[MUSIC PLAYING]
KENDALL: Thank you
very much, Francis.
Yesterday, Francis
took me aside and said,
in very earnest
terms, I very much
want you to give a
good talk, Henry.
[LAUGHTER]
I said, well, I will
do the best I can.
I can't promise anything.
I think it's an
unrealistic expectation.
People have unrealistic
expectations from time
to time in our society,
and that reminded
me, actually, of
a bumper sticker
that I saw here some time back.
It said, in clear block letters,
US out of North America.
Without arguing the merits of
that case or the lack of merit,
it did seem, like
Francis's suggestion,
to be somewhat unrealistic.
The subject of the talk today--
the subject, certainly, is well
known, I'm sure, to most of you
in the audience.
It is a series of experiments
that were carried out
at Stanford by an MIT/SLAC
collaboration that
started in the early 1960s.
It started to take data in
the deep inelastic reaction
in 1968, and wound down in
the early 70s rather slowly.
It was a very interesting
series of experiments
for the people in it.
We enjoyed it
enormously at the time.
We were aware of how much
fun it was to do that.
Part of this has to do with
what Martin and other people--
Martin Deutsch in his
earlier talk, and others--
referred to as the golden age.
And if you remember the rather
poignant financial diagram
that Bill Wallenmeyer showed
at lunch the other day,
you remember that the
funds, in what I referred to
as the golden age, climbed up
in the period up to about 1970,
and then coasted down again,
and leveled out for some years.
So the golden age is associated,
at least in some part,
with another
translation of the word
gold, which is "gelt," which
was the funds that kept it
all going.
And it really was,
in many ways, an era
which had, for a
period, apparently
unlimited possibilities.
The MIT/SLAC collaboration
was the collaboration-- part
of this was initiated by Jerry
and myself in the early 1960s.
We had both worked at Stanford
and been on the Stanford
faculty, working in
Robert Hofstadter group
on electron scattering, and
when the large machine--
the two mile accelerator--
was being contemplated,
and in fact, construction
plans were being laid,
we wrote Pief Panofsky
a letter and said
we would like to join in that
group, almost all of whom
were our old friends.
Well, it was not just the
two of us that were involved.
This is a list of the
collaborators in that,
and I've taken the liberty--
because this is an
LNS camp gathering--
to underline in red
those people who
either were at MIT at the
time of the collaboration
or had been educated at
MIT, and you could see
there were enough of us so the
SLAC people could not reliably
get away with anything.
[LAUGHTER]
We-- Jerry and I, particularly--
were enormously well,
bountifully supported,
not just financially--
although that seemed to
be the tenor of the time--
but also, in some
sociological sense,
by the physics department under
then-chairman Bill Buckner,
who many of us remember.
He basically
allowed Jerry and me
to become a single hyphenated
professor in the department,
and we were able to split
the travel to SLAC between us
in any way we chose.
I, being single at the time,
over not quite 10 years,
spent nearly a third
of my time out there.
It was one of the first big,
heavy-duty collaborations
that people in the physics
department had engaged in,
and it set the tone for a
lot of the subsequent good
collaborations that have
occurred between LNS people
and work at distant
accelerators.
Now, to begin, to lead into the
subject of electron scattering,
both of us, Jerry
and I, as I said,
had been with
Hofstadter's group.
Hofstadter's principal and
quite great contribution
was to study the elastic
scattering of high energy
electrons from the proton
and from the neutron,
and in summary, the
sort of thing he found
was that as you increase
the momentum transfer,
the observed scattering
cross-sections coasted
down much faster with
momentum transfer
than one would expect from the
scattering of a point charge.
And this is due directly
to the fact that,
as you increase the momentum
transfer, the contributions
to the outgoing wave from
components distributed
over space interfere
more and more
and give you this
dramatic decrease.
And this is interpreted, and
was interpreted at the time,
as the result of the
finite distribution
and finite structure
of the proton.
And later experiments have
carried that curve out further.
And unlike the
nuclear atom, there
was no hint in this extended
data of any hard single center
in the proton.
And there were physicists
who concluded publicly
that therefore, the proton
had no hard constituents
and no core in it.
At least, certainly
not a single core.
Now, the reaction,
which we studied
was the inelastic
scattering of electrons.
This is the Feynman
diagram for them.
The electron travels
along here in vacuum.
There is a single interaction.
Here comes the proton.
There is some momentum transfer,
which can, in the laboratory,
be adjusted, so that
one knows what it is.
