searches for anomalous top quark production at the tevatron

Searches for Anomalous Top Searches for Anomalous Top Quark Production at the TevatronQuark Production at the Tevatron

Andrew Ivanov University of California, Davis

for the CDF and D0 Collaborations

Top Quark Symposium April 08, 2005

Apr-08-2005 A. Ivanov, Top Quark Symposium 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


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


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


Outline: Searches for 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


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’


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


Run 1: Search for tt Resonances

Dominant background is from W + jets

Likelihood fit is performed using X->tt templates with various masses

CDF


No Evidence for tt Resonance in Run 1

Phys.Rev.Lett. 92, 221804 (2004) Phys.Rev.Lett. 85, 2062 (2000)

CDF


Run 1: Limits on Mass of the Topcolor Boson

Model independent search for a narrow resonance Xtt exclude a narrow, leptophobic X boson with a natural width of X = 0.012 MX

MX < 560 GeV/c2 and MX < 480 GeV/c2

MX < 780 GeV/c2 for X = 0.04 MX

CDF

CDF


Run 2: Search continues …

CDFMX = 500 GeV/c2

X = 0.012 MX = 1pb

Monte Carlo

Fit Mtt distribution to combination of shapes (lepton + jets, use b-tag)

Use Neural Nets trained with different X masses

Use large statistics - lepton + >=3 jets events sample (no b-tag information)

MX = 700 GeV/c2 SM ttbar W + >= 3 jets


Run 2: Search for Resonances Using Matrix Element

Employ matrix element (similar to the top mass measurement) information to weigh each parton configuration for direct M tt

reconstruction

CDF

better reconstruction

Reconstructed events

Generator Level


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/9902273; K. Lane, Phys. Rev. D52, 1546 (1995))

e.g. Anomalous chromomagnetic moment


Run 1: Top Quark pT Spectrum

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

Response functions CDF


Run 1: Top Quark pT Spectrum

Phys.Rev.Lett. 87, 102001 (2001)

Upper limit:

R4(225<Pt<425GeV/c)<0.16 @ 95% C.L.

True pT Bin (d/dpT) / Measurement SM Expectation

R1 0.41

R2 0.43

R3 0.13

R4 0.025

R1+R2 0.84

GeV 75p0 T ≤≤

GeV 150p75 T ≤≤

GeV 225p150 T ≤≤

GeV 300p225 T ≤≤

GeV 150p0 T ≤≤

)()(. ..

.

. syststat210 100080

220210

+−

+−

)()(. ..

.


230230

+−

+−

)()(. ..

.


140120

+−

+−

)()(. ..

.

. syststat0000 02400000

03100000

+−

+−

)()(. ..

.


170170

+−

+−

CDF Run 1

Top Quark pT Spectrum

CDF


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


Run 1: Anomalies in the Top Dilepton Sample?

An excess of events with large missing transverse ET

and lepton pT

Flavor asymmetry: an excess of e events

CDF

1 ev.1 ev.7 ev.


A Subset of Run 1 Dilepton Events

Two (out of 9) CDFI di-lepton events have unexpectedly large MET+ΣEt

lepton,(bothgiveverypoor“fits”totthypothesis);onesucheventexistsinD0sample.(FlaggedbyHallandBarnettascandidatesforSUSYeventsintheirDPF96’paper).

MEt+Et(l1)+Et(l2) [GeV]

max(MT1,MT2) [GeV]sqrt(MT1*MT2) [GeV]

l [deg]

CDFID0

CDFI

hep-ph/9609313In better agreement with decays of SUSY quarks with masses around 300 GeV-

[Barnett and Hall, Phys. Rev. Lett. 77 3506 (1996)]

tt MCSUSY MC

D0

CDF

Data:

SUSY ???

Stnd Model


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?!)

CDF

SUSY fraction Chance to find 3 evidence

50% 50%

30% 25%

10% 7 %

Sensitivity given 13 events

observed(kinematics only)


Kinematics in Run 2 Top Dilepton Sample

Missing ET Leading lepton pT

(leading lepton, met) “topness” = ttbar decay goodness-of-fit

Overall agreement of 1.0-4.5% mainly due to an excess at low lepton pT

more top-like

?

CDF


Run 2 Dilepton events

Low pT-lepton events are

accompanied with b-jets -

likely being from ttFlavor asymmetry remains?!..

More data to come

“topness”

CDF

Phys.Rev.Lett. 93, 142001 (2004)FERMILAB-PUB-04-396-E( Subm. to Phys.Rev.Lett.) CDF

1 ev.3 ev.9 ev.


New Particles Decaying to Wq?

Can be a fourth generation up-type quark He/Polonsky/Su (hep-ph/0102144) 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/ 0109097) 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)


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

CDF

Data does not prefer t’ contribution


Projected Limits: Higher Luminosity / New NN Analysis

CDF

Use Neural Nets trained with different t’ masses

Perform likelihood fit with the NN output variable

HT likelihood sensitivity study

W + >= 3 jets ttbar t’->Wb


Top Charge

Is it the Standard Model top ?

W.-F. Chang et al.,hep-ph/9810531 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/9909537)


Top Quark Charge Measurement

bbdduu

B0

-

bbdduu

B0

+

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

CDF


Top Quark Charge Measurement

Jet Charge Algorithm: Qjet = Σqi pTi

a/ Σ pTia

Sensitivity Study: Limit depends on

lepton- b-jet mismatching

(fraction of mismatches)


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


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

searches for anomalous top quark production at the tevatron

Documents

quark symposiumrun

quark ordinary

quark symposiumis

quark production

quark symposiumoutline

quark symposiumwhy search

quark symposiumno evidence

new physics