Physicists Detect a Particle That Isn’t a Particle at All

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By Staff Reporter

April 6, 2019
4:44 am
Los Angeles, CA

It sounds like the start of a very bad physics riddle: I’m a particle that really isn’t; I vanish before I can even be detected, yet can be seen. I break your understanding of physics but don’t overhaul your knowledge. Who am I? It’s an odderon, a particle that’s even more odd than its name suggests, and it may have recently been detected at the Large Hadron Collider, the most powerful atom smasher, where particles are zipped at near light speed around a 17-mile-long (27 kilometers) ring near Geneva in Switzerland. It’s just complicated First off, the odderon is not really a particle. What we think of as particles are usually very stable: electrons, protons, quarks, neutrinos and so on. You can hold a bunch of them in your hand and carry

Atlas Cavern, at CERN’s Large Hardron Collider

It’s an odderon, a particle that’s even more odd than its name suggests, and it may have recently been detected at the Large Hadron Collider, the most powerful atom smasher, where particles are zipped at near light speed around a 17-mile-long (27 kilometers) ring near Geneva in Switzerland.

It’s just complicated

First off, the odderon is not really a particle. What we think of as particles are usually very stable: electrons, protons, quarks, neutrinos and so on. You can hold a bunch of them in your hand and carry them around with you. Heck, your hand is literally made of them. And your hand isn’t vanishing into thin air anytime soon, so we can probably safely assume that its fundamental particles are in for the long term.

There are other particles that don’t last long but still get to be called particles. Despite their short lifetimes, they remain particles. They’re free, independent and able to live on their own, separate from any interactions — those are the hallmarks of a real particle.

And then there is the so-called quasiparticle, which is just one step above being not-a-particle-at-all. Quasiparticles aren’t exactly particles, but they’re not exactly fiction, either. It’s just … complicated.

As in, literally complicated. In particular, interactions of particles at superhigh speeds get complicated. When two protons smash into each other at nearly the speed of light, it’s not like two billiard balls cracking together. It’s more like two blobs of jellyfish wobbling into each other, getting their guts turned inside out and having everything get rearranged before they return to being jellyfish on the way out.

Feeling quasi

In all of this complicated messiness, sometimes strange patterns appear. Tiny particles pop into and out of existence in the blink of an eye, only to be followed by another fleeting particle — and another. Sometimes these flashes of particles appear in a particular sequence or pattern. Sometimes it’s not even flashes of particles at all, but merely vibrations in the soup of the mixture of the collision — vibrations that suggest the presence of a transient particle.

It’s here that physicists face a mathematical dilemma. They can either attempt to fully describe all the complicated messiness that leads to these effervescent patterns, or they can pretend — purely for the sake of convenience — that these patterns are “particles” in their own right, but with odd properties, like negative masses and spins that change with time.

Physicists choose the latter option, and thus the quasiparticle is born. Quasiparticles are brief, effervescent patterns or ripples of energy that appear in the midst of a high-energy particle collision. But since it takes a lot of legwork to fully describe that situation mathematically, physicists take some shortcuts and pretend that these patterns are their own particles. It’s done just to make the math easier to handle. So, quasiparticles are treated like particles, even though they definitely aren’t.

It’s like pretending that your uncle’s jokes are actually funny. He is quasifunny purely for the sake of convenience.

Evening the odds

One particular kind of quasiparticle is called the odderon, predicted to exist in the 1970s. It’s thought to appear when an odd number of quarks— teensy particles that are the building blocks of matter — briefly flash in and out of existence during proton and antiproton collisions. If odderons are present in this smashup scenario, there will be a slight difference in the cross sections (physics jargon for how easily one particle strikes another) of collisions between particles with themselves and with their antiparticles.

So, if we slam a bunch of protons together, for example, we can calculate a cross section for that interaction. Then, we can repeat this exercise for proton-antiproton collisions. In a world without odderons, these two cross sections ought to be identical. But odderons change the picture — these brief patterns we call odderons appear more favorably in particle-particle than antiparticle-antiparticle collisions, which will slightly modify the cross sections.

The trouble is that this difference is predicted to be very, very small, so you’d need a ton of events, or collisions, before you could claim a detection.

Now, if only we had a giant particle collider that regularly smashed protons and antiprotons together, and did it at such high energies and so often that we could get reliable statistics. Oh, right: We do, the Large Hadron Collider.

In a recent paper, published March 26 on the preprint server arXiv, the TOTEM Collaboration (in the hilarious jargon acronyms of high-energy physics, TOTEM stands for “TOTal cross-section, Elastic scattering and diffraction dissociation Measurement at the LHC”) reported significant differences between the cross sections of protons smashing other protons versus protons slamming into antiprotons. And the only way to explain the difference is to resurrect this decades-old idea of the odderon. There might be other explanations for the data (in other words, other forms of exotic particles), but odderons, as odd as it seems, appear to be the best candidate.

Did TOTEM discover something new and funky about the universe? For sure. Did TOTEM discover a brand-new particle? No, because odderons are quasiparticles, not particles in their own right. Does it still help us push past the boundaries of known physics? For sure. Does it break known physics? No, because odderons were predicted to exist within our current understanding.

Paul M. Sutter is an astrophysicist at The Ohio State University, host of Ask a Spaceman and Space Radio, and author of Your Place in the Universe.

Originally published on Live Science.com