1. Electroweak Symmetry Breaking without Higgs Bosons in ATLAS Ryuichi Takashima Kyoto University of Education For the ATLAS Collaboration

2. 2 Outline Possible scenarios of EWSB Little Higgs Model Chiral Lagrangian model Performance studies on boson scattering Summary

3. 3 Electroweak Symmetry Breaking (EWSB) SUSY (m)SUGRA GMSB AMSB Mirage Split SUSY RPV … SUSY (m)SUGRA GMSB AMSB Mirage Split SUSY RPV … Extra-Dimension LED(ADD) Randall-Sundrum Universal ED(KK) … Extra-Dimension LED(ADD) Randall-Sundrum Universal 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 Breaking Strong EWSB, Chiral Lagrangian, Technicolor, Composite Higgs, Top-quark Condensation Dynamical Symmetry Breaking Strong EWSB, Chiral Lagrangian, Technicolor, Composite Higgs, Top-quark Condensation Exotics: Compositeness, Lepto-quarks, Monopole … J.Lykken, Physics at LHC (Vienna) Precision EW data Precision EW data

4. 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  =10 16 GeV: Suggest GUTs of SU(3) C  SU(2) L  U(1) Y forces –Higgs radiative correction mass 2 has a quadratic term of cutoff parameter. Hierarchy problem in GUTs. –If Higgs  hierarchy problem: fine tuning in rad corr to Higgs mass solution: new physics at TeV scale (SUSY, Little Higgs, etc…) –If NO Higgs solution: dynamical symmetry breaking (Technicolor, Chiral Lagrangian etc…) –Unitarity violation in longitudinal WW scattering at high E solution: Higgs boson or other new particle with mass < 1 TeV

5. 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 these corrections up to  >10TeV Some discussion on T-parity of heavy top and bosons. Require pair production. To suppress the quadratic divergence the mass of M T and M W should not be too large

6. 6 Little Higgs: heavy top search Production: via QCD (gg  T T bar, qq  T T bar ) via W exchange (qb  q’ T) dominant for M T > 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 tbZ 5 signal up to ~1.0-1.4 TeV –T  t h  b l b b bar < 5 –T  b W  b l main bkg is t t bar 5 signal up to ~2.0-2.5 TeV SN-ATLAS-2004-038 M = 1 TeV 300 fb -1 bkg

7. 7 Little Higgs: heavy bosons A H, W H and Z H discovery in lepton modes up to M ~ 6 TeV (depending on param cot ) Discrimination against other models predicting dilepton resonances via observation of decay modes like W H  W h, Z H  Z h, and W H  t b (important at cot  ≈ 1) ATL-PHYS-PUB-2006-003 M = 1 TeV cot  = 1 30 fb -1 300 fb -1 SN-ATLAS-2004-038 W H  t b observation up to ~3 TeV 5  discovery

8. 8 Symmetry Breaking by Chiral Lagrangian Model SM cross section for W long W long 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 a 4 and a 5 would correspond to different choices for the underlying (unknown) theory.

9. 9 Performance studies on boson scattering W L W L with no resonances (Continuum) by J.M. Butterworth, P. Sherwood, S. Stefanidis. W L W L with resonances by S.E. Allwood, J.M. Butterworth, B.E. Cox. W L Z L 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. 10 WW Boson Scattering

11. 11 WW Boson Scattering Event Selection Backgrounds: W+jets (W  l ), σ~60,000 fb, and, σ~16,000 fb tt bar (cf signal σ<100 fb). high p T lepton high E T miss Jet(s) with high p T and m ~ m W. Little hadronic activity in the central region (|η|<2.5) apart from the hadronic W. Tag jets at large η (|η|>2). high p T W

12. 12 Resonant WW Boson Scattering preliminary

13. 13 Resonant WZ Boson Scattering choose parameters of a 4 and a 5 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) q1q1 q’ 1 q2q2 q2q2 W W Z Z Lq.Ar FCAL  <4.9

14. 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 radiation also t t bar & 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 forward jet 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. 15 Summary Many scenarios for EWSB being studied. Heavy Top is reachable. W H  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. 16 References –G. Azuelos; P. A. Delsart ; J. Idarraga; A. Myagkov,ATL-COM-PHYS- 2006-041ATL-COM-PHYS- 2006-041 –S.Willocq,http://ichep06.jinr.ru/reports/150_11s5_15p10_willocq.ppthttp://ichep06.jinr.ru/reports/150_11s5_15p10_willocq.ppt –S.Stephanidis,http://indico.cern.ch/conferenceOtherViews.py? view=standard&confId=a057#2006-07-06http://indico.cern.ch/conferenceOtherViews.py? –F. Ledroit,http://susy06.physics.uci.edu/talks/1/ledroit.pdfhttp://susy06.physics.uci.edu/talks/1/ledroit.pdf –S. González de la Hoz; L. March; E. Ros,ATL-COM-PHYS-2005-001ATL-COM-PHYS-2005-001 –G. Azuelos et al, SN-ATLAS-2004-038SN-ATLAS-2004-038