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General Physics:
Particles - Types of Particles

Sub-divide Electrons?
Latest on Neutrinos
Charge of Neutrinos
Storing Antimatter
When Matter and Antimatter Collide
Spooky Particles

  1. Sub-divide Electrons?

    Can electrons be divided into sub-particles or are they pure energy?

    There is no evidence that electrons can be sub-divided. They appear to be pure, primary particles. Although matter and energy are in some ways different forms of the same thing, electrons have a rest mass and so are considered matter and not pure energy.

    Dr. Eric Christian
    (May 2000)

  2. Quarks

    What is a quark? Subsequent to early work on the theory of relativity, what mathematical concept or scientific finding has been the most significant?

    A quark is a subatomic particle that is the building block for the entire family of hadrons (protons, neutrons, pions, etc.). There are six types of quarks: up, down, charm, strange, top, and bottom (the last two are sometimes called truth and beauty), and their six antimatter counterparts.

    You never see "free" quarks, they always appear in doublets or triplets. This seems to be because the force between quarks actually increases with distance (unlike gravity, electromagnetism, etc.). So if you try and pull apart two quarks, you have to put in energy, and eventually you put in enough energy that it converts into two more quarks, and you end up with two particles of two quarks each, instead of two free quarks.

    The theory of quarks (Quantum Chromodynamics) is certainly a candidate for the answer to your second question, but that is just personal opinion.

    Dr. Eric Christian

  3. Leptons

    If two "up" quarks and one "down" quark make a proton, and two "down" quarks and one "up" quark make a neutron, then how many leptons, and in what combination, make an electron, and what makes a positron?

    Electrons and positrons are *not* made up of quarks. They are in a separate "family" of particles known as LEPTONS. Leptons and quarks are "fundamental" (indivisible) particles. Leptons do not experience the "strong" or "hadronic" force that protons and neutrons do. There are also six known leptons (electrons, electron-neutrinos, muons, muon-neutrinos, tau, and tau-neutrinos) and their six antimatter counterparts (positrons are antimatter electrons). Add the Gauge bosons (photons, W+ boson, W- boson, Z boson, and gluons), and you've got everything that has been proven to exist. There are plenty of theories for other more exotic particles (photinos, gluinos, etc.), but with the ones listed here you can get all normal matter.

    Drs. Louis Barbier and Eric Christian

  4. Muons

    How do muons travel to Earth? Why do most arrive vertically and not horizontally?

    Most muons that are measured originate in the Earth's atmosphere when energetic cosmic ray particles (primaries) from space collide with atoms in the atmosphere to produce secondary particles, including muons. The primaries are thought to originate from stellar explosions or some other violent astronomical event, and there are many more low-energy particles than high-energy particles produced in these events. The direction of the primary is fairly well preserved by the muon, which means vertical muons are typically produced from vertical incident primaries.

    A muon is produced after the primary passes through a critical amount of atmospheric mass. For vertical primaries this occurs about 20 km above the surface. However, the altitude at which muons are produced is higher for primaries coming in from an angle, because their path carries them past a greater number of atmospheric atoms.

    Since the muon is electrically charged, it continuously loses energy or decelerates from collisions with atomic electrons in atmospheric molecules. This effect is much like braking a fast moving car; i.e., the faster the car the longer it takes to bring it to a complete stop. As the muon penetrates deeper within the atmosphere, the atmospheric density increases and more collisions per unit of distance occur. Moreover, muons don't live very long before turning into other types of particles (electrons and neutrinos).

    So a muon is created fairly high in the atmosphere and will reach Earth's surface if it gets there without colliding with too many air molecules. A muon coming from the side takes a longer time to reach you from the production point above the Earth and moves past many more air molecules, which requires a higher-energy primary to reach the surface than does a vertical primary. Recall that high-energy primaries are rarer than low energy primaries, so there is another reason why there are fewer muons reaching the Earth from the side.

    It's all about lifetime and energy loss. The muons that come from the side are required to have higher energy, and therefore rarer parent primaries, than those that come from directly above; while those that come from directly above have the shortest path through the least atmosphere and the best chance of being observed. Other than that, they can originate from any direction.

    Drs. Charles Smith and John Clem
    (April 2003)

  5. Latest on Neutrinos

    How can the recent announcement from Takayama, Japan that neutrinos have mass be squared with:
    1. what I had always read previously, that neutrinos move at the speed of light, and
    2. findings from studies of supernovae remnants that indicate the expansion rate of the universe is increasing?

