Understanding CP Violation in Two-Body Decay of K Mesons

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Discussion Overview

The discussion revolves around the concept of CP violation in the two-body decay of K mesons, specifically referencing a historical article that discusses the expected behavior of decay angles in two-body versus three-body decays. Participants explore the implications of momentum conservation and the observed decay angles.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions the reasoning behind the assertion that the decay angle should be zero for two-body decays, suggesting that momentum conservation implies a small angle for highly boosted kaons.
  • Another participant clarifies that the angle being discussed is indeed small for highly boosted kaons but notes that it is still significant in three-body decays due to the energy levels involved.
  • There is a discussion about the nature of the angle, with one participant initially misunderstanding it as the angle between the momentum of a single pion and the original direction of the kaon, later correcting this to refer to the vector sum of the momentum and the kaon's direction.
  • One participant asserts that for a two-body decay, the angle must be zero, attributing this to momentum conservation, while acknowledging that three-body decays allow for different angles.

Areas of Agreement / Disagreement

Participants express differing views on the implications of momentum conservation for decay angles, with some agreeing that the angle should be zero for two-body decays while others question this assertion based on the conditions of the decay.

Contextual Notes

There are unresolved aspects regarding the specific conditions under which the decay angles are measured, including the effects of resolution and the energy levels of the kaons in the experiments discussed.

Vinci128
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Hi everyone,
i was reading the article of Cristenson,Cronin,Fitch and Turlay of 1964, the one that discovered CP violation in the system of neutral K mesons. There is one point in it that i don't get it. They say "the angle should be zero for two body decay and is, in general, different from zero for three body decay". Based to what i know, it must be conserved the longitudinal and transversal component of the momentum, so if the boost is high, the angle should be small. It's this the right explanation for the very small angle of decay observed?

I really appreciate any help you can provide.
 
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Which angle? I don't find the quoted text in the original work.

Edit: Oops, typo, found it.

The angle is small for highly boosted kaons, but still notable in most (edit: three-body!) decays - the kaon energy was not that high in their beam.
The observed peak at 1 in the right mass range (and only there) is a clear evidence for two-body decays.
 
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I was thinking the same thing. That's why i don't understand why the angle must be so near to zero.
 
For a two-body decay, it must be zero (just smeared out by resolution effects). This is just momentum conservation - momentum before is the same as momentum after the decay.

For a three-body decay, the angle can be different.
 
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Thanks, reading the article better i have seen that the angle is between the vector sum of the momentum and the direction of the k meson. I thinked it was between the momentum of the single pion and original direction of the kaon
 

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