Top as a Window Top as a Window to New Physicsto New Physics

Robin D. ErbacherRobin D. ErbacherUniversity of California, Davis

Aspen Winter Conference -- January 9, 2007

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Mark Kruse gave us the big picture…Mark Kruse gave us the big picture…

New Physics?!?

Just beginning to study topJust beginning to study top

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Top can reveal new physics…Top can reveal new physics…

• Top results point to new physics:

Properties lead to expectations of partners or other new particles.

• Top is Not what we expect:

Measured top properties are anomalous, contrary to SM.

• Top is Not all that we find: New physics mimicks top signatures.

Top can be our window beyond the Standard Model in various ways:

Top as Indicator of Top as Indicator of Where New Physics LiesWhere New Physics Lies

Measured top parameters could point to something new.

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Top mass points to a new paradigm?

Top mass points to a new paradigm?

• Rainer Wallny’s Talk: Precise top mass (and W) places constraints on Higgs boson mass.

• Further, top important constraint to models of any new BSM paradigm.

• Top mass in the coming decade(s) precise enough to provide important consistency checks?: if SM top, what is the interplay with the new physics we are seeing?

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What can we expect for Mtop?What can we expect for Mtop?

• Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower.

(talk by Wallny)

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What can we expect for Mtop?What can we expect for Mtop?

• Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower.

• LHC: Pushing for Mtop~1 GeV.

Assume MW~15 MeV, 2004 central

values.

SM constraint on Higgs: MH = 63 ± 20 GeV ((mmHH/m/mH H 32%)32%)

Winter 07 constraint: MH = 80 ± 31 GeV

((mmHH/m/mH H 39%)39%)

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What can we expect for Mtop?What can we expect for Mtop?

• Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower.

• LHC: Pushing for Mtop~1 GeV.

Assume MW~15 MeV, 2004 central

values.

• ILC: Will benefit from a scan in

√s, allowing a threshold scan for

top production. Expect to

Improve uncertainty such that

Mtop~100 MeV!

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Top mass for different decay channels

Top mass for different decay channels

• Are the channels consistent?

• We compare them taking into account their correlated systematic uncertainties

=> Determination of Mtop from the 3 different channels is consistent with one another

Mtop(All Jets) = 173.4 ± 4.3 GeV/c2

Mtop(Dilepton) = 167.0 ± 4.3 GeV/c2

Mtop(Lepton+Jets) = 171.3 ± 2.2 GeV/c2

Rainer’s talk yesterday:

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Is Top Produced as Expected?Is Top Produced as Expected?

Measure ratio of qq/gg top pair production. (M. Kruse)

• Tevatron: 85% qq annihilation, 15% gg fusion.• LHC: 13% qq annihilation, 87% gg fusion.

Signs of new, heavy particles decaying to t-tbar:• Heavy Z’ boson decaying to ttbar (TopColor)• MSSM Higgs, strong EWSB, technicolor• RS gravitons or other resonances decaying to ttbar• Some theories with heavy top t’ decay to top (talk by L. Wang)

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Resonances decaying to top pairs

Resonances decaying to top pairs

Invariant mass of t-tbar system:• Compare with Standard Model expectations.• Add signal of new physics, such as a narrow leptophobic Z’ resonance. €

pp → X 0→ tt

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Resonances decaying to top pairs

Resonances decaying to top pairs

Exclude a narrow leptophobic

Z’ resonance.

370 pb-1

MX< 680 GeV

680 pb-1

MX < 725 GeV

955 pb-1

MX <~725 GeV!

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Resonances decaying to top pairs

Resonances decaying to top pairs

•LHC: Atlas studied resonance X once x, x and BR(Xtt) is known.•Reconstruction efficiency for semileptonic (L+J):

20% mtt = 400 GeV

15% mtt = 2 TeV

xBR required for a discovery

mtt [GeV/c2]

σxB

R [

fb]

30 fb-1

300 fb-1

1 TeV

830 fb1.6 TeV resonance

Mtt

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Expected EWK top productionExpected EWK top production

0.9 pb 2 pb

Tevatron: See Single Top talks by Sullivan & Coaddou tomorrow

Tevatron:

LHC: 10 pb 62 pb 245 pb

0 pb

s-channel t-channel (Wg fusion) W-associated

•Small signals (~1/2 ttbar production) at Tevatron together with large W+2jets background make it difficult to find.

