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Perspectives on single-top-quark production. Zack Sullivan Aspen Winter Conference 2007. What is single-top-quark production?. Tevatron. LHC (s-chan?). “ t -channel”. “ s -channel”. “Wt associated ”. For details see ZS, PRD70, 114012 (04). - PowerPoint PPT Presentation
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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?)
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 33/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 44/15/15
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.
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 55/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 66/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 77/15/15
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.
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 88/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 99/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1010/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1111/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1212/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1313/15/15
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
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1414/15/15
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)
Zack Sullivan, Aspen 2007 January 10Zack Sullivan, Aspen 2007 January 10 1515/15/15
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.