Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Physicists in Japan and US find new form of matter

14.07.2003


Analysis of data from Jefferson Lab’s CEBAF Large Acceptance Spectrometer supports the pentaquark discovery recently announced by the SPring-8 physics lab in Japan.


Physics Lab in Japan reports evidence for the Pentaquark; Jefferson Lab data supports discovery

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 till 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. 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 (http://www.aip.org/mgr/png/2003/193.htm).

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, upcoming article, probably 11 July 2003; text at www.aip.org/physnews/select; contact Takashi Nakano, nakano@rcnp.osaka-u.ac.jp)



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 Dept. of Energy’s 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 (http://www.jlab.org/Hall-B/ ). The TJNAF result was announced at the Conference on the Intersections of Nuclear and Particle Physics (http://www.cipanp2003.bnl.gov ) 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 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.

Linda Ware | EurekAlert!
Further information:
http://www.aip.org/mgr/png/2003/193.htm
http://www.jlab.org/

More articles from Physics and Astronomy:

nachricht Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst

nachricht Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>