    1. If neutrinos have mass then they don't move at the speed of light, but no one has actually measured the speed of neutrinos. It appeared that they were moving at close to the speed of light, but it's never been taken as fact that they were moving at c.
    2. If the expansion rate of the universe is increasing, then there is a "Cosmological Constant" that essentially generates a repulsive force for mass in the universe. A significant neutrino mass would increase the cosmological constant needed, but has no other effect on the observations.
    It's important to note that the measurements currently don't even give a range of masses for neutrinos. All they've measured is a combination of the difference in mass between two flavors of neutrinos and a mixing angle (that tells you how intertwined the neutrino flavors are).

    Dr. Eric Christian

  6. Charge of Neutrinos

    Are electron neutrinos electrically charged? If so, are they negatively charged like the electron?

    All neutrinos (electon neutrinos, muon neutrinos, and tau neutrinos) are electrically neutral. If they were charged, they would be much easier to detect.

    Dr. Eric Christian
    (June 2002)

  7. Antimatter

    What is antimatter?

    The definition of antimatter is in the glossary of Cosmicopia.

    Beth Barbier

  8. Storing Antimatter

    How can anti-matter be stored without disintegrating? I know that when matter and anti-matter make contact with each other, they almost cancel each other out.

    Electric and magnetic fields can be used to focus, confine, and store antimatter. If they are cold, antiprotons can be stored in a Penning trap for several days.

    Incidentally, when matter and anti-matter collide, they do not disintegrate. They annihilate each other, which means that the two original particles disappear and their energy is converted into other forms.

    Dr. Louis Barbier and Beth Barbier
    (August 2000)

  9. When Matter and Antimatter Collide

    When matter and antimatter collide, the result, according to my high school chemistry textbook, is massless particles and a huge energy discharge. Doesn't the 'massless particle', accompanied by a fantastically high energy, violate the law of conservation of mass and energy?

    Mass and energy are different forms of the same thing (or, in a better way of thinking about it, rest mass is one form of energy). The sum of all energy (including mass) is conserved. When matter and antimatter collide, they turn their rest mass energy into photons (massless particles of light). Energy is still conserved.

    During the annihilation of matter and antimatter, how is the energy release calculated? Based on information provided by a physics major friend of mine, this energy release cannot be calculated using E=mc2. Is this statement true? Or can the accompanying energy release truly be calculated by Einstein's equation?

    The energy released is E=mc2 plus any kinetic energy the two particles started with. The "m" is the combined mass of the two particles. The energy is typically released as two or more photons (you need at least two to conserve the momentum vector).

    Dr. Eric Christian
    (August 2000)

  10. Spooky Particles

    What are "spooky particles"?

    The term "spooky particles" refers to quantum entangled photons.

    Photons are the massless "particles" that make up light (and gamma-rays and x-rays) - they always travel at the speed of light. In more technical terms, photons carry the electromagnetic force.

    Quantum mechanics is the theory of how particles behave at the atomic and subatomic level. Quantum mechanics says that particles have properties that are quantized (have fixed values) - such as spin and charge. The values of these properties are referred to collectively as the "state" of the particle. It also says that any given particle at any time can be described as a combination of states with different properties. (In quantum mechanics this combination is called a superposition.) For example, imagine a weather vane that can only point in the 4 cardinal directions (north, south, east, west) - but can't point anywhere in between. (Of course it's not of much use!) Anyway, in quantum mechanical terms you could describe the "state" of the weather vane (its position at any time) as a combination of the four states: north, south, east, and west, each with some associated probability. When you aren't looking at the weather vane, it's in all four states simultaneously. It's only when you look at it that you force it into one of the four positions. That's what this means in quantum terms.

    Now entangled particles are ones (say pairs of particles for simplicity) such that, measuring one property of one of them affects the second particle. For example, with entangled photons, measuring the spin of one of them will affect the measured spin of the other. (Aside: the photon is a "spin-1" particle. It has a spin of either +1 or -1. That is, its spin is either parallel (+1) or anti-parallel (-1) to its direction of motion.) Another example is when the pi-0 - pronounced "pi-zero" - (a neutral charge, elementary particle) decays into an electron and a positron (its antiparticle). The electron and positron are entangled.

    Quantum entangled photons - or spooky particles - are being used in the design of quantum computers. The information contained in the entangled particles is called a "qubit", analogous to the bits used in ordinary digital computers. They are also being used in making better, more precise atomic clocks.

    Two web sites you can check out are:

    Spooky Atomic Clocks
    Spooky bits propel quantum computer

    A Google search for "spooky particles" will turn up many sites. Happy reading!

    Dr. Louis Barbier
    (February 2004)

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