boosted searches for ww/wz resonances in the ℓνj final state · 2016-08-07 · description of...

Boosted searches for WW/WZ resonances in the ℓνJ final stateBILLIE LUBIS

COLUMBIA UNIVERSITY REU 2016

CERN◦ Founded in 1954 by 12 Western European countries → Now 22 member countries

◦ Aims to conduct cutting-edge particle physics research and foster collaboration

◦ Scientific accomplishments include development of WWW, creation of anti-hydrogen atoms, discovery of Higgs boson

◦ Home to LHC as well as many other accelerators

23 August 2016 BILLIE ELIZABETH LUBIS

Large Hadron Collider - LHC◦ Built from 1998 – 2008

◦ Largest and most powerful particle collider in the world

◦ 27 km ring, 175 m below ground

◦ Numerous detectors including ATLAS, CMS, ALICE, and LHCb

3 August 2016 BILLIE ELIZABETH LUBIS 3

ATLAS◦ “A Toroidal LHC ApparatuS”

◦ General purpose detector at LHC

◦ Studies collisions of high energy protons

◦ Over 3000 physicists from 138 countries


ATLAS Detector◦ 46 meters long, 25 meters in diameter

◦ 7000 tons

◦ Components

◦ Inner Detector

◦ Electromagnetic calorimeters

◦ Hadronic calorimeter

◦ Muon detectors

◦ Magnets


Standard ModelQuarks◦ ½ integer spin

◦ Have color charge

◦ Interact via strong force

◦ Combine to form hadrons (baryons, mesons)


Leptons◦ ½ integer spin

◦ Electron, muon, tau interact electromagnetically

◦ Neutrinos interact via weak force

Standard ModelBosons◦ Integer spin

◦ Force carriers for the different types of interactions


Particle Identification


VV Resonances


◦ Searching for VV resonances in semileptonic decay mode

◦ Specifically VV → ℓνqq

◦ WW or WZ resonances

◦ W decays leptonically to ℓν pair

◦ Reconstruct W boson from lepton and neutrino vectors

◦ W/Z decays hadronically to quark and anti-quark

◦ Reconstruct in a large-R jet using anti-kt algorithm

◦ Calculate VV mass of event

◦ Signals used are Heavy vector triplet (HVT) or graviton (RS G*)

Objects SelectionLeptons◦ We require a final state with one lepton

◦ Veto events with more than one loose lepton while keeping signal candidate events with one tight lepton

◦ “Tight” and “loose” based on preselection cuts


Objects Selection


Triggers◦ Applied missing transverse energy trigger to muon channel

◦ Applied electron trigger to electron channel

Objects Selection


Small-R jets◦ ΔR > 1 between small-R and large-R jets

◦ Classified as b-jet if b-tagging variable MV2C10 > 0.1758

Objects SelectionLarge-R jets◦ ΔR > 1 between large-R jet and lepton (removed overlap)

◦ |η| < 2.0

◦ 𝑚𝐽 > 50 GeV

◦ 𝑝𝑇 > 200 GeV

◦ Use mass cut and substructure cut to identify jets from hadronic W/Z decays◦ Mass cut: ~65 – 120 GeV

◦ Substructure cut (based on the D2 variable): Differentiate W/Z from QCD jets


Description of Background/Data◦ Data is from 2015 and 2016 → Luminosity = 13.2 fb-1 and center of mass energy = 13 TeV

◦ Background composed of W+ jets, t ҧ𝑡, Z+ jets, and SM dibosons

◦ QCD is negligible

◦ Generators◦ V+ jets: Sherpa v22 & Njets correction applied

◦ t ҧ𝑡: Powheg-Pythia

◦ SM db: Sherpa

◦ HVT/Gravitons: MadGraph+Pythia8, with a mass width of ~6%

◦ Signal is normalized

◦ Backgrounds scaled to cross sections


Control and Signal Regions


◦ High purity regions pass substructure cut

◦ Low purity regions fail substructure cut

Control and Signal Regions


High purity WCR plots


High purity TCR plots


High purity SR plots


Low purity WCR plots


Low purity TCR plots


Low purity SR plots


Data/MC Summary


Conclusions◦ Added low purity region to increase sensitivity

◦ Overall normalization problem

◦ Background fits shape of data fairly well


Acknowledgements◦ Thank you to

◦ John Parsons for this REU opportunity

◦ Poppy Iordanidou for her help and encouragement, and immense knowledge of ROOT

◦ The Columbia ATLAS group for their support


Questions?

boosted searches for ww/wz resonances in the ℓνj final state · 2016-08-07 · description of...

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