1. The SLAC Summer Institute
Fred Gilman
Leith Symposium: Physics and Friendships
December 12, 2014

2. The SLAC Summer Institute
We owe David Leith for the creation and success of the SLAC Summer Institute.
The talks at the 40th Anniversary session at the 2012 SSI provide an excellent view of the whole history of the SSI, its beginnings, directors, staff, pictures, all coupled to the progress of science over those 40 years and new generations of lecturers and participants.
I was a lecturer ; became a co-Director in 1976 (and occasional speaker); and in recent years I have been a student.

3. A Personal View
I will give a personal view, concentrating on the SSI’s early years within a broad scientific context on the one hand, and its special role for SLAC in that period on the other.
• I will “benefit” from hindsight over many
decades, which can be a big advantage
(or not).
There is always the pitfall of recalling only how smart we all (well, almost all) were.
Nevertheless, I will set the stage from my own experiences.

4. A Wonderful “Coincidence”
• The early years of the SSI overlap with the revolutionary period from the late 1960s to the late 1970s that took us from the rapid and often unanticipated discoveries of the 50s and 60s – with conflicting paradigms contending to understand a wealth of phenomena – to a spectacularly simple theory that successfully represents nature in the domain of energies that we have been able to probe so far.

5. My Perspective Pre-Revolution
As a Princeton grad student “dispersion theory” was in vogue, and the word “quarks” went unspoken by the faculty. ( )
Arthur Wightman: Can relativistic quantum field theory be formulated as a mathematically fully understood theory and represent nature?
As a Caltech postdoc, the algebra of currents, abstracted from currents involving quarks, was at its peak. But one carefully threw away the quarks, kept the resulting physical currents, and disavowed real quarks. “Do you mean concrete quarks made of concrete?”

6. My Perspective Pre-Revolution II
At SLAC (1967- ) a more open minded flow of ideas was in the air as the Linac began operations. The idea of a “quasi-elastic” peak in electron-proton inelastic scattering due to electrons striking the quarks inside the proton made a prominent appearance in Bjorken’s 1967 Lepton-Photon Symposium talk at SLAC. I remember this well as Bj’s scientific secretary.
In 2 years at the Lepton-Photon Symposium Liverpool, scaling – the consequence of point-like quarks in the proton, was the centerpiece and SLAC jumped to the center of HEP.

7. It Was the Best of Times Into this era, the SSI was born in 1973.
From data on electron, muon, and neutrino scattering experiments over a large kinematic range, the picture of quark constituents of the nucleon quarks had become conclusive.
The theorists had caught up, with gauge theories of the electroweak and strong interactions, plus the understanding of how to compute their consequences systematically.
In November 1974, the J/Ψ was discovered, and …

8. Other Evidence for Quarks: A Parallel Piece of the History
The algebra of currents leads to relations between amplitudes for π N → N* → π Δ
David’s group took data for these processes and analyzed them to provide the amplitudes for many different N* resonances in the 1970s.
The relative sign is predicted correctly by the algebra of currents (or quark models) of ~25 pion and photon amplitudes. The likelihood this is an accident is extremely small, and gives strong evidence for quarks. Feynman loved it, but everyone believed by then anyway.

9. The SSI in the Best of Times
As many of the great discoveries occurred at SLAC, it wasn’t hard to get excellent speakers for the SSI lectures or topical conference.
First, concentrate on the 1975 SSI (just before the Lepton-Photon Symposium), in the middle of a dizzying pace of discoveries: charmonium spectroscopy; R is a constant (twice); jets; and possible evidence of a heavy lepton ( π – μ, déjà vu), undisguised even with the name U for “unknown.”

10. SSI 1975 – The Peak

11. SSI 1975: Harari

12. SSI 1975: Jets Gail Hanson – Quarks Again

13. SSI 1976 – The Triumph of Charm
Charmed particles were discovered at SPEAR during the summer of 1976, in time for the SSI in mid-August.
We were treated to excellent lectures on the “new particles” by Gary Feldman, Dave Jackson, and David Hitlin, plus the triumphant talks by Shelly Glashow and Alvaro de Rujula in the Topical Conference.

14. SSI 1976: Dave Jackson

15. SSI 1976: Dave Jackson II

16. SSI 1976: Alvaro de Rujula

17. SSI 1977 Preface and Purpose

18. The Role of the SSI The SSI fulfilled the role envisioned for it.
It went beyond that role by building links in the world-wide fabric of particle physics.
Even more important in my view, the SSI provided a recurring venue for the whole SLAC science community to interact informally, to understand the breakthrough science being produced, and to feel a part of a great laboratory changing the course of particle physics. In a way, it continued and expanded the tradition of talks in Pief’s living room and feelings of inclusion.

19. The Role of the SSI (continued)
Important as well were the social events, from the opening reception to the informal buffet dinners, which brought spouses and families into the tradition.
Thanks to Doreen and Barbara and our families and to many other SLAC families.

20. Conclusion
The SLAC Summer Institute was much more than an educational effort; it helped make SLAC a very special place at a magical time, the coming together of one of the great intellectual achievements of the 20th century.
Congratulations David, and thanks for the many years of friendship and our work together.