•Similar signatures as Higgs, demonstrational challenge: increase acceptance, multivariate methods, modeling, resolutions, sophisticated techniques get us there…

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Expected EWK top productionExpected EWK top production•Single top: primary access to top CC interaction. Already test the W-t-b weak interaction (W helicity), and measure |Vtb| indirectly through branching ratios.

•We know |Vtb| to four decimal places: CKM unitarity. New physics (eg: 4th gen) would modify this. Other new physics (charged Higgs, FCNC) modifies channels differently. (Tait, Yuan ‘01)

LHC can get t-channel to / ~9% with 10 fb-1. s, Wt channels more difficult.

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Does top decay as expected?Does top decay as expected?

•Top decay branching ratios (Tevatron) shown by Kruse, gives us |Vtb|. Precision poor, improves at LHC.

•Light charged Higgs?

CDF looked for tH+b

affecting four channels

in a correlated way,

excluding when

data inconsistent: Topdilepton (ee, , e)+jetsTopdilepton (e, )+jetsToplepton(e)+jets+1 b-tagToplepton(e)+jets+2 b-tags

Varying model parameters changes:BR(tH+b)

BR(H+)BR(H+cs)BR(H+t*b)BR(H+W+h0)BR(H+W+A0)

Shown here: Variations as a function of tan particular set of MSSM parameters

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Does top decay as expected?Does top decay as expected?

•Calculate BR(tH+b) and H+ BR’s as function of MA and tan

•6 MSSM benchmarks used, #1 is shown below. No evidence yet!

Collab with M. Carena, thanks!

Anomalies in Top Anomalies in Top PropertiesProperties

Is it simply Standard Model top?

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Many properties could show anomalies…

Many properties could show anomalies…

•Top charge (Kruse: D0 results, CDF soon!): -4/3e close to ruled out. LHC gets 5 separation with 24 pb-1, easy.

•W helicity Kruse: D0/CDF consistent with V-A within statistics,

still poor. LHC gets F+ (FR) to 0.02 with 10 fb-1. However…

• Separate channel fits still look funny!

750 pb-1

Dil+LJ 200 pb-1

Dilepton only 200 pb-1

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Forward-backward asymmetry in top pair production

Forward-backward asymmetry in top pair production

• Afb typically associated with parity-violating weak processes•Not expected in top, but for BSM.•Diagram interference at NLO predicts 3.8% effect. (Kuhn, Rodrigo 99)

•Massive neutral gauge boson Z’ could produce an asymmetry.

•Look for Moriond results from the Tevatron.

500 GeV Z’

mc@NLO

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Flavor-changing Neutral Currents

Flavor-changing Neutral Currents

No FCNCs in SM at tree level▪Allowed in higher order penguins

Light quark penguins observed

▪e.g. b→sγ observed by CLEO in 1995, BR O(10-4)

Not yet observed for top ▪SM BR: O(10-12)

New Physics models predict BRs up to O(10-2)

▪SUSY, Higgs doublet, Warped extra dimensions (J. A. Aguilar-Saavedra, Acta Phys. Polon. B35 (2004) 2695)

Tree level FCNC

Penguin

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FCNC limits so far…FCNC limits so far…

Search in tt sample, tZ, CDF Run I:•ttWb qZ, Wjj, Zl+l-•Limit: BR(tqZ)< 33% @95% CL•ttWb q•Limit: BR(tq)< 3.2% @95% CL

Search for single top, LEP:•e+e- γ*/Z* t q•Limit: BR(tqZ)< 13.7% @ 95% CL•Best limit so far for tZ

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FCNC from Tevatron, LHCFCNC from Tevatron, LHC

New CDF search, ~1fb-1: example exclusion (not final)

Expected limit at 95% C.L. (no signal):▪Anti-tagged sample: 23-30%▪Tagged sample: 18-24%▪Combined: 10-15%▪Previous limits: 13.7% (LEP), 33% (CDF Run I)

CMS sensitivity:

Expected sensitivity (5):▪BR ~ 1.5 x 10-3 (L=10 fb-1)▪BR ~ 4 x 10-4 (L=100 fb-1)

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More top properties to look for anomalies…

More top properties to look for anomalies…

Properties that we are measuring (and LHC/ILC are studying that I didn’t have time to discuss):

•Top anti-top spin correlations: top decays as a bare quark, transfers properties to decay products.

•EWK Top couplings (ttZ, tt): (LHC/ILC) form factors: vector, axial vector, anom mag moment, electric (weak) dipole mom.

