HL-LHC実験 - KEKresearch.kek.jp/people/nojiri/masterplan/Hanagaki.pdfATLAS日本グループ 5 名古屋大京都大京都教育大大阪大神戸大岡山大広島工大九州大

HL-LHC実験

花垣和則（KEK/大阪大学）

Big Questions

2

23

Fit ΩM Ωk wSNe 0.287+0.029+0.039

−0.027−0.036 0 (fixed) -1 (fixed)

SNe+BAO 0.285+0.020+0.011−0.020−0.009 0 (fixed) −1.011+0.076+0.083

−0.082−0.087

SNe+CMB 0.265+0.022+0.018−0.021−0.016 0 (fixed) −0.955+0.060+0.059

−0.066−0.060

SNe+BAO+CMB 0.274+0.016+0.013−0.016−0.012 0 (fixed) −0.969+0.059+0.063

−0.063−0.066

SNe+BAO+CMB 0.285+0.020+0.011−0.019−0.011 −0.009+0.009+0.002

−0.010−0.003 -1 (fixed)

SNe+BAO+CMB 0.285+0.020+0.010−0.020−0.010 −0.010+0.010+0.006

−0.011−0.004 −1.001+0.069+0.080−0.073−0.082

TABLE 6Fit results on cosmological parameters ΩM, Ωk and w. The parameter values are followed by their statistical (σstat) andsystematic (σsys) uncertainties. The parameter values and their statistical errors were obtained from minimizing the χ2 ofEq. 3. The fit to the SNe data alone results in a χ2 of 310.8 for 303 degrees of freedom with a ∆χ2 of less than one forthe other fits. The systematic errors were obtained from fitting with extra nuisance parameters according Eq. 5 and

subtracting from the resulting error, σw/sys, the statistical error: σsys = (σ2w/sys

− σ2stat)

1/2.

0.0 0.1 0.2 0.3 0.4 0.5

-1.5

-1.0

-0.5

0.0

mm

w 0.2 0.3 0.4

-1.0

-0.7

w

0.2 0.3 0.4

w/ sys

w/o NB99

-1.3

-1.0

-0.7

w

-1.3

SNe

BAO

CMB

Fig. 14.— 68.3 %, 95.4 % and 99.7% confidence level contours onw and ΩM, for a flat Universe. The top plot shows the individualconstraints from CMB, BAO and the Union SN set, as well as thecombined constraints (filled gray contours, statistical errors only).The upper right plot shows the effect of including systematic errors.The lower right plot illustrates the impact of the SCP Nearby 1999data.

straints from combining SNe, CMB and BAO are consis-tent with a flat ΛCDM Universe (as seen in Table 6). Fig.15 shows the corresponding constraints in the ΩM − ΩΛplane.

Finally, one can attempt to investigate constraints ona redshift dependent equation of state (EOS) parameterw(z). Initially we consider this in terms of

w(z) = w0 + waz

1 + z, (10)

shown by Linder (2003) to provide excellent approxima-tion to a wide variety of scalar field and other dark en-ergy models. Later, we examine other aspects of timevariation of the dark energy EOS. Assuming a flat Uni-verse and combining the Union set with constraints fromCMB, we obtain constraints on w0, the present valueof the EOS, and wa, giving a measure of its time vari-ation, as shown in Fig. 16. (A cosmological constanthas w0 = −1, wa = 0.) Due to degeneracies within theEOS and between the EOS and the matter density ΩM,the SN dataset alone does not give appreciable leverageon the dark energy properties. By adding other mea-surements, the degeneracies can be broken and currentlymodest cosmology constraints obtained.

Fig. 16 (left) shows the combination of the SN datawith either the CMB constraints or the BAO constraints.

0.0 0.5 1.0

0.0

0.5

1.0

1.5

2.0

FlatBAO

CMB

SNe

No Big Bang

Fig. 15.— 68.3 %, 95.4 % and 99.7% confidence level contourson ΩΛ and ΩM obtained from CMB, BAO and the Union SN set,as well as their combination (assuming w = −1).

The results are similar; note that including either one re-sults in a sharp cut-off at w0+wa = 0, from the physics asmentioned in regards to Eq. 9. Since w(z ≫ 1) = w0+wa

in this parameterization, any model with more positivehigh-redshift w will not yield a matter-dominated earlyUniverse, altering the sound horizon in conflict with ob-servations.

Note that BAO do not provide a purely “low” redshiftconstraint, because implicit within the BAO data anal-ysis, and hence the constraint, is that the high redshiftUniverse was matter dominated (so the sound horizon

時空構造の統一的理解を目指して⇒ LHC/ATLAS実験

多面攻撃

3

1.2 Introduction 5

BigIdeas

Big Questions

SUSY

Dark Matter

Origin of

EWSB

Minimal

Compositeness,Extra dimensions

ExtendedHiggs Sector

TopPartner

W’/Z’

Multiverse

Dark Matter

HiddenSector

NaturalnessUnification

Origin of

Matter

Origin of

FlavorNew Forces

Elementary

vs. Composite

? ? ?

Figure 1-2. Overlap between the questions and ideas discussed in the text.

equivalent (or ‘dual’) to composite theories. This has led to a deeper understanding of both extradimensions and compositeness, and led to many interesting and detailed proposals for new phyicsbased on these ideas.

• Unification of forces. The idea that all elementary interactions have a unified origin goes back toEinstein, and has its modern form in grand unification and string theory. There is experimentalevidence for the unification of gauge couplings at short distances, and string theory generally predictsadditional interactions that may exist at the TeV scale.

• Hidden Sectors. Additional particle sectors that interact very weakly with standard model particlesare a generic feature of string theory, and may play an important role in cosmology, for example darkmatter.

• ‘Smoking Gun’ Particles. Some kinds of new particles give especially important clues about the bigquestions and ideas discussed here. Top partners are required in most solutions to the naturalnessproblem; additional Higgs bosons are present in many models of electroweak symmetry breaking;contact interactions of dark matter with standard model particles are the minimal realization of WIMPdark matter; and unified theories often predict new gauge bosons (W /Z ) that mix with the electroweakgauge bosons.

• The Multiverse. String theory apparently predicts a ‘landscape’ of vacua, and eternal inflation givesa plausible mechanism for populating them in the universe. The implications of this for particlephysics and cosmology are far from clear, but it has the potential to account for apparently unnaturalphenomena, such as fine-tuning.

These questions and ideas are summarized in Fig. 1-2, along with the connections between them.

Community Planning Study: Snowmass 2013

SUSY信者

ダークマター至上主義

様々な信者

多面攻撃

3

1.2 Introduction 5

BigIdeas

Big Questions

SUSY

Dark Matter

Origin of

EWSB

Minimal



TopPartner

W’/Z’

Multiverse

Dark Matter

HiddenSector


Origin of

Matter

Origin of

FlavorNew Forces

Elementary

vs. Composite

? ? ?









SUSY信者


様々な信者

無神論者

high q2でSMからのズレを探る

ヒッグスの精密測定　など

多面攻撃

3

1.2 Introduction 5

BigIdeas

Big Questions

SUSY

Dark Matter

Origin of

EWSB

Minimal



TopPartner

W’/Z’

Multiverse

Dark Matter

HiddenSector


Origin of

Matter

Origin of

FlavorNew Forces

Elementary

vs. Composite

? ? ?









SUSY信者


様々な信者

無神論者

high q2でSMからのズレを探る

ヒッグスの精密測定　など

LHCの発見能力の高さ探索範囲の広さ

LHC/ATLASへの日本の貢献

4

加速器検出器

人的資源（運転）

1" BNL" 15.2"2" CERN" 6.1"3" SARA0NIKHEF" 4.7"4" FZK" 4.7"5" AGLT2" 4.6"6" RAL" 4.5"7" MWT2" 3.8"8" TOKYO" 3.8"9" INFN0T1" 3.5"10" NORDUGRID" 3.3"

10"

"

52"

あらゆる面で重要な貢献

国際協力

LHC：1995年欧州以外の国で最初に正式参加（138.5億円の拠出）

HL-LHC(2026-)を見据えた長期計画

コンピューティング

ATLAS：36MCHFを負担（全体で537MCHF）

開発費や人件費等含まず

ATLAS日本グループ

5

名古屋大京都大京都教育大大阪大神戸大岡山大広島工大九州大

長崎総合科学大

KEK

筑波大

東大

早稲田大

東工大

首都大学東京

お茶の水女子大

信州大

スタッフ～80人博士課程学生～40人修士課程学生～50人

日本の高エネルギーで最大（？）のグループ

学位数修士 198博士 31博士は過去5年に集中

加速器・コンピューティング

6

陽子陽子衝突点

KEK製作ビーム収束用電磁石

#%!

