Thank you very much, Professor Fuchs, for that nice introduction. I would like to talk today on some applications of some new methods of detection to high energy processes. And as you know, with experiments

in elementary particles and high energy physics, there generally is a rather large group needed to carry out such work. And in this particular case, I would like to mention the names of my collaborators who've actually

done almost all the work. B.L. Barron, J.F. Crawford, R.L. Ford, E.B. Hughes, Reinhold Koze, Av Bon, Pierre Lacoutre, Terry Martin, L.H. O'Neill, R. Rand, R.F. Schilling, J. Simpson,

and Rolf Vadimaya of Bon also. So we have had a collaboration here with physicists from this country, and actually there are some others there who are working with us from England. Although there are many individuals involved

in these experiments, there is a personal side to this, too. And with your permission, I'd like to mention this and go back a little into the history of development of the subject

that I'm going to be talking about. First of all, in 1948, I was working at Princeton. And after the pioneering work of Kalman with scintillation counters, I started to work with a crystalline material

called sodium iodide. And I put a little thallium impurity into this crystal and observed that it made a very good scintillation detector. In 1950, with John McIntyre, we could

show that these crystals gave very good spectroscopic information. That is to say, we could detect gamma rays with these crystals. And by the size of the light flash, we could tell what the energy of the gamma ray was.

And the accuracy was something better than had been achieved by any other method up to that time, at least any other method with such a high efficiency, close to 100%.

I dropped that field after going to Stanford University and began to do electron scattering work there. And in 1955, observed a structure in the proton, in the charge distribution of the proton, you might say.

And at that time, the work was done with Robert McAllister. We gave an interpretation of the experimental findings in terms of a form factor, or that amounts to, in a loose way of talking,

to a charge distribution within the proton. Now, in order to make that kind of interpretation, one had to assume that quantum electrodynamics was valid at such small distances. And the distances were on the order of 10 to the minus 13 centimeters.

About five years ago, or five or six years ago, several of us at Stanford took up the sodium iodide technique again, the scintillation technique, and tried to make large-sized detectors so that we could measure the energies of gamma rays and other particles

of very high energy. And I've already spoken, I think, twice at these meetings about this subject. Now, it turns out that by some kind of accident, these large crystals, and I'll show some samples

of the kind of thing that we're using nowadays, have a direct application to the testing of electrodynamics at the highest energies and momentum transfers ever observed. And I want to show you some of that material today.

It isn't quite complete because it isn't complete at all, because our actual running time starts in about four or five days. But I have some information already

which was involved in setting up the experiment that will give you an indication of what we may be finding in the next month or so. And some of the information I'm going to present today is presented here for the first time anywhere. So it is really original material.

The electrodynamics test that I'm referring to has been carried out and will be carried out at SLAC, at the Stanford Linear Accelerator Center at Stanford, in what is called the colliding beam facility SPEAR.

And in that machine at the present time, one has a positron circulating beam and an electron circulating beam that collide in two interaction regions. And our experiment is in one of those interaction regions. And the energy in the positrons and in the electrons

is individually about 2.6 or 2.7 GeV. But before I go into the details, I would like to give you an introduction to the techniques

because a great many of you have not been here before. And I think the best way I can do this is to show you some slides. And I have a rather large number of slides. And I hope I won't bore you with those.

But before I begin, I'd just like to make a comment here. This talk is going to be developed around the following items. The large crystal techniques to which I referred

can be applied to many different things. And we have carried out essentially two experiments. And I want to use these as illustrations of what can be done. The first was an inclusive reaction using negative pions on protons,

giving neutral pions plus anything. This is called an inclusive reaction. And all that one studies in our experiment is the neutral pion. We determine the angular distribution and the energy of the neutral pion produced in this reaction.

I'll show some details. We've also done pi plus plus proton going to pi 0 plus x. And then it's possible to compare these two reactions with those that are already known

and have been investigated using charged pions here and charged pions here. And I'll show that comparison. These two experiments were done at about 14 GeV for the incident pion. So this is the first experiment, which

I will talk about in the form of an application of these techniques. The second experiment is the one that I've already referred to. And this is carried out at the colliding beams apparatus.

And this involves E plus plus E minus going to several different things. First of all, you can have E plus plus E minus. That is just the elastic scattering.

