PowerPoint プレゼンテーション

Physics @ LHC
(Physics @ TeV)
Status of LHC/ATLAS/CMS and
Physics explored at LHC
Fundamentalist of High Energy Physics (U. Tokyo)
[4] SuperSymmetry
O(TeV) SUSY provides GUT and good candidate of
cold dark matter.
[4-1] Production cross-section at LHC
( g˜ g˜ , g˜ q˜ , q˜ q˜ )

g˜ : 2TeV

q˜ :1TeV



These couplings are just strong
interaction (αs):
 large cross-section is expected
q˜ : 2TeV model independent except for mass
m(q˜ )  m(g˜ )  0.5TeV
g˜ :1TeV
m(q˜ )  m(g˜ ) 1TeV

m(q˜ )  m(g˜ ) 2TeV
σ〜100pb
g˜ g˜
σ〜3pb
σ〜20fb
u˜u˜, u˜d˜
[4-2] Events topology of SUSY Gluino/squark are produced copiously,
(Gravity- mediation + R-parity) Cascade decay is followed.
Many high Pt jets emit in this cascade ,
Finally nu1 escapes from detection
event topologies of SUSY
multi
leptons
ET + High PT jets (+ b-jets )
τ-jets
Especially no or one lepton mode is promising for Discovery
[4-3] background
Meff distributions after SUSY cut
High Pt jets are estimated with
Matrix Element (ALPGEN 2.05)
ME + PS matching is applied:
1 lepton mode
Count /400GeV/1fb-1
Count /400GeV/1fb-1
0 lepton mode
Meff  Pt  mEt
OPEN HIST show the SUSY signal M( g˜ ) ~ M(q˜ ) ~ 1TeV
L=1fb-1
Meff  Pt  mEt
(tanβ=10)
Main Background processes are top-pair ,W and Z with
 jets,
They include
high Pt neutrino(s):
QCD jet (with fake mET, due to the limited resolution of detector) also contributes
to no-lepton mode (mET
performance is crucial for SUSY hunting)
 Clear excess can be observed in one-lepton mode & no-lepton mode.
SUSY signal M( g˜ ) ~ M(q˜ ) ~ 0.9TeV
Red: co-annihilation (light stau)
Black: bulk
Dilepton mode
Opposite Sign dilepton

ATLAS Preliminary
Number/1fb^-1
Number/1fb^-1
ATLAS Preliminary
Same Sign dilepton
mET (GeV)
Almost Background Free
mET (GeV)
 Stat. is limited but excess can be observed also in dilepton mode.
Top pair is dominant BG for one-lepton and di-lepton modes.
BG can be estimated with real data easily.
[4-4] Understanding of the background processes
Background is estimated with “real data itself” (not estimated with MC):
We have good control samples of Z(→ee/mumu)+jets, W(→lν)+jets and tt→bblνqq with MT<MW.
From them, the background of Z(→νν),W(→lν), tt with large mET & MT>MW:) can be estimated.
For examples: these four plots show mET spectra for various processes
ATLAS Preliminary
Z and W
background
for no-lepton mode
Top pair background
for one lepton mode
R:tt BG
B:estimated
Without SUSY signal
With 1TeV SUSY signal
Background could be estimated with real data itself with accuracy of about 50%
[4-5] Discovery Potential (including systematic errors)
tanβ=10, L=1fb-1
Band shows the effect of systematic errors coming
from background estimations
tanβ=50, L=1fb-1
Results do not strongly depend on tanβ …
One lepton & no lepton mode have the similar potential:
q˜ , g˜
g˜
up to 1.5TeV if m0 <1TeV
up to 1TeV (if squark heavy)
m(g˜ )  2.5m1/2
2
m(q˜ )  m20 +6m1/2
We can discover SUSY with
various event topologies:

multi
leptons
ET + High PT jets + b-jets
τ-jets
Not only
Lepton,
But also..
These carry
information
about
EW gaugino
sector
Let’s combine ATLAS & CMS
With L=1fb-1
q˜ , g˜
M (TeV)
Up to 1.6TeV
(2TeV for 95%CL
exclusion)
2.5
These do not strongly depend on
model:
Important parameters are
masses of q˜ , g˜ and the mass
difference between them and
LSP(>= 400GeV)
2

