The CMS Detector
Paoti Chang
National Taiwan University
Workshop on LHC Physics and the
Strategies for Discovery
Taipei, Taiwan, Jan. 14, 2008
1/14/08 NTU, Taipei
The CMS Detector
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Detector Requirement
Good Muon identification;good dimuon mass resolution
(~1% at 100 GeV); distinguish charge at 1 TeV.
 Good momentum resolution for charged tracks. Efficient
triggering and off-line tagging on t and b-jets.
 Good EM energy resolution; good diphoton and dielectron
mass resolution; wide geometrical coverage; p0 rejection
and efficient photon and lepton isolation
 Good missing-transverse-energy and dijet mass resolution
 high-field solenoid, full-silicon-based inner tracking
system and a homogenous scintillating-crystal-based
electromagnetic calorimeter

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The CMS Detector
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Overview of the CMS Detector
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The CMS Detector
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Superconducting Magnet
Special features:
1. Winding composed of
four layers
2. Mechanically reinforced
with aluminum alloy
3. Large dimension
6.2 m cold bore, 12.5m length,220-t mass
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The CMS Detector
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Main parameters
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CMS decides to use lower field, 3.8T.
The CMS Detector
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CMS Barrel Yoke ready for coil
and muon Detector
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The CMS Detector
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Inner Tracking System

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Provide precise measurements of track trajectories
and secondary vertices.
L= 1034 cm-2 s-1  1000 particles from >20 inter.
high granularity and fast response of electronics
⇕
Keeping minimum amount of material
 3 layers of pixel to reduce occupancy (4.4-10.2 cm)
10 layers of silicon strip detectors (R ~ 1.1 m)
endcaps: 2 disk pixel and 3 plus 9 strip on each side
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Overview of the tracker layout
Acceptance |h|<2.5, 200 m2 silicon area, 1440 pixel and 15148 strip modules.
pixel: 100x150 mm2; Inner silicon: 10cm x 80mm; outer silicon: 25cm x 180 mm
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Expected Hadron Fluence and
Radiation Dose
L = 500 fb-1, 10 years of LHC running
 Surface damage on readout chips  0.25mm CMOS chip (rad. hard)
 Increasing leakage current  low temperature -10C to -27C
 transient phenomena
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Pixel Detector
Layout overview
barrel support structure
 material budget
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Barrel Pixel Detector Modules
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Forward Pixel
Sketches of two types of FPix panels
Half cylinders
Sketch of of a plaquette mounted in a panel
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Status of Pixels
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Overview of Silicon Strip Detector
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Silicon sensor
320 mm sensors
Active region
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500 mm sensors
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Silicon Tracker
Inner Barrel and Endcap
Exploded views of a module of
two sensors
Three TIB modules in a shell
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Outer Silicon Tracker
Each sector consists of 9 front
petals and 9 back petals
d = 2.3 m
TOB wheel
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Endcap outer silicon strip detectors
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Rod an Petal
Double sided rod
Front and
back panels
for TEC
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Expected Performance
Transverse momentum
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Impact parameter in r
The CMS Detector
Impact parameter in z
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Electromagnetic Calorimeter
The CMS ECAL consists of a hermetic homogenous
calorimeter made of 61200
lead tungstate (PbWO4) crystals in the central barrel part,
~7324 crystals in each of the two endcaps, and a
preshower detector in front of the endcap crystals.
 Advantages of PbWO4:
1. high density (8.28 g/cm3); 2. shorter rad. Length (.89 cm)
3. short Moliere radius (2.2 cm);
4. fast radiation decay time (80% of the light in 25 ns)
 fine granularity, radiation hardness and compact calor.

