Search for Supersymmetry in Dilepton Final States with Energetic Two-jets in Vector Boson Fusion-like Topology

Using the CMS Detector at the LHC

Ali Celik, Will H. Flanagan On behalf of the CMS Collaboration

Mitchell Institute for Fundamental Physics and Astronomy Texas A&M University

19th of October,2014

Texas APS Meeting

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Outline

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• Motivation-Standard Model, Supersymmetry• How-LHC and CMS• VBF• Analysis, background and limit• Summary

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Standard Model Problems?

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• Inability to explain CDM• Why are there three fermion generations?• Why are there large differences on the masses of each generation?• Hierarchy problem in Higgs mass.• Why do neutrinos have mass?

Standard Model (SM)• SM includes 12 elemantary particles known as

fermions and 3 force carriers known gauge bosons +Higgs boson.

• SM Lepton/Quarks —>Spin-1/2 particles Gauge bosons —> Spin 1 particles

• Higgs boson—>Spin 0

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

SUperSYmmetry?

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• Supersymmetry (SUSY) introduces a set of new particles by symmetrizing the theory between fermions and bosons.

• Slepton/Squarks —>Spin 0 particles • Gauginos —> Spin 1/2 particles• it has great potential for solving theoretical

problems of the SM• Stable Lightest Supersymmetric particle (LSP) is a

leading candidate for dark matter

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Large Hadron Collider (LHC)

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• Largest and most powerful particle collider, launched in 2008 at CERN • 27 km in circumference, 4 main experiments • 8 TeV Collision energy currently at about speed of c (13 TeV in 2015) •Understand the Higgs mechanism and search for evidence of new

physics, such as supersymmetry

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

COMPACT MUON SOLENOID (CMS) DETECTOR

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• INNER Tracking system, ECAL, HCAL, Magnet and Muon System.

• Muon chambers are located at most outside of the detector system.

• One of the 4 detectors built at LHC. • 21 m long and 15 m in diameter and

weighs 12500 tons. • 5 wheels in the barrel and 4 stations

in the end-cap region.

Extracted from [2]

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Colored SUSY Searches

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• Many SUSY searches focused on the colored sector• These type of signatures have final states with MET+multijets

+leptons• No excess at 8 TeV so far, either SUSY wrong or objects heavy

-1

-1

-1

1

1

1

1

• R=(-1)3B+L+2S

• R=1 for SM particles, R=-1 for SUSY

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 8

SUSY Electroweak Searches with VBF

• All searches are based on direct pair production of electroweakinos with final states to leptons

• Note there is no good sensitivity for compressed spectra scenarios

• Not easy to search for direct weak production of SUSY w/o dedicated trigger

• Even with trigger selection, still huge backgrounds• VBF tagging useful in tackling some of the

interesting physics channels• A VBF triggered data sample will be powerful in

searching for colorless SUSY particles.

Why Vector Boson Fusion?

e

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Backgrounds

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• top pair largest background source to VBF• b-jets from the top quark decay• real e-mu pairs and MET from leptonic

decay of the W

φ

η

e jetsμ

• W+jets: W decaying leptonically (W—>μ/e/τ+ν ) and a jet can fake to an electron.

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 10

VBF Kinematics?

• One jet pair with mjj >250 • Jet PT > 50

• MET>75• |Δη| >4.2

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Data-Driven Background Estimation

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• Our general strategy to predict backgrounds across all channels:• Scale background estimation before VBF

cuts with a control region ‘CF(CR w/o VBF)’ where CF is correction factor data to MC

• Determine efficiency of VBF cuts with another (independent) control region ‘∊VBF’

Predicted BG rate in the SR Predicted rate in MC

without VBF selection

Data-to-simulation correction factor

VBF eff determined from data in CR.For small BG’s it is taken from MC

Taken from Alfredo Gurrola

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Backgrounds for e-mu channel

12Taken from Andres Florez

Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

Summary

• Search for SUSY with 8 TeV data from proton-proton collisions by using lepton trigger.

• In the future VBF trigger will be used for the same analysis. • Perform MC simulations for production of SUSY particles with

the final states previously mentioned• Data-driven methods used for background estimation• No signs of new physics at 8 TeV but 13 TeV more promising.

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Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014

References

• [1] C. Lefevre, “The CERN accelerator complex. Complexe des accelerateurs du CERN." https://cds.cern.ch/record/1260465, Dec 2008.

• [2] CMS Collaboration, Technical Design Report Volume I: Detector Performance and Software.

CMS Physics, 2006• [3] CMS Collaboration, “Summary of observed limits for EWKino models," https://twiki.cern.ch/twiki/pub/CMSPublic/SUSYSMSSummaryPlots8TeV/EWKino_exclusion_Combined_observed_SUSY2013.pdf.• [4] D. I. Kazakov, “Beyond the Standard Model (In Search of Supersymmetry),"

ArXiv High Energy Physics - Phenomenology e-prints, Dec. 2000.

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