Seeking consensus

27 January 2021

Joachim Mnich discusses the opportunities and challenges he faces as CERN’s new director for research and computing, and how the best of particle physics is yet to come.

Joachim Mnich

You started out studying electrical engineering. Why the switch to physics, and what have been your main research interests?

Actually, I studied them both in parallel, having started out in electrical engineering and then attending physics courses after I found myself getting a bit bored. I graduated with a Masters in electrical engineering, and then pursued a PhD in particle physics, working on the MARK-J experiment at DESY studying muon pairs, which allowed us to make estimates of the Z mass and sin2θ. To some level at MARK-J we could already test electroweak theory. Afterwards, I did a postdoc at CERN for two years on the L3 experiment, and ended up staying on L3 for 12 years. My background in engineering has helped several times during my career. For example, I acted as an interface between the physicists at CERN and the engineers in Aachen who designed and built the complicated L3 readout electronics, as they couldn’t always speak the same language.

How do you remember your LEP days?

It was a marvellous time, certainly some of the best years of my life. For the firsts few years at L3 I didn’t do any physics analysis – I was down in the tunnel dealing with the readout electronics. After a few years I was able to pick up physics again, going back to electroweak physics, and becoming the coordinator of the line-shape group that was in charge of measurements of Z parameters. I later became L3 analysis coordinator. I was there for essentially the whole duration of LEP, leaving CERN at the end of 1999 and joining the CMS group at Aachen University.

What are your key achievements since becoming DESYs director for particle and astroparticle physics in 2009?

I came to DESY shortly before the experiments at HERA stopped and became director as the analyses were ramping down and LHC activities were ramping up. Certainly, one of the biggest achievements during this time was helping DESY transition from having local experiments onsite to a laboratory that now plays a key role in the CMS and ATLAS experiments. DESY became one of the largest Tier-2 data centres of the worldwide LHC computing grid, plus it had a lot of experts on proton structure and in detector operation who were highly welcomed by the LHC experiments. DESY joined the LHC relatively late, in 2008, but now has a very strong involvement in the ATLAS and CMS trackers, for example, and has set up a large infrastructure to build one end-cap tracker for ATLAS and one for CMS. DESY also joined the Belle experiment at KEK, and continues to be one of the leading labs in the development of detector R&D for future colliders. Smaller scale experiments at DESY also picked up speed, in particular axion searches. Recently the 24th dipole for the ALPS-II experiment was installed, which is really impressive. The motivation for astroparticle physics was always more concentrated at DESY’s Zeuthen site, and two years ago it was decided to create an independent division for astroparticle physics to give it more visibility.

How has the transition from collider physics to X-ray science changed life at DESY?

Well, there is no longer the burden at DESY to operate large accelerators and other facilities for particle physics, so those resources are now all directed towards photon science, such as the operation of the PETRA light source, the FLASH facility and the European XFEL. On the other hand, the laboratory has also grown over the last decade, to the benefit of photon science. However, if you count the number of DESY authors in ATLAS and CMS, it is still the second or third largest laboratory, so DESY is still very significant in particle physics.

How would you sum-up the state of high-energy physics today?

I’m optimistic, otherwise I wouldn’t be here! Often when I talk to students, I tell them that the best is yet to come in particle physics. Yes it’s true, we do not have at the moment a scenario like we had for the LHC, or for the SppS, which had clear targets to discover new particles, but if you look back in history, this hasn’t been the case very often. We would not have built several machines, including LEP, if that was the case. Discovery doesn’t have to necessarily mean new particles. So that’s why I am optimistic for the future of the field, because we have the Higgs boson now, which is a very special particle. It’s the first of its kind – not another quark or lepton. Studying the Higgs in detail might be the key to new insights into fundamental physics. This is also the central theme of the recent European strategy update.

I dont think the question of linear vs circular is a technology one

What do you see as your main opportunities and challenges during the next five years?

CERN is a very complicated thing. I have been away for 20 years now, so I am still in a learning phase. It is very clear what our challenges are though. We have to make the next LHC run a success, and we also need to prepare for the HL-LHC. The world is looking on us for that. The second most important thing is the implementation of the European strategy update, and in particular, the preparation for the longer-term future of CERN. We have to prepare a convincing plan for the post-LHC collider, to be ready for decision at the next strategy update at the latest.

What is in store for computing?

