Message of small mass neutrino

How to study neutrinos will help physicists go beyond the standard model? Why did not scientists at first believe that neutrino possesses mass? How did Bruno Pontecorvo come to the idea of ​​neutrino oscillations? How did the United Institute of Nuclear Research arise and develop? This is in an interview with Jan Mahonin is told by Professor Samikhelevich Bieleneky , an adviser at the Directorate of the Laboratory of Theoretical Physics of Jini. This year he turned 92, but he retains the vigor of the spirit and clarity of the mind.

Expansion of the standard model

- In your opinion, what are the prospects for the development of physics outside the standard model?

- In fact, this is not a model, but a theory. It is based on reliable principles, and everything that it predicts is observed on experience. The most striking confirmation of the standard model is the opening of the Higgs boson in 2012. This is such a great discovery that literally the next year Higgs and Engler received the Nobel Prize. The standard model really describes nature. But for many years it is known that this model has a theoretical problem - the so -called problem of the hierarchy. In order to solve it, super -symmetry was proposed. It was assumed that super -symmetry would be found in experiments on a large Adron Collider, but so far they find nothing. It changes the whole situation. There are also phenomena that the standard model cannot explain; One of these phenomena is dark matter. We know that there is matter that we do not see - we can judge its existence by the observation of gravitational effects. What it is, we do not know. There are no “candidates” in the standard model who could explain the dark matter. There was a wonderful “candidate” - the easiest super -symmetric particle; It should be quite massive and stable to satisfy all conditions. However, so far we do not see super -symmetry. There are currently many other ideas about what dark matter is. Another very serious problem is dark energy, it is 70% of the density of the universe. But we, again, do not know what it is. Thus, there are facts that say that the standard model is incomplete.

- What role in the search for a new theory can a neutrino play?

- We think that the observation of neutrino oscillations, which means that neutrino has masses, is the observation of the effects of the theory of Beond the Standard Model. We definitely do not know the significance of all masses, but we know that the mass of the most severe neutrino is approximately equal to 0.1 electronwall (EV). There is a problem of the hierarchy of masses, and it will be solved by neutrian experiments.

- Can the standard model explain the meaning of the mass of the neutrino?

- In fact, she does not explain the mass. There is a Higgs mechanism that generates the masses of particles such as quarks and leptons. The standard model cannot predict the value of the masses. Neutrinas cannot be generated by the Higgs mechanism - there should be a different mechanism. It is necessary to build another theory in which such a mechanism exists.

- Are there any facts confirming the existence of a new mechanism?

- This is the three generations of quarks and leptons. All particles, including neutrinos, have masses. However, we do not really understand why the electron is so light, and the top-soda and tau-klepton are so heavy. We do not really understand the structure of the masses. We also do not know why there are three generations (and not four or one). However, we can say that the masses of neutrino are distinguished: they are twelve orders less than the masses of quarks and leptons. This means that there should be a special mechanism for generating the masses of neutrinos. We must understand why the masses of neutrinos are so smaller than the masses of the remaining particles. This is the main thing that we must explain.

- Do possible explanations already exist?

- In principle, yes. Many of them include exotic capabilities: the additional number of degrees of freedom, the additional measurement of space (not four, but more), strings, etc. However, if you remain within more ordinary theories, then, from my point of view, the most convincing physical explanation is that the small masses of the neutrino indicate the existence of new physics outside the standard model, physics of particles with heavy masses. (These heavy masses set the scale of new physics.) All this is difficult to check quantitatively, but still we believe that heavy particles exist.

- Let's say this is so. How is the mass of neutrinos in this case?

- Roughly speaking, the mass of the neutrino is given by the work of the standard mass (leptons and quarks) to a certain factor, which is the attitude of the two scale: the one that determines the standard model, and the one that determines the new physics. The scale that determines the standard model is known: 246 gigaelectron volt (GEV). This number determines the constant Fermi. But the new scale is unknown to us. But if we assume that it is big, we immediately understand why the masses of neutrinos, which are generated by a new mechanism, are small compared to the masses of leptons and quarks. We can try to estimate the new scale: about 1014 GEV.

- Can this be proved experimentally?

- Neutrino is a particle that does not have an electric charge. This allows you to study with the help of a neutrino a physics of very large scale - as I said, about 1014 GEV. Such energies are not available and will never be available on Earth, we can get information about physics on such a scale only from cosmology. Neutrino observations play a large role here. From my point of view, there are two types of experiments that will allow you to check this point of view. One type is experiments on the observation of a immunityine double beta-decay of nuclei (Gerda, Nemo, Cuore and others). This is an extremely important process. If it is observed, then this will mean that the neutrino are particles of major.

