%
%  Trent CAP Colloquium - Discovering Top, Mar 2001
%
\documentstyle[epsfig,colordvi,trent]{slides}

\input latex.macros
\input top.macros
\def\DZero{D$\mbox{0\kern-.55em /}$}
\def\mDZero{{\rm D}\mbox{0\kern-.55em /}}
\def\mGeVcc{{\rm GeV\, c^2}}
%

\newcommand{\tit}[1] {
        \begin{center}
        \normalsize
        \fbox{\Red{#1}} \vspace{.25in}
        \small
        \end{center}
}


\def\met{\mathbin{E\mkern - 11mu/_T}}

\begin{document}

\small

\tit{The Discovery of the Top Quark}

\Start
\vspace{0.5in}
\begin{center}
Pekka Sinervo\\
{\it University of Toronto}
\end{center}

\vspace{0.5in}

\Red{Overview}

\tiny
\begin{itemize}
\item Quarks and the Standard Model 
\item The Role of the Top Quark
\item The Hunt
\item The Discovery
\item What We Know About Top Today
\item Prognostications
\end{itemize}

\tiny

\pagebreak
%
\tit{Structure of Matter}
\small
Some ``high school'' science
\tiny
\begin{itemize}
	\item Matter is made up of atoms
	\item There are about 109 different species!
	\item Atom itself has structure:
	\begin{itemize}
		\item consists of small hard ``core'' (nucleus)
		\begin{itemize}
			\item nucleus made of protons and neutrons
		\end{itemize}
		\item large cloud of electrons 
	\end{itemize}
	\item We can describe all atoms using 3 particle types
	\begin{enumerate}
		\item electrons ($e^-$)
		\item protons ($p$)
		\item neutrons ($n$)
		\\[0.1in]
	\end{enumerate}
\end{itemize}
\small
But there are hundreds of particles like $p$\ and $n$'s
\tiny
\begin{itemize}
	\item Hadrons ($\pi$, K, $\Delta$, N$^\ast$, $\phi$, $J/\psi$,
...)
	\item Leptons ($e^-$, $\mu^-$, $\tau^-$, $\nu$'s)
\end{itemize}
\tiny
\pagebreak
%
%  Intro to SM 
%
\tit{The Standard Model}

\small
The ingredients of the SM are
\tiny
\begin{itemize}
	\item 12 fermions
	\begin{itemize}
		\item 6 quarks (u, d, s, c, b, t)
		\item 6 leptons	($e^-$, $\nu_e$, $\mu$, $\nu_\mu$,
			$\tau$, $\nu_\tau$)
	\end{itemize}
	\item 3 electroweak bosons ($\W^+$, $W^-$, $Z^\circ$,
			$\gamma$)
	\item 8 gluons to describe the strong force
	\item ?? to describe gravity
\\[0.05in]
\end{itemize}

\small
Enormously successful paradigm! 
\tiny
\begin{itemize}
	\item Predicts rich phenomenology
	\item Accurate! (eg. $\delta_{M_z}/M_z \sim 8\times 10^{-5}$)
\\[0.05in]
\end{itemize}

\small
Predicted existence of top quark in late 1970's
\tiny
\begin{itemize}
	\item Higgs boson the only other ``essential'' missing element
\end{itemize}

\pagebreak
\tit{The Quark Picture}
\small
``Quarks R Us''
\tiny
\begin{itemize}
	\item Up-Up-Down $\leftrightarrow$ proton
	\item Up-Down-Down $\leftrightarrow$ neutron
\\[0.05in]
\end{itemize}

\small
Heavier quarks are unstable
\tiny
\begin{itemize}
	\item Decay by emitting a $W^+$\ or $W^-$\ boson
	\begin{itemize}
		\item[] $c \rightarrow W^+ s$
		\item[] $b \rightarrow W^- c$
	\end{itemize}
	\item Lifetimes are $\tau \sim 10^{-12}$~s
\\[0.05in]
\end{itemize}

