Quarks and Antiquarks

• Quarks are never found alone (it takes more energy to seperate them than the rest mass of a quark so by seperating them you create quarks!)
• Recall that a meson is a pair (quark and antiquark) so has baryon number zero
• Baryons are three quarks or three antiquarks and have baryon number +1 and -1 respectively

• Pions are made from combinations of quarks that mean that the total strangeness is zero
• Kaons are mesons that have a strangeness of +1 and -1. They can decay into pions

• Strangeness is a quantum property (like charge)
• Strangeness is conserved in strong interactions. This means that when kaons are created you must conserve strangeness (make both a matter and an antimatter quark somewhere in the formula/diagram)
• Strangeness is not conserved in decays that use the weak interaction which allows kaons to decay into pions or other baryons (quarks are changing flavourn from strange into something else)

π0 = up/antiup or down/antidown

π+ = up/antidown

π- = down/antiup

K0 = down/antistrange or antidown/strange

K+ = up/antistrange

K- = Strange/anitup

• To make a neutron turn into a proton, as in beta minus decay, a down quark must turn into an up quark. To make a proton turn into a neutron, as in beta plus decay, an up quark must turn into a down quark.