept 13-18, 2009

the lhcb environment
The LHCb Environment


doesn’t occur






A dedicated b-physics experiment

  • Designed to maximize B-acceptance within cost and space constraints.
  • Forward spectrometer ( 1.9 < |h| < 4.9 ), where b are maximally boosted, benefits proper time measurement.
  • One arm is OK since bb directions are correlated.
  • Production sbb~500 mb, Min. bias: sinel ~ 80 mb.
  • Choose to run at <L>~21032 cm–2s–1(2 fb–1/year),~1012 bb pairs produced per year.
  • Maximize probability of single interaction per crossing.
  • Clean environment (average interactions per crossing <n>~ 0.5 ), easier to reconstruct.
  • Less radiation damage ( the closest tip ~7 mm away from beam).

Jianchun Wang, Vertex 2009

the lhcb detector
The LHCb Detector
  • VErtex LOcator
  • primary vertex
  • impact parameter
  • displaced vertex

VErtex LOcator

Trigger Tracker

Tracking Stations

Ready to go !

  • s(IP) ~ 14 mm + 35 mm / Pt
  • Primary vertex ~10 mm in X/Y, ~50 mm in Z.
  • B proper time resolution ~ 40 fs.

Jianchun Wang, Vertex 2009

limitation of current trigger system
Limitation of Current Trigger System

muon trigger

hadron trigger

  • To improve the physics sensitivity LHCb plan to increase the luminosity by a factor of 10.
  • Current trigger system has two stages:
    • L0 hardware trigger, reduce to 1 MHz.
    • HLT software trigger, reduce to 2 kHz.
  • L0 trigger limit is driven by 1 MHz maximum readout rate.


  • With increased L, the L0 criteria has to be tighten to stay below 1 MHz. There is not much net gain, especially in hadron channel.
  • Increasing L to 1033 will not introduce too much complexity to event. Most events have 1 or 2 interactions. Increasing to 2x1033 the average number of interactions increases to ~ 4,
  • At L=2x1033, unacceptable increase in CPU time due to large combinatorics.

Jianchun Wang, Vertex 2009

lhcb upgrade strategy
LHCb Upgrade Strategy
  • Run at 2x1033 cm-2s-1 for 5 years (~100 fb-1). This plan is consistent with, but independent of the sLHC upgrade program.
  • LHCb will readout all sub-detectors at 40 MHz  replace FE electronics of most detectors.
  • The trigger decision will be performed entirely on CPU farm.
    • Removing L0 trigger, thus no limit on the data rate.
    • Software trigger allows sophisticated triggering scheme with lower Pt cuts and use of IP to maximize the signal yields.
    • Preliminary studies show that at current L the hadronic channel efficiency improves by ~2 (the goal), and the yield increases proportionally to L.
    • Increases in statistics by ~20 for hadronic channels and ~10 for leptonic channels.
    • More complicated events significantly increase trigger processing time, increasing granularity is mandatory.
  • Improve or maintain efficiency and resolution.

Jianchun Wang, Vertex 2009

current vertex locator
Current Vertex Locator

~ 1 m

RF foil

3cm separation

interaction point

pile-up veto (R-sensors)

  • Silicon micro-strip, n+ in n-bulk sensors.
  • Detector halves retractable (by 30mm) for injection.
  • 21 tracking stationsper side.
  • R-Φ geometry, 40–100μm pitch, 300mm thickness.
  • Optimized for
    • tracking of particles originating from beam-beam interactions.
    • fast online 2D (R-z) tracking.
    • fast offline 3D tracking in two steps (R-z then f).

r=42 mm

r=8 mm

( ~7 mm)



Jianchun Wang, Vertex 2009

current velo detector for upgrade
Current VELO Detector for Upgrade?

