Search for H->WW in semileptonic decay
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Transcript of Search for H->WW in semileptonic decay
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summer school2007@FNAL 1
Search for H->WW in semileptonic decay
Ai Mochizuki
University of Tsukuba
2007.07.31IntroductionHiggs Mass reconstructionSearch sensitivity at 2fb-1
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j
j
This channel has 3 times larger statistics than WW→lνlν decay mode
We can reconstruct Higgs mass
BUT 、、、 Huge QCD/W+2jet Background
So,
We try to optimize c-tag (Jet probability),
kinematics cuts for best sensitivity.
IntroductionWW→lνjj decay mode
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Higgs Mass ReconstructionEvaluated neutrino Pz to reconstruct Higgs mass. M(lepton+nu)=M(W=80.419GeV) 0 solution case using real part of this solution.
two solutions case
Which NuPz is better??We adopt the solution with |NuPz| closer to 0.(We considered 4 methods.)
j
j
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hepg levelNuPz HiggsMass NuPz-hepgNuPz
Adopted
solutionD
iscarded solution
・ all・ correct・ imagunary
MH=150
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detector level HiggsMass NuPz-hepgNuPz
jets matched to hard process p
artons
No matching to hepg
MH=150
・ all・ correct・ imagunary
RMS=50.0
RMS=27.620.6(MH=170)24.6(MH=200)
RMS=62.449.5(MH=170)54.4(MH=200)
RMS=60.9
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summer school2007@FNAL 6
Search sensitivity at 2fb-1C-tagging with Higgs Mass reconstruction
Why c-tagging??(1)Highly reject the huge W+LF background(2)Effective background rejection using spin information through angular correlation
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Event SelectionH->WW->lvcs
One lepton (Pt>20GeV, CEM/PEM/CMUP/CMX) electron |eta|<2, muon |eta|<1
Missing Et>20GeV Two jets with Et>20GeV (level 5), |eta|<2.4Cut 1 : C-taggingCut 2 : anti heavy flavor-taggingCut 3 : kinematic cut Rls⊿ We didn’t analyze lvud decay mode.
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background
WW/WZ/ZZW+c+jetsW+bbbarW+ccbarW+LF
purpose : crudely estimate the potential of this search channel.We only consider dominant background.
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Cut1 : Charm tagging
Aim to identify W->cs decay
Cut at jet probability=0.05Cut2 : anti HF tagging
cut
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Cut 3 : kinematic cut
Looking at angular distribution in Lab frame.
⊿Rls is angle between lepton and strange.
⊿Rls <2.2
s c
νl
⊿Rls
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Signal vs BackgroundHiggs Mass(150GeV)
Beforecut
C-tag
Anti HF ⊿R
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Expected number of events before cut
process # event 140<MH<200WW/WZ/ZZ 1036.9 419.0
Wc 2521.9 1202.5
Wbb 1118.0 451.7
Wcc 1982.7 832.2
W+LF 39766.3 18466.5
Background Sum 46425.8 21372.0
H->WW,MH=170 44.7 32.1
S/N 0.00096 0.0015
S/√N 0.21 0.22
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Expected number of events after all cuts
process # event 125<MH<195WW/WZ/ZZ 55.1 25.3Wc 207.4 101.9Wbb 187.8 83.4Wcc 170.1 76.7W+LF 1456.6 650.5Background Sum 2076.9 973.7H->WW,MH=170 3.4 3.0S/N 0.0019 0.0032S/√N 0.087 0.098
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Summary&Plans We developed a tool to reconstruct neutrino Pz.
RMS on reconstructed Higgs mass = 20.6GeV for events with right jet correction,for MH=170
We performed sensitivity study at 2fb-1 C-tagging and angular correlation used in event sel
ection. Challenging channel, our analysis needs improvem
ent. W+LF background is dominant , while few signal re
mains after cut. Need to optimize tag conditions??
Thank you!!
