Val Fitch American physicist, winner of the 1980 Nobel Prize in Physics Date of Birth: 10.03.1923 Country: USA

1. Early Life and Education
2. Military Service and Los Alamos
3. Academic Career
4. Discovery of CP Violation
5. Nobel Prize and Later Career

Early Life and Education

Val Logsdon Fitch Jr., an American physicist and Nobel laureate, was born on March 10, 1923, on a cattle ranch in Cherry County, Nebraska, near the South Dakota border. His parents were Francis M. (Logsdon) Fitch and Fred B. Fitch. When Fitch was young, his father sustained severe injuries while breaking a horse, and the family relocated to nearby Gordon, where his father pursued an insurance career.

Military Service and Los Alamos

After graduating from high school, Fitch was drafted into the army and in 1943 was assigned to a special engineering unit in Los Alamos, New Mexico, supporting the Manhattan Project, the secret program to develop the atomic bomb. Appointed as a lab technician in the group led by British physicist Ernest Titterton of the British Mission to Los Alamos, Fitch encountered prominent physicists such as Enrico Fermi, Isidor Isaac Rabi, J. Robert Oppenheimer, Niels Bohr, James Chadwick, and R.C. Tolman. Their professional and personal qualities left an enduring impression on him. Fitch later recalled that it was during this time that he learned to "not just take an existing piece of apparatus that would make measurements, but to sit down and try to think through a new way of doing this."

Fitch witnessed the first atomic test in the New Mexico desert, where his group laid the cable that transmitted the signal to detonate the bomb.

Academic Career

After being demobilized in 1946, Fitch earned his B.S. in electrical engineering from McGill University in Montreal in 1948 and continued his studies at Columbia University in New York City. Under the guidance of James Rainwater, Fitch completed his doctoral dissertation on mesoatoms in 1954. The topic was suggested by Aage Bohr, who was a deskmate of Rainwater at the time. Mesoatoms are atoms in which muons—particles originally discovered in cosmic rays—orbit the nucleus instead of electrons. Muons are identical to electrons in every way except that they are approximately 200 times heavier. Calculations showed that the extra mass would amplify the differences between closely spaced energy levels, thereby affecting the pattern of radiation emitted by the atom. During his final year as a graduate student, Fitch began teaching physics at Columbia University.

Fitch joined the faculty of Princeton University as an instructor in physics and became a full professor in 1960. In 1976, he was appointed Dean of the Faculty.

Discovery of CP Violation

In 1963, Fitch and James W. Cronin, along with Cronin's student James Christenson and French physicist René Turlay at the Centre d'Études Nucléaires, conducted an experiment at the Brookhaven National Laboratory on Long Island, New York, involving neutral K mesons (kaons). Kaons are unstable particles with a mass about half that of a proton that are produced in high-energy particle collisions. They had been described in a 1956 paper by Lee Tsung-Dao and Yang Chen-Ning as unusual particles in so-called "weak" reactions, where one of three fundamental symmetries, or conservation laws, could be violated. These symmetries are denoted by the letters C, P, and T.

Conservation of C (charge conjugation) means that reactions should occur the same way if particles are replaced by their antiparticles (mirror particles with opposite electric charge), such as electrons by positrons and protons by antiprotons. Conservation of P (parity) means that reactions should occur the same way if the particles' spatial properties are replaced by their mirror images, such as left by right, clockwise by counterclockwise. Conservation of T (time reversal symmetry) means that a reaction proceeds the same forward as in reverse.

Lee and Yang proposed experiments to test their theoretical predictions, and Wu Jian-Xiang and her collaborators at Columbia University found that parity is not strictly conserved in beta decay (electron emission) of radioactive nuclei; the nucleus predominantly emits "left-handed" electrons. Other experiments showed that C was also not exact; certain reactions between particles occur more likely than reactions between antiparticles.

The theoretical puzzle was partly resolved when it was suggested that a combined CP symmetry should be conserved; a violation of charge conjugation C must be compensated by a simultaneous violation of parity P, just as in algebra, the product of two positive numbers remains positive if both factors are made negative simultaneously. Since conservation of the overall CPT symmetry is supported by general principles, and CP was then thought to be invariant, time reversal symmetry T must also be conserved. A violation of T symmetry could not be compensated by the highly improbable violation of CP symmetry.

