Top%20Physics%20at%20CDF

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Top Physics at CDF

• Gervasio Gómez
• Instituto de Física de Cantabria
• Seminari del IFIC, 3-May-2005

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History I

• 1964 CP violation in Kaon system
• 1973 Kobayashi Maskawa predict 3 quark
  generations
• 1970-73 Standard Model (SM)
• 1975-77 discovery of t lepton (3rd generation)
• 1977 resonance observed in pnucleon?mm-
  ?(b-bbar) discovererd
• Study of b quark properties
• Qb-1/3 (1978) y (1982)
• I3-1/2 (1984)
• Implies existence of an additional quark (top)
  3rd generation
• weak isospin partner of the b quark

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Why must top exist?
Once determined
Cancellation of anomalies such as
Requires existence of a t quark with
All anomalies cancel exactly if, for each family
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History II

• 1983 Discovery of W, Z with masses as predicted
  in SM
• 1994 G(Z) in LEP SLC exclude a 4th generation
  neutrino with MnltMZ/2
• Top is almost certainly the last SM fermion
• 1995 precision EW measurements
• Mtop inferred from higher order EW corrections
• which depend on the fermion masses
• Mtop ? 178 GeV/c2
• 1995 discovery of top in CDF and D0
• Mtop ? 175 GeV/c2
• By far the heaviest fundamental particle
• about 200 times heavier than the proton!
• Mass ? EW scale
• Special role in EWSB? (origin of fermionic mass)
• Higgs is the only SM particle which has so far
  eluded detection

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The Standard Model (SM)
SM Fermions
Fermion masses are free parameters of the SM. For
quarks
175 GeV
330 MeV
1.5 GeV
500 MeV
330 MeV
5 GeV
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Mass in the SM
Mechanism through which fermions acquire mass not
fully understood
In SM, Higgs mechanism doublet of scalar
fields weak isospin space
With potential
with m2lt0
ground stateminimumvev
EW scale
Mass term in lagrangian
ground state does not have original L symmetry
spontaneous EWSB
Scalar particle (spin 0) Higgs (not yet observed)
Boson masses
Yukawa coupling for each fermion
Fermion masses
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Tevatron

• P-Pbar
• Collisions every 396 ns
• Beam energy 980 GeV
• ?s 1.96 TeV
• Inst. Lum. 5x1032 cm-2s-1

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CDF Detector
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Top Production at Tevatron
single top
top-antitop pairs
85
2 pb
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1 pb
one top event every 10 BILLION inelastic
collisions
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Top Decay
final state given by W W- decays
Event Classification tt?lnlnbb dilepton
5 tt?lnqqbb leptonjets 30 tt?qqqqbb hadronic
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here lepton e or m
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Top Detection

• Events are energetic
• Large total transverse energy Ht
• Events are central and spherical
• ?lt 2.0, aplanarity
• High energy jets and isolated leptons
• missing Et from neutrino in leptonic modes
• High Et jets
• Two high ET b-jets
• Displaced secondary vertex
• Soft lepton inside jet
• Possible additional jets from gluon radiation
  (isr,fsr)

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Tagging B-jets

• Top events contain B hadrons
• Only 1-2 of dominant Wjets background contains
  heavy flavor
• Great S/B improvement

Top Event Tagging Efficiency False Tag Rate (QCD
jets)
55 0.5
15 3.6
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Top Pair Cross Section

• Measure in different samples
• Understand top kinematics
• Understand heavy flavor content
• Cross check results
• Validate top samples for other top measurements
• Test of SM predictions
• Sensitivity to physics beyond SM
• Background to Higgs and SUSY searches

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Cross Section dileptons

• Selection 2 leptons (e, m), 2 jets, high MET
• Second lepton can be loose -- even an isolated
  track
• Main backgrounds DY, dibosons, fakes
  j?lepton

CDF most precise
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Cross Section ljetsB-tag

• Selection 1 lepton (e, m), gt3 jets, high MET
• Btag
• Main backgrounds WHF, QCD, Wjets (mistags)

