The Muon Trigger in ATLAS

Sez. di Lecce

Universita` degli Studi del Salento

The Muon Trigger in ATLAS

Giovanni SiragusaOn behalf of the ATLAS Muon Trigger group

2007 April 24 Giovanni Siragusa - ACAT 2007

2

Outline• The LHC and Trigger system requirements• The ATLAS detector:

– The Muon Spectrometer– The Trigger System

• Muon Trigger System architecture and performance:

– Level 1– Level 2– Event Filter

• Trigger Commissioning• Conclusions


3

LHCCenter of Mass Energy:– 14 TeV (p-p)

Design Luminosity:– L = 1034 cm-2s-1

Integrated Luminosity per year (@ 1034) Ldt 100 fb-1

The cross sections of interesting physics processes are highly suppressed w.r.t. tot

– Calibrations and precision physics

• Leptonic W decay– New Physics

• Higgs boson production

10-6

10-9

Event rate at LHC (@ design lumi) is ~1 GHz– 40 MHz (BC frequency) x 23 interactions per BC

Maximum allowed acquisition rate is ~200 Hz– Bandwidth ~ 300 MByte/s

– Event Size ~ 1.5 MByte Trigger with high

rejection capability

Trigger with high

selection efficiency


4 The ATLAS detector

General purpose detector

– Capability to observe a wide range of Physics processes

Study of the Physics of the Standard Model and beyond it

– SUSY, Extra Dimensions

– Any exotic scenario of new Physics at TeV energy scale

First collisions for physics in 2008

Now commissioning detector and trigger with cosmic rays

Inner Detector:

– Silicon detectors: pixel, micro-strips

– TRT

– Thin superconducting magnet with a solenoidal field of 2T

Electro Magnetic Calorimeter

– Sampling Pb - Argon

(liquid @ 80K)

Hadronic Calorimeter

– Scintillation tiles

Muon Spectrometer (MS)

– Toroidal magnetic field in air (bending in the z- plane

– High resolution

(e.g. ~50 m sagitta)

Physics

Design


5The ATLAS Muon Spectrometer

CSCCSC

RPCRPC

TGCTGCMDTMDT

Design resolution on the sagitta measurement:

50 m

10% of relative resolution for muons with

pT ~ 1 TeV

•High-pT muons are an important signature for many known (and predicted) processes at TeV energy scale•Low-pT muons are the major source of Level1 trigger rate

Muons loose in the calorimetric system ~3GeVMuons with pT above 3 GeV arrive at the MS

1. Precise measurements of high pT muons

2. Identification of low pT muons

Inhomogeneous toroidal magnetic field in air

1. Max field 4T2. Multiple

scattering

suppression


6

~100 kHz

~2 kHz

~200 Hz

2.5 s

10 ms

2 s

The ATLAS Trigger systemLevel 1 (hardware)•Coarse granularity data from CALO and MUON detectors•Selects Regions Of Interest (ROI) in the detector

Level 2 (software)•Algorithms optimized for fast rejection•It accesses full granularity data, only inside ROIs

Event Filter (software)•Uses the Offline algorithms•It can access data from the entire event (after the Event builder)•Seeding strategy

Reduced bandwidth at Level 2 input

Full event access


7 The ATLAS Muon Trigger

FasFastt

B Physics processor

TileTile

CombComb

TrigDiMuoTrigDiMuonn

IsolIsolComCombb

10 ms latency time

TrigMooreTrigMoore

MOOREMOORE

2 s latency time

Level 1Level 1 SimulationSimulation

capability to run on the HLT farms to optimize the

hardware selection

Level 2 SelectionLevel 2 Selection EF SelectionEF Selection

RPCRPC

TGCTGC

CTPICTPI CTPCTP

2.5 s latency time

MuId SAMuId SA

MuId COMBMuId COMB

MSMS

CALOCALO

IDID

H i g h L e v e l T r i g g e r

High-pT physics

Low-pT physics


8 Level 1 selection

The selection is based on the definition of allowed geometrical roads, the

Coincidence Windows, whose center is defined by the infinite momentum track

The width of the road defines a pT threshold

ToroidToroidToroidToroid

Three pT thresholds can be applied for a Level 1 configuration

• 6, 8, 10 GeV (Low-pT)• 11, 20, 40 GeV (High-pT)

The Coincidence Window is implemented with FPGA

Can be reconfigured to optimize the algorithm for different running conditions


9Level 1: Acceptance

~30% of barrel inefficiencies are due to feet and elevator sectors

3-station coincidencetrigger efficiency of TGC

Endcap6 GeV20 GeV

Level 1 barrel acceptance:Level 1 barrel acceptance:•83%83% Low-p Low-pTT

•79%79% High-p High-pTT

Level 1 simulation results

Barrel Low pT OK, NO High pT

NO Trigger

single muons, pT 100 GeV


10

pT

Level 1: Efficiency curves

1. The value at the plateau is due to the acceptance

2. The sharpness of the ramp-up is a function of the resolution

3. The efficiency above the threshold is due to fake tracks impact on the trigger rates

•6 GeV

•8 GeV

•10 GeV

Low-pT thresholds

•11 GeV

•20 GeV

•40 GeV

High-pT thresholds

Level 1 simulation

6 GeV20 GeV

Endcap

0.4

0.8

Barrel


11 Level 1: Rates

Ri Ld i

dpTpT _ inf

pT _cutoff

(pT ) dpT

Inclusive μ cross-section @ LHC

(prompt μ and /K decay)

