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จากนักเรียนท้ายแถวสู่นักฟิสิกส์รางวัลโนเบล (6)

Koshiba:
I was employed by a private university called Tokai University, and I was given an office and part-time secretarial help. I also took a few graduate students. But the working environment is entirely different from my days in the University of Tokyo. For instance, my research funding was only 300,000 yen.
DeVorkin:
About three thousand dollars?
Koshiba:
Yes.
DeVorkin:
Per year?
Koshiba:
Per year.
DeVorkin:
So that's what the university gave you. It wasn't much.
Koshiba:
No, not at all.
DeVorkin:
Did that include travel money too?
Koshiba:
Yes. Everything. This appointment also came to an end this last March, so I am now a completely free man now — jobless. [laughs]
DeVorkin:
That's what you said, you were free as a bird, when you sent a fax back to me. Yes. But you have been traveling around, visiting different major facilities in Europe I understand, and you had a 2-year appointment in the United States.
Koshiba:
Yes. That was not quite an academic appointment. There is a society, the Japan Society for the Promotion of Science, which is under the jurisdiction of the ministry of education. This organization has a liaison office in Washington, D.C., and I was assigned to that office for two years.
DeVorkin:
Is there a reason? Did you deliberate over whether you wanted to take the job or not? What were the duties?
Koshiba:
Duties? There weren't any, but the general idea was to keep up good relations with the NSF people, the DOE people, and the Academy people. And as I said, I organized the science forum once a year.
DeVorkin:
Right. Mm-hmm [affirmative]. The nature of the forum, you brought in people to speak. What was the character of it?
Koshiba:
Well, I wanted to present the status of Japanese science and technology and I wanted to make the DOE and the NSF people very informed of Japanese trends in these areas. So I invited from Japan very distinguished scholars, like Esaki, Leo. Esaki, who is now the president of Tsukuba University. He got the Nobel Prize many years ago for finding the tunnel effect in semiconductor junctions. — also Oda.
DeVorkin:
Yes, Minora Oda.
Koshiba:
I invited four distinguished scientists from Japan, and as a guest speaker I invited Leon Lederman. You know him?
DeVorkin:
I know the name, yes.
Koshiba:
And also another big name, another Nobel Laureate in biophysics who was the president of Johns Hopkins at that time. His name was Nathans. This year I invited Burt Lichter of SLAC as a guest speaker.
DeVorkin:
At the forum you would then have an audience, you would have an invited audience?
Koshiba:
We invited about a hundred people.
DeVorkin:
Yes.
Koshiba:
And the bioscience speaker was a deputy director of NIH. I don't remember his name.
DeVorkin:
Oh, that's okay. Alright. But I get a sense of what it was like. Let's talk about the Kamiokande part, and of course your plans for Super-Kamiokande.
Koshiba:
I told you how I helped to get the funds.
DeVorkin:
Yes, I would like you to repeat that discussion. That's very important. Now Super-Kamiokande was operational in April of '96, and my interest is to find out what arguments were made for scaling up to 32,000 tons of water —
Koshiba:
The correct figure is 50,000 tons.
DeVorkin:
Fifty thousand tons of water. And how you worked to get the support for it. Because you were retired, were you not?
Koshiba:
[laughs] Yes. I was at that time a guest professor at DESY and the University of Hamburg. As I said, I retired at the end of March that year, and then after attending the international conference in Kyoto at the end of April, I went on to Hamburg. I appointed Totsuka as the spokesperson of the Kamiokande experiment. At that time, the Institute for Cosmic Ray Research was headed by a man called Arafune, a theoretical physicist. He's a good theoretical person. It was a time when the minister of education was seriously thinking of abolishing this cosmic ray institute because —
DeVorkin:
The ICRR.
Koshiba:
Mmm [affirmative].
DeVorkin:
And why was that?