- What are their distinctive properties?

- There are two types of particles that we call farmions. One type is Dirakovo particles, such as electrons, muons, quarks and others. They are characterized by the fact that each particle has an appropriate antiparticles that differs from a particle with a sign of an electric charge: for example, an electron and a positron, quark and antiquely, and so on. The second type of farmions is majority particles. These particles do not have antiparticles - only a particle of major can be a particle with an equal zero. When the particles have an electric charge, the general quantum theory of field theory works: if there is a particle with a minus charge, there should be an antiparticles with a plus charge. Neutrino is the only particle that can be a particle of major. In fact, thanks to this neutrino, they allow you to explore physics on a very large scale. This is a search for physics at very small distances, or on very large energies.

-Why is the bastard double beta-decompad so important?

- This is the only process that the study of which will allow us to tell whether the neutrino are Dirakovo or major particles. If the immunitrin double beta-decay is observed, then it is confirmed that the neutrino is major particles. If not, nothing can be said.

- What role in the study of this process do scientists of JINI play?

- Dubna makes a great contribution to these experiments. In the experiments of Gerda, NEMO and others, scientists from Dubna are involved. One of the main specialists in the theory of this process is the Slovak physicist Fyodor Shimkovitz, who works in a JIN. Its contribution to the theory of immunityine double beta-decay is difficult to overestimate; He calculates matrix elements and much more.

- You mentioned the second type of important experiments that will allow us to advance in understanding the nature of the neutrino mass. What is it?

- This is the search for the so -called sterile (i.e., non -current -appropriate) neutrinos. Many years ago, the transitions of ordinary muon antineutrinos to sterile states were observed on a neutrong detector in Los Alamos. We can see the effects of sterile neutrinos, observing neutrino oscillations at short distances. There are many experiments in which sterile neutrinos seem to be observed, but in many experiments they are not seen. The time has come to finally install whether there are sterile neutrinos or not. One of the best reactor experiments, which may allow us to answer this question, is conducted by scientists from Dubna at the Kalinin nuclear power plant - it is called Danss. Unfortunately, one of the main participants in this experiment Vyacheslav Egorov recently died. This is a big loss for Dubna and physics in general.

View in the past: work with Bruno Pontecorvo

- Please tell us how you reacted to the idea of ​​neutrino oscillations proposed by Bruno Pontecorvo in 1957?

- Then I was not at all interested in neutrino. I began to engage in neutrino physics with Bruno Maksimovich only in 1970. In general, for many years, no one has been interested in neutrinos by the oscillations, because physicists firmly believed that neutrino had no mass; And if there is no mass, then oscillations are impossible. Our cooperation with Bruno Maksimovich was associated with a completely different problem. At this time, the preprint of the very famous American physicist Frederick Reines appeared, who first watched the neutrino and subsequently received the Nobel Prize for these studies. He published a very strange experimental work, in which he measured neutrino scattering on electrons. The cross -section of this process was two hundred times more than predicted by theory. This caused bewilderment and great interest, in particular Bruno Maksimovich.

- What was his reaction?

- He studied this work and told about it at the seminar in the laboratory of nuclear problems of JIND. I was at this seminar and, when it ended, I decided to discuss with Bruno Maksimovich the question of how such results could appear. Then I was still far from studying the neutrino, but, nevertheless, I asked Bruno Maksimovich if this could not be the result of a strong interaction between the neutrino. At first, he did not particularly react, almost did not answer. And the next morning he called and said: “You know, this is a very interesting idea, let's work on it.” And we started working.

- What was your work?

- Even people who were far from neutrinos, it was clear that we did not know anything about the interaction of neutrino among ourselves. The interaction of neutrinos with protons and electrons was known - at least theoretically. We began to think what experiments would allow information about the interaction between the neutrino. Soon Raynes found a mistake in his experiment: it turned out that a rather significant gamma-fage gave electrons of return. Accordingly, the result of Reines disappeared, but the question of the interaction between the neutrino remained. And for two years, Bruno Maksimovich and my students checked different opportunities. From experimental data at that time it was possible to conclude that even a strong interaction between neutrino is not excluded. The experiments that we proposed were fulfilled. Now it is already known that the interaction between the neutrino is really weak.

- Did you continue to cooperate with Pontecorvo and in other areas?

