Searching exotic decay channels of the SM Higgs boson at CEPC

Transcription

1 Searching exotic decay channels of the SM Higgs boson at CEPC Hao Zhang Theoretical physics division, Institute of High Energy Physics, Chinese Academy of Sciences For International Workshop on High Energy Circular Electron Positron Collider, Beijing, Nov 7th, 2017 Base on Chinese Phys C 41 (2016) 0632 in collaboration with Zhen Liu and Lian-Tao Wang.

2 New Physics beyond the SM The particle physics SM is one of the most successful model in the last century. It is an effective field theory up to electroweak symmetry breaking scale for particles interact with our sector strongly enough. In principle, NP must be introduced at some scale due to lots of theoretical and phenomenological reasons. Although there are some comments according to the naturalness defined by the preference of Homo Sapiens, in practice, nobody really knows when it will appear. TeV? TeV? 0TeV? (tree level, 1-loop level, 2-loop level, ) Seesaw? GUT or Planck scale?

3 New physics particles : where are they? Interaction strength Cheers! Weakly interacting light particles, very challenging Indirect search: effective operators Weakly interacting heavy particles, very challenging Mass

4 What can we do with CEPC? As a Higgs factory, CEPC will generate ~ 1,000,000 SM Higgs bosons. From Manqi Ruan

5 e+ e+ e+ What can we do with CEPC? H W Z e+ e Z H H As a Higgs factory, CEPC will generate ~W 1,000,000 SM Higgs Z e bosons. e e Z e e One of the most important +scientific motivation of CEPC is Figure 3.6 Feynman diagrams of the e e! ZH, e e! H and e e! e e H processes. understanding the properties of the SM Higgs and the nature of the SM EWSB. CEPC Preliminary CEPC Preliminary Z µ+µ-; Entries/0.2 GeV σ(fb) -1 CEPC Simulation S+B Fit Signal Background Total 150 Ldt = 5 ab 2000 HZ Entries/0.2 GeV HZ( νν) WW H e+e- f f H [GeV] µ +µ Mrecoil[GeV] CEPC-SPPC precdr, (a) Volume I-Physics & Detector, The CEPC-SPPC Study Group (b)

6 What can we do with CEPC? The combination of different Z decay modes gives: 1 Precision of Higgs coupling measurement (Contrained Fit) LHC 300/3000 fb -1 CEPC 250 GeV at 5 ab -1 wi/wo HL-LHC Relative Error κ b κ c κ g κ W κ τ κ Z κ γ CEPC-SPPC precdr, Volume I-Physics & Detector, The CEPC-SPPC Study Group

7 What can we do with CEPC? The combination of different Z decay modes gives: LHC HL-LHC CEPC: 1ab -1 3ab -1 5ab -1 Precision (%) κ Z κ W κ γ κ g κ b κ c κ τ κ µ BR inv Γ h What can we do beyond the SM? CEPC-SPPC precdr, Volume I-Physics & Detector, The CEPC-SPPC Study Group

8 What can we do with CEPC? As a Higgs factory, CEPC will generate ~ 1,000,000 SM Higgs bosons. s schemes σlo (fb) σ NLO (fb) σ NNLO (fb) α(0) ± ± α(m Z ) ± G µ ± α(0) ± ± α(m Z ) ± G µ ± ± ~ 1% theoretical error at NNLO (EW+QCD) level TABLE II from Q.-F S, F Feng, Y Jia, W.-L Sang, Phys. Rev. D96 (2017) , see also Y Gong, Z Li, X Xu, L.L Yang, X Zhao, Phys. Rev. D95(2017)

9 What can we do with CEPC? Higgs boson is sensitive to the NP. It decays VERY VERY slow! Γ H [GeV] 3 2 LHC HIGGS XS WG 2013 H VV, H VV* It is possible to measure the NP effect in the Higgs decay process even it is tiny M H [GeV] Z W t H Width (GeV) M/Γ CEPC-SPPC precdr, Volume I-Physics & Detector, The CEPC-SPPC Study Group

10 Exotic decay of the SM Higgs boson NP at high energy scale can modified the branching ratios of the Higgs decay modes. If the effect is significant, ~percent level, we may discover it indirectly. On the other hand, there are chances that the Higgs boson decays into exotic light particles in the NP! H H NP NP SM decay mode Exotic decay modes

