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 Texas APS Meeting 19th of October,2014
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 2 Outline Motivation-Standard Model, Supersymmetry How-LHC and CMS VBF Analysis, background and limit Summary
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 Standard Model Problems? 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? Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 3
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 4 SUperSYmmetry? 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
Large Hadron Collider (LHC) 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 5
COMPACT MUON SOLENOID (CMS) DETECTOR 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. INNER Tracking system, ECAL, HCAL, Magnet and Muon System. Muon chambers are located at most outside of the detector system. Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 6 Extracted from [2]
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 7 Colored SUSY Searches 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 R=(-1) 3B+L+2S R=1 for SM particles, R=-1 for SUSY -1 1-1
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 e Why Vector Boson Fusion? 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. Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 8
Backgrounds 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 W+jets: W decaying leptonically (W >μ/e/τ+ν ) and a jet can fake to an electron. e μ jets φ Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 η 9
VBF Kinematics? One jet pair with mjj >250 Jet PT > 50 Δη >4.2 MET>75 Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 10
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 11 Data-Driven Background Estimation 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 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 Taken from Alfredo Gurrola
Backgrounds for e-mu channel Taken from Andres Florez Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 12
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 13 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.
Ali Celik (Texas A&M University) Texas APS Meeting / Oct 19, 2014 14 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.