•6 GeV

•8 GeV

•10 GeV

Level 1 efficiency

Level 1 simulation

threshold [GeV]

Rat

e [H

z]

Expected single muon trigger rates at a luminosity of 1033 cm-2s-1

The cosmic configuration is showed as an effective threshold of 3 GeV

Barrel only


12

FastConfirm the Level-1 trigger with a

more precise pT estimation within a “Region of interest (RoI)”

Contribute to the global Level-2 decision.

“Global Pattern Recognition” involving trigger chambers and positions of MDT tubes (no use of drift time)

“Track fit” involving drift time measurements, performed for each MDT chamber

Fast “pT estimate” via a Look-up-table (LUT) with no use of time consuming fit methods

Refine the Fast pT using ID data

– more sharpness @ 6 GeV threshold

Identify the muon track in ID to ease the search for secondary muon tracks.

High reduction on the /K was obtained thanks to the pT match

Comb

Level 2

Isol uses calorimetric information to select isolated muons from W and Z decays

Tile identifies low pT muons using the measure of the energy loss in the calorimeters

Threshold Fast - Hypo Comb - Hypo

Low-pT

(6 GeV)

99.5 – 98.5

(10 GeV single )

96.3 – 96.1

(10 GeV single )

High-pT

(20 GeV)

99.6 – 96.7

(50 GeV single )

95.0 – 94.8

(50 GeV single )

Efficiencies


13 Level 2: Resolution

Barrel

End Cap

Fas

t

Comb

idScan

50 GeV 10 GeV 5 GeV


14

Event FilterThe Muon Event Filter

(TrigMoore) uses the same Algorithms as the Offline.

The Feature Extraction Algorithms (FEX) calculate the muon track parameters

Operating configurations:

– Seeded from Level 2 (Standard)

– Seeded from Level1 (Trigger studies)

– Unseeded (Full Event Reconstruction)

The Trigger Decision operates via the insertion (in any point of the trigger chain) of the Hypothesis Algorithms (Hypo)

MooAlgsMooMakeRoadsMooMakeTracks…

MooStatistics

MooEvent

TrigMoore

MooHLTAlg

MuonIdentification

Hypo and FEX define a trigger sequenceEvents are selected if they satisfy an item in the trigger menu

Offline


15

TrigMooreMOORE

– Reconstruction of the tracks in the Muon Spectrometer (MS)

Muid Stand Alone– Propagation of the tracks to the

Impact Point(using calorimetric measurement)

– Good pT resolution (less than 10% at 1 TeV)

Muid Combined– Combines the MS tracks with

Inner Detector (ID) tracks– Refines pT resolution

• ID improves resolution at low pT (less than 50 GeV)

• MS improves resolution at high pT

Moore AlgsMoore Algs

MuIdStandAloneMuIdStandAloneAlgs Algs

Seeding AlgsSeeding Algs

MuIdCombinedMuIdCombinedAlgs Algs

HypoHypo

HypoHypo

HypoHypo

CALOCALO

IDID


16

< 2.5

pT resolutions

100505

Single muonsTrigMoore: Resolution

The low amount of material in the Muon Spectrometer reduces the multiple scattering

The resolution performances are highly related to the chambers alignment

Single muons pT resolution is under 4%(for pT < 100 GeV)


17

Inefficiencies in the feet region

40 GeV muons selection efficiency

40 GeV muons selection efficiency

Barrel – End Cap transition

TrigMoore: EfficiencyEfficiency is defined with respect to the seeding level

Here the efficiency is referred to Level 2 (standard configuration)

High efficiency (95%) for muons up to 1 TeV transverse momentum


18

EF: Rates

10 33 cm -2s -1

At low pT the single muon rate is dominated by /K decays in flight

Muon sources6 GeV/c threshold

kHz/K/K 1.9

BB 0.67

CC 0.34

WW 0.003

TT negligible

TotalTotal 3.0 kHz3.0 kHz

Barrelmu(6) 3.0 kHzmu(20) 25 Hz

End-Capmu(6) 3.1 kHzmu(20) 27 Hz

Total (@ 1033 cm-2s-1):

mu(6) 6.1 kHz mu(20) 52 Hz

Bar

rel o

nly


19 Cavern backgroundThe p-p collisions generate a radiation that

interacts with the detector’s and accelerator’s materials

As a consequence neutral and charged particles are released(photons and neutrons)

– particles diffuse like a gas in the cavern, giving rise to time uncorrelated hits (fake tracks)

– This effect increases linearly with luminosity

Safety Factor (SF) = a factor that multiplies nominal background – it takes care of possible underestimations of the background

Co

un

tin

g r

ate

s (

kH

z/c

m2)10-1

10-2

10-3

Background from neutral and charged

L=1034cm-2s-1

Outer Station

Inner Station

Middle Station

Fake track prob. on single muon, SF=x5Fake track prob. on single muon events

x10

x5x2

no

No pT threshold applied !