Koshiba:
Because they didn't produce any academic results, and that institution was slated to be abolished. It just happened that Totsuka and Arafune were good friends from student days. I was also objecting. The Kamiokande experiment was sponsored by the ministry of education through the channel of the faculty of science of the University of Tokyo.
DeVorkin:
Not through the ICRR.
Koshiba:
It had nothing to do with ICRR.
DeVorkin:
Right.
Koshiba:
Because I didn't like the way things were done at ICRR. When I was in active service, I didn't want to have anything to do with the ICRR. Totsuka knew that. But after I handed the baton to him he wrote to me in Hamburg to the effect that he was seriously thinking of transferring the project to ICRR.
DeVorkin:
The Kamiokande project.
Koshiba:
Mmm [affirmative].
DeVorkin:
Okay.
Koshiba:
Also he wanted to prepare for Super-Kamiokande through the ICRR. I replied to him, "You know that I didn't want to have anything to do with ICRR. However, now you are the boss of the experiment. If you think it's good for the future of the experiments, go ahead." I didn't make any objection. So it was transferred to ICRR. Next spring, I received a letter from Arafune and Totsuka.
DeVorkin:
This was the spring of '88?
Koshiba:
I think so. They told me that they wanted to push the Super-Kamiokande proposal, but because of the amount involved they worried. They asked me for advice. I wrote back to them, "In dealing with bureaucrats, one has to be very careful, because if you ask some big shot to use his influence over the ministry of education, they would consider it as interference from the outside." I happened to know a number of scientists who won Nobel Prizes. So I wrote to them asking them to write a letter of recommendation for the Super-Kamiokande, and I asked them to address their letters to Arima, to the president of the University of Tokyo, who happened to be my junior in the physics department. About five or six distinguished physicists all over the world did write letters to Arima. Arima immediately made copies of those letters, and forwarded them to the attention of a big shot in the ministry of education. In this way, nobody felt pushed around, you see.
DeVorkin:
But didn't you also have friends in the ministry of finance?
Koshiba:
Yes, I had a good friend.
DeVorkin:
And wasn't there a step there too, wasn't there there?
Koshiba:
Yes, but I didn't have to make contact with my good friend in the ministry of finance at that time.
DeVorkin:
Uh-huh. But you did at one point, didn't you, for something?
Koshiba:
Some time ago.
DeVorkin:
And what was that for?
Koshiba:
Not for the Super-Kamiokande. I didn't have to contact the minister of finance for this project, because my good friend was already out of the ministry of finance. He was at that time the president of the Sakura Bank.
DeVorkin:
Okay.
Koshiba:
After a stint at the Sakura Bank, he became president of the Bank of Japan. Also the top bureaucrat of the ministry of finance was a classmate of mine, but I didn't like him, so I intentionally avoided contacting him.
DeVorkin:
Okay. Let's talk a little broader about the other different detectors and projects that are underway. By the late 1980s there were many new projects on the board. There was the Gran Sasso in Italy, that was a large argon drift chamber?
Koshiba:
Yes.
DeVorkin:
The LVD, the large liquid scintillator; GALLEX, which is the germanium detector; and the Sudbury project, which was a Canada-U.S. sort of a Kamiokande type detector using heavy water, deuterium oxide.
Koshiba:
Heavy water. Yes.
DeVorkin:
With all of these different projects, how were they complementary or competitive to Kamiokande?
Koshiba:
Let's talk about them one after the other. GALLEX is in a way similar to Ray Davis' experiment in the sense that they use the radio chemical method. The difference between the two experiments is that the detection threshold of GALLEX is considerably lower than Chlorine-37 of Ray Davis. Now, the operation of this Gallium-71 experiment is really a good thing, because it is the only experiment which can measure the flux of pp neutrinos, which is the main source of energy. Even though from the neutrino astrophysics point of view it lacks the directional information, energy information, and time information. But the fact that it can observe the flux of pp neutrinos is very important. And it did function as expected; I think it has already been closed, GALLEX. When it comes to SNO [Sudbury] it is a very nice detector if it works. In a sense it's complementary to the Super-Kamiokande. SNO stands for the solar neutrino observatory, and it's located in Sudbury, Ontario. My former collaborator, Gene Beier of Pennsylvania, is one of the main figures there.