CDF most precise
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x-sec ljetskinematics

• Selection 1 lepton (e, m), gt3 jets, high MET
• NO Btag higher statistics, worse S/B
• Main backgrounds Wjets, QCD, EW

kinematic distributions likelihood or NN
CDF most precise
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Cross Section Measurements
Measurements consistent with each other..
dilepton
lepton jets
and with theory
hadronic
error bars redstat, bluetotal
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Top Mass
Mt ? 175 GeV ? Yukawa coupling ? 1
Special role in EWSB?
Dominant parameter in radiative corrections
quadratic in mt , logarithmic in mH
Mt from precision EW measurements
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Top Mass in Run-I
Weight in average 6 7 22 58 7
mH (GeV)
Mtop all-jets D? result is not included in
Tevatron average Mtop 178.0?15.7 GeV/c2
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Measuring Mtop
Challenging
LO ME final state

• Leptonjets
• Undetected neutrino
• Px and Py from Et conservation
• 2 solutions for Pz from MWMln
• Leading 4 jets combinatorics
• 12 possible jet-parton assignments
• 6 with 1 b-tag
• 2 with 2 b-tags
• ISR FSR
• Dileptons
• Less statistics
• 2 undetected neutrinos
• Less combinatorics 2 jets

CDF sees
Largest uncertainty Jet Energy Measurement
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Jet Energy Corrections
Determine true particle, parton jet E from
measured jet E

• Non-linear response
• Uninstrumented regions
• Response to different particles
• Out of cone E loss
• Spectator interactions
• Underlying event

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Jet Energy Uncertainty

• 2004 uncertainty
• used for most mass results shown here
• Dominant systematic uncertainty

• New (2005) systematic uncertainty
• Significant Improvement
• Redoing mass analyses
• Improved results soon

factor of 2 decrease!
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Matrix Element Technique

• Determine mass of the top quark evaluating a
  probability using all the variables in the event,
  integrate over all unknowns
• Sum over all permutations of jets and neutrino
  solutions
• Background process probabilities are or not be
  explicitly included in the likelihood
• Top mass maximize ?i Pi (xMtop)
• Each event has its own probability
• Correct permutation is always considered (along
  with the other eleven)
• All features of individual events are included,
  thereby well measured events contribute more
  information than poorly measured events

W(y,x) is the probability that a parton level
set of variables y will be measured as a set of
variables x
dn? is the differential cross section LO Matrix
element
f(q) is the probability distribution that a
parton will have a momentum q
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Mtop DLM

• Dynamical Likelihood Method ME technique
• Likelihood vs. mt per event from LO ME for
  tt?l4j and transfer functions for quark ET ?
  jet ET
• Minimize -ln L (combined likelihood from all
  events)

Background mapping function measured to true
mass for a given bkg fraction (19 for l4j with
b-tag)
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Template Technique

• Determine mass of the top quark using a quantity
  strongly dependent on the top quark mass Mtop
  (usually Reconstructed Mtop)
• Determine the Reconstructed Mtop per event
  Minimize a ?2 expression for the resolutions and
  kinematic relationships in the ttbar system.
  Choose jet to parton assignment and P?z based on
  best fit quality. Build signal and background
  templates
• Obtain the measurement from the data Compare
  Reconstructed Mtop from data with same from
  randomly generated and simulated signal at
  various input top mass (Mtop) and backgrounds
  using an unbinned likelihood fit

Signal Template
Background Template
Data
Best signal background templates to fit the data
L Lshape x Lbackground
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Newest Template Result
Combined Log(L)
Expected error
NEW
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Other template measurements
b-tagged ljets
Dileptons

• b-tagged ljets w/ multivar templates
• Probability for Mt from likelihood based on MC
  multidimensional templates

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Best Mtop Measurements
error bars redstat bluetotal
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Single Top Search

