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So. Thank you very much for the invitation.

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It is a great honour to talk at. The symposium on Don Perkins and on the other aspect, namely neutral currents,

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in order to give you a complete picture of what his contributions are in your chain of physics.

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Well, I know I've done since 1968, and we remain in close contact.

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Uh, more than 50 years. He once told me how he became a neutrino physicist.

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In the context of the big project at CERN, is also intersecting story string.

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He was invited as an expert to discuss what kind of physics could come out of that project.

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He got to know at that moment, uh, Colin Rahm, who was the head of the NPA division at the nuclear physics apparatus.

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And later on, uh, uh, Colin invited Don to participate in this neutrino program.

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So Don arrived just at the moment when the improved neutrino experiment you have first of the failure of the first one, uh,

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came into operation and, uh, and, uh, made the first runs and done presented these first strands at the CNR conference.

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Uh, he made the first analysis of undercurrents, and he had observed 11 events with identified ons in the final state.

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You can see here in the black part, it was immediately clear.

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What's the real problem is you have to show that these events are not background.

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Now in a neutrino experiment. Neutrons are an automatic background because a neutron is generated in a neutrino interaction.

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And then if it enters a chamber, it has the same topology as a due to current event.

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Unfortunately. See, the dimensions of the chamber are of the same order and the interaction links of neutrons.

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So it was extremely difficult to make any uh, an a numerical statement.

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So he, it's an upper limit was given of the elastic cross-section compared to the charge current elastic cross-section of 5%.

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For many people this was a signal of probably so these objects don't exist.

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Here. Here is a report. Bernardini is a director.

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At that time was giving. And you can. You can see if you see 5%.

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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,

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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.

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So the idea was to build a large bubble chamber, which became a Gargamel.

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And you notice that the cross-sections, the number of events is proportional to the target must.

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Therefore you need a big chamber and also a heavy liquid.

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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.

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So in the meantime, like Eric was forming a collaboration consisting of seven European laboratories Aachen,

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Brussels, CERN, École Polytechnique, Milan, Ozone and University College London.

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So you can see, I suppose, experience in running a bubble chamber and also also and also experience in evaluating a neutrino experiment.

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It's a very large meeting, which was actually in October 1968.

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The dominant topic was the discovery of the proton substructure and its lack.

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Therefore, c outstanding question was what could a neutrino experiment contribute?

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You see, you have at slack as a probe.

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So electromagnetic current and with a new experiment in future you would have civic charge current to to to find out what happens.

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It's a proton. So your tools are said to have a neutrino and antineutrino.

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See see. Exploration of the of the prominent structure was therefore c see main topic and on the priority list of the of.

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Of the future experiment. Um, it ranged really at a top priority on the also hand.

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Since there was no evidence for neutral cards. It was not forgotten, but it was put on lowest priority.

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See experiment. See chamber itself arrived during 1970 and the first expansion was in December 1970.

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Data taking started a few months later in neutrino antineutrino.

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Light beam. Beam. It see, the initial aim was indeed to see a total cross-section and to investigate its nucleon structure.

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The data were taken on film and distributed amongst the seven laboratories.

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It was obvious that in such a situation you need extremely strict rules for scanning and measuring.

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Otherwise you cannot compare the data and putting data together.

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This was done before the start of the experiment.

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So the events that um distributed in four categories.

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So regular neutrino events so such which happen during candidate is a final state.

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Then a key category was those events which consist only of identified hot ones.

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These are supposed to be neutrons.

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And these were important in order to correct um, uh particles but uh, positive particle negative particles which are supposed to be immune,

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but in reality, uh, pion then there are events consisting of just one or more protons and finally events with an isolated electron,

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positron or photon. Here is the bubble chamber at its beginning, when it was, um, assembled and at the end, 19, uh,

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889, uh, when a crack, uh, occurred as far as these defines the end of the bubble chamber.

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Here are some technical details. You can see, um, the longitudinal cross-section.

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C beam comes from the right, penetrates the iron shielding, and then enters, uh, intrusive high total volume, which is marked in in blue.

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You can see that the chamber is within very heavy material, which will later be of great importance.

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The chamber was, uh, almost five metres long and had a diameter of 1.8,

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and so c five total volume was of C two metres and therefore a big target mass.

