Multigap Resistive Plate Chambers (MRPC) Osnan Maragoto Rodriguez CERN World Laboratory

Resistive Plate Chamber Introduction … Resistive Plate Chamber Electric field strong enough, so the avalanche process occurs instantaneously. The induced signal is the result of movement of avalanches. The signal observed corresponds to all avalanches in parallel. + kV E d V/d 2 mm gap 𝑁= 𝑁 0 𝑒 𝛼𝑥 Townsend Only clusters produced near the cathode (0.5mm), are going to produce a detectable signal. Increasing E the streamers are produced in the detector.

Resistive Plate Chamber Introduction … Resistive Plate Chamber (RPC) Experiments: CMS and ATLAS in LHC Muon detection system + kV Questions: Could be possible increase the gas gain until detectable signal occurs immediately? High gain it needed (snap signal production). It needed a way to stop the growth of avalanches (otherwise discharges and sparks occur in the gas). Solution: Add borders to stop the growth of avalanches. These borders must be invisible to the induced signals. Induced signals are the result of charge movement in each gap.

Counter rate (< 1 kHz/cm2) Multigap Resistive Plate Chamber (MRPC) a fast timing detector Stack of equally spaced electrodes with voltage applied to external surfaces (all internal plates are electrically floating) Pick up electrodes placed outside and insulated from electrodes (internal plates transparent to fast signal) Internal plates take correct voltage - first due to electrostatics, but kept at correct voltage due to flow of electrons and positive ions (feedback mechanism that dictates equal gain in every gas gap) Gaseous detectors with parallel geometry. Operating in avalanche mode . Built with commercial glass. Low production cost. Counter rate (< 1 kHz/cm2) Temporal resolution (<100 ps) High efficiency (>95%)

MRPC Key points Many very small gas gaps with very high electric field (𝐸~100 𝑘𝑉/𝑐𝑚) Gas avalanches starts immediately Induced signal is the sum of many avalanches acting together Space charge is the dominant effect: High fraction of recombination - small amount of charge produced - relatively good performance at high rates

Design and construction MRPC Design and construction 2 detectors MRPC (6/220) 6 gas gaps 220 μm. Float lime glass produced by AGC Glass of 280 μm thicknessr. Resistivity of the glass 4.2 x 1012 Ωcm. Active Area: 20 x 20 cm2 Gas: Mixture th C2H2F4+ SF6 (95/5) @ a continuos flux of 5 l/h. 24 readout strips MRPC-2. Painted edges

MRPC Assembly procedure

MRPC for the ALICE TOF New era for TOF systems!!! Requirenments TOF barrel 150 m2. Efficiency > 95%. Intrinsic Time Resolution <100 ps. High segmentation: 160 000 readout channels (2.5 x 3.5 cm2) Affordable cost Solution Double stack MRPC 10 gaps of 250 μm. Efficiency >99%. Overall Time Resolution: 85 ps (t). 160 000 channels all operated at the same voltage and threshold New era for TOF systems!!!

Detection of Extensive Air Showers (EAS) MRPC Detection of Extensive Air Showers (EAS) Extreme Energy Events Project Features 3 MRPC (160 x 80 cm2) 6 gas gaps de 300 μm Spatial information provided by 24 readout electrodes Temporal information (Absolute time stamp using a GPS system) Goals…. Reconstruction of EAS. Forbush effect monitoring. Muon flux at ground level.

Collisions Au+Au at 25 AGeV MRPC The CBM TOF wall Collisions Au+Au at 25 AGeV Unique characteristics Overall Time resolution: 80 ps. Efficiency >95 %. ~100000 channels, streaming DAQ Rate capability: depending on the region (0.5-25 kHz/ cm2 ) regions: – A: < 1.5 kHz/ cm2 – B: < 3.5 kHz/ cm2 – C: < 8.0 kHz/ cm2 – D: <25 kHz/ cm2 – E: 82 kHz/ cm2

Summary MRPC: excellent device for precise time measurements. Relatively low production cost. High efficiency (>95%). Good result at rates under 1KHz/cm2 ALICE ToF open a new era for large array of Time of Flight devices using MRPC.

Thank you for your attention