• Martin Block 1925–2016
• John Madey 1943–2016
• Roberto Petronzio 1949–2016
• Yoshio Yamaguchi 1926–2016

Martin Block 1925–2016

Particle physicist Martin M Block died on 22  July in Los Angeles, California, aged 90, following a short illness. His career was distinguished not only in terms of the contributions he made but also by its longevity: his first paper was published in 1949 and his most recent in 2016. Block was also an active participant in the Aspen Center for Physics, where he founded its enduring Aspen Winter Physics Conferences in 1985.

Block completed his doctorate at Columbia University in 1952, where he helped to design magnets for the Nevis Cyclotron. As a young professor at Duke University, he contributed the revolutionary notion that parity was not conserved in weak interactions. The idea, which came to him while he shared a room with Richard Feynman at a Rochester meeting on high-energy physics in 1956, offered a solution to the so-called “tau-theta” paradox: two otherwise identical particles that decay into different parity states and thus were believed to be distinct.

The story was recounted in Feynman’s 1985 memoir Surely You’re Joking, Mr. Feynman: “Anyway, I was sharing a room with a guy named Martin Block, an experimenter. And one evening he said to me, ‘Why are you guys so insistent on this parity rule? Maybe the tau and theta are the same particle. What would be the consequences if the parity rule were wrong?’ I thought a minute and said, ‘It would mean that nature’s laws are different for the right hand and the left hand, that there’s a way to define the right hand by physical phenomena. I don’t know that that’s so terrible, though there must be some bad consequences of that, but I don’t know. Why don’t you ask the experts tomorrow?’ He said, ‘No, they won’t listen to me. You ask.’ So the next day, at the meeting…I got up and said, ‘I’m asking this question for Martin Block: What would be the consequences if the parity rule was wrong?’ Murray Gell-Mann often teased me about this, saying I didn’t have the nerve to ask the question for myself. But that’s not the reason. I thought it might very well be an important idea.”

Important, indeed. The 1957 Nobel Prize in Physics went to Tsung-Dao Lee and Chen-Ning Yang for their theoretical analysis of the process, but it was not shared by Madame Chien-Shiung Wu for her 1956 experimental demonstration of parity violation in the beta decay of cobalt-60 nuclei, nor was Block’s contribution acknowledged at the time.

At Duke, Block developed the first liquid-helium bubble chamber and used it to study the properties of several newly discovered particles. He left Duke for Northwestern University in 1961, where he served on the faculty for the remainder of his experimental career. He co-discovered the eta meson and later worked on collaborations at ever-higher energies, involving heavy-liquid bubble chambers and, eventually, modern counter detectors. His work took him to accelerators all over the world, with extended experimental stints at Berkeley, Brookhaven, Fermilab – and particularly at CERN, which he visited in every decade from the 1960s until the 1990s.

His lifelong passion for the mountains, especially skiing and fly fishing, eventually took him to Aspen, where he purchased a home and joined the Aspen Center for Physics in its nascent years. There, he embarked upon a second career in theoretical and computational physics. A central focus of this work concerned the forward-scattering amplitudes of hadron collisions, specifically the issue of why the proton–proton interaction cross-section grows with the square of the logarithm of the energy. His work anticipated quantitatively measurements that were eventually performed at the LHC. In one of his final papers, he showed that data demonstrate convincingly that both the proton–proton and antiproton–proton scattering amplitudes asymptotically approach those of a so-called “black disc,” presumably as a consequence of gluon saturation.

Block is survived by his wife, Beate, his two children, Steven and Gail, and two grandchildren.

• Steven Block, Stanford University, and Francis Halzen, University of Wisconsin-Madison.

John Madey 1943–2016

The international accelerator community was saddened to learn about the passing of the pioneer of the free-electron laser, John M J Madey of the University of Hawaii at Mānoa, on 5 July.   

Raised in Clark, New Jersey, John Madey and his older brother Jules took an early interest in amateur radio. In 1956, when John was 13 and Jules was 16, they began relaying communications from the South Pole to families and friends in the US. Madey received a degree in physics and a masters in quantum electronics from the California Institute of Technology in 1964 and 1965, where he first raised the question of whether it was possible to enhance the transition rate for bremsstrahlung through stimulated emission. He continued thinking about the question while working on his doctoral degree at Stanford, at which time he invented the free-electron laser (FEL).

