So. Thank you very much for the invitation.
It is a great honour to talk at. The symposium on Don Perkins and on the other aspect, namely neutral currents,
in order to give you a complete picture of what his contributions are in your chain of physics.
Well, I know I've done since 1968, and we remain in close contact.
Uh, more than 50 years. He once told me how he became a neutrino physicist.
In the context of the big project at CERN, is also intersecting story string.
He was invited as an expert to discuss what kind of physics could come out of that project.
He got to know at that moment, uh, Colin Rahm, who was the head of the NPA division at the nuclear physics apparatus.
And later on, uh, uh, Colin invited Don to participate in this neutrino program.
So Don arrived just at the moment when the improved neutrino experiment you have first of the failure of the first one, uh,
came into operation and, uh, and, uh, made the first runs and done presented these first strands at the CNR conference.
Uh, he made the first analysis of undercurrents, and he had observed 11 events with identified ons in the final state.
You can see here in the black part, it was immediately clear.
What's the real problem is you have to show that these events are not background.
Now in a neutrino experiment. Neutrons are an automatic background because a neutron is generated in a neutrino interaction.
And then if it enters a chamber, it has the same topology as a due to current event.
Unfortunately. See, the dimensions of the chamber are of the same order and the interaction links of neutrons.
So it was extremely difficult to make any uh, an a numerical statement.
So he, it's an upper limit was given of the elastic cross-section compared to the charge current elastic cross-section of 5%.
For many people this was a signal of probably so these objects don't exist.
Here. Here is a report. Bernardini is a director.
At that time was giving. And you can. You can see if you see 5%.
At the end of the conference in Siena, people were thinking about what came really out and like Eric was one of them and said, well,
it's the potential of this new field is extremely big, so we have to think of a new detector in order to get more statistics.
So the idea was to build a large bubble chamber, which became a Gargamel.
And you notice that the cross-sections, the number of events is proportional to the target must.
Therefore you need a big chamber and also a heavy liquid.
It was a cylindrical chamber such that you can distinguish, uh, by an interaction versus you are dealing with a moon or with a pion.
So in the meantime, like Eric was forming a collaboration consisting of seven European laboratories Aachen,
Brussels, CERN, École Polytechnique, Milan, Ozone and University College London.
So you can see, I suppose, experience in running a bubble chamber and also also and also experience in evaluating a neutrino experiment.
It's a very large meeting, which was actually in October 1968.
The dominant topic was the discovery of the proton substructure and its lack.
Therefore, c outstanding question was what could a neutrino experiment contribute?
You see, you have at slack as a probe.
So electromagnetic current and with a new experiment in future you would have civic charge current to to to find out what happens.
It's a proton. So your tools are said to have a neutrino and antineutrino.
See see. Exploration of the of the prominent structure was therefore c see main topic and on the priority list of the of.
Of the future experiment. Um, it ranged really at a top priority on the also hand.
Since there was no evidence for neutral cards. It was not forgotten, but it was put on lowest priority.
See experiment. See chamber itself arrived during 1970 and the first expansion was in December 1970.
Data taking started a few months later in neutrino antineutrino.
Light beam. Beam. It see, the initial aim was indeed to see a total cross-section and to investigate its nucleon structure.
The data were taken on film and distributed amongst the seven laboratories.
It was obvious that in such a situation you need extremely strict rules for scanning and measuring.
Otherwise you cannot compare the data and putting data together.
This was done before the start of the experiment.
So the events that um distributed in four categories.
So regular neutrino events so such which happen during candidate is a final state.
Then a key category was those events which consist only of identified hot ones.
These are supposed to be neutrons.
And these were important in order to correct um, uh particles but uh, positive particle negative particles which are supposed to be immune,
but in reality, uh, pion then there are events consisting of just one or more protons and finally events with an isolated electron,
positron or photon. Here is the bubble chamber at its beginning, when it was, um, assembled and at the end, 19, uh,
889, uh, when a crack, uh, occurred as far as these defines the end of the bubble chamber.
Here are some technical details. You can see, um, the longitudinal cross-section.
C beam comes from the right, penetrates the iron shielding, and then enters, uh, intrusive high total volume, which is marked in in blue.
You can see that the chamber is within very heavy material, which will later be of great importance.
The chamber was, uh, almost five metres long and had a diameter of 1.8,
and so c five total volume was of C two metres and therefore a big target mass.
This ensured a high detection efficiency of the final state particles C optical system, which is uh shown uh it's it's a sight.
Um, there are flashlights, illuminating satellites and c pictures.