There is an energy transfer--
just the difference between the
incoming and outgoing electron
energies.
And there is some
amount of energy
communicated to the proton--
or neutron, as the case may be--
in simply blowing it up.
And that becomes, in
the inelastic case,
a variable, which is
subject to adjustment.
And you study the cross-sections
over a range of inelasticities.
This is a set of
all-purpose equations
that govern the process,
because the elastic scattering
is unique in that there
is no energy communicated
to the struck system,
except recoil energy.
The inelasticity here
has a unique value, which
is for that reaction alone.
Momentum transfer is given here.
I don't need to go over
these equations in detail,
except to note one
or two features
that I'll come to later and use
in some of the later slides.
Much of the development of the
central scattering equation
depends on known
quantum electrodynamics
and it is not a subject
of investigation.
But the unknown structure
of the target system
is buried in these
two functions--
W2 and W1, each of them,
in principle, a function
of two variables,
the inelasticity nu
and the momentum transfer.
Now, without going
into the details of it,
if you look at the scattering
in terms of virtual transverse
and longitudinal photons,
there is a quantity
of interest, which
was measurable
as in some of the later
stages of our experiments,
which is conventionally
called R,
the ratio of the longitudinal
to the transverse yields.
And it turned out, as
we will see in a minute,
to be useful to determine
that because of the role
it played in the validity
of some of the models.
Now it's one thing to write
down a Feynman-- diagram that
is simply paperwork,
but to get at the heart
of these measurements,
you need equipment.
And this is not Martin Deutsch's
tabletop equipment anymore.
Here is the two-mile linear
accelerator at Stanford.
This is Route 285,
which is indeed
out of the radiation field.
It is also not true that
the San Andreas fault cuts
across the accelerator line.
It is, in fact, a quarter
of a mile from the gun.
This machine, the actual
accelerator itself,
is roughly 40 feet underground.
It was at the time--
and may still be-- the single
largest single-cantilevered
structure that the human
race has constructed.
And at the time the
device was built,
it was certainly the most
precise machine of any sort
that had been built. The beams,
after the acceleration was
completed-- which would be
below that point roughly
on the diagram--
were sent into a beam
switchyard and could
be energy analyzed
and deflected into one
of several laboratories.
This early picture does not show
the colliding beam facilities
that were installed later.
Our experiments were done with
a deflection toward the north
into this rather large
250-foot shielded building.
These beams are
biologically very potent,
and the whole building
was heavily shielded.
One could not go in it
during machine operation.
The emergent beam came
out through a pipe
here, and then was
buried in the hill.
This hill never got
the quixotic names
that the earlier hill had in the
High Energy Physics Laboratory,
where it was called
Mount Panofksy.
And rumors were that giant
mutant frogs would lope around
in the evening, having been
affected by the radiation.
You will instantly
recognize this diagram
as an experimentalist's
Feynman diagram.
And like the earlier
Feynman diagram,
the initial beam comes
down here in vacuum.
In our case, in
an aluminum pipe.
I'm tempted to refer to
it as the false vacuum,
but it really isn't.
It's an imperfect vacuum.
Electrons are reflected
in a hydrogen target
there into a large one, or
another magnetic spectrometer,
which were built
for the purpose.
The detector arrays
enable one to determine
the precise scattering angle.
Actually, a number
of scattering angles
were accepted by the
equipment and determined
by the detectors.
The recoil system
in our experiments
was let go by itself.
We made no attempt
to do coincidences
or to study it at all.
This is just one diagram one
of the two large detectors
that we used.
They were fairly
substantial devices.
The primary beams came down
here and were measured, brought
to foci, their
intensities determined,
positions monitored, and so
forth with liquid hydrogen
targets.
They were typically 9 inches
or a foot in diameter or so,
some smaller, some larger, and
upward, a double flat magnet
bend into a substantial
shielded detector housing.
These devices are not large now,
by the conventional detector
sizes used at the
collider, but at the time,
they were very
large instruments,
weighing of the order,
with the shielding,
of several thousand tons.
These things opened
up like clam shells,
giving us access
to the elements.
MIT did much of the detectoral
design and construction,
as well as the electronic
systems in the counting house.
Now, let us leave the
experimenters to their switches
and fuses for a minute, and
turn to a theoretical interlude,
which I'll call the
1968 hadron, which
is the scene, so to
speak, at the time
our experiment started.
As far as the
experimental situation
was concerned in the
late 1950s and 1960s,
there had been a
remarkable series
of discoveries that involved
identifying dozens of hadrons--
hydronic resonances at the
strong interaction machines.
