11th Pisa meeting on advanced detectors La Biodola, Isola d’Elba, Italy, 24-30 May 2009 The ALICE muon trigger system: cosmic ray commissioning and first beam induced events Ph. Rosnet Université Blaise Pascal - CNRS/IN2P3 for the ALICE Collaboration Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

ALICE: A Large Ion Collider Experiment One of the 4 experiments at the Large Hadron Collider (LHC) at CERN: designed to produce proton-proton (spp=14 TeV) and nucleus-nucleus (sNN=5.5 TeV for Pb-Pb) collisions Collaboration of about 1000 scientists from 109 intitutes (31 countries) ALICE is the LHC experiment dedicated to study the hot and dense nuclear matter produced in heavy ion collisions: the so-called Quark-Gluon Plasma (QGP) ALICE Collaboration, J. Phys. G: Nucl. Part. Phys. 30 (2004) 1571-1763 ALICE Collaboration, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040 Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

ALICE Collaboration, JINST 3(2008) S08002 ALICE detector ALICE Collaboration, JINST 3(2008) S08002 General detectors at large || interaction trigger event centrality Muon spectrometer -4    -2.5 tracking to separate  states with  = 100 MeV/c2 L0 trigger up to 1 kHz Central detectors ||  0.9 hadrons electrons photons Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Muon trigger system 2 stations of 2 detection planes CERN Courier, Vol. 47, Dec. 2007 2 stations of 2 detection planes 72 Resistive Plate Chambers (140 m2) 21103 electronics channels fast decision electronics at 40 MHz defining 234 projective trigger zones To select tracks () with a pt cut and send a L0 signal 800 ns after the collision Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Muon trigger detector Main performances (in streamer mode) Detector characteristics Two bakelite electrodes of 2 mm (  109  cm) gas gap of 2 mm (gas mixture with 50% relative humidity) : streamer = 51% Ar + 41% C2H2F4 + 7% iC4H10 + 1% SF6 avalanche = 89.7% C2H2F4 + 10% iC4H10 + 0.3% SF6 nominal high voltage streamer  8 kV avalanche  10 kV readout strips  21103 bending plane  1, 2, 4 cm non-bending plane  2, 4 cm dual threshold front-end electronics with dedicated ASIC strips + strips - high voltage spacer bakelite gas graphite plastic insulation Main performances (in streamer mode) efficiency  98 % time resolution < 2 ns spatial resolution < 1 cm rate capability > 100 Hz/cm2 integrated yield > 100 Mhits/cm2 Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Muon trigger control tools Front-end Test (FET) generator injecting RPC like pulses to check front-end electronics: 3 dead channels over 21103 trigger electronics algorithm global timing by varying FET phase clock Test of readout stored data by applying Mask = 10101010… Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: detection The ALICE muon spectrometer can detect and reconstruct only muon cosmic rays with small angle w.r.t. horizontal 2° 9° Backward  Forward  Specific muon cosmic runs:  50 000 events in May-June 2008 - muon trigger alone  85 000 events in March-April 2009 – « entire » muon spectrometer event rate  0.18 Hz Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: event type Two types of events triggered: number of triggered zone = 1 & Nhits  9  single track else  shower Nhits ≤ 9: single muon Nhits > 9: shower 4 planes x 2 coordinates Nhits Single tracks  40 % Showers  60 % Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: polar angle distribution z y y Bending plane Polar angle distribution reflects cosmic rays (with edge effects) forward/backward asymmetry due to: hadware timing in FEE to take into account the distance between the two stations:1 m  3 ns  loss of efficiency for backward  Jura shadow ? Forward  Backward  Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: detector efficiency RPC efficiency estimated with the detection planes redundancy ¾ 3 planes (MT11 – 21 – 22) at nominal high voltage (HVnom) variation of high voltage for plane MT12: HV = HVMT12 – Hvnom RPC efficiency > 90 % MT11 MT12 MT21 MT22 Trigger efficiency > 95 % with ¾ planes required Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: detector stability At nominal high voltage: most of RPCs have a small and stable current < 1 µA counting rate (noise)  0.012 Hz/cm2 (< 0.04 Hz/cm2) Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Cosmic rays: muon tracking reconstruction Offline reconstruction with ALICE software (run=67188, event=96) Reconstructed track Beam line Noisy channels of tracking system Noisy channels of trigger system Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

First LHC beam injection induced events (1) First injection test near ALICE (red beam) performed in August 2008: bunch (few ns wide) of 5109 protons from SPS every 48 s more than 220 (over 234) trigger decision zones fired, to be compare to only some zones for cosmic rays Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

First LHC beam injection induced events (2) Almost all strips fired more than one time per beam bunch: 5000 hits in bending plane / 3744 strips per plane 2000 hits in non-bending plane / 1504 strips per plane Effect due to a beam screen (15 µm Ti) placed in injection line about 350 m from ALICE resulting in a shower of  5 particles/cm2 in ALICE Noise level  (0.01 Hz/cm2)  (35 m2) = 3500 hits/s on each detection plane Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Conclusions The ALICE muon trigger system is in good shape It has been tested in streamer mode with cosmic rays: electronics chain (front-end + trigger + DAQ) works since more than one year RPCs are stable with a low counting rate the whole reconstruction chain (including tracking system) is working The first LHC beam injections were detected by the system Ready for first LHC data taking… Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Backup slides Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Sources of muons in central Pb-Pb collisions Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Muon trigger principle Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

Muon trigger electronics FEE signals sampled at 40 MHz Trigger decision send to Central Trigger Processor 800 ns after the collision Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009

RPCs current Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, 24-30 May 2009