the cms level 1 muon trigger
DESCRIPTION
The CMS Level 1 Muon Trigger. Jay Hauser –UCLA Slides from Frank Taylor (MIT), Darin Acosta (UF), Marco Dallavalle (Bologna), S.Tanaka (KEK), Claudio Wulz (Vienna). 4T solenoid. Muon chambers. Forward calorimeter. Silicon Strip & Pixel Tracker. PbWO 4 Crystals. - PowerPoint PPT PresentationTRANSCRIPT
The CMS Level 1 Muon Trigger
Jay Hauser –UCLASlides from Frank Taylor (MIT), Darin Acosta (UF), Marco Dallavalle (Bologna), S.Tanaka (KEK), Claudio Wulz (Vienna)
PbWO4 Crystals
Muon chambers
Silicon Strip & Pixel Tracker
4T solenoid
Hadronic calorimeterBrass/Scintillator
Forward calorimeter
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 2
Z′→ee, µµ: CMS Discovery Potential
“1 month”
“1 year”
Tevatron reach
2 Different models
2 different decay channels
Probe new territory in first month (maybe days if lucky!)
“1 day” At canonical LHC luminosity…
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 3
Level 1 muon trigger
Why high-momentum leptons? QCD (strong interaction) provides many jets and large energy
deposition, but generally not signatures of electroweak processes So signatures with large energy deposition face large QCD
backgrounds Electrons, muons, taus are signatures of W, Z bosons, top quarks,
higgs bosons, SUSY decays, etc., but are rare from QCD. Muons especially:
Excellent background reduction possible. Excellent momentum resolution for invariant masses etc.
Muon triggering: You must catch the fish before you can eat it. Typical W muon transverse momentum <40 GeV/c. Wish to
trigger above 15 or 20 GeV/c, typically.
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 4
Outline
The three types of muon detectors in CMS: Drift Tubes (DT) Cathode Strip Chambers (CSC) Resistive Plate Chambers (RPC)
Overview of triggering at the LHC Level 1 muon trigger algorithms Implementation in electronics Private concerns
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 5
Introduction
All modern collider detectors have these elements covering close to 4 solid angle…
Simplest muon detector: register a “hit” on the outside (following many of material)
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 6
CMS muons at =0, i.e. 90o to beam axis
Track curvature in return field of solenoid used for muon system
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The CMS Level 1 Muon Trigger 7
Generic types of muon systems
Simplest muon system: register a “hit” Useful if P measured by central tracker: greatly reduced
rate compared to pions Next simplest: hits pointing to the interaction region
Detectors outside the magnetic flux return, e.g. CDF Reduces non-interaction backgrounds: cosmic rays,
beam halo muons, neutron-induced hits CMS & Atlas: measure P using muon system alone
Do not necessarily need central tracker, so CMS quickly identifies muons within microseconds
Also reduces high rate of real but low momentum muons
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 8
Required momentum resolution for trigger
Left: efficiency curves for 10%, 30%, 50% curvature (1/Pt) resolution Right: muon trigger rate (Hz) per unit rapidity at 90% eff. point Note CMS TN-94/261 20% desirable, 30% acceptable
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The CMS Level 1 Muon Trigger 9
Added at the last second Spectra with perfect momentum resolution (dashed line),
10%, 30%, and 50%
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The CMS Level 1 Muon Trigger 10
Momentum resolution “theory” Fractional momentum resolution:
Flat at low momenta due to multiple coulomb scattering Rises at high momenta (low curvature) due to measurement error
.!)(
1)(
)()(
0
constPt
p
Px
PtxPt
p
MS
MS
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 11
Full simulation CMS momentum resolution
Multiple scattering in iron: constant term ~8 %Central tracker constant term much lower
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The CMS Level 1 Muon Trigger 12
CMS Muon System
Three types of
gaseous detectors:
• Drift Tubes in Barrel
(DTs)
• Cathode Strip
Chambers in
Endcaps (CSCs)
• Resistive Plate
Chambers (RPCs) in
both barrel and
endcaps
• Coverage: || < 2.4
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 13
CMS Muon Detectors
For triggering and precision position/angle measurement: Drift Tubes (DT)
Inexpensive large-area chambers Large drift cells and long drift times
Cathode Strip Chambers (CSC) Proportional chambers with 2.5-3.1mm wire spacing Cathode strips perpendicular to wires get ~200 micron position
by interpolating induced charge
Just for triggering: Resistive Plate Chambers (RPC)