Start upgrade studies from the current VELO

  • At L=2x1033 the occupancy will be high, especially at the inner region (particle/hit occupancy ~2%, strip occupancy ~4%). Higher granularity and lower noise are needed. Pixel architecture meets the need.
  • Analog readout of VELO data at 40MHz is unrealistic. Signals need to be digitized and sparsified at FE.
  • The data rates are enormous. Clustering reduces the data rates out of FE.
  • This triggered a dedicated R&D on radiation hard FPGAs.
  • Pixel architecture reduces pattern recognition difficulty.

Particle Hits / Event / cm2

Inner Radius

Radius (cm)

Fit to aRb

Jianchun Wang, Vertex 2009

pixel detector
Pixel Detector
  • Two main thrusts of R&D required for the upgrade are:
    • Front-End Electronics
    • Sensor
  • We had studied different types of sensors and readout schemes. We decide to focus on an upgrade solution based on pixel architecture.

Jianchun Wang, Vertex 2009

front end electronics
Front-end Electronics

Jianchun Wang, Vertex 2009

  • Must provide digitized data to trigger processor in real time: digitization, data sparsification, and pushing data to storage buffer.
  • Withstand same radiation environment as sensor TID: ~400 MRad.
  • Modern fabrication technologies may allow larger radiation tolerance – 130 nm, 90 nm.
  • Issues to be investigated
    • Analog electronics optimization: noise, peaking time, stability of performance with irradiation, leakage current compensation
    • Digitization: speed, effective number of bits.
    • Zero suppression: effective threshold, time walk, discriminator stability
    • Digital section: data rate capability, stability of performance with irradiation.
timepix readout chip
Timepix Readout Chip





Chip dimensions


See Richard Plackett’s presentation for more details



Comparator output



ToT = TE - LE

Pixel readout chip based on Medipix2

256 x 256 pixels 55 mm square, and chip is 3 side buttable. Single Layer Modules Possible!! (X0)

By using TSV (through silicon vias) dead side can be reduced to 0.8 mm in Medipix3 (out of 1.5 mm)

Analogue power consumption 6 mW per pixel. TOT provides better than 6 bit equivalent ADC resolution

Upgrade being considered to 90 nm technology (power consumption, density of logic and radiation hardness benefits)

Specifications for Timepix adaptation to VELO upgrade needs are under study.

Jianchun Wang, Vertex 2009

conceptual design
Conceptual Design

Beam position

Ground plane

(aluminised directly onto diamond)

Diamond thermal plane with

cutouts immediately above TSV regions

Silicon (1-3 pieces)

55x55 mm pixels

+ 800 mm pixels in

areas under chip


10 Tiimepix chips

(periphery indicated in white)

Power strips and

signal routing area

Cooling channel

Advantage: Single layer, less material, very important for IP.

Challenges: power tape + TSV, Thinned electronics / sensor.

Cross section

cutout region

Jianchun Wang, Vertex 2009

timepix in real beam
Timepix In Real Beam


6 plane Timepix/Medipix telescope

Track reconstructed

A telescope was constructed with 6 double rotated (9o) around both axes. 4 Timepix and 2 Medipix sensors were used.

The DUT (in this case another Timepix chip) position and angle are controlled by a stepper motor to reduce the number of interventions

Jianchun Wang, Vertex 2009

quick look at timepix testbeam data
Quick Look at TimePix Testbeam Data



Normal Incidence




Unbiased Residual (mm)



Angle (Degree)

Total Charge


(Npixel=N) / All




Angle (Degree)

More to Be Studied

  • Time walk, which could potentially affect physics.
  • Non-linear gain curve.
  • Investigate methods of moving data off chip at required speeds (started, digital processing within pixel array may be necessary).
  • Testbench features of baseline module.

Jianchun Wang, Vertex 2009

medipix3 x ray irradiation
Medipix3 X-ray Irradiation

Total ionizing dose measurement on a single chip up to 400Mrad (X-ray, continuously over 4 days)

Confirmation of previous single transistor studies on 130nm CMOS

Chip readout DACs, LVDS etc remained operational for full dose.

