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

oSCT Modules  Operation and characteristics oBeam test oBeam test results oStudy with 25 ns beam oReconstructing tracks with irradiated SCT modules  Efficiency and fake rate oConclusions SCT Beam test results ICATPP th October Outline 2

ATLAS ATLAS SCT 3 SCT Beam test results ICATPP th October Outer Module Inner Module Middle Module FORWAR DISC Barrel Module BARREL LAYERS Barrel Forward  <1 1 <  < 2.59 R=30-52 cm R=26-56 cm 2112 modules 1975 modules 34.4 m 2 of Si 26.7 m 2 of Si SCT characteristics

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 th October

SCT Beam test results ICATPP th October 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) 6 SCT Beam test results ICATPP th 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) 7 SCT Beam test results ICATPP th October

Irradiation 8 After 10 years of operation the SCT will receive a maximum radiation dose equivalent to 2·10 14 n eq /cm 2. 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 th October

Light tight, thermally insulating box Telescopes 180 GeV pion Beam Telescopes Scintillator Trigger Modules inside the beam test box. Setup 9 SCT Beam test results ICATPP th 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 studies 10 SCT Beam test results ICATPP th 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) 11 SCT Beam test results ICATPP th 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) Efficiency 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 beam 12 SCT Beam test results ICATPP th October TDC Range = 25 ns

Setup Reconstructing tracks 13 SCT Beam test results ICATPP th 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 Modules Telescope 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. Analysis 14 SCT Beam test results ICATPP th 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 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 independent of the bias voltage on the detector. Efficiency and fake rate 15 SCT Beam test results ICATPP th 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 In ATLAS occupancy due to real tracks will be 0.6 % in certain regions. More results… 16 SCT Beam test results ICATPP th 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 & Threshold 17 SCT Beam test results ICATPP th October

A simulation of beam test shows similar results to the ones obtained in analysis. For instance  (Z 0 ) sim = 0.18 or  (cot  ) sim = Helix fit… (II) 18 SCT Beam test results ICATPP th October TB  (Z 0 ) (cm) From simulation: resolution considering Pixels + SCT is better by an order of magnitude than the standalone SCT system.

oTest beams have been used for characterising different SCT prototypes. oCapability of working with a 25 ns beam has been proved. Modules fulfil the requirements. oTracking efficiency with irradiated to full dose modules has been checked with beam test data. oTracking performance after irradiation can be improved going from 1 fC threshold to 1.2 fC. oWork in progress:  The same study with magnetic field.  Data from different energies and momenta (P T ) have been taken, to compare with the existing simulations. Conclusions 19 SCT Beam test results ICATPP th October

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