ATLAS PHYSICS STUDY in CHINA 南昌高能物理大会 – 2010.4.18

冯 存 峰 ( 山东大学 )

On behalf of Atlas Chinese Cluster

(IHEP, Nanjing U., Shandong U., USTC)

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2Cunfeng Feng 2

Outline

• Introduction

• Standard model (electroweak) tests

• Top physics

• Higgs search and property

• SUSY

• Detector commissioning

• Summary

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Introduction

The LHC status

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Physics is now at our door !

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WZ studies

• WZ production can involve TGC and sensitive to new physics• First observed by CDF - PRL 98, 161801 (2007)•Little is known so far…

First observation of WZ at CDF First observation of WZ at CDF

D0 : 2.71.7 1.3 pb

CDF : 5.01.8 1.4 (stat) 0.4(syst)

• cross section measurement with early ATLAS data • a precision electroweak test • assess systematic effects for multi-lepton analyses – crucial for H->ZZ …

• cross section measurement with early ATLAS data • a precision electroweak test • assess systematic effects for multi-lepton analyses – crucial for H->ZZ …

As early as when MET and multivariate techniques are not fully commissionedApply basic cut based lepton identifications only. As early as when MET and multivariate techniques are not fully commissionedApply basic cut based lepton identifications only.

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CSC results of WZ analysis at ATLAS

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Prospect for 1/fb: event yield, cross section precision

eee eem mme mmm

WZ 20.2 25.6 29.7 47.6

ZZ 2.6 2.7 3.9 4.5

ZPhoton 29.8 0 8.1 0

ttbar 6.7 0.7 0.7 0

WW 1.7 0.1 0.1 0

Total background

40.8 3.5 12.8 4.5

Δσ/σ (stat) 38.7% 21.1% 22.0% 15.2%

Δσ/σ (total) 56.4% 22.4% 24.6% 16.8%

4-channel combination: uncertainty correlations accounted for.

Measured * BR 178.5 17.519.5

a 10% measurement!large room for optimization

based on v14 MC samples based on v14 MC samples

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Ttbar cross section

Ttbar Total:160pb

Semi-lepton: 48pb

Di-lepton: 8pb

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Ttbar semi-lepton @10TeV (200pb-1)

Event selection• Exactly one lepton (electron or muon) with pT> 20 GeV.• Missing ET > 20 GeV.• At least four jets with pT> 20 GeV.• at least three jets have pT> 40 GeV.

No b-jet tag used

ATL-PHYS-PUB-2009-087

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Ttbar semi-leptonic cross section

Wm cutCut and count

Top mass fit

Electron Mu

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uncertainties

systematic

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tt spin correlation parameters with final objectstt spin correlation parameters with final objects

)coscos1(4

1

)(cos)(cos

12121

21

2

Add

Nd

N

)cos1(2

1

cos

121

DAd

dN

NAngle between spin analysers

Angle between t(t) and spin analysers

W W polarizationpolarization analysis with final objects analysis with final objects

222

0 2

cos1

2

cos1

2

sin

2

3

cos

1RL FFF

d

dN

Nangle between lepton in W rest frame and W direction in top rest frame

(t t ) ( ) ( ) ( )

( ) ( ) ( ) ( )L L R R L R R L

L L R R L R R L

t t t t t t

t t t t t t t t

11, , 22 spin analyzer qualitiesFor V-A: (l(l++) =1, ) =1, (b)=-0.41(b)=-0.41….

SM predictions for these parameters

ttbar spin correlation and W polarization

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*due to unknown discrepancy between fast and full simulation

(730pb-1)

(220pb-1) *

Single lepton channel analysis

-- high BR with moderate background -- in situ W and top mass(transverse) constraints

SM predictions

W polarization:

Preparing for summer CONF note

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Single Top Quark Production at LHC

Single top production Weak production mechanism: Wtb vertex Signature: 1 central high-pt b-jet, W leptonic decay, 1-2 extra jets

14

σNLO ~3 pb (7TeV)

~11 pb (14TeV)

σNLO ~ 15 pb (7TeV)

~ 66 pb (14TeV)

s-channel Wtt-channel

σNLO ~ 60 pb (7TeV)

~246 pb (14TeV)

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Single top t-channel Analysis (14TeV)

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Event Selection

• harder b-jet cut: pT>50 GeV

• forward light jet cut |η|>2.5 (cut based analysis only)

1 BDT discriminant vs top pairs

Source δσ/σ cut-based δσ/σ BDT

Stat. error 5.0% 5.7%

MC stat. 6.5% 7.9%

Luminosity 18.3% 8.8%

B-tag efficiency 18.1% 6.6%

Jet energy scale 21.6% 9.9%

Lepton ID, trigger 2.3% 1.8%

Theory (xs, PDF, ISR/FSR…)

28.1% 13.5%

Total 1(10) fb-1 45% (22%) 22% (10%)

S~4412

S/B=0.12

S~540

S/B=1.3

BDT Cut

1fb-1

1fb-1

CSC note

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Top Yukawa coupling in ttH(HWW*)

gt

轻子和夸克通过与 Higgs 粒子的 Yukawa 耦合获得质量。 通过 ttH 过程研究 top 夸克的 Yukawa 耦合，可能是 LHC 唯一可测量的Yukawa 耦合常数

-- Cross section measurement coupling constant gt extraction

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Signal & Background

b

b

4 light jets

2 leptons

P

P

b

b

2 light jets

3 leptons

P

P

Signal 1： ttH2b4j2l2Vl

6jets + 2 same charge lep. + MissEt Possible BGs:

tt(1l), tt(2l), ttZ, ttW, tttt, ttWW, ttbb...

