K-MESONS: HISTORY AND BASIC THEORY

Francisco AntonioPhysics 129November 23, 2010

Li Zhengdao and Yang Zhenning, 1953

Overview:

Experimental History of Kaons Evolving Theory of Kaons with

respect to CP Current Technologies, Directions for

Kaon Science

Pre-Gellmann and Pais

The state of the yet to be conceived “Standard Model”

The Neutral Particle, one among the many particles of the 1953 particle extravaganza

Late 1950’s: The Intermediate Vector Bosons, courtesy of Yukawa

1964: The quark. 1960-1980’s: Parallel development of

Kaons’ and the Standard Model’s main concepts.

The Gellmann-Pais Paper

Theoretical proposition that there be a property of strangeness to allow for K0 < -- > K0 (Eigenstates of Mass)

CP|K0> = -|K0> By CP

conservation:K1 and K2 were restricted to 2 and 3 decays, respectively

Initially thought to be equivalent to KS and KLLater known as the Eigenstates of Weak Interaction

First Results: Lederman, 1956. 1 10^-10 sec. 2 10^-8 sec. Goal:

Kinematically confirming the events were related to a neutral secondary particle.

36 “ Magnet Cloud Chamber Design with Proton Beam incident on target (Brookhaven Bevatron)

Data On the Vo Events

Ruling Out the Possibilities

CP Violation After All

Cronin and Fitch, 1964.

First evidence for Indirect CP Violation.

Goal: Measured uncharacteristic 2 decays where only KL = K1 should have existed.

Again at the Brookhaven Bevatron, this time with spark chamber detectors

CP Violation: The Contenders

Direct CP Violation – Depends on decay process itself, penguin diagrams

Indirect CP Violation – related to mixing the eigenstates of mass to form the eigenstates of decay. Weak interactions of ΔS = 1 and superweak interactions of ΔS = 2.

The Weak Interaction

Asymmetry in the K0/K0 mixing that created KL and KS no longer equivalent to K2 and K1 respectively. Instead a mixture characterized by of K1 and K2 describe KL and KS in the eigenstate of weak interaction.

Result: Time/Space Dependent Oscillation between KL and KS

Is a measure of CP violation related to the mixing of K0/K0

The Kobayashi-Maskawa Model of Weak Interaction

Instead of a diagonal matrix relating the mass eigenstates to the weak interaction eigenstates, the off diagonals are present, allowing a small amount of mixing

The amount of mixing is parametrized by three angles ij and phase shift

Weak Interaction Eigenstates Mass Eigenstates

Superweak Interactions

Asserts that the ONLY CP violation in the neutral Kaon system is due to K0/K0mixing

Would accomplish this by allowing ΔS = 2 so that (for the superweak) is much larger than (from the second order KM weak interaction).

Direct CP Violation Measured! Alavi et. al. 1999, Data: from 96-97 Fermilab Run. Goal: To measure a non-zero Re(/)

to a high degree of accuracy

Note that in the case of Superweak models Re(/) = 0

Alavi Experiment, Fermilab.KTeV Experiment, E832, First to use Dual Kaon Beams for great

suppression of unwanted channels

The Modern Kaon Experimental Setup Beam – Dual Kaon Beams Regenerator – Takes advantage of

eigenstate oscillations Photon Veto – Rejects 2 and 2 decays. EM Calorimeter – particle “shower”.

Reconstruction Magnetic Spectrometer- Phase space

measurements (Intensity vs. Momentum) Collimators – maximize neutral beam

acceptance.

Is The Superweak Theory disproven? At least in the neutral Kaon system it

has been found to be “weak”-sauce. B Systems are currently being tested

for similar ratios of Re(/) with results pending.

Kaon Science Today

Direct vs. Indirect CP violation (only Kaons have the former)

The Strong CP Problem (QCD doesn’t break CP Symmetry)

Matter/Antimatter existence due to preferential decays that violate CP

The Standard Model’s take on CP Violation - Insufficient

References

Gell-Mann, Pais. “Behavior of Neutral Particles Under Charge Conjugation”. Phys Rev. 97. 1387.

Alavi et al. “Observation of Direct CP Violation in Ks,l 2Pi”. Phys Rev. Letters. 83. 22.

Cronin et al. “Evidence of the 2Pi Decay of the K2 Meson”. Physical Review Letters. 13. 138.

Lande et al. “Observation of Long-Lived Neutral V Particles”. Physical Review. 103. 1901.

Kobayashi, Maskawa. “CP-Violation in the Renormalizable Theory of Weak Interaction”. Progress of Theoretical Physics. 49. 652

Biino et al. “The Simultaneous Long and Short lived Neutral Kaon Beams for Experiment NA48”. European Organization for Nuclear Research CERN—SL Division.

Winstein. “The Search for Direct CP Violation”. Reviews of Modern Physics. 65. 1113