- We still had no joint work, but we remained very friendly. He invited me on all sorts of trips. Pontecorvo loved different sports, in particular, hunting with an underwater gun for fish. In one of these trips, we began to discuss - first in the car, and then by the fire - neutrino oscillation. All sorts of ideas arose. Then, in 1975, we began to work together on the oscillations of the neutrino. In 1977, we wrote the first review. There were few works on this topic then-physicists still did not believe in the oscillation of the neutrino. Until 1989-1990, we worked quite a lot with Pontecorvo - almost every day - on the problem of masses, mixing and oscillations of neutrinos. I often came to work in his office in the laboratory of nuclear problems, and we released a lot of joint work.

-Why did the general interest in the problem of oscillations of neutrinos arose only at the turn of the 1980s?

-In the early 1980s, we began to put special experiments on the search for neutrino oscillations. I have already said that a significant interest in this problem arose after the experience of Reines, who claimed to observe neutrino oscillations. Subsequently, it turned out that it was an erroneous experiment. The main interest in the problem of the masses and the oscillations of the neutrino arose in connection with the theories of the Great Association (Grand Unified theories, GUT). (Then the theories were very fashionable that unify the weak, electromagnetic and strong interactions.) In such theories, naturally, the masses of neutrinos appear. Physicists began to think that if you see the effects of the mass of the neutrino, this will indicate the correctness of GUT. In 1970, Reimond Davis, the largest American enthusiast of a research neutrino study, and his group began an experiment in which they first observed solar neutrinos and received data in favor of neutrino os checkers. In 2002, Davis received the Nobel Prize for the observation of the Sunny Neurino.

- Was Davis's experience associated with previous research by Bruno Maksimovich?

-Davis used the radiochemical chlorine-argon method, which proposed Pontecorvo in 1946. In his underground experiment, a large detector was used. He observed less neutrino than predicted the standard solar model. If you seriously perceive the model of the sun, then this is a crisis (it was called Solar Neutrino Puzzle). Many thought, however, that the “lack” of solar neutrinos could be due to the fact that we do not fully understand the sun and cannot predict the stream of neutrino from the sun. Pontecorvo, Davis, perceived quite seriously and thought that this was the effect of neutrino oscillations. I supported his idea in every possible way, and we wrote an article on this subject. Then it turned out that this is true, but the matter is not only in the oscillation of neutrino. The main role is played by the effects of coherent scattering of the neutrino in the substance of the sun, which lead to a weakening of the flow of solar neutrino (the so -called effect of Mikheev - Smirnov - Wolfenstein).

Pages of autobiography

“ Tell us, please, where you come from.”

- I was born in 1928 in Ukraine, in the city of Zhmerinka. There I lived a year, then we lived in another place for some time in Ukraine, then in Belarus, and since I have been living in Russia for ten years.

- Who were your parents by profession?

- My father was an engineer, my mother was an accountant. Most of their lives fell on Soviet times. They were normal Soviet people.

- Where did you live during the war?

- At the beginning of the war, I was 13 years old. We then lived in the city of Taganrog on the Sea of ​​Azov. From there they were evacuated to Kazakhstan. Father went to the army, and my mother and sister and I remained on the collective farm, where I worked for one year. And then we moved to Saratov, where his father was transferred from the army as a specialist - he worked at local factories, where we produced military equipment.

- In 1946, you graduated from high school in Saratov, entered MEFI, graduated with honors in 1952. Did you touch the campaign against cosmopolitanism, which unfolded at this time?

- Fortunately, this campaign almost did not touch me, I was lucky. I made a diploma with Professor Isaac Yakovlevich Pomeranchuk. In the city of Ivankovo ​​(later it was united with Dubnaya) the first accelerating center was created. Due to the secrecy, it was called a hydraulic laboratory-there was a damage with a hydroelectric power station nearby. The first accelerator of the laboratory of nuclear problems was built - synchrocyclotron; His energy was at that time 460 Meav. It was built in two years, it was a record. The accelerator was secret, it was not known about him in the world. Around it, a laboratory of nuclear problems, which was called a platform, grew up. Experimenters and a small group of theorists worked on the accelerator.

- How did you get to Dubna?