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Expected number of events after all cuts 2fb-1
process # event 130<MH<185WW/WZ/ZZ 55.1 20.5Wc 207.4 91.0Wbb 187.8 72.6Wcc 170.1 67.7W+LF 1456.6 581.3Background Sum 2076.9 833.1H->WW,MH=150 2.7 1.8S/N 1.27e-3 2.14e-3S/√N 5.81e-2 6.17e-2
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Expected number of events before cut 2fb-1
process # event 120<MH<375WW/WZ/ZZ 1036.9 976.7
Wc 2521.9 2433.3
Wbb 1118.0 1054.3
Wcc 1982.7 1874.3
W+LF 39766.3 38089.2
Background Sum 46425.8 44427.7
H->WW,MH=150 32.7 32.0
S/N 7.04e-4 7.2e-4
S/√N 1.52e-1 1.52e-1
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Different Higgs Mass withDetector level
MH=170
MH=200
HiggsMass NuPz-hepgNuPz
・ all・ correct・ imagunary
RMS=45.1
RMS=45.8
RMS=50.9
RMS=54.4
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back up
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Hepg level correct rate of each method
Method Adopped solution
Discarded
solution
1 50.3(%) 49.7
2 58.2 41.8
3 66.2 33.8
4 50.9 49.1
imaginary4.3%
Method3 is best !!
Correct : defined as the case where we pick the solution closer toHepg(MC truth) Pz
MH=150GeV
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introduction Higgs の崩壊過程
☆MH<135GeV ( 軽い Higgs)
・ lepton,quark pair に崩壊
・湯川 coupling の測定
☆MH>135GeV ( 重い Higgs)
・ほとんどが WW/ZZ へ崩壊
Higgs は重いものと結合しやすい!
解析しやすい
b : 4.2 GeV
1.8 GeV
c : 1.25 GeV
bb
cc
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introduction Higgs の生成断面積
LEP
dominant production
湯川 coupling に
よる Higgs の生成
Higgs と fermionとの結合
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Expected number of events cut1
process # event 130<MH<185H->WW,MH=150 4.0 2.5
WW/WZ/ZZ 145.8 42.0
Wc 501.7 183.7
Wbb 531.7 170.2
Wcc 422.8 138.5
W+LF 3467.4 1156.5
Background Sum 5069.4 1690.9
S/N 7.88e-4 1.47e-3
S/√N 5.61e-2 6.03e-2
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Expected number of events cut2
process # event 130<MH<185H->WW,MH=150 3.9 2.4WW/WZ/ZZ 136.6 39.6Wc 483.9 177.7Wbb 437.0 138.5Wcc 394.5 129.4W+LF 3359.0 1123.4Background Sum 4810.9 1608.5S/N 8.04e-4 1.48e-3S/√N 5.58e-2 5.95e-2
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Expected number of events cut1
process # event 140<MH<195H->WW,MH=170 5.7 4.0
WW/WZ/ZZ 145.7 53.4
Wc 501.7 213.2
Wbb 531.7 201.0
Wcc 422.8 162.0
W+LF 3467.4 1338.5
Background Sum 5069.4 1968.0
S/N 1.12e-3 2.04e-3
S/√N 7.99e-2 9.05e-2
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Expected number of events cut2
process # event 125<MH<195H->WW,MH=170 5.5 4.0WW/WZ/ZZ 136.6 51.0Wc 483.9 217.7Wbb 437.0 172.2Wcc 394.5 159.8W+LF 3359.0 1370.4Background Sum 4810.9 1971.3S/N 1.15e-3 2.04e-3S/√N 7.96e-2 9.07e-2
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150GeV Solution1 Imaginary
Hepg 66.1(%) 4.3
Detector 82.0 17.8
Jet-hepg 80.7 11.8
170GeV Solution1 Imaginary
Hepg 75.6(%) 6.7
Detector 81.8 29.4
Jet-hepg 80.4 26.7
200GeV Solution1 Imaginary
Hepg 73.7(%) 7.9
Detector 81.5 28.9
Jet-hepg 80.7 26.9
Method3 solution1 rate & imaginary rate
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<Higgs boson mass>
<Gauge boson mass>
gw, g’w : coupling constants
Higgs doublet の 4 つの自由度
3つ ⇒ 3個の重いベクトルボソンの質量
残りの1つ ⇒ 1個のスカラー粒子 (Higgs boson)の質量
を真空 0 のまわりで展開し、ラグラジアンを求める
