ATLAS SCT module performance beam test results Jos

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

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

ATLAS SCT Barrel 3 ATLAS <1 R=30 -52 cm 2112 modules 34. 4 m 2 of Si Forward 1 < < 2. 59 R=26 -56 cm 1975 modules 26. 7 m 2 of Si SCT characteristics Outer Module Middle Module Barrel Module Inner Module BARREL LAYERS ICATPP 2003 FORWAR DISC SCT Beam test results 6 th October

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 ABCD 3 TA) • Structures to hybrid connexion (fan-ins) ICATPP 2003 SCT Beam test results 6 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 ABCD 3 TA) • Glass pitch adaptor ICATPP 2003 SCT Beam test results 6 th October

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. ICATPP 2003 SCT Beam test results 6 th October

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

Irradiation • • 8 After 10 years of operation the SCT will receive a maximum radiation dose equivalent to 2· 1014 neq/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. ICATPP 2003 SCT Beam test results 6 th October

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

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

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 f. C S-Curve • 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. ICATPP 2003 SCT Beam test results 6 th October

25 ns beam Efficiency TDC Range = 25 ns 12 Time (clock cycles) Time (TDC counts) LHC beamarriving will have Mhz Particles in aa 40 wide time frequency. window. 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 ICATPP 2003 SCT Beam test results 6 th October

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

Analysis • 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 second track due to hard interaction with silicon. Telescope SCT Modules Example of a reconstructed event • • ICATPP 2003 14 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 6 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. All remaining tracks are labelled as fakes. The efficiency depends on threshold. The maximum efficiency is 97 % obtained at a threshold of 1. 2 f. C for a bias over 450 V. Fake rate is kept below 10 -3 independent of the bias voltage on the detector. ICATPP 2003 efficiency • 15 efficiency Efficiency and fake rate SCT Beam test results 6 th October

More results… 16 efficiency • 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 ICATPP 2003 SCT Beam test results 6 th October

Helix fit & Threshold 17 • 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 f. C with respect to 1. 2 f. C. • Work at 1. 2 f. C with irradiated modules will be possible without losing resolution. ICATPP 2003 SCT Beam test results 6 th October

Helix fit… (II) 18 • A simulation of beam test shows similar results to the ones obtained in analysis. For instance (Z 0)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. TB (Z 0) (cm) ICATPP 2003 SCT Beam test results 6 th October

Conclusions 19 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 f. C threshold to 1. 2 f. C. o Work in progress: Ø The same study with magnetic field. Ø Data from different energies and momenta (PT) have been taken, to compare with the existing simulations. ICATPP 2003 SCT Beam test results 6 th October

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