Federico Antinori - Vertex, Kona - Nov. 2002 The Alice Inner Tracking System Federico Antinori (INFN – Padova, Italy)

Federico Antinori - Vertex, Kona - Nov. 2002Federico Antinori - Vertex, Kona - Nov. 2002

The Alice The Alice Inner Tracking SystemInner Tracking System

Federico AntinoriFederico Antinori

(INFN – Padova, Italy)(INFN – Padova, Italy)


ContentsContents

• Introduction– Alice and the Inner Tracking System (ITS)

• ITS subdetectors (a bird’s eye view)– Si strips (SSD)– Si drifts (SDD)– Si pixels (SPD)

• ITS performance• Concluding remarks


ContentsContents





AliceAlice• Ultrarelativistic nucleus-

nucleus collisions at LHC • Why:

– study behaviour of hadronic matter under extreme conditions of heating / compression

– investigate confinement / deconfinement, generation of constituent masses


(B< 0.4 T)


An inner tracker in Alice…An inner tracker in Alice…• Vertexing (s, c, b)

– strangeness: production sensitive to decrease of effective quark mass in deconfined phase

– charm and beauty: “hard” probes of system formed in collision

• Improve TPC tracking– high pT (extend TPC lever

arm, improve spatial precision)

– low pT (standalone ITS)

• 1/2 particle id (analogue r/o for drifts and strips)

Challenge: track densities at r = 4 cm (1st pixel layer): up to 100 / cm2

(2º slice)


Alice ITSAlice ITS

longitudinal coverage:|| < 1 (tracking), ||<2

(multiplicity)

Rout=43.6 cm

2 strips

2 drifts

2 pixels


ContentsContents





Alice SSDAlice SSD

• 2 layers, r = 38.5, 43.6 cm

• double sided, stereo angle– (+ 27.5, -7.5) mradian

• strips: 95 µm × 40 mm• analogue r/o• module size: 75 × 42

mm2

• sensitive length (in z): 86.2 and 97.6 cm

• 1698 modules• 2.6 M channels


SSD front-end: HAL25SSD front-end: HAL25

• CMOS 0.25 µm radtol layout • 128 analog channels,

input pitch 80 µm• Design ENC 200 e- + 8 e-/pF

(1.5 µs shape)• Tuneable shaping 1.4 2 µs• Readout at 10 MHz, 200 Ω / 20 pF• Δ current output (±55 µA/MIP, 14

MIP range, linear 5%)• 2.5 V single power supply• JTAG digital, analogue and pulser

control


SSD moduleSSD module

• Al-kapton microcables• all connections are done by

TAB-bondingSSD Module

Carbon ladder

Cooling tubes

Detector Hybrid Input cables

Chips

Output cables

Federico Antinori - Vertex, Kona - Nov. 2002

First ladder: picturesFirst STAR ladder: december 01

IReS-Subatech


Alice SDDAlice SDD• 2 layers, r = 14.9, 23.8 cm• drift along r• 294 µm anode pitch• analogue r/o• module size: 75.3 × 70

mm2

• sensitive length (in z): 44.4 and 59.4 cm

• 260 modules• 133 k channels

24/4/2002 12th RRB J. Schukraft

Silicon Drift Silicon Drift DetectorDetector

guard regionguard region

implanted HV voltage dividersimplanted HV voltage dividers

256 anodes (294 256 anodes (294 m pitch)m pitch)

MOS charge injectors forMOS charge injectors for drift velocity monitoring drift velocity monitoring

Drif

tD

rift

segmented

2 x 256 anodes

Wafer: 5”, NTD, 3 k.cm, 300 m Active area: 7.02 7.53 cm2


SDD front-endSDD front-end

•CMOS 0.25 mm rad-tol•Full custom design: 10*9 mm2

•64 preamplifiers (t ~ 40ns, RC-CR2 shaping)

•64 analogue memory channels (256 cells)

•32 10-bit linear ADCs•Differential outputs

PASCAL-64 prototypePASCAL-64 prototype

•CMOS 0.25 mm rad-tol •4x16 kbytes SRAM buffers•40 MHz working frequency•Fast trigger-abort recovery• JTAG interface•Differential inputs