•Anomalous top couplings:

W helicity: right-handed PR

New coupling: no righ-handed,Interference effects (tough!)

New Physics in Top New Physics in Top Quark SamplesQuark Samples

Are top-like events really unknown physics?

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One of the first things to measure is the top pair production rate.

Why is measuring the rate of top production important?

• Higher cross section than predicted could be a sign of non-standard model production mechanisms

Resonant state X tt OR Anomalous couplings in QCD?

• It could also mean new physics in the top sample!

Production Cross Section

Nevents - Nbackground(tt) Luminosity *

Measuring top pair production Measuring top pair production

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Run 1: Excess in the b-tagged 2-jet bin sample

Run 1: Excess in the b-tagged 2-jet bin sample

Observed excess of b-tags in the 2 jet bin

Too many SVX double tags (more than one b-tagged jet/event)

Too many multiple tags (more than one b-tag/jet)

A lot of speculation, but nothing solid.

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Lepton+Jets: How’re the double tags?

Lepton+Jets: How’re the double tags?

L=695pb-1

Signal: lepton+ ≥3 jets, MET, ≥1 b-tag

(tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=8.8±1.2(stat)±1.7(sys) pb

CDF

7-input neural Network, no tag

required

signal

Signal: lepton+ ≥3 jets, MET, ≥2 b-tags!

signalCDF

L=695pb-1

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Lepton+Jets channel cross sections

Lepton+Jets channel cross sections

Signal: lepton+ ≥3 jets, MET

L=695pb-1

Signal: lepton+ ≥3 jets, MET, ≥1 b-tag

(tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=6.0±0.6(stat)±1.1(sys) pb

CDF

7-input neural Network, no tag

required

L=760pb-1

CDFsignal

Consistency 7%Consistency 7%

New physics in top samplesNew physics in top samples

•While on the energy frontier, we look for interesting events on the tails of the top quark distributions

•Can a t’ exist? Can it mimic top?

•Generic 4th chiral generation is consistent with EWK data; can accommodate a heavy Higgs (500 GeV) without any other new physics

• Several SUSY models provide for a 4th generation t’ or mimic top-like signatures (Beautiful Mirrors: Choudhury,

Tait, Wagner)

• Little Higgs models predict a heavy t’ -like particle Idea: use kinematics again to separate t’

from t

Search for massive topSearch for massive top•We use the top mass fitter, and fit observed 2D data distribution of HT vs Mrecon

Variables are ~model- independent, to maintain sensitivity to many BSM

scenarios

Limits on t'Limits on t'

Exclude with 95%CL region of t´ masses below 258 GeV

Data v. ProjectionsData v. Projections

1-d Projection: Fit results for M(t) = 350 GeV

2-d Scatter: Expected (MC) for M(t) = 400 GeV v. data (black), number points for

~7.5 fb-1

Couple of strange ones…Couple of strange ones…

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Top plus missing ETop plus missing ETTTop plus missing ETop plus missing ETT

•Search for anomalous events that look like top+MET.

SUSY cascades, TAht (L. Wang), … • Similar (based on) t’ search but optimize for extra MET.• Search underway at CDF.

ET mTW

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Physics with top is richPhysics with top is rich

•The top quark is the least known quark, and the most interesting for new physics.

•The top physics program is very active at the Tevatron, and studies are vibrant at the LHC and ILC.

•Beginning to have sensitivity to the unexpected in particle properties and the data samples!

•The top quark is the least known quark, and the most interesting for new physics.

•The top physics program is very active at the Tevatron, and studies are vibrant at the LHC and ILC.

•Beginning to have sensitivity to the unexpected in particle properties and the data samples!

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Forward to the Femtobarn Era!Forward to the Femtobarn Era!• More data makes us smarter !

• It is not just the luminosity factor. We become more daring and more creative.

• New techniques and ideas are making our results more sensitive than expected.

• Let’s hope nature is kind and top physics indeed becomes our window beyond the Standard Model!

Physics with top quarks is just starting !Physics with top quarks is just starting !

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Note to Slide Readers:Note to Slide Readers:•You are

•This talk is best viewed

•Fonts may not agree from

•Contains animations.

•Your mileage may vary.

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“Beauty is Truth, and Truth Beauty”

-- that is allYe Know on Earth,

and All Ye Need to Know!”

-Keats

“Beauty is Truth, and Truth Beauty”

-- that is allYe Know on Earth,

and All Ye Need to Know!”

-Keats

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