Development of an Interaction Trigger in ATLAS
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Development of an Interaction Trigger in ATLAS Regina Kwee CERN / Humboldt-Universität zu Berlin Gentner Day 18.November 2009, CERN
description
Development of an Interaction Trigger in ATLAS. Regina Kwee CERN / Humboldt-Universität zu Berlin. Gentner Day 18.November 2009, CERN. Outline. Motivation Introduction to Minimum Bias Events Designing an Interaction Trigger Trigger Performance Studies Summary and Outlook. - PowerPoint PPT Presentation
Transcript of Development of an Interaction Trigger in ATLAS
Development of an Interaction Trigger in
ATLASRegina Kwee
CERN / Humboldt-Universität zu Berlin
Gentner Day18.November 2009, CERN
Outline
• Motivation • Introduction to Minimum Bias Events• Designing an Interaction Trigger• Trigger Performance Studies• Summary and Outlook
R.Kwee Gentner Day at CERN 2
Motivation
• Operation of LHC with pp-collisions at (nominal) √s = 14 TeV L ≈ 1034 cm-2 s-1
bunch-crossing rate of 25 ns
→ high event rate r = L x σ ≈ 109 inel. pp-collisions/s
R.Kwee 3
• Pile-up expect per bunch-crossing
around 20 piled-up collisions
→ one of the biggest challenges at LHC: understanding QCD-background as basis for each physics analysis
Strategy at ATLAS
• study inelastic interactions at low luminosities L ≈ 1031 cm-2 s-1
larger bunch pitch of 75 ns
→ single pp-collisions
• pp-interaction rate is <<110 % of the bunch-crossings contain a pp-interaction
→ Minimum-Bias Trigger• selects any pp-
interaction• for pp-interaction rate
≈1→ pure random trigger
Gentner Day at CERN
Minimum Bias Measurments
• Physics processes are soft interactions: have low Q2
(small momentum transfer)• perturbative QCD is not
applicable for small Q2 :differential cross-section diverges for pT → 0
→ employ phenomenological models to describe soft QCD
→ Monte-Carlo predictions at LHC energies are highly uncertain!
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pse
ud
ora
pid
ity η
= -
ln(t
an
(θ/2
))
dNch/dη at η = 0
first measurements in ATLAS:
kinematic spectra of charged
particles dNch/dpT and dNch/dη
900 GeV900 GeV 7 TeV7 TeV 14 TeV14 TeV
CERN-OPEN-2008-020
Minimum Bias Events• inelastic cross-section can be sub-divided into its single contributions • prediction strongly depend on the theoretical model, here shown for
pythia 6.214 (phojet 1.12) at 14 TeV:
• dominant: non-diffractive events• precise definition of minimum bias events:given by the trigger system!
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Event TopologiesPythia Generator Level at 14 TeV
R.Kwee 6
pseudorapidity
track multiplicity
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transverse momentum
ndiffsdiffddiff
ndiffsdiffddiff
ndiffsdiffddiff
lower multiplicity in diffractive events (more
forward)
mostly low-pt tracks from all inelastic processes
diffractive events are more
forward directed
charged stable primary
particles
ATLAS – work in progress
ATLAS – work in progress
ATLAS – work in progress
Minimum Bias TriggerATLAS has 2 independent minimum bias triggers:
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Minimum Bias Trigger Scintillators (MBTS) relative simple detector
system: 16 scintillator counters per side between Inner Detector (tracking system) and LAr-calorimeter
cover 2.1< |η| < 3.8 will be used for
commissioning sub-detector systems
has a short lifetime due to radiation damages: 3-4 months at a luminosity of 5*1032 cm-2s-1
Minimum Bias TriggerATLAS has 2 independent minimum bias triggers:
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Inner Detector based Minimum Bias Trigger provide a complementary
approach cover central detector
region |η| < 2.5 trigger requirements:
• introduce as little bias as possible
• suppress efficiently empty bunch-crossing and beam-background events
→ my work!
