Testing the SM in tt and single top production
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Testing the SM in tt and single top production. António Onofre ([email protected]). On behalf of the ATLAS+CMS Collaborations. Moscow July 26 – Au gust 2, 2006 XXXIII International Conference on High Energy Physics. 1) tt @ LHC. tt Cross section Top spin correlations

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Ant nio onofre onofre lipc fis uc pt

Testing the SM in tt and single top production

António Onofre ([email protected])

On behalf of the ATLAS+CMS Collaborations

Moscow July 26 –August 2, 2006

XXXIII International Conference on High Energy Physics


Outline

1) tt @ LHC

  • tt Cross section

  • Top spin correlations

  • Probing the Wtb vertex

  • FCNC top decays

28 July 2006

Moscow, ICHEP 2006

Outline

2) Single top @ LHC:

  • Production Cross section

3) Conclusions


What do we know about the top quark

“t-quarks are produced and decay

as free particles”

thad = LQCD-1 >> tdecay

NO top hadrons

28 July 2006

Moscow, ICHEP 2006

What do we know about the top quark?

  • The top quark completes the three family structure of the SM

  • Its massive

  • Spin=1/2,

  • Charge=+2/3,

  • Isospin=+1/2

  • tbW

  • Large G=1.42GeV (mb,MW,as,EW corr.)

    Short lifetime

dm/m <2%

Not directly

-4/3 excluded @ 94%C.L.(D0)

Not directly

~100%

ct<52.5mm @95%C.L.(CDF)

The TEVATRON is probing better than ever the top sector…

The LHC will allow precision measurements of Top Quark Physics


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

  • tt cross section

+

(90%)

(10%)

W (had)

≥4 jets (DR=0.4)

pT>40 GeV

t (had)

pT>20 GeV

2 b-jets

t (lep)

pT>20 GeV

28 July 2006

Moscow, ICHEP 2006

Production X-section:

s ~ 833pb @ 14TeV

Semileptonic Topology:

Golden Channel

Clean Topology:

tt back to back

Used for several

studies


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

  • tt cross section

mt (had)

s =10.6GeV

Systematic Errors:

Comb.

28 July 2006

Moscow, ICHEP 2006

Selected 87000 signal events for L=10fb-1 (S/B~78, ~12 with tback)

(e=3.5%)

Althougherrors are dominated by systematics

It seems possibleto determine mt @ 1GeV level

(with L=10fb-1)


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

  • tt cross section

A) Semi-leptonic channel (ttbbqqmnl):

L=10fb-1

Dstt/stt= 9.7%(syst)±0.4%(stat)±3%(lum)

B) Di-leptonic channel (ttbb lnllnl):

L=10fb-1

Dstt/stt= 11%(syst)±0.9%(stat)±3%(lum)

  • Syst.(dominant):PDF(5%),btag(4%),JES(4%)

  • Back (dominant): ttll.(Wtnt, tleptons)

  • e = 5% (S/B=5.5)

With Tau leptons (ttbb tnt lnl, t hadrons):

Dstt/stt= 16%(syst)±1.3%(stat)±3%(lum)

[ e=2%, S/B~1, et-tag=30% ]

C) Fully Hadronic channel:

L=1fb-1

e=2%, S/B<1/9 (QCD)

Sys: JES(11%), PileUp(10%)

Dstt/stt= 20%(syst)±3%(stat)±5%(lum)

28 July 2006

Moscow, ICHEP 2006

CERN/LHCC 2006-021

CMS TDR 8.2

  • Syst.(dominant):

  • btag(7%), PDF(3.4%), PileUp(3.2%)

  • Back.(dominant):tt,W+jets

  • e = 6.3%


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

Testing the tt Production X-section:

Although t and t are produced unpolarized their spins are correlated

A=

q

s(tLtL) + s(tRtR) - s(tLtR) - s(tRtL)

s(tLtL) + s(tRtR) + s(tLtR) + s(tRtL)

flq

1 dN 1

( 1 – ADaXaX´cosf )

=

N dcosf2

l+,n

t

t

28 July 2006

Moscow, ICHEP 2006

  • Top Spin Correlations

SM:

New Physics affects A

Other angular distributions:

aX=spin analysing

power of X

SM:


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

t

q

ql,n

l,n

qq

SM

Mtt<550 GeV

Error (±stat ±syst)

(Eur.Phys.J.C44S2 2005 13-33)

