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00:00Let's go!
00:30Every age has produced people who think they can discover the hidden secrets of the universe.
00:36But often they tell such extraordinary tales about what they've discovered that it's difficult to believe them.
00:41The French writer Voltaire observed the scientists and natural philosophers of his day with great skepticism.
00:50Scientists who devise systems to explain the secrets of how the universe is made
00:54are like our travelers who go to Constantinople and describe the sultan's harem.
01:00They have seen only the outside walls, but claim to know every detail of what the sultan does with his concubines.
01:14Directly beneath the town that now bears Voltaire's name, Fernet Voltaire,
01:18is a particle accelerator, an atom smasher, that is a modern monument to the scientific enterprise Voltaire mocked.
01:25This is CERN, the European Centre for Nuclear Research.
01:30If Voltaire were alive today, it might be difficult to convince him that some of these scientists are discovering the secrets of the universe.
01:37But even scientists like to relax, and playing at being sub-nuclear particles is just one sign of their familiarity with the complex world of the atom.
01:53In recent years, two new particles have been discovered here, called the W and the Z, and led to a Nobel Prize for the discoverers.
02:06Now a team at CERN is on the track of another particle, called top quark, hoping to repeat the successes of their colleagues.
02:15The structure of the atom is fairly well known now, thanks to 90 years of deeper and deeper probes through the outer shell and into the nucleus,
02:25a hundredth-thousandth the size of the atom.
02:30The nucleus contains most of the mass of the atom in particles called protons and neutrons.
02:37Once scientists had discovered this fact, they were bound to ask,
02:41are there smaller particles that make up protons and neutrons?
02:45It turns out that there are. A group of particles, sometimes called quarks, and sometimes quarks, at the whim of individual scientists.
02:58Quarks come in pairs. The lightest are up quark and down quark.
03:03Then there's a slightly heavier pair called strange and charm.
03:07The heaviest so far discovered is bottom quark, and everyone believes that bottom has a partner, top quark,
03:13that is even more massive and waiting to be discovered.
03:17The race is now on to find top quark, and there are only two horses in the race, CERN and an American laboratory called Fermilab.
03:26The discovery will bring fame and glory to the winning team, and the competition is fierce.
03:31If CERN weren't there running, our guys would be a little more relaxed, and I don't want them to be relaxed.
03:36I don't want them to be on edge, so I think it's very good.
03:39And every time I get a little bit-net message saying what they've achieved with their luminosity, their machine, the number of collisions,
03:48I needle our guys in saying, look what they're doing at CERN. What's the matter with you sluggards?
03:52So I think the competition is, in that sense, beneficial.
03:55But fundamentally, I think the two machines, well, we have to remember, Fermilab machine has three times the energy.
04:02So we have a tremendous task beyond the top, and if I had a choice, if I could arrange the near future,
04:09I would give the top to CERN, and I would like to find the heavy Z, because the heavy Z is much more speculative.
04:16We know the top is there somewhere, but we don't know about the heavy Z, and the heavy Z is the road to grand unification.
04:23In any situation where the discovery potential is high, there's usually more than one experiment which is trying to make the same discovery.
04:32And of course, you want to be sure. You also want to be first.
04:38My opinion has always been that it's better to be right than to be first.
04:42And there have been several occasions in the past when the people who've been first have been wrong.
04:46Parker's caution is understandable, given where he works.
04:51Five years ago, CERN issued this press release announcing, somewhat prematurely, the discovery of top quark.
04:58No one at CERN wants that to happen again.
05:01But mistakes are easy to make in this business.
05:03An experiment to discover new particles is probably one of the most complex scientific experiments there is.
05:09The starting point for the two research teams is a bottle of hydrogen.
05:13Hydrogen is the simplest atom with one proton in its nucleus.
05:17The scientists plan to use a huge electric voltage to rip the protons out of the hydrogen nucleus
05:23and accelerate them to high speeds to create very energetic collisions.
05:30They do this in a high voltage generator.
05:33A powerful electric voltage can pull the atoms apart,
05:37and this apparatus can build up 700,000 volts to send through the container of hydrogen,
05:42releasing the protons from the heart of the atoms.
05:46The protons are pulled by an electric field towards a circular tube, a collider, several kilometres round.
05:51At Fermilab, this collider is called the tevatron,
05:53but there's a similar circuit.
05:54The protons are pulled by an electric field towards a circular tube, a collider, several kilometres round.
05:58At Fermilab, this collider is called the tevatron, but there's a similar circular collider at CERN called the SPS.
06:05The bunches of protons travel around the inside of the inside of the tube many times a second.
06:12Magnetic and electric fields around the tube give the bunch a series around the tube
06:19give the bunch a series of kicks to keep them on track and increase their speed.
06:24Then another bunch of particles called antiprotons is injected to travel in the opposite direction and collide energetically with the protons.