Computing will remain a major challenge. LHC Run 3 will start soon and we have to prepare for it now, including securing the necessary funds. On the horizon there is the high-luminosity LHC, with an enormous increase in data volumes that would by far exceed the available capacities in a flat-budget scenario. We will have to work in close collaboration with the experiments and our international partners to address this challenge and be open to new ideas and emerging technologies. I believe that the new Prévessin Computing Centre will be instrumental and enhance collaboration among the experiments and the IT department.

What involvement did you have in the European strategy update?

I was a member of the European strategy group in my capacity as research director for particle physics at DESY. The strategy group contained the scientific delegates to council, plus about a dozen people from the national laboratories. I was in Bad Honnef in January 2020 for the final drafting session – it was an interesting time. If you had asked me on the Monday of that week what the result at the end would be, I would have said there was no way that we could reach consensus on a strategy. But we did, even if deciding on the specific facility to be built was beyond the ESPP mandate.

Should a post-LHC electron–positron Higgs factory be linear or circular?

Its shape is not my principal concern – I want one to be built, preferably at CERN. However, if we can get additional resources from outside the field to have one built in Japan or China, then we should grab the opportunity and try a global collaboration. I think even for the next project at CERN, we also need support from outside Europe. I don’t think the question of linear vs circular is a technology one – I think we have already mastered both technologies. We have pros and cons for both types of machine, but for me it is important that we get support for one of them, and the feasibility study that has been requested for a large circular tunnel in the Geneva area is an important step.

Infrared imaging of an ATLAS tracker end-cap petal

Young people ask me which horse will win the race – I don’t know. I consider it as my task as CERN’s director for research and computing to unite the community behind the next collider because that will be vital for our success. The next collider will be a Higgs factory and there are so many things in common between the various proposals if you consider the detectors or the physics. People should come together and try to push the idea of a Higgs factory in whatever topology. Look, I am a scientist. At DESY I have been working on linear colliders. And in the European XFEL we essentially already have a prototype for the International Linear Collider. But if CERN or China build a circular collider, I will be the first one who signs up for an experiment! I think many others think like me.

What are the main challenges in getting the next collider off the ground?

We have competition now – very severe competition. I see that in Germany everybody is now speaking about life science and biology because of the pandemic, plus there are other key societal challenges such as climate and energy. These are topics that also have an interesting story to tell, and one which might be easier to understand. If someone asks me what the applications of the Higgs boson are, I reply that I don’t know. However, I am convinced that in 50 or 100 years from now, people will know. As particle physicists we have to continue to point out our role in society to motivate the investments and resources for our future plans, not just in science, but in technology and impact on society. If you look at the first accelerators, they were not built with other applications in mind – they were built to understand what the core of matter is. But look at the applications of accelerators, detectors and computing that have spun-off from this. X-ray science is one very strong, unforeseen example.

Would a lack of consensus for the next collider risk making physicists appear unsure about their ambitions?   

Of course, there will be people who think that. However, there are also politicians, who I know in the US for instance, who are very supportive of the field. If you compare us to the synchrotron field for instance, there are dozens of light-source facilities around the world. This discipline has the benefit of not having to converge on only one – each country can essentially build its own facility. We have the challenge that we have to get a global consensus. I think many politicians understand this. While it is true that particle physics is not a decisive topic in elections, we have a duty to share our scientific adventure and results with the public. We are very fortunate in Germany that we have had a scientist as chancellor for the past 15 years, which I think this is one of the main reasons Germany is flourishing.

I consider it as my task as a CERN director for research to unite the community

What would be the implication for European particle physics were Japan or China to proceed with a Higgs factory?

I do not have a “gold-plated” answer for this. It really depends on things that are beyond our direct control as physicists. It could be an opportunity for CERN. One of the things that the strategy update confirms is that Europe is the leader of the field scientifically and also technologically, thanks mainly to the LHC. One of the arguments that CERN could profit from is the fact that Europe should want to remain the leader, or at least “a leader” in the field. That might be very helpful for CERN to also get a future project on track. Being the leader in the field is something that CERN, and Europe, can build upon.

What is your philosophy for successful scientific management?

I believe in flat hierarchies. Science is about competition for the best ideas, and the capital of research laboratories like CERN are the people, their motivation and their creativity. Therefore, I intend to foster the CERN spirit of fruitful collaboration in our laboratory but also with all our partners in Europe and the rest of the world.

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