MICROMEGAS per l’upgrade delle Muon Chambers di ATLAS per SLHC

1. Arizona, Athens (U, NTU, Demokritos), Brookhaven, CERN, Harvard, Istanbul (Bogaziçi, Doğuş), Naples, CEA Saclay, Seattle, USTC Hefei, South Carolina, St. Petersburg, Shandong, Stony Brook,Thessaloniki MICROMEGAS per l’upgrade delle Muon Chambers di ATLAS per SLHC M.Alviggi, Atlas Italia, 16 marzo 2009

2. Micromegas for ATLAS Muon upgrade • Combine triggering and tracking functions • Matches required performances: • Spatial resolution ~ 100 m • Good double track resolution • Time resolution ~ few ns • Efficiency > 98% • Rate capability > 5 kHz/cm2 • Potential for going to large areas (1 m x 2 m) with industrial processes • Cost effective • Robustness

3. Prototype P1 Standard bulk micromegas fabricated at CERN • Drift gap: 2-5 mm • Homogeneous stainless steel mesh • 78 m pitch • wire diameter ~25 m • Amplification gap=128m • 450mm x 350mm active area • different strip patterns (250, 500, 1000, 2000 µm pitch; 450mm and 225 mm long)

4. Spatial resolution Micromegas Si tracker Scintillator Beam Gas: Ar:CF4:iC4H10 (88:10:2) Drift field: 200 V/cm ~73 um Strip pitch: 250 µm Strip pitch: 500 µm • Residuals of MM cluster position and extrapolated track from Si • Convolution of: • Intrinsic MM resolution • Tracker resolution (extrapolation) • Multiple scattering

5. Micromegas Efficiency Ar:CF4:Isob (88:10:2) Vmesh = 450 V; Vd = Vmesh + 100 V Pillars 300 µm diameter 2.54 mm pitch Inefficiency concentrated at location of mesh support Practically 100% efficient outside the pillars Mesh Strips Black: all tracks in Si tracker, extrapolated to MM Red: tracks without a hit in the MM Beam

6. Efficiency & Amplification vs HV > 99% efficiency Stable operating point 400 410 420 430 440 450 460 470 480 490 • Gas mixture: Ar:CF4:iC4H10 (88:10:2) • Drift gap 5 mm; drift field = 200 V/cm • Strip pitch = 250 µm • 1 ADC count = 1000 electrons

7. Micromegas as µ-TPC Each micromegas gap delivers a set of space points, the more the track is inclined the more space points are available  Solves the problem of spatial resolution for large track inclination MM as TPC will give track segments & excellent space resolution With electronics used in 2008 we can measure the relative times from strip to strip using sampling ADC in 2009 electronics would measure times (at least on few channels) Cluster Last strip First strip Track inclination: ≈ 50° Ar:CF4:iC4H10 (95:3:2) Drift field: 360 V/cm vD = 6.8 cm/µs

8. Small prototypes (end 2008) Test beam stopped  set up cosmics test stand in lab@CERN and in few other labs (Naples,Demokritos) to optimize gas mixtures wrt drift velocity, amplification, sparks… • Small prototype: 100x100mm2 with 1 readout pad • Amplification measurements @Naples with Fe55,also Ar+CO2!: Ar(86)+CO2(10)+C4H10(4)

9. Prototypes in 2009 • Ten small (100 x 100 mm2) MMs with 250 µm strip pitch @ CERN and other Labs (Naples,…) • One 50% size: active area 1.3m x 0.4m @CERN -Segmented mesh (cut) to reduce mesh capacity -Half-size MM board (under construction at CERN) with 250 and 500 µm strip pitches 1500 500 The stretched micromegas mesh on its frame

10. Milestones… • End 2009: • Full requirements on chamber (gas, strip pitch,…) and readout electronics (front-end,ADC,TDC,…) • 2010: • Full-size prototype • Ageing tests • γ- and n- irradiation of small MM chamber in ATLAS

11. UPGRADE PHASE I • Add MMs layers to each CSC chamber (5-10cm free space towards the IP) • Space points along tracks by operating MM as µTPC • out-of-time tracks not aligned! • Number of channels/precisionMM (250 µm pitch): 1200mm x 4 = 5 k • For ex. :4 precision layers 20 k channels , per 32 chambers  • Total # of channels : 640k Dt ≈ 10 ns Drift volume Dt ≈ 100 ns • Trigger and/or 2nd coordinate by thinner units (wider strips) • Trigger logic could use tracks position or angle • Fast time response from ‘first in time’ signals Spacer 10 mm 5–10 mm 5–10 mm 50 mm

12. Typical parameters • Track angles for CSC coverage: 10–20 degrees (MMs vertical?) • Drift gap: 7 mm => footprint: 1–2 mm • Strip pitch: 250 µm => 4–8 strips see signal • Average number of primary electrons (clusters): 15–20 • Max drift time: 100–200 ns (vdrift = 7–3.5 cm/µs) • Drift time range ‘per strip’: 20–35 ns • Requirements on readout electronics • Time resolution of a few ns should be sufficient • Charge measurement, if used, can be coarse

13. Expected performance Assume: track angle 100, 7 mm drift gap, 250 µm strip pitch • Determination of track coordinates from • time measurements (few ns resolution) • strip positions only (multiple layers) • charge weighting • will all give spatial resolution below 100 µm • More than one drift gap at a few x 10 mm distance will help to solve ambiguities and improve the resolution further

14. Richieste CSN1 • ME: TestBeam Micromegas (2ftex1,5 mesi=) 12k€ • CONS: • prototipi rivelatori 4k€  2k€ a marzo • gas stazione di test Napoli 3k€ • sonde gas infiammabile 2k€ (OK) • elettronica di front end per i prototipi 3k€ • INV: • TDC VME 5k€ (OK) • HV power supply (sensib.1nA) 3k€ (OK)

15. Backup

16. σ = 30 ns σm ≈ 1.2 ns ns*100

17. CSC replacement

18. CSC chambers

19. Inclined tracks Cluster Last strip Impact angle: 50° First strip

20. Micromegas as TPC (II) Track under 50° with relative time info

21. Richieste CSN1