1988 The Nobel Physics Prize to Lederman, Schwartz, and Steinberger         ^top^
“for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino”

     The Royal Swedish Academy of Sciences has decided to award the 1988 Nobel Prize in Physics jointly to Leon Lederman, Batavia, Illinois, USA, Melvin Schwartz, Mountain view, California, USA and Jack Steinberger, Geneva, Switzerland, for the neutrino beam method and the demonstration of the doublet structure of the leptons through the discovery of the muon neutrino.
      The 1988 Nobel Prize in Physics is awarded for the neutrino beam method and the discoveries made using this. The experiment was planned when the three researchers were associated with Columbia University in New York, and carried out using the Alternating Gradient Synchrotron (AGS) at Brookhaven National Accelerator Laboratory on Long Island, USA.
      Leon Lederman is currently Director of the Fermi National Laboratory in Batavia, near Chicago, Illinois, where the world's largest proton accelerator is situated.
      Melvin Schwartz, formerly professor at Columbia and Stanford Universities, is now president of his own firm specializing in computer communications, in Mountain View, California, USA.
      Jack Steinberger, who is an American citizen works since long ago as a Senior Physicist at CERN, Geneva, Switzerland, where he has led a number of large experiments in elementary particle physics, including experiments that employ neutrino beams.

Summary
      The work now rewarded was carried out in the 1960s. It led to discoveries that opened entirely new opportunities for research into the innermost structure and dynamics of matter. Two great obstacles to further progress in research into weak forces - one of nature's four basic forces - were removed by the prizewinning work. One of the obstacles was that there was previously no method for the experimental study of weak forces at high energies. The other was theoretically more fundamental, and was overcome by the three researchers' discovery that there are at least two kinds of neutrino. One belongs with the electron, the other with the muon. The muon is a relatively heavy, charged elementary particle which was discovered in cosmic radiation during the 1930s. The view, now accepted, of the paired grouping of elementary particles has its roots in the prizewinner's discovery. Background information Neutrinos are almost ghostlike constituents of matter. They can pass unaffected through any wall, in fact all matter is transparent to them. During the conversion of atomic nuclei at the center of the sun, enormous quantities of neutrinos (which belong to the electron family) are produced. They pass through the whole sun virtually unhindered and stream continually from its surface in all directions. Every human being is penetrated by sun neutrinos at a rate of several billion per square centimeter per second, day and night, without leaving any noticeable trace. Neutrinos are inoffensive. They have no electrical charge and they travel at the speed of light, or nearly. Whether they are weightless or have a finite but small mass is one of today's unsolved problems. The contribution now awarded consisted among other things of transforming the ghostly neutrino into an active tool of research. As well as in cosmic radiation, neutrinos, which belong to the moon family, can be produced in a multi~step process in particle accelerators, and this is what the prizewinners utilized. Suitable accelerators exist in some few laboratories throughout the world. Since all matter is transparent to neutrinos, it is difficult to measure their action. Neutrinos are, however, not wholly inactive. In very rare cases a neutrino can score a random direct hit or, more correctly, a near-miss, on a quark, a pointlike particle within a nucleon (proton or neutron) in the nucleus of an atom or on a similarly infinitesimal electron in the outer shell of an atom. The rarity of such direct hits implies that a single neutrino of moderate energy would be able to pass unhindered through a wall of lead of a thickness measured in light-years. In neutrino experiments the rarity of the reactions is compensated for by the intensity of the neutrino beam. Even in the first experiment, the number of neutrinos was counted in hundreds of billions. The probability of a hit also increases with the energy of the neutrinos. The method of the prizewinners makes it possible to achieve very high energies, limited only by the performance of the proton accelerator. Neutrino beams can reveal the hard inner parts of a proton in a way not dissimilar to that in which X-rays reveal a person's skeleton.