11 Exotic decay of the SM Higgs boson Light exotic particles weakly couple to the SM sector: - SUSY model: MSSM, NMSSM, light neutralinos, gravitino; - Hidden valley with Higgs boson as the mediator: Higgs portal ; - Dark matter: dark force, - Bayrogenesis: exotic light scalar; - Neutrino mass: N-loop radiative seasaw; -

12 Exotic decay of the SM Higgs boson Some technical assumptions: - The first decay is two-body decay; - In the final state, there are only SM particles or missing energy. (For exotic decay modes with displaced vertices, please see Nathaniel s talk. ) h h h h h 2 h 2 3 h h 2 (1 + 3) h h h h 2 4 h h 2 6

13 Exotic decay of the SM Higgs boson What can we do with HL-LHC? PHYSICAL REVIEW D 90, (2014) Exotic decays of the 125 GeV Higgs boson David Curtin, 1,a Rouven Essig, 1,b Stefania Gori, 2,3,4,c Prerit Jaiswal, 5,d Andrey Katz, 6,e Tao Liu, 7,f Zhen Liu, 8,g David McKeen, 9,,h Jessie Shelton, 6,i Matthew Strassler, 6,j Ze ev Surujon, 1,k Brock Tweedie, 8,11,l and Yi-Ming Zhong 1,m 1 C.N. Yang Institute for Theoretical Physics, Stony Brook University, Stony Brook, New York 11794, USA Assume we have 1,000,000 ZH events, with zero background, we still need the branching ratio to be ~ 5-5 to reach a 95% C.L. If the LHC can give a competitive result, we need to work hard to combine the data from other Z decay model and Higgs production channels. If the LHC gives a much better result than this. CEPC can hardly give better result.

14 Exotic decay of the SM Higgs boson What can we do with HL-LHC?

15 Exotic decay of the SM Higgs boson What can we do with HL-LHC?

16 Exotic decay of the SM Higgs boson Our simulation, what we do and what we do not do. Parton level event generation, with Higgs and Z boson decay; Gaussian smearing effect, b-tagging and veto; Parton level background event generation; Optimize cuts for each specific channel. X X X X X Full ISR and initial state effects ; Parton showering, hadronization, jet clustering ; Jet substructure analysis ; BDT or MVA technology ; Hadronic Z decay mode.

17 Exotic decay of the SM Higgs boson An example: - h Insert light (pseudo)scalar (a, s) or vector boson (Z ). - h ss(aa) (jj)(jj), h Z Z (jj)(jj). - Effective Lagrangian: L e = p 2" s vhss + p 2" a vhaa + " 1 g1vhz 0 1µZ 0 0µ 1 + " 2g2vhZ 0 2µZ 0 0µ 2 + y s s ff + iy a a f 5 f + sc s s + g 0 1Z 0 1µ f µ f + g 0 2Z 0 2µ f µ P R f sg µ G µ + sc a a ag µ Gµ Spin correlations are kept in our simulation.

18 Exotic decay of the SM Higgs boson An example: - Parton level simulation. - Detector effects (energy resolution, PID efficiency): E j E j = 0.3 p Ej /GeV 0.02 E E = 0.16 p 0.01 E /GeV 1 =2 5 3 PID Efficiency CEPC Preliminary cos(θ) < 0.98 µ ± e ± π ± p T,` p T,` sin ` P (GeV/c) 2 CEPC-SPPC precdr, Volume I-Physics & Detector, The CEPC-SPPC Study Group

19 Exotic decay of the SM Higgs boson An example: - Parton level simulation. - Main SM backgrounds: e + e - Zjjjj+X. - Systematic error of the simulation due to the ISR effect. (We thank M.-Q Ruan for helpful discussion. ) - A parton level simulation which could give a reasonable estimation of the significance with clearly error estimation is acceptable in current study.

20 Exotic decay of the SM Higgs boson An example: - Preselection cuts: cos j,` < 0.98,E j,` > GeV, y ij 2min E2 i,e2 j (1 cos ij ) Evis 2 a pair of OSSF leptons, `` > 80 >y cut, m`` m Z < GeV, m recoil m h < 5GeV. - MadGraph5_aMC@NLO. - The ISR effect of the background is roughly mimicked by generating events with 1 additional photon (with pt>1gev to avoid the IR divergence). (No ISR for signal events! ) - Additional cut to suppress the ISR effect: E vis > 225GeV.

