LHC-ATLAS におけるトップ
クォーク対生成断面積の測定
奥村恭幸(OKUMURA, Yasuyuki)
Nagoya University, Japan

素粒子標準模型とトップクォーク• 素粒子標準模型(Standard Model)– ゲージ原理による量子場の理論• 素粒子の相互作用を記述• ゲージ粒子の存在を予言– 質量獲得の機構が未解明• ヒッグス場 (相転移した真空) と素粒子の相互作用の理解• トップクォーク– 最大質量の素粒子(173 GeV/c2 )をもち、質量の起源の解明に対し重要なプローブとして働く

νe	

νµ	

ντ	

e

µ

τ

u

c

d

s

t
b

トップ
173GeV	
2	

トップクォークを用いた質量起源解明• トップクォークとヒッグス場(ヒッグス粒子)の結合– 湯川相互作用の理解を進める• ヒッグス場の質量の発散問題– トップとヒッグス粒子のループ効果の理解– ヒッグス場の安定化の機構の理解
超対称パートナー	  (Spin	  0	
  のトップクォーク)	

トップクォーク測定は質量起源の解明に対して重要なアプローチ	  エネルギーフロンティア実験	
  +	
  トップクォーク	
3	Large Hadron Collider
エネルギーフロンティア &ルミノシティフロンティア ハドロンコライダー:– Proton-Proton collider– 3.5 TeV + 3.5 TeV = 7 TeV– 瞬間ルミノシティ
L = 1033/cm2/s (2011 August)Process

Cross-section

Production-rate

PP inelastic (soft-QCD)

70 mb

70 MHzW production

100 nb100 HzZ production

30 nb

30 Hz

tt production

165 pb0.2 Hz4	陽子・陽子衝突の運動学

x1 ⇥ 3.5 TeV

x2 ⇥ 3.5 TeV• Center-of-mass-energy• Longitudinal momentum(proton-beam axis)• Transverse momentumppŝ = x1 x2 ⇥ 7 TeV(x1 x2 ) ⇥ 3.5 TeV

05	トップクォーク対生成断面積tt̄+X =

Z 1
0

dx1

Z 1
0

dx2

X

p

fi (x1 , µF )fj (x2 , µF )ˆij!tt̄+X ( ŝ)

ij

0.5

July 2009

α s(Q)

Deep Inelastic Scattering
e+e– Annihilation
Heavy Quarkonia

0.4

p

0.3

↵s

0.2

0.1
QCD
1

α s (Μ Z) = 0.1184 ± 0.0007
10Q [GeV]

1

100

Preliminary
Figure 2.3: Summary of measurements ATLAS
of αs asa function of the respective ener
2010 data e+jets prel.
173.8 ± 6.7 ± 4.8
The curves are QCD predictions for the combined world average value of αs (MZ 0 ).
2010 data µ+jets prel.
166.7 ± 5.0 ± 5.0(Date: August 15, 2011)2010 data l+jets prel.

169.3 ± 4.0 ± 4.9

2011 data e+jets prel.

173.9 ± 1.2 ± 3.1

2011 data µ+jets prel.

175.9 ± 1.0 ± 2.7

In p-QCD, an observable σ̂ij→tt̄+X (ŝ) can be expanded as:σ̂ij→tt̄+X (ŝ) = σ1 (ŝ)αs + σ2 (ŝ)αs2 + σ3 (ŝ)αs3 + . . . .

Each order of the cross section can be calculated by the Feynman diagram technique
2010+2011 data l+jets prel.
175.9 ± 0.9 ± 2.7
and Figure 2.4 show the diagrams of tt̄ production in the lowest order and the seorder approximation,
respectively,
the
Run-I
best (D0 l+jets)which are the leading-order (LO)180.1and± 3.6± next-le
3.9(NLO) approximation. In this analysis, the theoretical prediction of the tt̄ events
Run-II best (CDF l+jets)
173.0 ± 0.7 ± 1.1
the LO+NLO approximation of the p-QCD.

