2 A strongly first order EWPT generically requires a modified Higgs - PowerPoint PPT Presentation

Toyama, Japan Higgs as a Probe of New Physics 2015 T ESTING E LECTROWEAK B ARYOGENESIS VIA D I -H IGGS M EASUREMENTS Tao Liu Hong Kong University of Science and Technology Saturday, February 14, 15

EW Baryogenesis and Higgs Physics [A. Cohen et al’93, P. Huet and A. Nelson’96] � Baryon asymmetry may be generated during EW phase transition, if strongly first order - electroweak baryogenesis (EWBG) � Strongly correlated with Higgs physics: � The related CP-phase must enter Higgs couplings 2 � A strongly first order EWPT generically requires a modified Higgs potential Saturday, February 14, 15

Strongly First Order EWPT � Need to generate a bump for the Higgs potential at high temperature. � Not achievable in the SM 3 � How to achieve it in BSM physics? Saturday, February 14, 15

Mechanism (1): Higher Dim Operators [C. Grojean, G. Servant and J. Wells, ’04] ξ = h H ( T c ) i V ( H ) = µ 2 H † H + κ ( H † H ) 2 + 1 T c Λ 2 ( H † H ) 3 � A negative kappa helps achieve EWPT of strongly first order � Leads to a tri-Higgs coupling at zero temperature 2 v 4 λ = 1 + h Λ 2 = 1 + O (1) m 2 λ SM 4 [A. Noble and M. Perelstein, ’07] Saturday, February 14, 15

Mechanism (2): BSM Scalar (No Mixing with Higgs) � Typically a discrete symmetry is ξ = h H ( T c ) i introduced T c � The well-known stop-assisted strongly 1st order EWPT falls into this category � If colored or electrically charged, may modify Higgs gauge couplings and be probed at HL-LHC or ILC/ CEPC [A. Katz, M. Perelstein, ’14] � Numerically, 20% or more shift in [A. Noble and M. Perelstein, ’07] tri-Higgs coupling V 0 ( φ , T ) = − µ 2 | H | 2 + κ | φ | 2 | H | 2 + η | H | 4 V e ff ( H, T ) = V 0 ( H ) + V T 6 =0 ( H, T ) + V T =0 ( H, T ) H 2 − g φ κ 3 / 2 T − µ 2 + g φ κ T 2 ✓ ◆ 1 2 π H 3 + λ 5 4 H 4 + V T =0 ( H, T ) = √ 2 24 24 Saturday, February 14, 15

Mechanism (3): Higgs-Singlet Mixing [Profumo, Ramsey-Musolf, Wainwright, Winslow. ’14] ‘ = 1 ✓ λ 0 v cos 3 θ + 1 4( a 1 + 2 a 2 x 0 ) cos 2 θ sin θ + 1 ◆ λ 2 a 2 v cos θ sin 2 θ + b 3 3 sin 3 θ + b 4 x 0 sin 3 θ 35 λ SM 6 � Multiple contributions => broad range of lambda Saturday, February 14, 15

Mechanism (3): Higgs-Singlet Mixing [Profumo, Ramsey-Musolf, Wainwright, Winslow. ’14] ‘ The measurements of the tri-Higgs coupling provides an efficient probe = 1 ✓ λ 0 v cos 3 θ + 1 4( a 1 + 2 a 2 x 0 ) cos 2 θ sin θ + 1 ◆ λ 2 a 2 v cos θ sin 2 θ + b 3 3 sin 3 θ + b 4 x 0 sin 3 θ for the EWPT strength and a direct test of the EWBG feasibility 35 λ SM 7 Saturday, February 14, 15

Di-Higgs Production in the SM [J. Baglio, A. Djouadi et. al., ’13] 8 Saturday, February 14, 15

General Comments [J. Baglio, A. Djouadi et. al., ’13] � Rare process! Mainly focus on pp -> hh production � Various decay modes have been studied 9 Saturday, February 14, 15

Current Focus: pp -> hh [R. Frederix et. al., ’14] � Good: simple topology; clean channel, e.g., hh -> bb+di-photon � Not good: negative correlation with lambda; with a positive shift in lambda � Lower signal rate � Weaker dependence on the tri-Higgs coupling 10 Saturday, February 14, 15

Complementary Method: pp -> tthh � ∆ λ � ∆ λ λ � λ / λ SM =1 = ⇣ ⌘ λ λ / λ SM − 1 λ λ SM exp 3 for pp -> tthh (same kinematics is assumed), with λ 0 < < 4 λ SM � Positive correlation with tri-Higgs coupling in the SM neighborhood � With a positive shift in lambda [TL, H. Zhang, 1410.1855] [C. Englert et. al.,1409.8074] � higher signal rate 11 � stronger dependence on the tri-Higgs coupling Saturday, February 14, 15

Illustration: pp -> tthh with hh -> bbbb pp > hh > bb + di-photon VS pp > tthh > ttbbbb Relatively low Xsection * high Br = 300 ab Relatively high Xsection * low Br = 35 ab [TL, H. Zhang, 1410.1855] � HL-LHC: > 2.0 sigma statistical significance is achievable in searching for the SM di-Higgs production; � Comparable to that of the pp -> hh -> bb + diphoton (cut-based): 1.3-2.3 sigma [Y. Yao, ’13; V. Barger et. al. ’13; ATL-PHYS-PUB-2014-019] 12 Saturday, February 14, 15

Tri-Higgs Coupling Measurement via pp -> tthh [TL, H. Zhang, 1410.1855] � Assuming that NP enters tri-Higgs coupling only, if any � Mechanism (1) and (2): HL-LHC shows a good sensitivity 13 � Mechanism (3): HL-LHC shows some sensitivity Saturday, February 14, 15

Outlook � Further improvements: e.g., consider pp -> tt hh -> ttWW bb: loses some signal rate, gains from same-sign leptons [suggested by A. Juste] t ¯ thh � A probe for new physics, e.g., ; Λ � Certainly needs to think how to disentangle various contributions to the di- Higgs production � What are the gains from 100 TeV pp collider. To what extent can we test EWPT of strongly first order (by combining with the other channels)? [R. Frederix et. al., ’14] 14 Saturday, February 14, 15

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T ank y o ! 16 Saturday, February 14, 15

General Comments 17 Saturday, February 14, 15