There had been
quite a body of work
done studying pion and proton
scattering from nucleon
targets, and the energies not
being as high as they are now
available, it turns
out that those studies
showed what you would
call soft constituents
and soft interactions.
Namely, cross-sections which
decreased exponentially
with increasing
perpendicular momentum.
And coupled with the
Hofstadter results,
the general picture
of the hadron
was a rather soft device,
which underwent what you
would call soft interactions.
With respect to classification,
Murray Gell-Mann and others
had helped elaborate the
so-called eightfold way, which
had classified these
numerous new discoveries
into identifiable
and sorted arrays.
And in 1964, Gell-Mann,
and independently,
George Zweig proposed that the
basis for these classification
schemes could be constructed
with a mathematical entity
which Murray called quark.
There's been some discussion
about the origin of the name,
and from its inventor,
I will tell you
that he invented the name first,
out of blue sky as a word.
Just a sound, which he would
have spelled Q-U-O-R-K. Later,
he found the word used in--
I think it was, what?
Finnegan's Wake.
And he adopted that
spelling, but retained
the old pronunciation.
So that's where it came from.
They had the unusual property
of requiring fractional charges,
and it was quite a successful
scheme, theoretically.
The proposal of
quarks stimulated
a number of quarks
searches, which
went on for a number of years.
And quarks were searched for
in cosmic rays without success.
They were searched
for by hopefully
being produced in accelerators
and identified there
without success.
And they were searched for
in an array of experiments
reminiscent of the Millikan
oil drop experiment,
searching for fractional
charges without success.
Separately, there was
a body of theory--
the S-matrix theory--
with a number
of elaborations,
which dealt quite well
with the then-known
scattering cross-sections
of various kinds.
Among these, and I don't want
to go into them in great detail,
was vector meson dominance.
Because of the failure to
identify isolated quarks
in the various classes of
experiments in which they had
been searched for,
the proposition
that nucleons were, in
fact, constructed of quarks
had a rather rough time.
There was a very small industry
that looked at the proposition
and tried to calculate
the nucleon properties
and resonance properties,
based on what was called--
is called-- the
constituent quark model.
And the constituent quark
model was, to some extent,
different than the
quarks that were
required as the basis of
the classification schemes.
And this constituent quark
model attracted very, very few
adherents and proponents.
A few people persisted--
Dalitz, Morpurgo, and others--
primarily dealing with
low-energy actions of one sort
or another and hadron
characteristics,
but not attempting to push these
to high-energy, high-momentum
transfer reactions.
The reason that most of
the theoretical community--
including, incidentally, some
of its very distinguished
members--
found that the whole proposition
of constituent quarks
was unattractive was based, as
I mentioned, partly on the idea,
partly on the experimental
evidence that nobody
had produced them or seen them.
Also, on the theoretical
requirement that in order
to be satisfactory
in the models,
they had to employ very,
very strong binding, which
was upsetting.
And the problem is that while
these things were expected
to be spin and a half, they
had symmetric statistics, which
was troublesome.
And of course, the
fractional charge
violated every piece of
experimental evidence
that had, before that
time, been accumulating.
Now, some of these constraints
were removed in some theories,
but nevertheless,
the aggregate of them
made a constituent quark
picture quite unattractive.
And it generally not believed.
One other thread was
the set of theories
called her current algebra.
It was initiated by
Murray Gell-Mann,
and was a quite abstruse theory.
The experimenters in our group--
I think we generally did not
understand it really very well.
And it did not play any
real part in its predictions
in the planning
of our experiment.
But it did have one
current, so to speak,
that affected us later.
Based on the current
algebra ideas,
there was started,
first by Adler, and then
Gross, and Llewellyn Smith and
others, a sum rule industry.
And Jim Bjorken, who
was an old friend,
became involved in that,
and used those techniques
to predict something which
I will come back to later,
called scaling.
So to summarize the
1968 hadron, there
was, at best, a rather
cloudy idea of the dynamics.
There was a quark
model whose successes
were in the mathematical domain,
but whose practical application
as constituents was simply
not really believed.
There were a number of
candidates with theories which,
in principle, would apply
to the sorts of reactions
we were about to study.
One of them, as I mentioned,
was vector meson dominance--
Sam has talked about that--
a heavy photon, if you like.
The reason it was
a live candidate
was because it had been quite
successful in processes that
involve real photons, and as
I've noted on this view graph
here, many people
believed that it
would succeed in dealing with
the virtual photons, which
we could adjust in
our experiments to be
quite far off the mass shelf.
