Posted on 11/15/2003 8:43:52 PM PST by Diddley
The Belle collaboration at the KEK laboratory in Japan has discovered a new sub-atomic particle which it is calling the "X(3872)". The particle does not fit into any known particle scheme and theorists are speculating that it might be a hitherto unseen type of meson that contains four quarks (arxiv.org/abs/hep-ex/0309032; Phys. Rev. Lett. to be published).
The discovery has been confirmed by the CDF collaboration at Fermilab in the US, where the new particle is being called the "mystery meson". Mesons are particles that contain a quark and an antiquark that are held together by the strong nuclear force.
Since there are six different "flavours" of quark - up, down, strange, charm, bottom and top - it is possible to form a large number of different mesons.
The Belle team measured the decay of B-mesons - mesons that contain a bottom quark - produced in electron-positron collisions at the KEK B-factory in Japan. The team plotted the number of candidate events for B mesons against mass and observed a significant spike in the distribution at 0.775 GeV. This corresponds to a mass of nearly 3872 MeV. The particle decayed almost immediately into other, longer lived particles.
The KEK team says that the mass of this new meson is higher than theoretical predictions. Moreover, the way in which it decays also differs from theory. One possibility is that current models of the strong force need to be modified. Alternatively it could be that X(3872) is the first example of a "molecular state" meson that contains two quarks and two antiquarks.
Until recently particle physicists had only ever detected particles that contain two or three quarks. However, in the past year evidence has emerged for another four-quark particle known as the Ds(2317) and a five-quark particle known as the pentaquark.
Author Belle Dumé is Science Writer at PhysicsWeb
Ever get the feeling that we are inventing needlessly complex explanations for some (as yet unseen) simple phenomenon?
If so that might explain why it softly and suddenly vanished away from general_re's hotel room.
Yup
This is a compilation of information between Physicist and myself.
1. THE STANDARD MODEL:
The best description of how matter and energy interact (sans gravity) is called “The Standard Model” It describes the organization of all of the particles and how they interact. The elementary particles are divided into two families called quarks and leptons. Each family consists of six particles and three of each of the particles in each group are acted on by a force carrier.
Quarks: Six called, up charm, top, down, strange, and bottom. All six quarks are acted upon by gluons and photons. This is because all of them carry electromagnetic charge (u,c,t have a charge of +2/3 e, while d,s,b have a charge of -1/3 e), and all of them carry a color charge. There are three kinds of color charge, which are commonly written as red, green and blue. Every quark in the universe has one of these charges. Each flavor of quark can have any color charge.
Note: Because there is one kind of EM charge, there is one photon, but since there are three kinds of color charge, there are eight gluons. Gluons themselves carry both a color charge and an anti-color charge, so you'd think that there would be nine gluons, but the combination red-antired + blue-antiblue + green-antigreen is colorless, so if you define a red-antired gluon and a blue-antiblue gluon, a green-antigreen gluon can be described as a superposition of the other two. Only eight gluons are needed to span the color space.
Leptons: Six called: e neutrino, u neutrino, t neutrino, electron, muon, and tau. All quarks and leptons couple to both W and Z bosons. A W, for example, transforms an electron to an electron neutrino, or a t-quark to a b-quark.
Gravity is not included in the standard model, however it is believed that is exchange force is a graviton.
THE FOUR FUNDEMENTAL FORCES OF NATURE:
Strong force
Weak force
Electromagnetism (EM)
Gravity
All of the fundamental forces are considered Exchange Forces. In other words the force involves an exchange of one or more particles.
The exchange particles are as follows:
Strong – The pion (and others)
Note: The pion does mediate the inter-nucleon force. That force isn't fundamental, however. The fundamental force is the inter-quark force that binds the quarks into hadrons (such as protons, neutrons and pions), and that is what we usually mean by the strong force, nowadays. The force between hadrons is a residual color dipole interaction that is analogous to the Van der Waals force in electromagnetism.
Lets explore this a bit further:
First, lets take a look at Van der Waals Forces:
Atom and molecules are attracted to each other by two classes of bonds. The Intramolecular bond and the Intermolecular bond.
The Intermolecular bond is divided into these categories; Van der Waals Forces, Hydrogen Bonds, and molecule-ion attractions.
The Intramolecular bond (which are much stronger than the Intermolecular bond) is divided into these categories; Ionic bonding, covalent bonding, and metallic bonds.
We will only concentrate on the Van der Waals Forces.
Van der Waals Forces arise from the interaction of the electrons and nuclei of electrically neutral atoms and molecules. How is this possible if these are considered electrically neutral I hear you ask. What is going on here is that the electrons and nuclei of atoms and molecules (for this description: from here out called particles) are not at rest, but are in a constant motion. Since this is the case, there arises an electrical imbalance (called an instantaneous dipole [another term is a temporary polarity]) in this electrically neutral particle. Two “particles” in this dipole state will attract. Also this dipole action in one particle can cause a dipole in an adjoining (nearby) particle. So the dipole-dipole attraction is what is known as Van der Waals Forces. If these “particles” kinetic energies are low enough (anc close enough together), the repeated actions of the instantaneous dipoles will keep them attracted together.