Minimum Bias Trigger Scintillators (MBTS) relative simple detector
system: 16 scintillator counters per side between Inner Detector (tracking system) and LAr-calorimeter
cover 2.1< |η| < 3.8 will be used for
commissioning sub-detector systems
has a short lifetime due to radiation damages: 3-4 months at a luminosity of 5*1032 cm-2s-1
Minimum Bias TriggerATLAS has 2 independent minimum bias triggers:
R.Kwee Gentner Day at CERN 9
Inner Detector based Minimum Bias Trigger provide a complementary
approach cover central detector
region |η| < 2.5 trigger requirements:
• introduce as little bias as possible
• suppress efficiently empty bunch-crossing and beam-background events
→ my work!
pixel detector
silicon strip detector (SCT)
transition radiation tracker (TRT)
The ATLAS Trigger System
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• The system has been designed to cope with ~ 1.5 PB data per second
• It follows the concept of an „early rejection“ → 3 trigger levels L1: hardware + internal trigger
L1 latency 2.5 μs L2: software trigger
reconstructs physics objectsfound by L1, tracks.
L2 latency 10 ms EF: software trigger
uses more detailed calibrations constants as L2, else same as L2
EF latency ~ 1 second
Generally „region-of-interests“,
RoI‘s, are processed –unlike in
minimum bias triggers!
ID based Minimum Bias Trigger
• L1: random trigger on filled bunches → avoids bias
• L2: SpacePointCounter forms 3d-detector hits in whole
pixel and SCT (spacepoints) detector
operate just above noise level → suppress empty bunch-crossing events
needs to be robust against HV trips → dynamic masking of noisy modules
• EF: TrackCounter reconstruct silicon low-pt-tracks require one track close to the IP →
suppress beam-gas/-halo events
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Features/Status algorithms are highly
configurable → provides flexibility to react on different beam background conditions
a back-up trigger using only TRT hits at L2 has been developed (TRT proved to be very stable during first beam operations)
all minbias triggers have already taken and still take (cosmic) data!
Performance Studies
• trigger efficiency at L2
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ndiffsdiffddiff
empty
cut at 3 SCT spacepoints at L2
suppresses all empty events
cut at 3 SCT spacepoints at L2
suppresses all empty events
SCT spacepoints
An SCT spacepoints is formed by a coincidence of 2 strips → intrinsic noise suppression
An SCT spacepoints is formed by a coincidence of 2 strips → intrinsic noise suppression
ATLAS – work in progress
ATLAS – work in progress
Performance Studies
• trigger efficiency at L2
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cut at 3 SCT spacepoints at L2
suppresses all empty events
cut at 3 SCT spacepoints at L2
suppresses all empty events
cut at 3 SCT spacepoints at L2 +
additional cut at 1 track with |z0| < 200 mm at EF
cut at 3 SCT spacepoints at L2 +
additional cut at 1 track with |z0| < 200 mm at EF
• trigger efficiency at EF
ATLAS – work in progress
ATLAS – work in progress
Performance Studies
• trigger bias→ change in distribution (e.g. η, pT, Nch) which is introduced by the trigger condition (here shown for 3 SCT spacepoints)
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ndiffsdiffddiff
ndiffsdiffddiff
no bias expected in η (measure within ID range)
ID
more studies needed formultiplicity dependence
ATLAS – work in progress
ATLAS – work in progress
Summary and Outlook
• minimum bias studies are needed to understand properties of inelastic interactions → they form dominant QCD background in LHC enviroment
• minimum bias events will form pile-up at high luminosity runs→ study at low luminosities, designed an interaction trigger
• Thesis plan (adapted to new LHC schedule)→ prepare for detector and trigger commissioning with minimum bias triggers
• more performance studies ongoing → will determine the employment of (all) minbias triggers
• functionality provided, looking forward for collsions!
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Danksagung
Many thanks to my supervisorsNick Ellis (CERN) and Hermann Kolanoski (Humboldt-University)
and my former supervisorKlaus Mönig (DESY)
as well as to my ATLAS collegues and CMS friends
and the BMBF for creating the Wolfgang-Genter-Program!R.Kwee Gentner Day at CERN 16
