Higgs Physics - current status and future prospects Higgs physics - PowerPoint PPT Presentation

Higgs Physics - current status and future prospects Higgs physics at the LHC Higgs physics at the CEPC Jianming Qian (University of Michigan) ACFI workshop, Amherst, September 17-19, 2015

Higgs Productions and Decays Over 1,000,000 Higgs bosons produced at LHC so far ⇒ Higgs factory ! 2

Status at a Glance A long way since the discovery. 88% of the Higgs boson decays have been studied… Discovery-level significances in three bosonic decay modes; → Weakest signal in H bb , the decay mode with the largest BR ! 3

ATLAS and CMS Combination → γγ → →  Combining measurements in H and H ZZ* 4 taking into account correlations of uncertainties ( ) ( ) m = ± ± = ± 125.09 0.21 stat. 0.11 syst. 125.09 0.24 GeV H arXiv:1503.07589 4

Indirect Width Measurement σ 2 2 g g d → → i f  Process i H f : ( ) 2 2 dm − + Γ 2 2 2 2 m m m H H H 2 2 g g σ d i f  On-peak: 2 Γ dm 2 2 m H H 2 2 g g σ d i f  Off-peak: ( ) 2 2 dm − 2 2 m m H Γ Extract by comparing the on-shell H and off-shell measurements, but complicated by backgrounds: Kauer & Passarino, arXiv:1206.4803 Caola & Melnikov, arXiv:1307.4935 Campbell & Ellis, arXiv:1311.3589 5

Indirect Width Measurements → → → * The key issue is to extract the gg H VV signal from the gg VV → background. Assumptions are made about the gg VV cross section. arXiv:1503.01060 (ATLAS) arXiv:1405.3455 (CMS) ( ) ( ) ( ) → = → → * Assuming K gg VV K gg H VV , the observed expected 95% CL limits: [ ] [ ] ( ) ( ) Γ < Γ < 22.7 33.0 MeV ATLAS ; 22 28.0 MeV CMS H H 6

Spin/CP Tests 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 arXiv:1411.3441 (CMS) SM prediction of J p =0 + is strongly favored, most alternatives studied are excluded @ 95% CL or higher 7

Differential Distributions Going beyond inclusive distributions, study kinematics of candidate events. Reasonable agreements between data and the SM expectations, need to watch out arXiv:1504.05833 (ATLAS) a few distributions with more statistics…. 8

Signal Strengths and Couplings With the current precision, the production rates agree with the SM prediction and the Higgs boson couples to fermions and vector bosons as expected. 9

Constraints on the Heavy Higgs Boson ( ) κ = θ κ = θ 2 2 2 2 The mixing of H and leads to the modifications S cos and ' sin SM σ = κ × σ Γ = κ ×Γ = 2 SM 2 SM SM , , BR BR , h h h h h h κ 2 ' ( ) σ = κ × σ Γ = ×Γ = − × 2 SM SM SM ' , , B R 1 BR BR − H H H H H new H 1 BR new The measurement of the light Higgs boson can constrain the heavy Higgs boson: ( ) ( ) σ × σ × BR BR ( ) ( ) ( ) µ = = κ ⇒ µ = = κ − = − µ − 2 2 h H ' 1 BR 1 1 BR ( ) ( ) h H new h new σ × SM σ × SM BR BR h H independent of the mass of the heavy Higgs boson m . H 10

Constraints on 2HDM Assuming no change in Higgs decay kinematics and no new production process, the measured rates of (125) can be turned into constraints h α β on the two 2HDM parameters: and ( ) β β − α Parametrized using tan and in s g g htt hVV ( )( ) 2 2 σ ⋅ → →     BR gg h WW g g ≈ × htt    h VV  ( ) ( )  σ → ⋅ →  SM SM gg h BR h WW  g   g    htt hVV S M 11

BR inv from direct and indirect constraints = Assuming BR BR , i.e., all new decays are invisible decays, NEW inv < κ ≤ constraints from: - the rate measurements: BR 0.49 for 1; inv V < - the direct searches: BR 0.2 5 inv Combining the direct searches with the indirect (rate measurements) in κ κ κ the most general model: , , , W Z t κ κ κ κ κ κ , , , , , , BR with τ µ γ γ b g Z inv The total Higgs boson width κ ⋅Γ 2 SM Γ = h h − h 1 BR inv ( ) < BR 23% 24% at 95% CL inv arXiv:1509.00672 (ATLAS) 12

