Prospects of Top Quark Properties @ ATLAS

RHUL-Royal Holloway, University of London: 16th November 2007

Prospects of Top QuarkProspects of Top QuarkProperties @ ATLASProperties @ ATLAS

A.Onofre A.Onofre ([email protected])([email protected])


Top Properties (T7 CSC Note+ST)

Outline

Top Mass Top Charge Top Spin and Spin Correlations Top tWb decay tt Resonances Top FCNC decays Single Top FCNC Production

Conclusions


2 b-jets

pT>20GeV

pT>20GeV

≥4 jets,R=0.4 pT>40GeV

t(had)

t(lep)

W(had)

Semileptonic TopologySemileptonic Topology Dileptonic TopologyDileptonic Topology

e,

e,

b

b

W

W

2 b-jets

2 leptons

Studies done with tt Events

Top Mass, Top Charge, Top Spin and Spin Top Mass, Top Charge, Top Spin and Spin Correlations, Top tCorrelations, Top tWb decay and tt Wb decay and tt ResonancesResonances

Top FCNC decays (tTop FCNC decays (tqX, X=qX, X=,Z,g) and Single-,Z,g) and Single-toptop


Top Mass

Many analyses performed in the past or being developed recently:

Cut based Kinematic fit Template method, Matrix Element method, Analyses with soft muon b-tagging, high pT top, Analysis in leptonic final states with J/ Correlation between lepton pT and mt


Top Mass

SACLAY Analysis: choice of light jet pair and in-situ re-calibration using a 2 fit to the PDG W mass

Systematic uncertainties: Jet energy scale

1% on light jet 0.2 GeV/c2 on mt

1% on b-jet 0.7 GeV/c2 on mt

ongoing ISR/FSR , b-quark fragm.

Efficiency* 3.44 ± 0.04%

S/B 100 ± 11

Purity 63.8 ± 0.8 %

<Mtop> 175.8 ± 0.4 GeV/c2

FULLSIM (CSC) L=1fb-1

(SN-ATLAS-2004-040)L=10fb-1 ATLFAST (reminder)

Tot(sys) = 1.3 GeVTot(stat) = 0.1 GeV


Top Charge

Exotic

t(-4/3)

b(-1/3)

W-

l-(-1)

lSM

t(2/3)

b(-1/3)

W+

l+(+1)

l

SM SM ((QQtoptop==++2/32/3): ): ExoticExotics s ((QQtoptop= -4/3= -4/3):):

13/13/2 Wbt13/13/4ˆ Wbt

1el

1el

Critical momentCritical moment For top quark determinationFor top quark determination

I) Determination of b-jet chargeI) Determination of b-jet chargeII) Correct (lepton, b-jet) pairingII) Correct (lepton, b-jet) pairing

(Atl(Atlfastfast, , PHYS-2003-35)PHYS-2003-35)


Top ChargeI) Determination of b-jet Charge:I) Determination of b-jet Charge:

II) Correct (lII) Correct (l±±, b) Pairing:, b) Pairing:

m( l ,b2 )

m( l , b1 )

Mtop=175 GeV

A) Weighting Technique:A) Weighting Technique:

Ni

k

i

Ni

k

iijetb

pj

pjqQ

B) Semileptonic B) Semileptonic Decay:Decay:

ljetb qQ

Invariant mass Invariant mass criteria:criteria:

b1

b2

l


Top Charge(B.Zilka,S.Tokar)

A) Weighting Technique:A) Weighting Technique:b

b

-0.0842 -0.0842 0.0044 0.0044

0.0868 0.0868 0.0043 0.0043

( Eff.=4.1% Purity: 89.3% )

L~0.5fb-

1

B) Semileptonic Decay:B) Semileptonic Decay:(A. Tonoyan, E.Khramov)

l+l+

l-l-


Top Spin and Spin Correlations

LO) (SM0.31)σ()σ()σ()σ()σ()σ()σ()σ(

A

Mtt<550 GeV A=0.42

Double Angular Distributions:

Mtt<550 GeV AD =-0.29

tt Spin Correlation Parameters: Although t and t not polarised in tt pairs, their spins are

correlated

)coscos1(4

1

)(cos)(cos

1 2

XXXXXX

Add

d

)cos1(2

1

cos

1XXXXD

XX

Ad

d

(Zhu Chengguang)



Semileptonic + Dileptonic Syst (Eb-jet,mtop,FSR) 4-6% precision

(Eur.Phys.J.C44S2 2005 13-33)L=10fb-1 ATLFAST (reminder)

FULLSIM (CSC) L=1fb-1

SemileptonicSemileptonicSelection efficiency 2.9% (2.7% for Rome)

Preliminary



Trigger Studies:

Isolated single electron trigger

Single muon trigger

L=1fb-1

Results (Preliminary):

Level of Precision of A, AD

~40%


Spin Asymmetries can also be used:

Error versus Luminosity:SM (LO): Alj=-0.0396

spin analysing power l+=1.0, j=-0.51)

Alj

L=1fb-1

Level of Precision of Alj~40% (Low MC)

Alj~30% (High MC)

0)N(0)N(

0)N(0)N(

XXXX

XXXX

cosθcosθcosθcosθ

cosθcosθcosθcosθ

ˆˆ

ˆˆ

0)N(0)N(

0)N(0)N(

XXXX

XXXX

coscos

coscos

ˆˆ

ˆˆ



Top Decays: 1) the ttWbWb decay

By measuring the fraction of longitudinal W´s in top quark decays we are:

V-A S

UPPRESSED

Testing a Standard Model prediction: F0=0.7 FL=0.3 Probing the structure of the Wtb vertex


Top tWb decay (SM)

Angular Distribution @ W c.m.