And you can also have this, of course. Then this same reaction can go to a 2 gamma annihilation. And then this can go to mu plus plus mu minus and that.

And then there is another reaction here, E plus plus E minus, typically, plus a gamma ray, where the gamma ray is very energetic and has about the same properties as one of the electrons. The other one is kind of a spectator in the process.

Then, of course, there are many other processes that go on, such as hadron production and so on. And while our apparatus can detect these things, in the proposal for the experiment, we only talked about doing these experiments.

And so there isn't enough time, really, to investigate any of the other things. And furthermore, the proposal to do this experiment, by the way, this is done at 2.7 GeV for the positron

and 2.7 GeV for the electron. So the energy in the center of mass system is about 5.4 GeV. So it's a very high energy as far as these kinds of processes go.

Now, it turns out that in the original proposal to do this work, it was assumed that the SPIR installation would give luminosity that corresponds to somewhere between 10

to the 31st and 10 to the 32nd centimeter square per second beams. And unfortunately, the performance has not yet come up to that schedule, so that we're about a factor of 10. I mean, the performance of the machine

is down about a factor of 10 from the desired performance and also the duty factor, the time when the machine is on has turned out to be less than expected. So it's only on about 40% of the time. When you put those factors together, we're losing something like a factor of 20

in the luminosity that we expected to have. So the data are coming in much more slowly than originally anticipated. And as you can imagine, we're in the process now of asking for more time. But if we ask for 20 times the time we've had,

I'm sure we're going to get a refusal. So I don't exactly know what's going to happen. But this particular experiment was set up in such a way that there are three running periods. In the first period, which lasts typically about a month, you set up the apparatus.

And in the second period, you try to make it work and get all the errors out of it and so on. And in the third period, you actually take data. Now, we've gone through the first period and the second period. And in a few days, we will start actually taking data, the real data for the experiment.

Then finally, I want to talk very briefly about the application of these large detectors to the detection of strongly interacting particles. This is an acronym for Total Absorption Nuclear Cascade

Detectors. And we hope in September to take the large crystals away from the SLAC installation and take them to the National Accelerator Laboratory in Batavia,

where we will try to see how these detectors behave at energies in the 200, 300, 400 GeV range. And if they work well, as we expect that they will, then we will try to take some total cross-section

measurements. So I think the best thing for me to do now is to go through the slides. There are a large number of them. And I hope that I won't put you to sleep in seeing them. I'll be very brief about a number of these.

I'll go through them very rapidly, because I think that the main idea is a rather simple one and doesn't need much explanation. This is a slide that shows what we call a task detector. That stands for Total Absorption Shower Counter.

This is typically used to detect electromagnetic cascades. And here is an electromagnetic cascade in which pair production and bremsstrahlung are the principal agents by which the original energy gets divided into a bunch of small packages.

And then if you have a large enough detector, you can capture all the radiation. And if you look at this, if this is sodium iodide, for example, then you can look at the size of the light flash. And as I mentioned earlier, the size of the light flash is then proportional to the energy of the incoming particle.

So that this detector will detect the particle. It will detect the time of arrival. And it will detect the energy of the electron or gamma ray. A gamma ray behaves in essentially the same way, except that the gamma ray comes in and interacts and makes a pair, an electron-positron pair.

Then the pair goes through this process. It's clear that if you make this large enough, you can prevent the escape of almost everything and then have some kind of a true measure of the energy. May I have the next slide, please? This shows an early formulation of such a detector.

And you can see the kind of size of the device. This is a sodium iodide thallium detector of four disks, one, two, three, four, with the photomultipliers shown here. And the dimensions are about 24 centimeters this way. And each one was, let's see, about 12 centimeters this way.

So this was an assembly of four detectors. May I have the next slide, please? And this shows the next stage of development. This was a larger crystal than the ones

that you have seen in the previous slide. This one was about 15 centimeters this way. And about maybe 30 centimeters this way. This is an appreciably large crystal and this weighed about 250 pounds.

And you could see the photomultipliers here. Next slide. This shows how you assemble those various units together. And this represents an experiment that was done at SLAC some years ago in which an electron beam or a pion beam would come through this aperture and be detected here.

