The Physics
Hypertextbook
Opus in profectus

Quantum Chromodynamics

search icon

Problems

practice

  1. The mass of the top quark is 173.21 GeV/c2 — heavier than some atoms. Identify the heaviest element that is lighter than the top quark.
  2. What fraction of the mass of you and me, the air, earth, oceans, and everything else we deal with in our ordinary lives is due to the strong force?
  3. The sigma baryons are a family of particles with two first generation quarks (u, d) and one higher generation quark (s, c, b). Top quarks probably cannot form sigma baryons since they decay before they can interact with other quarks. Sigma baryons can have a charge of −1 e, 0 e, +1 e, or +2 e.
    1. What combination(s) of quarks will produce a sigma baryon with a charge of −1 e?
    2. What combination(s) of quarks will produce a sigma baryon with a charge of +0 e?
    3. What combination(s) of quarks will produce a sigma baryon with a charge of +1 e?
    4. What combination(s) of quarks will produce a sigma baryon with a charge of +2 e?
  4. Write something.

conceptual

  1. Pions (π) are particles in the meson family that were proposed in 1935 as carriers of the strong force within the nucleus. Pions are made of up and down quarks and are charged or neutral. Charged pions were first detected in 1947 followed by the neutral pion in 1950.
    1. What combination(s) of quarks will produce a positive pion (π+)?
    2. What combination(s) of quarks will produce a negative pion (π)?
    3. What combination(s) of quarks will produce a neutral pion (π0)?
  2. Kaons (K) are a group of mesons that were important in the development of the quark model. The particles normally found in the nucleus (protons, neutrons, and virtual pions) behaved in a way that was considered ordinary in the early days of particle physics. The quarks that made up these particles were given ordinary sounding names — up and down. Kaons behaved in a way that was considered strange, so a strange quark was proposed to explain this behavior. It was eventually determined that kaons are mesons with one strange quark and one up or down quark. Kaons can be positive, negative, or neutral.
    1. What combination(s) of quarks will produce a positive kaon (K+)?
    2. What combination(s) of quarks will produce a negative kaon (K)?
    3. What combination(s) of quarks will produce a neutral kaon (K0)?
  3. D mesons are the lightest particles that contain charm quarks. They are mesons where a single charm quark is paired with an anitup, antidown, or antistrange antiquark. When D mesons decay, the charm quark always transforms into another flavor of quark. Flavor changes are mediated by W or Z bosons — the cariers of the weak force — and D mesons have been important to understanding this fundamental interaction. WHAT'S THE QUESTION?
  4. B mesons are composite particles made from an antibottom antiquark paired with an up, down, strange, or charm quark. (A bottom-antibottom meson is called bottomonium. A top-antibottom meson probably can't exist.) Neutral B mesons have been observed to spontaneously transform into their own antiparticles and back in a process known as flavor oscillation. The study of B-B̅ (B-Bbar) changes may help us understand why matter is more common than antimatter in our universe.
    1. Which quark combinations result in neutral B mesons?
    2. Which quark combinations result in neutral anti-B mesons?

combinatorics

  1. A quark-antiquark pair is called a meson. For example, a positive pion is an up-antidown quark pair (π+ = ud̅).
    1. How many mesons can be made from the first generation quarks only?
    2. How many mesons can be made from all six flavors of quark?
    3. What charges are possible?
  2. A triplet of quarks is called a baryon. For example, a proton is two up quarks and one down quark (p+ = uud) while a neutron is one up quark and two down quarks (n0 = udd). Permutations of quarks are considered identical (for example, uds = usd = sud =…).
    1. How many baryons can be made from the first generation quarks only?
    2. How many baryons can be made from all six flavors of quark?
    3. What charges are possible?
  3. According to some theoreticians, groups of six quarks may be moderately stable.
    1. How many six-quark particles can be made from the first generation quarks only?
    2. How many six-quark particles can be made from all six flavors of quark?
    3. What charges are possible?
    4. Invent an appropriate name for this class of particles.

investigative

  1. top-quark.pdf
    The purpose of this activity is to determine the mass of the top quark from proton-antiproton collision data gathered at Fermilab in 1995.