Little Higgs at the LHC: Status and Prospects

Transcription

1 Little Higgs at the LHC: Status and Prospects Marco Tonini DESY Theory Group (Hamburg) based on: Reuter/MT, JHEP 1302, 077 (2013) Reuter/MT/de Vries, hep-ph/ Reuter/MT/de Vries, DESY (in prep.) SUSY August 2013

2 Motivation How to constrain a generic model in HEP? direct searches for resonances electroweak precision tests flavour constraints nowadays: Higgs sector Higgs sector is the key to understand EW-scale physics (and beyond?) 2 / 17

3 Two paradigms for EWSB hierarchy problem as guideline to answer the following question: what is the dynamical origin of EWSB? weakly coupled answer Ñ Supersymmetry strongly coupled answer Ñ Composite Higgs, Little Higgs... 3 / 17

4 Strongly coupled answer Original idea: pions of low-energy QCD E QCD - quarks as d.o.f. - perturbative th. for E>Λ low-energy QCD - pions: pngb of SSB (new d.o.f.) - eff. theory valid up to E<Λ Λ 1 GeV: SSB of QCD-flavour symmetry SU(2)xSU(2) SU(2) L QCD = 1 4 Ga µνg µν a + qi/dq q=u,d L 2 = f 2 4 tr µ Σ 2, Σ =exp i π 0 π + f π π 0 Composite/Little Higgs Ansatz Higgs as pngb of a new (approximate) global symmetry which is spontaneously broken at a scale Λ 4πf 4 / 17

5 Strongly coupled answer Original idea: pions of low-energy QCD E QCD - quarks as d.o.f. - perturbative th. for E>Λ low-energy QCD - pions: pngb of SSB (new d.o.f.) - eff. theory valid up to E<Λ Λ 1 GeV: SSB of QCD-flavour symmetry SU(2)xSU(2) SU(2) L QCD = 1 4 Ga µνg µν a + qi/dq q=u,d L 2 = f 2 4 tr µ Σ 2, Σ =exp i π 0 π + f π π 0 Composite/Little Higgs Ansatz Higgs as pngb of a new (approximate) global symmetry which is spontaneously broken at a scale Λ 4πf 5 / 17

6 Summary The Little Higgs paradigm: it is an effective theory valid up to the cut-off Λ: no UV-completion of the strongly coupled regime E ą Λ Higgs as a pngb of a global SSB at Λ 4πf (like pions!) new fermionic/vector states with masses f besides SM-ones EWSB is triggered naturally (Collective Symmetry Breaking), i.e. v Op100 GeVq for f 1 TeV with only log-sensitivity to Λ 6 / 17

7 Outline of the work purpose: constraining the parameter space of the three most popular Little Higgs models Simplest Little Higgs (SLH) [Schmaltz, 2004] Littlest Higgs (L 2 H) [Arkani-Hamed et al., 2002] Littlest Higgs with T parity (LHT) [Low et al., 2003] scrutinizing the available public data from the 7-8 TeV LHC runs Electroweak Precision Tests (EWPT) Higgs Searches Direct Searches for BSM states 7 / 17

8 EWPT & Higgs: Data used Precision constraints of the EW sector: M H M W W M Z Z 0 had 0 Rlep 0,l A FB A l (LEP) A l (SLD) 2 lept sin eff (Q ) FB 0,c A FB 0,b A FB A c A b 0 Rc 0 Rb m c m b m t (5) 2 had (M ) Z G fitter SM May Higgs results expressed in terms of µ i ř p ɛp i ř σp p ɛp i σsm p BR ph Ñ X ix iq BR ph Ñ X ix iq SM ñ best fit for each decay of the Higgs W,Z H bb H s (*) H WW l l s s H s s (*) H ZZ 4l s s Combined s s -1 = 7 TeV: Ldt = 4.6 fb -1 = 8 TeV: Ldt = 13 fb -1 = 7 TeV: Ldt = 4.6 fb -1 = 8 TeV: Ldt = 20.7 fb -1 = 7 TeV: Ldt = 4.8 fb -1 = 8 TeV: Ldt = 20.7 fb -1 = 7 TeV: Ldt = 4.6 fb -1 = 8 TeV: Ldt = 20.7 fb -1 = 7 TeV: Ldt = fb -1 = 8 TeV: Ldt = fb [ATLAS-CONF ] ATLAS Preliminary s s s -1 = 7 TeV: Ldt = 4.7 fb -1 = 8 TeV: Ldt = 13 fb µ = 1.30 ± 0.20 m H = GeV (O - O meas ) / fit meas [GFitter Collaboration] Signal strength (µ) up to 25 fb 1 at 7 ` 8 TeV! 8 / 17