No wires, narrow high-voltage gaps for very fast signal Coarse pad-type segmentation
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The CMS Level 1 Muon Trigger 14
Drift Tube (CMS)
12 layers per station: 4 axial, 4 longitudinal, thick
honeycomb, 4 axial Gas : Ar(85) + CO2(15) HV = 3.6 kV Single cell space resolution:
< 250μm
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The CMS Level 1 Muon Trigger 15
UCSB Nov. 16, 2007
The CMS Level 1 Muon Trigger 16
CMS CSC EndcapsCMS CSC Endcaps
• 468 CSCs of 7 different types/sizes• > 2,000,000 wires (50 m)• 6,000 m2 sensitive area• 1 kHz/cm2 rates
UCSB Nov. 16, 2007
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About the CMS Cathode Strip Chambers
Mechanical design of the CMS CSC chambers (exploded view)Principle of CSC operation
(invented by Charpak 1979)
x/w ~ q/q ~ 1% possible
With w=1 cm x ~ 0.1mm
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The CMS Level 1 Muon Trigger 18
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The CMS Level 1 Muon Trigger 19
Cathode Strip Chamber details
Wires spaced at 3.2mm, ganged in groups of ~10 wires Drift times 0-50 ns with small tail up to 75ns 6 layers of information for both anodes and cathodes Anodes:
Preamp has constant-fraction discriminator to eliminate time slewing Hits recorded at 1 bx (25ns) intervals. Fine delay adjustment (2.2ns steps) for various times-of-flight Time history (16 bx) recorded for each wire group
Cathodes: Low noise but slow preamp (150 ns peaking time) Precision charge information stored every 50 ns Trigger comparators find position to ½-strip on each layer
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Resistive Plate Chambers (RPC)
Resistive Plate Chambers are gaseous, self-quenching parallel-plate detectors.
They are built from a pair of electrically transparent bakelite plates separated by small spacers.
Signal are induced capacitively on external readout strips.
Double gap chambers.
Gas: C2H2F4:isoC4H10 (97:3)
HV : 9kV
Double gap chambers.
Gas: C2H2F4:isoC4H10 (97:3)
HV : 9kV
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The CMS Level 1 Muon Trigger 21
RPC – used in both CMS & ATLAS
• Intrinsically fast response ~ 3 ns
• R&D effort to understand long term characteristics• Rate handling depends on electrode resistivity
• observed to increase by 2 orders of magnitude
3 mm gap
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LHC trigger overview I
CMS Level 1 trigger (all types) must reduce the rate 400:1 based on crossings
LHC bunches collide at 40 MHz Front-end readout/data acquisition can handle <100 kHz
8000:1 based on collisions (~20 collisions/crossing) Contrast with
a) No trigger: e.g. bubble chambers took a picture every expansion
b) Simple trigger case, e.g. e+e- experiments that recorded data if any tracks were found in central tracking chamber
What should trigger look for? High-momentum electrons, photons, muons, (taus), jets, missing-Et More than one of these (at lower momenta, perhaps)
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LHC trigger overview II – how to Triggering takes much more time than the 25ns between
crossings (bx) Speed of light c = 7.5 m / bx Calculations:
Electrons, photons, and jets: energy clusters are calculated Missing-Et: all calorimeter energies are summed Muons: tracks are found and Pt calculated
Path to electronics cavern is ~100 m (not straight-line) Therefore, store temporary data while trigger does its
calculations…
Detector n front-end Local trigger
electronicsGlobal trigger electronics
0 Time (bx) 128
100 bx
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LHC trigger overview III: CMS specifics
Front-end data pipelines Trigger electronics makes a single event decision
(~0.1%) KEEP or (99.9%) DUMP this crossing Front-end electronics (if KEEP)
Freezes interesting data Starts to send data blocks ~asynchronously through DAQ Data blocks include ID of which trigger number and which LHC bunch
crossing (0-3563) DAQ system
Sends data blocks for a given event into one computer in the farm Further selections applied (Level 2 trigger)
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Event decision: Global Trigger crate
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Level-1 Trigger Scheme
Boxes represent electronics boards or systems
Calorimeters for electrons, photons, jets, MET Muon detectors
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Muon Level 1 trigger
Trigger on high Pt muons based on track curvature in muon system of DT, CSC, RPC
