The latest in Ph-word: March ’21

Particle physics are back this month, and so are black hole photos! Read on for gory details and check out the end of the post, for a small list of geeky things to look out for in April.

A surprising asymmetry is found in decays of elementary particles

Impressive: 9/10. Certain: 3/10.

This title is a little plain. I have seen the exact same piece of news under headlines such as “new force of nature discovered!” in the last weeks. As always, the truth is somewhere between plain and sensationalist.

LHCb is an experiment which uses the collisions of protons at the Large Hadron Collider at CERN to take a close look at bottom quarks (I didn’t choose their name, okay?). Why? Because some larger particles made up of quarks that include bottoms behave strangely from time to time.

To make more sense of why “behave strangely” is a thing, let me say that almost all current research in particle physics is about trying to catch particles doing things differently than the Standard Model says – the “Standard Model” being the ultra-successful theory that describes the world of elementary particles sickeningly well.

To cut to the chase, LHCb looked at how bottom quarks “decay”, that is how they change spontaneously and give off lighter particles. Some of the times they give off electrons and sometimes muons. Muons are particles much heavier than electrons but otherwise same as them; this often makes the press describe them as “electrons’ heavier cousins”. Let’s forget this cheesy name and get back to physics.

Now, according to the Standard Model bottoms should decay equally often to electrons and to muons. But, as you have guessed, LHCb saw that they don’t. They decay slightly more often to electrons.

This would be huge news, but if it sounds too good to be true then it probably is, etc. LHCb has gathered enough data to know that there is a chance of 1 in 1,000 that the difference between the two types of decay is just a coincidence. This is too high a chance for particle physics, where people start taking something seriously only when the chance of a coincidence is around 1 in a million. History has shown that anything less than this almost always disappears when more data are gathered. That’s why the only people who got excited about this so far are tabloid editors.

Of course the good thing is that there are ways to settle this. The more straightforward is LHCb to gather more data. Or, other experiments to look for the same decay, and indeed there are a few around that can do so. A few more years will be needed for this in any case, but I wouldn’t hold my breath.


The first image of a black hole now shows its magnetic field

Impressive: 7/10. Certain: 9/10.

In 2019 the Event Horizon Telescope (EHT), a collaboration of eight radio telescopes around the world, gave us the first photo of a black hole. Now they are back with more. Now they made the polarized version of the same photo.

Around the hole there is, naturally, a lot of hot material that swirls around it as it falls in. Doing so it sends out light. However, if there is any magnetic field present, it will make the light waves vibrate in specific directions, which is actually what polarization is.

Luckily polarization is something that can be observed (think polarized sunglasses) and measured, and that led eventually the astronomers to calculate and map the magnetic field around the hole’s edge. If you want the details, the strength of the field is between 1 and 30 Gauss (with the Earth’s surface magnetic field being 0.65 Gauss) and apparently it pushes against the gas as it is falling in.

EHT also made a cool video that takes you into the depths of the sky 53 million light years away to galaxy M87, where the massive black hole sits. They also have the picture version of the last leg of the trip, actually created by a reader of this blog, so, bragging rights.


The odderon was discovered

Impressive: 7/10. Certain: 8/10.

In the esoteric news of the month, a particle that was first hypothesized half a century ago was confirmed for the first time. This is the odderon, a composite made of three gluons. Gluons are the elementary particles holding together quarks to form larger composites, like protons and neutrons, and yes, they are named after glue. Now they are finally seen to come together to form larger particles themselves.

Odderons might not be a new building block of the universe or a new force of nature, but they are a fun animal that was expected to show up for so long. They play a role wherever many quarks and gluons come together in intense conditions, e.g. in proton colliders. And this is where they were spotted: at the Large Hadron Collider by the experiment TOTEM and at the second-largest accelerator ever, at Fermilab, by the experiment D0. D0 stopped working several years ago, but the combination of some of its data together with TOTEM’s showed signs of odderons in the way that some of the protons bump off each other. What’s more, the combination brought the chance of a coincidence down to the famous 1 in a million, so it is now taken seriously (see first item above).


High-temperature superconductivity was achieved at less extreme pressure

Impressive: 5/10. Certain: 10/10.

Last autumn we wrote about a lab that achieved almost room-temperature superconductivity. Superconductivity, i.e. the flow of electricity without resistance, is usually achieved at a couple of hundred degrees below zero; if it is ever achieved at temperatures anything else than this it will probably bring a tech revolution.

Then why is everything still the same since autumn? Because the lab at the University of Rochester created superconductivity at 15 degrees Celsius, which is fine, but at pressures so high that approach those at Earth’s core…

But now, the same team did it again at -11°C and at “only” two thirds of the previous pressure. Yes, still not room-pressure, but a second step in the right direction is big news for the particular direction.


Bonus track: What to look out for in April

7/4 Announcement of first results from Fermilab’s Muon g-2 experiment. This will be either a big one or a big disappointment for particle physicists. More in next month’s post, for sure.

11/4 Ingenuity will (hopefully) become the first vehicle to fly on another planet. The mini helicopter will be released by the Mars rover Perseverance.

22/4 Peak of Lyrids meteor shower. Look towards the constellation of Lyra an hour before dawn, if you are so inclined.

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