1" BNL" 15.2"2" CERN" 6.1"3" SARA0NIKHEF" 4.7"4" FZK" 4.7"5" AGLT2" 4.6"6" RAL" 4.5"7" MWT2" 3.8"8" TOKYO" 3.8"9" INFN0T1" 3.5"10" NORDUGRID" 3.3"

10"

"

52"

分散型コンピューティング

東大処理されたジョブの数

ATLAS検出器への貢献

7

20%

ミューオン検出器用 ASIC: 100%エンドキャップトリガー (TGC) 検出器 : 30% 電子回路 : 100%

シリコンストリップ飛跡検出器ソレノイド電磁石

TDC ASIC20,000個

100%

搬入・設置・運転も

貢献度合いで研究の範囲が決まる

日本グループの活躍検出器‣ エンドキャップミューオントリガー‣ ピクセル・ストリップ検出器‣ コンピューティング

運営における責任あるポスト‣ Collaboration Board chair‣ Trigger Coordinator‣ Speaker Committee chair‣ 各種解析グループリーダー‣ 他多数

8

[GeV]T

p-110×4 1 2 3 4 5 6 7 8 910 20

m]

µ) [ 0

(dσ

0

50

100

150

200

250

300

350

400

ATLAS Preliminary < 0.2η0.0 <

= 8 TeVsData 2012,

= 13 TeVsData 2015,

ATLAS実験運用に日本グループが不可欠

Run1の成功～ヒッグスの発見～

9

引用回数5516 2016年2月12日朝

Run 1 H→ZZ(→μμμμ) 事象候補

10

日本グループが建設・運転しているSCTとTGCがμを捕捉

ヒッグス発見 ⇒ ノーベル賞

HL-LHC Motivation～ポスト・ヒッグスの素粒子物理学～

唯一のエネルギーフロンティア‣ ヒッグスファクトリー‣ 人類未踏の領域の探索

高エネルギーパートンは少ない⇒ 高輝度化で探索領域拡張

放射線損傷‣ ビーム収束磁石や飛跡検出器は2020年過ぎに交換๏ 高輝度化：3000fb-1を目指す

11

10-4 10-3 10-2 10-1 100

x

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6x

f (x,

Q2 )

g CJ12mid

Q2 = 100 GeV2

d_

+u_

d_−u

_

d

us

/10

0 0.2 0.4 0.6 0.8 1x

0

0.2

0.4

0.6

0.8

x f (

x,Q

2 )

g

CJ12mid

Q2 = 100 GeV2

d_

+u_

d_−u

_

du

s

FIG. 3: Uncertainty bands for the u, d, d + u, d − u, s and g PDFs for the CJ12mid fit at

Q2 = 100 GeV2, shown on logarithmic (left) and linear (right) scales in x. Note that in the left

panel the gluon is scaled by 1/10.

well constrained by proton DIS data. The χ2 for the W asymmetry data does show a

significant increase as the magnitude of the nuclear corrections increases beyond its middle

value, indicating a preference for mild to medium nuclear corrections.

In this regard it is interesting to compare our results to those of the recent analysis

in Ref. [83], which included nuclear corrections for deuterium targets in DIS using a 4-

parameter, Q2-independent phenomenological function with the parameters varied in the

fit. The resulting correction factor, shown in Fig. 11 of Ref. [83], can be compared to those

in Fig. 2 above. Their fitted form lies between the curves for the CJ12min and CJ12mid

fits, as might be expected since these two fits have nearly identical values for χ2, while the

CJ12max value is higher. As noted above, much of the increase in χ2 for the CJ12max set is

due to the CDF W asymmetry data, which is also included in the fit of Ref. [83]. Although

this comparison is not exact, since our nuclear corrections are Q2 dependent [84] and those

in Ref. [83] are not, it is consistent with our observation that the nuclear model choices

made for the CJ12min and CJ12mid sets are preferred by the data.

The CJ12mid PDFs are shown in Fig. 3 at Q2 = 100 GeV2 with the PDF error bands

calculated as described in Sec. II E, on both logarithmic and linear x scales. The latter more

graphically illustrates the behavior of the PDFs at large values of x, where the uncertainties

from nuclear and finite-Q2 corrections are greatest. The error bands are shown in more

detail in Fig. 4, and compared to the CJ12min and CJ12max sets. It is clear that the

effects of nuclear corrections are strongest on the d PDF, with the others showing little or

14

CERN Medium Term Plan (MTP)

毎年，６月にCERN理事会は翌年の予算案と向こう５年間の計画を提示

2014年は，HL-LHCを入れた10年間計画を発表‣ CERNがHL-LHCを承認した

2014年までは，Performance Improving Consolidation と HL-LHC の2つに別れていた予算‣ 一体化し，LHCからのアウトプットを最大化๏ European Strategy Report を反映

12

高エネルギー物理学将来計画検討小委員会答申

13

本小委員会は日本の高エネルギー物理学の基幹となる大規模将来計画に関して、以下の提言をする。•LHCにおいて1TeV位までにヒッグスなどの新粒子の存在が確認された場合、日本が主導して電子・陽電子リニアコライダーの早期実現を目指す。特に新粒子が軽い場合、低い衝突エネルギーでの実験を早急に実現すべきである。一方でLHCおよびそのアップグレードによって間断なく新物理の探究を続けていく。新粒子・新現象のエネルギースケールがもっと高い場合には、必要とされる衝突エネルギーを実現するための加速器開発研究を重点強化する。•大きなニュートリノ混合角θ13が確認された場合、.....

HL-LHC 日本グループスケジュール2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026

shutdown shutdownLHC

13-14 TeVL=1×1034

14 TeVL=2×1034300fb-1

HL-LHC14 TeVL=5×10343000fb-1前段

加速器

衝突点磁石

ATLAS測定器

建設

建設

建設

設置

設置

設置

開発

開発

Run2 Run3

磁性体コアKEK分担の決定

D1実機製造　　（横試験）D1試作機1号完成

2号完成

マンパワーstrip TDR

pixel TDR

pixelモジュール製造

strip sensor/hybrid製造strip module preproduction

pixel module preproduction

calendar year

Run4

入札・製造

入札

空洞組立

μエレキ製造

HL-LHC

KEKがビーム分離双極電磁石（D1）設計開発を担当

15

HL#LHC

Nominal,LHCNC,D1

IT,Quads. w/,Nb3Sn

IP(ATLAS,,CMS)

SC,D1

IT,Quads.&,D1Corrector,Package

Q1Q2aQ2b

Q3

分離電磁石口径定格磁場磁場長磁場エネルギー線材

LHC 52mm gap 1.4T 3.4m×6 0.014MJ/m 常伝導

HL-LHC 150mm 5.6T 6.27m 0.34MJ/m NbTi

HE-LHC (FCC)へ向けた磁石開発

16

NbTi &&Nb3Sn:&<&12&T NbTi &&Nb3Sn(Al)*&*HTS:&~20&T

0 50 100 150 200 250 300 350 400 450 500

0.0.20.40.60.81.1.21.41.61.82.2.22.42.62.83.3.23.43.63.8

|B| flux density (T)

ROXIE10.2

15/06/27 10:54The new D1, MSmod4, Ver3, Triangular notch, After optimization

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120

G10 (Epoxy, E glass) -VG10 (Epoxy, E glass) -HBT (BT2160&2170, S2 glass) -VBT (BT2160&2170, S2 glass) -H

Flex

ural

Str

engt

h (M

Pa)

Dose (MGy)

V H

"

,+%$ 2 <&10^14

.#! -

FEM&/CAD/CAM

Nb3Al/Nb3Sn.*

HTS,1-

FCC0.('

HTS.+ 1)

ATLAS検出器アップグレード

17

内部飛跡検出器総取り替え（all Si）

ミューオントリガー用エレキ交換

ミューオン検出器追加

これら全てに日本グループは貢献

チャレンジ

18

σ興味ある物理 ≤10-12b vs σtotal ~10-1b 陽子≠パートン ⇒ 興味あるパートン衝突以外のゴミバンチ交差あたりの衝突数（≡pileup）= 断面積[cm2] × ルミノシティ[cm-2s-1] × バンチ間隔[s]　>> 1

pileup 78 @ CMS

チャレンジ

18

σ興味ある物理 ≤10-12b vs σtotal ~10-1b 陽子≠パートン ⇒ 興味あるパートン衝突以外のゴミバンチ交差あたりの衝突数（≡pileup）= 断面積[cm2] × ルミノシティ[cm-2s-1] × バンチ間隔[s]　>> 1

pileup 78 @ CMS微細化高速化

放射線耐性強化

検出器アップグレードに対する日本の寄与現行検出器建設と同等以上の貢献が期待されている

内部飛跡検出器‣ ピクセル/ストリップ・センサー‣ モジュール（センサー＋ASIC）

エンドキャップミューオントリガー‣ 電子基板の開発製造‣ 追加された検出器を使う新たなロジック

19

0

100

200

2007 2009 2012 2014 2016

修士含む修士含まず

ATLAS日本

メンバー数

（若手）研究者の増加

アップグレード予算建設経費‣ HL-LHC　～10億CHF

‣ ATLAS　～2.7億CHF（人件費，開発費含まず）日本の貢献希望（開発費と臨時雇用費を含む）‣ 加速器（磁石，入射器） 58億円，ATLAS 46億円←運転経費含まず