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Trigger Hardware Organization
Calorimeter Trigger
RPC Trigger CSC TriggerDT Trigger
CAL Readout
PACT Pattern Comparator
BTI Bunch & Time ID
Wire Cards
Strip Cards
Motherboard
Trigger Server
TRACO Track Correlator
Port Card
DT Barrel Track Finder
CSC Endcap Track Finder
CSC SorterDT SorterRPC Sorter
CAL Regional Trigger
Global Muon Trigger
Global Level 1 Trigger
Global Calo Trigger
4
444
MIP & Quiet Bits
Match muons, eliminate ghosts
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Trigger boards housed in on-chamber MiniCrates•A single large synchronous 40 MHz digital system of 55000 ASICs
•Two best muon segments on output from each chamber:
DT “local trigger”
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Basis of DT triggering Bunch and Track Identifier (BTI) ASIC, 1 per 4 wires, 55000 in the system Any 3 hits define a straight line and a time stamp E.g. max. drift time = Tmax = (TA+2TB+TC) /2 does not depend on track angle or
drift distance If 4 layers all agree, HTRG==high quality, else if 3 layers agree (delta ray?),
LTRG== low quality 80 MHz clocking 1.25mm bin sizes Ghost cancellation for LTRG in nearby crossings in time
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BTI performance Overall efficiency about 95%
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• Put out two best muon segments from each chamber• Correlate inner and outer superlayers• HH, HL, LL, and uncorrelated muon segments
• ~44% HH, 23% HL, 3% LL, 17% singles, 3% nothing
TRack Correlator (TRACO) and Trigger Server
UCSB Nov. 16, 2007
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BTI, TRACO, and TS trigger electronics, etc.
DT minicrates
An average MC has 15 boards:6 ROB, 6 TRB, SB/CCB, LB
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Tower Near
Sector Collector crates
TTC fiber ck, LV1A, bgo
DCS fibersTRIG data LVDS
TDC data LVDS
Local DAQ
LV 5V;3.3V
fibers to DDU
fibers to DTTF
TTC ck,LV1A,bgo local-LV1A (veto)
local-LV1A (veto)
CMS trigger streamCMS DAQ stream
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The CMS Level 1 Muon Trigger 35
Drift Tube In-Situ Local Commissioning
YB0
S10S11
S12
S01
About 80% commissioned, YB+2 to go
CSC underground commissioning just starting
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DT “regional” trigger• Accepts DT segments
from 4 stations in a sector + neighbours
• Accepts also CSC segments in “overlap” region
• Combines segments into full tracks
• Assigns Pt,,,quality to each muon track
• Accepts DT segments from 4 stations in a sector + neighbours
• Accepts also CSC segments in “overlap” region
• Combines segments into full tracks
• Assigns Pt,,,quality to each muon track
Sector Processor ( PHI Track Finder) (J.Ero)
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DTTF Racks
TrackFinderCrates
CentralCrate
Test Crate
TF Rack TF Rack Central Rack
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CSC Muon Triggering
Trigger primitives are wire and strip segments Wires give 25ns bunch crossing Strips give precision information, time matched +-1 bx to wires
Link trigger primitives into tracks Assign pT, , and Send highest quality tracks to Global muon trigger
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CSC cathode trigger primitives Comparator ASIC finds half-strips hit FPGA (programmable) finds 6-layer patterns
Patterns are different, depending on Pt of the muon Pt threshold around 3 GeV/c
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CSC anode trigger primitives
FPGA looks for a pattern of hits
Anodes “non-bend plane” Pattern the same for all muons
from interaction point Bunch ID
Look for crossing where 2nd hit arrives
Various times-of-flight: Anode fine delays (2.2ns steps)
optimize ID of correct bunch crossing
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The CMS Level 1 Muon Trigger 41
CSC Track Finder Links the CSC muon trigger primitives into a track Difference in coordinate between stations gives
transverse momentum (left plot from TDR)
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Basis of CSC track-finding logic
Road Finder:
•Check if is consistent with bend angle measured at each station.
•Check if in allowed range for each window.
Quality Assignment Unit:
•Assigns final quality of extrapolation by looking at output from and road finders and the track segment quality
Extrapolation Units utilize 3-D information for track-
finding.
IP
IP
Road Finder:
•Check if track segment is in allowed trigger region in
•Check if and bend angle are consistent with a track originating at the collision vertex.
