Abstract

The ATLAS pixel detector is a high precision silicon tracking detector located closest to the LHC interaction point. It belongs to the first generation of its kind in a hadron collider experiment. It will provide crucial pattern recognition information and will largely determine the ability of ATLAS to precisely track particle trajectories and find secondary vertices. It has been the last detector to be installed in ATLAS in June 2007 and has been fully connected and tested in-situ during spring and summer 2008. We present in this poster the highlights of the past and future commissioning activities of the ATLAS pixel project.

Spring 2007: Pixel package integration

Integration with service panels, beampipe and the support structure

Connectivity test in parallel to mechanical work to verify functionality before installation

Operation and commissioning of complete detector using the full readout chain for the first time

Tuning of optolink communication of every module in the detector

Figure 13: 1st service panel

connected to the detector

beam pipe

end-cap

service panel

Figure 14: Connection of

cooling pipes

Figure 15: Permanent

connection of micro cables

Future commissioning

plans, as time permits:

1.) Cosmic data taking:

Expect a fraction of a Hertz

through pixel detector

One week enough to align

exposed part of barrel

to < 10 µm

2.) Beam-halo and

beam-gas events:

First alignment of

pixel end-caps

3.) Combined data taking with

SCT, TRT and rest of ATLAS

4.) Be ready for collision!

July 29th-31st 2008: LHC beampipe bake-out

Heating up beampipe to ~200-300°C to improve vacuum

Required cooling of the B-layer and end-caps to avoid

permanent damage

2001-2005: Production & QA

of chips, sensors, modules, opto-boards

at several production sites

1996/98-2003:

FE/MCC chip development

FE-I3/MCC-I2.1 DSM 0.25 µm CMOS

Test beam studies, 24-180 GeV charged pions

H8 beamline of the SPS / irradiation facility at CERN

Irradiation tests to 5 years @ design lumi. for b-layer

Depletion depth

Charge collection

Charge trapping

Detection efficiency

(up to 1.4 maximum occupancy, 108 hits/cm2/s)

Noise

Timing studies

Spatial resolution

Lorentz angle

2004: Combined Test Beam

ATLAS slice, including 6 Pixel modules

calibration, tracking, alignment procedures

Summer 2006: The sub

elements arrive at CERN

Figure 7: With “Bob” (aka end-cap)

first class from Berkeley to CERN

June 2007: Pixel package installation

Subsequent test of electrical connections showed that the pixel package suffered no

permanent damage as a result of the installation. At that stage, 99.7% of the detector

was known to be operational (0.1% module/opto-board failures, 0.2% pixel/FE-level failures).

Figure 16: June 25th 2007

7 m long pixel package lowered

100 m into ATLAS cavern

Figure 17: June 26th 2007

Insertion into Inner Detector

volume

Figure 18: June 27th 2007

Pixel detector in final position

May 1st 2008: Cooling plant accident

prevented completion of sign-off

3 out of 6 compressors that liquefy the C3F8 fluid affected

No significant fluid contamination reached detector

April 2008: No more access to Inner Detector

July 18th 2008: Cooling plant recovery

Equip compressors w/ additional sensors to prevent failures of same kind

Cooling plant fully cleaned and refurbished with additional filters

New clean coolant purchased

Figure 19: The pixel PP1 region

before connections...

Figure 20: ...and after connections

Figure 21:

Corrosion in

exhaust pipes –

had to rebuild

pipes

(10 days delay)

Feb-March 2008: Final connection

Permanent connection of pixel detector to services at the end of the Inner Detector

volume (PP1) which was on the critical path with the ATLAS overall schedule

1.) Connection of electrical cables (high-, low-voltage and module temperature)

Verification of connections in parallel using pixel slow control system

~10/1744 modules with un-repairable HV broken connections were found

2.) Installation of optical fibers

Monitoring of light power output in both directions using the full DAQ chain

No on-detector failures observed during tests

37/1904 dead but exchangeable off-detector VCSEL channels (keep dying with time)

Diode IV curve consistent with electro-static discharge (ESD) failures

investigation ongoing, new production batch ordered w/ improved ESD safety

3.) Connection of cooling pipes to the cooling plant (shared with the SCT)

Leak tests showed that 3/88 cooling

loops had leaks, all in pixel end-cap

Studies are underway to determine

whether there are long-term problems

with operation of these cooling loops

Figure 22: Mapping problem – had

to reconnect half of the fibers

End of March 2008:

April 2008: Commissioning of cooling system

Final tests before closing of end-cap calorimeters and losing direct access to the Inner

Detector: verify that the cooling system can handle the heat load of the detector

Switch on each cooling loop one at a time, make sure the system is stable, check NTC

sensors, validate module/cooling loop mapping

Switch on modules in the cooling loop and increase heat load gradually

Initial (1 W/mod)

Nominal operation (4 W/mod)

End-of-lifetime/highest power (6 W/mod)

Long term cooling operation, run threshold scan on full quadrant to check functionality

Sep 10th 2008 (next Wed):

First LHC beam @ 0.45 TeV

Commissioning of the ATLAS Pixel Detector

Tobias Golling (Lawrence Berkeley National Laboratory)

on behalf of the ATLAS Pixel Collaboration

The ATLAS Pixel Detector

Physics & Performance Requirements:

Track reconstruction in high multiplicity events up to ||<2.5 (~1000 tracks/event at lumi.~1034 cm-2s-1)

