

New Particle Hints at Four-Quark Matter - Mithrandir
http://physics.aps.org/articles/v6/69

======
ISL
I'd leapt at the title, thinking that the article claimed evidence for a
fourth-generation (u,d), (c,s), (t,b), (something new) quark, which would be
incredible news. This article describes the potential observation of a four-
quark bound system, made up of known quarks in a novel arrangement.

~~~
jessriedel
Although a 4th generation would certainly be a bigger deal, tetraquarks have
never been seen and would have important implications for our understanding of
QCD.

[http://en.wikipedia.org/wiki/Tetraquark](http://en.wikipedia.org/wiki/Tetraquark)

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ideonexus
A quick tutorial on how all this fits together in a single atom:

[http://ideonexus.com/2008/10/07/elementary-particles-at-
the-...](http://ideonexus.com/2008/10/07/elementary-particles-at-the-quantum-
zoo/)

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ChuckMcM
Fun times in high energy physics. Can someone point to a reference describing
particles with both regular and anti- flavors of quark? There is a mention
here of particles with both charm and charm- quarks in the same particle.

~~~
ISL
It's perhaps not the easiest read, but a quark/anti-quark particle is called a
meson.

[http://en.wikipedia.org/wiki/Meson](http://en.wikipedia.org/wiki/Meson)

~~~
ChuckMcM
That was fine, flavourless mesons. Clearly I'm behind in my reading.

~~~
ISL
[http://xkcd.com/1053/](http://xkcd.com/1053/) !

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pjdorrell
Misleading headline alert: the hinted particle is two quarks and two anti-
quarks, which is not quite the same thing as "four quarks" (which would be
_very_ surprising because four is not a multiple of three).

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jes5199
can this be explained in terms of quark-color theory or is that unrelated to
this phenomenon?

~~~
gus_massa
(If it exists, and they have the correct model ...) This particle is composed
by 2 quarks and 2 antiquarks. One possible combination of the colors is
painting the 2 quarks red and the 2 antiquarks antired, so the total color is
"0". Another possibility is 1 red and 1 blue quarks and 1 antired and 1
antiblue aniquarks. There are many combinations but it's possible to combine
them in a way that the total color is "0". (Inside the particles, they
interchange the color "constantly", so the exact colors don't mater.) (There
are some technical details, that involve the symmetry properties, but this is
the main idea.)

The problem is that this system can split in two subsystems with total color
"0" (for example, a pion and a J/psi mesons, or two D mesons. Each one of them
is composed by a quark and an antiquark with opposite colors. The exact
decomposition depends on the details of the theory. The discussion is if this
is a real particle or are only two D mesons traveling together.

An easy conclusion from the color theory is that we will never [1] see
particles with for quarks, because it's impossible to sum 4 colors and get
"0". This proposed particle has 2 quarks and 2 antiquarks, so it's possible
but no particle of this kind has been confirmed.

[1] (unless we use an incredible^10 amount of energy, and perhaps neither in
that case)

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sukuriant
Reading some of these articles makes me feel like that line from Thor where
you get to a point where magic and science sort of blend together as we use
and build enormous alchemist machines with reproducible effects.

I greatly look forward to the day where we can apply what we've been learning
through all this experimentation to design and create things that actively and
usefully manipulate particles at this level.

~~~
PhantomGremlin
Very interesting observation. I hadn't thought of quantum physics as magic
before. But it's so weird that "magic" might indeed be the best word to
describe it.

~~~
ISL
Physics _is_ magic, just measured, tested, and quantified.

No need to go as far as the quantum to see it. Play with two bar magnets for
twenty minutes on a quiet day [1], try to twist a spinning bicycle wheel [2],
or, if you're pressed for time, just hold a thing at least six inches away
from everything else and let go [3].

No strings, no wires, no-one behind a curtain nor sleight of hand, but it's
still magic, and it happens [4].

[1] Relativistic consequences of quantum-mechanical charge carriers screaming
around nuclei generates a field that virtually interacts with other fast
moving charge carriers to generate a dipolar force? Occam's razor might land
on the side of magic.

[2] The first time I did this, with a lead-lined wheel, it threw me across the
room, as I was sure everyone else in the class had been faking.

[3] We have no idea how it is that things fall. We have a really good theory
for it, that agrees with every experimental test ever done, but it gives
little insight into the way in which momentum is exchanged between massive
bodies.

[4] Campy, yes, but when you're studying Physics, you're studying the
Force(s).