トップクォーク対生成断面積の精密測定は、標準模型( QCD, EW ) の 7 TeV 陽子・陽子衝突での精密検証
2.2.3

173.2 ± 0.6 ± 0.8

Tevatron July 2011

The parton
distribution function
8160

0.0 ± 0.0 ± 0.0

180

200

The partonic cross-section for collisions of two partons with x1 and x2 is integrated
mtop
[GeV]
range of the momentum with the appropriate
weightfunction, which is called thetribution function (PDF). It is denoted as fi in Equation 2.1, where i denotes the flinitial partons (u, d, c, s, g, and b), and the fraction of momentum carried by thethe interaction is given by x. For the different parton flavor, the PDF is very diffe*46	

The PDF normalization and basic requirements are mentioned in the Appendix A.2.

ATLAS 検出器
汎用型検出器• 精密飛跡検出器• 電磁カロリメータ• ハドロンカロリメータ• ミューオン検出器

終状態の再構成Y: |η|<2.5: |η|<3.2: |η|<4.9: |η|<2.7

X
Z

Figure 3.2: The ATLAS detectorTracker	
consists ofEM-­‐calo	
tracking H-­‐calo	
detectors, calorimetersMuon	
chambers. It is 25 m in height and 44 m in length. The overall weight ofElectron	approximately
7000 tons.

Photon	Components• 粒子識別Charged	
  Hadron	
Tracking– 電子, ミュー粒子,
光子, ハドロン

EM calorimetry
Neutral	  Hadron	Hadroncalorimetry
barrel and end-cap
forwardMuon	
Muon spectrometer• 運動量測定– レプトン (a few %)ハドロン (10%)

Resolution
σpT /pT = 0.05%p√ T ⊕ 1%σE /E = 10%/ E ⊕ 0.7%√
σE /E = 50%/√E ⊕ 3%
σE /E = 100%/ E ⊕ 10%
σpT /pT = 10% at pT =1 TeV

η coverage
Measurements
Trigg|η| < 2.5
|η| < 3.2
|η| <|η| < 3.2
3.1 < |η| < 4.9|η| < 2.7
|η| <Table 3.2: Main components of the ATLAS detector.

3.2.2

Tracking

The innermost part of the ATLAS detector is a precise tracking system, so7	detector (ID) system. The ID system surrounds the interaction point of pp

トップクォーク対生成の終状態
Wボソンの崩壊終状態で定義:– Lepton + hadron– Dilepton

(35%)
(7%)

• ee, µµ, eµ	– All hadron

Leptonic decay 26%

22%
Wàe/µ+ν	 	Wàτ+ν	 τàe/µ+ν+ν	
 4%τàq+q'+ν	7%
	
67%
Wàqq'		
Hadronic decay 74%(55%)

ダイレプトン終状態の特徴– 2 本の異符号のレプトン– b クォーク
– ニュートリノ

l-	

l+	

ν	

ν	
W-­‐	
 ―	
ｔ	
 ｔ	
 W+	
―
b	

b	
8	

終状態の再構成• クォークやグルーオン– ハドロン化し、運動量が分散– ハドロンカロリメータで、“ハドロンジェット”として再構成• 電子・ミュー粒子– “単一飛跡” として検出• 高横運動量• アイソレーション• ニュートリノ– “Missing ET” として再構成

l+	
W	

ν	

B

D
ν l	

“Fake	
  lepton”	

9	

トップクォーク候補事象
Muonü Inner tracker
ü Muon detector
PT = 54 GeV

Two Hadron jetü H-CalorimeterPT
1st = 173 GeV
2nd = 44 GeV

Neutrinoü All detectors
Missing ET = 129 GeVElectronü Inner detectorü EM-CalorimeterET 66 GeV
10	

生成断面積測定
数え上げによるtt̄ 測定Ndata BGtt̄ =AL

– 候補事象数– 背景事象数推定– 信号のアクセプタンス– 積分ルミノシティ( Ndata )( BG )( A )( L )

高精度達成のための戦略:– 検出器を良く理解• レプトン測定 (e/µ)• ハドロンカロリメータ測定 (Hadron jets, Missing ET)– “効率的”にかつ “効果的” に信号を選別する手法を確立– 含まれる背景事象を良く理解
11	Data samples
陽子・陽子衝突データ• シングルレプトントリガー– 電子– ミューオン(20 GeV)(18 GeV)• “GOOD Data quality” 条件を満たす 0.70 0.03 fb-1 を使用

