ATLAS SCT module performance:ATLAS SCT module performance:beam test resultsbeam test results

José E. GarcíaJosé E. García

o SCT Modules Operation and characteristics

o Beam test o Beam test results

o Study with 25 ns beam

o Reconstructing tracks with irradiated SCT modules Efficiency and fake rate

o Conclusions

SCT Beam test resultsICATPP 2003 6th October

OutlineOutline 2

ATLAS

ATLAS SCTATLAS SCT 3

SCT Beam test resultsICATPP 2003 6th October

Outer Module

Inner Module

Middle Module

FORWAR DISCFORWAR DISC

Barrel Module

BARREL LAYERSBARREL LAYERS

Barrel Forward

<1 1 < < 2.59

R=30-52 cm R=26-56 cm

2112 modules 1975 modules

34.4 m2 of Si 26.7 m2 of Si SCT characteristics

SCT ModulesSCT Modules 4

Module components

• 4 silicon wafers with 768 p-in-n strips

• TPG Spine (heat conductor) with arms (mechanical stability)

• Hybrid readout circuit (flex circuit on carbon-carbon)

• Binary readout chips (12 ABCD3TA)

• Structures to hybrid connexion (fan-ins)

SCT Beam test resultsICATPP 2003 6th October

SCT Beam test resultsICATPP 2003 6th October

SCT Modules (II)SCT Modules (II) 5

Module components

• 4 silicon wafers with 768 p-in-n strips

• 1 TPG baseboard with epoxy coating and four beryllia facings fused onto the structure.

• Hybrid readout circuit (flex circuit on carbon-carbon)

• Binary readout chips (12 ABCD3TA)

• Glass pitch adaptor

• A module is composed by two planes of silicon detectors two make a double sided detector. The stereo angle (40 mrad) between both planes allow to reconstruct X-Y points as the intersection of the two strips with signal.

• Strips parallel to the beam in the barrel part and radials in the forward.

SCT Modules (III)SCT Modules (III) 6

SCT Beam test resultsICATPP 2003 6th October

Variation of efficiency and noise occupancy with comparator threshold. Horizontal lines are the ATLAS specifications.

SCT modules use binary readout. Signal left by crossing particles is compared with a threshold in the electronics readout.

SCT Modules (IV)SCT Modules (IV) 7

SCT Beam test resultsICATPP 2003 6th October

IrradiationIrradiation 8

• After 10 years of operation the SCT will receive a maximum radiation dose equivalent to 2·1014 neq/cm2.

• Radiation causes damage on the module.– Radiation creates defects. Charge

is lost due to trapping. – Type inversion of the substrate n

p (changes the position of the p-n junction)

– A higher bias voltage is needed to deplete the detector.

– Leakage current increases. – Electronics noise increases from

1500 e- before irradiation to 2000 e- after.

SCT Beam test resultsICATPP 2003 6th October

Light tight, thermally insulating box

Telescopes

180 GeV pion Beam

Telescopes

Scintillator Trigger

Modules inside the beam test box.

SetupSetup 9

SCT Beam test resultsICATPP 2003 6th October

Typical SCT beam test setup with different types of modules

• Resolution is measured. SCT modules are almost single-strip. The detector pitch is 80 m in order to avoid charge sharing and preserve a good resolution.

Beam test studiesBeam test studies 10

SCT Beam test resultsICATPP 2003 6th October

Position predicted by SCT module compared with the telescope.

~ 23 m

The pulse shape can be reconstructed from beam test data and compared with the theoretical response of the shaper

• The Lorentz angle has been measured using a 1.56 T magnet and different incidence angles. The most sensitive parameter to these changes is the cluster size

L = 3.3 º 0.3 º (at 150 V)

Beam test… (II)Beam test… (II) 11

SCT Beam test resultsICATPP 2003 6th October

• Noise increases due to ghost hits (cross talk...) has been measured to be small ( < 1 % )

• Signal to noise ratio for the SCT modules is 14.

• The median charge observed on binary SCT prototypes is around 3.4 0.2 fC

S-Curve

Particles arriving in a wide time window.LHC beam will have a 40 Mhz frequency.

Time (TDC counts)

Effi

ciency

Time (clock cycles)

Variation on efficiency when particles cross a channel (strip) with a difference of a few clock cycles (25 ns) between them.

For delays bigger than 50 ns efficiency is not affected by previous crossing particle. No effect in the efficiency is seen if following particles hit in a different strip in the module

25 ns beam25 ns beam 12

SCT Beam test resultsICATPP 2003 6th October

TDC Range = 25 ns

SetupReconstructing tracksReconstructing tracks 13

SCT Beam test resultsICATPP 2003 6th October

Four irradiated modules

• For reconstructing tracks only the position measurements of the SCT modules are used. The beam telescope is only read out for comparison.

Example of a reconstructed event

Example of a second track due to hard interaction with silicon.

SCT ModulesTelescope

• Only events with one perfectly identified track in the telescope are used for tracking.

• Cuts are used to avoid events with two tracks or with hard interaction with sensors.

AnalysisAnalysis 14

SCT Beam test resultsICATPP 2003 6th October

• The analysis searches for tracks in an event using a linear fit.

• After a cut in the 2 track candidates are compared with the track reconstructed by the telescope.

• Only tracks compatible with a telescope’s track are considered efficient.

efficiency

efficiency

• All remaining tracks are labelled as fakes. • The efficiency depends on threshold. The

maximum efficiency is 97 % obtained at a threshold of 1.2 fC for a bias over 450 V.

• Fake rate is kept below 10-3 independent of the bias voltage on the detector.

Efficiency and Efficiency and fake ratefake rate 15

SCT Beam test resultsICATPP 2003 6th October

• The same study has been done with three instead of four irradiated modules.

• Using three increases the number of fakes to the level of 10-3.

• In ATLAS occupancy due to real tracks will be 0.6 % in certain regions.

More results…More results… 16

SCT Beam test resultsICATPP 2003 6th October

efficiency

Four modules

Three modules

• The same analysis has been done with an helix fit. One more degree of freedom appears.• Parameters of the helix fit from beam test and ATLAS can be connected.• Slight deterioration for 1 fC with respect to 1.2 fC.• Work at 1.2 fC with irradiated modules will be possible without losing resolution.

Helix fit & ThresholdHelix fit & Threshold 17

SCT Beam test resultsICATPP 2003 6th October

• A simulation of beam test shows similar results to the ones obtained in analysis . For instance (Z0)sim =

0.18 or (cot)sim = 0.0045

Helix fit… (II)Helix fit… (II) 18

SCT Beam test resultsICATPP 2003 6th October

TB

(Z0) (cm)

• From simulation: resolution considering Pixels + SCT is better by an order of magnitude than the standalone SCT system.

o Test beams have been used for characterising different SCT prototypes.

o Capability of working with a 25 ns beam has been proved. Modules fulfil the requirements.

o Tracking efficiency with irradiated to full dose modules has been checked with beam test data.

o Tracking performance after irradiation can be improved going from 1 fC threshold to 1.2 fC.

o Work in progress:

The same study with magnetic field.

Data from different energies and momenta (PT) have been taken, to compare with the existing simulations.

ConclusionsConclusions 19

SCT Beam test resultsICATPP 2003 6th October

ATLAS SCT module performance:ATLAS SCT module performance:beam test resultsbeam test results

José E. GarcíaJosé E. García