Phenomenology for Higgs Searches at the LHC

Transcription

1 Phenomenology for Higgs Searches at the LHC in Composite Higgs Models Margherita Ghezzi Supervisor: dott. Roberto Contino Roma, 21/02/2012

2 Introduction Standard Model: SU(2) L U(1) Y U(1) Q Higgs mechanism - 1 scalar boson SU(2) L SU(2) R SU(2) V custodial symmetry What guarantees unitarity? W L W L W L W L scattering Which is the dynamics that origins the symmetry breaking? LHC is testing the sector that accomplishes the spontaneous symmetry breaking of the SM symmetry group

3 Experimental bounds for the SM Higgs boson CMS - Combined Results [arxiv: ]

4 Different Approaches to Unitarization Higgs Models SM A Higgs mechanism generates Higgs bosons through the breaking of the gauge symmetry. Its contribution prevents the amplitudes from unitarity violation Strong Dynamics Technicolor a whole tower of heavy resonances guarantees the unitarity non-linear σ model - Prototype: QCD Composite Higgs Models [Georgi & Kaplan, 80s] Strong sector with a spontaneously broken global symmetry light Higgs SM particles have a small component of compositeness Heavy resonances have a large component of compositeness and accomplish unitarity Connection to models with extra-dimensions via AdS/CFT correspondence

5 Higgs Boson as a Composite Nambu-Goldstone Boson of a Strongly Interacting Sector Pattern of symmetry breaking G = global symmetry of the EW sector Global symmetry breaking: G H 1 n = dim(g) dim(h 1 ) Goldstone bosons H 0 = gauge group H = H 0 H 1 unbroken symmetry group n 0 = dim(h 0 ) dim(h 1 ) Goldstones eaten by the gauging of H 0 Including the Standard Model: H 0 = G SM H 1 G/H 1 contains the Higgs SU(2) L doublet

6 The most general Lagrangian for a light Higgs Contino, Grojean, Moretti, Piccinini, Rattazzi, JHEP 1005 (2010) 089 Assuming only custodial symmetry: SU(2) L SU(2) R SO(4) SO(3) L = 1 2 ( µh)2 V(h) ( ) [ + v2 4 Tr D µσ D µ Σ 1+2a h ] v +bh2 v v ( ) u (i) L d (i) L Σ (1+c hv ) ( h 2 2 +c2 v + λ u ij u (j) R 2 λ d ij d (j) R +... i,j V(h) = 1 2 m2 hh 2 +d ( ) 3m 2 h h 3 1 +d 4 v 24 ) ( ) 3m 2 h h 4 +. v 2 +h.c. SM: a = b = c = d 3 = d 4 = 1; c 2 = 0

7 Explicit Examples SO(5) f SO(4) v SO(3) ξ v2 f 2 [0,1] MCHM4: spinorial representation Fine tuning 1 ξ a = c = d 3 = 1 ξ, b = 1 2ξ, c 2 = ξ 2 MCHM5: fundamental representation a = 1 ξ, b = 1 2ξ, c = d 3 = 1 2ξ 1 ξ, c 2 = 2ξ

8 Double Higgs Production via Gluon Fusion Work in progress with Contino, Panico, Piccinini, Wulzer High invariant mass limit ŝ = m 2 hh m 2 t,m 2 h A c 2 α s m 2 t v 2 mh 2 A c d m2 t 3 v 2 ŝ A NR c 2 m 2 t v 2 [ ln m2 t ŝ [ ln m2 t ŝ +ıπ ] 2 +ıπ ] 2

9 Double Higgs Production via Gluon Fusion R = σ(pp hh) σ(pp hh) SM σ(pp hh) SM = 15.5 fb Large enhancement compared to the SM first noticed by: Grober and Muhlleitner, JHEP 1106 (2011) 020 LHC 14 TeV m h = 120GeV

10 Higgs Decay Channels Our choice: hh b bγγ, with m h = 120 GeV

11 The gg hh b bγγ Channel h γγ rare decay, but with low background Very low cross-section in the SM: σ(pp hh) SM BR(hh b bγγ) SM = 0.045fb SM analysis by Baur, Plehn and Rainwater, Phys. Rev. D 69 (2004) Possibility of cross section enhancement in the composite Higgs scenario Σ pp hh bbγγ 4 MCHM5 Useful channel in the region of the parameter space around the SM σ = 0 in the fermiophobic limit (c = 0) (ξ = 1 in MCHM5) Ξ

12 Background and Cuts Cuts p T (b) > 45 GeV, η(b) < 2.5, R(b,b) > 0.4, m h 20 GeV < m bb < m h +20 GeV, p T (γ) > 20 GeV, η(γ) < 2.5, 0.4 < R(γ,γ) < 2.0, Efficiencies and fake rates m h 2.3 GeV < m γγ < m h +2.3 GeV, R(γ,b) > 1.0. ǫ γ = 0.8, r γ = 2500, ǫ b = 0.7, r b = 20. Detector effects: 79% efficiencies of reconstructing the Higgs invariant masses [cfr Baur et al. (2004)] analysis stage bbγγ bbγj jjγγ bbjj γjjj jjjj after cuts after tags

13 A Bayesian Statistical Analysis Bayes Theorem p(n th N obs ) = p(n obs N th )p(n th ) N th = N hh +N bkg Likelihood: p(n obs N hh +N bkg ) = (N hh+n bkg ) N obse (N hh +N bkg) Prior: p(n hh +N bkg ) = 1 N hh = N hh (a,c,c 2,d 3 ) N obs!

14 Exclusion Regions Preliminary - Cuts efficiency taken from SM analysis [Baur, Plehn, Rainwater (2004)] N obs = N bkg a = c = 1 A point in the parameter space is excluded at a given luminosity if the probability of finding a number of events larger than (σ hh +σ bkg )L is below 5% fb fb 1 d fb fb fb fb 1 a = c = 1 m h = 120 GeV LHC 14TeV fb c 2

15 Discovery Regions Preliminary - Cuts efficiency taken from SM analysis [Baur, Plehn Rainwater (2004)] N obs = N hh +N bkg a = c = 1 A point in the parameter space is discoverable at a given luminosity if the probability of finding a number of events smaller than σ bkg L is below 1% fb fb 1 d fb fb fb fb 1 a = c = 1 m h = 120 GeV LHC 14TeV c 2

16 Confidence Intervals σ(pp hh b bγγ) = fb (after cuts) L = 300 fb Benchmark point: d a = 1 c = 1 d 3 = 0 c 2 = c 2

17 Conclusions An appreciable enhancement of the cross section for double Higgs production can be present in Composite Higgs Models Cross section depends on parameters that accomplish modification of the SM vertices A new diagram containing a non-renormalizable vertex dominates in the high-invariant-mass limit Large regions of the parameter space can be excluded at LHC (14TeV) with reasonable integrated luminosity Perspectives: Alpgen package for single and double Higgs production in Composite Higgs Models Constraints for the couplings from kinematic distribution Contribution of the heavy resonancies to the double Higgs production [dim-6 and dim-8 effective operators]...