シミュレーションサンプル• 信号アクセプタンス ( A )• 背景事象数見積もり (BG)
Signal sample
	
  
	

tt̄

Background sample

Z + jets

W W, W Z, ZZ

Wt
12	信号サンプル & コントロールサンプル
ν

l-	
W-­‐	

l+	

ν

W+	

―	

―
b

Events that include two lepton in their ﬁnal states

t	
 t	

b

tt(àll) (σBFSM=11pb)

Z (àee/µµ) + jets (1.0 103pb)

Single top (1.0pb) Diboson (7.6pb)

Z ボソンコントロールサンプル– 検出器の理解Z à ee / µµ の背景事象の理解

信号サンプル– トップクォーク対生成事象を抽出– Missing ET, Large #jets,
Out of Z resonance13	レプトン検出器の性能評価
電子・ミュー粒子の検出効率の実機性能は、正確に断面積を測定する際に必要不可欠: µ+	
– 信号のアクセプタンス評価 (A )– バックグラウンド評価
(BG )

µ-	
Z ボソンコントロールサンプルを用いた“Tag & Probe” 法

Z

e+	
Z

e-	

測定手法の例 (トリガー効率測定)• 2 本の isolated & high pT レプトン & Z ボソン質量• 内 1 本がトリガー条件を満たしていること• もう一本は効率測定の “probe” として使用可能
14	

レプトン検出器の性能評価
トリガー効率、レプトン再構成効率、
アイソレーション条件の効率を、別々に測定– pT, η, #jets, #vertices の関数として測定

測定結果を、トップクォーク事象や、その他のバックグラウ
ンドの検出数理解に用いる à 実機性能に基づいた評価
Top	
  events	

ee	

Two	
  lepton	
  selecJon	

19%	
 36%	
 26%	

Uncertain)es	

electron	 muon	

Trigger	

±0.5%	

±1.0%	

ReconstrucJon	

±1.0%	

±0.3%	

IsolaJon	  cut	

±3.0%	

±0.03%	

µµ	

eµ	

15	

ハドロンカロリメータとパイルアップ
パイルアップ衝突数は平均 6個 / バンチ交差• #jets & Missing ET が影響を受ける

シミュレーション中で正確に再現し、その影響を理解した上で測定を遂行する
Collision	
  data	Zàµµ	

≈10cm	

SimulaJon	

Average of #interactions
16	Jet multiplicity• Validation with Z+jets control region
BeforeCorrection

After
Correction17	Missing ET• Validation with Z+jets control region
BeforeCorrection

After
Correction

18	

5

10

4

10

µµ channelµ10µ channel

∫ ∫

-1

-1 fb
L dt = 0.70
105L dt = 0.70 fb
4

10

tt tt
γ *+jets
Z/ γZ/*+jets
Fake leptons
Fake leptons
DibosonDibosonSingle top
Single top60µµµµchannel
channelfb fb∫∫L Ldtdt= 0.70
= 0.70
-1

1022

10

-1

tt tt
Z/ γ *+jets
Z/ γ *+jets
Fake leptons
Fake leptons
DibosonDibosonSingle top

Single top

50

40

30

103

10

3

10

20

10

102

102
10

Events / 35 GeV

10

3

10
103

6

Events/ /44 GeV
GeV
Events6

Events / 10 GeV

ee/µµ チャンネル
1. A pair of high-pT
isolated leptons
2. Missing ET > 60 GeV
3. Z veto (|Mll-MZ|>10 GeV)
4. # jets≥2

Events / 10 GeV

Event Selection

10

10

1

1

10 20 40 60 80 100 120 140 160 180 200
Mll [GeV]eµ チャンネル
0 20 40 60 80 100 120 140 160 180 200 600
10
E
[GeV]
µ
µ
channelµµchanneleµ channel(b)tttttt
1. A10 pair of high-p
isolated
leptons(a)TZ/ γ *+jets
Z/ γ *+jets
Z/ γ *+jets
500
L
dt
=
0.70
fb
L
dt
=
0.70
fb
L
dt
=
0.70
fb
Fake
leptons
Fake
leptons
Fake leptons∫> 130 GeVDiboson∫ Figure 5.13: (a)Expected∫ of kinematic
2. HT
10
(b)
distributions
variables
that
DibosonDiboson10
400Single top
Single top
Single top
signals. The red lines and arrows correspond to the used cut valu
3. #10 jets≥2
6