20

2016 2017 2018 2019 2020 2021 2022 2023 2024 2025億CHF 0.7 0.9 0.9 1.0 1.2 1.5 1.3 1.2 0.7 0.4

(百万円) 2018 2019 2020 2021 2022 2023 2024 2025加速器 942 1,689 1399 940 550 272 28 0検出器 534 855 800 679 683 597 316 128合計 1,476 2,544 2,199 1,619 1,233 869 344 128

運転経費 LHC運転経費‣ CERN加盟国による負担＝日本は負担なし‣ 日本がもし払うと...๏ 年間220億円程度のCERN運営分担金 40億から170億円がLHC関連の運転経費

ATLAS運転経費‣ 実験に参加する各国で負担๏ 日本は毎年～2億円程度共通インフラなどに1億円，検出器に1億円

21

~100億円/年程度のディスカウント

期待される物理

グルイーノ・スクォーク

23

(Naturalnessを一瞬忘れれば) まだまだ広い未探索領域

24

Well-tempered

2468

1012141618202224

0 2 4 6 8 10 12 14

A0 0 and 0

mqTeV

mg TeV

0 2 4 6 8 10 12 14

24681012141618202224

A0 0 and 0

mg TeV

mq TeV

0 2 4 6 8 10 12 142468

1012141618202224

mg TeV

mqTeV

A0 0 and 0

0 2 4 6 8 10 12 1424681012141618202224

mg TeV

A0 0 and 0

mq TeV

FIG. 4.2.2: The squark mass versus gluino mass plane for points in the well-tempered region. Each

plot only includes points from the corresponding quadrant. Also plotted are contours corresponding

to 10 squark and/or gluino events for 30 fb1 integrated luminosity ats = 8 TeV [solid], 300 fb1

integrated luminosity ats = 13 TeV [dashed], and 3000 fb1 integrated luminosity at

s =

33 TeV [dotted].

squark masses tend to be larger than the gluino mass because larger values ofM0 are required

in order to achieve a Higgs boson mass of 125 GeV. The squarks in these models will lie

outside the range of the 13 TeV LHC. Only a small range of these models will be testable

at colliders through the direct production of gluinos.

√s=8TeV, 30fb-1

√s=13TeV, 300fb-1

√s=33TeV, 3ab-1

CMSSMでMHとΩh2を説明できるポイント

arXiv:1305.2914

[GeV]g~

m500 1000 1500 2000 2500 3000

[G

eV

]10 χ∼

m

0

500

1000

1500

2000

2500

Decay

forb

idden

= 10%bkg

σ

1

0χ∼ qq → g~ production, g~-g~

= 14 TeVs, -1

L dt = 300, 3000 fb∫0-lepton combined

= 8 TeV, 95% CLs, -1

ATLAS 20.3 fb

= 140⟩µ⟨, -1

95% CL limit, 3000 fb

= 60⟩µ⟨, -1


= 140⟩µ⟨, -1

disc., 3000 fbσ5

= 60⟩µ⟨, -1

disc., 300 fbσ5

ATLAS Simulation Preliminary

(a) gg

[GeV]q~

m500 1000 1500 2000 2500 3000 3500 4000

[G

eV

]10 χ∼

m

0

500

1000

1500

2000

2500

Dec

ay fo

rbidde

n

= 10%bkg

σ

q~ >> m

g~ (Herwig++), m

1

0χ∼ q → q~ production, q~-q~

= 14 TeVs, -1


= 8 TeV, 95% CLs, -1

ATLAS 20.3 fb

= 140⟩µ⟨, -1


= 60⟩µ⟨, -1


= 140⟩µ⟨, -1

disc., 3000 fbσ5

= 60⟩µ⟨, -1

disc., 300 fbσ5


(b) qq, decoupled g

[GeV]q~

m500 1000 1500 2000 2500 3000 3500 4000

[G

eV

]10 χ∼

m

0

500

1000

1500

2000

2500

Dec

ay fo

rbidde

n

= 10%bkg

σ

= 4.5 TeVg~

(Herwig++), m1


= 14 TeVs, -1


= 8 TeV, 95% CLs, -1

ATLAS 20.3 fb

= 140⟩µ⟨, -1


= 60⟩µ⟨, -1


= 140⟩µ⟨, -1

disc., 3000 fbσ5

= 60⟩µ⟨, -1

disc., 300 fbσ5


(c) qq, mg = 4.5 TeV

Figure 9: Expected 95% CL exclusion contours (dashed) and 5 discovery contours (solid) for Lint =

300fb1 (black) and 3000fb1 (red) for gluino and squark pair-production. For squark pair-production,the gluino mass is either (b) decoupled or (c) set to 4.5 TeV. The bands reflect the 1 uncertainty on theproduction cross-section. The stepping along the diagonal in the top left figure is a non-physical eectcaused by the granularity of the grid.

18

squark decoupled

[GeV]g~

m500 1000 1500 2000 2500 3000

[G

eV

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forb

idden

= 10%bkg

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= 140⟩µ⟨, -1


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= 140⟩µ⟨, -1


= 60⟩µ⟨, -1


= 140⟩µ⟨, -1

disc., 3000 fbσ5

= 60⟩µ⟨, -1

disc., 300 fbσ5


(c) qq, mg = 4.5 TeV

Figure 9: Expected 95% CL exclusion contours (dashed) and 5 discovery contours (solid) for Lint =

300fb1 (black) and 3000fb1 (red) for gluino and squark pair-production. For squark pair-production,the gluino mass is either (b) decoupled or (c) set to 4.5 TeV. The bands reflect the 1 uncertainty on theproduction cross-section. The stepping along the diagonal in the top left figure is a non-physical eectcaused by the granularity of the grid.

18

mgluino=4.5TeV

ヒッグスファクトリー　　　　　　　　　　～世代の謎へ迫る～

24Particle mass [GeV]

-110 1 10 210

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Vκ

or

vFm F

κ

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ATLAS Preliminary-1 = 7 TeV, 4.5-4.7 fbs

-1 = 8 TeV, 20.3 fbs

ObservedSM Expected

素粒子で唯一のスカラー(？) フェルミオン質量‣ ゲージ対称性と無関係‣ 湯川結合（第５の力）の導入..

やっぱり怪しい...

[GeV]im

-110 1 10 210

γκF,

iy

OR

γκV,

iy

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-110

1g

W

Z

µ

τ

t

b


-1Ldt=300 fb∫-1Ldt=3000 fb∫

= 14 TeVs

第２世代

真空の安定性とトップクォーク質量

25

安定な宇宙

不安定な宇宙

102 104 106 108 1010 1012 1014 1016 1018 10200.06

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gsqu

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Figure 1: RG evolution of the Higgs self coupling, for dierent Higgs masses for the central value of mt

and s, as well as for ±2 variations of mt (dashed lines) and s (dotted lines). For negative values

of , the life-time of the SM vacuum due to quantum tunneling at zero temperature is longer than the

age of the Universe as long as remains above the region shaded in red, which takes into account the

finite corrections to the eective bounce action renormalised at the same scale as (see [11] for more

details).

2 Stability and metastability bounds

We first present the analysis on the Higgs instability region at zero temperature. We are

concerned with large field field values and therefore it is adequate to neglect the Higgs mass

term and to approximate the potential of the real field h contained in the Higgs doublet H =

(0, v + h/2) as

V = (|H|2 v2)2

4h4 . (1)

Here v = 174 GeV and the physical Higgs mass is mh = 2v at tree level. Our study here

follows previous state-of-the-art analyses (see in particular [9, 11, 12]). We assume negligible

corrections to the Higgs eective potential from physics beyond the SM up to energy scales of

the order of the Planck mass. We include two-loop renormalization-group (RG) equations for all

the SM couplings, and all the known finite one and two-loop corrections in the relations between

3

エネルギースケールμ[GeV]

arXiv:1112.3022ヒッグスポテンシャル

トップクォークの質量が真空の安定性に大きな寄与‣ Pole mass を知りたい

ハドロンコライダーでのトップ質量測定

”直接”測定：MCへのインプット質量との整合性‣ Pole massへの変換手法不明←パートンシャワーの評価方法未確立

高統計なら：mblのendpointなどから測定可能

26

6 Top quark working group report

Ref.[14] Projections

CM Energy 7 TeV 14 TeV

Luminosity 5fb1 100fb1 300fb1 3000fb1

Syst. (GeV) 1.8 1.0 0.7 0.5

Stat. (GeV) 0.90 0.10 0.05 0.02

Total 2.0 1.0 0.7 0.5

Table 1-2. Projections for the uncertainty in mt determined using the CMS end-point method [14].Extrapolations are based on the published CMS analysis.

should, ideally, be immune to contamination from beyond the Standard Model physics – a scenario that isconceivable if there is top-like BSM physics at the energy scale close to 2mt. For example, if mt is determinedfrom the total cross-section pptt and if the measurement of pp tt receives unknown contributions fromtop-like BSM physics, the extracted value of the top quark mass will be smaller than the true mt. Thisscenario can occur for example in SUSY models with light stop squarks mt mt that are still not excludedexperimentally (cf. discussion in Section 1.6.1.2).

