Muon Detectors in CMS
Darin Acosta
University of Florida
CMS Muon System Design Goals
Exploit full potential of LHC physics with muons
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Higgs decays (4µ
µ, 2µ
µ), SUSY (multi-lepton), top, Z’, B physics
Quarkonia in Heavy Ion collisions
Requires reliable offline muon identification for η < 2.4
Muon trigger capability for η < 2.1, with pT thresholds
from a few GeV to 100 GeV
Precision ∆pT/pT measurements for muons with
pT < 100 GeV :
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~2% resolution in combination with the central tracker
~10% standalone resolution
Muon sign determination with 99% confidence level
up to the LHC kinematic limit (p < 7 TeV)
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
CMS Muon Detectors
Three technologies:
Traditional technology
for low occupancy
Drift Tubes (DT)
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Central coverage: |η
η| < 1.2
Measurement and triggering
12 layers each chamber: 8 in φ, 4 in z
Designed for high
B-fields and neutron
backgrounds up to
1 kHz / cm2
Cathode Strip Chambers (CSC)
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Forward coverage: 0.9 < |η
η| < 2.4
Measurement and triggering
6 layers each chamber: each with φ, z
Resistive Plate Chambers (RPC)
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Central and Forward coverage: |η
η| < 2.1
Redundancy in triggering
2 gaps each chamber, 1 sensitive layer
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
Quarter Cross-Sectional View
(RPC)
(DT)
(CSC)
Rapidity
coverage:
|η
η| < 2.4
4T
solenoid
Muon momentum measurement uses return field of iron yoke
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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DT Barrel Muon System
4 stations in radius
5 wheels in z
250 drift chambers
Staggered in φ
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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DT Chamber – XY View
plates
I-Beams
φ
z
Honeycomb
2 superlayers in φ
1 superlayer in z
Each superlayer has
4 layers of drift-tubes
φ
Dimensions:
27cm
MB1
2
3
MB4
Anode wire +3.6 kV
250cm
Electrode +1.8kV
200 – 400 cm
Ar/CO2 gas mixture
400 ns maximum drift time
250 µm resolution for single cell
100 µm resolution for chamber
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
–1.8 kV
Cathode
13 mm
40 mm
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Darin Acosta
DT Local Trigger
µ
h
9
5
1
B
7
3
x
6
2
4
Bunch & Track Identifier (BTI) uses
shift registers to search for
patterns and to assign correct BX
A
C
D
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Track Correlator (TRACO) correlates
segments in inner and outer superlayers
to improve measurement
ψ
Trigger Server chooses best 2
segments per chamber
µ
Out 0
Out 1
Out 2
Out 3
Out 4
Out 5
Out 6
Out 7
Out 8
Out 9
Out 10
Out 11
Outer
Layer
D = 23.7 cm
Xcal
Kcal
Inner
Layer
In 0
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
In 1
In 2
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CSC Endcap Muon System
2 endcaps
4 stations (disks) in z
2 or 3 rings in radius
540 chambers
6000 m2 active area
2.5 million wires
0.5 million channels
Chambers overlap in φ and η
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
Cathode Strip Chambers
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Up to 3.4 m long, 1.5 m wide
6 planes per chamber
9.5 mm gas gap (per plane)
50 µm wires spaced by 3.2 mm
60 ns maximum drift-time per plane
5 to 16 wires ganged in groups
Wires measure r
6.7 to 16.0 mm strip width
Strips run radially to measure φ
150 µm resolution for chambers
(75 µm in station 1)
muon
cathode
wires
cathode
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Gas: Ar(40%)+CO2(50%)+CF4(10%)
HV ~3.6 kV
B-field up to 3 T in station 1
induced charge
cathode with strips
avalanche
wires
plane cathode
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
100 ns
pre-amp
SCA analog
storage
Amplitude
CSC Electronic Readout
Time
(50 ns/bin)
µ
Planes
ADC
Comparator
(for trigger)
γ-rays from
n background
Strips
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
CSC Local Charged Track Trigger
Cathode strips
Anode Wire Group Hits
Muon Track
Bunch ID and AL
Muon track
Layers
6
5
4
3
2
1
Hit
Layers
N 6
5
Comparator Bits
4
3
2
1
Charges
Wire group hit
Strips
Efficiency to get the right
bunch crossing at the
optimal phase is >98%
Efficiency (%)
~1 mm position resolution
Muon time (ns)
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
A
N
bx:
N 2
e.g.
