Baryon meson.

Presentation on theme: "Baryon meson."— Presentation transcript:

1 Baryon meson

2

3 What we knew about Weak interaction in the beginning:
β Decay

4 Weak Interaction β Decay 衰變的交互作用：
這個作用中中子不帶電，所以不是電磁力。強度又較核力弱很多，比重力強很多，所以只能是一個新的交互作用，稱為弱交互作用。

5

6 e ν p ? n

7 P318

8 The electron energy spectrum shows the interaction has “no structure”!
ν ν p p ? n n The spectrum can be produced by phase space alone! M only need to be a constant!

9 π μ e π 與 μ是透過弱交互作用來衰變？

10 Muon decay

11 Positron energy spectrum in muon decay

12 νμ νe e μ This Fermi theory describes Weak decays very well!
But it can’t be the final theory. It’s non-renormalizable! It has to change when energy gets higher. But how?

13 弱交互作用也可以想像如核力一樣由一個媒介子來傳播!
p e ν W - n 弱交互作用的媒介粒子：W± boson

14 p e ν e ν p W - n n

15 νμ νe e μ νμ νe e μ W

16 The weak vertices of leptons coupling with W
μ νμ -ig W

17 The weak vertices of quarks coupling with W
d u s c -ig W

18 The weak vertices of leptons coupling with W
μ νμ -ig W

19 For a toy ABC model Three scalar particle with masses mA, mB ,mC Factors External Lines 1 Internal Lines C Vertex -ig A B

20 The weak vertices of leptons coupling with W
μ νμ -ig

21 The weak vertices of leptons coupling with W
μ νμ -ig

22 2 × 2 matrices

23 W e νe μ νμ -ig

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26 A e νe Z

27 p n p p p

28 質子中子都是由夸克組成，因此基本上，β衰變是夸克的衰變：

29 交互作用不只改變粒子的動量，也可能改變粒子的身分！
n p p n