optimizing selection and sensitivity results for vv-> lvqq, 6.5 pb … · 2015. 8. 9. ·...

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

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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


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)


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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


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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


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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)


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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


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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


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Resonance and Decay cont.


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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


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Monte Carlo Scale •  Signal -> HVT Signal 2 TeV ▫  MadGraphPythia


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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


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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


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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


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[GeV]lvJM0 500 1000 1500 2000 2500 3000

Even

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7

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ZJetsWJetstt

SignalData

ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb!

MET Plots


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[GeV] lvJMET100 150 200 250 300 350 400 450 500 550 600

Even

ts

0

2

4

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8

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ZJetsWJets

tt SignalData


[GeV] lvJMET20 40 60 80 100 120 140

Even

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600

800

1000

1200

1400

1600

ZJetsWJets

tt SignalData


MET with before cuts, low mass excess is QCD

MET after > 100 GeV cut

Extrapolations of Signal and Background at various luminosities


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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


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Significance Plots


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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.


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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


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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


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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)


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Multivariate Analysis Input Variables


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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


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Multivariate Analysis cont.


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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


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Topology Plots cont.


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!electrons 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5

Even

ts

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2

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ZJetsWJetstt

SignalData

ATLAS Work in Progress = 13 TeVs, -1 L = ~6.5 pb#

Telectrons P100 200 300 400 500 600 700

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ZJetsWJetstt

SignalData


!muons 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5

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ZJetsWJetstt

SignalData


Tmuons P100 200 300 400 500 600 700 800 9001000

Even

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02468

101214161820

ZJetsWJetstt

SignalData


Electrons η

Muons η

Electrons PT

Muons PT



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!J 2" 1" 0 1 2

Even

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0.5

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1.5

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2.5

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3.5

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ZJetsWJetstt

SignalData


[GeV]TJ P200250300350400450500550600650700

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ZJetsWJetstt

SignalData


[GeV]JM200 400 600 800 10001200140016001800

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ZJetsWJetstt

SignalData


J D2

0 0.5 1 1.5 2 2.5 3 3.5 4

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0123456789

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ZJetsWJetstt

SignalData


Large-R Jet η

Large-R Jet D2

Large-R Jet PT

Large-R Jet Mass



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!lv 2.5" 2" 1.5" 1" 0.5" 0 0.5 1 1.5 2 2.5

Even

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0.5

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1.5

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3.5

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ZJetsWJetstt

SignalData


[GeV]Tlv P300 400 500 600 700 800 900 1000

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0123456789

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ZJetsWJetstt

SignalData


[GeV]vvM400 500 600 700 800 900 100011001200

Even

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ZJetsWJetstt

SignalData


lvJ/MlvJTP

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

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ZJetsWJetstt

SignalData


Lepton Neutrino η

Lepton Neutrino Mass

Lepton Neutrino PT

Lepton Neutrino & Large-R Jet

PlvT/MlvJ



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J y2! 1! 0 1 2

Even

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1

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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


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!


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optimizing selection and sensitivity results for vv-> lvqq, 6.5 pb … · 2015. 8. 9. ·...

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