This needs to be followed up by hadron irradiation.

Jianchun Wang, Vertex 2009



s=11.3 mm

Number of Hits (arb Unit)

Number of Rows

Residual (mm)

Pixel X/Y

Current VELO

Pixel Y

Pixel X/Y

5 stations

6 modules per station

4 chips per module

Total 120 FPIX2 chips

Aperture 35 x 35 mm2

~ 1 m

Jianchun Wang, Vertex 2009

electronics development
Electronics Development

Two main avenues of investigation in LHCb Upgrade


  • Features (selected):
    • Derived from BTeV
    • Columnar architecture (50mm x 400 mm)
    • Flash ADC (3-bit)
    • Data driven readout.
    • Sensor and electronics successfully thinned down to 200 mm.
    • Separate X/Y precision measurements. Large digital periphery requires overlap material.
  • Need to Study (selected):
    • Modern fabrication technology
    • Radiation hardness study.
    • Stability of front end electronics
    • Readout speed, with designed for 132ns.
    • Cooling.
  • Focus resources on a single chip development (still useful for sensor R&D).


  • Features (selected):
    • Derived from MediPix
    • Square pixel (55mm x 55mm)
    • Time over threshold
    • Single layer module possible, edgeless possible
  • Need to Study (selected):
    • Modern technology: 130nm or 90nm.
    • Radiation hardness study.
    • Optimization of analog front end
    • Time walk
    • Digitization precision and readout scheme
    • Data flow and data rate
    • TSV technology
    • Detector and sensor thinning
    • Cooling
  • Development continues.

Jianchun Wang, Vertex 2009

  • Sensor requirements
    • Radiation hardness
    • Low leakage current, heat dissipation
    • High granularity
    • Minimize material
  • Sensors investigated:
    • Sensors of current type: n-type, strips
    • Sensors with small modifications: p-type
    • Sensors with large modifications: pixels
    • Sensors using new technology: 3D
    • Alternative material: diamond

Jianchun Wang, Vertex 2009

test of irradiated sensors
Test of Irradiated Sensors


  • VELO sensors of n-type and p-type were differentially irradiated.
  • They were tested in the beam at Fermilab using FPIX2 pixel system for tracking (in collaboration with Dave Christian).
  • Irradiation particle flux ~ 0.86x1015 neq/cm2 (~6 years running of current L at inner radius).
  • More results on irradiated sensors are coming soon.

N type sensor

1 MIP Qmp


~ 25% drop


Measured in 120 GeV proton beam @ -10C

Jianchun Wang, Vertex 2009

double sided 3d sensor
Double-sided 3D Sensor

Optimisation for SLHC: Nucl. Instr. Meth. A 592 (2008) 16

Glasgow / CNM

Test beam results: Nucl. Instr. Meth. A 607 (2009) 89

Pixel on Medipix detector

SEM after polysilicon deposition and etching

  • novel double sided structure
  • n-bulk and p-bulk detectors produced & tested


Jianchun Wang, Vertex 2009

double sided 3d sensor1
Double-sided 3D Sensor

2.3V lateral depletion

~9V back surface depletion



Glasgow / CNM

  • Measurements of:
  • Charge loss in holes
  • Charge sharing
  • Irradiations
  • Two presentations at IEEE NSS with full results


Tesbeams at Diamond Light Source (X-rays), CERN (MIPs)

3D, 15keV



Charge sharing


Jianchun Wang, Vertex 2009

sensor r d
Sensor R&D
  • Diamond sensor
    • Ultra radiation hard,
    • Very low leakage current (~nA instead of mA)
    • Needs no guard ring and can be edgeless.
    • CVD diamond can also be used as heat conductive spine.
    • Joined RD42 collaboration for investigate this option.
    • Planning test beam studies of different solutions.


