Current Status of Top Quark Physics at ATLAS

Current Status of Top Quark Physics at ATLAS

A. Onofre

[email protected]

Jornadas LIP, Praia da Consolação, 21-22 Dezembro 2005

Current Status of Top Quark Physics at ATLAS

1) Mass measurement

2) Charge determination

3) Asymmetries in top decays and top spin

correlations

4) W polarisation, AFB and New Angular

Asymmetries

5) Rare decays of top quarks and FCNC

6) Single Top

7) Full Simulation @ Coimbra

8) Conclusions

Outline

1) Mass measurement

MMtt(had)(had)

SN-ATLAS-2004-040

Sistematic Errors:Sistematic Errors:

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

protons protons

W b

t

qq|

quark

quark Jet 2

Jet 1

Semileptonic Semileptonic TopologyTopology

pp tt bbWpp tt bbW++WW-- (833pb) (833pb)

2) Charge Determination

Using the Using the Semileptonic Semileptonic TopologyTopology

Which one of these?

iqi(j.pi)k

i(j.pi)kQb-jet=

b-jet

b-jet

Conclusion: determination of b-quark charge (associated with l±) fixes top charge

3) Asymmetries in top decays and top spin correlations

Study Study top spintop spin by looking to angular by looking to angular distributions of the decay products:distributions of the decay products:

Top Top Spin Correlations in pp Spin Correlations in pp tt: tt:

hhxx = spin analysing power of particle x = spin analysing power of particle x

hhxx

hhxx

Top Top SpinSpin

The Aj Asymmetry:

The Alj Asymmetry:Semileptonic tt Events:

The Ãlj Asymmetry:


ATLFAST

(x=l, x´=j)_

(x=,x´=j)_

(x=l, x´=j)_


(L=10fb-1)For Alj:

For Ãlj:

For Aj:

N>0

0>N

ATLFAST Counting Experiments (2-bins)

Similar Precision to Full Distribution Results

Physics:

Results:

Axx´=(A.hx.hx´)/4

(A defined as in SN-ATLAS-2005-052)

A=0.361±0.028(stat)±0.048(sys)

(semileptonic channel only)

For Alj

For Ãlj

For Aj

(L=10fb-1)


4) W polarisation, AFB and New Angular Asymmetries

t

W0 Longitudinal

F0

W

b

+1/2

+1/2

0

WL Left

FL

tb

W

+1/2

-1/2

+1

WR Right

FR

tW

b

+1/2+1

-1/2V-A

SUPRESSED

The W has 3 helicity states: “Right”, “Longitudinal” and “Left”The top quark decay is the most important source of longitudinal Ws


The Measurement of the W polarisation is a: Test of a SM Prediction: F0=0.7 e FL=0.3 (FR=0.0) Test of the tWb vertex structure: (V-A)

F0 0.890.340.30 (stat)0.17(syst)

F0 0.25@95%CLF0 = 0/t = 0.699±0.004(stat)

±0.021(sys) FL = L/t = 0.299±0.004(stat)±0.019(sys) FR = R/t = 0.002±0.003(stat)±0.003(sys)

cos(lW)=-cos(bl)

ATLAS (10fb-1): (semileptonic only)

CDF

ATLFAST

AFB=a0(FL-FR) = 0.222 (LO)

A- =a1FL-a2F0 = 0.840 (LO)

A+ =-a1FR+a2F0=-0.549

(LO)

The AFB, A+ and A- Asymmetries

Results (Counting Experiments):

Definition of AFB, A+ and A-: AFB= 0.223±0.004(stat)

±0.013(sys)A+ =-0.547±0.003(stat)

±0.010(sys)A- = 0.839±0.002(stat)

±0.003(sys)

For A-

For A+

For AFB

(FL,FR,F0 defined as in SN-ATLAS-2005-052)(semileptonic channel only)


ATLFAST

Limits on the anomalous couplings:

The AFB, A+ and A- AsymmetriesAnomalous couplings at the Wtb

vertex:

VR [-0.10 , 0.16]

gL [-0.08 , 0.05]

gR [-0.02 , 0.02]

Phys.Rev.D67 (2003) 014009(mb taken into

account)

(semileptonic channel only)

(L=10fb-

1)



● The top decays almost of the time through tWb [ B(tWb)~1 ]

● Top Rare Decays are Really Rare: B(tWs)<0.18%, B(tWd)<0.02% ● FCNC Top Decays: B(t c) +B(t u)<3.2% at 95% CL

B(t Zc) +B(t Zu)<33% at 95% CL

At 1-loop:At 1-loop:



A) ATLAS Sensitivity (5A) ATLAS Sensitivity (5):):

B) Absence of Signal (95% C.L.):B) Absence of Signal (95% C.L.):

C) Dominant Systematic Errors: MC) Dominant Systematic Errors: Mtt e e b-tagb-tag < < 20%20%


Significant Gain Significant Gain in sensitivity in sensitivity

with respect to with respect to present present

experimental experimental data from CDF, data from CDF, LEP, and HERALEP, and HERA

6) Single Top Quark

A) Single Top Production A) Single Top Production (SM):(SM):

((t-channel t-channel ~245pb; ~245pb; s-channels-channel~5.1pb)~5.1pb)

B) Associated Production B) Associated Production (SM):(SM):

((assass ~31pb) ~31pb)

C) FCNC Production (Beyond SM):C) FCNC Production (Beyond SM):

(hep-ph/0510087 v2)(hep-ph/0510087 v2)

Signal: MC@NLO tt samples (e,μ) - AOD ref. T1

Full SimulationWith EventView (to remove overlap between containers)

174860 events (120897 with weights) → ~0.6 fb-1

TopReX tt samples (e,μ) - AOD ref. 4520 and 4521159274 events → ~1.3 fb-1

Background: MC@NLO tt samples (τ,ℓℓ) - AOD ref. T1 (as above)

TopReX TopReX TopReX

N non b jets N b jets N leptons

TopReX Single-t samples - AOD ref. 4511,4530,4531 and 4540

143636 events → ~37.7 fb-1


Full SimulationComparison ATLFAST / MC@NLO / TopReX

mW hadronic (GeV)

mt leptonic (GeV) mt leptonic (GeV)

ATLFAST ATLFAST ATLFAST

MC@NLOTopReX

MC@NLOTopReX

MC@NLOTopReX

(L=0.3fb-1) (L=0.3fb-1) (L=0.3fb-1)

(L=10fb-1) (L=10fb-1) (L=10fb-1)


Full Simulation at Coimbra


A) Test in Standalone Machine (Pentium [email protected], 512-RAM) Physics Channel: ppttbWbW

kB

s

B) Test in CENTOPEIA:

• 108 CPU´s (Pentium IV)• Full ATLAS Simulation

Software Installed (ATHENA) and running

• First Tests under way• Results expected soon

CFC/DF-UC

Conclusions

b)The Asymmetry measurements are important tools to understand top-quark physics. They are sensitive to W polarisation, Top spin Correlations, New Couplings, etc. Counting experiments seam to work.

c) Studies with full simulation under way Comparison ATLFAST - MC@NLO - TopReX

d) and…

8) Conclusions

a)Top-quark physics is getting momentum at ATLAS

8) Conclusions

e) Yes, you can spy on us…

http://mars.fis.uc.pt/~atlas-top/index.shtml

Updated Information on Outreach, people, presentations, meetings, publications, etc…

http://nautilus.fis.uc.pt/personal/top2006/

8) Conclusions

http://nautilus.fis.uc.pt/personal/top2006/8) Conclusions

f) Why not showing up at the top workshop?

Documents

Current Status of Top Quark Physics at ATLAS