-1

5

4

Acceptance (%)

103
102

ee

6.6

0.9

10

mm

13.0

1.0

1

em

20.0

1.1

0

20 40 60 80 100 120 140 160 180 200
Emiss
[GeV]
T

0

20 40 60 80 100 120 140 160 180 200
Emiss
[GeV]
T

3

miss
T

-1

2

0

20 40 60 80 100 120 140 160 180 200
Mll [GeV]

Events / 35 GeV

Events / 4 GeV

Events / 10 GeV

1-1

Figure5.13: Expecteddistributionsof kinematic
distribution
after applying
the 300µµ requirements.
(b) variables
Invariant m
missselectedmuons
after andthe Earrows> 60
GeV cut application.
ThecutETmv#events(data)
signals.
The
red lines
correspondto the used10T
veto cuts after
are applied
to ee theand 200µµ channels
to reject(b)theInvaria
large codistribution
applyingµµ
requirements.
misseµ requirement. This cut is applied t(c) H165
afterEthe
T distribution
selected
muons
after
the
>10060 GeV cut application. The
T
∗
from
the
Z/γ
→
τ
τ
process.
1
301
veto
cuts
are applied to ee and µµ channels to reject the larg0(c)HT40 distribution
0 20
60 80 100 120 140after
160 180the
200 eµ requirement.
0
100 200 300This
400 cut
500 is600appli
700
963 andMTll [GeV]
HT [GeV]∗cut
pointsthepthresholdincounting
number
of
jets.
The
c
from the Z/γ → τ τ process.

been chosen as optimal selection criteria. By the application of t
to the pp collision data, 165 events, 301 -1
events, and 963 19	
events arstates,Table 5.5,
Table 5.6,number
and Tablesum
cut final
pointsand respectively.
the pT thresholdin countingof 5.7jets.
T

1400 candidates are collected from 0.70 fb

dataBackground estimation(a)

Events / 10 GeV

Figure 5.1: The event topology of the tt̄ signal events in the dBackgrounds due to detector
the either eﬀects
of an electron or a muon. (b) shows a topology inclu
105

µµ

∫

4

10

Data
tt
Z/ γ *+jets
Fake leptons
Other EW
uncertainty-1

L dt = 0.70 fb

103
102
10
1
0

Z (àee/µµ) + jets (1.0 103pb)

20

40

60

80 100 120 140 160 180 200
Emiss
[GeV]
T

(a)

W (àeν/µν) (b)+ jets (104pb)

data/MC

Backgrounds that have similar
event
topologies(two (a)leptons,
neutrino)
Figure 5.2:
Backgroundcandidates:
Z/γ ∗ +jets,(b) W+jet
2

1.8
1.6
1.4
1.2

1

0.8

production events.
0.6
0.4
0.2
0

0

20

40

60

80

100

120

140

160

180

200

Adding to the pair of two leptons, the dilepton channel is chatransverse energy (ETmiss ) corresponding to undetected neutrino
two jets with large pT corresponding to two b-quark from a tt̄ designal is illustrated in Figure 5.1. Other processes that have si
Single top (1.0pb)
Diboson (7.6pb)
multi-jets, W +jets, Z/γ ∗ +jets, di-boson (W W , W Z, ZZ), andpollute the signal samples. Figure 5.2 shows diagrams of the ba
20	
The cross-section of the tt̄ production is measured with
follo

he
signalregionwithout
GeV
requirement.
The
numberjets
distrisignalregionwithout
HTH>
130130GeV
requirement.
(b)(b)
The
numberof of
jets
distribu
T >hesignalregionwithout
Njets
2 requirement.
signalregionwithout
Njets≥≥
2 requirement.

channels
AllAllchannels

1000
1000

∫∫

-1

-1

= 0.70
L dtL=dt0.70
fb fb

800800600600

Data
Data
tt tt
γ *+jets
Z/ γZ/*+jetsFakeleptons
Fake
leptons
DibosonDibosonSingleSingletoptopEvents / 10 GeV
Events / 10 GeV