06:36Although the teams have different circular colliders, they work on the same principle.
06:40If they can produce enough energetic collisions, they may create new atomic particles, including, the scientists hope, top quark.
07:02Now these look like very similar machines and they're both avidly searching for this top quark.
07:09That's a hot subject.
07:11But one has to remember that, at least in the Fermilab Collider, the top quark, when we started building this,
07:17we sort of assumed it would already have been discovered.
07:20We didn't know it would be so elusive.
07:22And that depends, of course, on its mass.
07:24We still don't know where it is.
07:25It may be so heavy that it'll be difficult for us to find it.
07:29But we built the collider as a discovery machine, if you like.
07:32It's got the highest energy.
07:34It's exploring beyond the W and the Z, which was the CERN discovery.
07:38For their collider.
07:40We're both looking for the top now because that's obviously something that's there.
07:45You know, one shoe dropped the bottom.
07:47The other shoe has to drop the top.
07:48If we have a bottom, we must have a top.
07:50So where is it?
07:52The most important piece of equipment for each team is the detector, a cluster of sophisticated instruments arranged around the collision point.
08:00The team with the most sensitive detector has a better chance of discovering top quark among the debris of the collisions.
08:06The Fermilab team in America is called CDF, Collider Detector at Fermilab.
08:11And the CERN team is named UA2 after their detector in Underground Area 2.
08:20Today, August 28, 1988, is an important day for the UA2 scientists.
08:25The detector has been moved away from the collider beam to undergo maintenance and tuning up to make sure that all its components are working at peak efficiency.
08:34Over the next three months, the SPS Collider will produce billions of collisions for the UA2 team to analyze for evidence of top quark.
08:42There are 80 scientists in the team, and they come from eight different European countries.
08:57This is the beam pipe, where there will be 150,000 particle collisions a second, timed so that they occur in the center of this circle.
09:05All around the collision point are measuring devices which detect electric charge, or flashes of light, for example,
09:12created by the fragments of debris that spray out from the individual collisions.
09:18The readings from the instruments are fed back to computers that reconstruct a picture of the collision.
09:24Somewhere in the pattern from one collision in a billion, there may be the signature of top quark.
09:30Today, the 600-ton detector is being moved back into the collider path on air cushions like miniature hovercraft,
09:38helped by liberal sprinklings of talcum powder.
09:42Guide rails keep the detector on target as it moves towards the arch between the maintenance hall and the beamline of the accelerator.
09:49As the massive detector moves forward at an inch a second, there's some concern that it doesn't get damaged.
09:59There's a worrying moment as the detector edges towards the gap in the wall.
10:03It looks as if it won't go through.
10:05In fact, some of the foil covering has come loose, making it look as if the detector is larger than it really is.
10:13And the whole instrument slides easily into place, past reminders on the wall of earlier accidents.
10:22Overseeing the operation is Luigi Di Lella, the spokesman for UA2, the nearest they have to a team leader in such a democratic group.
10:30Each of the individual elements is worth hundreds of thousands of pounds.
10:35The challenge of detecting subatomic particles has led scientists and engineers to stretch to the limits their knowledge of materials, electronics and computing.
10:45This device, the inner silicon detector, is wrapped round the beam pipe and is the nearest layer to the collision.
10:51The proton beam from one side and the anti-proton beam from the other side will collide about in the center of this tube.
10:58And on the average, when an interesting interaction has happened, about 30-40 charged particles will emerge from this collision point,
11:07which is infinitesimally small.
11:09So what's happening is these 30-40 particles, they cross one layer after the other.
11:15So once they are out of the vacuum pipe, they cross the first layer of the UA2 detector, which is this inner silicon,
11:23where we have arranged now, on the surface of this cylinder, 192 silicon crystals,
11:29where each crystal is about 300 micron thick.
11:34Here you have a sample of it.
11:36So of these objects, we have 192, once the detector is complete, which sit on this drum.
11:45The device is not just a sensitive detector.
11:47It contains complex computing circuitry to make an instantaneous selection of the most interesting collisions.
11:54The job of the scientists is to produce as many highly energetic collisions per second as possible,
11:59in the hope that a few of them will create top quark.
12:02There's an important figure called the luminosity that measures how well their colliders perform that task.
12:09One of the CDF team explains.
12:11These particles have a certain size.
12:14We call it cross-section.
12:16And it's literally that.
12:17It's just a cross-section.
12:18If you imagine a whole beam of them coming at you,
12:21then the size of the particle depends what chance you have of hitting it.
12:26That's a cross-section.
12:27We measure that in barns, as in can't hit a barn door.
12:31That's the unit.
12:32That's where it comes from.
12:34Now a nanobarn is one billionth of a barn.
12:37And this tells you, luminosity tells you how many events you would get for a cross-section of a nanobarn.
