Light generations partners at the LHC

Transcription

1 Light generations partners at the LHC Giuliano Panico CERN IPNL Lyon 21 March 2014 based on C. Delaunay, T. Flacke, J. Gonzales, S. Lee, G. P. and G. Perez [hep-ph]

2 Introduction

3 Introduction Main goal of the LHC: unveil the nature of the EWSB mechanism First step discovery of an Higgs-like particle m h 125 GeV Local p-value CMS Preliminary s = 7 TeV, L 5.1 fb s = 8 TeV, L 12.2 fb 1σ 2σ 3σ Combined obs. Exp. for SM H H bb H ττ H γγ H WW H ZZ 4σ 5σ 6σ 7σ 8σ m H (GeV) Need for theoretical framework to interpret the data: look for a motivated scenario develop and test hypothetical models

4 Introduction: The Hierarchy Problem The Standard Model solution Higgs as an elementary scalar Minimal realization Excellent agreement with EW and flavor data... but the Higgs mass is unstable under radiative corrections h t t h δmh 2 1 loop λ2 top 8π 2 Λ2 UV this is known as the Hierarchy Problem

5 Introduction: The role of New Physics New physics can solve the Hierarchy problem by cancelling the quadratic divergence. The cut-off is set by the scale of the new dynamics: δmh 2 1 loop λ2 top 8π 2 Λ2 NP Some tuning is unavoidable if the new physics is at high scale δm2 h m 2 h ( ΛNP ) 2 ( 125 GeV 400 GeV m h ) 2

6 Introduction: Solutions to the Hierarchy Problem The solutions to the Hierarchy Problem belong to two broad classes Weakly coupled UV physics known example: low-energy Supersymmetry Strongly coupled UV physics presence of an Higgs-like state coming from the strong sector

7 Introduction: The Composite Higgs Higgs as a composite state from a strong dynamics [Georgi, Kaplan] l H The Hierarchy Problem is solved Corrections to m h are screened by the finite size Higgs mass is IR-saturated

8 Introduction: The Composite Higgs Postulate a new strongly-coupled sector The SM fermions and gauge fields belong to an elementary sector weakly coupled to the composite dynamics Elementary Sector q L, t R A µ Composite Sector ρ, Ψ h The Higgs must be lighter than the other composite resonances naturally obtained if the Higgs is a Goldstone (analogous to pions in QCD)

9 Introduction: Light top partners A low amount of tuning generically requires the presence of light fermionic resonances [G. P., Redi, Tesi, Wulzer] the top loop is regulated by the top partners: Λ NP m ψ h t t h ψ h h + finite The minimal amount of tuning is ( ) 2 ΛNP ( m ψ 400 GeV 400 GeV ψ ) 2

10 Introduction: Light top partners A low amount of tuning generically requires the presence of light fermionic resonances [G. P., Redi, Tesi, Wulzer] the top loop is regulated by the top partners: Λ NP m ψ h t h ψ h h + finite t The minimal amount of tuning is ( ) 2 ΛNP ( m ψ 400 GeV 400 GeV A bound on the partners implies a bound on the tuning Natural SUSY: light stops ψ ) 2 Natural CH: light top partners

11 - Introduction: Light top partners The top partners are colored and strongly mixed to the top quark they are expected to light (m ψ 1 TeV) they are easily produced at the LHC current bounds m ψ 700 GeV + X) (pb) ± l ± l W + ttw BF(T 5/3 T 5/3 σ CMS -1 L = 19.5 fb 1 Observed Limit Expected Limit s = 8 TeV Expected Limit ± Expected Limit ± T 5/3 mass (GeV) 1σ 2σ Signal Cross Section + BF(T tw ) = 100% 5/3

12 Introduction What happens if we take into account the flavor structure?

13 Introduction: The flavor structure Anarchic scenarios [Grossmann, Neubert; Gergetta, Pomarol; Huber, Shafi] flavor anarchic strong dynamics large compositeness only for third generation all resonances have large mixing with the top u, d c, s t, b Composite Sector flavor anarchic Light generation quarks are almost elementary negligible impact on collider phenomenology bounds on resonances analogous to the ones on top partners

14 Introduction: The flavor structure Flavor universal scenarios [Cacciapaglia et al. 07; Barbieri et al. 08; Delaunay et al. 10; Redi, Weiler 11] strong dynamics flavor symmetric large universal compositeness for one chirality hierarchical mixing for the other chirality u L c L t L Composite Sector flavor symmetric u R c R t R Good features: protection of flavor observables through MFV (residual tension still there) compatible with EW data if R chirality is composite

