SM and Fermiophobic Higgs to γ γ

SM and Fermiophobic Higgs to γγ Benjamin Auerbach on behalf of the CDF Collaboration Yale University Benjamin Auerbach Photon 2011

Outline Introduction to Standard Model Higgs Search Outline Photon Identification Developing Signal Selection Background Model Limits on the Higgs Cross Section Fermiophobic Higgs Results Benjamin Auerbach Photon 2011

Introduction • Tevatron is 1.98 TeV proton antiproton collider • Two detectors (CDF and Dzero) • Both are trying to discover the Higgs Boson Benjamin Auerbach Photon 2011

Benjamin Auerbach Photon 2011 Introduction • Useful for mH between 100 – 150 GeV/c2 • Branching ratio is < 0.25% But have gg->H production • Great Resolution of Final State

Benjamin Auerbach Photon 2011 Outline of the Search Identify events with γγ coming from the vertex Find the invariant mass of the 2 photons Look for a resonance in the invariant mass Use the side bins to model the backgrounds Place limits on how large the Higgs signal could be

Benjamin Auerbach Photon 2011 Electromagnetic Calorimeter And ShowerMax Central Tracker p p Muon Chambers Silicon Vertex Detector CDF Detector Hadronic Calorimeter Solenoid Photon ID and Efficiency - Introduction

Benjamin Auerbach Photon 2011 Identifying Central Photons Start with loose requirements for EM objects Fidicucial in ShowerMax, Veto Tracks, Had/EM < 12.5%, Isolation (EtotT– EEMT) in 0.4 Cone Use NN for Central photons Diphoton and dijet MC samples Above variables used and Ratio of Energy at ShowerMax to total EM Energy, Shower Shape, Lateral Sharing

Benjamin Auerbach Photon 2011 Identifying Plug Photons Standard CDF Selection Criteria Fiducial in ShowerMax, Ratio of Had/EM transverse Energy < 5%, Calorimeter isolation < 2 GeV, Track Isolation < 2 GeV, Lateral shower shape consistent with prompt photon.

Benjamin Auerbach Photon 2011 Converted Photons The material in CDF may cause photons to convert This happens 15% of the time Electron-positron pairs are identified We use the pair's ET and pT to reconstruct the photon's ETand pT Only do this in the Central region Less material than the plug region Recover 26% of events Reject “trident events” (photon brehmmed, converts) port cards, cables ISL outer screen L00, L0-L4 L6 L7

Signal Shape Expectation Very narrow γγ mass spectrum • Width < 3 GeV • H->γγ decay width << 0.01 GeV for low mass • Mass resolution limited only by electromagnetic (EM) calorimeter • Width ~3 GeV or less • Resolution ~4x better than best jet algorithms for H->bb • Great background discrimination using Mass alone • Sideband fits can be used to estimate background Benjamin Auerbach Photon 2011

Benjamin Auerbach Photon 2011 Background Modeling Backgrounds come from: Drell-Yan Decay (both electrons mis-id'd) 1 or 2 Jets decaying to photons SM γ+γ events Backgrounds are very smooth 6-degree polynomial and Exponential Contamination In the plug region Modeled with a Breit-Wigner Constrained to be at the Z-mass

Benjamin Auerbach Photon 2011 The Search Looking for a spike on a long smooth tail Use a window that is 12 GeV/c2 wide If we do not see any evidence of Higgs Place limits on how large the cross section could be

Benjamin Auerbach Photon 2011 The Central-Central Search Looking for a resonance in 5 GeV/c2 increments Examine 12 GeV/c2 windows around mass Use the sidebands to model the background

Benjamin Auerbach Photon 2011 The Central-Plug Search Looking for a spike on a long smooth tail Examine 12 GeV windows around mass Use sidebands as background shape Breit-Wigner models photons from Z contamination

Benjamin Auerbach Photon 2011 Results from the 120 GeV Mass • Can see a slight excess of events over background model • But have to require the signal be between 16-32 * SM

Benjamin Auerbach Photon 2011 Results How large could the cross section be and see no bump? Overall improvement over previous Diphoton result Does not include trials factor

Benjamin Auerbach Photon 2011 Tevatron Combination Results Combination of both DØ (8.2/fb) and CDF's (7.0/fb) results Improves sensitivity in low mass region by ~sqrt(2).

Benjamin Auerbach Photon 2011 Fermiophobic Higgs Similar analysis can be performed Hf breaks EW symmetry does not couple to fermions At low mass, dominantly decays to γγ The photons recoiling against something High transverse momentum of the pair leads to higher significance.

Benjamin Auerbach Photon 2011 Fermiophobic Higgs Phenomelogy This higgs can only be produced by bosons We expect a larger signal yield than SM Higgs, because H->bb is suppressed Associated Production~ 225 fb @ 120 GeV Vector Boson Fusion ~ 70 fb @ 120 GeV

Benjamin Auerbach Photon 2011 Event Selection We use the same 4 photon candidates as before Make use of Ptγγ, PT < 35 GeV, PT > 75 GeV, 35 GeV < PT < 75 GeV Background modeled as before The 120 GeV bump is in the least sensitive bin

Benjamin Auerbach Photon 2011 Fermiophobic Higgs Results Observed (expected) 95% C.L. limits on σxB(hf ->γγ) exclude a Fermiophobic Higgs boson with a mass < 114 GeV (111 GeV)

Benjamin Auerbach Photon 2011 Summary & Conclusions NN and forward photons improved sensitivity No significant excesses but new limits on size of Higgs boson cross section Significant sensitivity gains in low mass Higgs At 95% confidence: Higgs mass constrained to < 15 * SM prediction Expected sensitivity was 9 * SM prediction Fermiophobic Higgs ruled out below 114 GeV Expected was 111 GeV

Benjamin Auerbach Photon 2011 Back Up Slides

SM and Fermiophobic Higgs to γ γ