That large crystal that I just showed you is this one. And the next slide, please. I think that could be focused a little better. Again, this shows the next stage in the development. This was the largest crystal that we had worked with up to that point. This one is about 60 or 70 centimeters long

and about 38 centimeters this way. And this crystal weighed 1,000 pounds. And the container for it is shown here.

And this is quite large enough to detect gamma rays up to the highest energy that anybody cares to measure right now. Next slide, please. This shows the crystal in place, again at SLAC, with the photomultipliers around here

and some small photomultipliers on the side which were intended to tune up and improve the performance of the crystal. The idea was to balance the various photomultipliers in an attempt to get the best energy resolution.

May I have the next slide, please? Now this shows the best result we've ever had. And this represents a resolution of 7 10ths of 1% full width, half maximum. This is the number of counts versus the pulse height. This was obtained with the crystal that I just showed you.

And this was the data obtained for 15 JAV electrons. This represented just the best tuning up of that crystal that we could make. And in actual experimental work, we never have the time to do things as well as that,

so the performance is not really this good. But this shows what can be done, and there is some hope of doing better than this too. May I have the next slide, please? This shows a typical performance of that 24 by 16 inch crystal.

This is a resolution curve, and typically it's about 1% or so at 15 JAV. It's possible to think of a much improved performance which depends only on the statistics of collecting the electrons at the photocathodes

or the photomultipliers, but we're very far from that. And this performance is probably due to the escape of low energy gamma rays from the sides and from the end of the crystal. May I have the next slide, please? This shows that the crystal is linear in its performance,

which is a very nice thing to have. May I have the next slide, please? Now, this shows the next stage. I think that the focus could be improved a little bit. This is a large crystal of sodium iodide

in an aluminum container. This one is about 76 centimeters across, and it's about 25 centimeters thick. And this crystal by itself weighs half a ton or a thousand pounds.

And this is Barry Hughes, one of the principal persons who has developed this technique. Through the kindness and the confidence of the National Science Foundation, we have been able to purchase some six units

of this kind and some other units as big in diameter but smaller in thickness so that we have assembled something like three and a half tons of sodium iodide. And this is a far cry from the one-centimeter crystals that I worked with in 1948.

These are required if you want to make wide angle studies of gamma radiation and other things of the type that I'm going to show you now. May I have the next slide, please? This is a slide which will just tell you

what the time performance of these crystals is. Normally, the decay of a sodium iodide pulse takes 250 nanoseconds. And here is a typical decay in a large crystal of this type, which is 20 inches thick

and 30 inches in diameter. This represents two thicknesses of the kind of crystal I showed in the previous slide. And this represents an energy of 580 MeV, a rather low energy with a resolution of 2.35%.

See, 100 nanoseconds is this interval from here to here. So in addition to the decay time, you have some contribution, which is not very great in this case, of the rattling time, the time that the light travels around

inside that big crystal. That takes some time. Not important here, but as you try to clip the pulse and make it faster, then it becomes important. May I have the next slide, please? Now, this shows how the width has increased to 3.1% when you clip the pulse, as seen here,

so that it's 210 nanoseconds across the base. And this is typically what you may expect to use. Now, it's possible to use other techniques as well for timing, and in fact, these crystals have been used to time events with a precision of 10 to 20 nanoseconds,

and that becomes important in time of flight considerations in some of the experiments that we're doing. May I have the next slide, please? Now, this shows the first experiment that I described there, the one in which we have negative pions and positive pions interacting with protons

to produce neutral pions. Here is the experimental setup of that arrangement. This experiment was carried out at SLAC with a beam of about 14 GeV pions, negative and positive,

with a liquid hydrogen target and a clearing magnet here, which bends the main pion beam off to the side here and out of the way, and then a helium bag to replace air. This causes less absorption of the gamma rays

and also makes less noise and background around the apparatus. In the liquid hydrogen target, you produce neutral pions, and as you know, the neutral pions decay practically instantaneously into two gamma rays, and in the center of mass system,

the two gamma rays have the same energy, but the orientation can be anything. So you get a whole distribution of gamma ray energies in the laboratory system. So each of the gamma rays produced in the decay of the pi naught go into one or the other

of these crystal assemblies, and the crystal assembly is shown on a magnified scale here. You have an anti-coincidence counter here to tell you that you have a gamma ray and not an ionizing particle, and then you have a converter to tell you that the gamma ray

has materialized into an electron-positron pair and a shower, then you have a hodoscope in here with 10 elements this way and 10 elements the other way in order to determine the angle of emission of the gamma ray, and then you have a total absorption detector here.