- The laboratory of nuclear problems was led by Mikhail Grigoryevich Meshcheryakov. Pomeranchuk was the leader of her theoretical department. In MEPHI, he gave us lectures. Once he stopped during the lecture and said the following: “You know, a large accelerating center is being created in the Soviet Union. I can’t tell you exactly where (it's secret). There are theorists there. Which of you wants to try to get to this center, contact me. ” There were then ten people in the group. In those years, there was a severe concept - Moscow registration, and in this sense I was lucky - in our group everyone was Muscovites, with Moscow registration, they did not really want to leave Moscow. I also had a Moscow residence permit, but I did not see another way out for myself. I went to Isaac Yakovlevich and said that I would like to go to work in this center. He replied: I do not promise, but I will try. I made a diploma with him, and he somehow convinced Meshcheryakov to hire me. Then the laboratory belonged to the so -called laboratory No. 2, where the atomic project was developed - today it is the Kurchatov Institute. Meshcheryakov, apparently, was supposed to convince Kurchatov, and in 1952, immediately after the end of the MEPHI, they hired me to work in the supposedly hydraulic engineering laboratory. Через четыре года, в 1956 году, в Дубне образовался ОИЯИ.

— Вы помните момент создания института?

— Я очень хорошо это помню. На заседаниях я, конечно, не присутствовал. Тогда работал ускоритель Лаборатории ядерных проблем, а синхрофазотрон еще только строился. Было решено создать центр на базе этих двух ускорителей. Было также решено создать Лабораторию теоретической физики. Было две теоретические группы: одна в Лаборатории ядерных проблем; другая, которой заведовал академик Моисей Александрович Марков, —в Лаборатории физики высоких энергий. Когда создали ЛТФ, этих теоретиков решили взять в лабораторию, но с отбором. Директором ОИЯИ был назначен Дмитрий Иванович Блохинцев. Он собрал нас всех в административном корпусе, в кабинете директора, чтобы решить, кто перейдет в ОИЯИ. Каждый должен был ему рассказать, чем он занимается. Публикаций у нас особо не было — публиковаться долгое время не было разрешено. Дмитрий Иванович фактически принял на работу всех и затем спросил: а кого нам назначить директором? В нашей группе был теоретик Вадим Георгиевич Соловьёв, тогда аспирант Николая Николаевича Боголюбова, хорошо его знавший. Он предложил Дмитрию Ивановичу пригласить Боголюбова. На что Дмитрий Иванович ответил: наверное, Боголюбов не согласится, ведь он работает в Стекловском институте и в МГУ, он очень известный академик и, главным образом, математик. Однако в то же время Боголюбов очень интересовался физикой и внес в нее серьезный вклад. Вадим Георгиевич сказал: «Давайте я попробую убедить Боголюбова перейти в ОИЯИ». Николай Николаевич, действительно, согласился. Когда он перешел в Дубну, то пригласил в ЛТФ группу молодых людей, с которыми в то время работал: Ширкова, Логунова, Медведева, Поливанова, Бланка (он рано погиб в горах). Так создавалась Лаборатория теоретической физики.

— Все они переехали в Дубну?

— Нет, они сюда приезжали раз в неделю, в тот день, когда в лаборатории бывали семинары. Приезжали на машинах — электричек тогда еще не было. Через некоторое время Логунов стал заместителем директора и переехал в Дубну.

— Жизнь в Дубне тогда, наверное, была спартанская…

— Да, действительно, это была специальная жизнь. Добираться до Москвы было очень трудно. Вначале надо было доехать до Дмитрова, потом на так называемой кукушке (это был очень медленный поезд) —до Большой Волги. Оттуда до института пешком, автобусов тоже тогда не было (позже появился автобус до Дмитрова и обратно, на который нам давали какие-то пропуска). Магазинов было два. Один — продовольственный, возле административного корпуса, там, где сейчас «Пятерочка». А еще был товарный магазин, на площади Мира, там, где сейчас ювелирный магазин. В административном корпусе была очень дешевая столовая. Еще была гостиница, на улице Векслера, — там сейчас находится здание управления гостинично-ресторанного комплекса. Даже нитки-иголки в Дубне купить было невозможно, нужно было ехать в Москву… Жизнь действительно была спартанская.

— Период, когда институтом руководил Блохинцев, 1956–1965 годы, по атмосфере и общему настрою соответствовал духу оттепели?

— Дубна в это время была довольно открытым городом, здесь царила свободная атмосфера. «Службы» были, но они не так сильно о себе заявляли. И это, конечно, была заслуга Дмитрия Ивановича Блохинцева, а впоследствии Николая Николаевича Боголюбова. Большую роль играло и то обстоятельство, что в Дубне работали иностранцы. Чтобы пригласить в гости иностранного коллегу, я не нуждался ни в каком специальном разрешении. При тогдашней советской жизни это было нечто исключительное — в других местах такое было просто непредставимо. Западных физиков домой приглашать я не мог, а чехов, например, — пожалуйста. Мы жили на одной лестничной площадке с семьей Юры Паточки и были с ним и его женой Либой очень дружны. Вообще, у меня и моей жены в Чехии было много друзей. Мы были очень близки с Франтишеком Легаром, который работал с моей женой. Легар был в Америке и попал на распродажу военных палаток, спальных мешков и тому подобного. Когда мы собрались в поход, Франтишек всё это нам одолжил. Альтернатив тогда не было.