12:45That is, if the particle had a size of one nanobarn, we would have made 50 of them at this point.
12:52The higher the luminosity they can achieve, the more steeply this curve will rise in the coming months,
12:58showing that they've accumulated a good number of collisions.
13:01As the experiment begins, each team weighs up the relative merits of the other.
13:06There are all sorts of factors that could give one team an advantage over the other,
13:10from equipment design to the number and skills of the members of each team.
13:15But there's another factor that's important, the energy the accelerators give to the particles.
13:21The more energetic the collisions, the more likely they are to produce new particles.
13:25And here, Fermilab has a distinct advantage.
13:29The key differences between our run this fall and CERN have to do, of course, with the energy.
13:34We'll be running three times higher energy, and that helps us from a physics point of view.
13:39UA2 has a substantial amount of new equipment, new hardware, to make them more suited for this kind of measurement.
13:48So they will be in a very similar situation to us.
13:53Even though those experiments have run for several years,
13:56they have enough new equipment that they will have to continue to do some check out of that apparatus
14:02in the beginning of their run.
14:04But I'm fully confident they'll get running rather quickly and begin accumulating data.
14:10And their problems, as I say, will be much like ours.
14:13Get the new gear running and then settle down into steady running and collect as much data as you can
14:19and hope, like crazy, the top mass is within your range of detectability.
14:25One factor that might act in UA2's favour is the number of collisions they produce.
14:31We hope very much that we'll get the highest possible number of collisions,
14:37and we are brainwashing the machine people in order to also themselves feel the competition with the United States.
14:44Yesterday I pointed out to them that the previous two quarks, the charm and the bottom quark, had been discovered in the United States,
14:53hoping that they would do also their share of work to have the top discovered here.
14:59As some of the UA2 scientists meet at the beginning of the experiment, they're keen to see whether Luigi's brainwashing has worked.
15:06Earlier they'd been pessimistic about how much useful data they would be able to gather in the experimental run.
15:12Now Luigi brings them news from a meeting he's just had with the accelerator scientists.
15:17The figure they're all interested in here is the luminosity, the measure of the number and intensity of the collisions they might accumulate by Christmas.
15:25If the accelerator scientists can deliver more than two inverse picobarns, the quirky units that measure luminosity, they'll be happy.
15:37Three inverse picobarns is a healthy total to work with, and the prediction is a promising start to the run, provided the promise can be fulfilled.
15:54Over at Fermilab, the CDF team are also confident that they can get off to a good start, as they settle into a daily and usually nightly routine.
16:03The FDA is running over here.
16:05The FDA is running.
16:06In the Teletron control room, dozens of screens tell the scientists how well they're doing.
16:12At the beginning of each run, they're interested in whether or not they've succeeded in injecting six bunches of antiprotons, known as P-bars,
16:19so that they collide regularly with six bunches of protons.
16:23Okay, Terry, go ahead, fire at will.
16:25Okay, injecting P-bars.
16:26Each hump at the top of the screen marks a bunch of protons.
16:29Now they've been joined at the bottom by the first bunch of antiprotons.
16:32Okay, so now this is going to repeat every 40 seconds, okay, for another 160 seconds.
16:39So in 160 seconds, we'll have all of our antiprotons in, evenly spaced in between the six proton bunches, and then we will accelerate.
16:52So now we're actually accelerating.
17:02In case nobody's mentioned that, we're about 99.99998975% the speed of light.
17:11Okay, well, now we have, you can see we have 12 indications of our beam.
17:17We have six proton bunches in, and we have six antiproton bunches in.
17:24Okay, so we have all of our beam that we require for this store, and we have an initial luminosity of what we call 1.64E30.
17:33That tells us that this was a very good shot, considering we get the amount of antiprotons that we took out of the accumulator.
17:42We're much more efficient with this shot, and each shot we try to improve things, okay, and this one is a success.
17:49Okay, so it has lots of beam for the experimenters.
17:53Hopefully they'll get lots of events recorded on tape and make whatever discoveries they're going to make.
17:59So that's it.
18:01During the autumn, everything runs very smoothly, and the team acquires a new spokesman.
18:05It has been a problem in recent weeks, and as I've said to a number of people in my years in experimental physics,
18:13it is the most pleasant problem I've ever had, the problems associated with having too much good data.
18:18We never expected that the accelerator would work this well this soon so that we would have so much data so quickly,
18:24and it's a marvelous problem to have. I recommend it.
18:29At UA2 during the same period, the nightly routine is exactly the same, trying to get enough protons and antiprotons circulating in their accelerator, the SPS,
18:41to produce a good number of collisions. On this evening in November, the results are failing to live up to expectations.
18:47They came in looking very well. Then as we started to accelerate, they stayed in all right, but then as we went through the squeezing process to try and bring the beams down to a very small size,
19:01at the point of interaction where the experiments are, then we lost quite a bit of beam, and so maybe we've got to chew that up a little bit.