      When the neutrino beam method was invented by the Columbia team at the beginning of the 1960s the quark concept was still unknown, and the method has only later become important in quark research. Also of later date is the experimental discovery of an entirely new way for a neutrino to interact with an electron or a quark in which it retains its own identity after impact. The classical way of reacting implied that the neutrino was converted into an electrically charged lepton (electron or muon), and this was the reaction utilized by the prizewinners. The prizewinners' experiment The very first experiment using a beam of high-energy neutrinos originated in one of the daily coffee breaks at the Pupin laboratory, where faculty and research students would relax together for half an hour. In this stimulating atmosphere around Nobel Prizewinners T.D. Lee, C.N. Yang (Nobel prize for physics 1957) and others at the end of the 1950s, the need to find a feasible method of studying the effect of weak forces at high energies was discussed. Hitherto it had only been possible to study processes of radioactive decay, spontaneous processes at necessarily relatively low energies. Beams of all common particles (electrons, protons and neutrons) were discussed. While these are relatively simple to produce, they were found to be unusable for this purpose. The apparently hopeless situation suddenly changed when Melvin Schwartz proposed that it ought to be possible to produce and use a beam of neutrinos.
      During the next two years he, together with Leon Lederman and Jack Steinberger, worked on the proposal in order to achieve a sufficiently intense beam of neutrinos free from all other types of particle, and to design a detector for measuring neutrino reactions. The group at Columbia also included G. Danby, J.M. Gaillard and K. Goulianos and N. Mistry. The neutrinos in the Columbia experiment were produced in the decay in the flight of charged pi-mesons. In a first step protons were accelerated to high velocities and directed at a target of the metal beryllium. As the next step high-velocity pi-mesons were produced in a forward-directed beam. Mesons are radioactive, and they decayed into a muon and a neutrino each when allowed to travel a path of free flight, which was set at 21 meters. In this step high-energy neutrinos were produced as a forward-directed beam, still containing quantities of leftover pi-mesons and myons which had been formed at the same time. To eliminate these unwanted particles completely from the beam, a 13.5~meter~thick wall of steel was needed. The material came from scrapped warships. The measuring device (detector) was built behind the wall, which of course was transparent to the neutrinos. So that the detector should not be entirely transparent, it was thought best to build it as a 10-ton spark chamber, then a new and fairly untested type. The detector consisted of a large number of aluminum plates with spark gaps between them. A muon or an electron produced by a neutrino in one of the aluminum plates photographed its own track as a series of sparks, using a special self-exposing device. A burning problem had arisen at the time of the experiment regarding the measurements of muon radioactive decay.
      The measurement results, to which Jack Steinberger and Bruno Pontecorvo among others contributed, disagreed with accepted theoretical calculations. The problem was addressed by many researchers, among them G. Feinberg and T.D. Lee, as well as methodologically by Pontecorvo, and they indicated that one way out of the dilemma would be the existence of two entirely different types of neutrino. If the neutrinos in the Columbia experiment beam were identical to the neutrinos common in beta decay, the reactions in the detector should convert the neutrino to a fast electron as often as to a fast muon. On the other hand only muons would result if there were two different kinds of neutrino. The prizewinners and their collaborators arranged their detector so that the cause of the spark tracks could be interpreted. The results showed that only muons were produced by the neutrinos in the beam, no electrons. Thus there exists a new type of neutrino that forms an intimate pair with the muon. Consequently the electron forms its own delimited family with its neutrino. The discovery thus had immediate consequences. Knowledge of the role of the family concept and the great importance of the method within elementary particle physics has grown during the time that has elapsed since the discovery was made. A question that is still current is whether or not small departures from strict family membership occur.

Leon M. Lederman Fermi National Accelerator Laboratory Batavia, IL, born 1922
Melvin Schwartz Digital Pathways Inc. Mountain View, CA, born 1932
Jack Steinberger CERN Geneva, Switzerland born 1921

Detailed presentation of the research.

Photosynthesis - the most important chemical reaction on earth

Summary
Johann Deisenhofer, Robert Huber and Hartmut Michel are the first to succeed in unraveling the full details of how a membrane-bound protein is built up, revealing the structure of the molecule atom by atom. The protein is taken from a bacterium which, like green plants and algae, uses light energy from the sun to build organic substances. All our nourishment has its origin in this process, which is called photosynthesis and which is a condition for all life on earth.

The organic substances serve as nourishment for both plants and animals. Using the oxygen in the air, they consume these nutrients through what is termed cellular respiration. The conversion of energy in photosynthesis and cellular respiration takes place through transport of electrons via a series of proteins, which are bound in special membranes. These membrane-bound proteins are difficult to obtain in a crystalline form that makes it possible to determine their structure, but in 1982 Hartmut Michel succeeded in doing this. Determination of the structure was then carried out in collaboration with Johann Deisenhofer and Robert Huber between 1982 and 1985.