Nevertheless, the expectation is
that this process would happily
let us understand the deep
inelastic cross-section.
And one of the consequences
of adopting this view
was that it was not expected
that one would see anything
more than a continuously
fuzzy proton and neutron.
A couple of quotations on the
possibility of real quarks
being constituents of nucleons
and other strongly interacting
particles--
this is a remark of Murray
Gell-Mann's, or two remarks
taken from a Physics
Letters paper of 1964,
in which it is quite
clear from what
he said that while
he doesn't utterly
reject the idea that there
might be constituents in there,
he certainly doesn't think
that's the first thing.
He's certainly not saying,
well, I think they're there.
Go look for them, folks.
Quite the opposite.
And an even stronger statement
in Kokkede's book on the quark
model, in which he almost refers
to the idea in scathing terms,
referring to it as tentative and
simplistic expression and ill
founded.
Well, so I think one could
feel that we were not too badly
off-base designing equipment
to study the rather
low cross-sections
that were expected
on the basis of the
current thinking.
When we got to make the
first inelastic measurements,
we found something
quite surprising.
This is one of the
first surprises.
And this is the earliest data
in which we observed it--
as a function of momentum
transfer horizontally,
two different cuts
at 2 GeV and 3.
You see the data
moving across here
with hardly any momentum
transfer dependence at all,
and compared with this,
just arbitrarily normalized.
The consequences of
elastic scattering
and the enormous
decrease in yield--
that is a consequence
of the finite structure
of the aggregate
proton when it is
undisturbed in the
elastic reaction.
So this was certainly
a discovery.
And when the dust had
settled and we had a chance
to look around later and compare
what our measurements were
with what our earlier
expectations had been,
we found this.
Measurements that were enormous.
predictions on which the
experimental equipment
had been based.
Lo, there's a factor
of over 40 here.
This was taken at
a primary energy
of 16 GeV, primary
electrons at a scattering
angle of 6 degrees.
Such deviations become
even more pronounced
at larger momentum transfer.
The second discovery,
in a sense,
it was directly suggested to us.
I happened to be doing the
data analysis at the time,
so I was by chance the
fellow that first saw this.
What happened was we--
and I-- had been looking
at the inelastic spectra.
And here are six of them
at different-- this is now
plotted in a different way
than the earlier graph.
Each of these spectra is at
a constant momentum transfer,
and it's plotted as a
function of energy laws.
These are the two independent
variables that you have,
in principle, available.
And you can see on this plot
that the data scatters around.
And you can take my
word that if one expends
the range of momentum transfer,
the rest of this region in here
eventually gets
filled with data,
and there's no obvious
pattern in that.
Jim Bjorken came
to see me one day,
and in his rather
gentle, hesitant way,
he had something
very powerful to say.
He said, well, why don't
you look at the data
that you have accumulated as a
function of a single variable,
a combination of
nu and Q squared,
and see whether this
doesn't explain,
in a consolidated way,
what you are measuring.
And I did that.
There was one parameter in this
that we did not, at that stage,
know, not having
any measurements
of it-- that was that
quantity R that I
mentioned earlier, the ratio
of longitudinal to transverse.
I took that data and plotted
it for the two limiting cases,
R equal infinity
and R equals zero.
And what happened
was a spectacle.
I mean, essentially
under my eyes,
this data consolidated into
a compact universal curve
for either of the
two limiting cases.
And I remember at the
time the little tingle
I had looking at
this, and I recall
thinking how Bohr must have--
not Boher, but
Balmer must have felt
when, with his empirical
expression, whose origins he
had no idea of
theoretically, he had
found this beautiful
understanding
of the series in the
hydrogen atomic spectrum.
So it was clear that
B.J. had really gotten
his hands on something here.
And that was scaling.
And this is the first
plot that you see here,
was the discovery of scaling
deep in the last electron
scattering.
As time went on and as
the program advanced,
we got much better data.
We were able to unscramble
and separate the contributions
from the two inelastic form
factors that I mentioned.
Each of them turned out
indeed to be a function
of a single variable.
I'll come to its
specifications in a minute.
But you see them
here, consolidating
a wide range of new and Q
squared in two relatively
universal curves.
Now, as the experiments
continued and became
more precise and
we got more data,
it was found that there
were minor variations--
that this was not an
absolutely strict rule.
There was some scale
breaking, but it
was of a very small character
compared to the gross scaling
that was observed.
So this has ultimately
become, effectively,
almost a law of nature.