In 1955, Murray Gell-Mann and Abraham Pais proposed that a beam of kaons consists of mixtures of particle-antiparticle combinations that appear in experimental observations as two distinct electrically neutral kaons: KS0 (S for short-lived) and KL0 (L for long-lived). The lifetime of the KL0 is only about one ten-millionth of a second, but this is about 500 times longer than the lifetime of the KS0 kaon. Conservation of combined CP symmetry allows the KS0 kaon to decay into two pi mesons (pions), one positively charged and one negatively charged (pions are associated with the strong interaction that holds the atomic nucleus together). However, such a decay is forbidden for the KL0 kaon, which can only decay into three pions—a positive, a negative, and a neutral. The theoretical prediction was confirmed in 1956 when the decay of the KL0 kaon into three pions was experimentally demonstrated. The two types of kaons could be separated because in a typical experimental setup, short-lived particles travel only a few centimeters before decaying, while long-lived particles travel tens of meters, allowing the observation of KL0's only.

Fitch, Cronin, and their collaborators began their investigation using improved equipment, such as a spark chamber, which allowed them to determine the tracks of the decay products with much greater precision and to select the reaction to be observed. To obtain the kaons, the experimenters bombarded a beryllium target with high-energy protons accelerated by the Brookhaven Alternating Gradient Synchrotron (AGS), an accelerator capable of accelerating particles to energies of several billion electron-volts. They placed their detectors 17 meters from the target where the kaons were produced, a distance far enough for the KS0 kaons to decay, leaving behind a beam of KL0 kaons only.

However, one of the puzzling features in the behavior of the kaons observed in the experiment was that after passing through an absorber block that was supposed to absorb the KL0's, KS0 kaons would reappear in the beam. This phenomenon was called regeneration. In studying it, the scientists used blocks of tungsten, copper, carbon, and liquid hydrogen and found the theoretical predictions to be confirmed with no anomalies. The results allowed the experimenters to be confident that regeneration would have a negligible influence on the crucial test they performed later, when a vessel of helium was introduced into the KL0 kaon decay region.

The results of the experiment, which were initially met with disbelief, showed that in 45 out of the 23,000 photographed events in the spark chamber, the KL0 kaon decayed into two pions, instead of the three-pion decay predicted by theory. Given the significance of the results, the experimenters verified them with repeated tests and spent six months unsuccessfully searching for alternative explanations before deciding to publish their findings on the violation of combined CP symmetry.

The violation of CP symmetry implies that, with CPT symmetry conserved, time reversal symmetry T is also violated, leading to the conclusion that nature is not indifferent to whether time runs forward or backward. This symmetry violation allowed scientists to make certain assumptions that could explain why, despite the fact that matter and antimatter were created in equal amounts in the "big bang" at the birth of the universe, not all of them annihilated. If matter has even a slightly longer lifetime than antimatter, it would lead to the present-day universe being the leftover matter that survived the mutual annihilation and eventual disappearance of antimatter due to its faster decay. This annihilation is also the source of most of the cosmic electromagnetic radiation.

Nobel Prize and Later Career

Fitch and Cronin were awarded the 1980 Nobel Prize in Physics "for the discovery of violations of fundamental symmetry principles in the decay of neutral K-mesons." In presenting the laureates at the award ceremony, Gösta Ekspong of the Royal Swedish Academy of Sciences described the three fundamental symmetries as "guiding rules that enable us to unravel the mathematical laws of nature." Referring to Gell-Mann's work on neutral K mesons and the discoveries of Lee and Yang, he noted that Cronin and Fitch "interpreted the results of their experiments as a weak, but clear violation of symmetry," and emphasized that "nobody, absolutely nobody, had expected anything like this." The CP symmetry violation could be explained by new theories postulating the existence of fundamental particles, called quarks, from which other subatomic particles are made up. The existence of quarks was first postulated by Gell-Mann. Six types of quarks are distinguished: u-quark (up), d-quark (down), s-quark (strange), c-quark (charmed), b-quark (bottom), and t-quark (top, or truth).

In 1949, Fitch married Elise Cunningham. They had two sons. Four years after his first wife's death in 1973, Fitch married Daisy Harker, who had three children from her previous marriage. Since childhood, Fitch has been an avid outdoorsman, enjoying hiking