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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.

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Um, there are flashlights, illuminating satellites and c pictures.

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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.

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At 1971. Uh, just and Feldman proved zero mobilisation at that moment.

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The white belt model, uh, attracted high attention.

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At this moment, it was clear that weak and electromagnetic interactions are on the same footing.

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However, there was no W, there was no Z, there was no Higgs, there was no neutral current.

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It's a collaboration meeting which took place, uh, a few months later.

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Now see category B events. It the important role if if you treat neutral cards exist.

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They would already be present a category B so initially foreseen to, to get C uh neutron background.

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But you have in addition C data to.

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In effect if it is there it is already there.

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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.

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Now in a very long bubble chamber. It is clear that C interaction is only 70 or 80cm.

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Therefore you won't have any events if cu uh to to new to cons.

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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.

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Now. From that moment on, it was a decision to make a dedicated search for neutral currents, both in electronic and in hadronic channels.

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And so the analysis continued simultaneously with both user in charge current.

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It just a few weeks later. Dan Perkins wrote a memo where he recalculated also knowledge into previous neutrino

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experiments and distributed search at sea to see collaboration to see neutrino collaboration.

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Here. You can see here. Um.

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In order to interpret the data, he used a very simple model, a linear model.

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Just assuming that any neutrino interaction emits a neutrino just in the same direction as a sad beam,

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then a neutron interaction can appear in two ways.

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If you observe a neutral, a star is either associated to its source signature, you know, or else, since source is outside.

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So these events have been called, in our jargon, as events, background events, and associated events.

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It is very easy to calculate it because you know, what is the interaction probability of a neutron into a liquid,

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and c c the ratio of the mass effects of the to um of the two media.

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Now. What are said? Lessons from previous experiments.

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He had c c c CS of his PhD student.

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You know Hyung, you have already heard about him. Um, a full analysis of the of of the data.

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Then, um, 1967, there was a second one with propane in the chamber.

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The advantage was that you have not only bound protons, but also free protons.

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And a very important insight.

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Uh, uh, came said si initial value.

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Of the 5% you have seen before was underestimated because single unidentified positive tracks were taken as pions.

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And that explained very well why it is so small, so reanalysis.

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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.

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This was published and in Japan for pi candidate um.

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Don Perkins on the basis of this very simple model.

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Evaluate. It's a neutral background.

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This evaluation is simple because the only thing you need is to calculate it by a waste ratio and number of associated events.

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So the product of the two is a prediction of how many nutrients a background events you are expecting.

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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.

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Unfortunately, this excess cannot be interpreted as a discovery because the model was far too simple.

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So Perkins conclusion was existing data are indicative but not conclusive.

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The prospects for discovery. We are still at the beginning of 1972.

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Um, which looks promising because of the links of the chamber and a very strong warning he was given to him.

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What neutron background is? This is a quote from from his, uh, memo.

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Also, I know that many people at CERN are working on this problem.

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There appear to be innumerable pitfalls in the analysis, and a thorough discussion at an early stage would be worthwhile.

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So she started. She for the analysis was very clear.

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And, uh. Yeah. Oh, it's just too much.

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How can I go back? It's a collaboration.

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Was very clear about the challenge. Say they were given to.

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It was so. Signal was obvious. An event.

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We'll say it's no charged lepton. It was also clear what the background is.

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So c c challenge consisted in proving sets.

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The number of background events is small compared to the number of candidates.

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It was also known that an American group, uh, was H.

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Harvard, Pennsylvania Wisconsin group was, uh, searching for the same effect.

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And so there was competition between them.

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So it's a collaboration felt very well. So tension between being first and being right.

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It's the end of the year.

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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.

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It was originally misclassified, and a PhD student in charge said.

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Well, maybe it is an electron and not a moon with an overlay.

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So he went up to see, uh, supervisor, which was called Schulz.

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And sure, she looked at it. Well, such looks more like an electron.

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So they went up to find snow and I. Oh, such is the discovery.

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And he immediately took the next line to work on.

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Poking was already biting. And he left the event in his hand.

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Intern Perkins was shouting, neutrino or antineutrino?

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When he answered antineutrino, they were very happy and had a big embracement.