DeVorkin:
Yes, you mentioned former collaborators. I know that the University of Pennsylvania-Japan collaboration has ended. Was this a planned ending, or did something happen to cause it to end? They're not here now, right?
Koshiba:
One of the reasons I suspect is that Totsuka and Al Mann didn't get along. That's my guess. I was away in Europe, I don't know exactly what happened.
DeVorkin:
Because Mann doesn't say a thing about it in his book. Okay, but that's all you know at this point.
Koshiba:
Mm-hmm [affirmative].
DeVorkin:
What about the fate of the IMB detector? I understand that's closed?
Koshiba:
Yes, it's closed.
DeVorkin:
And why is that?
Koshiba:
I don't know. [laughs]
DeVorkin:
Who should I ask?
Koshiba:
There is a professor at UC-Irvine who is at present one of the Super-Kamiokande collaborators. His name doesn't come to my mind. He is a successor of Fred Reines at UC-Irvine. This man may be able to tell you about the fate of IMB.
DeVorkin:
Okay. I wonder how I would find out his name. Fred Reines is no longer —?
Koshiba:
Fred Reines is still alive, but the actual work is done by this man. He is already a full professor there.
DeVorkin:
We'll try to get his name. The important thing is that the IMB did close, but there are other types of detectors now worldwide. At one point you called for a worldwide network of Super-Kamiokandes. But it seems as though —
Koshiba:
It's not practical.
DeVorkin:
It's what?
Koshiba:
It's rather difficult to form such a network.
DeVorkin:
People seem to be more interested in building different types of detectors.
Koshiba:
That's right.
DeVorkin:
Is there a reason?
Koshiba:
I don't blame them. [laughs]
DeVorkin:
What was the advantage of a worldwide network of Super-Kamiokandes?
Koshiba:
When you have only one Super-Kamiokande, even if a supernova occurred at the center of our Milky Way galaxy, we can use the directional information only from the first few millisecond burst of electron neutrino, which makes an electron scattering, which gives you the directional information. Even so, the accuracy of detection is something like 2 or 3 degrees from the number of expected events.
DeVorkin:
Yes.
Koshiba:
If we had a world network of Super-Kamiokande type detectors, you could use the timing of first burst to make a triangulation, which gives you much better accuracy in directional information.
DeVorkin:
Finding out which star had done it.
Koshiba:
Yes.
DeVorkin:
Assuming that it's not obvious.
Koshiba:
Yes.
DeVorkin:
In the case of 1987 A, you had 14 hours before the optical?
Koshiba:
I don't remember. You better check with the article.
DeVorkin:
It was a good numbers of hours.
Koshiba:
Mm-hmm [affirmative].
DeVorkin:
Now before we end up with just some general questions, I think a while ago we said we would go back and talk about some of the earlier projects that you were asked to head and that you refused to, thinking that it wasn't a good idea, and one of them was DUMAND. Is that right?
Koshiba:
[laughs] Yes.
DeVorkin:
Could you describe again what you had said last night to me about DUMAND, Deep Underwater Muon —
Koshiba:
Muon and Neutrino Detector. Well, it was well over 20 years ago. One day, Fred Reines called me long distance while I was in my University of Tokyo office. He said that he was now discussing with possible colleagues a new project which would be a very large detector deep underwater. He said he wanted me to join the discussion. I replied, "Fred, I'm sorry, I used up all the foreign travel money this year. I cannot possibly go." The next week I received a telephone call from the ministry of foreign affairs in Tokyo, and was told that they had the travel money in hand. My guess is that Fred worked on the Japanese Embassy in Washington, D.C. so that the minister of foreign affairs got involved. Now that travel funds were available, I went there. It was at the time APS meeting in Utah, and there were about 20 people gathered in a small room, discussing what they could do with this underground detector, how to build it, and so forth. I sat quietly listening to the discussion all around, and my intention was to say goodbye at the end. I wasn't interested in the project.