Searches for H→ µτ Decay τ τ → τ → CMS: decay final states considered: e, hadrons, categorization according to number of jets: 0, 1 and 2 jets An excess with a significance of σ 2.4 is observed, corresponding ) ( ) ( + → µτ = 0.39 to BR H 0.84 % − 0.37 → µτ → µτ ATLAS result from H : had ( ) ( ) → µτ = ± BR H 0.77 0.62 %. Consistent with both null and the CMS result, more information is needed… arXiv:1502.07400 (CMS) arXiv:1508.03372 (ATLAS) 13

Higgs Boson Pair Production Non-resonant production offers a direct probe of the Higgs boson self-coupling, but the rates are low and backgrounds are high λ ( ) ( ) ( ) 2 V φ = µ φ φ + λ φ φ 2 † † ( ) σ → ≈ gg hh 9.9 pb in SM Dolan et al, arXiv: 1206.5001 arXiv:1509.04670 (ATLAS) 14

Higgs Boson Pair Production → Resonant production: H hh γγ ττ bb and bb have comparable sensitivities at low mass, bbbb dominates at high mass arXiv:1509.04670 (ATLAS) 15

hMSSM Scenario 16

Coupling Projections Many studies done for US Snowmass process, Europe ECFA studies. Snowmass Higgs report, arXiv:1310.8361 300 fb -1 (Extrapolated from 2011/2012 results) Two as sumptions on sys tematics : 1. no change ( ) ∆ ∝ 2. theory / 2, r est 1 Lumi (Based on parametric simulation) Even with the projected precisions at HL-LHC, the couplings  are not expected to be constrained better than 5%. 17

Case for a Precision Higgs Program How large are potential deviations from BSM physics? How well do we need to measure them to be sensitive? To be sensitive to a deviation ∆ , the measurement precision needs to be much better than ∆ , at least ∆ /3 and preferably ∆ /5! Since the couplings of the 125 GeV Higgs boson are found to be very close to SM ⇒ deviations from BSM physics must be small. Typical effect on coupling from heavy state M or new physics at scale M: 2 υ   ∆      6% @ M 1 TeV   M (Han et al., hep-ph/0302188, Gupta et al. arXiv:1206.3560, …) MSSM decoupling limit ∆ at sub-percent to a few percent, will be challenging to distinguish the MSSM decoupling limit from the SM in the case of no direct discovery. (ILC DBDPhysics) ⇒ Need percent-level or better measurements! 18

e + e - Collider Electroweak production cross sections are predicted with (sub)percent level precisions in most cases Relative low rate can trigger on every event Well defined collision energy allow for the “missing” mass reconstruction ( eg recoiling mass) Clean events, smaller background small number of processes Ideal for precisions: measurements or searches 19

Higgs Boson Production − →  At s 240 250 GeV, ee ZH production is maximum and → νν dominates with a smaller contribution from ee H . Beyond that, the cross section decreases asymptotically as → → νν 1 s for ee ZH and increases logarithmically for ee H . = σ ≈ σ ≈ s 250 GeV: 200 fb, 10 fb νν ZH H 20

Cross Sections and Event Rates − = 1 5 ab @ s 250 GeV >1,000,000 Higgs boson events 21

Recoil Mass Distributions Unique to lepton colliders, the energy and momentum of the Higgs → boson in ee ZH can be measured by looking at the Z kinematics only. Recoil mass reconstruction: ( ) −  2 recoil = − 2 2 m s E p Z Z ⇒ identify Higgs without looking at Higgs. ( ) σ → Measure ee ZH independent of the Higgs boson decay ! 22

Mass and Cross Section → The Higgs boson mass and the ee ZH cross section can be extracted from the recoil mass spectra: ( ) ≈ σ →  resonance peak M , resonance height ee ZH H → Z qq → µµ Z ∆ ∆ σ σ   M 5.5 MeV 0.5% H ZH ZH → µµ from Z ee, and qq decays → µµ from leptonic decays Z ee, ( ) ( ) statistics important resolution important 23

Accessible Decay Modes Higgs boson decays can be studied by examining the system recoiling against the Z boson decays Limitations: statistics even with 1 million events At HL-LHC: trigger and systematics CEPC will be sensitive to unknown Higgs boson decays 24

Branching Ratios Examining the rest of the events to study Higgs boson decays and measure ( ) ( ) σ → × → ee ZH BR H XX thus allowing the measurements of Higgs decay BR without assumptions. → H hadrons → Apply flavor tagging to separate H bb cc gg , , → → H gg → H cc H bb 25