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You can see here when she celebrated, she often event.

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You can see in the middle, uh, see head of the neutrino group and two persons later on,

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uh, was, uh, uh, Helmut Feist, now the director of the institute and just scanning girls.

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Here are two candidates. Beautiful candidates of neutral cards.

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Um, you can see direct by your IEC interactions.

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There was no doubt about it. Now in March.

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So precisely one year later.

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Look, Eric, it says in meeting with a big smile.

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He. In the meantime, uh, 38,000 neutrinos and 207,000 antineutrino pictures have been scanned.

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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.

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In order to make a direct comparison, a charge card sample was used well beyond.

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It was ignored and exactly the same criteria applied to the final state um of of of of the event.

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Now, uh, there was a clear expectation.

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If these events are all due to neutrons, then there must be a fall off at the beginning,

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since the bubble chain is much longer, four times longer since the interaction links of a neutron.

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So if you then observe events in the second part, you have a discovery.

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So she she she also is. If they are all to you, to your consent, you must have a flat distribution.

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Therefore, there could be everything in between these two.

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So if you look at your data, you can see that the ratio is very well consistent with being a constant.

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And therefore, uh, there was the intriguing situation.

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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,

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wait, you have forgotten something, namely C Newton's May Cascades.

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Therefore it is not C interaction things which is relevant potsie cascade links which is which could be much bigger.

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Background can be much bigger, on the other hand.

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So in Latino flux is not just centring, uh, at the entrance window, but extending over a full range where lots of material is.

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This means that many, many more neutrino interactions, uh, outside if sent by chance.

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Since a neutron is emitted at a certain, uh, angle towards the chamber, it was filling completely, uh, said chamber and CFO.

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There was no distinctive feature left. So therefore c euphoria was attempt and there was no distinctive feature left.

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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.

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This system meant one had to make an A prediction.

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A serious prediction of all the details of the experiment.

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And since you have seen. See how it set up, it's very, um, complex.

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Only a monte Carlo method was able to cope with this.

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Uh, we had we needed five different ingredients.

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One was set geometry of the set up as it was known.

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Symmetric distribution that was also known since the dino flux was measured.

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So dynamics of the neutrino interactions could be taken directly from the experiment.

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So see real problem which remained was uh, to propagate the final state particles during uh see how material which was there.

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Uh, is this where we are requested to come up with a result in a few weeks?

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Because, uh, many people were believing they had already made a discovery.

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Now, finally, um, a breakthrough came by recognising that the bison component is inactive.

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So the only thing which was left is, uh, is the elasticity of a proton or a neutron, um, along its path.

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This required um an a c c c probability, how much energy is deposited and how much energy is transported away.

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Uh, this could be obtained from, uh, from, uh, data directly from the important data or the nutrient data.

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And therefore the result was an absolute prediction with no free parameter.

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Which means if you make a predictions and you stick out your head.

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Now and in July of 73.

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So four months after meeting at at CERN,

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um Polya had uh finalised C but number of uh associated events and he came up with 15 neutrino and 11 antineutrino events

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on C also and C neutron background program was also ready and predicted over x equals one plus or minus point three.

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Now we made this possible hypothesis saying that all candidates we have observed are due to background.

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In that case, you can directly calculate what po boys is,

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namely 6.8 plus or minus point three to be compared with a calculation which is one plus or minus points.

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So there was a huge discrepancy and see hypothesis could be rejected, and so claim could be formulated that there is a new effect.

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See, uh, on all um, our uh, collaborators, our colleagues in H1 and sorry, in intercultural verse and thinking of uh, flows into calculation.

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And this lasted for about two weeks of discussions.

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And finally everybody was convinced.

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See, see the result percent presented by we see in Sassoon Auditorium in July 19th and a few years a few days later,

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see paper was submitted in Physics letters. Well see as a see also event was already published.

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It's a beginning. Yeah. Here are the authors of the discovery, 16 authors altogether a collaboration.

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See. The result was.

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Then the discovery was presented to an electron photon conference.

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One month later, in August 2731, and Jeremiah was presenting data.

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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.

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By Fred Bullock. As speaker said,

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details were given as soon as he opened his most servers to make an intervention and asking very nasty questions about Newton background.