Methods for top quark mass determination that are based on the analysis of kinematic distributions of topquark decay products are as close to an ideal method as possible. The main reason is that, up to small eectsrelated to selection cuts and combinatorial backgrounds, the kinematic variables involved in the analysis canoften be chosen to be Lorentz invariant in which case they decouple the production stage from the decaystage. This minimizes impact of any physics, BSM or SM, related to tt production on the top quark massmeasurement. Some of these methods are also insensitive to the physics of top quark decay and are entirelydriven by energy-momentum conservation. We will describe two of the methods that belong to this category– the “end-point” method developed recently by the CMS collaboration [14] and the “J/ method suggestedlong ago in Ref. [15].

The idea of the end-point method is based on the observation that the invariant mass distribution of a leptonand a b-jet contains a relatively sharp edge whose position is correlated with mt. Therefore, by measuringthe position of this end-point, one can determine the top quark mass. The number of events close to the end-point is fitted to a linear combination of a flat background and a linear function Nlb Nbck + S(mlb m0),where m0 gives the position of the end-point. The attractive feature of this method is that it is (almost)independent of any assumption about the matrix element and that it clearly measures either the pole massor some “kinematic” mass which is close to it. At the small expense of being more model-dependent,one can actually improve on this method by utilizing not only the position of the end-point but also theshape of the mlb distribution. Note that away from the kinematic end-point the shape of mlb distributionis accurately predicted through NLO QCD including o-resonance contributions and signal-backgroundinterferences [16, 17]. Close to the end-point re-summed predictions are probably required and are notavailable at present.

Nevertheless, even without potential improvements, the end-point method oers an interesting alternativeto conventional methods. Uncertainties in mt that one may hope to achieve are estimated in Table 1-2.We note that by using the end-point method we do gain in precision by going to high-luminosity LHC.Our projections show that the error as small as 0.5 GeV can be reached. The dominant contributions tosystematic uncertainty for each of these studies are the jet-energy scale and hadronization uncertainties.Similar to estimates of mt that can be achieved using conventional methods, we add 300 MeV to thesystematic uncertainty in Table 1-2, to account for unforeseen sources of the systematics.


高統計のご利益

エネルギーフロンティア !!

LHCによる重い粒子生成能力の高さ何らかの新発見への期待

27

[GeV]γγm200 400 600 800 1000 1200 1400 1600

Even

ts /

40 G

eV

1−10

1

10

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310

410ATLAS Preliminary

-1 = 13 TeV, 3.2 fbs

Data

Background-only fit

[GeV]γγm200 400 600 800 1000 1200 1400 1600

Dat

a - f

itted

bac

kgro

und

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[TeV]jjReconstructed m2 3 4 5 6 7

Even

ts

1

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510

|y*| < 0.6Fit Range: 1.1 - 7.1 TeV

-value = 0.67pQBH (BM)

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data

- fit

Sign

ifica

nce

2−

02

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a-M

C

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0

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ATLAS-1=13 TeV, 3.6 fbs

DataBackground fitBumpHunter interval

= 4.0 TeV*q*, mq

= 6.5 TeVth

QBH (BM), m

mjj[TeV]

結論

ILCまでは，LHCが唯一のエネルギーフロンティア‣ 圧倒的な発見能力‣ ヒッグスファクトリーなど精密測定

日本の得意分野での貢献がHL-LHCの成功に不可欠‣ 貢献のタイミングは重要

日本の高エネルギー物理の中で最大級のグループが精力的な活動‣ 若手研究者の急増加

28

今やるべきプロジェクト

backup

精密測定で見えてくるもの

30

施設元々の目的発見

CERN PS (1960) πN散乱 Neutral current

Brookhaven AGS (1960) πN散乱ニュートリノ2種類

チャーム

FNAL (1970) ニュートリノ物理ボトム，トップ

SLAC Spear (1970) ep, QED パートン，チャーム

PETRA (1980) トップグルーオン

Super Kamiokande (2000) 陽子崩壊ニュートリノ質量

Hubble Space Telescope Galactic survey 宇宙の曲率

ダークエネルギー

ヒッグスファクトリー

31

1.2 Coupling Measurements 15

Table 1-14 summarizes the expected precision on the Higgs couplings for the two aforementioned assumptionsof systematic uncertainties from the fit to a generic 7-parameter model. These 7 parameters are , g, W ,Z , u, d and . In this parameter set, and g parametrize potential new physics in the loops ofthe H and Hgg couplings. u t = c, d b = s and = µ parametrize deviations toup-and down-type quarks and charged leptons respectively assuming fermion family universality. Only SMproduction modes and decays are considered in the fit. The derived precisions on the Higgs total width arealso included. The expected precision ranges from 5 15% for 300 fb1 and 2 10% for 3000 fb1. Theyare limited by systematic uncertainties, particularly theoretical uncertainties on production and decay rates.Statistical uncertainties are below one percent in most cases. Note that the sensitivity to u is derived fromthe ttH production process and only H and H bb decays have been included in the projection.

The fit is extended to allow for BSM decays while restricting the Higgs coupling to vector bosons not toexceed their SM values (W ,Z 1). The resulting upper limit on the branching ratio of BSM decay isincluded in the table. Note that the BRBSM limit is derived from the visible decays of Table 1-13 and isindependent of the limit on BRinv from the search of ZH with H invisible.

Also listed in the Table 1-14 are the expected precisions on Z and µ, coupling scale factors for H Zand H µµ decay vertices. Given the small branching ratios of the two decays in the SM, they havenegligible impact on the 7-parameter fit. With the noted dierences above, ATLAS estimates are similar.

Table 1-14. Expected per-experiment precision of Higgs boson couplings to fermions and vector bosonswith 300 fb1 and 3000 fb1 integrated luminosity at the LHC. The 7-parameter fit assumes the SMproductions and decays as well as the generation universality of the couplings (u t = c, d b = s

and = µ). The precision on the total width H is derived from the precisions on the couplings.The range represents spread from two assumptions of systematic uncertainties, see text.

Luminosity 300 fb1 3000 fb1

Coupling parameter 7-parameter fit

5 7% 2 5%

g 6 8% 3 5%

W 4 6% 2 5%

Z 4 6% 2 4%

u 14 15% 7 10%

d 10 13% 4 7%

6 8% 2 5%

H 12 15% 5 8%

additional parameters (see text)

Z 41 41% 10 12%

µ 23 23% 8 8%

BRBSM < 14 18% < 7 11%

Apart from contributions from ATLAS and CMS collaborations, several independent studies [58–60] havebeen performed. In Ref. [58], authors investigate top-quark Yukawa coupling through the ttH productionand H WW decay. It is estimated that the t can be measured with a precision of 14 16% and 6 9%


1.2 Coupling Measurements 15

Table 1-14 summarizes the expected precision on the Higgs couplings for the two aforementioned assumptionsof systematic uncertainties from the fit to a generic 7-parameter model. These 7 parameters are , g, W ,Z , u, d and . In this parameter set, and g parametrize potential new physics in the loops ofthe H and Hgg couplings. u t = c, d b = s and = µ parametrize deviations toup-and down-type quarks and charged leptons respectively assuming fermion family universality. Only SMproduction modes and decays are considered in the fit. The derived precisions on the Higgs total width arealso included. The expected precision ranges from 5 15% for 300 fb1 and 2 10% for 3000 fb1. Theyare limited by systematic uncertainties, particularly theoretical uncertainties on production and decay rates.Statistical uncertainties are below one percent in most cases. Note that the sensitivity to u is derived fromthe ttH production process and only H and H bb decays have been included in the projection.

The fit is extended to allow for BSM decays while restricting the Higgs coupling to vector bosons not toexceed their SM values (W ,Z 1). The resulting upper limit on the branching ratio of BSM decay isincluded in the table. Note that the BRBSM limit is derived from the visible decays of Table 1-13 and isindependent of the limit on BRinv from the search of ZH with H invisible.

