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ATLAS SCT module performance: beam test results

ATLAS SCT module performance: beam test results. José E. García. Outline. 2. SCT Modules Operation and characteristics Beam test Beam test results Study with 25 ns beam Reconstructing tracks with irradiated SCT modules Efficiency and fake rate Conclusions. SCT Beam test results.

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ATLAS SCT module performance: beam test results

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  1. ATLAS SCT module performance:beam test results José E. García

  2. Outline 2 • SCT Modules • Operation and characteristics • Beam test • Beam test results • Study with 25 ns beam • Reconstructing tracks with irradiated SCT modules • Efficiency and fake rate • Conclusions SCT Beam test results ICATPP 2003 6th October

  3. ATLAS 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 Outer Module Middle Module Barrel Module Inner Module BARREL LAYERS FORWAR DISC ATLAS SCT 3 SCT Beam test results ICATPP 2003 6th October

  4. SCT 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 results ICATPP 2003 6th October

  5. 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 SCT Beam test results ICATPP 2003 6th October

  6. SCT Modules (III) 6 • 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 Beam test results ICATPP 2003 6th October

  7. SCT Modules (IV) 7 SCT modules use binary readout. Signal left by crossing particles is compared with a threshold in the electronics readout. Variation of efficiency and noise occupancy with comparator threshold. Horizontal lines are the ATLAS specifications. SCT Beam test results ICATPP 2003 6th October

  8. Irradiation 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 results ICATPP 2003 6th October

  9. 9 Typical SCT beam test setup with different types of modules Setup Scintillator Trigger Telescopes Telescopes 180 GeV pion Beam Light tight, thermally insulating box Modules inside the beam test box. SCT Beam test results ICATPP 2003 6th October

  10.  ~ 23 m Position predicted by SCT module compared with the telescope. Beam test studies 10 • 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. The pulse shape can be reconstructed from beam test data and compared with the theoretical response of the shaper SCT Beam test results ICATPP 2003 6th October

  11. S-Curve Beam test… (II) 11 • 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) • The median charge observed on binary SCT prototypes is around 3.4  0.2 fC • 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. SCT Beam test results ICATPP 2003 6th October

  12. Efficiency LHC beam will have a 40 Mhz frequency. Particles arriving in a wide time window. 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 Time (clock cycles) 12 TDC Range = 25 ns 25 ns beam Time (TDC counts) Variation on efficiency when particles cross a channel (strip) with a difference of a few clock cycles (25 ns) between them. SCT Beam test results ICATPP 2003 6th October

  13. Reconstructing tracks 13 Setup Four irradiated modules SCT Beam test results ICATPP 2003 6th October

  14. Example of a second track due to hard interaction with silicon. Analysis 14 SCT Modules Telescope • 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 • 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. SCT Beam test results ICATPP 2003 6th October

  15. efficiency efficiency Efficiency and fake rate 15 • 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. • 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. SCT Beam test results ICATPP 2003 6th October

  16. efficiency More results… 16 • 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. Four modules Three modules SCT Beam test results ICATPP 2003 6th October

  17. 17 Helix fit & Threshold • 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. SCT Beam test results ICATPP 2003 6th October

  18. TB (Z0) (cm) 18 Helix fit… (II) • 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 • From simulation: resolution considering Pixels + SCT is better by an order of magnitude than the standalone SCT system. SCT Beam test results ICATPP 2003 6th October

  19. Conclusions 19 • Test beams have been used for characterising different SCT prototypes. • Capability of working with a 25 ns beam has been proved. Modules fulfil the requirements. • Tracking efficiency with irradiated to full dose modules has been checked with beam test data. • Tracking performance after irradiation can be improved going from 1 fC threshold to 1.2 fC. • 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. SCT Beam test results ICATPP 2003 6th October

  20. ATLAS SCT module performance:beam test results José E. García

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