Signal 2： ttH2b2j3l3Vl

4jets + 3leptons + MissEt Possible BGs:

tt(2l),ttZ,ttW,tttt,ttWW,ttbb

Lepton Isolation is crucial

Balance between statistic and s/b, only study:

2 same change lepton channel, &

3 lepton channel

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Isolation in Calorimeter and tracker

Clusters around the lepton

Lepton

Cone size 0.2

Tracks around the lepton

Inner detector

Calorimeter

Tracker Isolation:The maximum pt of extra tracks in ID around the lepton in a cone size of 0.2 should smaller than 2 GeV

Calorimeter Isolation:The total energy deposited in the calorimeter around the lepton in a cone size of 0.2 should smaller than 10GeV

Electron MuonC

alotrack

Isolated lepton

Uniso. lepton

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Combined systematic uncertainties

Take 10% Take 10%

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Expectec direct measurement results

Result uncertainties dominated by Background systematic uncertainty, to estimate and correct it by a real data driven method is essential !

precision(160GeV):

2L : 69%

3L : 66%

Combined: 47%

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If 20% systematics WH2L WH3L Combined

Significance 1.6 1.9 2.4

67% 64% 47%

Apr 2, 2008 Lian-You SHAN, CACC7 21

@ 30 inverse fb , accepted in ATLAS CSC-NOTE

WH coupling measurement needs more work to improve

WH coupling in: WH(H->WW*)

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γ Trigger Efficiency plot with 10pb-1

This plot is using γ+jet events, which corresponding to 10 pb-1.It is possible to implement these methods with low statistic.

Work in progress

g20_loose trigger near 100% for pT>25GeV

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寻找 R 宇称破坏的 e超对称粒子

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Expected Limits@1/fb（ preparing for summer CONF note ）

M = 100 GeV M = 125 GeV

M = 150 GeV M = 175 GeV

311 3120.0006 0 001= . ’@

311 3120.0006 =5 0.001 ’@

311 3120.001 0 001= . ’@ 311 3120.002 0 001= . ’

@

311 3120.0017 0 005= . ’@ 311 3120.0033 0 005= . ’

@

311 3120.0039 0 005= . ’@ 311 3120.0038 0 005= . ’

@

ATLAS:

D0:

ATLAS:

D0: 在 1fb-1 相同亮度下， ATLAS 对 R宇称破缺参数灵敏度预期，好于现有D0 实验测量 PRL 100, 241803 (2008) 近一个量级

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Single top meetingFCPPL workshop, Wuhan

27Cunfeng FengFrom D. Liu@SDU

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b-jet tag

B Tagging Efficiency

Light Jet Mistag Rate

B Tagging Efficiency Light Jet Mistag Rate

B Tagging Efficiency

W+jets eventsQCD events

W+jets eventsQCD events

B Jet Identification

Tag. eff. & Mistag on going

J. Yu@NJU ,Y. Bai@IHEP

J. Wang@SDU

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SV0 b tag studies

PrimaryVertex

SecondaryVertex

d..............

Tracks

jr

Jet Direction

Decay Length Significance:

Performance studies Correlation between Btag estimator studies Miss-tag rate estimate from data

Discrimination Power: Heavy Flavor Jet: tend to be positive Light Flavor Jet: presence of a secondary vertex (resolution effect of light jet)

In parallel, tracking DPD maker validation (on data)

1Td jd C d r r

Bai Yu @IHEP

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Summary

• LHC and ATLAS is almost ready for physics now, need more performance study

• Many works done Hardware, Detector commissioning, Computing facility MC study Few conf notes are preparing

• Many subjects are in exploration Many challenges ahead Your suggestion are welcome.

Looking forward to exciting physics!

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ATLAS 中国组欢迎你的建议和帮助！

谢谢！

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backup

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(Di-)Boson

• Electroweak boson production at LHC From Standard Candle to

Physics

• ATLAS electron identification

W,Z

WW

For each 100pb-1 , 1M W->eν, 200 pure leptonic WW! (7 TeV PP)

concentrate on ee channel now. From Y. Liu@USTC

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WW

•Two isolated leptons, pT>20 GeV, |η|<2.5

•Veto events with a jet of pT>20 GeV, |η|<3.

•MET > 50 GeV

•Veto on events with a Z peak.

•Angular cuts among leptons and MET (different for WW cross section measurement and anomalous coupling sensitivity) .

CERN-OPEN-2008-020

200 pure leptonic WW events in each 100pb-1

Need re-optimize for 7 TeV

Higgs, of course! gg->H->WW

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Z+γ production on going: (σ (zγμμγ)=1.4pb @10TeV)

From M. liu@USTC

SM forbidden