\small
All sorts of questions:
\tiny
\begin{itemize}
	\item Why are there so many flavours of quarks?
	\item Why do they have their unique properties?
	\item What forces act on them?
\end{itemize}

\pagebreak

\tit{Why a Top Quark?}

In 1977, Lederman et al. discovered a new particle
\tiny
\begin{itemize}
	\item Mass of $9.54\pm0.04$~\GeVcc
	\item Decayed to $\mu^+\mu^-$\ pairs
	\item[$\Rightarrow$] A fifth quark
	\begin{itemize}
		\item $e^+e^-$\ production rate $\Rightarrow$\ $Q=-1/3$
\\[0.05in]
	\end{itemize}
\end{itemize}

\small
Studies implied that the $b$~quark had a missing partner
\tiny
\begin{itemize}
	\item ``Flavour-changing neutral current''
	decays didn't occur
	\begin{itemize}
		\item decays like $b\rightarrow \mu^+\mu^- d$\ not observed
	\end{itemize}
	\item $e^+e^-\rightarrow b\bar{b}$\ scattering suggested
	an $SU(2)$\ state
	\item[$\Rightarrow$] A sixth quark, known as ``top'' or
``truth''
	\begin{itemize}
		\item Would have $Q = +2/3$
	\end{itemize}
\end{itemize}

\pagebreak
\tit{The Top Quark in the Standard Model}
\small
The SM ``needs'' a heavy top quark
\tiny
\begin{itemize}
	\item Loop effects in SM driven by $M_{top}$
	\begin{itemize}
		\item $W/Z$\ boson mass ratio
		\item $b-\bar{b}$\ mixing
	\end{itemize}
\end{itemize}
\vspace{0.3in}
\vbox{
\vskip+0.0in
\hskip+3.0in
\special{psfile=physics_figures/mass_loops.eps  hscale= 50.0 vscale= 50.0}
\vskip-0.2in
}
\vspace{1.8in}
\vbox{
\vskip+0.0in
\hskip+0.0in
\special{psfile=figures/physics_figures/b_bbar_mixing.eps  hscale= 80.0 vscale= 80.0}
\vskip-0.0in
}

\small
However, exact value of $M_{top}$\ not constrained
\tiny
\begin{itemize}
	\item In 1983, knew it had to be large ($\gessim 20$~\GeVcc)
	\item Searches limited by collider centre-of-mass energies
\end{itemize}
\pagebreak

%
\tit{SM Top Quark Phenomenology} 

\small
Top quarks decay via the weak force
\tiny
\begin{itemize}
	\item Predict $\sim100$\% $t\rightarrow W^+ b$
	\item For heavy top ($M_{top}\gessim 100-120$ \GeVcc), decays
	before it hadronises \\[0.1in]
\end{itemize}

\small
Can be viewed as ``pure'' $\beta$\ decay
\tiny
\begin{eqnarray}
\Gamma_{\rm top} &=& {{G_F M_t^3}\over{8\sqrt{2} \pi}} 
   \left( 1 - {{M_W^2}\over{M_t^2}} \right)^2 
   \left( 1 + 2{{M_W^2}\over{M_t^2}} \right) \nonumber \\
&\sim& 175\ {\rm MeV}\ \left( {{M_t}\over{M_W}} \right)^3\ \sim\ 2\
{\rm GeV} \nonumber
\end{eqnarray}
\begin{itemize}
	\item Toponium ($t\bar{t}$) doesn't have time to form
	\item $T$~mesons ($t\bar{q}$) $\sim$\ degenerate (if they had time...)
\\[0.1in]
\end{itemize}

\small
Decay dominated by ``longitudinal $W^+$''
\tiny
\begin{itemize}
	\item Means the $W^+$\ prefers helicity 0
	\item Result of large top and $W^+$\ mass
\end{itemize}	

