4 THE STANDARD MODEL
5. The Δ++ baryon is doubly charged. Use the table of quark properties (Table 9 in this chapter) to identify its correct quark composition.
9. In particle decays, which of the following is true? A Strangeness is never conserved in decays mediated by the strong interaction.
A ddd ___ B ddd
B Strangeness is always conserved in decays mediated by the strong interaction.
C uuu ___ D uuu
C Strangeness is always conserved in decays mediated by the weak interaction.
6. Which of the following statements is not correct? A Baryons are always formed from three quarks. B Mesons are always formed from a quark and an antiquark. C Leptons are always lighter than baryons.
D Strangeness is conserved in all decays. 10. Conservation laws are very important in physics. They reflect underlying symmetries in nature and are a clear guide as to what is possible. This applies to particle physics. Murray Gell-Mann has said: “Anything that is not expressly forbidden, will happen.”
D All mesons are hadrons. 7. During beta-minus decay, which of the following is correct? A An up quark is transformed to a down quark by the strong force. B An up quark is transformed to a down quark by the weak force. C A neutrino is emitted, so that charge is conserved. D An antineutrino is emitted to conserve charge. 8. In which row in Table Q2 are all the statements true?
Read excerpts A and B and then answer the following questions. Excerpt A ‘Conservation’ (the conservation law) means this … that there is a number, which you can calculate, at one moment – and as nature undergoes its multitude of changes, this number doesn’t change. That is, if you calculate again, this quantity, it’ll be the same as it was before. An example is the conservation of energy: there’s a quantity that you can calculate according to a certain rule, and it comes out the same answer after, no matter what happens, happens. — Richard P. Feynman From ‘The Great Conservation Principles’, The Messenger Series of Lectures, No. 3, Cornell University, 1964
Strong force
Weak interaction
Electromagnetic
Gravity
A
Acts only between hadrons
Acts only between leptons
Acts only between charged particles
Acts between masses
B
Holds nucleons together
Causes radioactivity
Holds molecules together
Holds galaxies together
C
Shortest range
Short range
Infinite range
Infinite range
D
Bosons are massless
Bosons are massless
Bosons are massless
Bosons are massless
Table Q2
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