1. Searches for Anomalous Top Quark Production at the Tevatron
Andrew Ivanov
University of California, Davis
for the CDF and D0 Collaborations
Top Quark Symposium
April 08, 2005

2. Why the top quark is so special …
Mass of order electroweak scale
May play a special role in the dynamics of EWSB
Serves as a powerful probe of physics beyond the SM
Apr
A. Ivanov, Top Quark Symposium

3. Is the top quark ordinary or exotic ?
Exotic in some way ?! New Physics might reveal itself through
Oblique radiative corrections
Exotic top quark decay modes (scalar bosons, FCNC)
Exotic intermediate heavy states – new gauge bosons or resonances
Ordinary ? Becomes a major background to new physics
Top sample might contain an admixture of exotic processes
Apr
A. Ivanov, Top Quark Symposium

4. Is the top quark ordinary or exotic ?
Exotic in some way ?! New Physics might reveal itself through
Oblique radiative corrections
Exotic top quark decay modes (scalar bosons, FCNC)
Exotic intermediate heavy states – new gauge bosons or resonances
Ordinary ? Becomes a major background to new physics
Top sample might contain an admixture of exotic processes
Focus of
this talk
Apr
A. Ivanov, Top Quark Symposium

5. A. Ivanov, Top Quark Symposium
Outline: Searches for
Resonance in mass of ttbar system
Top quark pT
Anomalous kinematics in top dilepton sample
Anomalous kinematics in lepton + jets sample
Top Charge
Apr
A. Ivanov, Top Quark Symposium

6. Why search for structure in the Mtt spectrum?
Various exotic models predict the existence of particles decaying to tt
Topcolor-Assisted Technicolor
(Hill, Phys Lett. B345, 483 (1995); Hill and Parke Phys. Rev. D49, 4454 (1994))
Extends technicolor models and attempts to explain EWSB by introducing a new strong interaction
Predicts new massive bosons “topgluons” and a topcolor Z’
Apr
A. Ivanov, Top Quark Symposium

7. Run 1: Search for tt Resonances
Each lepton+jets event fit to ttbar hypothesis by constraining W and top masses
Distribution smeared by:
ambiguity in correct jet-parton assignment
detector resolution
B-tagging reduces combinatorics
Select configuration with best 2 fit
Apr
A. Ivanov, Top Quark Symposium

8. Run 1: Search for tt Resonances
Dominant background is from W + jets
Likelihood fit is performed using X->tt templates with various masses
Apr
A. Ivanov, Top Quark Symposium

9. No Evidence for tt Resonance in Run 1
Phys.Rev.Lett. 92, (2004)
Phys.Rev.Lett. 85, 2062 (2000)
Apr
A. Ivanov, Top Quark Symposium

10. Run 1: Limits on Mass of the Topcolor Boson
Model independent search for a narrow resonance Xtt exclude a narrow, leptophobic X boson with a natural width of GX = MX
MX < 560 GeV/c and MX < 480 GeV/c2
MX < 780 GeV/c2 for
GX = 0.04 MX
Apr
A. Ivanov, Top Quark Symposium

11. Run 2: Search continues …
MX = 500 GeV/c2
GX = MX
 = 1pb
MX = 700 GeV/c2
SM ttbar
W + >= 3 jets
Monte Carlo
Use Neural Nets trained with different X masses
Use large statistics - lepton + >=3 jets events sample (no b-tag information)
Fit Mtt distribution to combination of shapes (lepton + jets, use b-tag)
Apr
A. Ivanov, Top Quark Symposium

12. Run 2: Search for Resonances Using Matrix Element
Generator Level
Reconstructed
events
better reconstruction
Employ matrix element (similar to the top mass measurement) information to weigh each parton configuration for direct Mtt reconstruction
Apr
A. Ivanov, Top Quark Symposium

13. Why search for structure in top quark pT spectrum ?
Many exotic models predict sizeable enhancements in the tt cross section at high transverse momenta pT > 200 GeV/c
(T.G. Rizzo , hep-ph/ ; K. Lane, Phys. Rev. D52, 1546 (1995))
e.g. Anomalous chromomagnetic moment
Apr
A. Ivanov, Top Quark Symposium

14. Run 1: Top Quark pT Spectrum
Response functions
Use an iterative procedure to unsmear the distribution of reconstructed top pT momentum
Perform a likelihood fit to extract true top pT
Use superposition of response functions in 4 bins of pT and background template
Apr
A. Ivanov, Top Quark Symposium

15. Run 1: Top Quark pT Spectrum
True pT Bin
(d/dpT) / 
Measurement
SM Expectation R1
0.41 R2
0.43 R3
0.13 R4
0.025
R1+R2
0.84
Top Quark pT Spectrum
Upper limit:
95% C.L.
CDF Run 1
Phys.Rev.Lett. 87, (2001)
Apr
A. Ivanov, Top Quark Symposium

16. Run 2 Search: Top Quarks Kinematics
Variables of interest:
hadronic/leptonic top pT,
ttbar system pT and,
 of the two top quarks, …
Additional jets are source of combinatorial background
Apr
A. Ivanov, Top Quark Symposium