DeVorkin:
Could you tell me why you weren't interested?
Koshiba:
Because their idea of the DUMAND detector was so crude. How should I describe my feelings? When you want to accomplish something by an experiment you define what you want to identify, what you want to measure. First of all, your detector has to be able to detect, and then measure the characteristics of the particular type of event in your experiment. I got the impression that the people in that room just decided to place a photomultiplier, at say 150 meters apart, to see what would happen. It seems to me that before you decide on a separation of 150 meters between phototubes, you have to specify the type of event you are searching for — whether this 150 meter separation is appropriate or not. It was like a group of amateurs trying to do something different from existing experiments. It's good to be different, but one has also to be able to accomplish something.
DeVorkin:
I see.
Koshiba:
I wasn't impressed at all.
DeVorkin:
I see. You look for specific characteristics in an experiment, where the parameters are well defined.
Koshiba:
Yes, if I were the one who has proposed this big experiment, I would first make a number of simulations to determine the appropriate relative distance of phototubes and what will be the expected event rate, and so forth.
DeVorkin:
Did you do that for Kamiokande?
Koshiba:
Oh yes, of course.
DeVorkin:
This had been your general experimental style. Why do you think they did not do this?
Koshiba:
I don't know. My impression was this. Fred Reines is a great physicist. He always has good ideas. However, he's not an experimentalist. So when he had a good collaborator like Cowan, who didn't have any theoretical knowledge, but was a really good experimentalist. Cowan, mm-hmm. He's the one who did the atomic power neutrino experiment with Fred. At that time Fred had a good experimental collaborator, and he got good results. Unfortunately, since then Fred hasn't had a good experimental collaborator.
DeVorkin:
I see.
Koshiba:
Probably Fred himself didn't trust those 20 people as experimental collaborators, and that was the reason why he wanted me to get involved.
DeVorkin:
But it must have meant something to him when you didn't want to get involved. Did that sort of send a message to him that there was something wrong with —?
Koshiba:
Because I kept quiet all during the discussions which lasted more than an hour, all of a sudden he asked me, "Toshi, you had the experience of directing a very large scale international collaboration experiment."
DeVorkin:
This was the Marcel Schein project. Now I understand.
Koshiba:
Fred said, "Why don't you take, direct this DUMAND project?" I replied, "Fred, I'm sorry, I cannot possibly direct this big project." Fred asked, "Why?" I answered, "In order to bring this big project to a successful conclusion, the director has to be able to pick up the telephone and talk directly to the Queen of England or the President of United States, which I cannot do." Then Fred asked, "Can you think of somebody who could direct this project?" I thought it over for a few minutes and said, "Yes, I can think of one person." "Who is that?" I said, "Professor Blackett." And then I told Fred, "I'm sorry I cannot join this project, but if you need a liaison person in Japan, I would recommend Professor Miyake."
DeVorkin:
Now which Professor Miyake is that?
Koshiba:
Professor S. Miyake, who was the director of ICRR for many years.
DeVorkin:
You were not recommending yourself.
Koshiba:
No.
DeVorkin:
Right. Okay.
Koshiba:
So, I thought I washed my hands of the project. But there is an after story. A few years later I received a letter from the DOE asking me to referee the DUMAND proposal. But the proposed experiment looked to me just the same crude plan as before, so I graded it at the lowest level. Still, the DOE supported it.
DeVorkin:
And why was that do you think?
Koshiba:
I later found out there were two more people in Japan who were asked to give a reference. One was S. Miyake, whom I just mentioned. The other was Jun Nishimura. I mentioned his name in relation with ballooning.
DeVorkin:
Right. And they both gave it good marks?
