Evidence of the most massive antinucleus
Antiparticle: In particle physics, every particle has a corresponding antiparticle. A particle and its antiparticle have identical mass and spin but have opposite values for all other non-zero quantum number labels. These labels are electric charge, color charge, flavor, electron number, muon number, tau number, and baryon number.
Every fermion (lepton and quarks) carries some charge – like quantum number labels, and each has a distinct antiparticle partner with opposite values for those labels. For example, the antiparticle of an electron is a positron — it has exactly the same mass as an electron but positive electric charge. (The positron is the only antiparticle with its own name. In all other cases, the name of the antiparticle is anti- in front of the name of the particle, such as proton and anti-proton.)
Charged bosons always have an antiparticle partner of opposite charge and equal mass. For charge zero mesons with different types of quark and antiquark, there is an antiparticle partner of that reverses the role of quark and antiquark.
For charge zero mesons with the same type of quark and antiquark, and for the charge zero force carriers (photon and Z), the particle and the antiparticle are identical. The antiparticle of a photon is a photon, likewise the antiparticle of a phi meson (s quark and anti-s quark) is a phi meson.
Gluons are force carriers with zero electric charge, but each type of gluon has a color charge. Thus each gluon has a corresponding antiparticle with a related color charge.
Matter and Antimatter: Any particle built from quarks, (charges +2/3 and -1/3), negatively charged leptons and left handed neutrinos is called matter. Any particle built from antiquarks (charges of -2/3 or +1/3), positively charged leptons and right-handed neutrinos is called antimatter.
Source: http://www2.slac.stanford.edu/vvc/theory/antiquarks.html
Strangeness is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic reactions, which occur in a short period of time. The strangeness of a particle depends on the the number of strange quarks and the number of strange antiquarks the particle has. Nuclei containing one or more strange quarks are called hypernuclei. For all ordinary matter, with no strange quarks, the strangeness value is zero.
Evidence of the most massive antinucleus
An international team of scientists studying high-energy collisions of gold ions at the Relativistic Heavy Ion Collider (RHIC) at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, has published evidence of the most massive antinucleus discovered to date. The new antinucleus, discovered at RHIC’s STAR detector, is a negatively charged state of antimatter containing an antiproton, an antineutron, and an anti-Lambda particle. It is also the first antinucleus containing an anti-strange quark.
The STAR team has found that the rate at which their heaviest antinucleus is produced is consistent with expectations based on a statistical collection of antiquarks from the soup of quarks and antiquarks generated in RHIC collisions. Extrapolating from this result, the experimenters believe they should be able to discover even heavier antinuclei in upcoming collider running periods. Theoretical physicist Stoecker and his team have predicted that strange nuclei around double the mass of the newly discovered state should be particularly stable.
Theoretical physicist Horst Stoecker, Vice President of the Helmholtz Association of German National Laboratories says, “This experimental discovery may have unprecedented consequences for our view of the world. This antimatter pushes open the door to new dimensions in the nuclear chart — an idea that just a few years ago, would have been viewed as impossible.”
Consequences of this discovery
This study of the new antihypernucleus (antinucleus containing an anti-strange quark) also yields a valuable sample of normal hypernuclei, and has implications for the understanding of the structure of collapsed stars. Jinhui Chen, one of the lead authors, a postdoctoral researcher at Kent State University and currently a staff scientist at the Shanghai Institute of Applied Physics, says, “The strangeness value could be non-zero in the core of collapsed stars. So the present measurements at RHIC will help us distinguish between models that describe these exotic states of matter.”
The findings also pave the way towards exploring violations of fundamental symmetries between matter and antimatter i.e. the predominance of matter over antimatter. According to Brookhaven physicist, Zhangbu Xu, another one of the lead authors, “A solution will require measurements of subtle deviations from perfect symmetry between matter and antimatter, and there are good prospects for future antimatter measurements at RHIC to address this key issue.”
Source: http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1075
March 5, 2010