17. Run 1: Anomalies in the Top Dilepton Sample?
1 ev.
7 ev.
Flavor asymmetry:
an excess of em events
An excess of events with
large missing transverse ET
and lepton pT
Apr
A. Ivanov, Top Quark Symposium

18. A Subset of Run 1 Dilepton Events
In better agreement with decays of SUSY quarks with masses around 300 GeV -
hep-ph/
[Barnett and Hall, Phys. Rev. Lett (1996)]
MEt+Et(l1)+Et(l2) [GeV]
max(MT1,MT2) [GeV]
sqrt(MT1*MT2) [GeV]
ql [deg]
CDFI D0
tt MC
SUSY MC
Data:
Stnd Model D0
SUSY ???
CDF
Apr
A. Ivanov, Top Quark Symposium

19. SM Kinematic Test with Run 2 Dilepton Events
Stay model-independent
Choose a-priori potentially sensitive to new physics kinematic variables
Perform Kolmogorov-Smirnov consistency test between data and Monte Carlo expectation
Search for and isolate a subset with the most non-SM features (SUSY events?!)
SUSY fraction
Chance to find 3 evidence
50%
30%
25%
10%
7 %
Sensitivity
given 13 events
observed
(kinematics only)
Apr
A. Ivanov, Top Quark Symposium

20. Kinematics in Run 2 Top Dilepton Sample
Missing ET
Leading lepton pT ?
Df (leading lepton, met)
“topness” = ttbar decay
goodness-of-fit
more top-like
Overall agreement of % mainly due to an excess at low lepton pT
Apr
A. Ivanov, Top Quark Symposium

21. Run 2 Dilepton events FERMILAB-PUB-04-396-E
Phys.Rev.Lett. 93, (2004)
FERMILAB-PUB E
( Subm. to Phys.Rev.Lett.)
1 ev.
3 ev.
9 ev.
“topness”
Low pT-lepton events are
accompanied with b-jets -
likely being from tt
Flavor asymmetry remains?!..
More data to come
Apr
A. Ivanov, Top Quark Symposium

22. New Particles Decaying to Wq?
Can be a fourth generation up-type quark
He/Polonsky/Su (hep-ph/ )
a generic 4th chiral generation is consistent with EWK data; accommodates a heavy Higgs (500 GeV) without any other new physics
“Beautiful Mirrors” model
Wagner et al (hep-ph/ )
predicts a new heavy up-type quark decaying to Wb; naturally accomodates the LEP b forward-backward asymmetry results
From the precision EWK data the mass splitting between a t' and a b' quark is relatively small. Therefore if Mt’ < Mb’ + MW: t' -> l  b' (virtual W)
Apr
A. Ivanov, Top Quark Symposium

23. Run 2: Search for t’->Wq
Lepton + jets channel
Use the variable HT = sum of transverse momenta of all objects in the event
Sensitive to any new high-pT physics
Perform a likelihood fit and set a limit on non-SM processes
Data does not prefer
t’ contribution
Apr
A. Ivanov, Top Quark Symposium

24. Projected Limits: Higher Luminosity / New NN Analysis
HT likelihood
sensitivity study
Use Neural Nets trained with different t’ masses
Perform likelihood fit with the NN output variable
t’->Wb
ttbar
W + >= 3 jets
Apr
A. Ivanov, Top Quark Symposium

25. A. Ivanov, Top Quark Symposium
Top Charge
Is it the Standard Model top ?
W.-F. Chang et al.,hep-ph/ proposes an exotic doublet of quarks (Q1, Q4) with charges (-1/3,-4/3) and M ~ 175 GeV/c2
while Mtop ~ 274 GeV/c2
q = -4/3 is consistent with EW data, new b-couplings improve the EW fit (E. Ma et al. , hep-ph/ )
Apr
A. Ivanov, Top Quark Symposium

26. Top Quark Charge Measurement
Determine:
charge of W (lepton)
pairing between W and b
flavor of b-jet
Use both dilepton and lepton + jets samples
Variables to use for flavor b-tagging:
sign of max pT track in b-jet cone
jet charge - sum of charge for tracks inside of the cone
sign of min pT track
sign of fragmentation track
Expect with 500 pb-1 to rule out q = -4/3 b d u B0 p- p+
Apr
A. Ivanov, Top Quark Symposium

27. Top Quark Charge Measurement
Sensitivity Study:
Limit depends on lepton- b-jet mismatching
(fraction of mismatches)
Jet Charge Algorithm: Qjet = qi pTia/  pTia
Apr
A. Ivanov, Top Quark Symposium

28. Near Future is Very Exciting ...
Current Run 2 top analyses in progress utilize datasets of integrated luminosity ~340 pb-1
Results with this amount of data are expected to be reported at the Summer conferences
A lot of work was performed on reducing systematic uncertainties in the past months
Expect better limits and more precise measurements very soon
Many new analyses testing various top properties are in preparation
Apr
A. Ivanov, Top Quark Symposium

29. More Distant Future is Even More Exciting…
More data is on tape
Peak Luminosity beats new records every day
Improved trigger system guarantees a higher purity data
Stay Tuned
Apr
A. Ivanov, Top Quark Symposium