\pagebreak

\tit{The Hunt for the Top Quark}

\small
SM didn't tell us the top quark mass
\tiny
\begin{itemize}
	\item Search for top quark production in $e^+e^-$\ and $p\bar{p}$\
	\begin{itemize}
		\item Rate decreases sharply with $M_{top}$
		\item Production and decay signature change with mass
		\begin{itemize}
			\item $p\bar{p}\rightarrow W \rightarrow t\bar{b}$\
			\item $e^+e^-  \rightarrow t\bar{t}$\
			\item $p\bar{p}\rightarrow t\bar{t}
\rightarrow W^+b\, W^-\bar{b}$\
\\[0.05in]
		\end{itemize}
	\end{itemize}
\end{itemize}

\small
UA1 experiment at CERN had one ``false call''
\tiny
\begin{itemize}
	\item Observed a handful of $W\rightarrow t\bar{b}$\
candidates in 1983
	\begin{itemize}
		\item Turned into a limit of $M_{top}>42$\ \GeVcc\ by 1985
	\end{itemize}
	\item A search by CDF in 1988-89 found $M_{top}>77$\ \GeVcc
\\[0.05in]
\end{itemize}
\small
By 1992, had new measurements of $M_Z$\ and $M_W$
\tiny
\begin{itemize}
	\item SM predicted top quark with $M_{top} \gessim 140$~\GeVcc
	\item Only place to look was in high-energy $p\bar{p}$\ collisions
	\item Two experiments
	\begin{itemize}
		\item \DZero\ and Collider Detector at Fermilab (CDF)
	\end{itemize}
\end{itemize}
\pagebreak
\pagebreak
\tit{The CDF Detector}
%
\small
Designed to record high-energy \pbarp\ collisions
\tiny
\begin{itemize}
	\item A 5000-ton cylindrical device
	\item Can create an ``image'' of the collision
	\item Originally built in 1982-86 
	\item Seen it's third (and final?) upgrade
\end{itemize}

\centerline{\parbox{6.0in}{\epsfxsize=14cm\epsffile{figures/cdfiso_transp.eps}}}

\pagebreak
%
%  Techniques
%
\tit{Reconstructing Top}

\small
Since top is pair-produced and $\beta$\ decays
\tiny
\begin{itemize}
	\item Expect to see 6 final state particles
\end{itemize}
\vspace{2.0in}
\vbox{
\vskip+7.8in
\hskip-2.0in
\special{psfile=figures/prd_plots/feynman_top_decay.ps  hscale=100.0
vscale=100.0}
\vskip-7.8in
}
\small
Life is normally not that easy -- in reality:

\begin{center}
\epsfysize=3.5in
\epsffile{physics_figures/ttbar_lepton_jets.eps}
\end{center}
\pagebreak
%
% Selecting top decays
%
\tit{Identifying Top Decays in $p\bar{p}$\ Collisions}

\small
In order to identify top candidates
\tiny
\begin{itemize}
	\item Only 1 collision in $\sim 10^{10}$\ expected to
produce a top quark
	\item Search for $W\rightarrow l \nu_l$\ candidate
	\begin{itemize}
		\item Electron or muon with $P_T>20$~\GeVc
		\item Missing transverse energy $\mMEt>20$~GeV
	\end{itemize}
	\item Search for at least one $b$~jet
	\begin{itemize}
		\item Most effective tool is to find a secondary
		vertex
	\end{itemize}
	\item Some evidence of other $W$\ in event
	\begin{itemize}
		\item Either two more jets or another lepton
	\end{itemize}
\end{itemize}

\vbox{
\vskip+3.6in
\hskip+1.3in
\special{psfile=figures/run1b_blessed_plots/dil_57621_45230_tracking_only.eps
hscale= 100.0 vscale= 100.0}
\vskip 0.5in
}
\pagebreak
\pagebreak
\tit{Tagging B Quarks}
%
\small
Must be able to ``see'' b quarks when searching for top
\tiny
\begin{itemize}
	\item Secondary vertex tagging primary technique (SECVTX)
	\begin{itemize}
		\item Identify tracks with large impact parameter 
		\item Search for 2 or 3-track combinations with large $L_{xy}$
	\end{itemize}
% \begin{center}
\parbox{2.0in}{\epsfxsize=5in\epsffile{../higgs_01/shw/btag/perigee-sec2.eps}}
% \end{center}
	\item Can tag $\sim 40$\%\ of top quark events 
\end{itemize}