• Direct measurement of Vtb2
• Sensitive to new physics
• W, anomalous couplings, FCNC
• Final state lepton, MET, 2 jets at least 1
  b-jet
• Challenging
• Small cross section
• tt now background
• Large additional backgrounds

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Single top
MC Templates
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W Helicity
SM (V-A) prediction t?WT left handed W
(30) t?W0 longitudinal W (70)
test of V-A tWb vertex
Kinematic distributions for the different
helicity states are different
Lepton Pt
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W Helicity
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Search for H
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Search for 4th generation t

• Same selection as kinematic top xs
• Fit Ht to t,t,Wjets and QCD
• Likelihood for different Mt

(one such plot for each point)
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Other Top Measurements
Measurement Result
162
126
193
193
109 (runI)
300
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Summary Outlook

• All measurements consistent with SM
• Recently published or submitted
• Measurement of the t anti-t Production Cross
  Section in p anti-p Collisions at S(1/2)1.96
  TeV Using Dilepton Events, Phys. Rev. Lett 93,
  142001 (2004)
• Search for Electroweak Single Top Quark
  Production in p anti-p Collisions at
  S(1/2)1.96 TeV, Phys. Rev. D 71, 012005
  (2005)
• Measurement of the W Boson Polarization in Top
  Decay at CDF at S(1/2)1.8 TeV, Phys. Rev.
  D71, 031101(R) (2005)
• Measurement of the t anti-t Production Cross
  Section in p anti-p Collisions at S(1/2)1.96
  TeV Using Kinematic Fitting of B-Tagged
  LeptonJet Events, hep-ex/0409029
• Measurement of the t anti-t Production Cross
  Section in p anti-p Collisions at S(1/2)1.96
  TeV Using LeptonJet Events with Secondary Vertex
  B-Tagging, hep-ex/0410041
• Search for Anomalous Kinematics in t anti-t
  Dilepton Events at CDF II, hep-ex/0412042
• Reduced Jet Energy Scale uncertainty
• Hope for 2 fb-1 or more by end of 2007
• ds 10 (now 30)
• dm 2-3 GeV (now 4.3 GeV from RunI)
• Single Top possible observation
• dF0 reduced uncertainty (now 50-100)
• Mass limit on t

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Backup Slides
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Template Result from CDF
Log Likelihood vs Mtop, JES
Systematic uncertainties
Source ?Mtop(GeV/c2)
B-jets modeling 0.6
Method 0.5
ISR 0.4
FSR 0.6
Background shape 1.1
PDF 0.3
Other MC modeling 0.4
Total 1.7
JES(s)
Mtop (GeV)
Most of these can be reduced with more data

• Measurement is more precise than the current
  world average!

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SM quick review
SM quark and lepton lagrangian
Predicts all experimental observations of quark
and lepton interactions
Covariant derivative fixed by gauge invariance
under U(1)xSU(2)xSU(3) transformations
Defining
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W Helicity from lepton Pt
l jets
dilepton
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Publishing Mtop for 15 years
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Matrix Element at D?

• Last result from Run I June, 2004
• Reduced the statistical uncertainty from 5.6 to
  3.6 (expected error from 7.4 to 4.4) gt 2.4 times
  more data
• Total uncertainty from 7.3 (leptonjets CDF) to
  5.3 (D0)
• Run II results from D? and CDF coming soon!

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Mass D0 RunI

• Statistical uncertainty reduced 5.6 to 3.6
  GeV/c2
• Equivalent to Lx2.4 !
• Likelihood vs. mt for each event

• Likelihood gives effective weigh to each event
• Maximize combined likelihood to extract mt

mt 180.1 ? 3.6(stat) ? 3.9(syst) GeV/c2
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Template Results from D?

• Topological
• No b-tagging requirement
• Construct a discriminant using topological
  variables (DLB) to improve S/B

ttbar candidates 69 S/B3/1
Reconstructed Mtop (GeV)

• At least one b-tagged jet
• no requirement on discriminant DLB
• First top mass at D? top mass measurement with
  b-tagging

ttbar candidates 94 S/B1/1
Reconstructed Mtop (GeV)
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Other Matrix Element based Mtop

• DLM only a signal probability, requires
  b-tagging
• New results with decrease JES and more data
  coming soon!