Photosynthesis in bacteria is simpler than in algae and higher plants, but the work now rewarded has led to increased understanding of photosynthesis in these organisms as well. Broader insights have also been achieved into the problem how electrons can, at an enormously high speed (in a billionth - 10^-12 - of a second), be transferred in biological systems.

Background
Photosynthesis is the most important chemical reaction in the biosphere, as it is the prerequisite for all higher life on earth. In this process light from the sun is converted into chemical energy, which is used as nutrition not only by the photosynthetic organisms themselves but also by animals which eat such organisms (e.g. cows eating grass), by other living beings (e.g. humans) eating these animals, and so on through the nutritional chain.

The energy necessary for life processes is to a large extent liberated in the combustion of carbohydrate and fats by the oxygen of the air in cellular respiration. This can, however, continue indefinitely only because the nutritional substances consumed are remade in the photosynthesis of green plants. Here the plants build up, with aid of solar energy, complicated organic compounds from two simple inorganic molecules, carbon dioxide and water, with the concomitant liberation of oxygen. Photosynthesis and respiration thus have as a result that the sun drives a continuous cyclic process in the biosphere:

A simpler form of photosynthesis, which leads to the formation of organic material without liberation of oxygen, is found in certain bacteria.

Photosynthesis and respiration comprise electron transfer between proteins, which often contain metal ions, e.g. iron, in specific electron-transport chains. The principles for electron transfer between simple metallic compounds have been analyzed in detail by the Nobel Prize winner for chemistry in 1983, Henry Taube. An important goal in the chemical research of today is to extend these contributions in order to explain electron transfer between the more complicated biochemical molecules.

The electron-transport proteins in photosynthesis as well as in respiration are organized as complicated molecular aggregates bound to membrane systems of two specific cell organelles, chloroplasts and mitochondria. The energy liberated during the electron transport is used to pump protons across the membranes, so that a difference in pH and electrical potential between the two sides is created. This electrochemical potential is then used to drive the synthesis of adenosine triphosphate (ATP), the universal energy storage molecule in living cells, according to the chemiosmotic mechanism formulated by the British biochemist Peter Mitchell (Nobel Prize for chemistry 1978).

Membrane-bound proteins are difficult to obtain in solution and to purify to a form allowing a determination of their detailed structure in three dimensions. Before 1984 there were only fuzzy structural pictures of two membrane proteins available. These pictures had been obtained by an electron microscope technique developed by Aaron Klug, the Nobel Prize winner for chemistry in 1982. The situation changed drastically, however, in 1982, when Hartmut Michel in systematic experiments succeeded in preparing highly ordered crystals of a photosynthetic reaction center. from a purple bacterium, allowing the determination of the structure in atomic detail. The structural work was performed in the period 1982-85 in collaboration with Johann Deisenhofer and Robert Huber.

Schematic illustration of a reaction center. in a membrane in a photosynthesizing bacterium. The figure shows how the photosynthetically active components bacteriochlorophyll (BK), bacteriopheophytin (BF), quinone (Q) and iron (Fe) and the haemgroups of the cytocrome are arranged in the four proteins forming the reaction center.

As already mentioned, the photosynthetic apparatus in bacteria is simpler than in algae and higher plants. The structural work has, however, shown that there is a close relationship between the bacterial reaction center. and the oxygen-evolving protein complex in higher plants, so that the structure determined can be used also to increase our understanding of photosynthesis in general. The structural picture agrees well with the order of the electron transfer steps established earlier by more indirect methods. The detailed structure now forms the basis for more precise attempts to explain theoretically the course of the individual chemical steps.

The structural determination rewarded has considerable chemical importance far beyond the field of photosynthesis. Many central biological functions in addition to photosynthesis and cell respiration are associated with membrane-bound proteins. Examples are transport of chemical substances between cells, hormone action and nerve impulses. The structure of the reaction center. has clarified the principles governing the three dimensional structure of proteins spanning biological membranes, e.g. ion pumps and other transport proteins. Thanks to the method of crystallization developed by Hartmut Michel the prospects of obtaining detailed structural information also for other membrane proteins have improved. Not least important is the fact that the reaction center. structure is an indispensable tool in the attempts of theoretical chemists to understand how electron transfer in biological systems can occur with very high velocities (even in one billionth [US, trillionth] of a second) across large distances (more than ten intervening atoms) on the molecular scale.