\pagebreak
%
%  Detailed strategy
%
\tit{Strategy for Detection}
\small
Identify events with a $W^+ \rightarrow l^+ \nu_l$\ signature
\tiny
\begin{itemize}
	\item Require evidence of a second $W$\ boson
	\begin{itemize}
		\item $W \rightarrow e^+\nu_e$\ or $\mu^+\nu_\mu$
		\item $W\rightarrow q^\prime \bar{q}$
	\end{itemize}
	\item At least one more jet ``tagged'' as a $b$~quark jet
\end{itemize}

\small
Look for an excess of such events
\begin{center}
\epsfysize=3.5in
\epsffile{top_counting/svx_njet_top.eps}
\end{center}

\pagebreak

%
%  Its there
%
\tit{Discovery of Top}

\small
Hints of top production appeared as early as 1993
\tiny
\begin{itemize}
	\item CDF published a 61 page PRD in Sep 1994
	\item Gave ``cagey'' label to the reports
	\begin{itemize}
		\item ``Evidence for top quark production...''
	\end{itemize}
	\item \DZero's analysis not as definitive
\\[0.05in]
\end{itemize}

\small
With a factor of two more data, result was unequivocal
\tiny
\begin{itemize}
	\item April 1995, both collaborations announced discovery
	\item Confirmed SM predictions -- $M_{top} \sim
			170-190$~\GeVcc
	\item Gave us a ``free quark'' system to study
	\begin{itemize}
		\item Decays before combining with other quarks
		\item No complications associated with QCD force
	\end{itemize}
\end{itemize}
\pagebreak
%
%
\tit{Convincing ``Smoking Gun'' Events}

\begin{center}
\epsfysize=5.5in
\epsffile{svx_display.eps}
\end{center}

\pagebreak
%
%  Techniques
%
\tit{Status of Collider Experiments}

\small
CDF and \DZero\ collected $\sim110$~\invpb\ of data in 92-96
\tiny
\begin{itemize}
	\item 1.8 TeV $p\bar{p}$\ collisions
	\item Collected events with
	\begin{itemize}
		\item High $P_T$\ leptons ($P_T\gessim10$~\GeVc)
		\item $\MEt>25$~GeV
		\item High $P_T$\ jets ($P_T\gessim100$~\GeVc)
\\[0.05in]
	\end{itemize}
\end{itemize}

\small
Studies have strengthened top quark interpretation
\tiny
\begin{itemize}
	\item Different techniques used to look at the same data
	\begin{itemize}
		\item Kinematic distributions
		\item Neural network approaches
	\end{itemize}
	\item Verified that all decay modes appear to be OK
	\begin{itemize}
		\item See reasonable signals in $\tau$\ lepton final
states
		\item All hadronic modes are also understood
	\end{itemize}
\end{itemize}

\pagebreak
%
%  What do we have now
%
\tit{The Status of Top Today}

\small
CDF has now detected top in virtually all decay modes
\tiny
\begin{itemize}
	\item Lepton + Jets mode (for mass analysis)
	\begin{itemize}
		\item lepton $P_T>20$~\GeVc\ and $\mMEt>20$~GeV
		\item $\ge3$\ jets, $E_T>15$~GeV and $|\eta|<2$
		\item Require 1 $b$-tagged jet OR a 4th jet
		with $E_T>15$
		\item[\Blue{$\Rightarrow$}] \Blue{76 candidates}\
		(expect $31\pm7$\ bkg) \\[0.05in]
	\end{itemize}
%
	\item Dileptons
	\begin{itemize}
		\item 2 leptons with $P_T>20$~\GeVc
		\item Remove Drell-Yan and $Z^\circ$\ background
		\item[\Blue{$\Rightarrow$}] \Blue{9 candidates} 
		($2.4\pm0.5$\ events bkg) 
\\[0.05in]
	\end{itemize}