1 2
1
2
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The CMS Level 1 Muon Trigger 43
PT measurement (simulated)
IP
1
2
Pt LUT
4 MBPT
Residual Plot
Res=22%
Constant Pt Contours for: 3, 5 ,and 10 GeV s.
Pt = f(, , )
Use information from up to 3 chambers
Look-up tables use: 12, 23, and
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Single and Double Rates (TDR)
L=1034 cm-2s-1
L=1033 cm-2s-1
Target Rates
15 GeV threshold:
Requires 3-station PT measurement at high luminosity
Rat
e (k
Hz)
/
un
it r
apid
ity
/ L
=10
34
Threshold defined at 50% efficiency
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Rate ‘Cross section’ vs. PT - ATLASb
/GeV
ddPtd ~ 4.4 x 103
Pt4.7
b/GeV
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Anode timing: test beam results
Efficiency of correct bunch taggingversus rate of random hits per wire group
Probability for tagging correct bunch-crossing vs. shift betweenALCT board clock and LHC clock
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The CMS Level 1 Muon Trigger 47
Comparator and cathode pattern performance in test beam 2003
Left: position resolution Right: efficiencies to find the correct position versus cluster charge
Low to high: correct half-strip, correct full strip, and correct or adjacent (±1) half-strip.
Bottom: efficiency to find a cathode trigger pattern vs. chamber tilt angle
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The CMS Level 1 Muon Trigger 48
1999 test beam for CSC:Gamma Irradiation Facility tests
Study LHC-like neutron background conditions (gamma ray source) Left: one event, charge per strip as a function of time (into page) Right: comparator performance versus irradiation Perfect resolution
0.29 half-stripNo source:
=0.36 half-strips
CMS max rate: =0.38 half-strips
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CSC Synchronization: predicting timing based on cable lengths
Plot measured value vs. predicted value… Line indicates equal values…
CFEB rx communication phase: ALCT tx communication phase:
~ 2*(ALCT-TMB cable length)~ 2*(CFEB-TMB cable length)
• 2 ns per setting
Communication data are consistent with model
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Predictions of anode fine timing delays
Including cosmic ray time-of-flight corrections
Plot differences between predicted and measured settings for 480 AFEBs…
Note: time-of-flight corrections should be simpler for muons from the CMS Interaction Region than for cosmic rays…
RMS=2.0 bins (~4.4 ns)
Model – data (2.2nsec bins)
• Good agreement of the model with the data for minus side slice test
• Predictions exist for 468 chambers
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Trigger primitive efficiencies online
• Simple “N-layer” trigger configuration• Get immediate feedback from TMB counters
the counters are read out by VME in real time
• Elog 2592 example: (ALCT) = N(ALCT*CLCT) / N(CLCT) = 38022/38040 = 0.9995 (CLCT) = N(ALCT*CLCT) / N(ALCT) = 38022/38399 = 0.9901
Chamber: 2/1/8 2/1/9 2/1/10 2/2/15 2/2/16 2/2/17 2/2/18 2/2/19
ALCT eff: 0.999 0.999 0.999 0.998 0.999 0.998 0.998 0.998
CLCT eff. 0.991 0.990 0.993 0.766 0.988 0.992 0.991 0.992
Chamber: 3/1/8 3/1/9 3/1/10 3/2/15 3/2/16 3/2/17 3/2/18 3/2/19
ALCT eff: 0.999 1.000 1.000 0.999 0.999 0.998 0.999 0.999
CLCT eff. 0.993 0.987 0.995 0.998 0.993 0.998 0.992 0.998
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The CMS Level 1 Muon Trigger 52
Full disclosure: missing from this talk
Discussion of the RPC trigger Note that singles rates may fluctuate widely depending on chamber
noise as well as beam conditions Performance of DT trigger: efficiency and momentum
resolution versus Pt and eta Discussion of effect of high neutron background rates in the
forward region Discussion of beam halo backgrounds in the forward region
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The CMS Level 1 Muon Trigger 53
Good sources of information Surprisingly, Technical Design Reports:
Muon TDR, CERN/LHCC 97-32 (December 1997) Trigger TDR, CERN/LHCC 2000-38 (December 2000)
CSC electronics Twiki page https://twiki.cern.ch/twiki/bin/view/CMS/CSCelectronics
CMS muon trigger home page (very outdated, basics OK) http://cmsdoc.cern.ch/cms/TRIDAS/mutrig/html/