Higgs boson(s) in the NMSSM

Transcription

1 Higgs boson(s) in the NMSSM U. Ellwanger, LPT Orsay Supersymmetry had a bad press recently: No signs for squarks/gluino/charginos/neutralinos... at the LHC Conflict (?) between naturalness and the Higgs mass of 126 GeV Still: No convincing alternatives solving the hierarchy problem, including dark matter, Grand Unification... (the goodies of supersymmetry) Moreover: Supersymmetric extensions of the Standard Model are not unique (see talks by G. Ross, N. Weiner...)! The minimal extension (MSSM) has its shortcomings (see below), many constraints are MSSM specific; notably those from the Higgs mass of 126 GeV! Why?

2 The quartic Higgs coupling In the Standard Model, the mexican hat potential of the Higgs field V(H) = m 2 H 2 +λ 2 H 4 allows to express the physical Higgs mass M h in terms of the known vacuum expectation value v (given by the Z/W masses) and λ: M 2 h = 2λ2 v 2 Larger M h corresponds to larger λ If we would have known the coupling λ, we could have predicted the Higgs mass M h MSSM: two SU(2) doublets H u, H d : The quartic self couplings are given by the electroweak gauge couplings upper tree level bound on the lighter Higgs mass M h M Z Large (unnatural?) radiative corrections needed for a 126 GeV Higgs

3 The NMSSM Note: The SU(2) doublets H u and H d of the MSSM have neutral and charged fermionic superpartners Ψ Hu, Ψ Hd which are not observed at LEP a fermionic supersymmetric mass term µψ Hu Ψ Hd with µ O(M Weak ) must be present (µ appears also in the scalar potential) an accident? (The µ-problem, see Kim+Nilles 1984) Better: recall how fermionic mass terms are generated in the SM: introduce a Yukawa coupling λsψ Hu Ψ Hd to a scalar (here: a gauge singlet S) S has automatically a vev v s of O(M Susy ) due to the soft Susy breaking terms generates a mass term µ eff = λv s of the desired order

4 Additional benefits of the NMSSM: An extra quartic coupling λ 2 H 2 u H2 d due to SUSY Larger mass M hsm > M Z at tree level (if tanβ < 5, λ > 0.5) An additional singlino Ψ S (mixes with higgsinos/bino a good dark matter candidate) complicates squark/gluino decay cascades; weaker bounds from sparticle searches via E miss T?

5 E.g. in the m 0 M 1/2 plane (with D. Das, A. Teixeira): snmssm, 3-6 jets snmssm, 7-9 jets cmssm, 3-6 jets M 1/ m 0 Slightly lower bounds on M 1/2 for m 0 < 1 TeV stronger reduction possible if constraints at the GUT scale are relaxed

6 NMSSM: Three physical scalars, superpositions of H u, H d and S with vevs v u, v d, v s where v 2 u +v 2 d = v2 SM, but v u/v d tanβ and v s unknown Moreover: Two physical pseudoscalars, possibly a very light one The scalar masses have to be obtained by diagonalising a 3 3 mass matrix, typically: a mostly SM like eigenstate h SM, a mostly singlet like eigenstate h S, a heavy MSSM-like scalar H The tree level mass of the mostly SM like h SM is M 2 h SM = M 2 Z cos2 2β +λ 2 (v 2 u +v 2 d )sin2 2β ± (... ) ± (... ): From mixing of the mostly SM like scalar h SM with the mostly singlet like scalar h S (dep. on unknown parameters); positive if M hs < M hsm! Larger mass M hsm > M Z at tree level, all in all: M hsm 126 GeV does not require large (unnatural) radiative corrections

7 If M hs < M hsm : Visible in Higgs pair production/measurements of triple Higgs coupling(s)? (h S +h S ) + (h S +h SM ) + (h SM +h SM ) production cross section relative to the SM as function of h S = GeV (U.E ): 2,4 2,2 2 σ TOT /σ SM 1,8 1,6 1,4 1, M H1 [GeV] Possibly, but not necessarily enhanced

8 The measured signal rate in H γγ ATLAS-CONF (in Higgs prod. via Vector Boson Fusion, VBF): VBF 0 Local p 2 VBF Observed p 0 VBF Expected p 0 H γγ ATLAS Preliminary Data 2012, s = 8 TeV Data 2011, Ldt = 20.7 fb s = 7 TeV Ldt = 4.8 fb -1-1 m H [GeV] 1σ 2σ 3σ After combining with Higgs production via gluon fusion: R γγ measured signal rate Standard Model signal rate = 1.65±0.32

9 CMS H γγ (HIG PAS, comb. VBF+ggF) Confirmation of the enhanced γγ rate in the cutbased analysis (r.h.s.), but not in the MVA analysis (l.h.s.)