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22 Exotic decay of the SM Higgs boson (jjjj) Branching ratio h (j j ) (j j ) h ss(aa) qqqq h Z'Z' qqqq h ss(aa) gggg Branching ratio h (j j ) (j j ) (b-veto) h ss(aa) qqqq h Z'Z' qqqq h ss(aa) gggg m X (GeV) m X (GeV) Branching ratio h (cc) (cc) h ss(aa) cccc h Z'Z' cccc Branching ratio h (bb) (bb) h ss(aa) bbbb h Z'Z' bbbb m X (GeV) m X (GeV)

23 Exotic decay of the SM Higgs boson (jjjj) Branching ratio ATLAS Collaboration, EPJC76(2016)605 h (j j ) (j j ) h ss(aa) qqqq h Z'Z' qqqq h ss(aa) gggg Branching ratio h (j j ) (j j ) (b-veto) h ss(aa) qqqq h Z'Z' qqqq h ss(aa) gggg m X (GeV) m X (GeV) Branching ratio h (cc) (cc) h ss(aa) cccc h Z'Z' cccc Branching ratio h (bb) (bb) h ss(aa) bbbb h Z'Z' bbbb m X (GeV) m X (GeV)

24 Exotic decay of the SM Higgs boson (jj+met) Another topology h h h h 2 (1 + 3) Benchmark model: supersymmetry. h 02 H 01 j j h j j 01 h h 2 (1 + 3) 01

25 Exotic decay of the SM Higgs boson (jj+met) dσ/bin (fb) with 2! 1 e + e! `+` ` `jj bution of the dilepton CEPC, s = 240 GeV, 5 ab -1 Zh Z+jj+met background. Br(h jj+met)~1%, σ(zh)~240fb, without cuts, it gives ~0.17fb background m recoil (GeV)

26 Exotic decay of the SM Higgs boson (jj+met) 2 1 with 2! 1 e + e! `+` ` `jj (GeV) bution of the dilepton dσ/bin (ab) E T m (GeV) jj 0

27 Exotic decay of the SM Higgs boson (jj+met) Off-shell χ2 decay. Large m2: mjj~2m2/3. h 02 H j j h h 2 (1 + 3) h j j

28 Exotic decay of the SM Higgs boson (jj+met) h H j j 01 h 2 3 4

29 Exotic decay of the SM Higgs boson (jj+met) h H j j 01 h 2 3 4

30 Summary and outlook BR(h Exotics) % C.L. upper limit on selected Higgs Exotic Decay BR HL-LHC CEPC ILC(H20) FCC-ee -4-5 ME T (bb)+me T (jj)+me T (ττ)+me T bb+me T jj+me T ττ+me T (bb)(bb) (cc)(cc) (jj)(jj) (bb)(ττ) (ττ)(ττ) (jj)(γγ) (γγ)(γγ) The sensitivity to the invisible Higgs decay has been well studied and the results are from literatures. The tau channels are extrapolated from our simulation with 40% tau tagging rate and more backgrounds considered. The ILC(H20, polarized) and FCC-ee results are rescaled with luminosity.

31 Summary and outlook BR(h Exotics) % C.L. upper limit on selected Higgs Exotic Decay BR HL-LHC CEPC ILC(H20) FCC-ee -4-5 ME T (bb)+me T (jj)+me T (ττ)+me T bb+me T jj+me T ττ+me T (bb)(bb) (cc)(cc) (jj)(jj) (bb)(ττ) (ττ)(ττ) (jj)(γγ) (γγ)(γγ) The accuracy of the measurement of the total width of the Higgs boson is expected to be ~ 2.7%. Thus this offers a much worse sensitivity to most of the exotic decay channels. The initial state effect, parton showering and hadronization effect, full detector simulation, hadronic Z decay mode, and jet substructure analysis are neglected in this work. However, they should be considered in a more complete version of the investigation of these NP signals.

32 Thank you!

33 Backup

34 Exotic decay of the SM Higgs boson (jjjj) ycut=0.001 dσ/bin (fb) 2 1 CEPC, w ISR w/o ISR + - s = 240 GeV, e e Z+4j fb m recoil (GeV)