Kaon
The neutral Kaons represent symmetricantisymmetric mixtures ofquark combinations down-antistrangeantidown-strange.The charged kaonsmesons which havequark compositionup-antistrange forpositive kaonantiup-strange fornegative kaon. They decayabout 10-8 seconds.
Decay timesthis range indicate decay byweak interaction. None ofdecay products hasstrange quark, so this decay violates conservationstrangenesscannot proceed bystrong interaction.
Describingneutral kaonsmuch more complex. Theretwo versionsthis particle withsame mass but different decay lifetimes. Onecalled K-zero-short;othercalled K-zero-long. These two particlesconsideredbe combinationsdown-antistrangeantidown-strange quarks respectively. These particles decay into pions byexchangetwo W bosons.
The neutral kaonsimportant historicallytheir partadvancing our understandingquark processes. When first discovered inlate 1940s,were labeledtq mesonstheir decay wasgreat mystery, labeledt-q puzzle. The particles were identicalmass, andonlywhich apparently differentiated them was their decay processes andfact thattwo different setsdecay products had different parity. Particle decays bystrong or electromagnetic interactions had been observedconserve paritytheir decays. Theoretical physicists T. D. LeeC. N. Yang proposed1956 that parity need not be conservedweak interaction decays. In 1957 Chien-Shiung Wu showed this violationparity conservation inbeta decaycobalt. Even withviolationparity,was thought thatcombinationcharge conjugationparity would leavesystem invariant (CP invariance). An experiment by CroninFitch1964 showed that there wassmall CP violation inkaon decay, sokaon has playedcentral role indiscussionsthese symmetries since that time.
When RochesterButler discoveredshort-lived version ofneutral kaon1946,did so by observingcharacteristic "V" pattern incloud chamber. The neutral kaon did not leavetrack incloud chamber, so"V" trackpions revealed its presence upon decay.