19:11The bunches of particles show themselves as peaks on the screen.
19:15There's no problem getting the protons circulating in the right positions, it's the antiprotons that seem to be a problem, as the scientists try to capture them and squeeze them into tight enough bunches.
19:29As the night wears on, the scientists try to work out why they aren't seeing the expected number of antiprotons.
19:36We're going to have other problems, I think, with the cue. Because when we took shots before, the cue was completely wrong.
19:48So let's take this shot and measure it, see what to do next.
19:54There's a real program in here.
19:56Any major experiment will have bad patches like tonight. With equipment as complex as the SPS, there are a million things that can go wrong.
20:04Electric fields, magnets, the vacuum in the tube, the computing circuitry, all have to be considered.
20:13How is the cue, Roger?
20:15The cue? I can't measure it.
20:19We're setting the cue on the currents. We're going to the currents that we know are right.
20:23In fact, overall, during the autumn, the CERN accelerator has been producing more than 70% of the target number of useful collisions.
20:39And nights like this are a frustrating interruption, as UA2 try to gather as much data as possible before Christmas.
20:46UA2.
20:50At the end of the evening, Vince Hatton sums up the day's events.
20:55The way I see it for tonight is that we've got a shot in, and it's quite a reasonable shot.
21:00The physicists can now work for the next 15 or 16 hours.
21:06Tomorrow, we'll try again, and we'll look at some of the problems we've seen today,
21:10and in the quiet of tomorrow morning, look at the results which are all stored on the computer,
21:15look to see where things didn't go quite as well as they should have gone,
21:19and then prepare things for the shot tomorrow afternoon.
21:24It's not up to the standards that we were achieving at the beginning of October.
21:31And, well, we're not sure yet.
21:34It looks as if we're losing more of the antiprotons than we should.
21:38The transmission of the beam into the machine and accelerated and through into squeezing
21:44is not very efficient, and that's something we'll have to look at tomorrow.
21:51For Luigi Di Lella, the fact that the experiment was running in the winter
21:55led to additional complications during the three months from September.
22:01The machine started on schedule on the 12th of September,
22:06I would say within three or four days, was working at Peak Luminosity,
22:11and we were all pleased, and during the first three weeks,
22:15it worked like a Swiss clock, with no fault whatsoever.
22:22And, well, we thought we had succeeded in motivating the machine people
22:28to the point that they had felt really their pride at stake,
22:34and therefore they really had tuned the machine to the best.
22:42And then since then, the machine has been working in sort of an average way,
22:47working very nicely for two or three days, and then being off for various failures.
22:54For example, a thunderstorm would trip the machine off,
22:57and it would be off for something like 24 hours.
23:00And then finally, last week, there was a cold spill over Europe,
23:05and there is a contract between CERN and the French electricity company
23:12that provides electricity to CERN, by which if they decide so,
23:17they can switch us off during working days,
23:20but when the machine goes off for four days, then it's very painful to start it up again.
23:26And, in fact, we are now suffering from the fact that the machine has been off.
23:31They have difficulties in turning it on again and running it at the maximum performance.
23:36When a particle of matter, like a proton, collides with antimatter like antiprotons,
23:41the quarks that make up the particles can produce enough energy to create new particles,
23:46including, the scientists' hope, top quark.
23:49And it really is creation that's taking place, as we now know, thanks to Einstein.
23:55Einstein's famous equation, E equals MC squared, says that energy and mass are forms of the same thing.
24:02The sun, for example, produces heat by continually changing atoms into energy.
24:07This has had at least two modern consequences, the atom bomb and the creation of new subatomic particles.
24:13Just as a small amount of mass in an atom bomb produces a large amount of energy,
24:18the reverse can be made to happen.
24:20If a large amount of energy is concentrated in a very small area,
24:23it can turn into a small amount of new matter,
24:26either a new type of particle or, more often, just other examples of familiar ones.
24:32Most people, I think, have heard of one equation in physics,
24:37which is a famous Einstein equation, E equals MC squared.
24:41What this tells you is that energy and matter are interchangeable.
24:45So the sort of thing which is done in an accelerator
24:48is that you take, say, a proton or an electron, relatively light particles,
24:53you accelerate them in electric fields up to extremely high energies.
24:59Then you've got, say, a proton, for example,
25:02which has, well, in the case of the accelerator here,
25:05about 300 times as much energy as it would do if you just picked it off the table.
25:10Now you collide two of these,
25:12which gives you a total of about 600 times the energy of a normal proton.
25:17This energy, then, can be converted either into energetic particles
25:23or into very massive particles, again, using E equals MC squared,
25:26but in the opposite direction.
25:28What we do is we annihilate matter with antimatter.