One of the interesting things about this that the more electrons are in play the greater the Van der Waals Force. This is why the noble gas Krypton liquefies at a higher temperature than the noble gas Neon.
Back to the Standard Model.
A brief background: How does a nucleus stay together when it is packed with positively charged protons? Since “like” charges repel, you would think that the nucleus would fly apart. The force that keeps this from happening is the Strong Force. The binding energy that holds the nucleus together is directly related to the strength of the strong force. "Binding energy" is considered a negative energy.
So just what is this Strong Force anyway? The Strong force has an effect on quarks, anti quarks and gluons. After much research, it was discovered that the protons and neutrons in the nucleus were made up of smaller particles called quarks. It turned out that two types of quarks were needed to “produce” a proton or a neutron. However, there are six types of quarks in normal matter. The strong force binds these quarks together to form a family of particles called hadrons which include both protons and neutrons.
To simplify this discussion, quarks have a “color charge” (red, green, and blue). BTW, this was a convenient way of describing the charge, it is not referring to color as we commonly use it). Like colors repel and unlike colors attract. There are also antiquarks. If it is a quark/antiquark (same color) it is called a meson. If it’s between quarks it is called a baryon (protons and neutrons fall in this category). Here is the rub, baryonic particles can exist if their total color is neutral (colorless); i.e. have a red green and blue charge altogether. Both mesons and baryons are "colorless" with respect to the outside world. In baryons red + blue + green = colorless. In mesons, for example, red + anti-red (or, if you like, red - red) = colorless.
Without getting into too much more detail, quarks can interact, changing color, etc. so long as the total charge is conserved.
Super geek alert (this from Physicist)
Note: The quark interactions are cause by exchanging particles called gluons. There are eight kinds of gluons each having a specific “color” charge. The symmetry group of Quantum Chromodynamics is SU(3). In the minimal representation of SU(3), there are three generators...the color charges. In the non-minimal representation, there are 3²-1 generators...the eight gluons! This was spookily mirrored by Murray Gell-Mann's original (1964) quark theory, which also exploited the SU(3) symmetry. Only this time, the minimal representation was the three light quark flavors (up, down, strange), and the non-minimal representation was Gell-Mann's famous Eightfold Way, which correctly(!) predicted the properties of all the light hadrons, including some that had not yet been discovered.
So back to the original paragraph: Neutral (all three colors) hadrons (which include protons and neutrons) can interact with the strong force similarly to the way atoms an molecules react via the Van der Waals forces.
Electromagnetic (EM) – The photon
Weak – The W and Z
Gravity – The graviton
So to sum this up:
The Strong Force:
It is a force that holds the nucleus together against the repulsion of the Protons. It is not an inverse square force like EM and has a very short range. It is the strongest of the fundamental forces.
The Weak Force:
The weak force is the force that induces beta decay via interaction with neutrinos. A star uses the weak force to “burn” (nuclear fusion). Three processes we observe are proton-to proton fusion, helium fusion, and the carbon cycle. Here is an example of proton-to-proton fusion, which is the process our own sun uses: (two protons fuse -> via neutrino interaction one of the protons transmutes to a neutron to form deuterium -> combines with another proton to form a helium nuclei -> two helium nuclei fuse releasing alpha particles and two protons). The weak force is also necessary for the formation of the elements above iron. Due to the curve of binding energy (iron has the most tightly bound nucleus), nuclear forces within a star cannot form any element above iron in the periodic table. So it is believed that all higher elements were formed in the vast energies of supernovae. In this explosion large fluxes of energetic neutrons are produced which produce the heavier elements by nuclei bombardment. This process could not take place without neutrino involvement and the weak force.
Electromagnetism:
The electromagnetic force is the forces between charges (Coulomb’ Law) and the magnetic force which both are describe within the Lorentz Force Law. Electric and magnetic forces are manifestations of the exchange of photons. A photon is a quantum particle of light (electromagnetic radiation). This particle has a zero rest mass The relativistic mass of a photon is also zero. Gravity couples to energy density, which is typically dominated by mass. But even in Newtonian gravity, massless light particles will bend in a gravitational field (the trajectory of a test particle doesn't depend on mass). The speed of light in a vacuum is a constant and is unobtainable by baryonic matter due to the lorentz transformation. Electromagnetism obeys the “inverse square law”.
Gravity:
Gravity is the weakest of the forces and also obeys the inverse square law. The force is only attractive and is a force between any two masses. Gravity is what holds and forms the large scale structures of the universe such as galaxies
Explanations actually get simpler as time goes on. First, chemistry reduced all the infinite varieties of matter to 90 some kinds of atoms, then atoms were reduced to thre kinds of particles, plus a zoo of mysterious sub-atomic particles. the current model has six particles and four forces.
The math gets harder but the number of entities goes down.
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