Searches for Rare Higgs Decays and an Additional Higgs Singlet Learning from the current measurements Searches for rare Higgs decays Searches for an additional Higgs singlet Jianming Qian University of Michigan Unlocking the Higgs Portal, UMass Amherst, May 1-3, 2014
What Now? Discovery has been made… Nobel prize has been awarded But many questions remain Is the new boson solely responsible for the electroweak symmetry breaking? What’s the nature of dark matter? Can the new boson help to understand it? Two-pronged approaches A precision program measurements of Higgs properties A search program Use the newly discovered particle as a tool to explore potential new physics Jianming Qian (University of Michigan) 2
Productions and Decays Over 1,000,000 Higgs bosons “produced” at LHC in Run 1! Jianming Qian (University of Michigan) 3
H(125): Rates and Couplings ( ) λ ∝ SM: m fermions ( ) ∝ 2 g bosons m Rates and couplings are very Standard Model like Jianming Qian (University of Michigan) 4
H(125): Spin and CP Higgs decay kinematics depends on its properties → γγ → → * of spin and parity. H , H Z Z 4 and → → ν ν * H WW final states have been analyzed to determine these properties. → γγ H SM prediction of J p =0 + is strongly favored, most alternatives studied are excluded @ 95% CL or higher Jianming Qian (University of Michigan) 5
Higgs Boson Width Γ ≈ SM @ 125 GeV: 4.07 MeV smaller than the experimental h resolutions of direct measurements For measurements: hard to measure experimentally though indirect measurements can significantly improve the precision For searches: Even a small contribution to the width from potential new physics can lead to a sizable decay BR Jianming Qian (University of Michigan) 6
Direct Width Measurement The Higgs width can be in principle extracted from the m or m distributions γγ 4 with the signal lineshape ( ) ( ) Γ ⊗ σ Breit-Wigner m , Gaussian H Limited by detector mass resolution and large background CMS-PAS-HIG-13-016 ( ) Observed expected limit ( ) Γ < 6.9 5.9 GeV @ 95% CL H ×Γ SM 1500 H Jianming Qian (University of Michigan) 7
Indirect Width Measurement 2 2 σ g g d → → i f Kauer & Passarino, arXiv:1206.4803 Process i H f : ( ) 2 2 dm − + Γ 2 2 2 2 Campbell & Ellis, arXiv:1311.3589 m m m H H H 2 2 g g σ d i f On-peak: 2 dm Γ 2 2 m H H 2 2 g g σ d i f Off-peak: ( ) 2 2 dm − 2 2 m m H ( ) 2 Γ on-shell measures g g , i f H ( ) 2 off-shell measures g g i f Γ Extract by comparing H the two measurements (thanks to the large off-shell contributions) Jianming Qian (University of Michigan) 8
Indirect Width Measurement The key is to isolate off-shell Higgs signal from the continuum background, → → such as qq gg WW ZZ , for the case of H WW ZZ , ( ) → → νν * CMS has studied H ZZ 4 , with the combined observed expected ( ) ( ) Γ < ×Γ SM limit: 17.4 35.3 MeV or 4.3 8.7 @ 95% CL H H Γ = + 6.1 Or as a measurement 1.4 MeV − H 1.4 However, there is the issue whether theory uncertainty is under control. Jianming Qian (University of Michigan) 9
Rate Decay: H→ µµ CMS-PAS-HIG-13-007 2 m ( ) ( ) µ ATLAS-CONF-2013-010 → µµ × → ττ ≈ BR H BR H 0.022% m τ Clean signature, but suffer from large Drell-Yan background ( ) Observed expected upper limits ( ) ( ) ATLAS: 9.8 8.2 and CMS: 7.4 5.1 ( ) ( ) σ × σ × on BR BR at 95% CL SM Jianming Qian (University of Michigan) 10
Rare Decay: H→Z γ ( ) → Z γ ≈ BR H 0.15% @ 125 GeV = At m 125 GeV: Search for a narrow resonance over H ( ) σ × → γ → γ γ Br H Z ~ 2.3 fb continuum (mostly Z ) backgrounds H ~ 55 events in 2011+2012 dataset × Current sensitivity is about 10 the standard model expectation arXiv: 1307.5515 (CMS) arXiv: 1402.3051 (ATLAS) Jianming Qian (University of Michigan) 11
Other Rare Decays → ψ γ H J decay has been proposed as a way to access Hcc coupling, but the ( ) ( ) → ψγ → µµγ ≈ → γ → µµγ rate is very low: N H J N H Z 340 Bodwin, Petriello, Stoynev and Velasco, arXiv:1306.5770 Relative easy to search, but rate is too late even for high luminosity LHC or even for any proposed lepton collider There are other potential rare decays, but backgrounds are likely too large to be feasible Isidori, Manohar and Trott, arXiv:1305.0663 Jianming Qian (University of Michigan) 12
