Micromegas for the ATLAS Muon System Upgrade Jörg Wotschack (CERN) MAMMA Collaboration Arizona, Athens (U, NTU, Demokritos), Brandeis, Brookhaven, CERN, Carleton, Istanbul (Bogaziçi, Doğuş), JINR Dubna, LN Frascati, MEPHI Moscow, LMU Munich, Naples, CEA Saclay, USTC Hefei, Roma 1 and 3, South Carolina, Thessaloniki, … (growing community) Work performed in close collaboration with CERN/TE-MPE PCB workshop (Rui de Oliveira) Lots of synergy from the RD51 Collaboration

ATLAS Small Wheel upgrade Today: MDT chambers (drift tubes) + TGCs for 2nd coordinate (not visible) 2.4 m Equip the Small Wheels*) with 128 micromegas chambers (0.5–2.5 m2) Combine precision and 2nd coord. measurement as well as trigger functionality in a single device Each chamber comprises eight active layers, arranged in two multilayers a total of about 1200 m2 of detection layers 2M readout channels CSC chambers *) combined systems of MMs and TGCs LAPP, Annecy, 26 April 2012 Joerg Wotschack (CERN)

Rates: measurement vs simulation Measured and expected count rates and in the Small Wheel detectors Data correspond to L = 0.9 x 1033 cm-2s-1 at √s = 7 TeV Ratio between MDT data and FLUGG*) simulation (CSC region not shown) Rate in Hz/cm2 as a function of radius in the large sectors *) FLUGG simulation gives rates about factor 1.5 – 2 higher than old simulation Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

At least two reasons for new Small Wheels Small Wheel muon chambers were designed for a luminosity of L = 1 x 1034 cm-2 s-1 The rates measured today are 2–3 x higher than estimated All detectors in the SW will be at their rate limit at L ≥ 5 x 1034 cm-2 s-1 Eliminate fakes in high-pT (> 20 GeV) triggers Currently over 95 % of forward high pT triggers are fake (removed at LV2) Use tracks in SW as LV1 confirmation Requires pointing precision of 1 mrad Today 2018 Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Small Wheel performance requirements Rate capability 15 kHz/cm2 (L ≈ 5 x 1034 cm-2s-1) Efficiency > 98% Spatial resolution ≤100 m (Θtrack< 30°) Good double track resolution Trigger capability (BCID, time resolution ≤ 5–10 ns) Radiation resistance Good ageing properties All requirements can be met with micromegas Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

The micromegas technology Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Micromegas operating principle Micromegas (I. Giomataris et al., NIM A 376 (1996) 29) are parallel-plate chambers where the amplification takes place in a thin gap, separated from the conversion region by a fine and semi-transparent metallic mesh The thin amplification gap (short drift times and fast absorption of the positive ions) makes it particularly suited for high-rate applications The price to pay is time resolution, e.g., compared to RPCs -800 V -550 V Conversion & drift space Mesh Amplification Gap 128 µm (few mm) The principle of operation of a micromegas chamber Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Micromegas µTPC principle Access to 3rd coordinate Wide conversion and drift region (typically a few mm) with moderate electric field of 100–1000 V/cm Narrow (100 µm) amplification gap with high electrical field (40–50 kV/cm) With drift velocities of 5 cm/µs (or 20 ns/mm) electrons for Ar:CO2 (93:7) need 100 ns for a 5 mm gap By measuring the arrival time of the signals a MM functions like a TPC => Track vectors for inclined tracks Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

The bulk-micromegas* technique The bulk-micromegas technique, developed at CERN, opens the door to industrial fabrication Pillars ( ≈ 300 µm) Mesh Photoresist (64 µm) r/o strips PCB *) I. Giomataris et al., NIM A 560 (2006) 405 Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Bulk-micromegas structure Pillars (here: distance = 2.5 mm) Standard configuration Pillars every 2.5 – 10 mm Pillar diameter ≈300 µm Dead area ≈1–2% Amplification gap 128 µm Mesh: 350 wires/inch Wire diameter 20 µm Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Sparks made inoffensive by the resistive-strip protection concept Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Joerg Wotschack (CERN) Spatial resolution & efficiency for R12 (250 µm strips) Analysis of data taken in July 2010 Inefficiency compatible with area of mesh support pillars (d=2.5 mm) Resistive strip chambers are fully efficient (≈98%)over a wide range of gains Spatial resolution with 250 µm strip: ≈30 µm with Ar:CO2 (93:7), even better with 85:15 Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Micromegas in ATLAS cavern Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

2011: four resistive MMs installed behind EO station Stand-alone readout Worked through the full year flawlessly Nice, clean tracks and background measurement R11 R12 R13x R16xy Trigger (strips) DCS mmDAQ Laptop in USA15 ≈120 mm R16 Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Joerg Wotschack (CERN) 2012 Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Joerg Wotschack (CERN) Small Wheel: four small (10 x 10 cm2) MMs Installed four MMs on CSCs on Small Wheel (Side A, Sector 9) in early 2012 Readout (standalone) of chambers after this Tech. Stop Readout integration into ATLAS DAQ being prepared (M. Byszewski et al.) Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Joerg Wotschack (CERN) MBT0: Double gap chamber with x and u (v) readout Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Joerg Wotschack (CERN) MBT0: Double gap chamber with x and u (v) readout MBT0 chamber switched on last week Only HV/current monitoring so far (readout as of this week-end) Current follows very nicely the luminosity (max: 5 x 1033 cm-2s-1) Rate ≈100 kHz/cm2 (extrapolated from current measurement) Frascati, 7 Dec 2011 Joerg Wotschack (CERN)

Time line of Small Wheel project 2012: Large-area prototypes 1 x 1 m2 prototype (July) 1 x 2 m2 prototypes (end of year) 2013: Technology transfer to industry Optimization of production steps in industry Development of QA procedures Module 0 (1 x 2.4 m2; 2 x 4 planes) 2014: Setup of production & test facilities 2015/16: Production of about 1200 MMs Testing, assembly, commissioning (128 chambers) 2017: Installation on NSW structure 2018: Installation in ATLAS LAPP, Annecy, 26 April 2012 Joerg Wotschack (CERN)

Minimum-bias trigger (MBT) Disk of ≈2 m diameter on face of end-cap calorimeter, 60 mm thick Two disks (side A and C) Particle rates: ≤ 1 MHz/cm2 3–4 planes of MMs/disk 8 or 12 sectors Segmentation to be defined Max. dim. ≤ 0.6 x 0.8 m2 Total of 100 detectors to be made Time scale Design & production: 2013 Installation: early 2014 Project under discussion in ATLAS Replacement of MBT scintillator disks by micromegas detectors LAPP, Annecy, 26 April 2012 Joerg Wotschack (CERN)

Who is involved (CERN personnel) PH-ADE-MU Staff: J. Wotschack Fellow: Marcin Byszewski (DAQ, mon. & offline reconstruction) – until 31 July, if no extension (very critical) Techn. Student: Maria Hoffmann (as of 1 August 2012) PJAS: George Glonti (until July 2012); Givi Sekhniaidze (as of June 2012) (Also: MBT project: David Berge, Ch. Rembser, A. Salzburger, M. Schott) PCB workshop (TE-MPE-EM) Rui de Oliveira Olivier Pizzorusso, Antonio Texeira PH-DT-EM2 (support with mechanics, design and construction) Hans Danielsson et al. (small fraction of his time) also Leszek Ropelewski et al. (PH-DT-TP) for Lab space and support Hand Muller et al. (PH-AID-DT) for SRS readout support LAPP, Annecy, 26 April 2012 Joerg Wotschack (CERN)