What does a pentaquark mean for you?
Jon Butterworth
Almost - but not quite - buried on the icy plains of Pluto this week, the Large Hadron Collider revealed a completely new type of particle. What does that tell us?
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Inside a pentaquark? Photograph: Daniel Dominguez/CERN
Saturday 18 July 2015 18.35 BSTLast modified on Sunday 19 July 201508.50 BST
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Perhaps the first thing it tells us is that scientists at CERN are more focused on their results than on the attendant publicity, whatever the press office might advise them. New Horizons has been on the way to Pluto for more than nine years, and the data in which the pentaquark was discovered were recorded by the
LHCb experiment more than three years ago, so you might think they could have arranged things to avoid
announcing the new particle on the same day as
this. As a friend on the experiment put it, it “Shows how focussed we were on the science.”
Of more lasting importance, the discovery tells us something about the strong nuclear force and the way the smallest constituents of matter behave.
The strong force is responsible for binding quarks together inside hadrons such as protons, neutrons and now, it seems, pentaquarks. It also binds protons and neutrons together inside atomic nuclei, and it does this despite the fact that protons have an enormous mutual repulsion due to their electric charges. The strong force is called “strong” because in comparison to its might, electromagnetism is a
mere bagatelle.
There is another sense in which the force is strong, which doesn’t depend on comparing it to other forces.
When we calculate the probability of two particles interacting with each other - either fusing together, or scattering off each other, for example - a number enters the equation called the “coupling constant”. This number characterises the strength of the force - the bigger the coupling constant, the more likely it is that an interaction will occur. When this number is much smaller than one, we can use a technique called perturbation theory to get our results. But if the number is close to or bigger than one, perturbation theory doesn’t work. This is the case for those strong force interactions which confine quarks inside hadrons.
Because perturbation theory doesn’t work, it is very hard to predict the consequences of the strong force. One thing we do know is that the binding energy of the strong force which holds the quarks together inside them is responsible for almost all of the mass of protons and neutrons, and hence almost all of the mass of you. Calculations on supercomputers (such as the
DiRAC facility in the UK) use “lattice” methods to make calculations when perturbation theory doesn’t work. These involve approximating the space-time continuum by a lattice of discrete points and events; they are now able to make some pretty firm predictions, although calculating the details of pentaquarks remains in the future - the experiment is ahead here.
All the hadrons known until recently consist of either three quarks, or one quark and one antiquark. The reasons for this are nicely explained in a series of articles by Ben Still
here(using Lego!). Particles made of two quarks and two antiquarks (known as tetraquarks) have been seen by the
Belle experiment and by LHCb in the last few years, but this one - four quarks and one antiquark - is a new kind of beast.
We would like to know whether pentaquarks are made up of all four quarks and the antiquark clumped together, or whether they consist of a quark-antiquark pair more loosely bound to the other three quarks, as shown in the illustration below.
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Possible layout of the quarks in a pentaquark particle. The five quarks might be tightly bound (left). Or they might be assembled into a meson (one quark and one antiquark) and a baryon (three quarks), weakly bound together. Like Pluto and Charon. Only smaller, closer and less photogenic Photograph: Daniel Dominguez/CERN
In general, understanding the consequences of the strong force, and learning how to make and test calculations for strong forces, is an important area of physics. The other forces can also become strong (in the sense that perturbation theory fails) in some circumstances, and sometimes in materials and situations that are much closer to everyday life than what is happening in LHCb. It is a frontier of knowledge just as much as the high-energy frontier, or the outer reaches of the solar system.
I began the article asking “What does a pentaquark mean for you?” Maybe the answer is “Not too much, directly”. Certainly at least one columnist in this paper regularly insists that the money we spend on exploratory science is a frivolous waste, when we could be spending it on prisons, medicine, art or practically anything else I presume. However, it won’t be a surprise to you that I am of the strong opinion that allocating an amount (a small fraction of a percent at present) of our resources to such things is not only fun and interesting, but a worthwhile investment too, given the inherently unpredictable nature of exploration.
Pentaquark discoveries have been claimed before; I was
involved in one of them myself a few years ago, though we didn’t claim that the bump we saw was definitely a pentaquark, and whatever it was, the bump was nowhere near as clear as
those seen by LHCb. I think the force is strong with this one.
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The Force is strong with this one Photograph: Cine Text/Allstar/Sportsphoto Ltd./Allstar
Jon Butterworth’s book Smashing Physicsis available as “Most Wanted Particle”
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The Strong force is a very interesting subject and as much a mystery as Gravity. Gluons play an interesting role that probably holds the key to understanding how the Strong Force behaves. The whole Quark colours thing, relating to how the strong force is exchanged is a bit mind boggling. Though I guess colours are a frequency. My head hurts when trying to think that small 
The media are saying the opposite as are the libtards, just like with temp, the measurements don't fit the hysteria. 
. He I am sure also finally admitted to himself at elast that a singularity is not a physical thing but just a mathematical dead end brought about by diving by 0. Lets not forget the handy evoking of "infinity" and "near infinity" in mathematics, unquantifiable gibbering in lieu of a proper solution 
I often see it as a kid who started a science experiment which he forgot about until his mum tells him to clear under his bed at which point he finds the bag, looks inside to see a mess which has grown out of control and goes "Urrrghh!" before crushing it under his feet and throwing it in the bin!