The pi naught can be recognized by its invariant mass. Its invariant mass is the square root of twice the energy in the one counter times the energy in the other counter times the sine of the included,

sine of one half of the included angle, so that if one gamma ray goes here and the other gamma ray goes here, it is not sufficient just to know that they have gone into these two detectors to get the invariant mass, but you have to have a finer grid that tells you where in the crystal the gamma rays went,

and so that's the idea of the hodoscope. Now, the resolution that is associated with this invariant mass is dependent in this experiment not on the energy resolution of the crystal, but it is dependent on the hodoscope degree of fineness,

in other words, the smallness of the elements, and in this case, they were not very small, several inches, so that the resolution is limited by the size of the hodoscope elements. May I have the next slide, please? This shows the experimental arrangement. It shows the helium bag and the pipe

leading the negative pions off to the side. The focus could be improved, and here is one of the large detector systems, and here is the other one. Could you improve the focus a little bit? Because it's hard to see these hodoscope elements.

I guess, well, sorry. Anyway, there are 10 hodoscope elements here. Yes, you can see them. And this whole apparatus could be moved so that one could get an angular distribution. That's very good. May I have the next slide, please? This shows the invariant mass distribution

obtained for the pi zero, and the mass comes out at just about the right place here, 140 MeV or so, and the full width half maximum is about 11%. As I mentioned earlier, this width is determined

by the coarseness of the hodoscope elements and not by the resolution of the crystal. May I have the next slide? So, well, you see then that in that previous slide, one can pick out the pi naught events very clearly, and there is not very much background. Now here you see the cross-section for the process

with negative pions coming in, and here is the maximum energy that the pi naught can have, and here is the distribution, which is a function of the longitudinal momentum of the pi naught.

May I have the next slide, please? This shows the corresponding distribution as a function of the longitudinal momentum for pi plus. Pi plus is on protons, also giving pi naughts, and you see the distribution is very similar. This surprised us, but maybe after having seen it,

there's no reason to be surprised. May I have the next slide, please? I'm afraid this doesn't show completely, but what this is is for a given longitudinal momentum of the pion, there is a transverse momentum distribution,

and this is the transverse momentum distribution for the negative pion process at this longitudinal momentum. The scale down here goes from zero

to .7 GeV over C squared. That is Q squared, the square of the momentum transfer. This is an empirical fit to the data. May I have the next slide, please? The next few slides are all similar, but they are at different values

of the longitudinal momentum. So there you see what it looks like. May I have the next slide, please? And here is at nine GeV over C, and empirically, the distribution is starting to change a little bit here. This is again for negative pions. May I have the next slide, please?

This is also for negative pions at 10 GeV over C, and now the distribution looks more like that. Next slide, please. Now, here is a comparison between our results on neutral pions and the charged pion results of Albert et al.

And can you lift this slide up a little bit? Just lift the picture up. Yes, you see here, this is the pi naught distribution, which is fairly similar to the pi minus distribution at low values of the longitudinal momentum.

But at large values, you have this big peak in the charged pion distribution, and these are the so-called leading pions, and these are the produced pions. So the produced pions, as far as neutral pions in charged pions are concerned, look pretty much the same.

But clearly, this pi naught process is disfavored at the kinematic limit, and hence there is this very big difference. May I have the next slide, please? Now, this shows similar data for pi plus, and I'll just go through it very rapidly. Next slide, please.

And next one, it's very similar. The pi plus and the pi minus results are almost identical. Next slide, please. Yes, and that represents the end of the discussion on the first experiment. The interpretation of those results

is not yet clear and hasn't been worked out. The data have only been published recently, but I think that the data do support a theory of Professor Yang, who is here today, although I'm not sure that the energies involved here are high enough to meet the conditions of his theory.

But maybe he'll have a comment on that. Now, I come to the next experiment, the second experiment, which is the colliding beam experiment. And I should say, before I go into this, that there is and has been previous work on this subject by a group at Frascati,

collaboration between Bologna and CERN. They've done a very beautiful experiment on quantum electrodynamics, up to one and a half GeV for each of the positron and electrons. And there is another piece of work done by the Cambridge group, the MIT Harvard group.