Also listed in the Table 1-14 are the expected precisions on Z and µ, coupling scale factors for H Zand H µµ decay vertices. Given the small branching ratios of the two decays in the SM, they havenegligible impact on the 7-parameter fit. With the noted dierences above, ATLAS estimates are similar.

Table 1-14. Expected per-experiment precision of Higgs boson couplings to fermions and vector bosonswith 300 fb1 and 3000 fb1 integrated luminosity at the LHC. The 7-parameter fit assumes the SMproductions and decays as well as the generation universality of the couplings (u t = c, d b = s

and = µ). The precision on the total width H is derived from the precisions on the couplings.The range represents spread from two assumptions of systematic uncertainties, see text.

Luminosity 300 fb1 3000 fb1

Coupling parameter 7-parameter fit

5 7% 2 5%

g 6 8% 3 5%

W 4 6% 2 5%

Z 4 6% 2 4%

u 14 15% 7 10%

d 10 13% 4 7%

6 8% 2 5%

H 12 15% 5 8%

additional parameters (see text)

Z 41 41% 10 12%

µ 23 23% 8 8%

BRBSM < 14 18% < 7 11%

Apart from contributions from ATLAS and CMS collaborations, several independent studies [58–60] havebeen performed. In Ref. [58], authors investigate top-quark Yukawa coupling through the ttH productionand H WW decay. It is estimated that the t can be measured with a precision of 14 16% and 6 9%


SM particle

以外の寄与なし

ヒッグス自己結合定数

32

2

(a)

g

g

h

h

g

t, b

t, b

t, b

(b)

g

g

h

h

t, b

t, b

t, b

t, b

(c)

g

g

h

hht, b

t, b

t, b

FIG. 1: Sample Feynman graphs contributing to pp → hh+X. Graphs of type (a) yield vanishing contributions due to colorconservation.

cal configuration†, which is characterized by a large di-higgs invariant mass, but with a potentially smaller Higgss-channel suppression than encountered in the back-to-back configuration of gg → hh.The goal of this paper is to provide a comparative

study of the prospects of the measurement of the trilinearHiggs coupling applying contemporary simulation andanalysis techniques. In the light of recent LHC measure-ments, we focus our eventual analyses on mh = 125 GeV.However, we also put this particular mass into the con-text of a complete discussion of the sensitivity towardsthe trilinear Higgs coupling over the entire Higgs massrange mh

<∼ 1 TeV. As we will see, mh ≃ 125 GeV is arather special case. Since Higgs self-coupling measure-ments involve end-of-lifetime luminosities we base ouranalyses on a center-of-mass energy of 14 TeV.We begin with a discussion of some general aspects

of double Higgs production, before we review inclusivesearches for mh = 125 GeV in the pp → hh+X channelin Sec. II C. We discuss boosted Higgs final states in pp →hh+X in Sec. II D before we discuss pp → hh+j+X withthe Higgses recoiling against a hard jet in Sec. III. Doingso we investigate the potential sensitivity at the parton-and signal-level to define an analysis strategy before weapply it to the fully showered and hadronized final state.We give our conclusions in Sec. IV.

II. HIGGS PAIR PRODUCTION AT THE LHC

A. General Remarks

Inclusive Higgs pair production has already been stud-ied in Refs. [14–17] so we limit ourselves to the detailsthat are relevant for our analysis.Higgs pairs are produced at hadron colliders such as

the LHC via a range of partonic subprocesses, the mostdominant of which are depicted in Fig. 1. An approxima-tion which is often employed in phenomenological studiesis the heavy top quark limit, which gives rise to effective

†The phenomenology of such configurations can also be treated sep-arately from radiative correction contributions to pp → hh+X.

ggh and gghh interactions [20]

Leff =1

4

αs

3πGa

µνGaµν log(1 + h/v) , (2)

which upon expansion leads to

L ⊃ +1

4

αs

3πvGa

µνGaµνh−

1

4

αs

6πv2Ga

µνGaµνh2 . (3)

Studying these operators in the hh+X final state shouldin principle allow the Higgs self-coupling to be con-strained via the relative contribution of trilinear andquartic interactions to the integrated cross section. Notethat the operators in Eq. (3) have different signs whichindicates important interference between the (nested)three- and four point contributions to pp → hh + X al-ready at the effective theory level.On the other hand, it is known that the effective theory

of Eq. (3) insufficiently reproduces all kinematical prop-erties of the full theory if the interactions are probedat momentum transfers Q2 >∼ m2

t [11] and the massivequark loops are resolved. Since our analysis partly re-lies on boosted final states, we need to take into accountthe full one-loop contribution to dihiggs production torealistically model the phenomenology.

B. Parton-level considerations

In order to properly take into account the full dynam-ics of Higgs pair production in the SM we have imple-mented the matrix element that follows from Fig. 1 inthe Vbfnlo framework [21] with the help of the Fey-

nArts/FormCalc/LoopTools packages [22], withmodifications such to include a non-SM trilinear Higgscoupling‡. Our setup allows us to obtain event files ac-cording to the Les Houches standard [23], which can bestraightforwardly interfaced to parton showers. Decaycorrelations are trivially incorporated due to the spin-0nature of the SM Higgs boson.

‡The signal Monte Carlo code underlying this study is planned tobecome part of the next update of Vbfnlo and is available uponrequest until then.

[GeV]γγm

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25 ATLAS Simulation Preliminary-1=14 TeV, 3000 fbs

)γγ)H(bH(b

Othersγγbb

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ecte

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Exp. 95% CLsσ1 ±σ2 ±

-1 = 14 TeV: 3000 fbsATLAS Simulation Preliminary

ゲージーノ

33

The final states can contain three leptons/taus and missing transverse momentum as shown in Figure 2.It should be noted that the WZ-mediated scenario with 100% branching fraction is not realistic for largem0

2m0

1> mh, however, the limits would fall somewhere between those achieved for the WZ-mediated

and Wh-mediated scenarios for the same production cross-section.

(a) WZ-mediated

±1

02

W

hp

p

01

`

01

...

`

`

(b) Wh-mediated (h)

±1

02

W

hp

p

01

`

01

(c) Wh-mediated (h)

Figure 2: The diagrams for the two 02±1 simplified models studied in this note. The ±1 is assumed to

decay as ±1 W±()01 and the 0

2 either as 02 Z() 0

1 or 02 h() 0

1 with 100% branching ratio.Two final states are studied for the Wh-mediated scenario: 3 and 12. The dots in (b) depict possibleadditional decay products of the lightest Higgs boson decaying via intermediate , WW or ZZ states.

Two final states are considered for the ±1 02 simplified models studied in this note,

Three leptons (3): where leptons () refers to electrons and muons including those from the -leptondecays but do not include hadronically-decaying -leptons. This final state targets both the WZ-mediated and Wh-mediated simplified models.

One lepton + two (12): where the one lepton () plus two hadronically decaying taus () signatureis used to target the Wh-mediated simplified model.

The background for a signal with 3 or 12 and large EmissT is dominated by the irreducible processes

WZ(), tribosons and tt + Z/W. The assumed systematic uncertainty of 30% on the estimated sum of allbackgrounds is expected to hold under the hypothesis that the theoretical uncertainty on the tribosonbackgrounds is at the level of that of the diboson backgrounds for 14 TeV. The reducible process tt isalso an important background, producing two prompt leptons from the W decays and a third when oneof the b-quarks in the event decays semileptonically and is mis-identified as a prompt, isolated lepton.In the 12 channel, the reducible processes tt, W+jets, Z+jets are important backgrounds where jets aremis-identified as taus.

3.1 WZ-mediated Signal Region Selection

Candidate leptons are selected with pT larger than 10 GeV and ||< 2.47 (2.4) for electrons (muons).Candidate jets are selected with the anti-kt algorithm with a radius parameter of R

()2 + ()2 =

0.4, with pT > 20 GeV and ||< 2.5. Jets are required to be separated from candidate electrons withR(e, jet) > 0.2. Jets are tagged as originating from b-decays, “b-tagged jets”, with the chosen workingpoint of the b-tagging algorithm correctly identifying b-quark jets in simulated tt samples with an averageeciency of 70%, with a light-flavour jet misidentification probability of about 1% (parametrised as afunction of jet pT and ).

Leptons forming low mass Same-Flavour Opposite-Sign (SFOS) lepton pairs (invariant mass mSFOS <12 GeV) are discarded to remove leptons from low-mass resonances. Leptons are required to be isolated

5

fied models can be seen in Figure 4. In the case of the WZ-mediated simplified models and the luminosityscenario of 300 fb1, the exclusion contour reaches 840 GeV in ±1 ,

02 mass, while for the high luminosity

scenario with 3000 fb1, the contour extends as far as 1.1 TeV in ±1 , 02 mass. The discovery contour for

300 fb1 reaches 560 GeV in ±1 , 02 mass, and 820 GeV for the high luminosity scenario with 3000 fb1.