25:32By annihilating it, it annihilates completely all the characteristics
25:36of the matter and the antimatter, and you're left with pure energy,
25:39which has no reason to go back into its original form.
25:41It can go into any form that it cares to,
25:43and therefore it's a very good way to create new forms
25:45because it will produce every possible form of matter.
25:48So if you wanted to produce a new generation of quarks,
25:52you can take the good old generations, annihilate one with the other,
25:56and you'll have the energy available to make any of the available generations
26:01up to that mass.
26:02So that's how we aim to produce the top quark.
26:04Top quark has the same mass whether we produce it or not.
26:12It's not that suddenly by doing the experiment we invent a mass for the top quark.
26:18For example, we believe that the top quark, there were lots of them very early in the history of the universe,
26:24and that, for example, when the universe was less than a microsecond old,
26:29there might have been as many top quarks as any other type of quark.
26:33And the top quark then had a definite mass, but that mass was so large that it was unstable,
26:39it broke up, it decayed into lighter particles,
26:41and there weren't any more top quarks in the universe for a long time.
26:45Until now we come along, and by putting enough French electricity into the accelerator,
26:52we produce enough energy maybe to produce top quarks again.
26:56At Christmas 1988, both teams closed down their accelerators until the spring.
27:02After they've had a break, the scientists will start the important task of inspecting the data
27:07they have gathered from millions of collisions to see if any of them has produced top quark.
27:22At the end of each year at CERN, there's a Christmas show satirizing the work of some of the 5,000 scientists who work there.
27:34This year, the international race for the top is portrayed as two competing soap operas,
27:40CERNASTY and Dallas SC, a reference to the new American super collider that is to be built in Texas.
27:48Most of the humor is impenetrable to outsiders, as the men look for top quarks beneath the blouses of the women scientists,
27:55and the women inspect the men for missing energy, a key phrase in the data analysis that is about to start.
28:02But what we really need to beat CERNASTY in the ratings war is a much bigger range.
28:07The script for the Christmas show is written by John Ellis, a theoretical physicist at CERN,
28:12who spends his time thinking about quarks rather than looking for them.
28:15He's confident that UA2 have a good chance in the race.
28:19I think the UA2 group is by now very well prepared.
28:22I mean, they're working with a detector which has been operating for several years.
28:26They understand it reasonably well. They know where all the bodies are buried.
28:29And I think they have a fair chance of doing their analysis quicker than the guys at Fermilab.
28:35Of course, the guys at Fermilab have what's a really key advantage in this business
28:40is they have more energy than what we have here.
28:44That means that it's easier for them to produce the top quark.
28:49In particular, the heavier the top quark is, the more difficult it is to produce it here.
28:55So that's a big advantage of the Americans.
28:59I think the team here is very good. They're very enthusiastic. They're very keen.
29:04They've got all the analysis tools which they need.
29:07So if the top quark is there, I have no doubt they'll find it pretty quickly.
29:12In spite of Ellis' kind words, the experimental physicists often feel misunderstood by their theoretical colleagues.
29:20I think that it would be very instructive for you to interview a theorist in order to discover how little they know about the way experimentalists do their research.
29:37They probably, they don't know anything because they, I think they even don't want to know.
29:43They believe that we use screwdrivers and then whenever, sometimes we find results which we feed to them and it is to them to make sense out of them.
29:53But they haven't yet understood that many of them, not all, I mean, it depends.
30:00Many of them believe that the discovery of the top will be just like one or two events which you suddenly see reconstructed by the computer.
30:08You get a printout, possibly a color printout, and then you go around showing it like a flag and saying this is top, this is top.
30:15This happened for the W and the Z because there was no other process that could simulate events with that configuration.
30:22But for top we know many other background events that can appear like top and are not.
30:28In fact, in the early days of particle physics, new particles were often discovered on the basis of one observation, a golden event it was sometimes called.
30:37A photograph like this, for example, would show a collision that was only explicable if the scientists assumed that this tiny little track here was produced by a new particle.
30:47Champagne corks would pop, a paper would be quickly written, and a Nobel Prize could be in the post.
30:53But the search for top was far less simple.
30:57Out of the millions of collisions that occurred behind this concrete wall, only a few would even look as if they produced top quark.
31:06The streams of data that flowed through these 10,000 cables would have to be sifted to reject most of it and preserve only those collisions that looked promising.
31:20The information about the most promising collisions would be saved on cassette and stored so that the scientists could look at them later.
31:35Two-dimensional pictures could be created of the events that had occurred in the detector days or weeks before by using some of the world's most powerful computers.
31:44The lifetime of top quark was expected to be too short, a hundred million million millionth of a second, for it to show itself directly.
31:52Instead, the scientists looked for a pattern like this, called the signature of top quark.
31:58It consists of an electron, two jets of other particles, and a particle called a neutrino.
32:07But there was one complication. The neutrino was invisible and had to be revealed indirectly with a mathematical trick.
