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Top Quarks and New Physics
James Wells PASCOS, July 2011
aps.org
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top quark special
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* Most massive and strongly interacHng with EWSB * Flavor physics and other tests not as stringent as lighter flavors – opportuniHes for discovery * Tevatron "anomaly" with AFB(tops) – we will discuss this – LHC now over 4x number of tops
Top Asymmetry at the Tevatron
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p pbar
t
tbar
θ
Assuming CP which implies where
Standard Model PredicHon
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Asymmetry arises at αs3 order.
(Close analogy with QED α3 asymmetry, Berends et al. 1973)
Interference of ISR with FSR:
Interference of box with tree:
AFB(th) = 3.8 +-‐ 0.6 %
Tevatron Measurement
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Ref: CDF note 10436, 9724
Large BSM contribuHon difficult: Illustrate with Axigluons
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So-‐called chiral color theories of various origins.
SU(3)L x SU(3)R breaks to SU(3)c Leaving 8 massive axigluons. Coupling is QCD strength but with γ5
Problem is the asymmetry goes wrong way!
AFB = -‐ 0.13 for mA = 1 TeV
Limit on pure axigluon from AFB(t) may be stronger than from direct searches.
Try more general gV-‐gA couplings
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Ferrario, Rodrigo, 0809.3354
x
Pure axigluon coupling (large negaHve contribuHon to AFB)
Couplings are with respect to the QCD gauge coupling.
x
This point looks good!
Top cross-‐secHon constraint
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x Consistency with total rate is ok.
Ferrario, Rodrigo, 0809.3354
Generic Problem: Difficulty with differenHal cross-‐secHon
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Red line: MX=1.2 TeV gV=1.65 gA=1.55
Data from CDF, “Measurement of the mbar differenHal cross secHon … in 2.7 o-‐1 of CDF II Data”, CDF note 9602 (11 Nov 08).
ICHEP 2010
s-‐channel “fixes” – very challenging
For s-‐channel colored and parity-‐violaHng and flavor-‐diagonal Z’/axigluon:
Have Z’/axigluon couple with to uubar and mbar with opposite sign -‐> posi%ve asymmetry
Have Z’/axigluon mass be greater than 1 TeV -‐> keep direct rate down
Have Z’/axigluon couple with less magnitude to uubar than mbar -‐> keep direct qqbar dijet rate much lower than 9bar rate
Hard to make it all fit together with AFB>10% and evade Tevatron & LHC bounds.
LHC would find it already/soon. See Y. Bai et al. 1101.5203
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AFB from t-‐channel physics
11 Jung, Murayama, Pierce, JW [0907.4112]
V’ contribuHons to Wjj
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D0 not seeing it – resoluHon in the works
CDF: 256 +-‐ 57 events in ~ 150 GeV jj mass peak in 4.3 o-‐1
AFB and inclusive mbar at the LHC
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*
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* is a choice of MZ’ mass and αX compaHble with AFB and σ(mbar)
Jung, Pierce, Murayama, JW, ‘09
Like-‐sign top quarks
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In most basic V’-‐u-‐t or V’-‐d-‐t models, there is nothing to prevent the producHon of like-‐sign top quarks.
CMS [1106.2142]
These two applicable if MZ' > Mt
Like-‐sign top quarks (cont.)
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CMS [1106.2142]
EssenHally all simple t-‐channel AFB ideas are ruled out.
σ(pp-‐>m(j)) < 17 pb at 95% CL
More “complicated” t-‐channel physics
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Basic s-‐channel and basic t-‐channel explanaHons of AFB are not working, for different reasons.
s-‐channel looks more problemaHc to salvage than t-‐channel ideas.
Two t-‐channel ideas:
• Non-‐abelian horizontal symmetry: Jung, Pierce, JW, ’11 • Top quark condensate theories: Cui, Han, Schwartz, ‘11
Non-‐abelian Extension
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Put (t b)R together in an SU(2) doublet. W’+ and W’-‐ raises and lowers “top number” Z’ does not change “top number”
Thus, it is the W’ bosons that are exchanged in t-‐channel to produce the large asymmetry
Difference of W’ and Z’ masses allows mismatch between couplings to quark gauge and mass eigenstates: c=cos(θ)
Like-‐sign top signal is safe for now
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The conservaHon of “top number” forbids like-‐sign top quark producHon
However, violaHons of “top number” come from the small mismatch angle θ between gauge and mass eigenstate quark interacHons with the SU(2)’ bosons.
Processes such as uu -‐> m are forbidden to order sin2θ
Example benchmark points
Small θ angle allows W' to decay to uubar over tubar
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Constraints on model
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LHC 7 TeV predicHon:
AFB=15% for A,B,C
Jung, Pierce, JW, 1103.4835
Single Top ProducHon
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Jung, Pierce, JW, in preparaHon
u
g t t
V' j
j
b
ν
e,µ
Top Condensate Theories
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Top condensate parameter space compaHbility
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Cui, Han, Schwartz, ‘11
Conclusions
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AFB(tops) currently shows tension with the SM
CompaHbility with other top quark observables (like-‐sign tops, invariant mass distribuHon, total rate, single top, etc.) is challenging.
ResulHng theories are ones that would have never been considered otherwise.
AFB(tops) may be correlated with Wjj excess seen at Tevatron, although not necessary and D0 does not see this excess.
CriHcal updates of Tevatron analyses: AFB(tops), Wjj and single top especially.
LHC analyses to look for: dσ/dMmbar and single top especially. AFB(tops) less likely to show deviaHons at this early stage.
Careful: some analyses will not collect new physics contribuHons. See next slide
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q
bso�
W
t
q'
g b
This is targeted, largest contribuHon to single top in SM
CMS analysis: blj + MET for SM signature ("2D analysis") and maybe one extra b ("BDT")
g t t
V' j b
ν
e,µ
u j
New Physics: same signature except one extra non-‐b jet.
b
ν
e,µ
Standard Model
New Physics
