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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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


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


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)


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%


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:


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)


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:


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):


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


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:


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


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 ]


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)


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


28 July 2006

Moscow, ICHEP 2006

Backup Slides


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


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


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


28 July 2006

Moscow, ICHEP 2006

ATLAS Experiment

Time until Friday, August 31, 2007


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


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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