9 Little evidence Where do Little Higgs corrections to SM quantities come from? new Higgs decay channels, e.g. invisible decay h Ñ A H A H in LHT modified Higgs couplings with SM fermions and vector bosons # e.g. 2 m2 W v yw h W `W, 1 SM y W 1 ` O `v 2 {f 2 LH new Higgs interactions with heavy resonances e.g. m T v yt h T T m T f, y T O `v 2 {f 2 modified neutral- and charged-currents g ÿ SM e.g. fγ µ pgl ` δg LqP L ` pgr SM ` δg RqP R f Z µ c W f 9 / 17

10 EWPT & Higgs: Results parameters: f SSB scale, R ratio of Yukawa couplings in top sector f Á 694 GeV at 95% CL ñ lower bounds on heavy partners, e.g. m W 1 Á 453 GeV m T Á 984 GeV minimum required fine tuning: 5% results mainly driven by EWPT (ev. see backup) 10 / 17

11 Direct Searches: Data used ATLAS and CMS published results of many SUSY & Exotica searches for BSM states, using up to 20 fb 1 data of 8 TeV LHC runs final state topology ATLAS CMS monojet + {E T CONF PAS EXO CONF jets + {E T PAS SUS CONF lepton(s) + jets + {E T CONF CONF CONF mostly interesting for BSM theorists: 95% CL upper bounds on the visible cross section of a generic BSM signal over the SM background σ vis σ BSM prod BR loooomoooon th. pred. ɛ A lomon cuts efficiency 11 / 17

12 Direct Searches: Recasting Analysis our work: ñ recasting of available analyses assuming a Little Higgs signal 1 generate samples of LH signal events matching the final state topologies, and evaluate relative cross-sections evaluate ɛ A of the event samples applying the selection cuts of the different analyses if σvis LH ą σ 95% : parameter space point is excluded at 95% CL vis 1 only for the Littlest Higgs model with T parity 12 / 17

13 An example example: monojet + {E T final state topology possible LHT signal: p p Ñ Q H QH Ñ pqa H q p qa H q! " #$%&'(# +#,# * " #,# +# )# )# * " # +#! " #$%&'(# ATLAS-CONF selection cuts: σ LHT vis σ 95% vis ñ n j ď 2 w/ p T ą 30 GeV p T pj 1q ą 120 GeV, ηpj 1q ă 2.0 n L 0 w/ p T peq ą 20 GeV, p T pµq ą 7 GeV {E T ą 120 GeV φp {E T, j 2q ą 0.5 pf 400 GeV, κ 0.5q 21.5 pb 2.8 pb exclusion at 95% CL!! O 13 / 17

14 An example example: monojet + {E T final state topology possible LHT signal: p p Ñ Q H QH Ñ pqa H q p qa H q! " #$%&'(# +#,# * " #,# +# )# )# * " # +#! " #$%&'(# ATLAS-CONF selection cuts: σ LHT vis σ 95% vis ñ n j ď 2 w/ p T ą 30 GeV p T pj 1q ą 120 GeV, ηpj 1q ă 2.0 n L 0 w/ p T peq ą 20 GeV, p T pµq ą 7 GeV {E T ą 120 GeV φp {E T, j 2q ą 0.5 pf 400 GeV, κ 0.5q 21.5 pb 2.8 pb exclusion at 95% CL!! O 14 / 17

15 An example example: monojet + {E T final state topology possible LHT signal: p p Ñ Q H QH Ñ pqa H q p qa H q! " #$%&'(# +#,# * " #,# +# )# )# * " # +#! " #$%&'(# ATLAS-CONF selection cuts: σ LHT vis σ 95% vis ñ n j ď 2 w/ p T ą 30 GeV p T pj 1q ą 120 GeV, ηpj 1q ă 2.0 n L 0 w/ p T peq ą 20 GeV, p T pµq ą 7 GeV {E T ą 120 GeV φp {E T, j 2q ą 0.5 pf 400 GeV, κ 0.5q 21.5 pb 2.8 pb exclusion at 95% CL!! O 15 / 17

