LHCb Muon Detector MWPC & GEM Institutes: Cagliari, CBPF, CERN, Ferrara, Firenze, LNF, PNPI, Roma "La Sapienza", Roma "Tor Vergata" The task of the Muon System of LHCb is to provide (i) a high-Pt Muon candidate for the first trigger level (L0) and (ii) a good Muon identification for the off-line analysis. The system is composed of 5 stations M1-M5 (for a total active surface of 435 m2) separated by iron filters (iron is only permeable to energetic Muons). The system is equipped with 1368 Multi-Wire Proportional Chambers and 24 triple GEM detectors (in the M1 region close to the beam) of 20 different sizes (from 24x20 cm2 to 148x31 cm2) with spatial X-Y readout: this results in nearly 120k FE electronic channels. Most of the MWPCs (960) have anode-wire readout, while the others have cathode-pad or mixed (anode-wire + cathode-pad) readout. To ensure efficiency and redundancy, all detectors in M1 have two sensitive layers in OR, and those in M2-M5 have four layers. MWPC detector MWPC quality control MWPC detector MWPC assembly GEM detector Muon Filters GEM production GEM and MWPC efficiency MWPC & GEM GEM MWPC The LHCb L0 trigger is based on the 5-fold coincidence of stations M1 to M5 within 25 ns. It provides a fast and precise (20% accuracy) measurement of the Muon Pt and high efficiency in the bunch-crossing identification. The LHCb MWPCs and GEMs were designed in order to fulfill all those requirements. Track finding starts from M3. A track in M2-M5 is then extrapolated to M1 and to the interaction point to compute the momentum. The trigger efficiency for b mX is 46% at 100 kHz output rate. The decision time is 1 ms. Three custom radiation hard chips have been developed with IBM 0.25 micron process for use in the Front-end electronics: CARIOCA, DIALOG and SYNC. Track finding by the muon trigger CARIOCA 8 ch (+/-) Amplifier-Shaper-Discriminator. Peaking time ~ 10 ns DIALOG Front End Logic SYNC transmits data to DAQ and L0 trigger CARDIAC Front End Board Alessio Sarti. Email: asarti@lnf.infn.it