• Ideogram Uses same kinematic fit as D? template
  method, and includes DLB discriminant in
  likelihood fit
• Uses background probability

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Implications for MHiggs

• New combined D0 mass
• Mt 179.0 5.1 GeV/c2
• New World Average
• Mt 178.0 4.3 GeV/c2
• Global EW fit using new average
• LEPEWWG method
• (hep-ex 0312023)
• Best-fit MH ? 113 GeV/c2
• Upper limit _at_ 95 C.L.
• 237 GeV/c2

Yellow region excluded (direct search) MH lt
114.4 GeV/c2 _at_95 CL
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Futuro LHC
Una verdadera fábrica de top!
Tevatron x0.18 LHC x0.025
0.8 to 8 ttbar/sec
1 año a baja luminosidad 10 fb-1 8x106 sucesos
ttbar
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CMS y ATLAS
Detectores multi-propósito adaptados al
acelerador LHC Electrónica rápida Alta
granularidad Buena resolución Buena
identificación de jets, muones, missing Et,
vértices desplazados, trazas
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Masa del top en el LHC

• Leptónjets
• Tag 2 b-jets
• Identificar leptón y MET
• Usar jets con Mjj más cercano a Mw
• Reconstruir MtopMjjb

• Pares ttbar de alto Pt
• Back-to-back
• Hemisferios opuestos
• Menos fondo combinatorial
• Menor JES sys (alto Pt de los jets)
• Pero los jets del W se sobreponen
• Sumar todos los clusters en un cono alrededor de
  la dirección del top
• Restar Underlying Event
• Dependencia en DR

Combinando todos los canales dm 1 GeV
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Resonancias
Reconstrucción de Mtt para búsqueda de resonancias

• SM Higgs (BR smaller with respect to the WW
  and ZZ decays)
• MSSM Higgs (H/A, if mH,mAgt2mtop, BR(H/A?tt)100
  for tanß1)
• Otros modelos Technicolor, strong ElectroWeak
  Symmetry Breaking, Topcolor, colorons,

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Single top en LHC
Mecanismos de producción
1) Determinación del vértice tWb Vtb 2) Medición
independiente de la masa 3) Polarización del top
Con 30 fb-1 determinación de cada proceso por
separado
Proceso Señal Fondo S/B
Wg fusion 27k 8.5k 3.1
Wt 6.8k 30k 0.22
W 1.1k 2.4k 0.46
Proceso ?Vtb (stat) ?Vtb (theory)
Wg fusion 0.4 6
Wt 1.4 6
W 2.7 5
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FCNC en desintegraciones de top

• Desintegraciones de FCNC suprimidas
  (Brlt10-13-10-10) en SM
• t ? Zq (CDF Brlt0.137, ALEPH Brlt17, OPAL
  Brlt13.7)
• tt?Wb Zq con W ? ln o jj y Z ? ll-
• Reconstruir t ? Zq ? (ll-)j
• Sensibilidad a Br(t ? Zq) 1.1 X 10-4 (100
  fb-1)
• t ? ?q (CDF Brlt0.032)
• tt ?Wb gq con W ? ln
• Sensibilidad a Br(t ? ?q) 1.0 X 10-4 (100
  fb-1)
• t ? gq
• Fondo de QCD es enorme
• Buscar like-sign tops (ie. tt)
• Fácil identificar dileptones like-sign
• Sensibilidad a Br(t ? gq) 7 X 10-3 (100 fb-1)

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Top más allá del SM
En teorías SUSYGUT, Mtop causa EWSB

• Modelos de ruptura dinámica de la simetría
  electrodébil (EWSB)
• Interacciones modificadas del top en varios
  modelos
• Technicolor
• Top flavor, top seasaw, top-color assisted
  technicolor

Ventana a nueva física y al mecanismo de
generación de masas