3D vertexing ((d0) ~ 15 µm)

Good b-tagging efficiency (~60% for mistag rate < 1%)

Radiation hardness to 1015 neqcm-2, 5 years for innermost layer (~250-300 fb-1)

Facts & Numbers:

80 million channels

1744 identical modules

1.7 m2 silicon

Pixel size of 50x400 µm2 providing intrinsic

resolution of ~10 µm in R- and ~115 µm in z

Expected occupancy of 10-4 at 1034 cm-2s-1

Material budget: 0.1 X0 at =0

Evaporative cooling (C3F8): T~ -10°C

Optical data transmission:

Conversion at ~1 m from module

Up to 80 Mbit/s per optical fiber

Electrical→optical: data transmitted

by VCSEL

Optical→electrical: clock, level 1 trigger,

command, configuration received

by PiN diode

Figure 3: Each pixel is connected

to a charge sensitive preamplifier

and a discriminator with adjustable

threshold and feedback

Figure 4: Time over Threshold

(ToT = leading edge – trailing edge)

is proportional to the charge deposited

Calibration:

Tune feedback current so that

MIP (20 ke) corresponds to a

ToT of 30 bunch crossings.

Tune threshold to 4 ke, more

than 10 times the noise level.

Figure 5: Result of threshold scan

Figure 6: Threshold before (top)

and after (bottom) tuning

Figure 2: Detector system architecture

On-detector DAQ:

Controller chip (MCC):

Accepted hits are transferred to controller chip

Event building is performed

Data is sent off-detector

Front-end chip (FE):

Front-end subdivided in 9 column pairs x 160 rows

64-hit buffer in end-of-column electronics

Require level 1 trigger coincidence (3.2 µs latency)

with leading edge

14 TeV center-of-mass energy, 40 MHz bunch crossing frequency

Spring '07 Summer '07 Fall '07 Spring '08 Summer '08 Fall '08

Figure 10: Noise occupancy of ~10-10 per pixel after masking hot pixels

Figure 9: The cosmic test setup

Figure 11: Comparison between system test cosmic ray data (solid, black) and Monte Carlo (red, dashed): ToT distribution for 1-hit clusters (top left), individual hits of a 2-hit cluster (top middle) and the sum of the ToT for 2-hit clusters (top right); number of pixel clusters (bottom left), distribution of cluster size (bottom middle) and fitted track chi2 (bottom right)

Fall 2006: System test and cosmic rays operation

Detector operation of one pixel end-cap (aka Bob),

144/1744 modules (~8%), and production pixel services:

Commissioning of setup, including cooling and detector readout

Development of final protocol for services commissioning

Measurement of the analog performance of the pixel modules:

Average threshold: 4002±1.3 e-, threshold dispersion: 33±1 e-, average noise: 166±8.5 e-

Calibration of optical links:

Some optoboards with no or very little optical power, explained

by common series resistance ⇒ exclude 7% of total production

Power spread increases for lower optoboard temperatues,

makes tuning impossible (optoboard VCSEL output power,

threshold and delay at receiving end) ⇒ dedicated heaters

to be able to regulate temperature up to ~30°C

Data-taking with cosmic rays (Fig. 9): (6 Hz for tracks crossing all three layers)

Pixel efficiency of 99.5%, low noise, uncorrelated with timing relative to trigger (Fig. 10),

pixel clusters description in good agreement with simulation (Fig. 11),

alignment using 24% of tracks passing through overlap region ⇒ improve resolution from

23µm to 16µm, close to 14µm in the MC simulation (Fig. 12)

Figure 8: Scan

of receiver

parameters for

optical data link

Error

free

region

Error

free

region

Noise

Flips from 1 to 0

Sampling

on clock

edge

Figure 12: Overlap residual distribution before and after alignment corrections

2 ½ months

cooling plant

reparation

Considerable delay due to problems and

work on other Inner Detector sub-detectors

Fall 2007: Off-detector

cabling and testing

Commissioning achievements

since beginning of August:

First operation experience of full detector over a large period of time

Establish baseline of detector performance by running calibration

scans on full detector: threshold, noise, leakage current, timing...

Results:

Aug 28th 2008: the whole detector was configured for the first time

All 88 cooling loops can be operated at a time

Top hemisphere straightforward

Bottom hemisphere needs heat load from modules

More than 99% of all modules can be powered without any problem

Operate opto-heaters in stable way at ~20°C

Few show problem of temperature oscillations

Threshold scans were performed on modules in top hemisphere

1% of dead off-detector VCSEL channels (to be exchanged)

Less than 5% with instabilities in optical communication

Most of the problems expected to be fixed before turn-on

Data taking with random triggers up to 10 kHz

Pixel detector in ATLAS global run scheduled for 1st week of Sep

PSD 08, Sep 1st – 5th

Glasgow, Scotland

Carbon fiber

structure

~

16 front-end

chips

deco

ca

@ 5, 9, 12 cm

controller

chip (MCC)

Figure 1: The ATLAS pixel detector at a glance

(courtesy of T. Sluka and D. Dobos)

Solder or

indium

flip-chip technique

250 µm thick,

oxygenated

silicon

1.4 m

43 cm

Figure in the background: Outer pixel half-shell

before integration

'96 '98 '00 '02 '04 '06

1997-1998: Proposal for

Pixel electronic system

Slide 1

Jean-Francois Arguin

2008-07-10T16:23:12