【正文】 S 250252 Spring 2022 L6 Richard Kass Neutral Kaons, Mixing, and CP violation The k0 and k0 are eigenstates of the strong interaction. These states have definite strangeness, are NOT CP eigenstates, and are particle/antiparticle. They are produced in strong interactions (collisions) . 000 or ???? kpkp ppThe k1 and k2 are eigenstates of the weak interaction, assuming CP is conserved. These states have definite CP but are not strangeness eigenstates. Each is its own antiparticle. These states decay via the weak interaction and have different masses and lifetimes. 0002022 or ppppp ?? kkIn 1955 (!) GellMann and Pais pointed out that the k1 and k2 lifetimes should be very different since there was more decay energy (phase space) available for k1 than k2. mk2mp ? 219 MeV/c2 mk3mp ? 80 MeV/c2 Thus, expect k1 to have the shorter lifetime. The lifetimes were measured to be: t1 ? 9x1011 sec (194753) t2 ? 5x108 sec (Lande et. al. Phys. Rev. V103, 1901 (1956)) We can use the lifetime difference to produce a beam of k2’s from a beam of k0’s. 1) produce k0’s using pp?k0?. 2) let the beam of k0’s propagate in vacuum until the k1 ponent dies out. 1 GeV/c k1 travels on average ? cm 1 GeV/c k2 travels on average ? 3100 cm Need to put detector 100200 m away from target. m2 m1 = eV Mamp。S pages 240246 This left/right handedness is illustrated in p+?l+?l decay: p? S? pe,m Se,m p Angular momentum conservation forces the charged lepton (e, m) to be in the “wrong” handed state, . a left handed positron (e+). The probability to be in the wrong handed state ~ml2 4222222210)()BR( )eBR( ??????????????????mppmm?mp?pmmmmmm eeehandedness~2x105 phase space ~5 W+ e+ v pp=0 Sp=0 Spring 2022 L6 Richard Kass Charge Conjugation and Parity parity parity C C CP s p ? s p right handed ? s p left handed ? s p ? In the strong and EM interaction C and P are conserved separately. In the weak interaction we know that C and P are not conserved separately. BUT the bination of CP should be conserved! Consider how a neutrino (and antineutrino) transforms under C, P, and CP. Experimentally we find that all neutrinos are left handed and antineutrinos are right handed. So, CP should be a good symmetry Spring 2022 L6 Richard Kass Neutral Kaons and CP violation In 1964 it was discovered that the decay of neutral kaons sometimes (103) violated CP! Thus the weak interaction does not always conserve CP! In 2022 CP violation was observed in the decay of Bmesons. CP violation is one of the most interesting topics in physics: The laws of physics are different for particles and antiparticles! What causes CP violation ? (it is put into Standard Model) Is the CP violation observed with B’s and K’s the