  • P-type silicon sensor
    • “BTeV style” single chip pixel devices. Fabricated by Micron Semiconductor.
    • Depletion voltage 20-80V before irradition.
    • Started examining performance of irradiated detectors


Jianchun Wang, Vertex 2009

possible new rf foil for upgrade

Separates accelerator and detector vacua (must be ultra-high vacuum compatible)

Should have the smallest radiation length possible, esp. before first measured point

Must shield against RF EMI pick-up effects

Must carry beam image charge

Must allow for sensor geometry and overlap

Must withstand high radiation levels


Foil is 300 um AlMg3, coated with insulator and getter

Foil shape set by overlapping sensors, beam clearance and beam effects

Wakefield suppressors to adapt beam pipe geometry

Was a huge engineering effort (NIKHEF)


Replace AlMg3 by Carbon Fiber composite

Use large-modulus fibers (stiff, low density)

Resin with high rad tolerance, low outgassing (space-qualified), micro-crack resistant

Produce foil + box + flange as a single integrated unit

Avoids sealing problems

Can reduce mass thickness to ~50% current

Similar material mechanically stable to above 500 MRad (CERN 98-01)

Currently in development with industrial partner CMA (Composite Mirror Applications, Inc.)

Prototyping planned to start by End 2009, testing to start in early 2010


Dominant contribution to the average X0 of particle traversing VELO at 2<h<4.2




~200 mm x 1 m

Jianchun Wang, Vertex 2009

  • The LHCb detector is ready to take data. Initial plan is to collect 10 fb-1 in the first 5 years.
  • LHCb upgrade forseen for 2015/16, with luminosity increases to 2x1033 cm-2s-1, expected to collect 100 fb -1 in 5 years.
  • Key aspects of the upgrade are:
    • Readout of the full detector at 40 MHz  fully software-based trigger  flexibility.
    • Improved granularity in sub-detectors needed to cope with larger occupancies, provide better background suppressing and reduce CPU time/event.
    • Goal is to increase sample sizes by a factor of 10-20 with comparable or better S/B to current detector.
  • Many R&D projects associated with VELO upgrade are in progress: readout electronics, sensor, hybrid, mechanics, cooling cabling etc.
  • The VELO upgrade is feasible.

Jianchun Wang, Vertex 2009

backup mini strip plan
Backup Mini Strip Plan

p-stop or p-spray.

Inner radius at 7.5mm, 25-30 mm pitch

(edgeless sensors would bring 10% improvement)

Double sided module

20 Beetle40 chips

200 mm Diamond heat plane

routing out Beetle signals

200 mm thin

silicon sensor

Radiation length 0.6%.

Cooling channel

Need to study more on data readout scheme.

Jianchun Wang, Vertex 2009

trigger time in hlt di hadron
Trigger Time in HLT Di-hadron

L = 2 x 1032 cm-2s-1

L = 2 x 1033 cm-2s-1

L = 1 x 1033 cm-2s-1

  • At L=2 x 1032 cm-2s-1, the events are more complex.
  • With current VELO-like detector, the pattern recognition is very slow. And trigger can not be decided within 2.5 mm latency.

Jianchun Wang, Vertex 2009

irradiation issue
Irradiation Issue

Operating up to ~120 fb-1

Flux: 0.8x1014 neqcm-2 per fb-1

TID (Electronics): 3.7 MRad per fb-1

at tip

~ 7mm

  • After this dose @ 900V we expect
    • 102 uA / cm-2 at -25o C
    • CCE of ~ 8.5 ke-
  • Thermal runaway at the tip is the issue

Dose after 100 fb-1


T. Affolder



neqcm-2 x 1016

TID (MRad)


Radius (cm)

tip of current VELO

Jianchun Wang, Vertex 2009

fpix2 readout chip
FPIX2 Readout Chip

9.0 mm

0.7 mm


128x50 mm

FPIX2 Chip

6.4 mm

I/O & Control pads from Chip to HDI

10.3 mm

Jianchun Wang, Vertex 2009