AMBRA-4 prototypeAMBRA-4 prototype

preamplifiers

analoguememory

16+16 ADCs

derandomization&

data transmission


SDD resolutionSDD resolution

Corrections applied:

• doping inhomogeneity map

• residual non-linearity of voltage divider

• T-dependence of drift velocity

• drift-dependent non-linearity of centroid due to diffusion widening Drift distance (mm)

Res

olut

ion

(m

)

Anode axis (z)

Drift time axis (r)


SSD, SDD cooling & supportSSD, SDD cooling & support• lightweight, carbon-fibre

support ladders• liquid cooling

– C6F14 (H20 also considered)


Alice SPDAlice SPD

• 2 layers, r = 3.9, 7.6 cm

• sensitive length (in z): 28.6 cm (for both layers)

• hybrid (bump-bonded) silicon pixel assemblies

• In / PbSn bumps

• pixel size: 50 × 425 µm2

• binary r/o

• module size: 12.8 × 69.6 mm2

• 240 modules

• 9.8 M channels

Chip

Sensorbump-bonded assembly

Chip (150 µm thickness)

Sensor (200 µm thickness)

bump-bonded assembly

Picture of a solder bump bond (courtesy of VTT)


SPD front-endSPD front-end

• Alice1LHCb pixel chip mixed signal (analogue/digital)

• commercial 0.25 µm CMOS

• radiation tolerant design

• 50 µm x 425 µm pixel cell

• JTAG controls• 8192 pixel cells• ~100 µW / pixel

13.5 mm

15

.8 m

m


Carbon-fibre sector

Grounding foil

SPD half-staveSPD half-staveEach Stave is built of two HALF-STAVES, read out on the two sides of the barrel, respectively.

Bus

ALICE1LHCb chip

Cooling tube

MCM

Silicon sensor

Ladder: 5 chips+1 sensor

193 mm long


SPD busSPD bus

12

34

56

READOUT CHIP

PIXEL DETECTORAluminumPolyimide

12

56

GlueCOOLING TUBE

11mm2mm

7 77 7SMD component

7 layer Al-Kapton flex


SPD test beamSPD test beam

singles

ladder

July 2002, CERN-SPS H4 beam

online residuals

=16.4µm(along 50 µm axis)


SPD cooling & supportSPD cooling & support

• lightweight carbon fibre support sectors

• integrated cooling– evaporative C3F8


ContentsContents





Impact Parameter Resolution Impact Parameter Resolution (r(r))

• better than 50 µm for pT > 1.3 GeV/c

• ~10 µm at high pT


Impact Parameter Resolution Impact Parameter Resolution (z)(z)


Momentum ResolutionMomentum Resolution

• Large effect of ITS on momentum resolution at high pT

– high spatial precision– increase of lever arm


Benchmark: DBenchmark: D00 K K

• Initial S/B ~ 5 · 10-6

– Pb-Pb collisions at LHC with dN/dy = 6000

– invariant mass and particle-id cuts only

• Final S/B ~ 0.1– after vertexing and pointing

cuts

• Significance S/√(S+B) ≈ 35– for 107 events

(~15 days data taking)

total

bkgd-subtracted

107 events, all cuts applied


Benchmark: B Benchmark: B e e±± + X + X

• i.p. from ITS• electron id:

– TRD (transition radiation)

– TPC (dE/dx)

electron tags vs impact parameter


pT> 1 GeV

pT> 2 GeV

pT> 3 GeV

d0threshold (µm)

beauty / total e tags vs. impact parameter cut


ContentsContents





Concluding remarksConcluding remarks

• ITS will allow Alice to access heavy flavour sector in nucleus-nucleus collisions– essential information from hot, dense initial stages of

collision

• ITS design ~ frozen– very tight integration constraints: getting here has taken

years of hard work and dedication of tens of physicists and engineers

• Very challenging times ahead– tight construction plan in order to be ready for 1st beam

(installation in Alice in 2006)

Documents

Federico Antinori - Vertex, Kona - Nov. 2002 The Alice Inner Tracking System Federico Antinori (INFN – Padova, Italy)