EventsEventsSignal region plots
4
Allchannelschannels
10410All

3

∫∫

-1

-1

= 0.70
L dtL =dt0.70
fb fb

3

10 10

Data
Data
tt tt
γ *+jets
Z/ γZ/*+jetsFakeleptons
Fake
leptons
DibosonDibosonSingleSingletoptop2

10210

40040010 102002001 1
0 0
0 01 12 23 34 45 56 67 78 89 9
Numberof Jets
Numberof Jets

0 020 20
40 40
60 60
80 80
100100120120140140160160180180200200
missmissE[GeV]
ET T[GeV]

非常に純度の高いトップクォーク対生成信号のサンプル 83%
標準模型の予言の分布と精度の範囲内で一致(a)(a)(b)(b)

21	

ure
5.27:
multiplicity
signalregionwithout
Njets
2 requirement
5.27:(a)(a)
JetJetmultiplicity
in inthethesignalregionwithoutthetheNjets≥≥
2 requirementfo+11.5SM cross-section prediction (σ SM = 164.6 −15.8pb). The results indicate the presence of tt̄
tt̄
production clearly as an excess against the background estimation. The distribution could not
be explained without contributions of tt̄ signal√ events, and therefore, the presence of t-quark
has been confirmed at the pp collisions with s = 7 TeV.

Cross-section extraction
Drell-Yan+jets (DD)
Drell-Yan(→ τ τ )+jets (MC)Fake leptons (DD)Single top (MC)Diboson (MC)Total (non tt̄)tt̄ (MC)
Total expected events
Observed eventsee+2.5
4.0 −1.2
4.9 ± 2.6
2.5 ± 1.9
+1.2
6.4 −1.1
5.9 ± 1.0
23.6 ± 4.4
124.0 ± 17.2
147.6 ± 17.8165µµ14.4 +5.4−4.2
11.0 ± 5.0
0.3 ± 0.6
16.0 +1.9−2.2
8.7 +1.2−1.5
50.5 ± 8.4
241.3 +14.5−17.9
291.8 +16.6
−19.9
301

eµ
42.5 ± 16.1
44.0 ± 24.0
41.1 ± 5.5
32.9 ± 4.9
160.5 ± 34.1
745.5 ± 41.8
906.6 ± 53.9
963

(approx.
NNLO)
Table 5.18: The full breakdown of the expectedTheorytt̄-signal
andbackground in the signal region-1
Dataobserved
2011, Ldtevent= 0.70 yields,fbcompared to thefor each of mthedilepton
GeV channels (MC is simulationt = 172.5
832 +included
based, DD is data-driven)
after all systematic uncertainties
and the correlations
188 ± 17 1+- areee
24 1- 7
+ 15 + 8µµ
171 ±account.
12 1- 11 1- 7
between the different
background sources are taken into∫

15
177 ± 7 1+- 12±8eµ+ 14 missCombination
175 ± 6the1- 11E ± 8 distributions (ee, µµ) andIn Figure 5.24(a),Figure 5.25(a), and Figure 5.26(a),T(stat)±(syst)±(lumi)miss/ < 10%HT distribution (eµ) shown, after application of all the selections except for ET> 60 GeV
0
50
100
150
200
250
300
(in ee and µµ) or HT > 130 GeV (inσ tt [eµ)pb ] requirements. In Figure 5.24(b), Figure 5.25(b),and Figure 5.26(b), the number of selected jets are shown for ee, µµ and eµ channels. All the+11selection is applied except for Njets ≥ 2 cut. These variables in the signal16
region are in goodthe MC
simulation cross-sectionof tt̄ scaled withthethreecross-section
predicted
the SM.
Figureagreement
5.31: Thewith
measuredtt̄ production
for theindividual
channelsbyand5.27(a) of
andshow combined
distributionof thethethreechannels. predicted
for theFigure
combination
the5.27(b)three channels.
The yellow
band shows
cross-section
by the NNLO p-QCD.
22	

Consistent with SM prediction (165pb)

Uncertainty estimation
1. Data statistics (3%)–

Poisson error

2. Luminosity
–
–

(4%)

Denominator of x-sec
Background estimation

3. Modeling in simulation––

Ndata BG
tt̄ =
AL
(4%)

