LHC heads into new year with first particle discovery
January 3, 2012 | 9:18 am
The spectrum of the Chi-b states: the leftmost peak is the Chi-b(1P), the middle one the Chi-b(2P), and the rightmost the new Chi-b(3P). The photons are detected either by the electromagnetic calorimeter (unconverted) or by the ATLAS tracking detectors if they have interacted with material and converted to an e+e- pair. Courtesy: ATLAS collaboration.
The first new particle was seen at the Large Hadron Collider at CERN in Switzerland shortly before Christmas.
The ATLAS collaboration announced the discovery of the particle Chi-b (3P), which consists of a bottom quark and antiquark particle bound together by the strong force. This force holds all atomic nuclei together so understanding Chi-b (3P) could help physicists understand better how the tiniest components of matter hold together to form the basis of everything you see: planets, people, plants.
Theorists have long proposed the existence of the Chi-b (3P), but until now it was not observed at any experiments. The particle is slightly heavier than predicted, meaning the quark anti-quark pair are a little more loosely bound than expected.
“Normally, a new particle is discovered in one or at most two channels, and the first discovery is at the very edge of statistical significance. This time things are different: it’s seen in three different channels and the peak is unmistakable,” according to an email by Tom LeCompte, the physics coordinator for the ATLAS collaborator and a physicist at Argonne National Laboratory outside Chicago. “The outstanding LHC performance is responsible for this by delivering so many collisions in such a short time.”
The ATLAS collaboration consists of 3,000 physicists from 38 countries.
Chi-b (3P) particle belongs to the boson family of particles just as the sought-after Higgs boson does. While the Higgs boson is suspected of giving all particles mass, Chi-b (3P) could explain how the mass of various elementary particles join together to make more massive, complex structures.
The bound quark states that make up Chi-b (3P) are collectively called quarkonium, and are analogues of the hydrogen atom, with each new particle corresponding to a different energy level. As with the hydrogen atom, physicists can observe transitions between these states through emission of a photon, according to the ATLAS collaboration.
A publication has been submitted to Physical Review Letters.
Read the ATLAS white paper: “Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS”
Related coverage:
BBC News: LHC reports discovery of its first new particle
Wired: LHC discovers a new particle: the Chi-b (3P)
Popsci.com: LHC has discovered its first new particle
Science Daily: New Particle at LHC Discovered by ATLAS Experiment
Tona Kunz
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4 Comments »
January 3rd, 2012 at 10:59 am
“This force holds all atomic nuclei together so understanding Chi-b (3P) could help physicists understand better how the tiniest components of matter hold together to form the basis of everything you see: planets, people, plants.”
Planets, people, and plants contain absolutely no bottom quarks, and especially no excited states of bottomonium that only exist above 10 GeV.
Why not claim it might cure cancer? Solve the energy crisis? Help us clone dinosaurs? Those claims are equally likely … people need to stop claiming these sorts of discoveries are more than what they are. Chi-b(3P) might give a little bit of insight into fine details of the interactions of bottom quarks. But probably not much else.
Oh, and while I’m commenting, it’s not a new particle. Report the facts, cut the hype.
January 5th, 2012 at 10:17 am
Thanks for the comment. You’re right: People and planets don’t contain bottom quarks. It’s also true that the strong nuclear force doesn’t care about “flavor” — that is, the “bottomness” of the quarks.
Physicist Tom LeCompte tells me: “This is an opportunity to study this interaction in a different – and substantially simpler – system. In protons and neutrons, things are frightfully complicated, and it’s quite difficult to understand what’s going on. In bottomonium, things look much simpler.
“The state of understanding of this force today is not yet good enough to completely explain why, to take one example, the proton and neutron attract each other as strongly as they do, and not a little more or a little less. Now, you might not think this matters, but the nature of world around us depends very strongly on that number. Make it a little smaller, and the stars go out. Make it a little bigger, and the stars don’t last very long. Neither situation is good if you want to live on a planet like the earth. This also affects chemistry – make it a little smaller, and you have only light elements. Bigger, and you have only heavy ones.
“Seeing where the energy levels lie tells us the strength of the strong nuclear force at various distances. (Just like looking at the orbits of moons and planets tells us about the strength of the gravitational force at various distances.) The people who study the strong nuclear force – which binds the bottom quarks and antiquarks together in this particle – are excited because they now have one more point to compare with their models. It’s also a point right at the edge of stability – the quark and antiquark are almost whirling apart from each other. So it’s not just one more measurement – it’s one more measurement in an interesting place.”
January 8th, 2012 at 11:57 pm
Can you please explain why a more massive particle is more loosely bound?
January 11th, 2012 at 8:57 am
Sure. I went back to Tom LeCompte on this, and he said:
“You can think of the mass of a particle as the mass of its constituents *minus* the binding energy, where the binding energy is the energy you have to add to the system to take it apart. (If I glue two pieces of wood together, it takes more energy to separate them again than if I just tape them together).”
So the greater the binding energy, the lighter the particle is. Therefore, the more loosely bound the particle is, the heavier it is.
LeCompte added, “What’s kind of interesting about the Chi(3P), is that it is almost unbound – the quarks are just on the verge of flying apart and forming two other particles – a B meson and its antiparticle. The Chi(3P) weighs 10539 MeV and 10558 MeV is the point where it flies apart.
“Indeed, the peak we see is most likely two particles very close together (too close to resolve), and the heavier member of the pair is probably closer to 10550.
“So we’re exploring the behavior of particles at the very edge of stability. The shape of the particle is probably like a Cheerio placed in the center of a bagel, and if it were just a little rounder, it probably wouldn’t even exist at all.”