Uh um uh uh, transported through about two metres of the iron joke that needed to have very special, uh, scan tables and measuring tables.
At 1971. Uh, just and Feldman proved zero mobilisation at that moment.
The white belt model, uh, attracted high attention.
At this moment, it was clear that weak and electromagnetic interactions are on the same footing.
However, there was no W, there was no Z, there was no Higgs, there was no neutral current.
It's a collaboration meeting which took place, uh, a few months later.
Now see category B events. It the important role if if you treat neutral cards exist.
They would already be present a category B so initially foreseen to, to get C uh neutron background.
But you have in addition C data to.
In effect if it is there it is already there.
So Milan Group looked at the events which had only had turns into into final state and had C observation that there was no exponential fall off.
Now in a very long bubble chamber. It is clear that C interaction is only 70 or 80cm.
Therefore you won't have any events if cu uh to to new to cons.
Uh, so if uh yes, if uh uh send you if they are neutral cons say would surely appear in the second part of the public chamber.
Now. From that moment on, it was a decision to make a dedicated search for neutral currents, both in electronic and in hadronic channels.
And so the analysis continued simultaneously with both user in charge current.
It just a few weeks later. Dan Perkins wrote a memo where he recalculated also knowledge into previous neutrino
experiments and distributed search at sea to see collaboration to see neutrino collaboration.
Here. You can see here. Um.
In order to interpret the data, he used a very simple model, a linear model.
Just assuming that any neutrino interaction emits a neutrino just in the same direction as a sad beam,
then a neutron interaction can appear in two ways.
If you observe a neutral, a star is either associated to its source signature, you know, or else, since source is outside.
So these events have been called, in our jargon, as events, background events, and associated events.
It is very easy to calculate it because you know, what is the interaction probability of a neutron into a liquid,
and c c the ratio of the mass effects of the to um of the two media.
Now. What are said? Lessons from previous experiments.
He had c c c CS of his PhD student.
You know Hyung, you have already heard about him. Um, a full analysis of the of of the data.
Then, um, 1967, there was a second one with propane in the chamber.
The advantage was that you have not only bound protons, but also free protons.
And a very important insight.
Uh, uh, came said si initial value.
Of the 5% you have seen before was underestimated because single unidentified positive tracks were taken as pions.
And that explained very well why it is so small, so reanalysis.
See also data and showed that in reality C is the ratio in elastic into one pion channel was quite big 12 plus or -0.06, 0.08 and plus of minus 0.04.
This was published and in Japan for pi candidate um.
Don Perkins on the basis of this very simple model.
Evaluate. It's a neutral background.
This evaluation is simple because the only thing you need is to calculate it by a waste ratio and number of associated events.
So the product of the two is a prediction of how many nutrients a background events you are expecting.
Now you can see here in the case of rayon say about 78 events compared to predicted 12 and in propane 79 compared to predicted 31.
Unfortunately, this excess cannot be interpreted as a discovery because the model was far too simple.
So Perkins conclusion was existing data are indicative but not conclusive.
The prospects for discovery. We are still at the beginning of 1972.
Um, which looks promising because of the links of the chamber and a very strong warning he was given to him.
What neutron background is? This is a quote from from his, uh, memo.
Also, I know that many people at CERN are working on this problem.
There appear to be innumerable pitfalls in the analysis, and a thorough discussion at an early stage would be worthwhile.
So she started. She for the analysis was very clear.
And, uh. Yeah. Oh, it's just too much.
How can I go back? It's a collaboration.
Was very clear about the challenge. Say they were given to.
It was so. Signal was obvious. An event.
We'll say it's no charged lepton. It was also clear what the background is.
So c c challenge consisted in proving sets.
The number of background events is small compared to the number of candidates.
It was also known that an American group, uh, was H.
Harvard, Pennsylvania Wisconsin group was, uh, searching for the same effect.
And so there was competition between them.
So it's a collaboration felt very well. So tension between being first and being right.
It's the end of the year.
And in December 1972, there was great excitement because an event was formed which which you can see as its most famous event from from Clerkenwell.
It was originally misclassified, and a PhD student in charge said.
Well, maybe it is an electron and not a moon with an overlay.
So he went up to see, uh, supervisor, which was called Schulz.
And sure, she looked at it. Well, such looks more like an electron.
So they went up to find snow and I. Oh, such is the discovery.
And he immediately took the next line to work on.
Poking was already biting. And he left the event in his hand.
Intern Perkins was shouting, neutrino or antineutrino?
When he answered antineutrino, they were very happy and had a big embracement.
You can see here when she celebrated, she often event.