32:16Here's an analogy.
32:21This collision between two snooker balls could not happen in real life on a flat table.
32:26The collision could not leave both the balls going off upwards because all the force of the white ball was going from right to left before the collision.
32:35What actually happened was this.
32:40In fact, it's possible to work out mathematically from the faked collision that there must have been another ball involved, otherwise one of the laws of physics would have been broken.
32:50From this image alone, the path and the mass of the missing particle could be worked out.
32:56In the top signature, there's also a missing ball, the invisible neutrino, whose existence is only revealed when the scientists add up all the energy coming into the collision
33:05and find that some of it has disappeared after the collision, carried away by the neutrino.
33:13There was another problem with the data.
33:15They didn't know how heavy top quark was.
33:17It might actually be too massive a particle for their accelerators to produce.
33:21This possibility made Mel Schochit wary about predicting total success for CDF.
33:28There are two answers.
33:29Certainly, our confidence and our ability to see top, if it's in the mass range where we would be sensitive, has grown,
33:38because the accelerator is performing extremely well.
33:40And in fact, we should wind up with perhaps five times as much data as we had before.
33:46The other answer is one that there's no change because we don't know what mass the top quark has.
33:59And if its mass is too high, we just are not going to be able to see it because an accelerator of this energy won't be able to produce it.
34:07So it's a little bit of, we're doing well, but nature has to be kind to us and put it where we can see it.
34:16The five quarks that have already been discovered all weigh less than 5 GeV, the units of mass.
34:22The experiments are like trying to peer through a window, looking for particles of greater and greater mass.
34:28So far, previous teams have explored as high as 40 GeV without finding top quark.
34:34Now UA2 and CDF are lifting the blind to 60 or even higher.
34:39But the design of the CERN accelerator means that UA2 are unlikely to be able to detect anything heavier than 70 to 90 GeV at the most.
34:49However, CDF's more powerful accelerator could enable them to explore much higher masses.
34:54UA2 know this and pin their hopes on the possibility that top will lie below 85 or 90.
35:01If it doesn't, then CDF will have the feel to themselves.
35:05We have an advantage because the energy here is so much larger.
35:09The range of mass where we can find top in this run is probably up to 100 GeV, maybe a little higher.
35:17At CERN, they can find it if it's as high as 70 and probably not much higher.
35:23So if it's in the range below 70, there's a real dogfight on.
35:27If it's above 70, then we probably have it alone to ourselves.
35:32But of course, we don't know where it is.
35:35There are several different signatures for top.
35:37The Fermilab people, for example, are looking for one that includes a particle called a muon.
35:42But even when they think they've got a perfect signature, what might be a golden event,
35:46they may actually be looking at a forgery.
35:50The reason is that even though the types of event signatures that we're looking for are very rare
35:59and very characteristic of the production decay of a top quart,
36:03there are other processes that we know about that can occur at a very improbable level
36:09that could simulate or look the same.
36:11So consequently, if we observe one very characteristic event, such as, for example, an electron and muon,
36:18we cannot immediately conclude that that came only from the production of a top quart.
36:23We have to understand all of the other possible processes that could have taken place
36:28and in some way given a similar signature.
36:30Now, in general, it's therefore impossible to tell from the observation of a single event that once discovered something new.
36:37As the data analysis begins, the UA2 collaboration meets in Geneva to hear some early results.
36:47Andy Parker has boiled 45,000 promising collisions down to 19 events that have a top signature.
36:54But that's not enough.
36:55As Brig Williams explained, the scientists expect to see a certain number of collisions that look like top.
37:01The question is, have they seen significantly more than they expected?
37:05The more events you have, the more confident you can be of your analysis
37:14because you're attempting to dig out an excess of events over what you see.
37:18Now, if you have ten events in your sample and you expected five,
37:24you're not very confident that that's an excess.
37:26If you have 100 events in your sample and you expected 50, you're very confident that it's an excess.
37:32So, the amount of data counts.
37:35Even though you may, in principle, have what looks like a signal, you really need that data to be sure.
37:41Once serious results start emerging, rumours begin to flow between the two laboratories.
37:47UA2 that they had a candidate sample but that they didn't understand the background.
37:53Because I heard that second-hand from LA.
37:56With so many people in each team, it's difficult to keep things quiet.
38:00And the fierce competition inflates every result, however insignificant, to giant proportions.
38:05There was a rumour that was going through the halls of CERN last year that we had discovered the top at 60 GeV.
38:16And so, to be cute, one of the physicists here sent back a message saying,
38:22we have not discovered the top at 60 GeV.
38:25And, of course, we had nothing at all.
38:27But it's a bit of a game, but on the other hand, it's obviously very important.
38:32And if it's to be found, we want to find it first.