Higgs Portal Models de Simone, Giudice & Strumia, arXiv:1402.6287 The addition of a singlet scalar leads to a rich phenomenology: a dark matter candidate and h → resulting invisible decays additional Higgs production processes → → such as h aa or X hh No & Ramsey-Musolf, arXiv:1310.6035 Jianming Qian (University of Michigan) 13
SM + Singlet The simplest extension of the standard model Higgs sector is the addition of a singlet S: ( ) ( ) ( ) 2 φ = µ φ φ + − λ φ φ − ρ + κ φ φ 2 † 2 2 † 4 † 2 V , S m S S S S depending on the couplings, the two states can mix … Scenario 1: h(125) is the heavier one < → s is the lighter one. If m m 2, then h ss decay opens up. s h ⇒ → → If there is no mixing, s is sta ble h ss invisible (see the presentation by Ket evi) . → ⇒ → → ' ' Otherwise s ff similar final states a s h aa ff f f . Scenario 2: h(125) is the lighter one H is the heavier one. Assuming mixing, and have similar decay h H ⇒ → mode "SM-like" high mass searches such as H WW ZZ , . < → ⇒ If m m 2, the decay H hh opens up Higgs pair production. h H Jianming Qian (University of Michigan) 14
Coupling Modifications The mixing between the singlet scalar and the "SM" Higgs boson θ θ h cos sin H = SM θ − θ H sin cos S ( ) leads to the universal modification of the couplings of the h 125 Hig gs boson θ 2 g sin − to SM particles 1 g 2 SM Therefore the coupling measurements can help to constrain the model which are described by 3 additional parameters: ( ) ( ) θ → → cos (mixing angle), m (mass of the other Higgs), BR H hh or BR h ss s H ( ) The productions and decays of the h 125 Higgs boson are therefore modified. ( ) For the case of h 125 being the lighter one ( ) σ × BR σ = κ × σ Γ = κ ×Γ = µ = = κ 2 SM 2 SM SM 2 h , , BR BR , ( ) h h h h h h SM σ × h BR h κ = θ 2 2 here cos . Jianming Qian (University of Michigan) 15
Coupling Parametrization ( ) κ κ = Parametrizing deviations from SM using scale parameters: SM: 1 2 m 2 2 m = = ⇒ f V g , g υ υ hff hVV 2 2 m 2 m = κ ⋅ = κ ⋅ f V g , g υ υ hff f hVV V κ ⋅ κ 2 2 ( )( ) ( ) ( ) γ σ ⋅ → → γγ = σ → ⋅ → γγ × g For example: BR gg h gg h BR h κ 2 SM h assuming there is no new production processes. κ 2 is the scale factor to the total Higgs decay width h ∑ ∑ ( ) ( ) κ = κ ⋅ → → κ = κ ⋅ → 2 2 No BSM decays 2 2 BR h xx BR h xx h x h x SM x x ( ) → BR h xx ∑ → κ = κ ⋅ SM With BSM decays 2 2 − h x 1 BR x BSM Jianming Qian (University of Michigan) 16
Constraints from Couplings Higgs could have decays that are not accounted for in SM. The decays do not have to be invisible. They could be decays not detectable at LHC. ⇒ modified total Higgs decay width and therefore BRs of other decays, effectively leave the total decay width free. κ κ 2 2 ( ) ( ) ( ) Γ = Γ × → = → × − ⋅ SM h x , BR h x x BR h xx 1 B R − κ h h S M ne w 2 1 BR new h ATLAS-CONF-2014-010 A model allows for potential new physics in vertex loops and additional decays κ κ , , BR γ g new < BR 0.41 (0.55) @ 95% CL new < + / ( BR 0.37 (0.39) combining with Z E search) inv T Significant room for potential exotic decays Jianming Qian (University of Michigan) 17
Constraints on the Heavy Higgs κ 2 ' ( ) σ = κ × σ Γ = ×Γ = − × 2 SM SM SM ' , , BR 1 BR BR H H H − H H new H 1 BR new κ = θ = − κ 2 2 2 here ' sin 1 . The signal strength parameter for the heavy Higgs is ( ) σ × BR ( ) ( ) ( ) µ = = κ − = − µ − 2 H ' 1 BR 1 1 BR ( ) H new h new SM σ × BR H + + µ = ⇒ κ = − 0.17 2 0.17 From ATLAS measured value 1.30 ' 0.30 which leads − − h 0.18 0.18 κ < 2 to an upper bound of ' 0.12 @ 95% CL (restrict to physical region) independent of the mass of the heavy Higgs boson m . H Jianming Qian (University of Michigan) 18
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