X-sec prediction for background processes
Acceptance dependence of choice of a set of PDF

4. Detector performances (5%)–

Uncertainty on performance measurements

5. Data-driven background estimation–(2%)

Fake rate evaluation
23	

20
10

Signal region plots
data/MC0

Lepton & jet η distributions

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-2.5 -2 -1.5

– PDF, top quark mass
100 100
All channels
All channels

dt = 0.70
fb fb∫ L dt∫ =L 0.70
-1

-1

80 80
60 60

40 40

DataDatatt tt
Z/ γ *+jets
Z/ γ *+jets
leptons
FakeFake
leptons
DibosonDibosonSingleSingle
top top

40 40

30 30

20 20

20 20

10 10
0
data/MC

data/MC2
2
1.8 1.8
1.6 1.6
1.4 1.4
1.2 1.2
1
1
0.8 0.8
0.6 0.6
0.4 0.4
0.2 0.2
00-2 -1.5-1 -0.5
0-2.5 -2.5-2 -1.5-1 -0.5
0 0.5

0.5
1 1.5
2 2.5
1 1.5
2 2.5
electronηelectronη

02
2
1.8 1.8
1.6 1.6
1.4 1.4
1.2 1.2
1
1
0.8 0.8
0.6 0.6
0.4 0.4
0.2 0.2
00-2 -1.5-1 -0.5
0-2.5 -2.5-2 -1.5-1 -0.50 0.5(a) (a)1

1.5 2 2.5
electron η(b) (b)200
180 All channels-1
L dt = 0.70 fb
160
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60
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0

Data
tt
Z/ γ *+jets
Fake leptons
DibosonSingle top

∫

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
1.5
2 2.5 -2.5 -2 -1.5
2 2.5
µη µη

data/MC0data/MC00.5

Hadron jet η	Events / 0.10

60 60
50 50

Events / 0.10

∫ ∫DataDatatt tt
Z/ γ *+jets
Z/ γ *+jets
leptons
FakeFake
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top top

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Events / 0.10

90 All channels
90 Allchannels
80 80
-1
-1
L 0.70dt = 0.70
L dt =
fb fb
70 70

0

(a)

Muon η	

Electron η	

-1 -0.5

0.5
1
1 1.5

-1 -0.5

0

0.5

1

1.5

(c)

eV

10

eV

24	

00 200180 180

2 2.5
Jet η

Figure 5.28: Distributions of the kinematic

# jets distribution in ttbar
QCD parameters (ΛQCD, cut-oﬀ for p.shower )– Varied with range compatible to their uncertainty
0.45

data (BG subtracted)
center0.4

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0.35
0.3

isr -1#signa
fsr +1#signa
fsr -1#signa

0.25
0.2
0.15
0.1
0.05
0

0

1

2

3

4

5

6

7
8
9
Number of jets

The current P-QCD & EW theory (SM) gives well-consistent description of ttbar production at 7 TeV.
More tuning will enable us interesting study in ttbar + high jet multiplicity region

σ t [pb]Comparison with Tevatron
NLO QCD (pp)t

Approx. NNLO (pp)NLO QCD (pp)102

Approx. NNLO (p p)

220
210
200
190
180
170
160
150
140
130
120 6.8

CDF
D0

10

7

Dilepton (this work) 175

7.2
+17
-14

pb

l+jets 179 ± 12 pb
Dilepton (w/ b-tag) 183

1

1

2

3

4

5

6

+21
pb
-16

7

8
s [TeV]26	

Summary 1
初のトップ対生成断面積の精密測定結果 (10%)– ダイレプトン終状態に注目することで、soft-QCD 背景事象を効果的に抑制– 検出器の理解を進めることで、実機の評価に基づく断面積評価を実現+14tt̄ = 175 ± 6(stat.) 11 (syst.)± 8(lumi.)

7 TeV 陽子・陽子衝突中のトップクォーク対生成
事象が現在の SM でよく記述されていることを実験的に証明– PDF, strong coupling constant, top mass, BF of
top decay27	t-quark should have a partner with similar mass, below 1 TeV.