	\item All hadronic decays
	\begin{itemize}
		\item between 5 and 8 jets ($E_T > 15$~GeV and
		$|\eta|<2.0$)
		\item $\sum E_T > 300$\ GeV + additional kinematic
cuts
		\item[\Blue{$\Rightarrow$}] \Blue{Observe 187 $b$-tagged jets}
		($142\pm11$\ expected bkg)
	\end{itemize}

\end{itemize}

\pagebreak
%
%  What are the Interesting properties
%
\tit{What are the Interesting Top Properties?}

\tiny
\begin{itemize}
	\item Top Quark Mass
	\begin{itemize}
		\item SM constrains it to $M_W/M_Z$ 
		\item Important consistency check of theory
			\\[0.05in]
	\end{itemize}
	\item Top Quark Production Cross Section
	\begin{itemize}
		\item Predicted by QCD with less uncertainties than 
		$\sigma_b$
		\item Look for single top production 
			\\[0.05in]
	\end{itemize}
	\item Top Quark Decay Rates
	\begin{itemize}
		\item Measured $t\rightarrow W^+ b/
			t\rightarrow W^+ q$
		\item Look for $t\rightarrow H^+ b$
			\\[0.05in]
	\end{itemize}
	\item Top Quark Decay Kinematics
	\begin{itemize}
		\item SM expects decay to be polarized
		\item Have made first measurement of polarization
			\\[0.05in]
	\end{itemize}
	\item Single Top Production 
\end{itemize}

\pagebreak

%
%  Top Mass result
%
\tit{Top Quark Mass}

\small
Measurements now limited by statistical uncertainties
\tiny
\begin{itemize}
	\item Overall systematic uncertainty is $\sim 5$~\GeVcc
	\begin{itemize}
		\item Dominated by uncertainties in soft gluon 
		contributions and energy scale
	\end{itemize}
	\item Run I statistics limit systematic uncertainty 
\\[0.05in]
\end{itemize}

\begin{center}
\epsfysize=3.6in
\epsffile[30 140 520 630]{figures/top_mass/ljm_likfit1.ps}
\end{center}

\small
The final Run I values are 
\tiny
\begin{eqnarray}
	M_{top} &=& 176.1 \pm 6.6 \ \mGeVcc\ {\rm (CDF)} \nonumber \\
	M_{top} &=& 172.1 \pm 7.1 \ \mGeVcc\ {\rm (\mDZero)} \nonumber \\
	M_{top} &=& 174.3 \pm 5.1 \ \mGeVcc\ {\rm (Run I)} \nonumber
\end{eqnarray}

\pagebreak

\small
Latest $W$\ boson mass results
\tiny
\begin{eqnarray}
	M_W &=& 80.433\pm0.079\ \mGeVcc\ \ \ {\rm CDF} \nonumber \\
	M_W &=& 80.482\pm0.091\ \mGeVcc\ \ \  {\rm D0} \nonumber \\
	M_W &=& 80.427\pm0.046\ \mGeVcc\ \ \  {\rm LEP2} \nonumber
\end{eqnarray}

\vspace{.1in}
\begin{center}
\epsfysize=5.5in
\epsffile[30 140 520 630]{figures/top_mass/mwmt_cdf_d0_lep2.ps}
\end{center}

\pagebreak

%
%  Top Cross Section
%
\tit{Top Quark Production Cross Section}

\small
The cross section obtained by a fit to 
\tiny
\begin{itemize}
	\item Lepton + jets, dileptons and all hadronic event rates
	\item Depends on $M_{top}$\ because of acceptance
	\item Recent improvement is more accurate $b$-tagging
efficiency
\end{itemize}

