by Alexander Held

Last month, I had the pleasure to attend the 2017 edition of the European School of High-Energy Physics in Évora, Portugal. We were about 100 students, including my fellow ESR Pablo. The two week program included lectures on many high-energy physics-related topics, such as the Standard Model, cosmology, statistics, Higgs physics, and phenomena beyond the Standard Model. In the evenings, after the lectures, the program foresaw discussion sessions in smaller groups. These sessions were a great way to go over the content of the lectures again, clarify concepts, and answer questions.

ESHEP2017 group picture

Besides the physics content, the school also included a segment aimed at outreach. Each discussion group, comprised of about 15 students, had to prepare an eight minute talk on a particle physics topic. These talks were meant to be understandable by the general public. To help us with this, we had the chance to see a professional doing outreach in person: CERN Director General, Fabiola Gianotti, gave a public talk in Évora, followed by a panel discussion. The talk was recorded, you can find it here if you are interested.

Further training was provided by a pair of former BBC journalists. This included a few exercises; especially helpful to me was a simulated one-on-one radio interview about a fictitious physics discovery. Those interviews were recorded, too, so we had the chance to listen back to them again later and analyse our behaviour.

At this point you might wonder why the title of this blog post is about grandmas. This brings us back to the outreach projects, where my group was given the Higgs boson as a topic. Every good talk about the Higgs should contain some attempt at explaining the Higgs mechanism [1]. This mechanism describes how fundamental particles acquire mass, and it is a tricky beast to explain properly without reverting back to lots of algebra. Typically, analogies are used to give an idea as to how this mechanism works. A famous example is the analogy of a cocktail party by David J. Miller. I personally like this explanation from The New York Times a lot, which includes nice visualizations and contains a bit more than just an analogy.

My group after presenting our Higgs boson outreach talk

We wanted to come up with a new analogy, and this is where grandmas come in. Imagine a grandmother who hands out homemade cookies to people passing by. She likes her grandchildren a lot, so she gives out more cookies to them than to other people. Now imagine not only one grandmother, but many grandmothers, everywhere in the universe: this is a field of grandmothers. People passing by these grandmothers will receive cookies, they interact with the grandmother field. By interacting with the field, these people will acquire mass. The grandchildren have a stronger interaction with the field than the rest of the people (since they obtain more cookies!), so they consequently acquire more mass.

In order to translate this back into physics terms, just replace the grandmother field by a Higgs field, and replace the people interacting with the field by fundamental particles. The interaction strength of the various fundamental particles with the Higgs field varies, thus they have different masses. Our presentation at the school was recorded, you can find John explaining the mechanism in this video (650 MB file).

As it usually is the case with analogies, our grandma version has its shortcomings. I want to point out one important point: From the explanation above, you could imagine that particles acquire more and more mass while travelling through the Higgs field, since they keep on collecting cookies in our analogy. This is not the case! The particle masses are determined by an interaction strength, which we describe as the amount of cookies exchanged. The masses do not correspond to the total amount of cookies collected over time.

After attending the school, I explored Portugal a bit, this picture was taken somewhere along the West Coast.

I want to conclude with a recommendation: Try out Queijadas if you are in Portugal! They are a delicious, sweet pastry, which I was able to find in both Évora and Sintra.

[1] The mechanism goes by many names, and is often times also called Brout–Englert–Higgs mechanism. I do not intend to discredit any of the theorists instrumental to its prediction, but call it Higgs mechanism for brevity.