Discovery of 5-Quark State Confirmed

In summary, a five-quark state has been discovered by physicists at the SPring-8 physics lab in Japan. This new state, called the "pentaquark" particle, is made up of three quarks from a neutron and two quarks from a K+ meson. The discovery was made by scattering a laser beam from a beam of 8-GeV electrons at the SPring-8 facility. The particle was also confirmed by a team of physicists in the US working in the CLAS collaboration at the Thomas Jefferson National Accelerator Facility. This discovery provides evidence for the existence of pentaquarks and suggests a new classification of matter. The pentaquark can be considered as a baryon with
  • #1
Brad_Ad23
502
1
A FIVE-QUARK STATE HAS BEEN DISCOVERED, first reported by a group of
physicists working at the SPring-8 physics lab in Japan. All
confirmed particles known previously have been either
combinations of three quarks (baryons, such as protons or neutrons)
or two quarks (mesons such as pions or kaons). Although not
forbidden by the standard model of particle physics, other
configurations of quarks had not been found until now. The
"pentaquark" particle, with a mass just above 1.5 GeV, was
discovered in the following way. At the SPring-8 facility a laser
beam is scattered from a beam of 8-GeV electrons circulating in a
synchrotron racetrack. These scattered photons constitute a beam of
powerful gamma rays which were scattered from a fixed target
consisting of carbon-12 atoms. The reaction being sought was one in
which a gamma and a neutron inside a carbon nucleus collided,
leaving a neutron, a K+ meson, and a K- meson in the final state.
Efficient detectors downstream of the collision area looked for the
evidence of the existence of various combinations of particles,
including a
short-lived state in which the K+ and the neutron had coalesced
(drawing will be posted soon at www.aip.org/mgr/png[/URL] ). In this
case the amalgamated particle, or resonance, would have consisted of
the three quarks from the neutron (two "down" quarks and one "up"
quark) and the two quarks from the K+ (an up quark and a strange
antiquark). The evidence for this collection of five quarks would
be an excess of events (a peak) on a plot of "missing" masses
deduced from K- particles seen in the experiment. The
Laser-Electron Photon Facility (LEPS) at the SPring-8 machine
(http://www.rcnp.osaka-u.ac.jp/Divisions/np1-b/index.html ) is
reporting exactly this sort of excess at a mass of 1540 MeV with an
uncertainty of 10 MeV. The statistical certainty that this peak is
not just a fluctuation in the natural number of background events,
and that the excess number of events is indicative of a real
particle, is quoted as being 4.6 standard deviations above the
background. This, according to most particle physicists, is highly
suggestive of discovery. (Nakano et al., Physical Review Letters, 4
July 2003; contact Takashi Nakano, [email]nakano@rcnp.osaka-u.ac.jp[/email],)
Confirmation of this discovery comes quickly. A team of physicists
in the US, led by Ken Hicks of Ohio University (hicks@ohio.edu,
740-593-1981) working in the CLAS collaboration at the Thomas
Jefferson National Accelerator Facility, has also found evidence for
the pentaquark. A photon beam (each photon being created by
smashing the Jefferson Lab electron beam into a target and then
measuring the energy of the scattered electron in order to determine
the energy of the outgoing gamma) was directed onto a nuclear
target. The photon collides with a deuteron target and the
neutron-kaon (nK+) final state is studied in the CLAS detector
([url]http://www.jlab.org/Hall-B/[/url] ). The Jefferson Lab result was
announced at the Conference on the Intersections of Nuclear and
Particle Physics ([PLAIN]http://www.cipanp2003.bnl.gov [Broken] ) held on May 19-24,
2003, at New York City. Stepan Stepanyan (stepanya@jlab.org,
757-269-7196) reported at this meeting that the mass measured for
the pentaquark, 1.543 GeV (with an uncertainty of 5 MeV), is very
close to the LEPS value. The statistical basis of the CLAS
measurement is an impressive 5.4 standard deviations. (This result
is about to be submitted to Physical Review Letters.) These
results, together with the previous results from SPring-8, now
provide firmer evidence for the existence of the pentaquark. The
HERMES experiment at the DESY lab in Germany is also pursuing the
pentaquark particle.
The discovery of a 5-quark state should be of compelling interest to
particle physicists, and this might be only the first of a family of
such states. Not only that but a new classification of matter, like
a new limb in the family tree of strongly interacting particles:
first there were baryons and mesons, now there are also
pentaquarks. According to Ken Hicks, a member of both the SPring-8
and Jefferson Lab experiments, this pentaquark can be considered as
a baryon. Unlike all other known baryons, though, the pentaquark
would have a strangeness value of S=+1, meaning that the baryon
contains an anti-strange quark. Past searches for this state have
all been inconclusive. Hicks attributes the new discovery to better
beams, more efficient detectors, and more potent computing analysis
power. (Additional website:
http://www.phy.ohiou.edu/~hicks/thplus.htm )

From the American Institute of Physics update. Very interesting.
 
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  • #2
Arn't baryons supposed to be made of 3 quarks?
 
  • #3
Yes, Brad it can't be a Baryon if it's got 5 quarks, cos Baryon's are made out of three quarks. The name it's been given is a pentaquark.
 
  • #4
According to Ken Hicks, a member of both the SPring-8
and Jefferson Lab experiments, this pentaquark can be considered as
a baryon.

I think I'll take the word of a person working on the experiment
 
  • #5
I'm a bit new to this subject; so forgive my ignorance if I'm asking a stupid question..

Would a pentaquark, along with baryons and mesons, be classified in the hadron family?
 

1. What is the significance of the discovery of the 5-quark state?

The discovery of the 5-quark state, also known as the pentaquark, confirms the existence of a new type of subatomic particle. This discovery provides a deeper understanding of the fundamental building blocks of matter and can potentially lead to new discoveries in particle physics.

2. How was the 5-quark state confirmed?

The 5-quark state was confirmed through experiments conducted at the Large Hadron Collider (LHC) in Geneva, Switzerland. Scientists observed the decay of a particle called the Lambda baryon into a proton and a J/psi particle, which is composed of a charm quark and an anti-charm quark. This decay pattern is consistent with the existence of a pentaquark state.

3. What is a quark and how does it relate to the 5-quark state?

A quark is a subatomic particle that is one of the fundamental building blocks of matter. Quarks combine to form particles such as protons and neutrons. The 5-quark state is a combination of five quarks, specifically four quarks and one anti-quark, that are bound together by the strong nuclear force.

4. How does the discovery of the 5-quark state impact our understanding of the Standard Model?

The Standard Model is a theory that explains the fundamental particles and forces of the universe. The discovery of the 5-quark state provides evidence for the existence of a new type of matter that was not previously predicted by the Standard Model. This could potentially lead to revisions or extensions of the Standard Model.

5. What are the potential applications of the 5-quark state?

While the full potential of the 5-quark state is still being studied, its discovery opens up possibilities for new technologies and advancements in our understanding of the universe. It could also potentially provide insights into the formation of matter in the early universe and the behavior of matter in extreme conditions, such as in black holes.

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