Electroweak Symmetry Breaking Electroweak Symmetry Breaking without Higgs Bosons in ATLASwithout Higgs Bosons in ATLAS

Ryuichi TakashimaKyoto University of Education

For the ATLAS Collaboration

2

Outline

• Possible scenarios of EWSB• Little Higgs Model• Chiral Lagrangian model• Performance studies on boson scattering• Summary

3

Electroweak Symmetry Breaking (EWSB) 　

SUSY(m)SUGRAGMSBAMSBMirageSplit SUSYRPV…

SUSY(m)SUGRAGMSBAMSBMirageSplit SUSYRPV…

Extra-Dimension

LED(ADD)Randall-SundrumUniversal ED(KK)…

Extra-Dimension

LED(ADD)Randall-SundrumUniversal ED(KK)…

Extended Gauge Symmetry

Little Higgs, Higgsless, Left-Right Symmetric Model

Higgs-Gauge Unification

Extended Gauge Symmetry

Little Higgs, Higgsless, Left-Right Symmetric Model

Higgs-Gauge Unification

Dynamical Symmetry BreakingStrong EWSB, Chiral Lagrangian, Technicolor, Composite Higgs, Top-quark Condensation

Dynamical Symmetry BreakingStrong EWSB, Chiral Lagrangian, Technicolor, Composite Higgs, Top-quark Condensation

Exotics: Compositeness, Lepto-quarks, Monopole …

J.Lykken, Physics at LHC (Vienna)

PrecisionEW dataPrecisionEW data

4

EWSB possible scenarios

• ElectroWeak Symmetry Breaking (EWSB):

– ElectroWeak Gauge symmetry requires gauge boson and matter particles to be massless. The mechanism to give them mass: Standard theory of EWSB by scalar Higgs field

– Renormalization scheme predicts coupling constants of Strong and EW force

become same value near =1016 GeV: Suggest GUTs of SU(3)C SU(2)L U(1)Y

forces

– Higgs radiative correction mass2 has a quadratic term of cutoff parameter. Hierarchy problem in GUTs.

– If Higgs hierarchy problem: fine tuning in rad corr to Higgs masssolution: new physics at TeV scale (SUSY, Little Higgs, etc…)

– If NO Higgssolution: dynamical symmetry breaking (Technicolor, Chiral Lagrangian etc…)

– Unitarity violation in longitudinal WW scattering at high Esolution: Higgs boson or other new particle with mass < 1 TeV

5

Little Higgs Model•Evaluate the sensitivity to the Little Higgs models with the ATLAS experiment at the LHC•Little Higgs Models proposed as a solution to the Hierarchy problem•Loop corrections to the Higgs Mass: is an ultra-violet cut-off

•Models try to arrange new particles to cancel these effects •Little Higgs models add a minimal set of particles (and a symmetry) to cancel thesecorrections up to >10TeV •Some discussion on T-parity of heavy top and bosons. Require pair production.

To suppress the quadratic divergencethe mass of MT and MW should not be too large

6

Little Higgs: heavy top search

• Production: via QCD (gg T Tbar, qq T Tbar)

via W exchange (qb q’ T)

dominant for MT > 700 GeV

• Decays: T t Z, T t h, T b W

– cleanest is T t Z b l l+ l-

but small statistics, main bkg is tbZ5 signal up to ~1.0-1.4 TeV

– T t h b l b bbar < 5

– T b W b l main bkg is t tbar

5 signal up to ~2.0-2.5 TeV SN-ATLAS-2004-038

M = 1 TeV300 fb-1

bkg

7

Little Higgs: heavy bosons

• AH, WH and ZH discovery in lepton modes

up to M ~ 6 TeV (depending on param cot )

• Discrimination against other modelspredicting dilepton resonances via observation of decay modes

like WH W h, ZH Z h,

and WH t b (important at cot ≈ 1)

ATL-PHYS-PUB-2006-003

M = 1 TeVcot = 130 fb-1

300 fb-1

300 fb-1

SN-ATLAS-2004-038

WH t bobservationup to ~3 TeV

5 discovery

8

Symmetry Breaking by Chiral Lagrangian Model

• SM cross section for Wlong Wlong scattering diverges at high energy if there is no

Higgs new physics via diboson resonances?

• Chiral Lagrangian Model

– Describes the low energy effects of different strongly interacting models of the EWSB

sector.

– The differences among underlying theories appear through the values of the effective

chiral couplings.– The analytical complete form can be found in Dobado et al.,

Phys.Rev.D62,055011, but terms of major importance are:

•Different choices for the magnitude and the sign of a4 and a5 would correspond to different choices for the underlying (unknown) theory.

9

Performance studies on boson scattering

• WLWL with no resonances (Continuum) by J.M. Butterworth, P. Sherwood, S. Stefanidis.

• WLWL with resonances by S.E. Allwood, J.M. Butterworth, B.E. Cox.

• WLZL with resonances by G. Azuelos, P-A. Delsart, J. Id´arraga, A. Myagkov.

• PYTHIA has been modified to include the EWChL and to produce the resonances for different parameters.

• Detector response was studied using Athena computing environment of both fast and full simulators.

10

WW Boson Scattering

11

WW Boson Scattering Event Selection

Backgrounds: W+jets (W l), σ~60,000 fb, and , σ~16,000 fb ttbar

(cf signal σ<100 fb).

• high pT lepton

• high ETmiss

• Jet(s) with high pT and m ~ mW.

• Little hadronic activity in the central region (|η|<2.5) apart from the hadronic W.

•Tag jets at large η (|η|>2).

high pT W

12

Resonant WW Boson Scattering

preliminary

13

Resonant WZ Boson Scattering

• choose parameters of a4 and a5 such that new resonance M = 1.15 TeV

– qq qqWZ qq l ll ( x BR= 1.3 fb)– qq qqWZ qq jj ll ( x BR= 4.1 fb)– qq qqWZ qq l jj ( x BR= 14 fb)

q1q’1

q2 q2

W WZ Z

Lq.Ar FCAL<4.9

14

Resonant WZ Boson Scattering

• Selection for qqjjll: 2 forward jets + central 2jets and 2 leptons Require no additional central jet

• Bkg: gluon and /Z exchange with W and Z radiationalso t tbar & W+4 jets (need more stats)

• Experimental issues:– Merging of jets from high-pT

W or Z decay (need cone R = 0.2)

– Impact of pileup on forwardjet tagging?

• Promising sensitivity for jet modes at 100 fb-1 (need 300 fb-1 for WZ l ll)

study is ongoing

ATL-COM-PHYS-2006-041

W Z jj ll

100 fb-1

SMbg

15

Summary

• Many scenarios for EWSB being studied.

• Heavy Top is reachable. WH t b hadronic decay channel can be used to discriminate the Little Higgs model from other models.

• WZ boson scattering is studied extensively. Promising mode to test the dynamical symmetry breaking and various models including higgsless model.

• Atlas can explore the parameter space of Chiral Lagrangian model by WW scattering with 30 fb-1 data.

16

References– G. Azuelos; P. A. Delsart ; J. Idarraga; A. Myagkov ,

ATL-COM-PHYS-2006-041

– S.Willocq,http://ichep06.jinr.ru/reports/150_11s5_15p10_willocq.ppt

– S.Stephanidis,http://indico.cern.ch/conferenceOtherViews.py? view=standard&confId=a057#2006-07-06

– F. Ledroit,http://susy06.physics.uci.edu/talks/1/ledroit.pdf

– S. González de la Hoz; L. March; E. Ros,ATL-COM-PHYS-2005-001

– G. Azuelos et al, SN-ATLAS-2004-038