16 Direct Searches: Results parameters: f SSB scale, κ mirror fermions coupling (assumed to be flavour blind) f Á 638 GeV at 95% CL (Higgs & EWPT: f Á 694 GeV) mirror fermions mass Á 1 TeV hadronic final states searches still the most sensitive ones four-fermion operator bounds necessary to constrain f possible optimization with the assumption of LHT signal instead of SUSY signal ñ backup slide 16 / 17

17 Conclusions Little Higgs are a viable alternative to weakly coupled solutions like SUSY, where fine tuning is a guideline to understand the naturalness of a model Little Higgs models without T parity are already forced into the TeV range by Electroweak Precision Data for models with T parity, sub-tev life is still possible: in LHT f Á 650 GeV at 95% CL Electroweak Precision Data still represent the most severe constraints, but Higgs- and Direct Searches are getting quickly competitive (especially for T parity models) a comprehensive method to constrain the LHT model has been explored, as well as an optimization proposal for SUSY and Exotica searches to increase the exclusion potential increasing luminosity will improve the visible cross section upper bounds and reduce the uncertainties of the Higgs results 17 / 17

18 Thank you for your attention!

19 Optimization Proposal: monojet + {E T 19 / 17

20 Higgs Searches vs. EWPT the shape of the combined result is driven by the EWPT constraints (much smaller uncertainties) Higgs Searches: for f Á 600 GeV invisible decay h Ñ A H A H open and dominant Higgs Searches: subdominant dependence on R w.r.t. f is a well-known result in the context of the Higgs Low-Energy Theorem 20 / 17

21 L 2 H results parameters: f SSB scale, c mixing angle in gauge sector f Á 3.6 TeV at 95% CL ñ lower bounds on heavy partners, e.g. m W 1 Á 2.4 TeV m T Á 5.1 TeV minimum required fine tuning: 0.1% results driven by EWPT 21 / 17

22 SLH results parameters: f SSB scale, t β ratio of vevs of scalar fields φ 1,2 f Á 3.3 TeV at 95% CL ñ lower bounds on heavy partners, e.g. m W 1 Á 1.5 TeV m T Á 3.2 TeV minimum required fine tuning: 0.5% results driven by EWPT 22 / 17

23 Partial Decay Widths in LH 1-loop decays Γph Ñ ggq LH α2 sm 3 h 32π 3 v 2 ˇˇˇ ÿ f,col 1 ˇˇˇ2 2 F 1 px f q y f 2 Γph Ñ γγq LH α2 m 2 ÿ h 4 ˇˇˇ 256π 3 v 2 2 F 1 px f q y f ` ÿ F 2 1px vq y v ` ÿ F 0px sq y sˇˇˇ2 f,ch v,ch s,ch where x i 4m2 i ; F m ipx iq are loop functions; y 2 i the modified Yuk. couplings h ñ tree-level decays narrow-width approximation: σ ggh LH Γph Ñ σggh ggqlh SM Γph Ñ ggq SM Γph Ñ V V q LH Γph Ñ V V q SM ˆ ghv V g SM Γph Ñ f fq LH Γph Ñ f fq SM ˆ ghff g SM hff hv V 2 2 where g hv V m2 V v y V and g hff m f y v f 23 / 17

24 LHT typical Mass Spectrum 24 / 17

25 LHT typical Branching Ratios Particle Decay BR k 1.0 BR k 0.4 u H A H W H d 61% 0% Z H u 30% 0% A H u 9% 100% W ` H stable A H W 100% 2% u H d 0% 44% d H u 0% 27% l H ν 0% 13.5% ν H l 0% 13.5% Z H A H H 100% 2% d H d 0% 40% u H u 0% 30% 0% 14% ν H ν 0% 14% l H l 25 / 17

26 LHT 8 TeV Production Cross Sections (1) 26 / 17

27 LHT 8 TeV Production Cross Sections (2) 27 / 17

28 LHT 8 TeV Production Cross Sections (3) 28 / 17