You can see in the middle, uh, see head of the neutrino group and two persons later on,
uh, was, uh, uh, Helmut Feist, now the director of the institute and just scanning girls.
Here are two candidates. Beautiful candidates of neutral cards.
Um, you can see direct by your IEC interactions.
There was no doubt about it. Now in March.
So precisely one year later.
Look, Eric, it says in meeting with a big smile.
He. In the meantime, uh, 38,000 neutrinos and 207,000 antineutrino pictures have been scanned.
And a sample of uh, Yukon candidates consisting know of one is this one lepton event and, uh, 102 neutrino and 64 events in its own neutrino field.
In order to make a direct comparison, a charge card sample was used well beyond.
It was ignored and exactly the same criteria applied to the final state um of of of of the event.
Now, uh, there was a clear expectation.
If these events are all due to neutrons, then there must be a fall off at the beginning,
since the bubble chain is much longer, four times longer since the interaction links of a neutron.
So if you then observe events in the second part, you have a discovery.
So she she she also is. If they are all to you, to your consent, you must have a flat distribution.
Therefore, there could be everything in between these two.
So if you look at your data, you can see that the ratio is very well consistent with being a constant.
And therefore, uh, there was the intriguing situation.
Have you made a discovery or not yet? So it just it's a at the end of this conference, two guys was standing up and said,
wait, you have forgotten something, namely C Newton's May Cascades.
Therefore it is not C interaction things which is relevant potsie cascade links which is which could be much bigger.
Background can be much bigger, on the other hand.
So in Latino flux is not just centring, uh, at the entrance window, but extending over a full range where lots of material is.
This means that many, many more neutrino interactions, uh, outside if sent by chance.
Since a neutron is emitted at a certain, uh, angle towards the chamber, it was filling completely, uh, said chamber and CFO.
There was no distinctive feature left. So therefore c euphoria was attempt and there was no distinctive feature left.
And we are back to to the main problem, namely to prove such a pitch count is much smaller since the number of uh candidates.
This system meant one had to make an A prediction.
A serious prediction of all the details of the experiment.
And since you have seen. See how it set up, it's very, um, complex.
Only a monte Carlo method was able to cope with this.
Uh, we had we needed five different ingredients.
One was set geometry of the set up as it was known.
Symmetric distribution that was also known since the dino flux was measured.
So dynamics of the neutrino interactions could be taken directly from the experiment.
So see real problem which remained was uh, to propagate the final state particles during uh see how material which was there.
Uh, is this where we are requested to come up with a result in a few weeks?
Because, uh, many people were believing they had already made a discovery.
Now, finally, um, a breakthrough came by recognising that the bison component is inactive.
So the only thing which was left is, uh, is the elasticity of a proton or a neutron, um, along its path.
This required um an a c c c probability, how much energy is deposited and how much energy is transported away.
Uh, this could be obtained from, uh, from, uh, data directly from the important data or the nutrient data.
And therefore the result was an absolute prediction with no free parameter.
Which means if you make a predictions and you stick out your head.
Now and in July of 73.
So four months after meeting at at CERN,
um Polya had uh finalised C but number of uh associated events and he came up with 15 neutrino and 11 antineutrino events
on C also and C neutron background program was also ready and predicted over x equals one plus or minus point three.
Now we made this possible hypothesis saying that all candidates we have observed are due to background.
In that case, you can directly calculate what po boys is,
namely 6.8 plus or minus point three to be compared with a calculation which is one plus or minus points.
So there was a huge discrepancy and see hypothesis could be rejected, and so claim could be formulated that there is a new effect.
See, uh, on all um, our uh, collaborators, our colleagues in H1 and sorry, in intercultural verse and thinking of uh, flows into calculation.
And this lasted for about two weeks of discussions.
And finally everybody was convinced.
See, see the result percent presented by we see in Sassoon Auditorium in July 19th and a few years a few days later,
see paper was submitted in Physics letters. Well see as a see also event was already published.
It's a beginning. Yeah. Here are the authors of the discovery, 16 authors altogether a collaboration.
See. The result was.
Then the discovery was presented to an electron photon conference.
One month later, in August 2731, and Jeremiah was presenting data.
He was asked to include also a last minute contribution from HP W Group, and there was no discrepancy between these in the parallel session.
By Fred Bullock. As speaker said,
details were given as soon as he opened his most servers to make an intervention and asking very nasty questions about Newton background.
We were very prompt in answering all these things.
And finally, it's the epitome of C and young.
He stood up and said, due to have been discovered.
Now. Unfortunately. This. Yeah. I have to, uh, at the end of this, uh, we'll be.
