1. 11th Pisa meeting on advanced detectors
La Biodola, Isola d’Elba, Italy, 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, May 2009

2. 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)
ALICE Collaboration, J. Phys. G: Nucl. Part. Phys. 32 (2006)
Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, May 2009

3. 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, May 2009

4. 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, May 2009

5. 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% iC4H % 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, May 2009

6. 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 = …
Philippe Rosnet, Université Blaise Pascal – CNRS/IN2P3, 11th Pisa meeting on advanced detectors, Isola d’Elba, Italy, May 2009

7. 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:
 events in May-June muon trigger alone
 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, May 2009

8. 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, May 2009

9. Cosmic rays: polar angle distributionz 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, May 2009

10. 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, May 2009

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

12. 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, May 2009

13. 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, May 2009

14. 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, May 2009

15. 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, May 2009

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

17. 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, May 2009

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

19. 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, May 2009

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