[PluggyRug]

Another mystery solved.

http://www.cbc.ca/news/technology/penta ... -1.3150950

[DrCaleb]

$1:

CERN experiment spots two different five-quark particles
First evidence of "pentaquark-charmonium states." Yes, seriously.

In particle physics' youth, researchers started discovering a dizzying variety of ever heavier, unstable particles. Quarks brought some order to this chaos. The zoo of particles, along with the familiar proton and neutron, were built from combinations of the six quarks or their antiparticles. The system neatly explained the spin and charge of these particles and helped make sense of particles discovered as accelerators reached even higher energies.

All of the particles we knew of were built using either two or three quarks. But there was nothing in our theories that prevented larger assemblages having even more quarks. Discovery, however, lagged well behind the initial proposal, which came in the 1970s. A buzz of excitement about a five-quark particle came and subsided after other accelerator teams couldn't reproduce the result.

There seem to be four quarks involved, but nobody's sure how they're linked.

Just two years ago, however, two different teams announced evidence for a tetraquark particle, which picked up the name Zc(3900). And now, an experiment at the Large Hadron Collider (LHC) has come up with evidence of a five-quark behemoth.

The experiment is called LHCb, and it focuses on a limited number of the total collisions produced by the LHC: those that generate a bottom (or beauty) quark—hence the "b" in its name. The physics of these particles can potentially tell us about the limitations of the Standard Model or the asymmetry between matter and antimatter in the Universe. So LHCb is specialized to examine the behavior of particles containing bottom quarks.

Quarks never travel alone for long, so they're usually produced as part of a larger particle, containing one or two additional quarks. In this particular experiment, the LHCb team was looking at Λ0b baryons, which contain an up quark, a down quark, and a bottom quark. These decay by a pathway that goes through a pair of unstable particles (J/ψ and K−). The authors were measuring this decay in part because it can tell us something about the half-life of the parent Λ0b particle.

The problem was that these decays showed an unusual pattern. Rather than showing a smooth curve as energy increased, there was a jagged peak in it. This suggested that decay through certain intermediate particles was favored. There was just one problem: no particles could explain why the peaks were at the locations they were seen.

The authors got a computer to model what would happen if the decay went through an intermediate particle they called Pc+. This particle contains two up and one down quarks, along with a charm and anticharm—pentaquark-charmonium, which can exist in a number of possible energy states. Remarkably, it fit when there were two different five-quark particles: one with a mass of 4449 Mega-electronVolts (nearly five times the mass of a proton) and another at 4380MeV. The significance of the match was over nine sigma; only five sigma are required for physicists to announce discovery.

http://arstechnica.com/science/2015/07/ ... particles/

[PluggyRug]

raydan raydan:

I didn't know it was lost.

To some.

[DrCaleb]

raydan raydan:

I didn't know it was lost.

I know you and most people look at this and stare at it blankly, but it's actually big news!

$1:

"It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over 50 years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we're all made, is constituted."

The new discovery validates a long-held notion about the nature of matter. In 1964, physicist Murray Gell-Mann proposed that a group of particles known as baryons, which include protons and neutrons, are actually made up of three even tinier charged subatomic particles known as quarks. Meanwhile, the theory went, another group of particles called mesons were composed of quarks and their antimatter partners, antiquarks.

The theory was soon validated by experimental results, and Gell-Mann's work won the Nobel Prize in physics in 1969. But crunching the numbers in Gell-Mann's theory also led to the conclusion that other, more exotic particles could exist, such as the pentaquark: a group of four quarks and an antiquark. Over the past several decades, people have seen hints of pentaquarks in experimental data, but those all turned out to be false leads.

$1:

The new results not only validate the Standard Model, the dominant physics theory that explains the mess of subatomic particles that make up the world, but they also raise new questions.

For instance, it's still not clear exactly how the pentaquarks are "glued" together. Some theories suggest that constituents of the pentaquark are tightly bound together, while others propose a loose association between the teeny subatomic particles. Understanding how the strong force binding pentaquarks work could be important in other arenas, too.

"This may be important in star formation, for example," Stone said.

http://www.csmonitor.com/Science/2015/0 ... deal-video

It broadens our understanding of the Universe just a bit more.

[andyt]

It's no doubt interesting, but I always go to: so what are quarks made of? When you talk of building blocks, you think if the smallest bits of matter from which everything is made up. But that doesn't seem to be the reality. Every time they find a basic building block they find something more fundamental.

[PublicAnimalNo9]

It was behind my sofa the whole time.