15 Introduction: The flavor structure Interesting collider phenomenology of light generation partners relatively small mass (from naturalness) easily produced because of light quark compositeness decay mainly into light quarks (jets)

16 Introduction: The flavor structure Interesting collider phenomenology of light generation partners relatively small mass (from naturalness) easily produced because of light quark compositeness decay mainly into light quarks (jets) In this talk: 1 analysis of the collider phenomenology 2 direct bounds on light generation partners case with U(3) flavor symmetry case with relaxed universality assumption

17 The structure of composite-higgs models

18 The structure of composite-higgs models Composite sector with a spontaneously broken global symmetry SO(5) SO(4) Elementary Sector q L t R A µ Composite Sector SO(5) SO(4) h SO(5)/SO(4) Minimal realization with custodial symmetry SO(4) SU(2) L SU(2) R SO(3) c Higgs described by a non-linear σ-model L = f 2 U = exp[ihât â] D µ U i5 D µ U i5 2 D µ U = µ U iga µ U i

19 Partial compositeness SM fields obey partial compositeness L mix = y L f q L O L + y R f u R O R + h.c. In a low-energy effective description this translates into a mixing with fermionic resonances L mix = y L f q L Ψ R + y R f u R Ψ L + h.c. The SM fields are an admixture of elementary and composite states: generation of the Yukawas y u y L y R f m part t L y L y R tr T h T g ψ

20 Minimal models The SO(4) invariance implies the presence of extended multiplets of partners In minimal implementation resonances belong to fourplets and singlets [ ] U X5/3 Q = (2, 2) 2/3 =, Ũ = (1, 1) D X 2/3 2/3 we neglect flavor changing effects partners with the same quantum numbers are present for each quark generation

21 The limit of large u R compositeness We are interested in the limit of sizable u R compositeness: y R 1 For the first two generations the q L compositeness is negligible: y L y u/c 1 Custodial symmetry is (nearly) unbroken for the first two generations and determines the properties of the partners [ ] U X5/3 {D, U p, X 5/3 } triplet Q = D X 2/3 singlet U m Ũ singlet where U p,m (U ± X 2/3 )/ 2

22 Implications of custodial symmetry The mass spectrum and the couplings of the partners are fixed by the symmetry structure m 2 y 2 Rv 2 U m D, U p X 5/3 U triplet coupled to the SM quarks through the gauge bosons L g ( y R v D /W X 2 M 5/3 /W ) U p /Z u R + h.c. 4 c w singlets coupled to the SM quarks through the Higgs L y R U m h u R + h.c. L y R v f Ũ h u R + h.c.

23 Bounds on the partners masses

24 The singlets: Ũ and U m Production: pair production (mainly QCD) p p g Um/Ũ U m/ũ u/c u/c h Um/Ũ Um/Ũ single production in association with Higgs or W /Z g u/c Um/Ũ Um/Ũ h u/c Um/Ũ h W/Z W/Z q q Decay: main decay into Higgs and light quark (jet) h U m/ũ q Ũ hj subleading channels into multi-jets [Redi, Sanz, De Vries, Weiler] Um/Ũ ρ Q Q q g Ũ jj Um/Ũ ρ q q q Ũ jjj

25 The singlets: Ũ and U m Best channels to look for singlets: hhj, hwjj, hzjj, hhjj so far no dedicated experimental analysis Searches into multi-jets are difficult and disfavored by the small branching fractions only mild constraints on singlets mass

26 The singlets: Ũ and U m Bounds on the singlets can be derived by a recast of ATLAS single Higgs search in the h γγ channel. [Flacke, Kim, Lee, Lim 2013] Events with a heavy singlet lead to peculiar signatures Higgs is more boosted (large p γγ T ) high number of extra jets (N jets 3) harder leading jet distribution ΓΓ d N d p T GeV 1 Nevents 15 M 10 1 = 300 GeV Reconstructed p T GeV

27 The singlets: Ũ and U m 8 [Flacke, Kim, Lee, Lim 2013] 6 eff Λ mix 8 yr u d s c b MU h MU h GeV Universal bound from QCD pair production: M GeV For large compositeness (y R 1) much stronger bounds for first generation partners due to enhanced EW production Large space for improvement with dedicated experimental analysis

28 The triplets: D, U p and X 5/3 Production: pair production (mainly QCD) p p g X 5/3 X 5/3 EW single production (additional forward jet) q q W u/c X 5/3 Decay: Two body decays into EW boson plus light quark (jet) D W q D W j U p Z q U p Zj X 5/3 W + q X 5/3 W + j