Koshiba:
Yes.
DeVorkin:
Did you ever have arguments with them later?
Koshiba:
I later talked with them. They said, "Oh, we just wanted to be nice." [laughs]
DeVorkin:
Was this a particularly expensive project?
Koshiba:
DUMAND?
DeVorkin:
Yes.
Koshiba:
If you wanted to do it properly, it was a very, very expensive experiment. Not only that, because of the large pressures involved at depths of 4,000 meters, four hundred atmospheres, there were a lot of technical difficulties involved.
DeVorkin:
What happened to DUMAND? Did it work?
Koshiba:
They did try some experiments. A couple of times they lost the detectors, found them and then re-installed them. Oh, I don't know, it has a rather sad history.
DeVorkin:
Okay.
Koshiba:
John Learned of Hawaii has been involved in it from the very beginning. He can tell you all about it.
DeVorkin:
Fine. If I continue with that.
Koshiba:
You might remember this. One of the original collaborators came from the State of Washington. He was a good friend of the senator of the State of Washington. This man was a little bit queer in the sense that he wanted to propose a neutrino as a signal to communicate with an atomic submarine deep underwater.
DeVorkin:
This is the senator.
Koshiba:
No, the physicist.
DeVorkin:
The physicist!
Koshiba:
Yeah. [laughs] And he proposed a test experiment using the neutrino beam of Fermilab, but the director at that time, Leon Lederman, thought it was a crazy idea and didn't give him machine time. So, [laughs], he went to the senator of the State of Washington, and the senator, knowing nothing about such things, raised hell. And [laughs] Lederman had to allow this man to build a detector of his own just outside the fence of Fermilab. [laughs]
DeVorkin:
That's amazing. I know that, after talking to Professor Suzuki the neutrino beam from KEK is going to be used to test for neutrino oscillations here at Kamiokande. That's something very different. I mean, the impression I get is that you need something like it to make the submarine thing work, I mean how do you modulate a neutrino to get any information out of it?
Koshiba:
When I had published my paper on the atmospheric neutrino anomaly from the old Kamiokande, I made a number of personal guesses which I talked about five years ago at Cal Tech for the first time. One of my guesses was about the neutrino masses. I'm very happy that the new Super-Kamiokande confirmed, with much better statistics, the conclusion of old Kamiokande result on the atmospheric neutrino anomaly: the ratio 1:2 or 1:1. I was for a total of about four years, a member of the research council of KEK. I told Sugawara, who was director general of KEK at the time, "You better quit the job. Go back to physics." [laughs] Just before I left for the United States, about three years ago, I was attending this council, and made the following statement, "Take my advice. Now that we are quite sure that the neutrino has a mass of such-and-such range, Fermilab is now contemplating a long baseline neutrino oscillation experiment. It's called MINOS. "They already have a good high-energy neutrino beam, but they don't have the detector yet. Also, in Europe CERN is seriously considering the neutrino oscillation experiment with the Gran Sasso detector. There again they don't have a good detector. Here in Japan we have an excellent detector, the Super-Kamiokande. The only problem is that we don't have a high enough energy proton accelerator to produce a neutrino beam. So this is my advice. "Increase the energy of the proton accelerator to at least 35 GeV so that the resulting neutrino beam can produce tau-leptons." I made it very strong. Next year, when I was already in the Washington office, Sugawara came and stopped by. He then told me that his institution was now proposing a new proton accelerator which can go up to 50 GeV.
DeVorkin:
Oh, good.
Koshiba:
"We are following your advice." That was what he said.
DeVorkin:
That must have been very gratifying.
Koshiba:
Yes, I was happy.
DeVorkin:
Yes. But would it not have been possible to cooperate with Fermilab, or with CERN, and have them direct the neutrino beam here? Or is the distance too great?
