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Optimizing Selection and Sensitivity Results for VV->lvqq, 6.5 pb-1,
13 TeV Data Hallie Stidham Supervisor: Dr. Kalliopi Iordanidou 2015 Columbia University REU July 30, 2015
Home Institution: High Point University
1
July 30, 2015 Hallie Stidham
Summary 2
• Introduction • CERN and the Large Hadron Collider • The ATLAS Experiment • Particles
• Data and Monte Carlo Samples • VV Resonance and Selection
• Resonance and Decay • Selection
• Selection Optimization • Selection & Extrapolations • Significance Plots & Trigger Studies • Multivariate Analysis • Topology Plots
• Conclusions
July 30, 2015 Hallie Stidham
CERN
• In 1954 twelve countries ratified the European Council for Nuclear Research, CERN
• Located near Geneva, Switzerland along Franco-Swiss border
• Today there are 21 member states • Focused on particle physics research • Home to the Large Hadron Collider (LHC)
July 30, 2015 Hallie Stidham
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Large Hadron Collider • Largest and most powerful particle accelerator
in the world • 27 kilometer ring that holds superconducting
magnets • High energy particle beams travel in opposite
directions • Collisions at 4 main particle detectors, ALICE
ATLAS, CMS, LHCb • Run 1: March 2010-February 2013 • Run 2: April 2015-present
July 30, 2015 Hallie Stidham
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The ATLAS Experiment
• “A Toroidal LHC ApparatuS”, large general purpose particle detector
• 7,000 tonnes, 46m x 25m x 25m • Four major components ▫ Inner Detector: measures momentum of charged
particles ▫ Calorimeter: measures energies carried by
particles ▫ Muon Spectrometer: identifies and measures
momenta of muons ▫ Magnet System: bends charged particles for
momentum measurement July 30, 2015 Hallie Stidham
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Particles
• Leptons ▫ Elementary particles, do not undergo strong
interactions ▫ Six flavors, three generations First Generation: Electron e- & Electron Neutrino ve
Second Generation: Muon µ- & Muon Neutrino vµ
Third Generation: Tau τ -1 & Tau Neutrino vτ For all generations e- , µ-, τ -1: negative charge, elementary particle ve, vµ, vτ: no electric charge
Anti-Particles: Positron e+, Antimuon µ+, Antitau τ+ Same mass as respective particle, opposite charge
July 30, 2015 Hallie Stidham
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Particles cont.
• Gauge Bosons ▫ Type of vector boson ▫ Three types Photons: carry electromagnetic interaction W & Z Bosons: carry weak interaction Gluons: carry strong interaction
• Missing Transverse Energy (MET) ▫ Used to deduce presence of non-detectable
particles (ex: neutrino)
July 30, 2015 Hallie Stidham
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Particles cont.
• Hadrons ▫ Composite particles made of quarks ▫ Held together by strong force ▫ Two categories: Baryons & Mesons
Baryons (ex: protons and neutrons) Made of three quarks
Mesons (ex: pion) One quark, one antiquark
• Jets ▫ High-energy quark transformed into spray of hadrons ▫ Most commonly used in ATLAS
Regular Jets: 0.4 distance parameter Large-R Jets: 1.0 distance parameter
Boosted Jets
July 30, 2015 Hallie Stidham
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Resonance and Decay
• Resonance ▫ Peak at a particular mass when two particles’ cross
sections interactions are examined as a function of energy ▫ Cause: creation of a particle whose mass-energy is
energy of resonance ▫ Described by mass spectrum of dispersion type ▫ Maximum = resonance mass m ▫ Spectrum width = probability of resonance decay Γ Does not exceed mc2
July 30, 2015 Hallie Stidham
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Resonance and Decay cont.
