The ALICE muon spectrometer

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The ALICE muon spectrometer
M. Gagliardi Università degli Studi INFN,
Torino ItalyCERN, Genève Switzerland for the
ALICE collaboration
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Outline

• QGP and Heavy Ion Collisions ALICE
• Quarkonia suppression in HIC
• Design, performance and status of the ALICE
  muon spectrometer - Tracking system -
  Trigger system
• Selected physics topics quarkonia in Pb-Pb
• Conclusions

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QGP and Heavy Ion Collisions
QCD asymptotic freedom at high energy
and/or density, transition to a deconfined phase
with partonic DF the Quark-Gluon Plasma
QGP
Critical energy density? ? 1 GeV/fm3
TC
?20 fm/c
?1 fm/c
QGP
Tc ? 150200 MeV
Energy density at thermalisation ? 3 GeV/fm3 at
SPS ? 5 GeV/fm3 at RHIC gt 10 GeV/fm3 at LHC
F. Karsch, QM 2006
Location and nature of phase transition still
debated
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The ALICE experiment
LHC-CERN CollisionsPb-Pb (
5.5 TeV ) Ar-Ar ( 6.3 TeV ) p-p (
14 TeV) lighter A-A hybrid systems
(p-A, d-A)
(TRD)
Time Of Flight Detector
muon spectrometer(-4 lt ? lt -2.5)
A Large Ion Collider Experiment
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Quarkonia suppression by QGP
QGP signatures hidden by hadronisation medium
studied through probes. Quarkonia among the most
relevant
J/? suppression observed at SPS and RHIC in
central Pb-Pb, In-In, Au-Au collisions (NA50/60,
PHENIX)
QGP
lD Debye screening length T-1/2
When lD rQQ, suppression of bound states by
colour screening expected sequential melting of
resonances with increasing T gt TCRecent
estimates TJ/? ? 2TC , T? ? TC
(Matsui Satz, 1986)
Picture not clear yet (e.g. similar suppression
at RHIC and SPS, in spite of different e) -
which charmonium states are actually suppressed?
- final state regeneration of J/y enhanced at
RHIC?
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The ALICE muon spectrometer

• Studying heavy quark production via their muonic
  and semi-muonic decays
• mm invariant mass spectrum
• Forward rapidity (-4 lt y lt -2.5), xBj ? 10-5
• Large quarkonia acceptance down to pT ? 0
• Measurement of quarkonia production - as a
  function of centrality- as a function of pT, y-
  for different colliding systems (including
  p-A)- versus global observables- together with
  open charm/beauty

FRONT ABSORBER(composite material)
TRACKING SYSTEM (Cathode Strip Chambers)
m FILTER (Fe)
BEAM SHIELDING (W)
DIPOLEMAGNET B 0.7 T
TRIGGER SYSTEM (Resistive Plate Chambers)
19 m
Mass resolution 70 MeV/c2 at 3 GeV c2 100
MeV/c2 at 10 GeV/c2
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Tracking system

• 5 stations of 2 detection planes each
• Detection plane multi wire proportional
  chamber with bi-cathode pad readout (bending
  and non-bending)
• ST1 and ST2 4 quadrants/detection plane
• ST3, ST4, ST5 18 to 26 slats/detection plane
• Pad size min 4x6 mm2, max 5x100 mm2
• Expected hit density in central Pb-Pb 10-2 cm-2

Electronics- 1.1x106 channels- Front-End
18000 MANU boards 1
MANU 4 MANAS
(Multiplexed ANAlogic Signal
processor, 16ch.)
MARC ADC w/ zero suppr.- 20 CROCUS
readout of 1/2 chamber ( 50 000 ch.) with 1
CROCUS - 1 TCI manage busy and trigger for the
20 CROCUS
ST12
ST345
X
Pad plane
Z
Gas Ar(80) CO2(20)
Wire plane
5 mm
2.5 mm
Pad plane
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Tracking system performance and status
Goal 100 MeV/c2 mass resolution (_at_ 10 GeV/c2)
1 momentum resolution Space resolution lt 100 mm
(bending plane) lt 1 mm
(non-bending)

• All detectors installed in ALICE- 80
  commissioned
• First cosmic hits during ALICE commissioning
  runs (Dec 07, Feb 08, Jun 08)

Beam tests for both slats and quadrants with p
(PS) and m (SPS), chambers in final set-up -
space resolution within requirements- noise
1000-2000 e- (1-2 ADC channels)
Global Monitoring System being installed monitor
chamber displacement with accuracy lt 50 mm
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Trigger system
72 Resistive Plate Chambers arranged in 2
stations of 2 planes (6.5x5.5 m2) each

• Aim cut background from light meson muonic
  decays, reduce trigger rate to 1 kHz -
  Delivers single and di- muon triggers with 1(2 )
  GeV/c pT-cut, optimised for J/? (?)- pT
  estimated via the muon deviation in magnetic
  field- 3/4 fired planes condition (redundancy)

INSULATOR
HV
SPACERS
2 mm
RESISTIVE PLATES (BAKELITE)
2 mm
2 mm
GRAPHITE
GND
READOUT STRIPS

• Low resistivity RPCs (rate capability)- Both
  sides read out with orthogonal strips (1, 2, 4
  cm)- 2 operation modes streamer (Pb-Pb) and
  avalanche (p-p)- 21000 channels, 2384 FE
  boards dual-threshold discrimination (ADULT)
  2 DARC for readout- Trigger algorithm in FPGA
  234 local boards - 16 regional boards and 1
  global board. Trigger delay 800 ns

Trigger stations
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Status of the trigger system

• All detectors installed in ALICE and fully
  commissioned- Data taking with cosmics and
  during injection tests- Switching to external
  threshold mode

48 s
Cosmic hit
RPC counts during injection test
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Selected physics topics Quarkonia -gt mm- in
Pb-Pb
PbPb cent, 0 fmltblt3 fm
J/yfamily
? family
Baseline yields (106 s data taking)

• ?(1S) ?(2S) 0-8 GeV/c
• J/? high statistics 0-20 GeV/c
• ?, ?(3S) poor significance

mm- mass spectra after uncorrelated bkg
subtraction
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Quarkonia suppression studies
J/y nuclear modification factor For two
different suppression scenarios
3 fm lt b lt 6 fm
0 lt b lt 3 fm
6 fm lt b lt 9 fm
b gt 12 fm

• - Scenario 1
• Tc 270 MeV
• ?J/y/Tc1.7

• - Scenario 2
• Tc190 MeV
• ?J/y/Tc1.21

• Sensitivity to different suppression
  patterns- RAA also feasible for ?

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Conclusions

• With a mass resolution of 100 MeV/c2 at the ?
  mass and 70 MeV/c2 at the J/y mass, the muon
  spectrometer is a fundamental subdetector in
  ALICE for the study of heavy flavours and
  quarkonia
• After long RD phase, installation and
  commissioning, spectrometer will be ready for
  physics at LHC start-up
• Dedicated muon commissioning run to start in a
  few days. Goals fine tuning of detector
  parameters, reconstruct full tracks.
• Study of quarkonia suppression in Pb-Pb is the
  main goal, but also

• Heavy quarkonia in p-p
• J/y polarization
• Open beauty
• Low masses
• Electro-weak boson

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Thank you!