質量 0 の gauge boson に質量を与えることができた
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hadron collider での Higgs 粒子生成過程
<gluon fusion> <vector boson fusion>
<strahlung off vector bosons> <bremsstrahlung off top quark>
H
backgroundが多い
Pt が大きい jetが2本
jet
・ top quarkの湯川結合
・backgroundが少ない
・軽い MH には重要な過程
Tevatron では
主チャンネル
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dominant SM Higgs production
⇒gluon-gluon fusion dominant Higgs decay
⇒W boson
⇒lepton 1つ +neutrino 1 つ or
jet 2つ
search for the signal of a high-mass SM Higgs boson (135 GeV <MH<185GeV)
electrons,muons
gg->H->WW->lνlν (leptons + neutrinos)
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Eem,t>8GeV
Pt > 6GeV
Pt > 8GeV Pt > 4GeV
electron muon
具体的には… <hardware trigger の場合>
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Event Selection Pt > 20GeV (trigger lepton)
Pt > 10GeV(non-trigger lepton)
このような2つの lepton を選ぶ⇒calorimeter や track で間違った jet や重い quark の semil
eptonic decay からの lepton を落とすことができる
この 2 つのprimary leptonが必要
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Event Selection <jet veto>< 今捜している channel>
終状態 :lepton 2つ+ neutrino2つ
no jet
<background の一例 >
b
b
l
l
ν
ν
jet
jet
終状態 :lepton 2つ+ neutrino2つ
+ jet 2つjet を veto すれば
このような backgroundは
落とせるはず!
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ところが…hadron collider 大量の gluon が存在 gluon emission がちょく
ちょく起こる initial state gluon radiation (ISR) の soft jet は OK とする
soft jet
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jet veto for jet with Et>15GeV, |eta| < 2
ΔR=0.4
☆number of jet = 0
☆number of jet = 1 this jet Et< 55GeV
☆number of jet = 2 each jet Et< 40GeV
ISR が多いため、 soft な 1jet or 2jet event も使う
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Higgs boson: spin 0 の粒子 Higgs decay to WW: WW の helicity が揃う終状態で lepton 同士、ニュートリノ同士は同じ向き
にでやすい
large missing Et
small azimuthal angle between leptons
small dilepton invariant mass
Higgs boson の性質
φ
l+
l-
ν
ν
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cut 後の主な backgroundDrell-Yan 過程
Z/
hadron-hadron 衝突によるレプトン対の生成
e,μ,τ τ->ντ+ l +ν l
崩壊にニュートリノを含む
missing Et を持つ
missing Et はない
lepton に崩壊するのは、
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Conclusion
Searched for SM Higgs boson production leptonic decay (proton-anti proton collider at √s=1.96TeV) no excess was observed
LHC での期待が高まる!
gg->H->WW(*)->lνlν
SM background の期待値と data はよく一致
Higgs mass の関数としてσ×BR(gg->H->WW) の 95% CL upper limit を設定
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資料 http://www-cdf.fnal.gov/physics/exotic/r2a/20050929.HWW/ Conference note CDF 7893 hep-ph/9803257
Electroweak Symmetry Breaking And Higgs Physics Quarks And Leptons 素粒子物理学 原康夫 著
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Introduction
1990 年代、 LEP,Tevatron の実験結果により
☆ 標準モデル⇒非常に高い精度で検証
☆ 力の源⇒ゲージ対称性
<Standard Model>
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大統一理論
電磁力、弱い力、強い力の3つの力の統一
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Promising channels for SM Higgs (MH <140GeV)
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Promising channels for SM Higgs (MH>140GeV)
今回はこのchannel について見る
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Signal and SM background expectation summary
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