ILC の物理

1. ILCの物理 岡田安弘 (KEK) ILC測定器学術創成会議 ２００６年６月２８日　KEK

2. Fundamental questions in elementary particle physics • What are the elementary constituents of matter? • What are forces acting between them? • How has the Universe begun and evolved?

3. How have we come to the Standard Model ? gravity general relativity EM interaction Electroweak theory weak interaction Fermi theory Higgs mechanism strong interaction pion quark QCD nuclear force 2000 1900

4. Why TeV scale? • This is the scale of the weak interaction, in modern language, the Higgs vacuum expectation value (~246 GeV). • We expect to find a Higgs boson and “New Physics” associated to the electroweak symmetry breaking. • The answer to the question “what is the physics behind the electroweak symmetry breaking?” is a crucial branching point for the future of particle physics. Supersymmetry vs. Low cut-off theory (Little Higgs models, models with large extra-dimension, etc.)

5. Why do we expect physics beyond the Standard Model? • We do not know how the Higgs field arises. • There are evidences which require new particles and/or new interactions. Neutrino mass Dark matter Baryon-anti-baryon asymmetry of the Universe • Expectation of Unification. GUT, Superstring

6. TeV 100 GeV 1019 GeV Superstiring Gravity SUSY Dark Energy GUT Standard Model Higgs Physics EM Interaction Seesaw Neutrino Inflation Weak Int. Dark Matter Strong Int. Baryogenesis Alternative scenarios (Extra dim, Little Higgs model,etc)

7. Why do we need both LHC & ILC? • Two machines have different characters. • Advantage of lepton colliders: e+ and e- are elementary particles (well-defined kinematics). Less background than LHC experiments. Beam polarization, energy scan. g - g, e- g, e- e- options, Z pole option. LHC ILC

8. Goals of ILC physics • Higgs physics (Electroweak symmetry breaking and mass generation mechanism of quarks, leptons, and gauge bosons.) • New physics signals Direct search for new particles and interactions. Indirect search for new physics effectsthrough the SM particle processes. Capability of precise measurements of various quantities is a key.

9. [1] Higgs physics • A Higgs boson will be discovered at LHC as long as its properties (production/decay) is similar to the SM Higgs boson. • In order to study the Higgs mechanism at work, Higgs couplings to various particles have to be measured precisely.

10. 5 MH(GeV) Higgs boson search at LHC Higgs boson discovery at LHC SM Higgs boson branching ratio

11. Higgs physics at ILC • Production of 0(105)Higgs bosons. • Determination of spin and parity. • Precise mass determination . • Measurements of production corss sections and branching fractions TESLA TDR Higgs boson couplings to other particles Mass generation mechanism GLC report

12. Coupling measurements at ILC (Ecm>700 GeV) LHC: (10)% for ratios of coupling constants ILC: a few % determination Higgs self-coupling GLC Project mH=120 GeV, Ecm=300-500 GeV.L=500fb-1

13. New physics effects in Higgs boson couplings • In many new physics models, the Higgs sector is extended and /or involves new interactions. The Higgs boson coupling can have sizable deviation from the SM prediction. The heavy Higgs boson mass in the MSSM SUSY correction to Yukawa couplings B(h->WW)/B(h->tt) B(h->bb)/B(h->tt) LC LHC LC ACFA report J.Guasch, W.Hollik,S.Penaranda

14. Radion-Higgs mixing in extra-dim model The triple Higgs coupling in 2HDM in the electroweak baryogenesis scenario HEPAP report Little Higgs model with T parity S.Kanemura, Y. Okada, E.Senaha Deviation to 5-10 % level can be distinguished at ILC C.-R.Chen, K.Tobe, C.-P. Yuan

15. [2] Direct searches for New Physics • Some type of new signals is expected around 1TeV range, if New Physics is related to a solution of the hierarchy problem. (SUSY, Large extra-dimension, etc ) • The first signal of New Physics is likely to be obtained at LHC. (ex. squarks up to 2.5 TeV at LHC) • ILC experiments are necessary to figure out what is New Physics, by measuring spin, quantum numbers, coupling constants of new particles, and finding lower mass particles which may escape detection at LHC. • Beam polarization, energy scan, and well-defined initial kinematics play important roles in ILC studies.