And unfortunately, I left the physical review letters back in the States, and I don't remember what their maximum energy was, but it is something like the same thing, or maybe a little higher than the Frascati results. In both cases, it seems that quantum electrodynamics

is valid up to the conditions examined in each of those experiments. And roughly speaking, if you want to turn this into size language, this means that quantum electrodynamics is valid down to distances on the order of a few times,

10 to the minus 15th centimeters. So this is a few hundredths as small as the size of the proton. So this is quite a remarkable indication of the validity of electrodynamics, which works so well for these very small distances,

as well as macroscopic distances. May I have that same slide, please? This experiment that I want to talk about now was originally conceived to be done in this way. Here is the beam line in which positrons,

let's say, come this way, and electrons come this way. And then you have these total absorption detectors with conversion crystals, and these lines here represent multi-wire proportional counters, which serve as fine-grained hodoscopes.

The apparatus that we built then could be used at 90 degrees, or it could be turned to various angles like this. The apparatus will then measure and tell you whether you have charged particles, like electrons and positrons, which come in and shower, or gamma rays, or, in this early situation,

we were not going to detect the mu plus and mu minus, but subsequently we decided that this could be done with the same apparatus, and so the next slide will show, I think, the scheme that is now in actual use. This is the scheme that is now in actual use,

with the positrons coming in this way, electrons coming in this way. This is the interaction region here. And for example, the detectors are set here at 42 degrees. For example, if an electron-positron pair is produced or scattered,

it can go like this and like that, and it can go actually into any part of this assembly. And the multi-wire proportional chambers will give you the angular information so that you can project the track backwards and project it backwards here and see if it came from the interaction region.

If it does not come from the interaction region, then it is some kind of a spurious event or possibly a cosmic ray or something like that. Now, to detect when you have muons, a muon will go through a large amount of crystal with hardly any energy loss, a rather low energy loss,

go through another slab of iron, and then go into another sodium iodide detector here, a three-inch thick detector. And this gives typically a Landau distribution for the energy loss. So you can really fix that it is a muon by its energy loss.

Now also, you see here a converter plate. This is a plate of 1.25 radiation lengths of lead. And a gamma ray will convert with a high probability in that converter, and then the electron and positron are detected here.

A muon or an electron, well, an electron first will go through here and it will start to shower here and the energy is picked up here, but nothing gets through to this detector. A muon will just go right on through all of these devices and out the other end.

And so you can tell the difference then between the electrons, gamma rays, and muons, and you can do this all simultaneously. Actually, the converter here will broaden the angular distribution of the particle that goes through it

or of the pair produced by the gamma ray so that you lose some geometrical resolution by use of the converter plate. So to do the electron-positron scattering, we have actually taken the converter plate out. And if you take the converter plate out, you can do a very good job

on the electron-positron cross-section and then later put the converter plate back and do all these processes, all the other processes simultaneously. So that is the technique that we're using. May I have the next slide, please? Now, this is a very bad drawing, but it shows the idea of the mounting scheme

for these big assemblies. These assemblies weigh a few tons apiece, probably more than that, probably five tons apiece. And you have the, here's the beam line, and you have the ability to point them at any particular angle, production angle,

with respect to the beam line, but you also have the ability to rotate the system in azimuth. This was put in to be sure that there were no polarization effects that could affect the data, or put it another way, to study polarization effects if they are there. Actually, it turns out that if you investigate,

according to electrodynamics, the polarization phenomena for the electron-positron process, that if the azimuth angle is 45 degrees, the polarization effects are identically zero. So that's what we're doing. We're turning this apparatus,

we're using, for example, suppose we put these at 90 degrees, but then we put the azimuth at 45 degrees, and eliminate any possible polarization effects. May I have the next slide, please? This shows how the luminosity is measured. I won't go into the details here, but one uses the time of flight

of the electrons, or positrons, after being scattered from the interaction region, small-angle Coulomb scattering, and one uses a time-of-flight identification and a spatial identification. There's too much to go into,

so I don't want to describe that. The only thing I will say is that we use two lead-plastic sandwich-type detectors to detect the beam strengths, or the luminosity. Next slide, please. Now, this shows the apparatus, the beginning of the apparatus,

as it was assembled in the Stanford High Energy Physics Laboratory, and it shows these two big wagon wheels that were shown in the schematic drawing. This was the first time they were put together, and here is the carriage, or the bearing, for one of those wheels. May I have the next slide, please?

