Perspectives on single-top-quark production

PerspectivesPerspectives on single-top-quark on single-top-quark

productionproduction

Zack SullivanZack Sullivan

Aspen Winter Conference 2007Aspen Winter Conference 2007

Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 22/15/15

What is single-top-quark What is single-top-quark production?production?

Mt=175 GeVTevatron

Run I

Tevatron

Run IILHC

t (NLO)1 1.45±0.20 pb 1.98±0.28 pb 247±12 pb

s (NLO)1 0.75±0.10 pb 0.88±0.12 pb 10.7±1.1 pb

tW (LL)2 0.06±0.01 pb 0.09±0.02 pb 56±8 pb

Total 2.26±0.25 pb 2.95±0.33 pb 314±15 pb1 Harris, Laenen, Phaf, ZS, Weinzierl, PRD 66 (02) 0540242 Tait, PRD 61 (00) 034001; Belyaev, Boos, PRD 63 (01) 034012

Dominant

Uncertainties

PDFs, Mt

±2.5%Mt

PDFs & scale

For details seeZS, PRD70, 114012 (04)

“t-channel” “s-channel” “Wt associated”

Tevatron LHC (s-chan?)


Learning about the Learning about the WtqWtq vertex vertex• Measuring B(tWb) only tells us Vtb » Vtd, Vts

CDF, PRL 86 (01) 3233

• In the SM Vtb = 0.9991 ± 0.0001 (PDG 2004)

Relax Unitarity of CKM matrix

• Single-top cross section proportional to |Vtb|2

– Measure B(tWb) in t t, extract Vtb~ t/2

in each channel Stelzer, ZS, Willenbrock, PRD 58 (98) 094021

0.24- 0.31

)BR()BR( 0.94

2

tb2

ts2

td

2tb

VVV

VWqtWbt

521

21

tqigV

See polarization of topat production (~5 fb-1)

9993.0 0.0711.0 008.0 0

044.0039.0975.0968.0226.0213.0

0044.00030.02241.02174.09796.09730.0

Vtb


Current evidenceCurrent evidence

|Vtb|~0.3

|Vtb|=1.30.2

CDF results from:Note 8588Note 8585

New NN

D0 results from:hep-ex/0612052

Twice as much

data on tape.

We will know

better in summer.


New phenomena affectNew phenomena affectss- and - and tt-channel separately-channel separately

|Vtb|~0.3

|Vtb|=1.30.2

New NN

FCNC

d,s

Vtd, Vts

Vectorcurrents

Scalars (+T)

KK-modesetc.

Resonances New q-t-Xverticies

4th generation?t-T mixing?Suppress t not s?

Z

BR(tZc)<0.33CDF, PRL80,2525(98)

will soon change


Model independent searches forModel independent searches forWW at Tevatron and LHCat Tevatron and LHC

ZS, hep-ph/0306266

ZS, PRD 66, 075011 (2002)

• LHC can test SM-like W bosons up to 5.5 TeV

• Couplings of 10-1gSM up to 3 TeV


The lasting importance ofThe lasting importance ofsingle-top-quark productionsingle-top-quark production

Theory Experiment

A decade of intense collaboration and inspiration has led to a new or modified understanding of every aspect of the observable cross section.


How to see the initial stateHow to see the initial state

Heavy-quark (b, c) PDFs are more than a trick: b & c are full-fledged components of the proton structure.

– HERA is beginning to see evidence of intrinsic charm … stay tuned!

– Leads to other processes: , Zb/Zc, Zbj/Zcj, Wbj …

“W-gluon fusion”(circa 1996)

A “mathematical trick” let usresum large logs into a “b” PDF.

Gained newnomenclature

“t-channel”production

1st testable need for a heavy-quark PDF


Fully exclusive NLO calculationsFully exclusive NLO calculations

• Worked out analytically inHarris, Laenen, Phaf, ZS, Weinzierl, PRD 66, 054024 (02)

• Numerically studied using ZTOPZS, PRD 70, 114012 (04)

• Now in MCFM 5.1+Campbell, K. Ellis

# b-jets t j (W j j) t j j (W j j j)

s-channel = 2 0.620 pb 0.168 pb

= 1

0.022 pb (NNLO)

t-channel = 1 0.950 pb 0.152 pb

= 2

0.146 pb 0.278 pb

Cuts: ETj>15 GeV, |j|<2.5, no cuts on t

D0 w&c

HUGE

Required new methods to calculate fullyexclusive cross sections with massive states

New baseline

NLO standard


Paradigm of “jet calculations”Paradigm of “jet calculations”How do we interpret fully differential NLO?• We are calculating jets not partons

– Calculations are not well defined

w/o a jet definition

• “Bad things” happen if you treat jets as partons

NLO “d”bad idea

Highest ET jet

correct

• Choice of jet definition can have a larger effect than all theory uncertainties combined.

ZTOP

dNLO = jets/hadrons better partonsOur language should evolve to recognize this


NLO matching to event generators NLO matching to event generators required for required for tt-channel single-top-channel single-top

•HERWIG/PYTHIA Wbb 1/3 of LO prediction

Both used

IS radiation is too soft and forward, miss hard b

Background to W-Higgs ~3 times larger as well

•Feed LO events from MadEvent/CompHEP into HERWIG/PYTHIA and normalize to NLO tj, tb, tjj, tbj samples.– Other prescriptions: MLM, CKKW, etc. ZS, PRD 70, 114012 (04)

Wbb

bad shapes

ZTOP


Lessons of top-quark polarizationLessons of top-quark polarization

• The top quark decays before it hadronizes, and the pure V-A induce a 100% correlation between the d-jet in the event and the e+/+

• The angular variable is a nice discriminant

Stelzer,ZS,Willenbrock, PRD58(98)094021O’Neil et al., hep-ph/0003033

ATLAS

V-A

V-A

d


Angular correlations are importantAngular correlations are important

Many analyses do this (e.g. SUSY, HWW, etc.)Getting these right will be a big concern in a few years


Use the correlated informationUse the correlated informationWhat is used now

Why use these, whenthe primary informationis in the well-measuredangular correlations?

ZS, PRD 72, 094034 (05)


ConclusionsConclusions

Single-top-quark production forces us to reconsider our intuitions and develop new technologies that push the frontiers of perturbative QCD:– We will have precision measurements of

weak interaction structure.

– Single-top has changed how we think about the cross section.

Things not covered

• 1st PDF uncertainties

• “Modifed Tolerance Method” (what you use for PDF errors)

• Kinematic uncertainties• Push for “NN” b-tags and

clever uses

…

It will be vital to the success of the LHC to develop close interactions between theory and experiment of the type single-top-quark production has enjoyed.

Perspectives on single-top-quark production

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