This looks to be an unstable assemblage
that quickly falls apart. I suspect that
there will be larger assemblages produced in time with any luck. I would not be too excited about it per se.
This is all good.
Mysterious Subatomic
Particle May Represent Exotic New Form of Matter
BY ADAM MANN
06.17.13
In the course of exploring the
properties of a strange subatomic particle, physicists may have stumbled upon
something even stranger: a mysterious and exotic new form of matter.
The intriguing discovery was
made more or less simultaneously by two collaborations: the Belle
experiment at the Japanese High Energy Accelerator Research Organization
(KEK) and BESIII experiment run by the Institute of High Energy
Physics (IHEP) in China.
Both teams were looking at a
particle called Y(4260) that had been discovered in 2005 but whose
nature has mystified researchers since. By smashing together electrons and
their antiparticle, positrons, the experiments produced large numbers of
Y(4260), which lives for only 10-23 seconds before falling apart into
other particles. The teams noticed that their data had a peculiar
bump around 3.9 gigaelectronvolts (GeV), an energy corresponding to
roughly four times the weight of a proton.
“Inspired by this discovery,
we decided to further study the Y(4260) decay, which indeed did not disappoint
us,” said particle physicist Zhiqing Liu, lead author of a paper from the
Belle experiment that appeared in Physical Review Letters on June 17.
A second paper from BESIII, of which Liu is also a member, appears in the same
issue.
The data bump from Belle and
BESIII. Physical Review Letters
The teams have enough data to
conclude they have discovered something new, a putative particle named Z(3900).
But the scientists are still not entirely sure what to make of it. One
possibility is that Z(3900) represents a subatomic structure made of four
quarks, something that has never been solidly seen before.
Before we continue, let’s
break things down for those who get cross-eyed whenever subatomic lingo starts
getting thrown around. Much of the matter we see in our universe is made of
itsy-bitsy units known as quarks. There are six known quark types — named up,
down, strange, charm, bottom, and top quarks – and they can combine in various
ways.
The matter most people are
familiar with, namely protons and neutrons, is made when three quarks come
together. Another class of particles can occur when two quarks are bound
(technically, these are made from a quark and an antiquark). The most famous of
these two-quark particles are kaons and pions. Though there have been hints of
them in the past, no one has ever definitely discovered a particle with more
than three quarks.
A special force called the
strong force is responsible for gluing all these quarks together. The particle
carrying this force is called the gluon and it is akin to the photon, which
carries the electromagnetic force, except that it can only be found inside of
atomic nuclei.
The Y(4260) particle is
thought to be a certain exotic type of particle with two quarks and an extra
gluon, though its exact characteristics are still unknown.
“In trying to explore the
properties of this gluonic exotic, they found another exotic,” said particle
physicist Eric Swanson of the University of Pittsburgh, who was not
involved with the work.
The experiments have now
produced more than 460 of these strange Z(3900) particles, suggesting that they
are real phenomena and not simply a statistical fluke in the data. The new
exotic particle appears to have an electric charge and contains at least a
charm quark and an anti-charm quark. The simplest explanation for the rest of
the particle’s properties is that it also contains an up and anti-down quark
for a total of four quarks.
“We haven’t seen anything like
that before and for that reason it’s exciting,” said Swanson. While previous
experiments have detected hints of such particles, Belle and BESIII’s data is
the cleanest and most experimentally solid to date, he added.
But there could still be other
possible interpretations. Scientists already know that two-quark particles
exist. So what looks like four quarks bound together could actually turn out to
be two two-quark particles interacting so strongly that they look like a
four-quark particle. Such a finding would be known as a “hadron molecule” –
another strange object speculated to exist in the subatomic world but never
definitively seen. This is the explanation that Liu is leaning towards.
“The hadron molecule is just
my personal preference,” he said. “But the real nature could also be something
else.”
Swanson points out that there
is another, more prosaic interpretation: that Z(3900) is composed of two
two-quark particles interacting but not really strongly enough to stick
together. This explanation would fit the data but isn’t nearly as exciting.
The next step for both collaborations
is to produce many new Z(3900) particles and watch how they decay, which should
give some clues as to their properties. If the data shows they decay like
ordinary, known particles, it could rule out the exotic interpretations. But if
not, the scientists may have found something extremely interesting.
“We hope to reveal the nature
of this particle in the following year,” said Liu.
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