[GeV]0

2χ∼

=m±

1χ∼

m

200 300 400 500 600 700 800 900 1000 1100 1200

[G

eV

]0 1χ∼

m

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700

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=140, 95% CL exclusionµ, -1

L dt = 3000 fb∫ discoveryσ=140, 5µ,

-1L dt = 3000 fb∫



-1L dt = 300 fb∫

, 95% CL exclusion-1

L dt = 20.3 fb∫8 TeV,

0

1χ∼ <

m0

2χ∼m

Z

= m

0

1χ∼ -

m0

2χ∼m

= 30%bkg

σ

= 14 TeVs


3-lepton channel

0

1χ∼ Z

0

1χ∼ ± W→ 0

2χ∼ ±

1χ∼

0

2χ∼

= m±

1χ∼m

Figure 4: The expected 95% exclusion and discovery contours for the 300 fb1 and 3000 fb1 luminosityscenarios in the m(0

1) vs m(±1 , 02) plane for the WZ-mediated simplified model. The 8 TeV exclusion

contour is also shown in orange [19].

3.3 3 Wh-mediated Signal Region Selection

Leptons are selected as in Section 3.1. Events are selected with exactly three leptons and events with aSame-Flavour Opposite-Sign (SFOS) lepton pair present among the three leptons are rejected to suppressthe WZ background. This SFOS veto mainly selects Wh-mediated ±1

02 signal events where the hWW.

Events with b-tagged jets are vetoed to suppress tt and tt + V backgrounds. The WZ and tt samples aregenerated with a Emiss

T > 50 GeV filter, and so a requirement of EmissT > 100 GeV is imposed after

smearing. A requirement is made on the invariant mass of the two OS leptons closest in R, mminROS , to

reject the tt and WWW backgrounds. Large mT formed from each of the three leptons, mT(1), mT(2)and mT(3), is required to reduce the contributions from the tt and triboson backgrounds. The thresholdson mminR

OS , mT(1), mT(2) and mT(3) are optimised for high ZN . Four signal regions are defined forthe Wh-mediated simplified model: two loose regions “E” and “F” optimised for small mass splittingscenarios, a tight region “G” optimised for large mass splitting scenarios, and a very tight region “H”optimised for large mass splittings in the 3000 fb1 scenario, and these are summarised in Table 3.


Leptons and jets are selected as in Section 3.1. Candidate taus are selected with pT larger than 20 GeVand ||< 2.47. All taus are requested to be separated from candidate jets (jets are discarded if R(, jet) <0.2) and leptons (taus are discarded if R(, ) < 0.2). Due to limited statistics in some MC samples, MCevents are used 10 times with dierent seeds used for the reconstruction parametrisation. The events arethen weighted by 1/10 to account for this eect.

8

contour reaches 650 GeV in ±1 , 02 mass for the 300 fb1 scenario, and 940 GeV in ±1 ,

02 mass for the

3000 fb1 scenario. The discovery contour for 3000 fb1 reaches 650 GeV in ±1 , 02 mass, however,

a discovery contour is not achieved for the 300 fb1 scenario. For the 8 TeV analysis, the exclusioncontour reaches 150 GeV in ±1 ,

02 mass and 17 GeV in 0

1 mass [20].In the case of the 12 channel, the exclusion contour reaches 550 GeV in ±1 ,

02 mass for the

3000 fb1 scenario. An exclusion contour for 300 fb1 is not achieved, neither are discovery contoursfor either luminosity scenario. A statistical fluctuation in the WW background sample used for the anal-ysis leads to a conservative estimate of the WW background of 3.5 events. Using an ABCD methodwith the Emiss

T and |pT (1)| + |pT (2)| variables, the WW estimate is reduced to 0.1 events and the limitsimprove by about 50 GeV in ±1 , 0

2 and 01 mass. Despite the weak sensitivity to Wh-mediated scenarios

with h final states, the 12 channel gives excellent complementarity to 3 final states.

[GeV]0

2χ∼

=m±

1χ∼

m

200 300 400 500 600 700 800 900 1000 1100

[G

eV

]0 1χ∼

m

0

100

200

300

400

500

600

700

800



-1L dt = 3000 fb∫


L dt = 300 fb∫

0

1χ∼

< m

0

2χ∼m

h

= m

0

1χ∼ -

m0

2χ∼m

= 30%bkg

σ

= 14 TeVs


3-lepton channel

0

1χ∼ h

0

1χ∼ ± W→ 0

2χ∼ ±

1χ∼

0

2χ∼

= m±

1χ∼m

(a) 3 channel

[GeV]1±χ ~ = m

20χ ~m

200 300 400 500 600 700 800 900 1000

[GeV

]10 χ ~

m

0

100

200

300

400

500ATLAS Simulation Preliminary

=14 TeVs

10χ ~h

10χ ~± W→

1±χ ~

20χ ~

1±χ ~ = m

20χ ~m

-τ+τ →; h µ e, →W

=30%bgkσ

h

= m

01χ∼

- m

02χ∼m

=140, 95% CL exclusionµ, -1 L dt = 3000 fb∫

(b) 12 channel

Figure 5: The expected 95% exclusion contours for the 300 fb1 and 3000 fb1 luminosity scenarios inthe m(0

1) vs m(±1 , 02) plane for the Wh-mediated simplified model. The sensitivity using the 3 channel

is shown on the left, and the 12 channel on the right.

4 Strongly produced supersymmetry

Strongly produced SUSY particles are expected to have the highest production cross-section of all SUSYprocesses, provided they are light enough to be produced at the LHC. In this study, simplified modelsof gluino and squark pair production are considered. The gluino decays directly into two quarks and theLSP (0

1) with 100% branching ratio, as shown in Figure 6. The squark decays into a quark and the LSP(0

1) with 100% branching ratio. In both cases signal events are characterised by many jets, large EmissT

and no leptons.

4.1 Background processes

The SM background for a signal with many jets and large EmissT is dominated by Z+jets, W+jets, tt and

diboson production. Based on 8 TeV published results [22], the diboson background is set to 10% of thetotal of the other SM backgrounds, multijet production is assumed to be suppressed to negligible levelsby dedicated signal region requirements, and the uncertainty on the total SM background is assumed tobe 10%.

11

ゲージーノ

33

The final states can contain three leptons/taus and missing transverse momentum as shown in Figure 2.It should be noted that the WZ-mediated scenario with 100% branching fraction is not realistic for largem0

2m0

1> mh, however, the limits would fall somewhere between those achieved for the WZ-mediated

and Wh-mediated scenarios for the same production cross-section.

(a) WZ-mediated

±1

02

W

hp

p

01

`

01

...

`

`

(b) Wh-mediated (h)

±1

02

W

hp

p

01

`

01

(c) Wh-mediated (h)

Figure 2: The diagrams for the two 02±1 simplified models studied in this note. The ±1 is assumed to

decay as ±1 W±()01 and the 0

2 either as 02 Z() 0

1 or 02 h() 0

1 with 100% branching ratio.Two final states are studied for the Wh-mediated scenario: 3 and 12. The dots in (b) depict possibleadditional decay products of the lightest Higgs boson decaying via intermediate , WW or ZZ states.

Two final states are considered for the ±1 02 simplified models studied in this note,

Three leptons (3): where leptons () refers to electrons and muons including those from the -leptondecays but do not include hadronically-decaying -leptons. This final state targets both the WZ-mediated and Wh-mediated simplified models.

One lepton + two (12): where the one lepton () plus two hadronically decaying taus () signatureis used to target the Wh-mediated simplified model.

The background for a signal with 3 or 12 and large EmissT is dominated by the irreducible processes

WZ(), tribosons and tt + Z/W. The assumed systematic uncertainty of 30% on the estimated sum of allbackgrounds is expected to hold under the hypothesis that the theoretical uncertainty on the tribosonbackgrounds is at the level of that of the diboson backgrounds for 14 TeV. The reducible process tt isalso an important background, producing two prompt leptons from the W decays and a third when oneof the b-quarks in the event decays semileptonically and is mis-identified as a prompt, isolated lepton.In the 12 channel, the reducible processes tt, W+jets, Z+jets are important backgrounds where jets aremis-identified as taus.

3.1 WZ-mediated Signal Region Selection

Candidate leptons are selected with pT larger than 10 GeV and ||< 2.47 (2.4) for electrons (muons).Candidate jets are selected with the anti-kt algorithm with a radius parameter of R

()2 + ()2 =

0.4, with pT > 20 GeV and ||< 2.5. Jets are required to be separated from candidate electrons withR(e, jet) > 0.2. Jets are tagged as originating from b-decays, “b-tagged jets”, with the chosen workingpoint of the b-tagging algorithm correctly identifying b-quark jets in simulated tt samples with an averageeciency of 70%, with a light-flavour jet misidentification probability of about 1% (parametrised as afunction of jet pT and ).