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We were very prompt in answering all these things.

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And finally, it's the epitome of C and young.

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He stood up and said, due to have been discovered.

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Now. Unfortunately. This. Yeah. I have to, uh, at the end of this, uh, we'll be.

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I was waiting outside and she said, I have given you help, but I believe you are right now.

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His belief to be right lasted only a few weeks because, see, collaborations, HPE collaboration decided to postpone,

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say, a publication, and to make further runs, to get more statistics in order to do so.

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So introduced a 13 inch iron plate.

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Indeed. So he got a bigger acceptance of a far bigger number of it, but unfortunately, uh, see, see lost significant effect.

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And from that moment on, uh, almost the rest of the world was saying somebody must be wrong.

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It must be God. Campbell. So we were treated with English and critics.

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Uh, it uh uh uh, it didn't work at some moment would say director of general education.

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And uh, he describes very well as the situation of each of us here.

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So I will read it.

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It is published in Switzerland, Korea, when they claim to have found due to current single command, was followed by a report from Fermilab.

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So the NCO work ratio, they found, was consistently zero.

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Many physicists believe that the Gargamel result must be wrong.

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Indeed, one senior physicist at CERN.

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Well, everybody knows this. It was Stein Palco, uh, so heavily against governments that he lost half of his wine cellar.

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But he himself was always very supportive of the experiment.

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I did meet him on one occasion into CERN lived.

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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.

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My response. So Pushkin's response was that coming after split A2 Alpha, it would be an absolute disaster.

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However, I knew the group had gone. So I see event analysis many times,

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and for almost a year we had searched intensively for some other explanation for the effect observed without success.

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So I thought the result was absolutely solid and you should just ignore rumours from across the Atlantic.

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I don't know if my words reassured him, but he got out of the lift with a smile on his face.

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Now the situation for C collaboration and for soon became Russell um critical.

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Um, it boils down to this equation is a cascade broke?

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Um, right or wrong? We need a decision. And this was obtained by sending, uh, pulses from CPS proton pulses directly into the chamber.

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So you can see this, your eyes, what the cascade is.

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And, uh, the right side, you see a beautiful example of a seven GeV proton entering, uh, generating a very, uh, clear cascade.

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This, uh. Uh, I had to make a prediction of what to be observed, which is, uh, which is observed events beforehand.

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So it was clear what could happen.

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This.

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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.

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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.

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This was later on reported to APS meeting in Washington.

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So all aspects of the cascade are confirmed.

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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.

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So after all, Gargamel was also time, right?

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We did not change one iota. Gargamel.

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In the meantime, w statistics in in agreement with previous results.

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This is a beautiful new experiment by Barry Barish in a narrow neutrino beam and, uh, single pion production has been observed.

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And finally, also HB w group has confirmed a signal.

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And going from yes no to yes. Uh, sick joke.

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Uh, came said they discovered the alternating current.

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Now, uh, it was this discovery.

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Um. Countable later.

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Important contribution to high energy physics and soon gained a leading role by this discovery.

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Well, I went before I finished, but very quickly.

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Um, it it see, the impact of the discovery was most enormous.

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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.

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There were two immediate, um, uh, effects, namely, uh, duties.

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Effects. It's a is that it has has no coupling to two neutrinos.

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Um, see, um, since gravitational collapse, I don't you argument see also saying was in neutrino.

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Uh, um it. It 19 at 19 six at it.

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Ah. And uh, so neutrino conference was taking place at that moment.

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So sine squared theta was measured to plus or minus two uh plus or minus 0.05.

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And therefore within C uh um see we see simple uh Weinberg model.

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It was an easy to calculate since there was only one free parameter to calculate the mass of the W, which was 17 GeV.

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So it was clear said all the previous uh, uh, searches were just impossible.

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So neutrino experiments which uh, Steinberger find some in his said if it is 20 GB, I will discover it.

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But no you can see it was impossible.

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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.

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No. If you look at it at the right side, you can see some beautiful electroweak weights.

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Um, starting at 73, with the discovery of signal to Collins and A, W and Z and finally six.

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So it's the end of of these, uh, installing this, uh, sort of standard model in its full glory.

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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.

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So thank you. You're done.