This apparatus was assembled once at the High Energy Physics Laboratory to be sure it went together correctly. Then it was taken apart, and it was moved over to SLAC and installed in the SPEAR installation. And here is a picture showing

the parts being put in place. Here is the 20-inch task detector. Here is the slab of iron, which serves as a mu differentiator. And here is the beam pipe. And here, the wagon wheel, and there is a quadrupole of the colliding beam facility itself.

Next slide, please. It's pretty hard to see things here, but here is one detector at 42 degrees, and here is another detector at 42 degrees, and the beam pipe is right in there. May I have the next slide, please?

Here is another view showing the quadrupole and the two big wheels in their bearings. Next slide, please. This is another view of the same. There's not much that's too original here, but the pictures are pretty, so I thought I would show them to you. May I have the next slide?

And here is another view. You can see it's a big, complicated piece of apparatus. Next slide, please. Here, you see them at the angle of 45 degrees in azimuth, and this is the way the experiment is being carried out now with a production angle of 90 degrees for the moment

and an azimuthal angle of 45 degrees. Next slide, please. Now, the next set of slides will show you how one determines that the event is a good one, and these are the proportional wire chamber results.

These are portrayed on an oscilloscope screen. There are three proportional chambers in front of each task crystal, and the three proportional chambers with a drift space between them determine the direction in which the gamma ray or the electron or the muon,

it determines the direction of those particles. So this represents three wire chambers on one side and three wire chambers on the other side, and one gets an x and y for each traversal. So you put all of these things together in a computer, and then you can trace back where the particles went.

May I have the next slide, please? This shows the three planes, one, two, three, one, two, three on this side. This is the x-coordinate, and this is the y-coordinate, and where you have a discharge, you make a mark like that, that, and that,

and you project backwards in each case. Now, I don't know whether you can see it, but there are some little marks here which indicate the interaction region, and those are good events. Those go right through the interaction region. There are a lot of pieces of information that you can get.

For example, you measure the energy on each side. So the energy on this side was 2.67 GeV, and the energy on the other side was 2.73 GeV. That certifies that the event was the kind that you wanted. This is an electron-positron pair with the right energies.

Here is other information that has to do with the collinearity and the production angle. One is 89 degrees, the other is 87 degrees. These do not have to be exactly collinear because there are radiative effects that change the direction a little bit

and other things that can happen too. So they do not necessarily have to be collinear. Then here is the azimuthal information, and then here and here is information relative to the crossing points in the interaction region along the length and along the perpendicular to the length.

And then finally, here is information about the mu crystal, the mu detector. Well, I don't want to go into all of this detail at the present time, but I just would like to show you a few examples of events. Next slide, please.

Here is one where you saw nothing in the wire chambers. But then look at the, next slide, please. What this is is a two-gamma event. You can tell it's a two-gamma event because the energy in the first crystal is 2.75 GeV, and then the second crystal is 2.78,

or whatever it says there. So the gamma rays, by the way, this is a setup in which the converter is not used, and therefore you do not see the conversion of the gamma ray. The gamma ray gets converted right in the task crystal itself.

So you know that this is a two-gamma event. Next slide, please. This shows the crossing distance of a number of electron-positron pairs, and it shows they have a big peak around the place where they should cross. Next slide, please.

And this shows the crossing distance along the beam axis. The other one was perpendicular to it. The interaction region is typically about a foot long, and so that's reflected in this distribution. Now the next slide, please. And this shows the collinearity in the early data.

You see, they tend to be collinear, but then there is a distribution, and that distribution, of course, can be calculated by the use of the radiation formulas of Tavernier and others. These are all parts of quantum electrodynamics that can be checked against the experiments.

Next slide, please. And this shows an energy distribution. This shows the sum of the energies in the two crystals for the electron-positron situations. You see there is a peak here at 5.3 GeV or thereabouts, and then there is a distribution of other energies.

