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

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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…

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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.

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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

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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)

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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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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

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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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Added at the last second Spectra with perfect momentum resolution (dashed line),

10%, 30%, and 50%

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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

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Full simulation CMS momentum resolution

Multiple scattering in iron: constant term ~8 %Central tracker constant term much lower

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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

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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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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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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

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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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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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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

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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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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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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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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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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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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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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/