Heavy Graviton Search at LHC Yuhan Guo Vanderbilt University Standard Model (mediators) Electromagnetic interaction Acts on Mediator Weak interaction Acts on Mediator Strong interaction Acts on Mediator Gravitation Acts on Mediator??? • Laser Interferometer Gravitational-Wave Observatory (LIGO) • September 14, 2015 – GW from Colliding Black Holes • August 8, 2017 – GW from Colliding Neutron Stars Large Hadron Collider The Large Hadron Collider (LHC) Model & Parameters Can we produce enough graviton events at LHC? Production Mechanism & Decay Channel Kinematics Phenomenology Study Optimization Study What’s our optimal strategy Selection Criteria of detecting graviton? (maximize significance) Predictions page 1/5 3 2 2 4 a a g g 3 u u u u 5 a g g u u~ u~ 4 a g 6 5 g u~ 1 1 6 Production Mechanism & diagram 1 QCD=2, QED=2 diagram 2 QCD=2, QED=2 4 2 page 2/42 4 a Decay Channel a g g 3 u u~ u~ u 5 a 2 2 g g 6 6 d d u~ d u d u~ 3 page 5/8 a g 5 6 g 4 4 z a u~ a a 1 1 y2 y2 6 2 3 2 3 d a a d diagram 3 QCD=2, QED=2a a diagram 4 QCD=2, QED=2 d d a 3 z 3 d d a 6 2 z 6 2 u u u u3 3 u 5 u a 5 a 1 g 1 g 5 5 u u 4 4 u u u~ u~ diagram 7 DMT=2, QCD=0, QED=2 diagram 8 aDMT=2, QCD=0, QED=2 a g g u a u a u~ u u u~ 4 4 1 Vector Boson Fusion 1 5 6 2 Standard Model g 2 6 4 g 5 diagramd 25 QCD=0, QED=4 6 diagram 26 QCD=0, QED=4 a Diphoton channel d d y2 1 Background d a 1 2 3 4 2 3 d z a diagramd 5 QCD=2,a QED=2 d 3 diagram 6 QCD=2, QED=2 a y2 a 6 d~ a d~ a 4 a Diagrams4 made by MadGraph5_aMC@NLO z 3 d~ d~ u d u d u u 6 5 6 5 1 a 1 z u u u u 1 diagram 9 DMT=2, QCD=0,5 QED=2 1 diagram 10 DMT=2,5 QCD=0, QED=2 diagram 27 QCD=0, QED=4 diagram 28 QCD=0, QED=4 2 4 2 4 a a 2 d 2 d 3 3 d a y2 d a y2 d a a d 4 3 d 4 3 d~ d~ a a z d 6 d a 6 d d a 6 z 6 u u u u u u 5 u u 5 5 5 1 1 1 1 diagram 29 QCD=0, QED=4 diagram 30 QCD=0, QED=4 diagram 11 DMT=2, QCD=0, QED=2 diagram 12 DMT=2, QCD=0, QED=2 Diagrams made by MadGraph5_aMC@NLO Diagrams made by MadGraph5_aMC@NLO Vector Boson Fusion • Why VBF? • Significant reduction of the QCD background • Enhanced cross section at large mass scales • Features • Large dijet mass, energetic jets • Jets are forward & in opposite atmosphere (large ) | Δη jj | à Use the unique features of VBF to design the searching strategy! Cross Section – Graviton Mass 106 pp → G + 0j, κ = 1 g,q [pb] 5 σ 10 0 pp → G + jj, α , κ = 1 QCD B,W,H 4 10 0 pp → G + jj, α , κ = 1, |Δη | > 4.0 QCD B,W,H jj 103 102 10 1 10−1 10−2 10−3 10−4 0 500 1000 1500 2000 2500 3000 MG [GeV] N = σ ⋅ L (Event rate = cross section * luminosity) −1 Assuming : Lint =1000 fb 5 If , we have events mG = 500GeV 10 3 If , we have events mG = 3000GeV 10 page 1/1 2 u~ y2 3 u Compare: DY with varying 1 strong coupling constants diagram 1 DMT=1, QCD=0, QED=0 Diagrams made by MadGraph5_aMC@NLO Kinematics • Decay channel à Key variable: diphoton mass γ1 γ2 mγγ = 2 | pT || pT | cosh Δηγγ • VBF features: • Large dijet mass • Energetic & forward jets 1 -1 LHC s=13TeV Lint=100.0 fb 1 pp → j j G (→ γ γ), m = 100 GeV 10− G Events pp → j j G (→ γ γ), m = 500 GeV G pp → j j G (→ γ γ), m = 1000 GeV 10−2 G pp → j j γ γ pp → j j γ γ QCD = 0 10−3 10−4 10−5 10−6 0 500 1000 1500 2000 2500 M ( γ γ ) [ GeV/c2 ] 1 2 Diphoton Mass Dijet Mass Decay width scenarios WG =10GeV Decay width scenarios WG =10%M G WG =10GeV WG =10%M G Optimization study • Fix diphoton mass window at 2σ • Optimize the selection cuts for the kinematics to maximize S significance = S + B + (0.25B)2 • 3 mass points: 150 GeV, 250 GeV, 500 GeV • 2 decay width scenarios WG =10GeV WG =10%M G • Increase background statistics to optimize cuts for higher mass (1000 GeV) Selection criteria (not final) Delta eta (j1 j2) > 4.0 WG =10GeV WG =10%M G > 6.0 P_T (gamma2) > 30 GeV/c M (j1 j2) > 1000 GeV/c^2 P_T (j1) > 30 GeV/c P_T (j2) > 30 GeV/c P_T (gamma1) > 60 GeV/c Reference • http://www.physik.uzh.ch/en/researcharea/lhcb/outreach/ StandardModel.html • Alvarez-Gaume L., Ellis J., 2008, APJ, 672, 834 • http://cms.web.cern.ch/news/observation-new-particle- mass-125-gev • CMS Collaboration. Physics Letters B 716 (2012) 30–61. • A. Flórezb, A. Gurrola, W, Johns, Y.D. Oh, P. Sheldon, D. Teague, T. Weiler. Physics Letter B, Volume 767, 10 April 2017, Pages 126-132. .