1. Physics @ LHC (Physics @ TeV)
Status of LHC/ATLAS/CMS and
Physics explored at LHC
Fundamentalist of High Energy Physics (U. Tokyo)

2. [3] Origin of Mass (Higgs)
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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)

3. [3-1] Production processes of SM Higgs at LHC
Gluon Fusion
Vector Boson Fusion
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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

4. Vector Boson Fusion (1998 Zeppenfeld et al.)
VBF has an excellent potential because of : f
Detector Central η
(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)
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VBF
Number of jets η

5. [3-2] Decay Branching Fraction
Precision measurements of
the SM at LEP suggests
M(H)= GeV(95%CL)
[3-2] Decay Branching Fraction
In such a light region,
there are 5 important
decay modes.
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H→ bb,tautau,γγ
(M(H)<140GeV)
H→ ZZ(*),WW(*)
(M(H)>130GeV)
H → γγ　Br is small of about 10-3,
But promising mode due to good resolution of γ

6. [3-3A] H→ γγ in GF and VBF (small Br, but excellent Mγγ）
H+0j
huge BG. S/N ~1% qq_bar→ γγ　is 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)
H+1j
γ-ID and resolution are essential :
BG can be estimated with the side band.
Mgg(GeV)
H+2j
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ATLAS preliminary
Xsection (fb/GeV)
Mgg(GeV)
Good S/N and flat BG
but Stat. limited　
H→γγ indicates that spin
of Higgs is 0 (or 2).  scalar
Mgg(GeV)

7. [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
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M(H)=200GeV
M(H)=140GeV
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.

8. 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
ATLAS Fast
CMS Full
This mode is direct evidence of Higgs-fermion coupling (Yukawa)
Origin of fermion
mass
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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

9. Φ between di-lepton (Rad)
[3-3D] VBF Ｈ→　WW
Leptonic decays of W lead to the event topology of
Dilepton+mET
Leptons are emitted
in the same direction
MＨ=160GeV
ATLAS e- W+ W- e+
Higgs Spin0
CMS Full
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Clear Jacobian Peak is observed:
tt → bb lνlν is main BG:
Leptons are back-to-back in tt.
Φ between di-lepton (Rad)

10. [3-4] Discovery Potential of the SM Higgs
LO calculation
NLO calculation
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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-1 for both ATLAS and CMS
Different technologies are essential for various modes: (Safe and redundant)

11. Let’s combine ATLAS+CMS performance
preliminary 1 10
10-1
Needed Ldt (fb-1)
per experiment
mH (GeV)
 1 fb-1 for 98% C.L. exclusion
 5 fb-1 for 5 discovery
over full allowed mass range
% C.L. exclusion
5σ discovery is 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?
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critical test can be performed for “origin of mass”

12. [3-5] Measurements of Mass & coupling (L=300fb-1)
Relative coupling (Normalized to g(WH))
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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

13. Accuracy of “absolute measurements” of the couplings.
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.
Accuracy:
yt、yτ gZZH and gWWH 20%
yb %
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14. Higgs Self-couplings σ×Br is small Need very High Luminosity ー＞SLHC
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
ー＞SLHC
For 6000 fb-1 (SLHC)
Dl ~ 19% for 170 GeV MH
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15. ＳＭ Higgsの研究で有効なチャンネルの纏め
生成過程
崩壊過程
有効な領域とその効能
Gluon Fusion
　H ->　γγ
GeV
発見 Mass 測定
spin=0の傍証
H -> ZZ-> 4 l 　
発見・Mass, spin, coupling測定
H -> WW
GeV 発見
Vector Boson
Fusion
(鍵のチャンネル）
H -> ττ
発見・Mass, coupling測定
H -> WW
GeV
発見・W coupling測定
H -> γγ
発見　 (fake、高次効果研究）
Mass測定
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16. Asai KEK Topical

17. Diphoton background is now computed at NLO (Binoth et al, Eur. Phys. J
Diphoton background is now computed at NLO (Binoth et al, Eur.Phys.J.C16(2000)311, Bern,Dixon,Schmidt hep-ph/ , C.Balasz et al, Phys.Lett.B489(2000)157
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18. 1-6 ＭSSM Higgsの発見能力 軽いhはSM解析、 ほぼそのまま 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
L=30fb-1のrunで発見可能
ここら辺以外は１年でOK
(t →H+b がcover)
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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 )

19. H/A生成 tanβ ← tanβ２で数が 増えるので見える gg→bbH/A→ττ、μμ、（bb） ← μのyukawa*tanβ
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←　μのyukawa*tanβ
第２世代のYukawaを見るチャンス 10

20. H/A生成 tanβ gg→bbH/A→ττ、μμ、bb tanβを測定する重要なチャネル 軽いhがLEP見えない->大きなtanβ
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tanβを測定する重要なチャネル
軽いhがLEP見えない->大きなtanβ

21. Ｈ＋−
(t,b) Br=90%
(τν) 10%
の時suppress
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22. [6] 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

23. 2008 !! 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