Now this is very interesting, and we'd like to, you see there aren't many statistics here yet. We've just started. But we'd like to know what this distribution of energies is. So there are lots of interesting things to study given that we have enough time to make the experiment go. Next slide, please.

Now just for fun, I want to show you a series of slides that represent what happens when you put the converter in. When you put the converter in, this is apparently a gamma ray situation where you get nothing in the first wire chambers, but after going through the iron plate, you get a shower,

and you see a number of wires go off at the same time. And what you do is take the center of gravity of the wires or the median of the wires and then project back to get the particle direction. So this is a two-gamma event. May I have the next slide, please? And there it is as projected backwards.

You see nothing in the first wire chambers, but the second and third ones have events. And the energies are 2.45 and 2.55 GeV apiece. So this is a two-gamma event. Next slide, please. Here is one in which you have a gamma ray on one side

and nothing on the other side. May I have the next slide, please? There you see it. The gamma ray converted on this side, and it points towards the interaction region, but nothing on the other side. Maybe a neutrino or something. It will be very interesting to look at events like this. And of course, the energy is measured.

The energy is 2.66 on the one side. Next slide, please. Here is another event. Looks like it's a gamma ray, two gamma rays, and you see the showers that are produced. Next slide. Yes, you see it projects back to the interaction region.

So you have very nice clean criteria for looking at the pulses. Of course, you can also use the energy in the crystals as part of a trigger. Next slide, please. Now here's a big event. Looks like an electron-positron pair making a shower. Next slide.

And there it is. You see it project backwards to the interaction region. And the energy is 2.38 on one side and 2.27 on the other. That is a reflection of the fact that you're losing some energy in the converter plate. And that can be allowed for. That can be corrected for.

Next slide, please. Here's another event. Next slide. Electron-positron pair. There it is. Goes through the interaction region. But you see it's not collinear. Next slide, please. Here's another one. Next slide.

This is actually a muon, a production of two muons because the muon detector now gets a pulse here and gets a pulse here. So this is clearly a mu event. And here are the energies. The mu energy in the last crystal is .04 GeV.

And in the task crystal, the energy is, it looks like .33 GeV. And so this is clearly identified as a muon pair. Next slide. This one I think is a cosmic ray event. Next one.

Yes, you see this is a cosmic ray event and it's a muon which goes through the whole apparatus. But you see it does not go through the interaction region. So this is the way you can tell background events. Next slide, please. This has to do with luminosity. I won't go into that. Next slide, please.

We make measurements of luminosity. This shows how the luminosity of the sphere machine decays in time. This is time in hours. And here it's decaying and you charge it up again and then it decays. You charge it up again and then it decays.

And you take measurements during all these times when the machine is delivering colliding beams. Next slide, please. Well, this is a electron-electron crossing distance. It just shows that most of the events. I will go very briefly through this. This is how a strongly interacting particle

is detected in the crystal with nuclear cascades. Next slide, please. And here is a distribution in that crystal I showed you earlier, 24 by 16. Well, it's seven and a half GeV pions. And an electron beam is a calibration.

Here's the electron calibration. Here is the broad distribution due to the pions. And this is a muon contamination. And this is a Landau peak. May I have the next slide, please? Now this shows an assembly of three and a half tons of sodium iodide.

And this is what we intend to take to the National Accelerator Laboratory to make measurements of energies up to 200 and 300 GeV. Next slide, please. This shows a distribution again in another combination of crystals showing a calibration peak, a pion peak,

and a muon contamination peak. Notice the width here. So it's not really acting as a spectrometer yet. Next slide, please. Now here is a better distribution, somewhat better distribution. This is a 30 inch diameter crystal by 30 inches long using seven and a half GeV pions

and a calibration with electrons. And there you see the pion distribution. And there the muon contamination. Next slide. Now these are the best results we have obtained so far. And these show at,

this I believe is at 14 GeV and it was taken very hurriedly. It shows a symmetrical peak for the first time with a width with a suppressed zero. You can't tell exactly what it is. Of about 23 or 20%.

So for the first time, we have something like a spectrometer for use at high energies, high hadron energies. And we hope that at 200 GeV, this will go down to about 5%. But that's about all we can expect. I think that's the last slide.

Thank you. Okay. Thank you very much. Thank you.