Now, to be specific about what
B.J. had done, as I mentioned,
based on rather arcane
application of current algebra,
he had predicted what now bears
his name-- the Bjorken scaling
and the Bjorken limit.
And to be specific, in the limit
in which the energy loss goes
to infinity, the
momentum transfer
likewise goes to infinity--
that as this ratio is held
fixed to M nu over Q squared,
that the quantity omega
becomes the variable
on which these structure
functions depend.
I'll pass over the
lower part, which
is elaborated in
this next slide,
because it was not very long
after those first measurements,
when people were scratching
their head over their meaning,
that Feynman came up to visit
us in the summer of 1964
and heard about
these measurements.
And he had been attempting
to understand hadron-hadron
interactions on the basis
of a constituent model--
not quarks, just
constituent parts
of a proton, which he gave
the obvious name partons to.
And Feynman went down to
his motel for the night
after talking to
Jerry and others,
and the next day, he came
back full of interest
and excitement, and with
the following picture
that the electron virtual
photon was interacting
with a parton, nature unknown.
And one explained the large
cross-sections by the fact
that these partons
were soon to be,
essentially, point particles.
That took care of that part
of the paired discoveries.
And second, that the scaling
variable came directly out
of this picture, because we were
scattering elastically from one
or another of the
particles in there,
which were point-charged
scattering,
the difference between
scattering off of one of those
and the proton being that A,
they carried some fraction--
each of them--
of the proton's mass,
and they were in motion.
And the scaling
variable is, in fact,
just that relation
which I showed you
earlier for elastic
scattering from the proton
with the single proviso that
you have a quantity in there, x,
or it is an x.
It represents a
fractional mass, which
is that fraction of
the proton's momentum
that the parton happened to be
carrying when it was struck,
and it is struck as,
essentially, a free particle.
This is a picture that I
happened to snap of Feynman
when he came back
late that fall.
This is a muddy Xerox of it,
but there is a color picture
over in the Johnson
Center, where
you can see it in better detail
with his enormous vitality
and interest.
And In that October, he
gave his first public talk
on the parton theory,
the parton not yet
being identified with quarks.
It was a joy to see him operate.
Here is a little
paragraph from the book
he wrote where he put
these things together
a few years later.
Those of you who knew
him can kind of visualize
the enthusiasm he brought to it.
I mean, look at the
wording of this--
"an exciting adventure to try
the idea" that these things are
simply quarks, and
to meet and surmount
the then-still
outstanding obstacles
to that interpretation.
Well, the experiments
did not stop there.
It was a program that went
on for a number of years.
And the stimulation
of these results
into the theoretical community
initiated a very interesting,
almost fascinating interplay
of theory and experiment,
which went on for
a number of years.
And eventually drawing
in other laboratories
with other confirming
measurements,
the experiments
experimental results
were themselves
never challenged,
and were confirmed as
other laboratories looked
at similar analogous reactions.
But the interpretations took
a long while to develop.
It was like watching
the grass grow,
in total contrast to Richter's
discovery of the psi particle,
the J/psi, where at 4:00
in the morning, very little
was happening,
except the humdrum,
incremental studying of counting
rates, and by 8 o'clock,
they were breaking
open champagne bottles
and putting vodka
in the orange juice.
This is quite
different, in our case.
But within a few years--
no, very quickly,
almost the same year--
Callan and Gross showed that in
the framework of this Feynman
parton model, that
you could begin
to get a handle on the
spins of the constituents,
that a particular combination
of these form factors
was one if the spin was a
half and zero if it was zero.
And remember, the mathematical
quarks were to be spin one,
and very quickly, we had
an experimental result.
You see the red line is the
prediction for spin a half,
the green line is spin zero,
and you have no problem deciding
on that one.
The vector meson
dominance proposal
didn't last very long, either.
They, too, ran afoul
of some measurements.
Very soon, we were able to
make determinations of R
not only for the proton,
but for the deuteron,
and by subtraction,
for the neutron itself.
The vector meson dominance
predictions went up in here.
There was some
uncertainty of the angle,
but strikingly different
expected behavior than the data
showed.
And there went the
vector dominance models.
Well, as I mentioned,
this interplay
of theory and
experiment continued
on with more measurements
involving the nucleon now--
that is, our deuteron
and neutron measurements.
And let me just wind
this down by going
on a brief historical
tour of what
happened during the
decade of the 1970s
after the original discovery.
I've told you about the early
theoretical circumstances.