10 The γγ signal rate in the NMSSM 1) Recall: BR(H γγ) = Γ(H γγ) Γ(H bb)+... (Γ(H bb) gives 58% of the total width for a 126 GeV SM Scalar) Due to the mixing of H u, H d, S it is easily possible that, in the NMSSM, the mostly SM like h SM has a reduced coupling to bb, and hence a reduced width Γ(h SM bb) an enhanced BR(h SM γγ) nearly SM like couplings to the top quark (whose loops induce the coupling to gluons) and to the electroweak gauge bosons the production rates in gluon fusion and/or VBF are hardly reduced The γγ signal rate is enhanced (U.E. 20)

11 2) Recall: In the SM, Γ(H γγ) is induced via W-boson (and top quark) loops: Photon Higgs W boson t quark Photon In the NMSSM, the singlet S couples to the (charged) higgsinos ψ Hu,ψ Hd : λsψ Hu ψ Hd (recall the generation of the µ term through v s ) If h SM has a S-component, charged higgsinos contribute to the loop and to Γ(h SM γγ) unless λ is small or the higgsinos are heavy

12 Plot of the possible signal rates in the γγ and VV ZZ, WW final states relative to the SM: (semi-constr. NMSSM, with C. Hugonie, ) R 2 VV (gg) γγ R 2 (gg) R γγ 2 (gg) can be enhanced by a factor 2 (or larger); both mechanisms 1) and 2) contribute! If R γγ 2 (gg) < 2: R2 VV (gg) RZZ 2 R2 WW is not necessarily enhanced

13 R2 bb (VH) against Rγγ 2 (gg): In conflict with the SM-like signal rate h SM bb? R 2 bb (VH) γγ R 2 (gg) If R γγ 2 (gg) < 1.5: R2 bb (VH) is not necessarily reduced, the enhancement of Rγγ 2 (gg) results from the additional higgsino loop, not from a reduction of Γ(h SM bb)

14 If h SM mixes strongly with another mostly singlet-like scalar: The mass of this mostly singlet-like h S should be not too far from M hsm 126 GeV Are there hints for (at least weak bounds on) such a state? Unfortunately: The couplings/signal rates of h S are typically reduced relative to the ones of h SM, but it can still be visible in some SM Higgs search channels

15 If this state has a mass below 114 GeV: Bounds on the signal rate ξ 2 in Z Z +h SM at LEP: If ξ 2 (h S ) 0.2: Compatible with the weak bounds ( 2σ excess) around 95 GeV 95% CL limit on ξ (a) LEP s = 91-2 GeV Observed Expected for background m H (GeV/c 2 ) G. Belanger et al., : M hs 95 GeV with ξ 2 (h S ) 0.2 is a possible scenario in the semiconstrained NMSSM

16 Or: The 126 GeV signal could be due to the superposition of two scalars close in mass (J. Gunion et al., and ) possible enhancement of the diphoton signal rate (But: this would NOT resolve differences in mass measurements in the ZZ and γγ channels (ATLAS)!) Or: h S could be heavier than 126 GeV (G. Belanger et al., )? Some appetizers :

17 Recall: H γγ at CMS ( ): Additional 2σ excess around M H 136 GeV (MVA analysis, l.h.s.) or: confirmation of the enhanced γγ rate of the 126 GeV Scalar in cutbased analysis, r.h.s.; still: 1σ excess around M H 136 GeV

18 Recall: H γγ at ATLAS (ATLAS-CONF ): VBF 0 Local p 2 VBF Observed p 0 VBF Expected p 0 H γγ ATLAS Preliminary Data 2012, s = 8 TeV Data 2011, Ldt = 20.7 fb s = 7 TeV Ldt = 4.8 fb -1-1 m H [GeV] 1σ 2σ 3σ small additional excess around M H 137 GeV

19 Tevatron VH bb ( ): (Fits to the measured signal rate relative to the SM) σ/sm Tevatron Run II, L int fb -1 SM Higgs combination Observed σ ± 1 s.d. H x 1.5 (m H =125 GeV/c 2 ) σ ± 2 s.d. H x 1.0 (m H =125 GeV/c 2 ) SM= m H (GeV/c 2 ) small additional excess around M H 140 GeV (low mass resolution)

20 CMS VH bb (HIG PAS): small additional excess for M H > 130 GeV (low mass resolution)

21 (σ H x Br(H WW))/SM Tevatron VH WW ( ): Tevatron Run II, L int fb -1 SM H W + W - combination SM=1 Observed ± 1 s.d. ± 2 s.d. σ H x 1.5 (m H =125 GeV/c 2 ) σ H x 1.0 (m H =125 GeV/c 2 ) m H (GeV/c 2 ) small additional excess around M H 140 GeV (low mass resolution)

22 ATLAS VH WW (ATLAS-CONF ): 0 Local p ATLAS Preliminary (*) H WW lνlν Obs. Exp. m H = 125 GeV -1 s = 7 TeV: Ldt = 4.6 fb -1 s = 8 TeV: Ldt = 20.7 fb ±1 σ ±2 σ 0σ 1σ 2σ -3 3σ σ [GeV] m H small additional excess for M H > 135 GeV (low mass resolution)

23 But: only upper bounds < 0.2 SM on the signal rate of an additional 137 GeV boson in H ZZ, H ττ (ATLAS, CMS) Still: at least 6 ( 1 σ) excesses ( look elsewhere effect ) consistent with an additional 137 GeV Scalar Notably in Higgs search channels with low mass resolution WW, bb and ττ, the SM Higgs boson (assuming SM-like signal rates) should be considered as a background, allowing to set limits on/or find evidence for additional Higgs states with reduced couplings! (Part of the wishlist of On the presentation of the LHC Higgs Results, F. Boudjema et al., )

24 Conclusions Given M hsm 126 GeV, the NMSSM is the most natural SUSY extension of the SM: scale invariant SUSY interactions, no need for large radiative corrections, but gauge coupling unification and a good dark matter candidate as in the MSSM An enhanced Higgs pair production rate can be a hint for the NMSSM An enhanced γγ signal rate of h SM can be a hint for the NMSSM Additional signals (below the SM signal rate, channel dependent!) in Higgs searches at low mass below or above 126 GeV can be a hint for the NMSSM