Tests of ATLAS strip detector modules: beam, source, G4 simulations

1. Tests of ATLAS strip detector modules:beam, source, G4 simulations Pavel Řezníček • Content: • ATLAS SCT modules • Analog x binary readout • Source tests x beam tests • Testbeam simulation • Source tests simulation

2. ATLAS SCT @ LHC

3. ATLAS SCT - one of 3 inner detector subsystems: Pixel, SCT, TRT - length 5.6 m, diameter 1.2 m - rapidity coverage: |h| < 2.5 - placed in solenoidal magnetic field 2 T - optical readout - involved in 2nd level trigger – holds data in pipelines for 3 ms - provides 4 precise point measurement (16 x 580 mm) - 4 barrel layers (2112 modules) and 2 x 9 forward wheels (1976 modules) - radiation environment – tests of modules irradiated @ PS by 3·1014 p(24 GeV)/cm2 - SCT modules requirements: efficiency > 99%, noise occupancy < 10-5 • 2 x 768 strips, 6/12 cm long • strip pitch 80 mm (barrel), 54 ÷ 95 mm (forward) • 2/4 64mmx64mmx285mm p-on-n detectors (barrel) • opposite planes stereo angle 40 mrad • AC coupled readout • 2 x 6 readout chips (128 channels) • ~ 20 ns shaping time • calibration circuit (mV => fC) • data compression • binary readout

4. - monoenergetic signal (for example calibration pulse) + Gaussian noise (zero mean signal): threshold scan results in s-curve with s ~ noise and threshold of 50% efficiency = monoenergetic signal Analog readout Binary readout(digitized amplitude) (scanned threshold) Calibration process, noise measurement (QA tests of all modules) - particles passing through the detector: energy loss fluctuations + particle energy spectrum Test of few modules only Landau distribution 90Sr (90Y) b- spectrum Testbeam threshold scan b- test threshold scan sources of signal: calibration pulse, MIP, b- , laser working conditions: threshold ~ 1 fC

5. b- source tests Testbeam • - relativistic electrons (kinetic energy < 2.2 MeV) - MIP (180 GeV pions) • - simple construction - expensive • various geometrical settings - also possible + strong magnetic field (1.56 T) • repeated tests (before and after irradiation) - only few (up to ~ 15) modules can be tested • available at any time - available ~ 3x14 days a year • quick measurement and analysis - slower measurement, complicated analysis • (alignment) • no particle track measurement (except DUT) - analogue telescopes (microstrip detectors) • angular spread of particle tracks, multiple scattering - parallel tracks energy loss (Geant4)

6. efficiency (not reliable at low thresholds) - efficiency (reliable at all thresholds) • median (threshold of 50% efficiency) - median • noise occupancy (reliable measurement - noise occupancy and efficiency within • from QA tests – ENC in advance) specifications (99% efficiency, 5·10-4 noise occupancy) • average width of strips clusters …… charge sharing, - angular and magnetic field dependence at 1 fC • d-electrons, threshold for (un)irradiated modules • crosstalk b- source tests Testbeam - multiple scattering => stronger charge sharing => different results on both detector planes

7. bias voltage dependence of medians for (un)irradiated modules b- source tests Testbeam • checking bonding - dead or noisy channels can be found - dead and noisy channels are found as well, wrong • using standard QA tests, laser tests can be used as well bonding by using residuals (alignment, telescopes) • - detector • behavior • at its edges • wrong bonding - large clusters needed (incidence angle) - interstrip position dependences

8. bias voltage dependence of medians for (un)irradiated modules b- source tests Testbeam • checking bonding - dead or noisy channels can be found - dead and noisy channels are found as well, wrong • using standard QA tests, laser tests can be used as well bonding by using residuals (alignment, telescopes) • - detector • behavior • at its edges • wrong bonding - large clusters needed (incidence angle) - interstrip position dependences

9. to explain differences between source and beam tests • to compare simulation to newer beam tests results (2001) • Geant4 simulation – energy loss @ track segments, d-electrons, multiple scattering, … • Athena digitization – S. Gadomski, detectors and electronics response, magnetic field Simulation Geant4 simulation Digitization • histogram: deposited energy spectrum of 180 GeV pions from Geant4 simulation • solid curve: integral of the spectrum • dashed curve: efficiency threshold scan – result of digitization under Athena

10. median underestimated (can be fixed) and average cluster size @ 1fC overestimated (?), trends of angular and bias dependencies match • bias dependence – depleted region, diffusion, drift time Beam tests simulation – angular and bias dependence simulation measurement • angular and magnetic field (0T blue line, 1.56T red line) dependence – charge sharing, track length simulation measurement

11. h-dependencies: detailed study of the detectors • can be measured using laser (in development) • efficiency and average cluster size analyzed • low statistics @ beam tests perpendicular incidence Beam tests simulation – interstrip position dependence 16 degrees incidence angle measurement simulation measurement simulation • pure simulation • simulation corrected to particle track determination uncertainities (multiple scattering, telescopes resolution) and averaging over 6 mm wide interval as in testbeam analysis • beam tests

12. - ratio of medians from beam tests to the source tests: simulation: 1.12 ±0.02 measured: 1.11 ±0.07 • source tests sensitivity to geometrical settings – low on the detector plane nearer to the radioactive source (both simulation and measurements) Beam and source tests simulation simulation (efficiency, cluster sizes) beam tests (blue) and source test (red)