38:36Rumours become feverish as the two teams prepare to report their progress at an international physics conference
38:43to be held in Italy in February this year.
38:48The ski resort of La Tuile, in the Aosta Valley, is to be host to a conference about the current state of particle physics.
38:55And there's to be a session on the search for top quark, at which a member of each team will give a talk.
39:04Each team holds an in-house meeting before La Tuile, during which they discuss exactly how much information
39:10to allow their own representative to give away.
39:17The Fermilab meeting is a lively one.
39:19At the conference, the other delegates would be looking for some sort of statement
39:23from the CDF delegate, Mel Schochit, about a limit for the mass of top quark.
39:28But how strong could that statement be?
39:31Listen, John, you yourself said you would agree with 50 to 60, so what we're quibbling about is 45 to 50.
39:36Fine, 50, 60, fine, okay.
39:38But 45 to 60 is not fine, okay.
39:4045 by 34 is I don't believe that.
39:42I don't personally think that it's really important, at the present time, to really make a very strong statement on that.
39:49Because my worry is that if by some chance, I mean, mischance, we are wrong, then we are in a bad shape.
39:58In fact, some of the team feel in their bones that top quark is probably heavier than 80 GEV.
40:03But such gut feelings are no substitute for careful measurement.
40:06Is that acceptable or not?
40:08The thing that we have to be careful about is that we don't present things in a premature fashion.
40:17The last thing that you want to do is do a partial analysis, make a conclusion, announce it publicly, and then two weeks later find out that, in fact, you hadn't completed it.
40:29And when you completed it, it's not there.
40:31Over at CERN, the collaboration has similar worries about what to allow their representative, Jean-Paul Repelin, to report.
40:38We were afraid that already at this early stage, they could give limits which would have been much higher than the one, I mean much higher, higher say, than the one we were able to give.
40:53And that's not a nice situation where you come with a result and the physicist who is going to talk after you is going to show that, in fact, your results are not so interesting because he's pushing the results even further.
41:08So in that sense, that was our worry.
41:12And it seems that, in fact, in CDF they are also, strangely enough, they were also in the same situation where they were afraid that we were going to have results or limits higher than one could expect.
41:33As the two teams assemble at the conference hotel, Choquet and Repelin have a polite but wary conversation.
41:48Neither is giving too much away.
41:50Even at this stage, each of them is prepared for the other to pull something out of the hat.
41:54Although the rumor mill has ruled out the possibility that either team has yet discovered top, there is still a lot of latitude in the possible mass limit that will be reported.
42:03It's half a blessing if we can rule out the mass range that UA2 is sensitive.
42:08Because although it's true that our sensitivity goes well beyond theirs, in the current run, it doesn't go that far beyond theirs.
42:17And if we rule out the mass range where they're sensitive, we've ruled out more than half of our available mass range also.
42:24And it would be nice if we were the ones to discover it.
42:27On the other hand, I'd like someone to discover it.
42:30I'm not quite sure.
42:34And what we will say, even putting aside the semi-qualitative rather than quantitative statement, it will not rule out the full mass range that they're sensitive to.
42:45They're sensitive up to something over 70 GeV.
42:51And what I will say tomorrow is 60 GeV.
42:56So it's not there yet.
42:59And from what I hear, they will say something similar.
43:02That they think they would have seen something if it were between 40 and 60 and that they haven't.
43:07But that's the rumor I hear.
43:10Through that.
43:15Though Repelin is the UA2 delegate,
43:19at the last minute, Luigi these pipe and some other members of the team
43:22decide to battle their way through the snow to hear Schoquet's talk, just in case he has any surprises.
43:27In particular, Luigi wants to know whether CDF have seen any e-mu pairs,
43:32one of their possible signatures for top.
43:34If they haven't seen any, that could mean top is much heavier than they hoped.
43:39I don't know what Mel Schochert will say today,
43:42but he will probably say something of the order of 60 to 70.
43:46I really don't know.
43:47But in the near future, if their experiment works well,
43:52and if they don't see e-mu pairs,
43:53they should be able to then, say, exclude top quarks with a mass smaller than 80 to 90 GeV,
44:03which means exclude automatically our possibility to actually see the top.
44:07Now, since these masses are totally unpredicted by theory,
44:10I mean, then if they say the top quark is heavier than 75,
44:15we would still have about 15 GeV of window.
44:18But this window would be open for us only when we have taken the full statistics.
44:21So I would say, and analysed all the data,
44:25so I would say by the end of the summer we would be able to say something.
44:28And by that time, they may have pushed this limit even further.
44:32So if indeed they say today that they exclude a top larger than,
44:39a top lighter than 75 GeV,
44:43it would probably mean that we would not see it at CERN.
44:47The session on top quark is a reminder that even negative findings can be useful.
44:51I show no evidence for the presence of the top in the mass range 40 to 60,
44:57where the detector is found to have a good sensitivity.