July 30, 2015 Hallie Stidham
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• VV Resonance ▫ See Feynman diagram, studied in lvqq final state ▫ Example of how signal bump should show above
the background, if signal exists
Data and Monte Carlo Samples
• 6.5 pb-1 at 13 TeV • Signal ▫ Signal, Heavy Vector Triplet
• Background ▫ W + Jets ▫ Z + Jets ▫ ttbar
• No multijet or standard model diboson samples, estimated to be very small from Run 1
• Run 1 Multijets Extrapolation ▫ 29 recorded events with luminosity of 20.3 fb-1 at
8 TeV -> average of 6 events ± 3 events
July 30, 2015 Hallie Stidham
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Monte Carlo Scale • Signal -> HVT Signal 2 TeV ▫ MadGraphPythia
July 30, 2015 Hallie Stidham
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Selection
• Tight Electron ▫ PT > 25 GeV, η < 2.47, tight working point
• Medium Muon ▫ PT > 25 GeV, η < 2.5, medium working point
• Level 1 Trigger (L1 Trigger) ▫ Lowest level trigger
• Boosted case ▫ Close Quarks ▫ Reconstructions identified as Large-R Jets
July 30, 2015 Hallie Stidham
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Selection cont.
• Baseline Selection ▫ Tight electron, medium muon, L1 Trigger ▫ MET > 30 GeV ▫ Lepton Neutrino PT > 100 GeV ▫ At least on Large-R Jet with PT > 100 GeV
July 30, 2015 Hallie Stidham
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Selection Optimization
• Additional selection to study sensitivity of signal selection against background
• Increase in MET cut to MET > 100 GeV ▫ Clean selection of quantum chromo dynamics
(QCD) contamination • Large-R Jets mass between 60-105 GeV • Large-R Jet PT > 200 GeV • Lepton Neutrino PT > 200 GeV
July 30, 2015 Hallie Stidham
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[GeV]lvJM0 500 1000 1500 2000 2500 3000
Even
ts
0
1
2
3
4
5
6
7
8
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
MET Plots
July 30, 2015 Hallie Stidham
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[GeV] lvJMET100 150 200 250 300 350 400 450 500 550 600
Even
ts
0
2
4
6
8
10
12
14
ZJetsWJets
tt SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
[GeV] lvJMET20 40 60 80 100 120 140
Even
ts
0
200
400
600
800
1000
1200
1400
1600
ZJetsWJets
tt SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
MET with before cuts, low mass excess is QCD
MET after > 100 GeV cut
Extrapolations of Signal and Background at various luminosities
July 30, 2015 Hallie Stidham
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• Reflective of how yields will progress as luminosity increases
• Expect to get up to 100 fb-1 by the end of Run 2 ~3 years
Extrapolations of Signal and Background at various luminosities
July 30, 2015 Hallie Stidham
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Significance Plots
July 30, 2015 Hallie Stidham
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• Ratio of signal sample with respect to background • Signal is 2 TeV resonance signal
M [GeV]0 500 1000 1500 2000 2500 3000 3500
Even
ts
0
0.1
0.2
0.3
0.4
0.5
0.63!10"
ATLAS Work In Progress = 13 TeVs, -1 L = ~6.5 pb#
Significance plot of Large-R Jet mass between 60-105 GeV
Significance Plots cont.
July 30, 2015 Hallie Stidham
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lvJ/MlvTP
0 0.2 0.4 0.6 0.8 1 1.2Ev
ents
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012ATLAS Work In Progress = 13 TeVs, -1 L = ~6.5 pb!
D2
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Even
ts
0
0.05
0.1
0.15
0.2
0.25
0.3
0.353!10"
ATLAS Work In Progress = 13 TeVs, -1 L = ~6.5 pb#
Shows optimal cut is D2 < 1.4 Shows optimal cut is PlvT/MlvJ > 0.5
Significance plot of Large-R Jet D2
Significance plot of PlvT/MlvJ
Trigger Studies
July 30, 2015 Hallie Stidham
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• “Old Trigger” is passL1_EM18VH and passL1_MU10 ▫ L1 = Level 1 Trigger
• “New Trigger” is passHLT_j360_a10_sub and passHLT_j460_a10_sub in addition to old trigger ▫ HLT = High Level Trigger ▫ “a” = AntiKt4LCTopo ▫ A10 = Large-R Jet ▫ 10 = size of cone ▫ 460 = PT threshold ▫ Sub = pile-up subtraction Subtracts interference with objects
Trigger Studies
July 30, 2015 Hallie Stidham
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Large-R Jet mass between 60-105 GeV & D2 > 1.4
Large-R Jet mass between 60-105 GeV
Large-R Jet mass between 60-105 GeV
Large-R Jet mass between 60-105 GeV & D2 > 1.4
Multivariate Analysis
• 2 TeV targeted selection using Boosted Decision Trees
• Input Variables ▫ Large- R Jet Mass (FJMass) ▫ Lepton Neutrino PT (lvPT) ▫ Lepton Neutrino - Large-R Jet η (lvFJeta) ▫ Lepton Neutrino - Large-R Jet ϕ (lvFJphi) ▫ Large-R Jet PT (FJPt) ▫ Large-R Jet y (FJy) ▫ Large-R Jet D2 (FJD2)
July 30, 2015 Hallie Stidham
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Multivariate Analysis Input Variables
July 30, 2015 Hallie Stidham
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Multivariate Analysis cont.
