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Physics @ LHC (Physics @ TeV). Status of LHC/ATLAS/CMS and Physics explored at LHC. Fundamentalist of High Energy Physics (U. Tokyo). [3] Origin of Mass (Higgs). SSB of Higgs Potential gives mass to Gauge boson W/Z: (Freedom of ξ) Motion in η is corresponding to Higgs boson.

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Physics @ lhc physics @ tev

Physics @ LHC (Physics @ TeV)

Status of LHC/ATLAS/CMS and

Physics explored at LHC

Fundamentalist of High Energy Physics (U. Tokyo)

Physics lhc physics tev

[3] Origin of Mass (Higgs)

SSB of Higgs Potential

gives mass to Gauge boson W/Z: (Freedom of ξ)

Motion in η is corresponding to

Higgs boson

Simulated H→γγ events

Higgs boson will be observed

at LHC like this event (simulation)

Physics lhc physics tev

[3-1] Production processes of SM Higgs at LHC

4 processes

Gluon Fusion

Vector Boson Fusion

Associate production

with W/Z

GF & VBF are important for discovery:

Cross-section of ttH/bbH is small, but

give the direct information of Yukawa yt/yb.

Associate production with t/b

Physics lhc physics tev

Detector Central


Vector Boson Fusion (1998Zeppenfeld et al.)

VBF has an excellent potential because of :


(1) Scattered “high Pt” jets are observed in the forward regions. Pt 〜 Mw

(2) There is rapidity gap between two

jets because there is no color exchange.

Only the products from Higgs are observed in the central region.

These are very promising signatures in order to suppress the background.

QCD(color exchange)


Number of jets


Physics lhc physics tev

Precision measurements of

the SM at LEP suggests


[3-2] Decay Branching Fraction

In such a light region,

there are 5 important

decay modes.

H→ bb,tautau,γγ


H→ ZZ(*),WW(*)


H → γγBr is small of about 10-3,

Butpromising mode due to good resolution of γ

Physics lhc physics tev

[3-3A] H→ γγin GF and VBF (small Br, but excellent Mγγ)


huge BG. S/N ~1% qq_bar→ γγis dominante

BG is High but also signal stat. is high

Xsection (fb/GeV)

ATLAS preliminary

Two leading processes contribute to

three different event topologies:

S/N and shape of BG are different in 3 class.

Discovery potential of them are similar, and

we have good redundancy.

Xsection (fb/GeV)


γ-ID and resolution are essential :

BG can be estimated with the side band.



ATLAS preliminary

Xsection (fb/GeV)


Good S/N and flat BG

but Stat. limited

H→γγ indicates that spin

of Higgs is 0 (or 2).  scalar


Physics lhc physics tev

[3-3B] H→ZZ(*)→ 4leptons

Resolution and identifications of leptons are excellent.

Invariant mass distributions of 4 leptons are shown with BG contributions.

Irreducible BG is qq_bar → ZZ* → 4l (continuous distribution)

Reducible BGs are tt & Zbb (lepton comes from semileptonic decay of B

B contamination can be suppressed by isolation of track + anti-impact parameter

Track quality is essential for this mode )

CMS Full



ZZ*→ 4l has excellent discovery potential except for

M(H)<130GeV and M(H)=170GeV (Branching is small):

We can determine also CP, Spin of Higgs using this channel.

Physics lhc physics tev

This mode is direct evidence of Higgs-fermion coupling (Yukawa)

Origin of fermion


Tau decay includes neutrino, but

Momenta of ν’s can be calculated using mET information in the collinear limit.

 Tau can be reconstructed !!!!

[3-3C] VBF H→ττ


CMS Full

Resolution of mET is about 10GeV Mtautau has sharp peak (sigma 〜 10GeV)

Dominant Background process is Z(→tautau)+Njets. Peak appears at 91GeV.

 Resolution and tail of mET distribution are essential for this channel

Physics lhc physics tev

Higgs Spin0 (Yukawa)





[3-3D] VBF H→ WW

Leptonic decays of W lead to the event topology of


Leptons are emitted

in the same direction



CMS Full

Clear Jacobian Peak is observed:

tt → bb lνlν is main BG:

Leptons are back-to-back in tt.

