Pentaquarks and Tetraquarks Discovered

Three new exotic particles

Three new exotic particles have just been discovered — certainly not something that happens every day.

But this week (July 5, 2022), on the 10th anniversary of the announcement of the discovery of the Higgs Boson (the so-called God Particle), the LHCb Collaboration reported the observation of a strange pentaquark, a doubly charged tetraquark and its neutral partner.

Atoms contain smaller particles called neutrons and protons, which are made up of three quarks each. These new discoveries go beyond that.

What does it mean?

These latest finds takes the total number of particles discovered at LHCb to 21. That's Large Hadron Collider 'b' in case you were wondering. The LHCb experiment is one of eight particle physics detector experiments collecting data at the Large Hadron Collider at CERN.

The implications are that there are now enough of these particles to start organising them into a table, much as is done with chemical elements in the periodic table. Such a table would be a step towards creating a theory and set of rules governing exotic mass in this strange sub-atomic world.

“Finding new kinds of tetraquarks and pentaquarks and measuring their properties will help theorists develop a unified model of exotic hadrons, the exact nature of which is largely unknown,” said LHCb spokesperson Chris Parkes. “It will also help to better understand conventional hadrons.” — Phys.org

And these discoveries my help us understand more about the formation of our universe — and that’s something I puzzle about every day. From nothing we came, suddenly, just like that?

I hate singularities.

Scientific excitement

Each particle that was discovered is unique, but researchers are excited about the qualities of the three new finds.

The new pentaquark decays into particles that none of the others produce, while the two tetraquarks have the same mass (one is neutral), suggesting they may be the first known pair of exotic structures.

There’s very little doubt that these particles ‘exist’ — if only in peculiar circumstances and for only very brief moments in time— just a hundred thousandth of a billionth of a billionth of a second.

The finding has a statistical significance of 15 standard deviations, way beyond the 5 standard deviations that are required to claim the observation of a particle in particle physics (‘5-sigma’ — 5σ). That’s extremely high confidence.

Binding speculation

It’s not clear how these exotic particles are structured. In particular, the nature of the binding forces is not understood.

“The strong force is extremely difficult to calculate, and we don’t have firm predictions of how the exotic pentaquarks and tetraquarks are built,” says Prof Chris Parkes of Manchester University. “But we hope that by finding out about them we can develop theories that enable us to understand them better.” — BBC

Various interpretations have been proposed, including tightly bound pentaquark or tetraquark states as well as loosely bound molecular baryon-meson or meson-meson states.

And we can expect more

On the ten-year anniversary of the Higgs discovery this result reminds us of the diversity and importance of results produced by the LHC experiments. For example, already 66 hadrons have been discovered at the LHC, of which 59 by LHCb. We can look forward to many more discoveries in Run 3. — CERN

This hidden world is becoming ever more complicated, and to visualise it the researchers are having to invent more diagrams. I know what a Feynman diagram is (which I can just about grasp), but now we have Dalitz plots.

More particles, more diagrams. I love science but it’s all getting too deep for me.

I’ll just go back to puzzling about Day 1 of 7. Or take up animism and pray to my ancestors.

Let there be light.

I need some.

You can find the full details and a lots of data in the CERN announcement.

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This story was first published in Medium on 10 July 2022