Leptons forming low mass Same-Flavour Opposite-Sign (SFOS) lepton pairs (invariant mass mSFOS <12 GeV) are discarded to remove leptons from low-mass resonances. Leptons are required to be isolated

5

fied models can be seen in Figure 4. In the case of the WZ-mediated simplified models and the luminosityscenario of 300 fb1, the exclusion contour reaches 840 GeV in ±1 ,

02 mass, while for the high luminosity

scenario with 3000 fb1, the contour extends as far as 1.1 TeV in ±1 , 02 mass. The discovery contour for

300 fb1 reaches 560 GeV in ±1 , 02 mass, and 820 GeV for the high luminosity scenario with 3000 fb1.

[GeV]0

2χ∼

=m±

1χ∼

m

200 300 400 500 600 700 800 900 1000 1100 1200

[G

eV

]0 1χ∼

m

0

100

200

300

400

500

600

700

800

900

1000



-1L dt = 3000 fb∫



-1L dt = 300 fb∫

, 95% CL exclusion-1

L dt = 20.3 fb∫8 TeV,

0

1χ∼ <

m0

2χ∼m

Z

= m

0

1χ∼ -

m0

2χ∼m

= 30%bkg

σ

= 14 TeVs


3-lepton channel

0

1χ∼ Z

0

1χ∼ ± W→ 0

2χ∼ ±

1χ∼

0

2χ∼

= m±

1χ∼m

Figure 4: The expected 95% exclusion and discovery contours for the 300 fb1 and 3000 fb1 luminosityscenarios in the m(0

1) vs m(±1 , 02) plane for the WZ-mediated simplified model. The 8 TeV exclusion

contour is also shown in orange [19].


Leptons are selected as in Section 3.1. Events are selected with exactly three leptons and events with aSame-Flavour Opposite-Sign (SFOS) lepton pair present among the three leptons are rejected to suppressthe WZ background. This SFOS veto mainly selects Wh-mediated ±1

02 signal events where the hWW.

Events with b-tagged jets are vetoed to suppress tt and tt + V backgrounds. The WZ and tt samples aregenerated with a Emiss

T > 50 GeV filter, and so a requirement of EmissT > 100 GeV is imposed after

smearing. A requirement is made on the invariant mass of the two OS leptons closest in R, mminROS , to

reject the tt and WWW backgrounds. Large mT formed from each of the three leptons, mT(1), mT(2)and mT(3), is required to reduce the contributions from the tt and triboson backgrounds. The thresholdson mminR

OS , mT(1), mT(2) and mT(3) are optimised for high ZN . Four signal regions are defined forthe Wh-mediated simplified model: two loose regions “E” and “F” optimised for small mass splittingscenarios, a tight region “G” optimised for large mass splitting scenarios, and a very tight region “H”optimised for large mass splittings in the 3000 fb1 scenario, and these are summarised in Table 3.


Leptons and jets are selected as in Section 3.1. Candidate taus are selected with pT larger than 20 GeVand ||< 2.47. All taus are requested to be separated from candidate jets (jets are discarded if R(, jet) <0.2) and leptons (taus are discarded if R(, ) < 0.2). Due to limited statistics in some MC samples, MCevents are used 10 times with dierent seeds used for the reconstruction parametrisation. The events arethen weighted by 1/10 to account for this eect.

8

contour reaches 650 GeV in ±1 , 02 mass for the 300 fb1 scenario, and 940 GeV in ±1 ,

02 mass for the

3000 fb1 scenario. The discovery contour for 3000 fb1 reaches 650 GeV in ±1 , 02 mass, however,

a discovery contour is not achieved for the 300 fb1 scenario. For the 8 TeV analysis, the exclusioncontour reaches 150 GeV in ±1 ,

02 mass and 17 GeV in 0

1 mass [20].In the case of the 12 channel, the exclusion contour reaches 550 GeV in ±1 ,

02 mass for the

3000 fb1 scenario. An exclusion contour for 300 fb1 is not achieved, neither are discovery contoursfor either luminosity scenario. A statistical fluctuation in the WW background sample used for the anal-ysis leads to a conservative estimate of the WW background of 3.5 events. Using an ABCD methodwith the Emiss

T and |pT (1)| + |pT (2)| variables, the WW estimate is reduced to 0.1 events and the limitsimprove by about 50 GeV in ±1 , 0

2 and 01 mass. Despite the weak sensitivity to Wh-mediated scenarios

with h final states, the 12 channel gives excellent complementarity to 3 final states.

[GeV]0

2χ∼

=m±

1χ∼

m

200 300 400 500 600 700 800 900 1000 1100

[G

eV

]0 1χ∼

m

0

100

200

300

400

500

600

700

800



-1L dt = 3000 fb∫


L dt = 300 fb∫

0

1χ∼

< m

0

2χ∼m

h

= m

0

1χ∼ -

m0

2χ∼m

= 30%bkg

σ

= 14 TeVs


3-lepton channel

0

1χ∼ h

0

1χ∼ ± W→ 0

2χ∼ ±

1χ∼

0

2χ∼

= m±

1χ∼m

(a) 3 channel

[GeV]1±χ ~ = m

20χ ~m

200 300 400 500 600 700 800 900 1000

[GeV

]10 χ ~

m

0

100

200

300

400

500ATLAS Simulation Preliminary

=14 TeVs

10χ ~h

10χ ~± W→

1±χ ~

20χ ~

1±χ ~ = m

20χ ~m

-τ+τ →; h µ e, →W

=30%bgkσ

h

= m

01χ∼

- m

02χ∼m

=140, 95% CL exclusionµ, -1 L dt = 3000 fb∫

(b) 12 channel

Figure 5: The expected 95% exclusion contours for the 300 fb1 and 3000 fb1 luminosity scenarios inthe m(0

1) vs m(±1 , 02) plane for the Wh-mediated simplified model. The sensitivity using the 3 channel

is shown on the left, and the 12 channel on the right.

4 Strongly produced supersymmetry

Strongly produced SUSY particles are expected to have the highest production cross-section of all SUSYprocesses, provided they are light enough to be produced at the LHC. In this study, simplified modelsof gluino and squark pair production are considered. The gluino decays directly into two quarks and theLSP (0

1) with 100% branching ratio, as shown in Figure 6. The squark decays into a quark and the LSP(0

1) with 100% branching ratio. In both cases signal events are characterised by many jets, large EmissT

and no leptons.

4.1 Background processes

The SM background for a signal with many jets and large EmissT is dominated by Z+jets, W+jets, tt and

diboson production. Based on 8 TeV published results [22], the diboson background is set to 10% of thetotal of the other SM backgrounds, multijet production is assumed to be suppressed to negligible levelsby dedicated signal region requirements, and the uncertainty on the total SM background is assumed tobe 10%.

11

こういう領域までなるべく探索を拡げるのが重要，実験屋の腕の見せ所 ⇐ 例: low pT lepton (trigger)

Resonance Search

34

[TeV]ttm0 1 2 3 4 5 6

Even

ts /

400

GeV

1

10

210

310

410

510

610

710 tt

W+jets

kk4 TeV g

-1 L dt = 3000 fb∫ (Simulation)

PreliminaryATLAS

[GeV]KK

gm3000 4000 5000 6000 7000 8000 9000 10000

B [p

b]σ

-410

-310

-210

-110

1

10

210

310

410

510 = -0.20

s/g

KKqqg

gExpected limit

σ 1±Expected σ 2±Expected

(Simulation) PreliminaryATLAS

t t →KK

g = 14 TeVs

-1 L dt = 3000fb∫

Figure 15: Left: The reconstructed resonance mass spectrum for the gKK tt search in the lepton+jetschannel with 3000 fb1 for pp collisions at

s = 14 TeV. The highest-mass bin includes the overflow.

Right: The 95% CL limit on the cross section times branching ratio. Also shown is the theoreticalexpectation for the gKK cross section, for a ratio of the coupling to quarks to gs of -0.2, where gs =

4s.

