Dr Yannick Ulrich

Yannick is a tenure-track lecturer in theoretical particle physics at the Department of Mathematical Sciences. He works on precision predictions for low-energy experiments.

What is your research about and what types of scientific techniques do you make use of?

Particle physics is about studying the properties and interactions of the fundamental constituents of matter, such as electrons or quarks. Our best model for these interactions is the Standard Model of Particle Physics, which makes predictions that have been verified to very high precision, in some cases with ten or more significant digits. However, we know that the Standard Model can't be a complete description of nature, since it doesn't include a description of gravity. It also doesn't provide an explanation for Dark Matter, a form of invisible matter that we know must exist and accounts for over 80% of the matter in the universe.

To help address these questions and `break' the Standard Model, we investigate along three frontiers: Energy, which aims to directly produce new particles at colliders, such as the Large Hadron Collider (LHC) at CERN; Cosmic, which aims to detect new particles in astronomical observations; and Intensity, which aims to measure the effects that new particles have on known particles.

My work is mostly focused on the Intensity Frontier. Since the effects we want to measure are very small, we need to understand the background - that is, the Standard Model effects - very well. My collaborators and I are calculating theoretical predictions of the Standard Model that are used by experiments at CERN (Switzerland), Jefferson Laboratory (USA), Sendai (Japan), the Paul Scherrer Institute (Switzerland), Fermilab (USA), and KEK (Japan).

What attracted you to apply for a University of Liverpool Research Fellowship?

Particle physics is one of the main research frontiers of the University of Liverpool. The department of Physics has experiments across all three Frontiers of particle Physics, but it also has a specific focus on the Intensity Frontier, particularly through the Muon Physics Programme, which is funded by the Science and Technolofy Facilities Council (STFC) and the Leverhulme Trust.

Close contact with experimentalists is very important for my work, since we need to tailor our predictions to the exact experimental conditions in which they will be used. Liverpool is on its way to becoming the preeminent place for muon physics in Europe, and I'm excited to be part of that journey.

What or who first inspired you to be interested in your research subject?

Particle physics is a fascinating area of study. It continues to address the questions we have asked since antiquity, such as "Where do we come from?" and "What are we made of?", and provides falsifiable, scientific answers. While particle physics has led to countless spin-off applications, such as the World Wide Web or better medical scanners, for me the main motivation remains the study of nature for curiosity's sake.

What are you most proud of achieving during your research career so far?

I've spent the last nine years building the McMule (Monte Carlo for MUons and other LEptons) Collaboration, which develops a computer program for the prediction of Standard Model observables at the Intensity Frontier. McMule started out with just my PhD supervisor and myself. Since then, it has since grown into a group of 18 staff and students at ten institutes across Europe, as well as external and one-off collaborators.

The McMule framework that we've developed has enabled us to perform the first calculation of muon-electron scattering at next-to-next-to-leading order in QED. It was the first calculation of its kind that was ever carried out and I'm very happy to have been part of this.

What is the key to running a successful research project?

In my experience, the most important part of research is collaboration with a diverse group, in terms of both scholarly and personal background. This leads to more creative and interesting outputs. I often see my role in research as that of a matchmaker, bringing together experts from different fields to tackle complex problems.

All my greatest scholarly achievements have involved combining people from various areas of expertise, such as the calculation of integrals, automation, or nuclear physics, to solve problems that are important in experimental particle physics.

Which other subjects are important for your research?

As I've said, collaboration is very important for research. Often, this means collaborating with people in the same subject who have a different specialisation. More broadly, I work with experimentalists to understand their needs, and with experts in nuclear structure, which is an input to our calculations. Looking outside of physics, our research involves certain classes of mathematical functions that are independently studied in mathematics.

Finally, since McMule develops computer programs to assist in these calculations, computer science and especially software engineering practices are crucial. I also consider the latter to be a very important training opportunity for the students I work with.

How do you plan to develop your research in the future?

My plan is to continue working on the McMule project. I aim to improve the precision of its calculations and perform a calculation at next-to-next-to-next-to-leading order, a feat that has only been achieved in one or two highly specialised cases. Ours would be the first so-called fully differential calculation with massive internal and external particles, a significant milestone in the field.

I also plan to extend McMule to provide input for more processes and more experiments, including the proposed Future Circular Collider, a 100km electron-positron collider at CERN. This will require a substantial amount of automation, as many of the steps we currently perform manually will need to be streamlined.

What advice would you give to someone considering a career in research?

Don't be afraid to ask for help. The whole point of scientific research is to do things that no one has ever done before, and no one expects you to be magically good at every aspect of it. There will be aspects of your project that you aren't an expert on. When that happens, find someone who is and ask them for help. Who knows, you might even find new collaborators that way (this has happened to me many times).

Also, keep in mind that doing research can be a lot of fun, but it can also be isolating at times. Remember to look after your own well-being and make sure that you have a support network.

Where can readers learn more about your research?

Learn more about Dr Yannick Ulrich and the McMule project.