The road from CERN to space

The Agenzia Spaziale Italiana (ASI) – the Italian Space Agency – has the tag line “The road to space goes through Italy.” Make a simple change and it becomes a perfectly apt summary of the career to date of the agency’s current president. For Roberto Battiston, the road to space goes through CERN.

As a physics student at the famous Scuola Normale in Pisa, which has provided many of CERN’s notable physicists, he studied the production of dimuons in proton collisions at the Intersecting Storage Rings, under the guidance of Giorgio Bellettini. For his PhD, he moved in 1979 to the University of Paris IX in Orsay, where his thesis was on the construction of the central wire-proportional chamber of UA2, the experiment that went on, with UA1, to discover the W and Z particles at CERN. Until 1995, his research focused on electroweak physics, first at the SLAC Linear Collider and then, back at CERN, at the L3 experiment at the Large Electron–Positron collider. However, at the point when the LHC project was on its starting blocks, his interest began to turn towards cosmic rays. With Sam Ting, who led the L3 experiment, Battiston became involved in the Alpha Magnetic Spectrometer, which as AMS-02 has now been taking data on board the International Space Station (ISS) for four years (CERN Courier July/August 2011 p18). Three years after the launch of AMS-02, Battiston found himself closer to space, at least metaphorically, when he was appointed president of ASI in May 2014.

The decision to move away from experiments at the LHC will surprise many people. How do you explain your unconventional choice?

The LHC, a machine of extraordinary importance, as its results have shown, was the obvious choice for someone who wanted to continue a research career in particle physics. But I chose to take a less beaten path. In space, less has been researched and less has been discovered than at accelerators. I realized that, in both neutral and charged cosmic rays, we are presented with information that is waiting to be decoded, potentially hiding unforeseen discoveries. The universe is, by definition, the ultimate laboratory of physics, a place where, in the various phases of its evolution, matter and energy have reached all of the possible conditions one could imagine – conditions that we will never be able to reproduce artificially. For this reason, when I was discussing with Sam Ting in 1994 about what would be the most interesting new project – whether to go for an LHC experiment or, radically, for a new direction – I had no hesitation: space and space exploration immediately triggered my enthusiasm and curiosity. I absolutely do not regret this choice.

Was your experience and know-how as a high-energy physicist useful for the construction and, now, the operation of AMS?

The AMS detector was designed exactly like the LHC experiments. It has an electromagnetic spectrometer with a particle tracker and particle identifiers. Subdetectors are positioned before and after the magnet and the tracker, to identify the types of particles passing through the experiment. We use the same approach as at accelerators – 99% of the events are thrown away, the interesting ones being the few that remain. However, within these data, processes that we still do not know about remain potentially hidden. The challenge is to find new methods to look at this radiation and extract a signal, exactly as at the LHC. The difference is that the trigger rate is kilohertz in space, rather than gigahertz at the LHC: AMS gets one or two particles at a time instead of hundreds of thousands per event. Moreover, space offers some advantages and optimal conditions for detecting particles: surprisingly, it provides stable environmental conditions, so detectors that on the ground would suffer from environmental changes – such us too much heat or atmospheric pressure changes or humidity – enjoy ideal conditions in space. Silicon detectors, transition-radiation detectors, electromagnetic calorimeters and Cherenkov detectors have performed much better than the best detectors on the ground.

But in space you must face more complex challenges that put constraints on your instrument’s design?

Given the complexity of the current LHC experiments, the situation is comparable. Repairing a huge detector 100 m below ground is as difficult as repairing a detector in space. If something breaks down underground, dismantling the whole structure of a detector might require months if not a year. Everything in both environments must have sufficient reliability to operate for a long time. In space, radiation doses are relatively small compared with the doses that the detectors can sustain, but there are problems of the shock at launch, pressure drops, extreme temperatures and the ability to operate in a vacuum, so the tests that a detector must pass to be able to perform in space are severe. Shock and stress resistance at launch require the detectors to be more robust than those built to stay on Earth. Another huge difference is weight and power. On Earth there are no limits. In space, we must use low-weight instruments – a few tonnes compared with the 10,000 tonnes of the large LHC detectors. And because detectors in space are powered by solar panels, there are power limits – a few kilowatts compared with tens of megawatts at the LHC. So in space, resources are optimized to the last small part.

What about the choice of leading technology vs reliability, for an experiment in space?