I was waiting outside and she said, I have given you help, but I believe you are right now.
His belief to be right lasted only a few weeks because, see, collaborations, HPE collaboration decided to postpone,
say, a publication, and to make further runs, to get more statistics in order to do so.
So introduced a 13 inch iron plate.
Indeed. So he got a bigger acceptance of a far bigger number of it, but unfortunately, uh, see, see lost significant effect.
And from that moment on, uh, almost the rest of the world was saying somebody must be wrong.
It must be God. Campbell. So we were treated with English and critics.
Uh, it uh uh uh, it didn't work at some moment would say director of general education.
And uh, he describes very well as the situation of each of us here.
So I will read it.
It is published in Switzerland, Korea, when they claim to have found due to current single command, was followed by a report from Fermilab.
So the NCO work ratio, they found, was consistently zero.
Many physicists believe that the Gargamel result must be wrong.
Indeed, one senior physicist at CERN.
Well, everybody knows this. It was Stein Palco, uh, so heavily against governments that he lost half of his wine cellar.
But he himself was always very supportive of the experiment.
I did meet him on one occasion into CERN lived.
He told me he was worried about the Gargamel result because some people had told him it could be wrong and that would be very Petrosian.
My response. So Pushkin's response was that coming after split A2 Alpha, it would be an absolute disaster.
However, I knew the group had gone. So I see event analysis many times,
and for almost a year we had searched intensively for some other explanation for the effect observed without success.
So I thought the result was absolutely solid and you should just ignore rumours from across the Atlantic.
I don't know if my words reassured him, but he got out of the lift with a smile on his face.
Now the situation for C collaboration and for soon became Russell um critical.
Um, it boils down to this equation is a cascade broke?
Um, right or wrong? We need a decision. And this was obtained by sending, uh, pulses from CPS proton pulses directly into the chamber.
So you can see this, your eyes, what the cascade is.
And, uh, the right side, you see a beautiful example of a seven GeV proton entering, uh, generating a very, uh, clear cascade.
This, uh. Uh, I had to make a prediction of what to be observed, which is, uh, which is observed events beforehand.
So it was clear what could happen.
This.
As a result, we measured the apparent interaction links in the chamber and you can see it is completely flat and to around 80 to 90cm as expected.
And see also. It's also clear such a cascade links is indeed increasing with energy, and it was excellent agreement with the absolute prediction.
This was later on reported to APS meeting in Washington.
So all aspects of the cascade are confirmed.
And so for. Uh uh uh on over happiness was our final acceptance was in reached in one year after si si si claim, namely in spring 74.
So after all, Gargamel was also time, right?
We did not change one iota. Gargamel.
In the meantime, w statistics in in agreement with previous results.
This is a beautiful new experiment by Barry Barish in a narrow neutrino beam and, uh, single pion production has been observed.
And finally, also HB w group has confirmed a signal.
And going from yes no to yes. Uh, sick joke.
Uh, came said they discovered the alternating current.
Now, uh, it was this discovery.
Um. Countable later.
Important contribution to high energy physics and soon gained a leading role by this discovery.
Well, I went before I finished, but very quickly.
Um, it it see, the impact of the discovery was most enormous.
Uh, it it may change the, um, c policy of all laboratories, uh, to, uh, re structure, say, uh, broke them in order to explore as a new force.
There were two immediate, um, uh, effects, namely, uh, duties.
Effects. It's a is that it has has no coupling to two neutrinos.
Um, see, um, since gravitational collapse, I don't you argument see also saying was in neutrino.
Uh, um it. It 19 at 19 six at it.
Ah. And uh, so neutrino conference was taking place at that moment.
So sine squared theta was measured to plus or minus two uh plus or minus 0.05.
And therefore within C uh um see we see simple uh Weinberg model.
It was an easy to calculate since there was only one free parameter to calculate the mass of the W, which was 17 GeV.
So it was clear said all the previous uh, uh, searches were just impossible.
So neutrino experiments which uh, Steinberger find some in his said if it is 20 GB, I will discover it.
But no you can see it was impossible.
So this was the beginning of the, uh, people p uh, Collider, which was proposed and which was realised and at CERN within seven years.
No. If you look at it at the right side, you can see some beautiful electroweak weights.
Um, starting at 73, with the discovery of signal to Collins and A, W and Z and finally six.
So it's the end of of these, uh, installing this, uh, sort of standard model in its full glory.
So this is. See at my Tony Perkins. You remember perhaps how he often said to us, physics is simple, but you make it sometimes very complicated.
So thank you. You're done.