— В горы вы с ним ходили?

- No. В горные походы мы ходили с другими чехами. С Ярославом Цвахом, Иржи Страхотой, Павлом Экснером и другими. Иржи Страхота и его жена Мария до сих пор наши ближайшие друзья. Я был хорошо знаком также с Павлом Винтерницем, который сейчас живет в Канаде, в Монреале.

— Легар и Винтерниц после 1968 года эмигрировали. Вы не думали тогда над таким вариантом?

- No. Возможность, по-видимому, была: в 1970-е годы евреев из Советского Союза выпускали в Израиль. Но я тогда даже и не думал об эмиграции. Я абсолютно этого не хотел. У меня и моей семьи была нормальная жизнь, я любил и люблю Дубну, я много работал с Бруно Максимовичем. I was very lucky. Многие считают, что я был студентом или аспирантом Понтекорво. Но я был уже доктором наук, когда мы начали вместе работать. Мы работали фактически на равных, у нас были партнерские отношения. Он не был теоретиком, но у него была очень хорошая интуиция: он прекрасно понимал, что правильно, а что неверно. В физике это очень важно. И вообще, Бруно Максимович был очень глубокий человек и большой физик. Я с великим удовольствием работал с ним.

— Он чувствовал себя в Дубне как дома?

— Да, совершенно. Единственное, чего ему не хватало, — поездок в Италию. Его долго не выпускали за границу, наконец выпустили в 1976 году, после оттепели, но задолго до перестройки. Впервые он поехал на конференцию, посвященную семидесятилетию Эдуардо Амальди. Амальди был учеником Ферми, как и Понтекорво; они были членами его группы (« парни с улицы Панисперна »), куда, кроме них, входили Эмилио Сегре, Франко Разетти и Оскар Д'Aгостино. Итальянцы очень хотели, чтобы Понтекорво присутствовал на конференции, посвященной семидесятилетию Амальди. В конце концов, преодолев большие трудности, Бруно Максимович поехал в Италию — в первый раз после переезда в СССР. И после этого ездил на родину уже каждый год.

— Какую роль играет для вас пребывание за границей?

— Я провожу много времени за границей, много работаю с коллегами из разных стран, участвую в многочисленных конференциях. В Праге я никогда подолгу не работал, хотя часто приезжаю туда на месяц-два и сотрудничаю с пражскими коллегами. В конце 1980-х моему сыну сделали очень неудачную операцию в Сочи, после которой он может передвигаться только на коляске. Сейчас он живет в Канаде. В 2006 году мы решили с ним воссоединиться. С тех пор я живу в Канаде. Каждый год приблизительно на месяц я приезжаю в Дубну.

— Ваш юбилей, 90-летие, вы отметили в Праге и Дубне. How did it happen?

— Вместе с Александром Ольшевским, Фёдором Шимковицем и другими коллегами из Чехии и Дубны мы каждые два года проводим Международную летнюю школу по физике нейтрино имени Б. М. Понтекорво. Прежде она проходила в Алуште, в Крыму — всем очень нравилось, там прекрасное место. Но после известных событий нам пришлось эту школу организовывать в других местах. Первый раз это было в Словакии, второй раз школа проводилась в Праге; тогда мне было 89 лет. На будущий год, в связи с моим юбилеем, Иван Штекл и Руперт Лейтнер предложили мне провести нейтринный коллоквиум в Праге. Я с радостью согласился и приехал в Прагу с семьей. Туда пригласили моих коллег и друзей из Италии, Германии и других стран — они выступили на коллоквиуме. Было очень приятно и хорошо. Потом я поехал отмечать юбилей в мою альма-матер — Дубну. Был организован нейтринный семинар в Доме ученых. Пришло много друзей и знакомых физиков из разных лабораторий. Были директор ОИЯИ Виктор Матвеев и директор Лаборатории теоретической физики Дмитрий Казаков. Я, конечно, был очень рад и польщен.

— Большое спасибо за интересный рассказ! Я желаю вам здоровья и энергии!