Geant3Geant4


20 Trigger on complex events

The muon trigger selection has been performed on complex events (top events are shown)

Realistic simulation of trigger is included in Physics Analysis

Started the Monitoring and Data Quality activity to be ready for real data taking

Muons absorbed in Calorimeters

Feet region

Crack


21

Misaligned Geometry

Comparison of the resolutions of the EF algorithms for nominal and “real” geometry (material distortions, inhomogeneous magnetic field)

The Computing System Commissioning will be based on simulated data that will reproduce in the maximum detail real data

nominal-nominal misal-misal

• Blue = MOORE• Red = MuidSA• Magenta= MuidCB

misal-nominal


22

Trigger Commissioning:Run in February 2007 with cosmics data

Trigger (Level 1 + HLT) run OnlineUnfortunately MDT chambers off. Tested HLT workflow and architecture

RPC Chambers of Sector 13 provided cosmic-ray trigger signalFull hardware Central Trigger Processing chain in placeFull hardware and software for Level 2 handling (processors, readout links, HLT sw suite)Version of the Level 2 algorithm optimized for cosmic rays identification has been successfully running and triggering

First Cosmic Run

Efficiency (plateau)

pT @ 90%

83.3% 3.5 GeV

x

y

Sector 13

UX15

Reconstructed Muon Eta

Reconstructed Muon Phi

Level 2 – RPC only

Level 1 cosmic setting:opening the concidence windows as much as possible

•minimum Level1 threshold value is limited by RPC cabling

Level 1

simulation


23

Conclusions

• Next year we will have first collisions at LHC

• First test on cosmic data have been performed and all the systems are extensively checked and tested

• All the studies on the muon trigger indicate that the major requirements are satisfied

• Optimization of the trigger chain will be possible in the first stages of LHC operation (low luminosity)

• The ATLAS trigger system will be ready for Physics and data taking


24

Backup


25

LVL1 barrel: Cosmic setting

pT [GeV]

Cosmic setting is obtained by opening the concidence windows as much as possible, minimum lvl1 threshold value is limited by RPC connectivity. It have been used for Sector 13 data taking and for the future trigger commissioning

Level 1 simulation


26LVL1 barrel : Low-pT Trigger rates

Using the Level-1 Efficiency curves we may

estimate the rates with different threshold.

Muon sources

10 GeV10 GeV threshold

Lumi=1033


Lumi=1033


Lumi=1033


Lumi=1033

"Cosmic""Cosmic"thresholdLumi=1033

/K 5400 Hz 8830 Hz 10470 Hz 21800 Hz 62500 Hz

b 920 Hz 1160 Hz 1650 Hz 2220 Hz 3360 Hz

c 510 Hz 660 Hz 970 Hz 1400 Hz 2400 Hz

W 3 Hz 3 Hz 3 Hz 3 Hz 3 Hz

t Negligible Negligible Negligible Negligible Negligible

Sum 6.8 kHz 11 kHz 13 kHz 25.5 kHz 68.3 kHz

Level 1 simulation


27 Level 1 barrel :High-pT Trigger rates

Muon sources

11 11 GeVGeV threshold

Lumi=1034

2020 GeV GeV threshold

Lumi=1034

/K 7420 Hz 3540 Hz

b 2330 Hz 760 Hz

c 1100 Hz 340 Hz

W 28 Hz 26 Hz

t Negligible Negligible

Sum 12 kHz 4.7 kHz

Preliminary

Level 1 simulation


28

Level 1 endcap: Rates

Muon Sources

6 GeV6 GeVthreshold

Lumi=1033

/K 5.9

b 1.8

c 1.0

W negligible

t negligible

Sum 8.7 KHz

20 GeV20 GeV thresholdLumi=1034

40 GeV40 GeV thresholdLumi=1034

6.9 3.60

1.3 0.48

0.7 0.27

0.04 0.04

negligible negligible

8.9 KHz 4.4 KHz

Level 1 simulation


29 Level 2: Efficiency

GeVFast

eff.

6

GeV

Comb

eff.

6

GeV

Fast

eff.20

GeVComb

eff.

20

GeV

5 98.2% 20.5% 18.7% 0.2% ---- ---- ---- ----

10 99.5% 98.5% 96.3% 96.1% 99.5% 3.3% 3.2% < 0.1%

50 99.6% 98.8% 97% 97% 99.6% 96.7% 95.0% 94.8%

100 99.6% 98.5% 96.7% 96.7% 99.6% 96.5% 94.9% 94.9%

300 98.8% 98.1% 94.9% 94.9% 98.8% 94.2% 92.6% 92.6%

Low - pT High - pT

Hypo off Hypo on

The Efficiency is shown for FEX algorithm and after the HYPOTHESIS algorithm cut

Documents

The Muon Trigger in ATLAS