Koshiba:
When I was back from CERN and installed again in Tokyo. I received a letter from Carlo Rubbia, who was the director general of CERN at that time. Carlo said in his letter, "Toshi, we are studying two possibilities. One is to shoot our neutrino beam to Gran Sasso, and the other is to shoot our beam to the Super-Kamiokande. What do you think of these two possibilities?" My reply was this: "By all means concentrate on the possibility of using Gran Sasso. Because, you know, to shoot the neutrino beam to Kamioka, it has to go deep down, which is not easy, because the beam energy is not small. You have to bend vertical down.
DeVorkin:
You mean it isn't a linear beam?
Koshiba:
No. You see, when it is a horizonal bending, there is lots of space. But when you want to bend it deep underground, then not much space is available for bending, unless you dig a deep tunnel.
DeVorkin:
Oh, I see. Yes, as far as the wave guide is concerned.
Koshiba:
Mostly it is, yes. Mostly it's difficult because at this large distance, neutrino beams spread out. So even with a gigantic detector like Super-Kamiokande, the number of events you can detect is very, very small.
DeVorkin:
Yes. Okay. We've gone a good while, and I just have a few more kinds of questions to ask you about particle physics and about observational neutrino astrophysics. In 1996, Bahcall and others, I think in an article that was co-authored possibly by Totsuka, stated that most physicists and astronomers now believe that the observational discrepancies are not — you know, between observed neutrino flux and predicted — are not in the standard model, but in, and I'm quoting, "our overly simplistic view of what neutrinos can do after they have been created." By that he says we need better knowledge of the electro-weak interaction between the neutrino and the environment between the sun and the earth, or neutrino mixing in the sun or in space. Do you basically agree with that?
Koshiba:
Yes.
DeVorkin:
Is it a question that can be experimentally tested? Is neutrino oscillation one of the ways to go to better understand this?
Koshiba:
One of my personal guesses is related to this problem you just asked. Additional neutrino oscillation experimental result of not observing the expected amount of neutrino, this is called "disappearance experiment." You don't observe what you expected.
DeVorkin:
Right.
Koshiba:
Disappearance. The real clarification has to come from what is termed "appearance experiment." Okay? You shoot the neutrino you are sure of consisting entirely of nu-mu. After a certain distance, you detect a neutrino interaction in which tau-lepton is produced. That means during this passage some of the nu-mu were converted into nu-tau to eventually produce tau-lepton. This is called "appearance experiment." You detect something which was not in the initial condition. Yes?
DeVorkin:
Right, yes.
Koshiba:
So this appearance type experiment gives a finer picture of the neutrino oscillation. And that is a experiment I urged KEK to perform by increasing the proton energy so that it can produce neutrino beam of energy high enough to be able to produce a real tau-lepton in Super-Kamiokande.
DeVorkin:
Right. Okay, next question. You already mentioned this at the beginning of the interview, and also in your review paper, that observational neutrino astrophysics began in the years 1987 to 1990, despite Davis' work.
Koshiba:
That statement made John Bahcall very angry.
DeVorkin:
Well, that's what I wanted to know.
Koshiba:
Yes.
DeVorkin:
Yes. The arguments you gave were that you had to have data of astrophysical value, arrival time, direction —
Koshiba:
Time, direction and energy.
DeVorkin:
— and the energy spectrum. Yes. Why was he angry with this statement?
Koshiba:
Oh, he was attached to Ray Davis' experiment I guess.
DeVorkin:
But neutrinos were part of theoretical astrophysics before that time.
Koshiba:
Yes. But I said at the beginning observational neutrino astrophysics. Yes?
DeVorkin:
And did John Bahcall have any good arguments stating that at least Davis had found neutrinos?
Koshiba:
Well, there is a proceeding of an international conference held in Takayama around 1994. I don't remember exact year. That was the time when John Bahcall blew his top, and he made a rather nasty statement about my report.
DeVorkin:
Is it in print?
Koshiba:
Yes, it should be in print. Also, my reply is in print.
DeVorkin:
And where is that again do you think?