\small
\begin{eqnarray}
\sigma_{\mttbar} &=& 6.5^{+1.7}_{-1.4}\ {\rm pb} \nonumber
\end{eqnarray}

\begin{center}
\epsfysize=3.5in
\epsffile[30 140 520 630]{top_sigma/top_xs_cdf_d0.eps}
\end{center}

\tiny
\begin{itemize}
	\item Theory predictions range from 4.7 to 5.5 pb
\end{itemize}

\pagebreak
\tit{Comparison with \DZero}

Measurements by \DZero\ also quite consistent \\[0.5in]

\begin{center}
\epsfysize=5.5in
\epsffile[30 140 520 630]{top_sigma/top_xs_table_new.eps}
\end{center}

\pagebreak
%
%  Wrap up
%
\tit{Run II Forecasts}

\small
Run II has started this spring at $\sqrt{s}=2.0$~TeV
\tiny
\begin{itemize}
	\item CDF had an ``engineering run'' (partial SVX II) last fall
	\item Be taking physics data by July 2001
\\[0.05in]
\end{itemize}

\small
Will be worth the wait
\tiny
\begin{itemize}
	\item Begin with $\sim 1$~\invfb/year per detector
	\item Finish up with $\sim 5$~\invfb/year 
	\item Literal ``Top Factory'' with 
	\begin{itemize}
		\item 300 dilepton events
		\item 3000 tagged lepton+jet events
		\item 1500 events in ``mass sample''
	\end{itemize}
\end{itemize}

\pagebreak

\tit{Top Physics Goals in Run II}

\small
Mass analysis uncertainties scale with statistics
\tiny
\begin{itemize}
	\item Can expect $\delta M_t\sim 3.0$\~\GeVcc
	\item With $\delta M_W \sim 40$~\MeVcc
	\begin{itemize}
		\item Begins to hint at the Higgs boson mass 
		\item Less than $\sim 210$\ \GeVcc?
	\end{itemize}
\begin{eqnarray}
{{\delta M_{Higgs}}\over{M_{Higgs}}} \sim 40\%
\nonumber
\end{eqnarray}
	\item Powerful ``pointer'' for Higgs searches
\\[0.05in]
\end{itemize}

\small
Measure angular correlations and decay kinematics
\tiny
\begin{itemize}
	\item Tell us about the electroweak force
	\item Polarization of $W^+$\ will be measurable
	\item Spin correlations (expect 90\%) also detectable
\\[0.05in]
\end{itemize}

\small
Single top production 
\tiny
\begin{itemize}
	\item Measures the ``width'' of the top quark
	\item Measure $\sigma_t$\ with 10\%\ uncertainty
	\item Measure $V_{tb}$\ with 12\%\ uncertainty
\\[0.05in]
\end{itemize}

\pagebreak
\tit{Expected Run IIa Result}

\begin{center}
\epsfysize=6.5in
\epsffile[30 140 520 630]{figures/top_mass/mwmt_cdfrun2.ps}
\end{center}
\pagebreak

\tit{Summary}

\small
The debut of top is coming to close
\tiny
\begin{itemize}
	\item Have seen that it looks much like a SM fermion
	\item But top mass scale is enigmatic
			\\[0.05in]
\end{itemize}

\small
All this sets the stage for next set of experiments
\tiny
\begin{itemize}
	\item Run for 2-4 years, with goal of $\sim2-15$~\invfb
	\begin{itemize}
	\item[$\Rightarrow$] Increase top quark sample $\times 50$
			\\[0.05in]
	\end{itemize}
\end{itemize}

\small
By the time next generation collider turns on,
\tiny
\begin{itemize}
	\item Top will be pretty well-studied
	\begin{itemize}
		\item Reveal some property that points toward a more 
		complete theory?
		\item Will at least be an important background
	\end{itemize}
	\item Will be able to reconstruct millions at the LHC!
	\begin{itemize}
		\item It will become the ``high-statistics'' probe of
	the next energy scale
	\end{itemize}
\end{itemize}

\end{document}
