Burton Richter on the Future of Particle Physics

Burton Richter.
[Image: NobelPrize.org]

The 1976 Nobel Prize was jointly awarded to Burton Richter and Samuel Ting for the discovery of the J/Psi particle. Sounds like yet-another-particle, I know, but this morsel of matter was a big step forward in the development of the standard model. Richter, sadly, passed away last summer.

Coincidentally, I recently came across a chapter Richter wrote in 2014 to introduce Volume 7 of the “Reviews of Accelerator Science and Technology.” It is titled “High Energy Colliding Beams; What Is Their Future?” and you can read the whole thing here. For your convenience I below quote some parts that are relevant to the current discussion of whether or not to build a next larger particle collider, specifically the 100 TeV pp-collider (FCC), planned by CERN.

Some of Burton’s remarks are rather specific, such as the required detector efficiency and the precision needed to measure the Higgs’ branching ratios. But he also comments on the problem that particle colliders deliver a diminishing return on investment:

“When I was much younger I was a fan of science fiction books. I have never forgotten the start of one, though I don’t remember the name of the book or its author. It began by saying that high-energy physics’ and optical astronomy’s instruments had gotten so expensive that the fields were no longer funded. That is something that we need to think about. Once before we were confronted with a cost curve that said we could never afford to go to very high energy, and colliding beams were invented and saved us from the fate given in my science fiction book. We really need to worry about that once more.

“If the cost of the next-generation proton collider is really linear with energy, I doubt that a 100-TeV machine will ever be funded, and the science fiction story of my youth will be the real story of our field [...]”

He points towards the lack of technological breakthroughs in accelerator design, which is the major reason why the current method of choice for higher collision energies is still digging longer tunnels. As I mentioned in my recent blogpost, there are two promising technologies on the horizon which could advance particle colliders: high-temperature superconductors and plasma wakefield acceleration. But neither of those is likely to become available within the next two decades.

On the superconductors, Burton writes:

“I see no well-focused R&D program looking to make the next generation of proton colliders more cost effective. I do not understand why there is as yet no program underway to try to develop lower cost, high-Tc superconducting magnets [...]”

About plasma wakefield acceleration he is both optimistic and pessimistic. Optimistic because amazing achievements have been made in this research program already, and pessimistic because he doesn’t see “a push to develop these technologies for use in real machines.”

Burton also comments on the increasingly troublesome disconnect between theorists and experimentalists in his community:

“A large fraction of the 100 TeV talk (wishes?) comes from the theoretical community which is disappointed at only finding the Higgs boson at LHC and is looking for something that will be real evidence for what is actually beyond the standard model [...]

“The usual back and forth between theory and experiment; sometimes one leading, sometimes the other leading; has stalled. The experiments and theory of the 1960s and 1970s gave us today’s Standard Model that I characterized earlier as a beautiful manuscript with some unfortunate Post-it notes stuck here and there with unanswered questions written on them. The last 40 years of effort has not removed even one of those Post-it notes. The accelerator builders and the experimenters have built ever bigger machines and detectors, while the theorists have kept inventing extensions to the model.

“There is a problem here that is new, caused by the ever-increasing mathematical complexity of today’s theory. When I received my PhD in the 1950s it was possible for an experimenter to know enough theory to do her/his own calculations and to understand much of what the theorists were doing, thereby being able to choose what was most important to work on. Today it is nearly impossible for an experimenter to do what many of yesterday’s experimenters could do, build apparatus while doing their own calculations on the significance of what they were working on. Nonetheless, it is necessary for experimenters and accelerator physicists to have some understanding of where theory is, and where it is going. Not to do so makes most of us nothing but technicians for the theorists.”

Indeed, I have wondered about this, whether experimentalists even understand what is going on in theory-development. My impression has been that most of them regard the ideas of theorists with a mix of agnosticism and skepticism. They believe it doesn’t matter, so they never looked much into the theorists’ reasoning for why the LHC should see some fundamentally new physics besides the Higgs-boson. But of course it does matter, as Burton points out, to understand the significance of what they are working on.

Burton also was no fan of naturalness, which he called an “empty concept” and his judgement of current theory-development in high energy particle physics was harsh: “Simply put, much of what currently passes as the most advanced theory looks to be more theological speculation, the development of models with no testable consequences, than it is the development of practical knowledge.”

A wise man; gone too soon.