search for h->ww in semileptonic decay

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

summer school2007@FNAL 2/32

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


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


hepg levelNuPz HiggsMass NuPz-hepgNuPz

Adopted

solutionD

iscarded solution

・ all・ correct・ imagunary

MH=150


detector level HiggsMass NuPz-hepgNuPz

jets matched to hard process p

artons

No matching to hepg

MH=150


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

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


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.


background

WW/WZ/ZZW+c+jetsW+bbbarW+ccbarW+LF

purpose : crudely estimate the potential of this search channel.We only consider dominant background.


Cut1 : Charm tagging

Aim to identify W->cs decay

Cut at jet probability=0.05Cut2 : anti HF tagging

cut


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


Signal vs BackgroundHiggs Mass(150GeV)

Beforecut

C-tag

Anti HF ⊿R


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


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


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!!


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


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


H->WW,MH=150 32.7 32.0

S/N 7.04e-4 7.2e-4

S/√N 1.52e-1 1.52e-1


Different Higgs Mass withDetector level

MH=170

MH=200

HiggsMass NuPz-hepgNuPz


RMS=45.1

RMS=45.8

RMS=50.9

RMS=54.4


back up


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


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


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


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


S/N 7.88e-4 1.47e-3

S/√N 5.61e-2 6.03e-2



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



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


S/N 1.12e-3 2.04e-3

S/√N 7.99e-2 9.05e-2



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


150GeV Solution1 Imaginary

Hepg 66.1(%) 4.3

Detector 82.0 17.8

Jet-hepg 80.7 11.8


Hepg 75.6(%) 6.7

Detector 81.8 29.4

Jet-hepg 80.4 26.7


Hepg 73.7(%) 7.9

Detector 81.5 28.9

Jet-hepg 80.7 26.9

Method3 　 solution1 rate & imaginary rate


<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


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


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)


Eem,t>8GeV

Pt > 6GeV

Pt > 8GeV Pt > 4GeV

electron muon

具体的には… <hardware trigger の場合>


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


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！


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


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


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


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、


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


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　　　　　　　　　


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>


大統一理論

電磁力、弱い力、強い力の３つの力の統一


Promising channels for SM Higgs (MH <140GeV)


Promising channels for SM Higgs (MH>140GeV)

今回はこのchannel について見る


Signal and SM background expectation summary

search for h->ww in semileptonic decay

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