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CMS-PbWO4
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Layout of the CMS ECAL
Barrel: |h| < 1.479
360 fold in f
2x85 fold in h
crystal size:
Endcap:
front: 22x22 mm2
1.479< |h| < 3.0
back: 26x26 mm2
1 unit = 5x5 crystals.
length: 230 mm
crystal size:
25.8 X0
length: 220 mm
24.7 X0
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The CMS Detector
front: 28.62x28.62mm2
back: 30x30 mm2
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ECAL Modules
Barrel supermodule (1700 crystals)
Module of 200 crystals
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ECAL-Barrel
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Preshower Detector
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1.653<|h|<2.6; total length 20 cm.
Twp parts: lead radiators and silicon strip sensors.
Taiwan involvement:
NCU: 1/4 silicon
sensors
NTU: System
Motherboards
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Calibration and Resolution
channel-to-channel variation:
use lab. measurements on light yields and photo-dio.
response.  5% in barrel and 10% in endcap
 Beam test
 p0/h →gg in data; w →en.
 Laser Monitor system
 Energy resolution

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Performance of a typical 3x3 crystals
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Status of ECAL Endcaps &
Preshower
Preshower: testing micro modules, motherboards and
preparing to install in April
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Longitudinal View of the CMS Det.
HCAL Barrel
HCAL Endcap
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The CMS Detector
HCAL Forward
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HCAL Barrel (HB)


The HB consists of two half-barrels, each of which contains
18 wedges. Each wedge corresponds to 4 f sectors.
The absorber consists of a 40-mm thick front steel plate,
8 50.5-mm-thick brass plates,
6 56.6-mm-thick
16 h
brass plate, and
a 75-mm-thick
steel back
plate.
5.82 lI at 90
and 10.6 lI at
h=1.3
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wedge
Half barrel
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The HCAL Tower Segmentation
Plastic scintillators
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Endcap Calorimeter (HE)
Yoke
Close to
magnet, nonconducting
absorber has
to be used.

C26000
cartridge brass
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HCAL Endcaps
Scintillator Tray
HE Wedges
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Forward Calorimeter
Situate at |h| = 5
 Detect particles through its Cherenkov light.
Require good EM response (electrons).
 Serve as luminosity monitor
Methods: zero counting and average ET per tower

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Expected Performance
Jet energy resolution
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Muon System

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Identify muons, measure momentum and
trigger muon events.
The muon system consists of three types of
gaseous detectors:
1. four layers of drift tubes in |h|<1.2
2. cathode strip chamber covering |h| to 2.4
3. resistive plate chambers
6 layers in barrel and 3 in endcaps ( |h| < 1.6 )
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Layout of Drift Tube Chambers
One layer is
inside the yoke,
one is outside,
and the other two
are embedded
within the york.
One of the five
wheels.
60 chambers
in the first
three layers
and 70 in the
last.
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Sketch of Drift-Tube Cell
Gas:
85% Ar + 15% CO2
Top and bottom plates are grounded. The voltages
applied to the electrode are +320V for wires, +1800 V
for the strips and -1200 V for the cathode.
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Installation of MB1 on Wheel 2
Each DT chamber is
made of 3 (or 2)
superlayers, each of
which is made of 4
layers of rectangular
drift cells.
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Quarter view of the CMS Detector
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Layout of a CSC & a Schematic
View of a Single Gap
HV: 3.5-3.9 kV
7 trapezoidal panels forming
a 6 gas gaps.
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Gas:
40% Ar + 50% CO2 + 10% CF4
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Resistive Plate Chamber
Advantage: tagging the ionizing
time much shorter than 25ms
 good for triggers
Gas:
96.2% C2H2F4 +
3.5% C2H10 + 0.3% SF6
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Schematic Layout for Barrel RPC
r-f view
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Layout for Endcap RPC
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Expected Performance
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Status of the Muon System
1. DT muons:
a. Install tower electronics
b. Test and commission
2. CSC
a. All chambers and
electronics are installed.
B. Do more tests.
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Summary
 After so many year hardwork, majority of the
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detector and electronics are installed and
commissioned.
Problems and difficulties are foreseen before
collisions.
Tight schedule for Endcap ECAL and Preshower.
Keep testing and looking forward to LHC physics.
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