The LHCb 3 GEM detector for the inner

The LHCb 3 GEM detector for the inner region of the first station (M 1 -R 1) of the muon system M. Alfonsi 1, G. Bencivenni 1, W. Bonivento 2, A. Cardini 2, P. de Simone 1, F. Murtas 1, D. Pinci 4, M. Poli-Lener 1 , D. Raspino 2 and B. Saitta 3, 2 • 1 - Laboratori Nazionali di Frascati - INFN, Frascati , Italy • 2 - Sezione INFN di Cagliari – Cagliari, Italy • 3 – Universita’ di Cagliari - Italy • 4 – Sezione INFN di Roma 1, Roma, Italy Ageing is discussed in session N 39 -5 by P. De. Simone W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

The LHCb detector Muon detector: L 0 high p. T trigger + offline muon ID W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Side view: The LHCb muon chambers M 1 -R 1 Front view of a quadrant: Chamber Size Muon trigger: AND of 5 stations + BCID Layout by logical pads of different size four regions R 1 to R 4 W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration All equipped with wire chambers but for station M 1 -Region 1 triple-GEM Main reasons of the choice: ageing and cluster size (pad size 10 x 25 mm 2) S=0. 6 m 2 but about 20% of the triggered muons need it! IEEE- NSS 2004 - Rome

The M 1 R 1 detector Requirements for the station 430, 0 240, 0 310, 0 Ø Ø Rate capability (mostly hadrons) up to 0. 5 MHz/cm 2 , average 0. 2 MHz/cm 2 Efficiency on muons >96% in a 20 ns window Pad multiplicity or cluster size (<# >of hit pads/muon) <1. 2 Signal width (to limit trigger dead time) <50 ns Radiation hardness 10 years of LHCb The M 1 R 1 station 12 double detectors surrounding the beam pipe: each detector is a triple-GEM chamber of 20 x 24 cm 2 active area 55, 0 290, 0 200, 0 Ø Active area beam pipe 24 triple-GEM chambers (GEM foils from CERN-EST-DEM workshop) W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration 95, 0 IEEE- NSS 2004 - Rome

The main idea: an optimal gas mixture Time resolution (with leading-edge time pick-off) depends mainly on the intrinsic time resolution on the arrival of the first ionisation clusters on GEM 1 σ(t 1) = 1/(nclu vdrift) σ(ti) = f(i)/(nclu vdrift), f(i)>1 σ(t 1) Magbolz and Heed simulation Choice of the gas mixture High yield and fast Also good quenching properties and radiation hardness Ar/CO 2/CF 4 (45/15/40) W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration Drift field 3 k. V/cm More than a factor 2 of improvement w. r. t. Ar/CO 2 (70/30) IEEE- NSS 2004 - Rome

Prototype performance: efficiency and cl. size A protorype detector: 2 triple-GEM chambers OR-ed Pad board LV distributor board FE boards 96 % Working region 6 k gain Cluster size Efficiency in 20 ns 192 channels Working region 1. 2 20 k gain Working region about 70 V (a gain range of more than 200%) it allows for a) gain non uniformities over the surface (10 -15% measured with the prototype) b) P variations (-1. 5%/mbar) c) gain variations with rate W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Prototype performance: discharge rate Measurement done at π-M 1 beam 350 Me. V/c π (7% p) of PSI (CH) 300 Mhz beam + measurement of maximum number of discharges leading to detector death: With 241 Am source on 0. 5 cm 2 area To speed-up the test Geff=40 k (conservative result) Three detectors killed after 500, 700 and 800 discharges gain Working region W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration We derived a maximum safe value (10 y of operation of the detector at the nominal luminosity) for the discharge probability per incident particle We obtain a maximum safe gain value OK well compatible with the working region IEEE- NSS 2004 - Rome

Prototype performance: high rate behaviour Test performed at ENEA Casaccia Triple-GEM chamber: not direclty irradiated Compton electrons cosmic ray trigger 4. 5 m PC HV CONTROL ROOM 60 Co Calliope radiation dose 0. 2 Gy/h setup like in this figure (forbidden to take pictures) but with scintillators+PMs shielded by 10 cm of lead W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Prototype performance: high rate behaviour σ(ns) average count rate (k. Hz/cm 2) time spectrum of first triggered pad of the chamber with γ without γ gain No significant difference in time resolution With and without radiation W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Towards the LHCb chamber(I) 20 x 24 cm 2 GEM foils produced at CERN GEMs are stretched at ~ 1 Kg/cm A. Kachtchouk (PNPI) Strain Gauges Cdet Cblock>> Cdet Cross-talk from capacitive coupling through the common GEM 3 foil it is long-distance at high rate gives additional noise in the chamber It might be solved with micro-strip (incutance-less) blocking capacitor (100 n. F) to GND. The GEM foil is divided in 6 sectors It is the same idea as in CPC (wire termination by a to reduce the energy released in case of discharge capacitor) W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration STILL TO BE DECIDED (with the new readout chip) IEEE- NSS 2004 - Rome

Towards the LHCb chamber(II) Cathode GEM foils are assembled without internal spacers, thus avoiding geometrical dead zone. The G 10 frames glued on the GEM honeycomb structure (in front of EM calorimeter!) The three GEM frames are glued one on top of the other and tested with HV W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration In the frame 6 holes house 0. 1 -1 M SMD resistors for HV decoupling IEEE- NSS 2004 - Rome

Towards the LHCb chamber(III) 0. 4 mm Gas inlet 0. 6 mm Selected pad type: with ground grid W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Towards the LHCb chamber(IV) High voltage: Solution not easy large currents need to stay within working region a candidate solution with 3 dividers and 3 commercial power supplies monitor of GEM current ! 1 M 1)6 k. V/1 m. A still to be tested and aprroved 8 V ΔVgem 1, 2, 3 SPICE simulation based on measurements from our group: see TNS 49(2002)1638 2)4 k. V/2 m. A 3)1. 3 k. V/10 m. A ΔVg em 2 plateau 1280 V to 1350 V W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration G=Aexp(B Utot) B=0. 017/V total Power consumption 15 W at plateau end IEEE- NSS 2004 - Rome

Towards the LHCb chamber(V) Front-end electronics So far we tested the detector with fast low-noise ASD’s: • ASDQ (M. Newcomer-CDF) • CARIOCA 0. 25 m CMOS rad tol chip for LHCb muon chambers A new version of the CARIOCA chip was designed for GEM (without ion tail cancellation) and is in production phase at IBM if it works it might be useful also for other groups using GEM detectors W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Conclusions The triple GEM detector is part of the LHCb muon detector in the M 1 R 1 region The system will consist of 12 double chambers, built by INFN Cagliari and LNF. Construction foreseen to start this year and to end during the first half of 2005 (not on the critical path!) Status of the final detector: • mechanical design OK • first chamber in assembling phase • prototype FE board in production • FE CARIOCA-GEM chip in production • power supply divider in testing phase • decision on blocking capacitor taken after testing the detector with CARIOCA-GEM Portorico for the full detector built and tested! W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

Artist view Ancient architecture experts might have noticed this is not the Rome colosseo! …pictures from EL-JEM (Tunisia) … GEM? W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome

THE END W. Bonivento - INFN Cagliari - ITALY LHCb Collaboration IEEE- NSS 2004 - Rome