Question

Beta decay is caused by the weak force, as are all reactions in which strangeness changes. Does this imply that the weak force can change quark flavor? Explain.

Short answer

Yes, the weak force can change quark flavor.

Step-by-step solution

Concept Introduction

Quarks are divided into six flavors’: up, down, charm, weird, top, and bottom. The masses of up and down quarks are the smallest of all quarks.

Explanation

Except in the case of weak force interactions, flavor is a preserved quantity in a reaction. The W^_ boson, the positively charged W⁺boson, and the neutral Z⁰ boson are the three types of force carriers in the weak force. A weak interaction is mediated by one of the above-mentioned bosons in response to the electric charge change associated with the change in flavor, depending on the flavor change. Let's have a look at \({{\rm{\beta }}^{\rm{ - }}}\)decay as an example. The up-quark u in a proton, which carries charge \({\rm{q(u) = + }}\frac{{\rm{2}}}{{\rm{3}}}\), changes flavor into a down quark d, which carries charge \({\rm{q(d) = - }}\frac{{\rm{1}}}{{\rm{3}}}\), in \({{\rm{\beta }}^{\rm{ - }}}\)decay. We have a charge change of -1 overall, and since total charge must be preserved in an interaction vertex, we deduce that the reaction must be mediated by a W^_ boson with a charge of \({\rm{q}}\left( {{{\rm{W}}^{\rm{ - }}}} \right){\rm{ = - 1}}\). Taking into consideration the W^_ most likely decay route, which is

\({W^ - } \to {e^ - } + {\bar \nu _e}\)

we get a resulting interaction which is consistent with our knowledge about \({{\rm{\beta }}^{\rm{ - }}}\)decays.