SLAC itself had been
proposed in the period when
many of the
resonances were being
discovered for the first time.
The classification schemes
were in the early 1960s.
Getting SLAC approved
by the Congress
was a fairly arduous problem.
There was considerable
opposition to it--
to some extent, similar
to what has happened
with the superconducting
supercollider--
but was indeed approved in 1961.
The joint collaboration
between us and them
started the following year.
The shovels were out in 1963.
The machine went
on the air in 1967,
on time and within budget.
And they essentially
turned the switch,
and it came right up to beam.
We just got used to that.
What else?
That does not always
happen in later times.
In 1968, as I mentioned, the
first deep inelastic proton
scattering.
Very quickly, Feynman came
in on that with the results
I've discussed.
Those results were presented
in Vienna that September.
I've shown you the
slide of Feynman
actually giving his
first talk at SLAC.
Callan-Gross and the
determination of the spin
potential came in November.
Bjorken and Paschos were
doing sum rule evaluation
as part of BJ's work
on current algebra.
And 1969, our first
experimental results on R,
and the first paper's
published that year.
Then other laboratories
came in on the basis
of the general interest
and excitement that
had been generated.
One of the predictions
from the parton theories
was that the neutrino
scattering data
would show cross-sections
which increased linearly
with the primary energy.
And CERN went back and
looked at earlier data
they had taken on that reaction,
on neutrino cross-sections,
and discovered indeed that
it increased linearly.
So we were beginning to
get outside corroboration
of the results.
The following year, our electron
deuteron scattering program
started, and we very quickly
discovered that the neutron/
proton ratio was not one--
as a number of the
earlier soft proton models
suggested it might be--
but dropped dramatically.
And by the latter
part of that year,
it was already clear
that the parton model
was beginning to be accepted,
that the evidence was beginning
to accumulate.
By the following year,
the [INAUDIBLE] ratio
was found to decrease
dramatically,
down almost to a quarter.
And the theoretical
community simultaneously
was beginning to
focus more and more
on the nature of
the constituents,
on the nature of the partons.
There was a theory
that Drell looked at,
assuming they were
nucleons, if I remember.
But Julius Kuti and
Viki were beginning
to look at the first
of the quark models.
The dedicated
neutrino experiments
were beginning to show
results by late 1971,
and the whole body
of diffracted models
was beginning to be
weeded out and discarded.
And later, some of the
more abstruse predictions
of what then became called
the quark-parton model
began to get some
experimental verification.
The anti-neutrino/neutrino
cross-sections turned out
to favor spin and a half, as the
SLAC earlier results had done.
Because the neutrinos
have no charge,
the fractional
charge peculiarities
which were inherent in
the electron scattering
cross-section did not affect
the neutrino cross-section,
so it was possible to
make a cross determination
to see whether the fractional
electric charges were,
in fact, what one was
seeing in the SLAC yields.
And lo and behold,
the fractional charges
turned out to give
predictions in agreement
with the measurements.
There was a
confirming measurement
of the number of valence quarks.
We had found from some early
evaluations that we could not
account for all of the
momentum carried by the protons
by looking at sums
over cross-sections,
and it was concluded that
at least some fraction--
which looked like about half--
of the proton's
momentum was carried
by entities with which the
electrons did not interact.
And these are now
known as the gluons.
So this is quite
indirect determination,
but that's where
gluons first started
to show their heads
through the shrubbery.
By 1973, a theoretical
development
by Politzer, Gross,
and Wilczek began
to tell us how it
was that we could
conduct scattering from what
appeared to be a free quark.
And yet, these things
remained bound--
were not visible
as free entities.
That was a very important
theoretical development.
And then on the heels of
that came the formulation
of quantum chromodynamics,
and the beginnings
of the understanding of the
small, but quite clearly
observed scale breaking
was that we were seeing.
Well, you can look at the
rest of these results.
What we go through
the subsequent years
has been the subject
of a good deal of what
Sam has been talking
about and earlier talks,
and I think I don't
have to go through that.
But what happened over
the rest of this decade
was a slowly consolidating
feeling that indeed,
the partons were quarks.
Part of this was the
discovery of the J/psi
and other things, which you see.
And by the time the
decade had wound down,
the 1968 hadron was gone.
It was gone forever.
And it was replaced by a
nearly complete theory--
quantum chromodynamics--
which had, by then,
been linked with the
weak interaction theory
to form a theory which, in
principle, one could calculate
with, and which are
entirely replaced
what had been in place before
our experiments had started.
Thank you very much.
[APPLAUSE]