It is true that in space we have instruments that are dated, technologically speaking. But AMS is an exception: we made the effort of bringing to space technology developed at CERN since 2000, which has shown itself to be 10–100 times more powerful and effective than current space standards.]

Space is particle physics multiplied to the nth power.

Roberto Battiston

Now, with AMS-02 successfully installed on the ISS and reaping promising results, you have been appointed president of the ASI, one of the large European space agencies. What can a physicist like yourself bring to the management of the space industry at the European and international level?

Space is a place were human dreams converge: from photographing the Moon, to walking on Mars, to taking a snapshot of the first instants of the universe – these are global dreams of humanity. Yet, space is a different world from physics. In certain aspects, it’s wider. Particle physics is an international discipline, but is so focused that the bases for discussion are limited, however fascinating and however important might be the consequences of finding a new brick in the construction of the universe. Space is particle physics multiplied to the nth power. It is a context, not just one discipline. Many different sectors interact, but each has its own dynamics – my leitmotiv is “interdisciplinarity”. Many different things happen at a fast pace, which requires a great capacity for synthesis and ability to process a lot of data in a short time. Decisions must be taken so fast that a well-trained brain is needed. I can only thank my tough training in physics research for this. The tough discipline at the basis of research at CERN and in astroparticle physics, the continuous challenge of having to solve complex problems, the requirement of working in a large community made of people with different characters, cultures and languages, typical of experimental physics, are an asset within the context of a space agency.

How do large collaborations work in space research? Is it as global as the LHC?

The capability to keep the construction effort of very large accelerators or extremely complex detectors under direct control is still, today, an essential aspect of the high-energy physics community. Space research has not made the transition to a global collaboration in the same way as CERN, because it is still dominated by a strong element of international politics and national prestige. The amount of funding involved and the related industrial aspects and business pressures are so big, that decisions must be taken at the level of heads of state and government.

Is there a difference in approach between NASA and ESA?

They’re both huge agencies, although NASA has four times the budget of ESA. In the past, they’ve collaborated on large projects, but in the past 10 years this collaboration has dimmed, as is the case for LISA [the Laser Interferometer Space Antenna]. Sometimes, such projects are even done in competition, as in the case of WMAP and Planck. The US pulled out of Rosetta long ago, and is now focused on the James Webb Space Telescope. To do so, the US basically chose to stop most international collaborations in science, except for the ISS and exploration. The ISS exists because of a precise political will. It is a demonstration that collaboration in space is decided top-down instead of bottom-up, and it can hold or break according to politics.

AMS will soon be joined in space by new powerful instruments to study cosmic rays. Are we witnessing a change of focus, from particle physics in the lab back to the sky?

Space is a less-frequented frontier, and it is understandable that it is now attracting many physicists. Astroparticle physics is a bridge between the curiosity of particle physicists who try to understand fundamental problems and the tradition of astronomy to observe the universe. Two different aspects of physics converge here: deciphering vs photographing and explaining. In astroparticle physics we try to find traces of fundamental phenomena, in astrophysics, to explain what we are able to see.

So what would your advice be to young physics graduates? Where would they best fulfil their research ambitions today?

Physics in space is becoming enormously interesting, not just in the understanding of both the infinitely small and the infinitely large. In the coming decades, astrophysics and particles studied in space radiation will be the place from where surprises and important discoveries could come, although this will take time and more sophisticated technologies, because the limits of technology are farther from the limits of the observable phenomena in the universe than in the case of particle accelerators. Building a new accelerator will require decades and big investments, as well as new technologies, but most of all it will need a discovery indicating where to look. The resources required are so considerable that we will not be able to build such a machine just to explore and see what there is at higher energies, as we did many times in the past. This is less true in astrophysics. There will surely be decades of discoveries with more sophisticated instruments, the frontiers are not completely explored at all. However, physics keeps its outstanding fascination. With current computing capacity, latest technologies, the present understanding of quantum mechanics, the interactions between physics and biology, the amount of physics that you can do at atomic and subatomic level, using many atoms together, cold systems and so on – there are so many sectors in which an excellent physicist can find great satisfaction.

And after ASI, will you go back to particle physics?

For the moment I need to put all of my energy into the job that has just started. I have not lost the pleasure of discovery, and the main objective of the years ahead is to support the best ideas in space science and technology, trying to get results as quickly as possible. And of course, I will keep following AMS.