1.5
1

ATLAS + CMS
1
100
10
Luminosity/expt (fb-1)
1 fb-1/expt

~
g 〜1.6TeV
˜ 1  500GeV

˜ 10  250GeV

Naïve GUT assumption
Gaugino-like
[4-6] Exclusive Study: mass can be measured:
g˜
Select interesting decay chain:
Make kinematic distributions:
Edge carries the information
related to their masses:





˜ 10

q
q

˜ R
˜ 20

q˜



Sharp Edge Mmaxll
2
˜ 20 )2 )(m(
˜ 20 )2  m(
˜10 )2 )
(m(˜qL )  m(
max
Mllq

˜ 20 )2
m(
2
Mlqmax 

M
˜ 20 )2 )(m(
˜ 20 )2  m(l˜R )2 )
(m(˜qL )2  m(
˜ 20 )2
m(

max
Masses can be determined with an accuracy of about 1-10% (with help of model in general)
model independent study on the coupling/mass is difficult @ LHC

2
m( ˜ R ) 
m( 
˜ 10 ) 
0
˜
 m( 2 ) 1 
 1  ˜  
˜ 20 ) 
m( 
m( R ) 
[6] Introduction and Conclusion:
Most important/urgent topics in Particle Physics are:
(1) 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
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
Backup
2-1
m SUGRAの簡単な纏め
５つのパラメター：
mo, m1/2, tanβ, A0,
(mass @GUT)
sign(μ)
(VEV) (scalar 3点) (Higgsino mass)
一般的な傾向
˜ , q˜ ) は重い
•Coloured partciles ( g
• 
˜ 10 はLSPで安定(R-parity) Cold DMの良い候補
•Higgsino mass (|μ|) > 0.8m1/2(Wino)
(m0>>m1/2の場合以外)
→
0

˜0 0 ˜ 0  ˜  0
˜
˜ 1  B , 
˜ 2  W , 
˜ 1  W , 
˜ 3,4 , 
˜2  H



•第３世代の
f˜
は軽い。(Yukawa+LR mixingの効果)
˜ g˜ , g˜ q˜ , q˜ q˜ ) である。
ＬＨＣでの主なSUSY生成過程は、( g

生成断面積は、これらのmass以外にはモデル依存性が小さい。
ただのstrong
interaction

˜ 0 , 
˜  , l˜ らは、 g˜ , q˜ の崩壊過程で出てくる

（多段cascade崩壊）LEP,Tevatronとの大きな違い

g˜ , q˜
のdecay table
m( g˜ )  m(q˜ )


g˜
m( g˜ )  m(q˜ )
qq B˜ 0 ( 1)
g˜  qq W˜ 0 ( 2)

qq W˜ ( 4)
m( g˜ )  m(q˜ )
g˜  qq˜

tt˜1
g˜  ˜
bb
1

q˜ L
q˜ R


q˜ L  qg˜
q˜ R  qg˜


qW˜ 0 ( 1)
q˜ L 
qW˜  ( 2)
q˜ R  qB˜ 0
ここら辺はあまりモデルによらない。Massの関係やB,Wとχの関係、第３世代などがモデル依存
˜ , 
˜


1
0
2 の崩壊モードについて
2-Body decay chain
˜ 1 ),m( 
˜ 20 )  m(˜  )
m( 
I
˜ 1  ˜    
˜ 10

II
Decay to Higgs
˜ )  m( 
˜ )  m(h)
m( 
0
2
0
1
˜ 20  h
˜ 10



˜ 20  ˜ 

˜ W 
˜


1

0
1




˜ 10

Decay to W/Z
m(h)  m  m(W , Z )
˜ 20  Z 0 
˜ 10

˜ 1 W  
˜ 10


III
IV

3-Body decay m  m(W , Z )
˜ 20  ff
˜ 10

˜ 1  ff
˜ 10



これらは基本的にkinematics
だけであり、依存性は少ない。
Sfermion propagatorで3body
˜ 1 が軽くなり、τへのdecay branchingが増える。
tan  1 の時 
τ-IDが大切。Higgsino成分が多くなると、然り。

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