45:00And it's clear that we are not swamped by background.
45:03Not finding top quark so far tells the scientists something useful about its mass.
45:09If the experiment has been done properly and failed to find it up to 60 GeV,
45:13then the elusive particle must be heavier than the scientists hoped.
45:19Of course, Dilella already knows this,
45:21and he waits to hear whether Schochit has the same message.
45:23There's a number of final state channels.
45:26There's still a great deal of work which is in progress and has to be done.
45:29If the current analysis holds up and we accept the results from the E plus E minus colliders,
45:35then the mass of the top is not likely to be below approximately 60 GeV over C squared,
45:40again assuming the normal term...
45:41Schochit has also announced that top is heavier than 60 GeV,
45:44but Dilella senses that when the data are fully analyzed,
45:47the particle may well prove to be even heavier and out of UA2's reach.
45:51Well, I think it's certainly very difficult for us.
45:55If there is a top, it has to be lighter than 75 to 80,
46:01and there it's really very difficult.
46:03It's also difficult for them.
46:05Mel said it clearly that if the top has a mass that is similar to the W,
46:11it's very difficult to see, and I agree with him entirely.
46:14So that's why we say, well, we are sensitive.
46:17We can see it relatively easily, up to 70 GeV,
46:21and then it really becomes difficult.
46:23And since I believe now from my feeling is that it's heavier than 60,
46:28then our window is really very little.
46:30Knowing Luigi, I think his feelings are mixed.
46:34On the one hand, the result that we have indicates that they're less likely to find it.
46:43On the other hand, we haven't come out definitively and said that the mass of the top is above 75 GeV,
46:50which would really put him out of business.
46:51So he's probably not as happy as he would like to be,
46:56but not as despondent as he could have been.
46:58At a chamber music concert for the conference delegates,
47:10the two rival team members sit side by side.
47:14They must both be thinking about the implications of the failure to find top quark so far.
47:18It's looking as if the window of exploration has got to be opened wider,
47:27maybe up to 140 or 150 GeV,
47:30and only CDF have the energy to do that.
47:33It probably also means that they can relax a little,
47:36knowing that the heat is off.
47:37In July, the UA2 collaboration meet in Cambridge to discuss where they've reached
47:46and where to go next.
47:48The main topic of discussion is the failure to find top quark.
47:53In the UA2 collaboration, we feel that it was a little bit disappointing not to see the top,
48:00because the fact that we were able to establish a limit
48:03means that if it had existed, we would have seen it.
48:08And so, well, it's a dirty trick of nature to have put the top quark so heavy.
48:15So my impression is, at present,
48:19that if top is to be discovered at all,
48:22it will be discovered by CDF or the other new experiment called D0,
48:27which comes into operation in 1991 at Fermilab,
48:31provided the machine is improved.
48:34In other words, provided the luminosity of the Tevatron Collider is boosted up by a factor of about 5 to 10,
48:44for which they have plans, but not yet the money.
48:47It's the way life goes.
48:49There are only a very small number of fundamental particles in the universe,
48:53and you have to be very lucky to find one.
48:55We were in a unique position that we had the opportunity to look where nobody else could look and had looked before.
49:01And obviously the odds were reasonable,
49:05but we know that the theoretical upper limit on the top quark mass is at 200 GeV,
49:10which is a long way from 70.
49:12So I guess the odds were probably something like 3 to 1 against, always.
49:17And at least we did a good experiment and we've closed off that particular piece.
49:23I'm quite happy.
49:24I mean, the most disappointing thing would be to have failed to do the experiment properly
49:29so that we didn't have confidence in the result.
49:32That would mean that we'd done a bad job.
49:34But as it is, I'm content that we did a good job in the time,
49:38and I'm very pleased that CDF didn't find it before us.
49:42For the two teams, there's still plenty of physics to be done.
49:46Although the search for top has taken a lot of their energy,
49:48they're also exploring many other aspects of the intricate world of the atomic nucleus.
49:53Particles like Ws and Zs, muons and gluons, neutrinos and fotinos.
49:58And Mel Schochit, ever optimistic,
50:01finds cause for hope in the very elusiveness of the particle he and his team have failed to find.
50:06It's natural to have expected that there would be a great deal of disappointment
50:11that we didn't discover the top so far.
50:15And I think that there is a little bit of that.
50:18Certainly, we would rather have found it than not.
50:22But it's interesting in that not having found it,
50:26and let's assume that when we completely analyze this year's data,
50:29we will not have seen it.
50:31And that would indicate that the mass is above 80 or 90 GeV.
50:35The higher the mass of the top is, the more extraordinary the top quark is.
50:41Why is it so heavy where all of the other quarks are so much lighter?
50:45It becomes more and more extraordinary the heavier it becomes,
50:49and may point to rather deep implications
50:55about the structure of elementary particles.
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