Pentaquarks

jafuser writes "Physicists are quite confident that they have discovered a new baryonic state called a 'pentaquark' which is a particle composed of *five* quarks (4 quarks and one anti-quark to be precise). Up until now, quarks were only observed to come together in groups of two (mesons) or three (baryons). If you still haven't gotten comfortable with knowing your leptons from your hadrons, I suggest clicking through an excellent site at Particle Adventure."

Comments

Re:Easy mistake

[DustMagnet]

Most people find it hard to get excited that about states of matter that only exist for very short periods of time.

Five Quarks?

[Atario]

I suppose that's what happens when the last epsiode of Star Trek: The Next Generation collides with Star Trek: Deep Space Nine.

Re:Five Quarks?

[Suidae]

Does the Anti-Quark have a goatee? I'd like to see that.

Re:Easy mistake

[kurosawdust]

that's actually a valid component of matter - for example, in a wonderful bit of irony the dean of my college's physics department was composed mostly of hardons. The students bookbags generally contained ironons, too.

and if you read enough Frijtof Capra, youll find out about the zen-tastic yin and yang of the particle known as the "waxon", and its complement - the anti-waxon.

Ohh, I love it...

[joto]

They have an explanation for the general public, the general scientist, and the physicist. Obviously, they care about accurate science reporting.

Re:Ohh, I love it...

[Anonymous Coward]

No because it goes on to explain that it is actually 4 quarks and 1 anti quark hence the use of quote.

They're all just a bunch of reverse engineers!

[Bob Bitchen]

It's interesting to note that this form of reverse engineering is revered and those practicing are held in high esteem (usually) but that more meso-scale reverse engineering is considered lowly and usually is illegal. Ponder that....

Re:They're all just a bunch of reverse engineers!

[tenorX]

illegal? what do you mean by meso-scale?

Re:They're all just a bunch of reverse engineers!

[zangdesign]

Ponder it? I don't even know what the hell you just said! Spoke ... typed ... AAARRRGGGHHH!

My brain just exploded.

Re:They're all just a bunch of reverse engineers!

[KDan]

Well I guess God must have forgotten to file for patents on the nature of the universe...

Daniel

Color?

[Anonymous Coward]

I wonder what the color makeup of the pentaquark is. As I undestand it, for mesons it's red/anti-red, blue/anti-blue, or green/anti-green. For baryons it's red/blue/green or anti-red/anti-blue/anti-green. What do you do for five?

Re:Color?

[Christopher Thomas]

I wonder what the color makeup of the pentaquark is. As I undestand it, for mesons it's red/anti-red, blue/anti-blue, or green/anti-green. For baryons it's red/blue/green or anti-red/anti-blue/anti-green. What do you do for five?

RGB plus R!R or G!G or B!B.

Think of this as a merged baryon and meson.

Re:Color?

[Rares Marian]

Think of this as a merged baryon and meson.

No. They specifically said that the merged version would have different properties.

Re:Color?

[Christopher Thomas]

Think of this as a merged baryon and meson.

No. They specifically said that the merged version would have different properties.

"Merged" != "Bound".

A bound pair would not be a distinct particle (it would be two co-orbiting, which would have different particles). A pentaquark can be thought of has a merger of the two particles, containing the constituents of both but having its own energy structure.

List of the constituents is the same. Hence, my example.

Re:Color?

[Christopher Thomas]

(it would be two co-orbiting, which would have different particles) ...different properties. That's what I get for slashdotting at silly-o'clock in the morning.

Re:Color?

[Rares Marian]

I read it the way you meant it. That's what I get for reading at silly-o'clock in the morning.

Re:Color?

[Christopher Thomas]

So perhaps we can also get 7 and 9 quark particles.

In principle, we can get any number we please. The question is whether a particle with, say, 7 quarks would have lower energy than three separate particles (one baryon and two mesons). Depending on its internal energy structure, it would either be unstable, extremely unstable, or not bound as a particle at all (we know it's not stable because a) we don't see these around normally, and b) anything built from quarks and antiquarks decays [quickly if the Q and !Q have the same flavour, slowly if not]).

There has already been a search for tetraquark objects (same constituents but different energy structure than two mesons). I'm not sure how that turned out (mentioned, with paper citations, by another poster a few years back).

Re:Color?

[Mt._Honkey]

Here's a recent possibility for a tetraquark.

Re:Color?

[barawn]

With quarks it's difficult to say that there would be a difference between "merged" and "bound" - the strong force is very weird (it's confining, for one: it gets stronger the farther away the particle gets, and weaker the closer in the particles are) and so it's really quite difficult to distinctly say "yes, this is a distinct 5-quark 'merged' particle" or "no, this is a meson-baryon molecule where the quark-antiquark orbit the other three color-singlet quarks".