How to measure the W Helicity Fractions?

Using lepton angular distribution (with respect to top direction) in W cm system:

SM(LO): F0=0.703 , FL=0.297 , FR=3.6x10-4

(NLO): F0=0.695 , FL=0.304 , FR=0.001cos(l*)


(Eur.Phys.J.C44S2 2005 13-33)L=10fb-1 ATLFAST (reminder)

• Syst ( Eb-jet,mtop,FSR )• F0 F0 ~ 2% ; FR ~ 0.01

FULLSIM (CSC) L=1fb-1 Results (Preliminary)

• F0 F0 ~ 6% ; FR ~ 0.03

(Zhu Chengguang)

Top tWb decay (SM)

(CDF) First Simultaneous fit:


Anomalous Couplings @ the Wtb Vertex

VR,gL,gR Change F0,FL,FR

How to Probe Anomalous Couplings?

• Extract Limits from F0,FL and FR (and ratios) • Fit angular distr. with VR, gL and gR (mb≠0)• Use Angular Asymmetries

Eur.Phys.J. C50 (2007) 519-533

Top tWb decay (BSM)


Angular Asymmetries:

(NLO): AFB=-0.2269 , A+=0.5429 , A-=-0.8402

(SM, LO): AFB=-0.2225 , A+=0.5482 , A-=-0.8397

Top tWb decay (BSM)


Anomalous Couplings

Asymmetries

(N. Castro)

Error Versus

Luminosity

A+A-

Top tWb decay (BSM)

L~1fb-1 L=10fb-1


Discovery Potential of a Narrow tt Resonance

(E.Cogneras,D.Pallin)tt Resonances

Discovery Potential: Window in mass spec. Compute the number of resonance events required for discovery: nX = 5 deviation on nSM

SemileptonicSemileptonic

Resolution

Current Limits:


L=10fb-1 ATLFAST (reminder)

Expected 95% CL Limits:

Br(tqg) <1.3x10-3 5 Results:

Br(tqZ) >4.4x10-4

Br(tq) >9.4x10-

5

Br(tqg) >4.3x10-3

(SN-ATLAS-2007-059)

Top FCNC decays

FCNC in tt Events

tqZ tqgtq


FULLSIM L=1fb-1

Results Crucially Depend on Tagging Efficiencies (e, , b, jets and )

Likelihood Method works (need to have well defined shapes)

Gluon Channel more difficult

(F. Veloso)

5 Results:

Br(tqZ) ~ 10-2 - 10-3

Br(tq) ~ 10-3

Br(tqg) ~ 10-2

Top FCNC decays


FULLSIM L=1fb-1

(F. Veloso)

5 Results:

Br(tq) ~ 10-3

Top FCNC decays (w/o b-tag)

Minimize 2 by looping on jets (b,q=j1,j2) and scan on p

Z to reconstruct kinematics


FCNC in Single-t Production

kkqgqg=anomalous coupling =anomalous coupling =scale of new =scale of new physicsphysics

Event Selection: 1 lep ( pT>20GeV, <2.5 )

1 b-jet ( pT>40GeV, <2.5 )

pT > 20GeV

( W and t p( W and t pTT, m, mblbl, m, mTT(W), H(W), HTT, m, mtt ) )

Systematics:signal signal (8%), b(8%), btagtag (6%), ISR (3.5%), (6%), ISR (3.5%), PileUp (4%) PileUp (4%) Total ~ 12%Total ~ 12%

(ug)=1.08%, (cg)=1.81%Back: W+j(80%), single-

t(9%)

L=10fb-1 ATLFAST (reminder)

Results:

(hep-ex/0702005)

Br(tug)~O(10-3)

Br(tcg)~O(10-2)

Estimate:

“Direct”

(T.L. Cheng, P.Teixeira Dias)


The Direct Production is not the full Story


The ggqt Processes:

The gqgt Processes:

The X-section:

The X-section:

Phys.Rev. D74 (2006) 014006

(R.Santos, P.Ferreira)



Just To Have an Idea of the Results for :

5 and 95% CL Limits obtained

L=10fb-1

5 Discovery 95% CL Limit: 95% CL Limits:Br(tqg) ~O(10-4)

5 Discovery:

Br(tqg) ~O(10-3-10-4)

New Contributions Give Same Order of Magnitude Results as Direct Production Mechanism 1 Order of magnitude better than ttbar for the gluon channel


Conclusions Atlas will perform precision studies in the top sector

Several Methods Available to Extract Physical Observables

Already @ 1fb-1: Top Mass ~ O(few GeV/c2) Top Charge (2/3 versus -4/3) > 5significance Spin Correlation Parameters (A,AD) ~ 40% error Spin Asymmetries ~ 40% error W helicity fractions (F0, FL, FR ) ~ 6%, ~10% and ~0.03 error Angular Asymmetries (A+,A-) ~ 3% and 1% error Anomalous Wtb Couplings (VR, gL, gR ) ~ 0.1, 0.05 and 0.03 error tt Resonances (1TeV) ~ (×Br)≥ 8 pb FCNC top Decays (Br[tqX], X=,Z,g) ~ 10-2 - 10-3


Next Top Workshop(every 2 years)

2008


Spare Slides


Top Mass @ TEVATRON


tt @ TEVATRON

Prospects of Top Quark Properties @ ATLAS

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