early
n/γ
hit
Time (b
Resistive Plate Chambers
Double-gap design:
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– HV
2 gaps with common pick-up
Gap width: 2 mm
Bakelite thickness: 2 mm
Bakelite bulk resistivity: 1–2×
×1010 Ω cm
Gas mixtures: C2H2F4 (95%), i-C2H10 (5%)
Operating High Voltage: 8.5 – 9.0 kV
Mode of operation: avalanche, not streamer
3 ns time resolution
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
– HV
RPC Muon System
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612 total chambers
Six barrel stations in radius
p Long strips in barrel ⇒ high
intrinsic noise rate (~50 Hz/cm2)
p Linseed oil applied to surfaces to
reduce noise
p Trigger makes use of all 6 stations
Four endcap stations in z
p Rate capability to 1 kHz/cm2
using avalanche mode
Barrel sector
Endcap sector
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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CMS Muon Momentum Resolution
Standalone
Combined with Tracker
η
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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η
Darin Acosta
CMS Level-1 Muon Trigger
RPC:
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Pattern Comparator Trigger applies
coincidence logic along roads in η and φ
p ∆η × ∆φ = 0.1 × 0.005
DT and CSC:
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“Track-Finders” apply tracking algorithms
and swim track segments to next stations
using fine φ information
p CSC Track-Finder swims in 3D to reduce
backgrounds, handle non-axial B-field
Global Muon Trigger:
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Combines DT and CSC muons with RPC
patterns to reduce rate and improve efficiency
Programmable pT thresholds from 1 to 140 GeV/c
Single and di-muon trigger topologies
p η, φ topology selections, calorimeter isolation
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
Efficiency (%)
Level-1 Trigger Efficiency vs. η
100
80
60
40
DTBX
CSC
RPC
20
0
0
GMT
0.5
1
1.5
2
2.5
ηgen (units)
Overall high efficiency over |η
η| < 2.1 when systems combined
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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pT vs. η
5
p min
pt min
Minimum Trigger Threshold
efficiency
< 95%
< 90%
< 80%
< 50%
4.5
4
3.5
p vs. η
9
efficiency
< 95%
< 90%
< 80%
< 50%
8
7
6
3
5
2.5
4
2
error bars = 1λ = 16cm Fe
= 0.2 GeV (barrel)
= 0.2 GeV tan Θ (endcap)
1.5
1
0
0.5
1
1.5
2
2
2.5
η
Barrel: pT > 4 GeV
CMS Muon Detectors,
error bars = 1λ = 16cm Fe
= 0.2 GeV / sin Θ (barrel)
= 0.2 GeV / cos Θ (endcap)
3
H.I. Workshop, Feb. 2002
0
0.5
1
1.5
Endcap: p > 7 GeV
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2
2.5
η
Level-1 Trigger Rates
pp, L = 1034
Pb-Pb, L = 1027
10
10
10
10
CMS Note 1997/089
integrated trigger rate (Hz)
Trigger Rate (Hz)
whole detector: 0 < | η |< 2.4
6
5
4
10
3
Pb Pb
27
10
-2 -1
L=10 cm s
2
|η|<1.5
10
3
1
10
2
Generated
DT + CSC
RPC
GMT-opt
GMT-and
GMT-or
10
10
-1
-2
1
10
this plot was really hard work...
1
10
1
10
cut
T
10
cut
pt (GeV)
2
p (GeV/c)
pmuon
threshold
(GeV/c)
pT threshold (GeV/c)
T
Sufficient pt resolution to provide handle for rate reduction
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta
Conclusions
CMS has nearly hermetic and redundant muon coverage
over the region |η
η| < 2.4 using 3 detector technologies
Designed to achieve LHC physics goals including
heavy-ions
pT Resolution:
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~10% standalone measurement
~2% when combined with tracker
Single and Di-muon trigger capability for |η
η| < 2.1 with
pT thresholds from few GeV to 100 GeV
Mass production of chambers has already begun
CMS Muon Detectors,
H.I. Workshop, Feb. 2002
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Darin Acosta