Synopsis

How a Pentaquark is Put Together

Physics 12, s66
New Large Hadron Collider data reveal that exotic quark quintets, discovered in 2016, are composites of quark-antiquark mesons and three-quark baryons.  

Particles consisting of either three quarks or quark-antiquark pairs are some of the more familiar members of the standard model, but theory also predicts the existence of other exotic combinations. In 2016, relying on data from the Large Hadron Collider (LHC), the LHCb Collaboration spotted the signature of one long-sought example: a pentaquark, comprising four quarks and one antiquark (see 18 August 2016 Synopsis). Now, the same team reports that pentaquarks are formed by attractive forces between a three-quark baryon and a quark-antiquark meson, binding them loosely into a “molecular” state.

While the original pentaquark detection had high statistical confidence, it wasn’t clear how the component quarks were organized. Quantum chromodynamics—the theory that describes how quarks interact—allows for several possibilities, including a tightly bound quark quintet, composites of various species of baryons and mesons, or even a fleeting interaction between simpler particles and their decay products.

With new LHC results, the team had access to more than 9 times as much data as was used to make the initial pentaquark discovery. The larger dataset revealed that one of the particle types observed three years ago is actually two separate pentaquarks with nearly identical masses. The masses of these particles—along with a newly discovered lower-mass pentaquark—correspond closely with the masses of three candidate baryon-meson pairings.

While it’s possible that these masses could emerge by chance with other pentaquark architectures, the researchers say that such a match would be coincidental—though more experiments are needed before they know for sure.

This research is published in Physical Review Letters.

–Marric Stephens

Marric Stephens is a freelance science writer based in Bristol, UK.


Subject Areas

Particles and Fields

Related Articles

No-Show for Cosmic-Ray-Boosted, Lightweight Dark Matter
Astrophysics

No-Show for Cosmic-Ray-Boosted, Lightweight Dark Matter

Interactions with cosmic rays could make low-mass dark matter particles detectable by neutrino observatories. But an analysis of two decades’ worth of data shows no signs of the particles. Read More »

Detecting Dark Matter Decay
Particles and Fields

Detecting Dark Matter Decay

The first measurements from a newly built gamma-ray observatory have been analyzed for signs of the decay of heavy dark matter, putting a lower limit on the hypothetical particles’ lifetime. Read More »

Hunting for Axions in the Galactic Center
Particles and Fields

Hunting for Axions in the Galactic Center

A neutron star’s ultrastrong magnetic field could create the conditions for uncloaking a promising dark matter candidate. Read More »

More Articles