A FEL can produce coherent electromagnetic radiation of extremely high intensity and high quality that is tunable over a wide range of frequencies, which is of great interest for research in physics, chemistry, biology and medicine. While classical FELs use mirrors or optical cavities, a more recent FEL variant, operating at ever-shorter wavelengths, is the linac-based FEL such as the Linac Coherent Light Source at SLAC or the European X-FEL in Hamburg, Germany.

Madey was awarded a PhD in 1970 and appointed professor of electrical engineering in 1986. In 1988, he left Stanford to take up a tenured position at Duke University, moving his FEL research laboratory with him the following year. He joined the University of Hawaii at Mānoa in 1998.

Madey was bestowed with numerous awards and international recognitions, including the Stuart Ballantine Medal from the Franklin Institute in 1989, the 2012 Robert R Wilson Prize from the American Physical Society and the 2016 Willis E Lamb Award for Laser Science and Quantum Optics. He was also the keynote speaker at the 2015 Nobel Symposium on Free-Electron Lasers in Sigtuna, Sweden. Madey held 13 patents on FEL-related technological inventions and published many important papers. These included a seminal publication on stimulated emission in 1976 (Phys. Rev. Lett. 36 717) and, more recently, a comprehensive review article on the history of the FEL invention (Phys. Rev. ST Accel. Beams 17 074901).

John Madey was also a highly dedicated teacher, patiently mentoring his students and sharing with them his vast knowledge and wisdom.

• Pui Lam, University of Hawaii, Vladimir Shiltsev, Fermilab, and Frank Zimmermann, CERN.

Roberto Petronzio 1949–2016

Our dear colleague Roberto Petronzio passed away on 28 July at the age of 67. He was a CERN fellow from 1977 until 1979 and a staff member in the theory division from 1980 until 1986. He played a significant role in our field as professor at the University of Tor Vergata, president of the INFN (2004–2011) and as a member of the CERN Council. Roberto was a major contributor to the development of QCD. He was involved, among other projects, in the first complete calculation of the NLO anomalous dimensions, and in the resummation of soft-gluon emission in partonic processes.

He was also involved in the non-perturbative analysis of the theory. In particular, along with Cabibbo and Parisi, he was one of the first members of the APE collaboration, which managed to construct the famous series of supercomputers for numerical simulations. Together with Cabibbo and Martinelli, he proposed the use of lattice simulations to compute weak amplitudes. These results are of great importance in flavour physics, for example in analyses at B factories and in similar work carried out at CERN by the LHCb, ATLAS and CMS collaborations.

Roberto was well-anchored in the Standard Model but always looking for harbingers of new physics. He had an eclectic knowledge of particle physics and related subjects. His legacy is also represented by several generations of brilliant young physicists spread across different laboratories and universities throughout the world. He had a charming and wonderful personality and was a great asset to our community. He will be dearly missed.

• His colleagues and friends.

Yoshio Yamaguchi 1926–2016

Yoshio Yamaguchi, who propelled particle physics in the post-war world, passed away on 12 August. His research encompassed a wide field of particle physics.

After his education at the University of Tokyo, Yamaguchi joined Osaka City University and co-founded a particle-physics group. The group was soon attracted by the new particles that were being detected in collisions between cosmic rays and the atmosphere, and Yamaguchi proposed that they are created in pairs – marking the first step towards understanding strange particles.

Yamaguchi spent much time abroad and first went to the University of Illinois at Urbana, where he proposed a separable potential of nuclear interactions. Shortly afterwards, he was invited to the newly founded theory division of CERN, where he stayed from 1957 to 1961. Former CERN Director-General Viki Weisskopf wrote in his memoir: “Yamaguchi contributed much to the scientific atmosphere in the theoretical division at CERN.” He was very quick to catch the essence of new experiments and it was general lore at CERN that when you made an experimental proposal, you must go and talk to Yamaguchi in advance to convince him, or you would get in trouble in the proposal meeting.

Yamaguchi then moved to the Institute for Nuclear Study (INS) at the University of Tokyo, where he led the theory group. Besides theory, he helped to create a new particle-physics laboratory in Japan that was realised eventually as KEK. He later moved to the physics department at Tokyo to teach. His lectures were popular, although he worked his students hard and had high expectations.

Yamaguchi was not only an excellent and versatile physicist, but a first-class manager. He returned to the INS as director until his retirement, and was a co-founder of the International Committee for Future Accelerators in the 1970s, chair of the International Union of Pure and Applied Physics from 1993 to 1996, and contributed to creating the Asian Pacific Center for Theoretical Physics.

Yamaguchi also had a wide cultural background in European and Japanese classics. We will greatly miss this giant of particle physics.

• His friends and students.