[TeV]llm0.06 0.1 0.2 0.3 1 2 3 4 5 6 7

Even

ts /

Bin

-1101

10

210

310

410

510

610

710

810

910ll→*γZ/

5 TeV Z’


PreliminaryATLAS

[GeV]Z’m4000 6000 8000 10000

B [p

b]σ

-710

-610

-510

-410

-310

-210

-110

1

10Expected limit



ll→Z’

= 14 TeVs

-1 L dt = 3000fb∫

Figure 16: Left: The reconstructed dielectron mass spectrum for the Z search with 3000 fb1 of ppcollisions at

s = 14 TeV. The highest-mass bin includes the overflow. Right: The 95% CL upper limit

on the cross section times branching ratio. Also shown is the theoretical expectation for the ZS S M crosssection.

significantly enhanced [27]. Examples of BSM models with enhanced FCNC top decay ratesare quark-singlet (QS) models, two-Higgs doublet (2HDM) and flavor-conserving two-Higgsdoublet (FC 2HDM) models, the minimal supersymmetric model (MSSM), SUSY models withR-parity violation (/R), the topcolor assisted technicolor model (TC2) [28], and models withwarped extra dimensions (RC) [29]. FCNC decay are sought through t q and t qZchannels where q is either an up or a charm quark. Table 8 shows the Standard Model andBSM decay rates in the various channels. The best current direct search limits are 3.2% for t q [30] and 0.21% for t Zq [31]. A model-independent approach to top quark FCNC decaysusing an eective Lagrangian [32, 33, 34] is used here to evaluate the sensitivity of ATLAS inthe HL-LHC era. Even if the LHC does not measure the top quark FCNC branching ratios, itcan test some of these models or constrain their parameter space, and improve significantly thecurrent experimental limits on the FCNC branching ratios.

Top quark FCNC decays are sought in top quark pair production in which one top (or anti-

20

[TeV]ttm0 1 2 3 4 5 6

Even

ts /

400

GeV

1

10

210

310

410

510

610

710 tt

W+jets

kk4 TeV g


PreliminaryATLAS

[GeV]KK

gm3000 4000 5000 6000 7000 8000 9000 10000

B [p

b]σ

-410

-310

-210

-110

1

10

210

310

410

510 = -0.20

s/g

KKqqg

gExpected limit



t t →KK

g = 14 TeVs

-1 L dt = 3000fb∫

Figure 15: Left: The reconstructed resonance mass spectrum for the gKK tt search in the lepton+jetschannel with 3000 fb1 for pp collisions at

s = 14 TeV. The highest-mass bin includes the overflow.


4s.

[TeV]llm0.06 0.1 0.2 0.3 1 2 3 4 5 6 7

Even

ts /

Bin

-1101

10

210

310

410

510

610

710

810

910ll→*γZ/

5 TeV Z’


PreliminaryATLAS

[GeV]Z’m4000 6000 8000 10000

B [p

b]σ

-710

-610

-510

-410

-310

-210

-110

1

10Expected limit



ll→Z’

= 14 TeVs

-1 L dt = 3000fb∫

Figure 16: Left: The reconstructed dielectron mass spectrum for the Z search with 3000 fb1 of ppcollisions at

s = 14 TeV. The highest-mass bin includes the overflow. Right: The 95% CL upper limit

on the cross section times branching ratio. Also shown is the theoretical expectation for the ZS S M crosssection.

significantly enhanced [27]. Examples of BSM models with enhanced FCNC top decay ratesare quark-singlet (QS) models, two-Higgs doublet (2HDM) and flavor-conserving two-Higgsdoublet (FC 2HDM) models, the minimal supersymmetric model (MSSM), SUSY models withR-parity violation (/R), the topcolor assisted technicolor model (TC2) [28], and models withwarped extra dimensions (RC) [29]. FCNC decay are sought through t q and t qZchannels where q is either an up or a charm quark. Table 8 shows the Standard Model andBSM decay rates in the various channels. The best current direct search limits are 3.2% for t q [30] and 0.21% for t Zq [31]. A model-independent approach to top quark FCNC decaysusing an eective Lagrangian [32, 33, 34] is used here to evaluate the sensitivity of ATLAS inthe HL-LHC era. Even if the LHC does not measure the top quark FCNC branching ratios, itcan test some of these models or constrain their parameter space, and improve significantly thecurrent experimental limits on the FCNC branching ratios.

Top quark FCNC decays are sought in top quark pair production in which one top (or anti-

20

[GeV]TH0 500 1000 1500 2000 2500 3000 3500 4000

Even

ts /

200

GeV

1

10

210

310

410

510

610

710 tt

Z+jets

Diboson

kk4 TeV g


PreliminaryATLAS

[GeV]KK

gm3000 4000 5000 6000 7000 8000 9000 10000

B [p

b]σ

-410

-310

-210

-110

1

10

210

310

410

510 = -0.20

s/g

KKqqg

gExpected limit



t t →KK

g = 14 TeVs

-1 L dt = 3000fb∫

Figure 14: Left: The reconstructed resonance HT spectrum for the gKK tt search in the dileptonchannel with 3000 fb1 for pp collisions at

s = 14 TeV. The highest-HT bin includes the overflow.


4s.

to photon conversions which needs to be suppressed in the dielectron channel. The requiredrejection of this background is assumed to be achieved with the upgraded detector.

Templates of the m spectrum are constructed for the background plus varying amounts ofsignal at dierent resonance masses and cross sections. The Sequential Standard Model (SSM)ZS S M boson, which has the same fermionic couplings as the Standard Model Z boson, is usedas the signal template. The m distribution, for events above 200 GeV, and the resulting limitsas a function of ZS S M pole mass are shown in Figs. 16 and 17 for the ee and µµ channels,respectively.

The 95% CL expected limits in the absence of signal, using statistical errors only, are shownin Table 7. The increase of a factor of ten, from 300 to 3000 fb1 in integrated luminosity raisesthe sensitivity to high-mass dilepton resonances by up to 1.3 TeV.

model 300 fb1 1000 fb1 3000 fb1

ZS S M ee 6.5 7.2 7.8ZS S M µµ 6.4 7.1 7.6

Table 7: Summary of the expected limits for ZS S M ee and ZS S M µµ searches in the SequentialStandard Model for pp collisions at

s = 14 TeV. All limits are quoted in TeV.

8 Flavor-Changing-Neutral-Currents in Top-Quark Decays

Within the Standard Model, flavor-changing-neutral-current (FCNC) decays are forbidden attree level due to the GIM mechanism [22], and highly suppressed at loop level with branchingfractions below 1012 [23, 24, 25, 26], which are inaccessible even at HL-LHC. Therefore anyobservation of top quark FCNC decays would be a definite indication of new physics. FCNCdecays have been sensitively searched for in lighter quarks, placing strong constraints on manymodels of BSM physics. Tests of FCNC in the top sector have only recently become sensitiveenough to probe interesting BSM phase space in which the FCNC branching fraction can be

19

[GeV]q~m2000 2500 3000 3500 4000

[GeV

]g~

m

1500

2000

2500

3000

3500

4000

[pb]

σ

-610

-510

-410

-310

-210

[pb]σ Z axis

discovery reach-13000 fb

discovery reach-1300 fb

exclusion 95% CL-13000 fb

exclusion 95% CL-1300 fb

1/2>15GeVHT = 14 TeV MET/s = 0. LSP

Squark-gluino grid, m

Zn, sys=30%

ATLAS Preliminary (simulation)

Figure 13: Discovery reach and 95% CL limits in a simplified squark–gluino model with a masslessneutralino. The color scale shows the

s = 14 TeV NLO cross-section. The solid (dashed) lines show

the 5 discovery reach (95% CL exclusion limit) with 300 fb1 and with 3000 fb1, respectively.

The statistical analysis is performed by a likelihood fit of templates of these distributions, usingbackground plus varying amounts of signal, to the simulated data. The HT and mtt distribu-tions and the resulting limits as a function of the gKK pole mass for the dilepton and lepton+jetschannel are shown in Fig. 14 and Fig. 15, respectively.

The 95% CL expected limits in the absence of signal, using statistical errors only, are shownin Table 6. The increase of a factor of ten in integrated luminosity, from 300 to 3000 fb1 raisesthe sensitivity to high-mass tt resonances by up to 2.4 TeV.

model 300 fb1 1000 fb1 3000 fb1

gKK 4.3 (4.0) 5.6 (4.9) 6.7 (5.6)Ztopcolor 3.3 (1.8) 4.5 (2.6) 5.5 (3.2)

Table 6: Summary of the expected limits for gKK tt and Ztopcolor tt searches in the lepton+jets(dilepton) channel for pp collisions at

s = 14 TeV. All limits are quoted in TeV.

7.2 Searches for Dilepton Resonances

For studies of the sensitivity to a Z boson [21], the dielectron and dimuon channels are con-sidered separately since their momentum resolutions scale dierently with pT and the detectoracceptances are dierent. The background is dominated by the SM Drell-Yan production, whilett and diboson backgrounds are substantially smaller. Therefore, only the Drell-Yan backgroundis considered in this study. There is an additional background from non-prompt electrons due

18

Z’→ll 探索

t-tbar 共鳴

Documents

HL-LHC実験 - KEKresearch.kek.jp/people/nojiri/masterplan/Hanagaki.pdfATLAS日本グループ 5 名古屋大 京都大 京都教育大 大阪大 神戸大 岡山大 広島工大 九州大

HL-LHC実験 - KEKresearch.kek.jp/people/nojiri/masterplan/Hanagaki.pdfATLAS日本グループ 5 名古屋大京都大京都教育大大阪大神戸大岡山大広島工大九州大