1. Electroweak Symmetry Breaking without Higgs Bosons in ATLAS
Ryuichi Takashima
Kyoto 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)
Extended Gauge Symmetry
Little Higgs, Higgsless, Left-Right Symmetric Model
Higgs-Gauge Unification
J.Lykken, Physics at LHC (Vienna)
SUSY
(m)SUGRA
GMSB
AMSB
Mirage
Split SUSY
RPV …
Extra-Dimension
LED(ADD)
Randall-Sundrum
Universal ED(KK) …
Precision
EW data
Dynamical Symmetry Breaking
Strong EWSB, Chiral Lagrangian, Technicolor,
Composite Higgs, Top-quark Condensation
Exotics: Compositeness, Lepto-quarks, Monopole …

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 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. 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: L 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 L>10TeV
Some discussion on T-parity of heavy top and bosons. Require pair production.
To suppress the quadratic divergence
the 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 tbZ 5 signal up to ~ TeV
T  t h  b l n b bbar < 5s
T  b W  b l  main bkg is t tbar 5 signal up to ~ TeV
SN-ATLAS
M = 1 TeV
300 fb-1
bkg

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

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
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
Backgrounds: W+jets (W  l), σ~60,000 fb, and , σ~16,000 fb ttbar
(cf signal σ<100 fb).

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 ln ll (s x BR= 1.3 fb)
qq  qqWZ  qq jj ll (s x BR= 4.1 fb)
qq  qqWZ  qq ln jj (s x BR= 14 fb) q1
q’1 q2 W Z
Lq.Ar FCAL
h<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 g/Z exchange with W and Z radiation also t tbar & W+4 jets (need more stats)
Experimental issues:
Merging of jets from high-pT W or Z decay (need cone DR = 0.2)
Impact of pileup on forward jet tagging?
Promising sensitivity for jet modes at 100 fb-1 (need 300 fb-1 for WZ  ln ll)  study is ongoing
SMbg
ATL-COM-PHYS
100 fb-1
W Z  jj ll

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
S.Willocq,
S.Stephanidis, view=standard&confId=a057#
F. Ledroit,
S. González de la Hoz; L. March; E. Ros,ATL-COM-PHYS
G. Azuelos et al, SN-ATLAS