Koshiba:
In the proceeding of this international conference on — I don't remember the exact title — but the young people here would know. It was held in Takayama.
DeVorkin:
Oh, in Takayama. Okay, maybe I could actually even get the citation from John Bahcall.
Koshiba:
Yes. [laughs]
DeVorkin:
He was the one that recommended I come and talk to you.
Koshiba:
Oh yes? [laughs] I don't have any hard feeling against him. [laughs]
DeVorkin:
No. I mean, if you make a bold statement like that, you expect that somebody will say something.
Koshiba:
Oh yes. [laughs]
DeVorkin:
Do you know Ray Davis?
Koshiba:
Yes, he is a very nice man. I like him.
DeVorkin:
What did he say about this?
Koshiba:
He doesn't say. He just smiles.
DeVorkin:
Okay. Maybe it means less to him. As I mentioned, I'm building this exhibit, and I want to be able to link the neutrino detector work to the many ways that the universe is observed. We'll have a whole array of detectors from gamma ray and X-ray detectors and neutrino detectors, ultraviolet sensors, things like that. But what would your recommendation be for linking your neutrino work here to anything of cosmological significance? How would you describe the cosmological significance of the neutrino detection in supernovae in 1987-88 for instance? What did it confirm that would be of cosmological significance?
Koshiba:
Well, I have to go back to my personal guesses, again.
DeVorkin:
Sure.
Koshiba:
The third item included in my personal guesses is related to what is called the background neutrino flux, which corresponds to cosmic microwave background of 2.7 degrees Kevin. There also has to be a cosmic neutrino background at a temperature of 1.9 Kelvin degrees. We want to detect it.
DeVorkin:
How could you detect that?
Koshiba:
Good question. I was talking to my last crop, my students who are now associate professors, both of them are my students.
DeVorkin:
This is your last crop, you said? Okay. Again, this is for the transcriber. Now what you're talking about is observing a very low energy neutrino, a red-shifted neutrino.
Koshiba:
Mm-hmm. [affirmative].
DeVorkin:
Okay.
Koshiba:
Which you cannot possibly dream of detecting by the Super-Kamiokande. You have to use an entirely different technique. Yesterday I was talking to some young people. The next big project, you yourself have to conceive. They asked me for my advice. I talked about the possibility of detecting this background neutrino. I have been giving some thought for years to this problem, and I think I could make a mirror which reflects low-energy neutrinos.
DeVorkin:
A mirror.
Koshiba:
Mmm [affirmative]. I wasn't sure about this possibility, so I wrote a letter to Professor Nambu, whom I respect very much as a theoretical physicist.
DeVorkin:
Yes.
Koshiba:
And I asked if this possibility is substantiated theoretically. He replied in one and a half pages stating that this was indeed possible.
DeVorkin:
He thinks it's possible.
Koshiba:
Yes. However, Nambu's way of describing why this is possible was beyond my comprehension. So I asked Professor Takeda to make a more detailed explanation. I also respect Professor Takeda very much. He's a rather quiet type, but certainly a most reliable theoretical physicist. He also gave a proof that this is indeed possible. You can totally reflect neutrinos. This is one step forward. Yes? The next remaining problem is much more difficult: how to detect such low-energy neutrinos. I gave some ideas to these young people, but for this we have to wait for advances, and a very high frequency technology like terra-hertz devices.
DeVorkin:
Terra-hertz?
Koshiba:
Mm-hmm [affirmative].
DeVorkin:
Yes, I would say so. But, getting back to the detector that we would like to display in the museum, its significance really is—and I'm sort of looking for your advice here—in displaying it in a gallery that is essentially about cosmology, its significance is in verifying theories of supernovae reactions.
Koshiba:
That's one thing, yes.
DeVorkin:
And the neutrino flux that was measured, as I understand it, did pretty much agree with models for the nature of neutron capture and other processes in the explosion of supernovae. Is that correct?
