The latest in Ph-word: August 2020

Four exciting -in their own ways- things happened last month. One of them in an asteroid, two in labs studying subatomic particles, and one tidying up after an older enigmatic piece of news in the skies.

Water in Ceres

Ceres is the largest asteroid in the solar system and a trendy space exploration destination. Now it was revealed that data from NASA’s Dawn orbiter, collected a few years ago, suggest the existence of an underground reservoir of water in the asteroid. The hidden sea could be hundreds of kilometers wide and some of its water seems to seep to the surface, where it leaves salts marks that led to its tracking. I must add that anything bringing us closer to The Expanse can’t but be good.

Higgs speaks to muons

Experiments at the Large Hadron Collider have been seeing evidence for the existence of the famous Higgs boson for a decade now (god do I feel old). The Higgs itself is a particle that appears from the collisions for too brief a time before giving off other types of particles; this means that the way to “see” it is to detect groups of particles with a common origin; and the mass and other characteristics of that origin should be the ones expected from the Higgs according to the theory, if everything goes as expected.

Things so far have gone as expected, with Higgs having the predicted characteristics. However, the particles through which it is indirectly seen do not cover yet the whole collection of particles as we know it. The reason is that Higgs is more “connected” to heavier particles, so it gives them off more often and so they are easier to catch in experiments.

But now, the particle-watching just extended to some rather light ones. ATLAS and CMS, the two huge experiments using the Collider’s collisions, announced that Higgs is hereby known to also connect to muons. Muons are the particles often called the heavier cousins of electrons (so, the Dursleys of electrons?).

Like all things Higgs in the last decade, this happens in a way that agrees with the predictions of the theory. But even though there is no surprise here, discovering more and more of Higgs’ features is a big thing, as the latest particle to be discovered is still something of a half-explored party island.

An electron, a positron, some tension

As talked about above, what a lot of the experiments in particle physics do is comparing the behaviour of particles to that expected by the theory. The current theoretical framework, affectionately named the Standard Model, has proven extremely successful. Actually it is the scientific theory that has been tested to the most extreme extent in history, and always wins.

At the same time, anything that might be found to disagree with the Model will be music to the ears of physicists, as it will give clues about physics that may still be undiscovered. And that’s why experiments keep looking closer and closer at subatomic particles hoping to catch them misbehaving.

Even though I wrote that The Model always wins this was a simplification: there have been a couple of cases where measurements from experiments are “in tension”, as it is put nicely, with the predictions from theory. The jury is still out though as more experiments work on checking them.

Now, a new case might have joined them.

The new measurement in tension with the Standard Model is about the energy levels of positronium; the cool-sounding positronium consists of an electron and an anti-electron (aka positron) orbiting each other. Like it also happens in atoms, the energies that the electrons can have in these orbits are very specific and very narrowly defined by the properties of the involved particles. So much so that measuring these energies has been a staple in testing the Model.

The new positronium measurement by the University College London managed to get more accuracy than previous ones, and so found that one of the energies is a few per thousand larger than expected from the theory.

This could be big but, as always in such cases, it is a lot more likely that some experimental error played a role. Yes, the Standard Model is like the house at a casino, it is expected to win. The next step is that other experiments will check the result in the next years and see if it is a jackpot.

Betelgeuse revealed

Last winter the red supergiant Betelgeuse, found on the left shoulder of Orion, quickly lost most of its brightness. This made people hopeful that it’d turn into a supernova but after a while it came back. Still, nobody was sure why this happened.

Now images from the Hubble telescope might have explained it away: it looks like Betelgeuse was partially blocked by a cloud of gas, which it previously happened to throw in earth’s direction. Ejecting gas into space is something that stars are known to do, but this time its direction conspired to create a small mystery. (Interestingly though, Betelgeuse is once more getting darker since June.)

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