Φ between di-lepton (Rad)

Physics lhc physics tev

[3-4] Discovery Potential of the SM Higgs (Yukawa)

LO calculation

NLO calculation

Similar Discovery potentials are obtained at both ATLAS and CMS

(Notice LO calculation vs NLO)

VBF γγ+ exclusive 1,2 jets analyses will gain significance in low mass regions

H->γγ, tautau covers the region < 130GeV, WW,ZZ > 130GeV

5sigma discovery is possible with L=10fb-1for both ATLAS and CMS

Different technologies are essential for various modes: (Safe and redundant)

Physics lhc physics tev

Needed (Yukawa)Ldt (fb-1)

per experiment






mH (GeV)

Let’s combine ATLAS+CMS performance

 1 fb-1 for 98% C.L. exclusion

 5 fb-1 for 5 discovery

over full allowed mass range

--- 98% C.L. exclusion

  • 5σ discoveryis possible within

  • 2008(>130GeV) or

  • early of 2009(<130GeV)

  •  measurements of mass, coupling, spin

  • 98%CL exclusion (2008)

  • No Higgs model?

    invisible decay?

  • No resonance?

criticaltest can be performed for “origin of mass”

Physics lhc physics tev

[3-5] Measurements of Mass & coupling (Yukawa)


Relative coupling (Normalized to g(WH))

  • Yt, Yτ 10-15%

  • Yb 30-40%

  • Gz、5-10%

Mass can be measured

with accuracy of 0.1%

if M(H)<400GeV.

We can show couplings are proportional to their masses

Physics lhc physics tev

Accuracy of “absolute measurements” of the couplings. (Yukawa)

We assume the

SM branching fractions except

for the leading five processes:

Br(H->tautau,tt,bb,ZZ and WW)

Within this assumption,

Couplings of

yt、yτ、yb, gZZH and gWWH

can be calculated.


yt、yτgZZH and gWWH 20%

yb 50%

Physics lhc physics tev

Higgs Self-couplings (Yukawa)

In order to determine the shape of Higgs potential,

Slope of potential is correspond to Self-coupling

σ×Br is small

Need very High Luminosity


For 6000 fb-1(SLHC)

Dl ~ 19% for 170 GeV MH

Physics lhc physics tev

SM (Yukawa)Higgsの研究で有効なチャンネルの纏め

Physics lhc physics tev

Diphoton background is now computed at NLO (Yukawa)(Binoth et al, Eur.Phys.J.C16(2000)311, Bern,Dixon,Schmidt hep-ph/0206194, C.Balasz et al, Phys.Lett.B489(2000)157

Physics lhc physics tev

1-6 (Yukawa)MSSM Higgsの発見能力



  • tanβが大きいとbbH/Aの

  • 結合が大きくなる。

  • H/A→ττ・μμ・(bb)

  • tanβ>10で gb->tH-でcharged Higgs が観測可能

→MSSM Higgsも必ず



(t →H+b がcover)

この緑の部分は、HSMに似た性質のhが観測されるだけ。(SUSY decay )

Physics lhc physics tev

H/A (Yukawa)生成








Physics lhc physics tev

H/A (Yukawa)生成






Physics lhc physics tev


(t,b) Br=90%

(τν) 10%


Physics lhc physics tev

[6] (Yukawa)Introduction and Conclusion:

Most important/urgent topics in Particle Physics are:

Understanding of “the origin of mass”

(EW symmetry breaking)

SSB of Higgs field is most promising scenario,

but should be examined directly: & determine the potential:

(2) Beyond the Standard Model

Supersymmetry is most promising,

Large Extra Dimension,

unexpected scenario… are also exciting.

These are main purpose of LHC project:

and LHC will give the clear solutions

Physics lhc physics tev

2008 !! (Yukawa)

Appendix: Mt can be measured with accuracy of 0.9GeV,

Mw will be 15MeV(Very difficult task.

Z’ or high mass gauge boson 5TeV, Littele Higgs heavy top 1TeV