After all, no matter what, it's NOT a distinct particle! Any baryon (protons, neutrons, whatever) are 3 coorbiting quarks. All deep-inelastic scattering measurements have shown baryons to look like they're made up of three particles basically at rest (parton model), and this model does remarkably well. So no matter what, the pentaquark is NOT a "merged" particle. It's 5 quarks, hanging around each other.

This particle would be very much a mess. Most of the time it's referred to as a molecular meson-baryon state (look in the literature for this - specifically the SPring paper) and, to be honest, I'm not sure how you could tell the difference. The naive "quark-antiquark here, three quarks here" model is so terrible at these energies that it's really difficult to explain to people to just throw away their intuition for most things.

Truth is, it's probably best to think of this as the lowest energy level of a meson-baryon bound state.

(I have no idea what the grandparent poster was saying - "they specifically said the merged version...". That's crap - read the papers. No one's taking a stance between "5 quark bound state" and "meson-baryon bound state". All this showed is that there IS a bound state in an interaction between a neutron and a gamma ray which decays into some baryon and a kaon.)

'general public'

[Anonymous Coward]

here is the version of the press release they have for the general public:

Is it just me, or does the assumed sophistication of the target audience make anybody else really scared?

The pentaquark -- A description for the general public

If you're reading this web page, then you likely know that atoms are the basic building blocks of matter, and that atoms are made up of electrons swarming around a tiny nucleus. More than 99.9% of the mass of everyday objects is contained within the nucleus of the atoms. Now the nucleus is made up of protons and neutrons, which in turn are made up of quarks. Because of this, most of your body mass comes from subatomic particles that are made up of quarks. Now, knowledge of quarks won't help you lose weight, but it does help scientists to understand other aspects of nature, such as why the sun shines. In fact, the sun's warmth comes from a process called fusion, which turns some of the mass of the nucleus into energy.

When we examine subatomic particles, we find all strongly interaction particles (for example, protons and neutrons in the nucleus) are made up of quarks. There are hundreds of subatomic particles known, and all of the experimentally well-established particles fit into only two categories: so-called baryons (made up of 3 quarks) and so-called mesons (made up of "two" quarks--really a quark and an anti-quark). What is the nature of the force between quarks such that only two types of quark matter can exist? Certainly, there is a mathematical hypothesis (or "theory") for the strong force, called Quantum Chromodynamics (or "QCD"), but in addition to baryons and mesons, the theory allows other configurations of quarks, such as so-called pentaquarks (made up of "five" quarks--really 4 quarks and 1 anti-quark).

Until recently, no firm evidence of pentaquarks existed even though physicists have searched for these objects (also known as "exotic baryons") for over 30 years. In 2002, the first announcement was made for evidence of the pentaquark at an international scientific conference in Osaka, Japan. In 2003, a report of this work was submitted for publication in a peer-reviewed scientific journal by a group of physicists known as the LEPS collaboration from an experiment done at the SPring-8 facility in Japan. Other evidence for the pentaquark has recently been reported by other experiments, with perhaps the strongest evidence coming from the accelerator at Jefferson Lab (Newport News, Virginia) by the group known as the CLAS collaboration. With the advent of strong evidence for a pentaquark by several independent experiments world-wide, there is good reason to believe that the pentaquark does, indeed, exist.

Why should anyone care that the pentaquark exists? This question is difficult to answer at the present time, because the discovery is so recent. Many of the modern conveniences and medical treatments have come from scientific discoveries in the past that did not seem very useful at the time they were discovered. The answer to the initial question is: we don't know what discoveries of today will be important tomorrow. However, this answer is too general. Let's speculate about why the pentaquark is interesting.

First, the pentaquark just announced is the first, clear-cut evidence for a subatomic particle with "five" quarks. This means we have a new classification of particle: the pentaquark (more precisely, an "exotic" baryon). As a possible analogy, consider the classification of living things into two categories, plants and animals. If a new type of animal were found that did not fit into any of the usual classifications (mammals, birds, reptiles, etc.) then this would be an exciting discovery for biologists. Now this analogy is not completely appropriate, as for many analogies, but perhaps you get the idea why a new classification is important. The first type of pentaquark has now been seen! We now have lots of work to do to understand more of its properties, and what this implies for our knowledge of the for

Primes?

[Gamasta]

Well let's see... 2,3,5... maybe the next one will be 7 quarks. Just a crappy guess.

Re:Easy mistake

[Red Rocket]

You'll also find that, if you study the entire faculty and staff, you'll discover that they are actually made of individual particles called "persons".

Re: Easy mistake

[Anonymous Coward]

The restaurant down the street serves an interesting soup composed of wontons.

Pentaquark

[Muhammar]

I thought this was the term for a heat sink/overclock bummer

Re:Easy mistake

[Old Wolf]

That's what Viagra is for

Re:Easy mistake

[Thuktun]

and if you read enough Frijtof Capra, youll find out about the zen-tastic yin and yang of the particle known as the "waxon", and its complement - the anti-waxon.

...also colloquially known as a "waxoff".