  • Semileptonic + Dileptonic

  • Syst (Eb-jet,mtop,FSR)

  • ~4% precision

A

0.42

0.014 0.023

Ãxx´

AD

-0.29

0.008 0.010

t

A

N(cosf > 0) - N(cosf < 0)

1

= - ADaXax´

N(cosf > 0) + N(cosf < 0)

2

28 July 2006

Moscow, ICHEP 2006

  • Top Spin Correlations

L=10fb-1

A) Spin correlations and angular distributions:

(CERN/LHCC 2006-021, CMS TDR 8.2)

B) Spin Asymmetries can also be used (X-check)

(for L=10fb-1precision A,AD below 10% )

(hep-ex/0605190, subm. to Eur.Phys.J.C)


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

(Eur.Phys.J.C44S2 2005 13-33)

L=10fb-1

SM

Error

(±stat ±syst)

(1/G)dG/dcos(ql*)

(Mt=175 GeV)

Semilep.

+

Dileptonic

F0

0.703

 0.004  0.015

FL

0.297

 0.003  0.024

FR

0.000

(mb=0)

 0.003  0.012

  • Syst ( Eb-jet,mtop,FSR )

  • dF0/F0~ 2%;dFR ~ 0.01

cos(ql*)

28 July 2006

Moscow, ICHEP 2006

  • Probing the Wtb vertex

A) Test the tbW decay vertex

Measure W polarization(F0, FL, FR) through lepton angular distribution in W cm system:


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

A-

AFB

A+

AFB [t=0] A± [t= (22/3-1)]

±

cos(ql*)

28 July 2006

Moscow, ICHEP 2006

  • Probing the Wtb vertex

B) Anomalous Couplings in the tbW decay

(PRD67 (2003) 014009, mb≠0)

Angular Asymmetries: AFB, A+ and A-

SM(LO):


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

SM(LO):

rL=0.423

rR=0.0005 (mb≠0)

1s Results:

28 July 2006

Moscow, ICHEP 2006

  • Probing the Wtb vertex

L=10fb-1

B) Anomalous Couplings in the tbW decay


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

At LHC

Look for:

28 July 2006

Moscow, ICHEP 2006

  • FCNC in top quark decays

  • The top quarkalmostalways decays to a b quark,B(tWb)~1

  • B(tWs)<0.18%, B(tWd)<0.02% (other decays are really rare)

hep-ph/0409342

APPB35(2004)2695

FCNC decays are highly suppressed in the SM:


Ant nio onofre onofre lipc fis uc pt

1) tt @ LHC

L=10fb-1

L=10fb-1

28 July 2006

Moscow, ICHEP 2006

B) In the absence of signal:

  • FCNC top decays

ATLAS: Br(t[email protected]%CL)<0.14%

A) 5s Sensitivity:

 With 10 fb-1 already two orders of magnitude better than LEP/HERA/TEVATRON


Ant nio onofre onofre lipc fis uc pt

Vtb

Vtb

Vtb

Vtb

Wt-channel

t-channel

s ~ 250 pb

s ~70pb

W* (s-channel)

s ~ 10 pb

28 July 2006

Moscow, ICHEP 2006

2) Single top @ LHC

  • Production Cross Section

Three different Processes (never observed yet)

Powerfull Probe of Vtb ( dVtb/Vtb~few% @ LHC )

[ PRD 70 (2004) 114012, PL B524 2002 283-288 ]

Theoretical uncertainties:

  • Quark-gluon luminosity inside b-quark (PDF)

  • Renormalization scale (m)

  • top mass(Dmtop=4.3GeV  s(W*) changed by 3%)

Probe New Physics Differently:ex. FCNC affects more t-channel

ex. W´ affects more s-channel

[ PRD63 (2001) 014018 ]


Ant nio onofre onofre lipc fis uc pt

1 lepton, pT>25GeV/c

High Missing ET

2 jets (at least 1 b-jet)

Common feature:

Stat: 7000 events (S/B=3)

Syst: dominated by Eb-jet and Lum. Error

Back: tt, Wbb and W+jets

t-channel:

(Nj=2,Nb=1)

( ds/s <1.5%)

Stat: e~1% (S/B=15%)

Wt-channel:

( ds/s ~ 4%)

(Nj=3,Nb=1)

Stat:1200events for tb (S/B=10%)

Syst: Eb-jet, Lum. Error, back X-section

s-channel:

(Nj=2,Nb=2)

( ds/s ~7-8%)

  • t-channel: Ds/s= 8%(syst)±2.7%(stat)±5%(lum)

  • Wt-channel: Ds/s= 23.9%(syst)±8.8%(stat)±9.9%(MC)

  • s-channel: Ds/s= 31%(syst)±18%(stat)±5%(lum)

28 July 2006

Moscow, ICHEP 2006

2) Single top @ LHC

  • Production Cross Section

(ATL-COM-PHYS-2006-002)

L=30fb-1

Separate Channels by (Nj,Nb) in final state:

(ATL-PHYS-PUB-2006-014)

L=10fb-1

(CERN/LHCC 2006-021, CMS TDR 8.2)


Ant nio onofre onofre lipc fis uc pt

28 July 2006

Moscow, ICHEP 2006

3) Conclusions

  • The LHC will be a top factory

    (8 million events already with 10fb-1)

  • New era on precision Top Quark Physics

    will start with the LHC:

    couplings, asymmetries, decays, etc. will be measured with unprecedented precision

  • Stay tuned for next year


Ant nio onofre onofre lipc fis uc pt

28 July 2006

Moscow, ICHEP 2006

Backup Slides


Ant nio onofre onofre lipc fis uc pt

σ(W→lν)

σ(tt)

mt=175 GeV

  • s(pp tt):

g

g

10%

90%

28 July 2006

Moscow, ICHEP 2006

Cross-sections at the LHC

  • High Collision Rate

    • LHC (Tevatron) – every 25ns (396ns)

  • High Cross-Sections ~0.1b

    • 2-3 interactions per collision

      • LHC low/high lumi L=1033cm-2s-1

    • 20 interactions per collision

      • LHC design/high lumi L=1034cm-2s-1

  • W, Z, top are rare events

    • Requires High Luminosity

    • Trigger is crucial: sel. Leptons High pT


Ant nio onofre onofre lipc fis uc pt

  • Electromagnetic Calo

Pb-liquid argon

s/E ~ 10%/E

~1% uniform

  • Hadronic Calo

Fe-scint Tile Calo (10l)

s/E ~ 50%/E  0.03

  • Muon Detectors

  • MAGNETS

s/pT< 10 % at 1 TeV

Toroide+Solenoid (4 magnets)

in inner cavity

Calorimeters outside field

  • Tracker

Si pixels + strips

TRD alows particle ID

Solenoid B=2T

s/pT~ 5x10-4 pT  0.01

28 July 2006

Moscow, ICHEP 2006

ATLAS Experiment


Ant nio onofre onofre lipc fis uc pt

tt @ LHC

  • tt cross section and top mass

W=highest pT,2j

(in thad system)

3-jet invariant mass

electron+muon estimate for L=100 pb-1

Events / 4.15 GeV

ATLAS preliminary

thad=highest pT,3j

Top-combinatorialand W+jets background

Mjjj (GeV)

28 July 2006

Moscow, ICHEP 2006

With onlyL=100pb-1 (few days of nominal low-lumi LHC operation)

No b-tag and MW cut

(e=5.3%)

We can easily see top peak without b-tag requirement


Ant nio onofre onofre lipc fis uc pt

28 July 2006

Moscow, ICHEP 2006

ATLAS Experiment

Time until Friday, August 31, 2007


Ant nio onofre onofre lipc fis uc pt

  • Electromagnetic Calo

PbWO4 Crystals

s/E ~ 2-5%/E

no longitudinal segmentation

  • Hadronic Calo

Brass-scint. (> 5.8 l)

s/E ~ 100%/E  0.05

  • Muon Detectors

  • MAGNET

s/pT ~ 5% at 1 TeV

combining with tracker

1 Solenoid (B=4T)

Calorimeters inside field

28 July 2006

Moscow, ICHEP 2006

CMS Experiment

  • Tracker

Si pixels + strips

No particle ID

s/pT ~ 1.5x10-4 pT  0.005


Ant nio onofre onofre lipc fis uc pt

1s-bands ( sSM )

L=10fb-1

CERN/LHCC 2006-021

CMS TDR 8.2

L=10fb-1

  • t-channel: Ds/s ~10%(tot)

  • s-channel: Ds/s ~36%(tot)

28 July 2006

Moscow, ICHEP 2006

Single top @ LHC

  • Sensitivity to New Physics

Tait,Yuan PRD63 (2001) 014018


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