Koshiba:
Yes. The standard theory of supernovae explosion especially is length of the signal time of about 10 seconds. Our signal time had a spread of 10 seconds. That was rather important in understanding, in the sense that neutrino, even with its small cross-section, because of the extreme high density, it has to diffuse out. Yeah? If it comes straight, the signal time must be very, very short.
DeVorkin:
Right, right. So this is the diffusion, the scatter time, and that verified the physical conditions within the supernovae.
Koshiba:
Yes.
DeVorkin:
So the Irvine contact about the IMB is Hank Sobel?
Koshiba:
Mm-hmm [affirmative]. He's a nice man, very good-natured.
DeVorkin:
I think I've heard the name. Yes. I have a friend who is a historian at Irvine, and I might ask him to help out and contact him for me. So we could add that to the record.
Koshiba:
Another result of cosmological significance stemming from the Kamioka experiment had to do with the remnants of past supernovae explosions. Those first cases must have occurred in the past, and a remnant of those explosions may be detectable. We searched for them, and we set some upper limits. It wasn't very much in the way of information, but it did confirm certain aspects of present cosmology.
DeVorkin:
Alfred Mann talks about the missing mass and how the missing mass in the universe might be in the form of neutrinos. Do you believe in that?
Koshiba:
There is a very popular theoretical physicist whom I believe is the director of the Weizman Institute. His name is Harari. This gentleman publicized a guess that if a tau-neutrino had a mass around 10 electron volts, it could account for the missing mass. And he also added some of his theoretical speculation and so forth, and became an attractive target for some of the experimentalists. And indeed, there are experiments going on at CERN specifically searching for a tau-neutrino of mass around 10 electron volts. Yeah?
DeVorkin:
That is not anything that Kamiokande could detect. No.
Koshiba:
Instead we are setting the mass region much lower.
DeVorkin:
You believe the mass is a lot lower.
Koshiba:
Mm-hmm [affirmative]. From our result.
DeVorkin:
Uh-huh. Because your background is around that range, is it not, 10 electron volts?
Koshiba:
Oh, no. Our expected neutrino mass is less than one tenth of an electron volt.
DeVorkin:
Oh, a tenth of an electron volt. That would still be a cosmologically important finding.
Koshiba:
But that wouldn't account for the missing mass though.
DeVorkin:
No. But that would be an answer at least, even so.
Koshiba:
Mm-hmm [affirmative].
DeVorkin:
Okay. A final question about particle physics. After reading through your introduction and also my general feelings after reading popular literature about particle physics, I am always struck with the complexity of all of the interactions that are suggested. The field is so complex. Doesn't it sometimes seem kind of amazing that it all fits together as well as it does? Does that every bother you — that maybe you're making it fit together a little too much? "You" being the physics community—not you personally. I'm just thinking broadly here.
Koshiba:
Well, it is really amazing thing that people did come to this standard model, which is so good, explains almost everything we observe. But still, there are a number of unsatisfactory aspects to this model. For instance, too many unknown parameters, and also a gravitational force. These interactions are not explained at all. And also the way quarks and leptons are represented in this standard model is very artificial. So, people in the world try to find out where a standard model doesn't work so that you could get a hint of what other type of theory is to be sought for. And proton decay is also one of these things. And neutrino masses another thing, which definitely this present standard model cannot account for. You know, we are very happy about confirming our previous result on atmospheric neutrino anomaly.
DeVorkin:
Okay. Is there anything that we have not covered about your life, your career, something that you feel should be recorded that we have not managed to discuss in these three or four hours?
Koshiba:
No. [laughs] I must say you scrutinized my career thoroughly. [laughs]
DeVorkin:
Well, that's my job. Okay. Well then, I want to thank you very much for this long and exhausting, but very valuable, session. Thank you very much.
Koshiba:

Thank you for your interest.

http://www.aip.org/history/ohilist/24870.html


Create Date : 20 พฤษภาคม 2556
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