Summary 2

Figure2.9: Expected couplingof fermionsto thefermion mass,√
The t̃constantt̃¯ production
withproportional
similar event
topology
to tt̄ expressed
production
2mf
by v . The red points show the coupling for charged leptons and the blue points show the
The t-quark partners may be created at the LHC pp collisions if their mass iscoupling for quarks.
same event topology of the new t-quark partner can be the same as that oIn the supersymmetric models with R-parity conservation*5 , the t-quark p
boson, as shown in Figure2.10(b).
This
process
is very interesting
to understandthewell as tquark(t̃) andthet̃t̃¯ production
is expectedinatorderpp collisions[16]. As
coupling constant between
the Higgs
and t-quark.
Fortothispurpose,it is importantpresenceof a bosons
light partnerof t-quark
solve
the hierarchy
problem,tothis supunderstand the nominal preferstt̄ productionandas
itsa property
LHC between
pp collisions
a light cross-section
t-quark partner
result of atthethemixingright-handwithout the production of the Higgs bosons. Especially it is essential to control the additional
scalar partners (t̃R , t̃L ), effect of which is proportional to the t-quark mass [1jets (e.g. ISR jets) well in the tt̄ events so that we could handle the H → bb̄ decay signalof the light t-quark would motivate the t̃ at the LHC.
associated with the tt̄ events.
” particle (LSP) is a n
In a scenario where the lightest supersymmetric
T with the normal mattegravitino (G̃), which are unlikely to have interactions-1 into LSP particle and th
next lightest supersymmetric particle, a t̃ decaying
0.14
in Figure 2.12, is one of themost probable processes.
0.13
σt t +H prediction [pb]トップクォークをプローブとした “質量起源の解明”に対して重要な基礎を築いた :“tt+jets” や “tt+Missing-E
with more data in 2012 (15fb , 8 TeV)
total uncertainty

scale uncertainty

0.12
0.11
0.1
0.09
0.08
0.07
0.06
110

(a)

115

120

125

130
mH[GeV](b)

Higgs 生成 (tt + jets,
SUSY
生成 ( extension
tt + Missing
T , 0.1pb)
Figure0.1pb)
2.12: An example ofthe possibleof theESM
by the introdu

Figure 2.10: (a) An example of a tt̄H production diagrams. (b) Expected cross-section of
metry.
tt̄H production with the PDF and scale uncertainties. It is typically σtt̄+H = 0.1 pb and28	
−3≈ 10 × σ ¯ .

0.70 fb-1

Top pair + jets

ATLAS-­‐CONF-­‐2011-­‐142	

#jets distributions in top-pair productions• ISR + Higgs(?)
g

g

t

g
g

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g
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O(10 pb)q(1) Exactly one lepton (e/m)(2) large mT(W),(3) #jets ≥ 4 with pT > 25 GeV,
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t

g

H

b

O(0.1 pb)b̄t̄

pT>60GeV	• Understand detector performance• Tune ISR related parameters (ΛQCD)
and reduce the uncertainties
29	

80

∫

Other Backgrounds

same event topology of the new t-quark partner can be the sameas that of the SM tt̄
s=7 TeV*5 (2012)	
  041805	
Phys.Rev.Le[.	
  