• Significance of 3.667 with optimal cut value of -0.020
• Large-R Jet PT is best discriminant against background
July 30, 2015 Hallie Stidham
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Multivariate Analysis cont.
July 30, 2015 Hallie Stidham
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Signal and background efficiency for specific Boosted Decision Tree value
Shows difference between signal and background due to their responses to the Boosted Decision Tree
Cut Efficiencies Plot BDT Output Distributions
Topology Plots
• Show agreement between data and Monte Carlo • No cuts made on D2 for plot of Large-R Jet D2 • No cuts made on Plv
T/MlvJ for plot of PlvT/MlvJ
• All other plots made using baseline cuts
July 30, 2015 Hallie Stidham
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Topology Plots cont.
July 30, 2015 Hallie Stidham
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!electrons 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5
Even
ts
0
2
4
6
8
10
12
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb#
Telectrons P100 200 300 400 500 600 700
Even
ts
0
5
10
15
20
25
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
!muons 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5
Even
ts
0
2
4
6
8
10
12
14
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb#
Tmuons P100 200 300 400 500 600 700 800 9001000
Even
ts
02468
101214161820
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
Electrons η
Muons η
Electrons PT
Muons PT
Topology Plots cont.
July 30, 2015 Hallie Stidham
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!J 2" 1" 0 1 2
Even
ts
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb#
[GeV]TJ P200250300350400450500550600650700
Even
ts
0
1
2
3
4
5
6
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
[GeV]JM200 400 600 800 10001200140016001800
Even
ts
0
5
10
15
20
25
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
J D2
0 0.5 1 1.5 2 2.5 3 3.5 4
Even
ts
0123456789
10
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
Large-R Jet η
Large-R Jet D2
Large-R Jet PT
Large-R Jet Mass
Topology Plots cont.
July 30, 2015 Hallie Stidham
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!lv 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5
Even
ts
0
0.5
1
1.5
2
2.5
3
3.5
4
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb#
[GeV]Tlv P300 400 500 600 700 800 900 1000
Even
ts
0123456789
10
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
[GeV]vvM400 500 600 700 800 900 100011001200
Even
ts
0
1
2
3
4
5
6
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
lvJ/MlvJTP
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Even
ts
0
1
2
3
4
5
6
7
8
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
Lepton Neutrino η
Lepton Neutrino Mass
Lepton Neutrino PT
Lepton Neutrino & Large-R Jet
PlvT/MlvJ
Topology Plots cont.
July 30, 2015 Hallie Stidham
31
J y2! 1! 0 1 2
Even
ts
0
1
2
3
4
5
6
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb"
Number of J
0 0.5 1 1.5 2 2.5 3
Even
ts
02468
101214161820
ZJetsWJetstt
SignalData
ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!
Large-R Jet y Number of Large-R Jets
Conclusions • Cut based vs. Multivariate Analysis • Multivariate analysis gives better sensitivity results ▫ More difficult to estimate systematic uncertainties
using multivariate analysis approach • Cut based is proposed method ▫ Final cuts
Tight electron, medium muon L1 Trigger MET > 100 GeV Lepton Neutrino PT > 200 GeV At least 1 Large-R Jet with PT > 200 GeV Large-R Jet D2 < 1.4 Plv
T/MlvJ > 0.5 • I would like to Poppy for her mentorship and the
Columbia REU Program and Prof. Parsons for this opportunity!
July 30, 2015 Hallie Stidham
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