29 Pair production: universal bounds QCD pair production can be used to derive model independent bounds on the triplet states bounds valid for first and second generation partners Relevant channels: charge 2/3 state: U p U p ZZjj charge 1/3 state and exotic partner: X 5/3 X 5/3 WWjj and DD WWjj degenerate in mass, contribute to the same final state channel with best sensitivity

30 Pair production: universal bounds Experimental searches: Tevatron: M GeV [Phys. Rev. Lett. 107, (2011)] Σ fb TeV cross section 8 TeV cross section ATLAS limit CMS recast limit ATLAS (7 TeV): M GeV 200 [Phys. Rev. D 86, (2012)] M x 4 GeV 500 strong pair production Recast of leptoquark CMS search (8 TeV) [CMS-PAS-EXO ] final state: µ + µ + jets best bound on resonances: M GeV not optimized for partners, significant improvement possible

31 Single production Single production mainly due to t-channel EW boson exchange u u/c W/Z Q j W/Z j Relevant channels: charge 2/3 state: pp U p j Zjj charge 1/3 state and exotic partner: pp X 5/3 j Wjj and pp Dj Wjj degenerate in mass, contribute to the same final state channel with best sensitivity

32 Single production Important features: Cross section crucially depends on the gauge coupling with SM fermions g WuX = g WuD = c w g ZuUp g y R v 2 M 4 in flavor-universal models yr 1 for top Yukawa Big difference between first and second generation large cross section for up partners suppression for charm partners (from c PDF) u j u/c g W/Z Q W/Z j

33 Single production bounds from ATLAS Search for Wjj final state with the 7 TeV ATLAS data [ATLAS-CONF ] ur partner cr partner ATLAS limit Σ fb x y R = 1, f = 600GeV partially composite quarks M x 4 GeV Constraints for y R = 1 and f = 600 GeV: strong bound on first gen.: M u TeV mild bound on second gen.: M4 c 420 GeV

34 Single production bounds from CMS Search for Wjj final state with the 8 TeV CMS data [CMS-PAS-EXO ] Σ fb y R x = 1, f = 600GeV partially composite quarks ur partner cr partner CMS limit M 4 x GeV Constraints for y R = 1 and f = 600 GeV: strong bound on first gen.: M u TeV not sensitive to second. gen.

35 Combination of the exclusion bounds Bounds obtained by combining all the channels M u 4 = Mc y R x ur partner cr partner QCD prod. 0.3 f = 600GeV partially composite quarks y R c M 4 x GeV u y R Flavor-universal models (y R 1) with light partners are strongly disfavored

36 Models with fourplet and singlet The presence of a light SO(4) singlet in addition to a fourplet can significantly reduce the bounds y R u f = 600GeV M 4 u GeV fourplet only M u TeV M u GeV M u GeV partially composite u R Reduction of single-production coupling (due to the mixing of the SM quarks with the singlet) Chain decays through the singlet (eg. X 5/3 W Ũ Whj)

37 Fully composite SM quarks In flavor universal scenarios the large compositeness of the right-handed SM quarks suggests that they could be fully composite [De Simone et al. 12; Grojean et al. 13] strong dynamics flavor symmetric hierarchical mixing for the left chirality u L c L Composite Sector t L u R c R t R Caveat: composite dynamics can give rise to large 4-fermion operators stringent dijets constraints for first family

38 Fully composite SM quarks The collider signatures for the fourplet partners are similar to the case of partially composite quarks 10. relevant parameter c 1 : size of interactions between resonances c 1 x large cross sections for natural configurations: c f = 600GeV fully composite quarks ur partner cr partner QCD prod M 4 x GeV Stringent bounds, even for the second generation partners Full compositeness for all generations strongly disfavored

39 Conclusions

40 Conclusions Large compositeness for R-handed light quarks is a natural ingredient of flavor universal composite Higgs models Interesting collider signatures: light partners for the first and second generation quarks resonances easily produced at the LHC

41 Conclusions Partners in extended SO(4) representations (fourplets) already strongly bounded: QCD pair production, model-independent: M 4 > 530 GeV single production bound on up partners (yr u 1): Mu TeV bound on charm partners much weaker if universality is relaxed Singlet partners only mildly constrained by the LHC interesting channels with Higgs: hhj, hwjj, hzjj, hhjj bounds from recast of h γγ search: M GeV so far no dedicated experimental analysis