1
08	
  
R-parity
conservation,thet-quark
Background Uncertainty In the supersymmetric models with60
4 partner is a100¯
quark (t̃) and the t̃t̃ production is expected at pp collisions
As
Expected[16].
Limit (±
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presenceofalight
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to
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Obs. Limit (Theory Unc.)
m(T)=440 GeV, m(A )=100 GeV
prefers a light t-quark
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120
(t)
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scalarpartners
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t̃
,
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),
effect of
to Exclusion
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mwhich is proportionalCDF
R 200
L
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ATLAS
of the light t-quark would motivate
the t̃ at the LHC.
L dt=1.04 fb
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-m
In a scenario where theis a neutralino (χ”550(LSP)-16000T) lightest supersymmetric particle
150
200
250
350
400
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350
400
450
500
tt 300150
gravitino (G̃), which are unlikely to have interactions with
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T Mass[GeV]
next lightest supersymmetric particle, a t̃ decaying into LSP
and the t-quark, asparticle=7 TeV
Background Uncertainty in Figure 2.12, is one of the most probable processes.
60
100
90
,g̃
FIG. 2: Excluded region (under theq̃12
curve)
at theExpected
Limit (95%±t̃1σ) confi- ˜0m(T)=360
GeV
ATLAS
Data,
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-14080(1) Exactly(e/m),
L one
dt=1.04leptonfbObs. Limit (Theory Unc.)
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T
tt
20
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isshown.
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500
550
600
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30m(T)=440 GeV, m(A )=100 GeV
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  quark	
Figure2.12: FIG.
An example
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dence
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-1
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80
10
metry.
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L dt=1.04 fbon the
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tt
100
150
200
250
300
350
400the assumption
In
that the massisofshown.
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60
Other Backgrounds missaccessibleat the LHC
collisionenergyratio
andas
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50
Background Uncertainty section predicted by 1
the
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The
event
topologyisverysimilarto that o
the two masses.
events except for the additional presence of the LSP particles, which may mom(T)=360 GeV, m(A )=100production
FIG. 1: 40(a) Transverse mass of the leptonand missingGeV
energymisskinematic
distributionof the tt̄ events, especially the ETmiss distribution. These new pheand (b)30
ET
after applying all selection
exceptm(T)=440criteria
GeV, m(A )=100
GeV theScalar	  top-­‐like	
  quark	
0 Mass = 10 GeV
can bethe Acomparisonof the measured cross-section and kinematic distr
cut on the variable shown. MC background contributions
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Expected
Limit
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±
1
σ
)
20
ATLAS for the measurem
withis oneLimitof the important motivations
stacked on top of each other and normalized according
to the QCD prediction, which
Observed
10 corrections discussed in the text. The lines
NNLO
Spin-1/2
the withtt̄ production cross-section
at theLHC.TT Theory ±1σ-1data-driven
10-1
L dt=1.04 fb
NLO
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the arrows
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thatdefinethesignal0s=7 TeV
miss 250
100
150 and200
300
350
400
300
320
340
360
380
400
420
440
region (mT >150 GeVET> 100 GeV).
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T Mass [GeV]
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the SM
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isCross-section
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ATLAS Preliminary (simulation)

Parton Distribution Function
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2

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8/7

a larger increase.
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SUSY Searches

Charged Higgs
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FCNC

The search for supersymmetry is one of the key goals
Figure 1: The effective gain in the rate of interactions fromof LHC. CMS produced the first result on the total 201031	
raising the centre-of-mass energy to 8 or 9 TeV.
dataset [4], which placed limits on the CMSSM model us-

ATLAS Shift

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基本的なサイクルをすることができてラッキーでした– 検出器を触って(作って&動かして&校正して)– その性能を理解して– 自分が面白いと思う
物理測定につなげる“データをとって” “自分で解析する” ことの面白み
LHC-ATLAS 実験で活躍するために気をつけたこと– 素早いアクションでグループをリード
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N-lab Meeting 2007/06/07
Yasuyuki Okumura

活躍するのは若手 (博士大学院生 & ポスドク) で測定器運転でも物理解析でも活躍機会はいくらでもある

おしまい

f the cross-section measurement for the t-quark mass uncertainty (173.2 ± 0.9 GeV) is foundo be much less than other uncertainties.
Figure 5.33 shows the comparison between the measured cross-section and theoretical prediction given by the NNLO perturbative QCD calculation as a function of the assumed t-quark
mass from 160 GeV to 190 GeV. The t-quark mass which is preferred by the comparison be• Measurement
is robustforwithmass
diﬀerence.
ween measured
and predicted cross-section
is consistent
the world
average of the massmeasurements,
shownwith blue lines in the will
figure.match the best with the• Themeasurements
SM if the mtop = 170 GeV
σ t [pb]

Top masst

260
p-QCD prediction

240

Measurements

220

mt measurement world average

200
180
160
140
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160

165

170

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180

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190
mt [GeV]Cross-section summary
proton - (anti)proton cross sections

7 TeV LHC parton kinematics
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9

10

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WJS2010

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http://projects.hepforge.org/mstwpdf/	
35	

(a)

(b)

ure 2.6: Examples of (a) initial state radiation (ISR) and (b) final state radiation (Fx2

Q [GeV]The (x, Q) and (x1 , xof theparametertt̄ production eventsat the for
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