16. SM particles Super partners Spin 1/2 Spin 0 quark squark lepton Spin 1 Spin 1/2 slepton Spin 1 gluon gluino Spin 1/2 Spin 0 W,Z,g, H neutralino, chargino neutralino mixing chargino mixing Mixing angle determination SUSY studies at ILC SUSY is a symmetry between fermions and bosons. Spin determination is essential, ideal for ILC.

17. SUSY relation SUSY predicts characteristic relations among superpartner’s interactions. Right-handed selectron production M.M.Nojiri, K.Fujii, and T.Tsukamoto

18. Gaugino mass relation GUT relation If we combine information from LHC and LC, we can test whether SUSY breaking masses satisfy GUT and/or Unification conditions Gauge coupling unification Scalar mass relation B.C.Allanach, et al in LHC/LC report

19. Large extra-dimensions graviton • An alternative solution to the hierarchy problem. • LC physics: Size and numbers of extra-dimensions, The spin 2 property of Kaluza-Klein gravitons. matter Angular distribution -> Spin 2 exchange N.Delerue, K.Fujii, N.Okada G.W.Wilson

20. [3] Dark matter and collider physics • Energy composition of the Universe Dark energy 74% Dark matter 22% Baryon4% • Dark matter candidate WIMP （weakly interacting massive particle) a stable, neutral particle • WIMP candidates Neutralino (SUSY) KK-photon (UED) Heavy photon (Little Higgs with T parity)…

21. Dark matter profile in our galaxy Thermal history of the Universe Cosmological parameter determination WMAP, Planck, … Direct and indirect (g, e+,anti-p, n ) searches for dark matter Thermal relic abundance Detection rate Collider search for a dark matter candidate particle at LHC and ILC. ILC will play a particularly important role in distinguishing different models and determine properties of the dark matter candidate. See, E.A.Baltz,M.Battaglia,M.E.Peskin,and T.Wizansky, hep-ph/0602187

22. SUSY Dark matter at ILC SUSY mass and coupling measurements => Identification of dark matter ALCPG cosmology subgroup

23. [4] Precision measurements of SM processes • Improve precision of the fundamental parameters. • Search for new physics in indirect ways. The threshold scan improves the top mass measurement and determines the top width. Top quark threshold scan Deviation of the top width in the Little Higgs model. GLC report C.F.Berger,M.Pelestein,F.Petriello

24. Z’ and e+e-->ff processes e f Z’ e f Z’ coupling determination at ILC Even if ILC at 500 GeV cannot produce a new Z’ particle kinematically,we can determine left-handed and right-handed couplings from ee-> ff processes. This will give important information to identify the correct theory. LHC=> mass ILC => coupling m z’ =2TeV,Ecm=500 GeV, L=1ab-1 with and w/o beam polarization S.Godfrey, P.Kalyniak, A.Tomkins

25. [5] Physics Benchmarks for the ILC Detectors M.Battaglia, T.Barklow, M.E.Peskin, Y.Okada, S.Yamashita, and P.Zerwas, hep-ex/0603010 The big table • Benchmark processes for detector design and optimization. • Selected from important physics reactions

26. The short list

27. Conclusions • The LHC experiment is expected to open a new era of the high energy physics by finding a Higgs boson and other new particles. • Establishing the mass generation mechanism is the urgent question. This will be achieved by precise determination of the Higgs couplings, and ILC will play essential roles. • In order to explore New Physics, Higgs coupling measurements, direct study of new particles and new phenomena, and indirect searches through SM processes are all important at ILC. • TeV physics explored at LHC and ILC will lead to new understanding of unification and cosmology.