Carefully prepare lessons,prepare students and make preparations In the teching proce payto students'creative thinking,take and enhance students'sense of participation:Corresponding exercises and supplementary exercises after class. Problems: 1.Half the muons in a monoenergetic beam decay in the first 600 m.How fast are they going? 2.How much more does a hot potato weigh than a cold one (in kg)? 3.Particle A,at rest,decays into three or more particles:AB+C+D (a)Determine the maximum and minimum energies that B can have in such a decay,in terms of the various masses. (b)Find the maximum and minimum electron energies in muon decay, →e+。+v Chapter Four:Symmetries 1.Teaching aims Know some general remarks about the mathematical description of symetry (group theory)and the relation between symmetry and conservation laws (Notther's theorem): Take up the case of rotational symmetry and its relation to angular momentum and spin: Consider 'discrete'symmetries-parity,charge conjugation,and time reversal 2.Keypoints and Difficulties Keypoints:Symmetries Difficulties:Flavor Symmetries 3.Contents 4.1 Symmetries.Groups.and Conservation Laws 4.2 Angular Momentum 4.2.1 Addition of Angular Momenta 4.2.2 Spin Carefully prepare lessons, prepare students and make preparations before class; In the teaching process, we pay attention to cultivating students' creative thinking, take students as the main body and enhance students' sense of participation; Corresponding exercises and supplementary exercises after class. Problems： 1. Half the muons in a monoenergetic beam decay in the first 600 m. How fast are they going? 2. How much more does a hot potato weigh than a cold one (in kg)? 3. Particle A, at rest, decays into three or more particles: A→ B + C + D + …. (a) Determine the maximum and minimum energies that B can have in such a decay, in terms of the various masses. (b)Find the maximum and minimum electron energies in muon decay, ̅ݒ ൅ ି݁ → ିߤ .ఓݒ ൅ ௘ Chapter Four: Symmetries 1. Teaching aims Know some general remarks about the mathematical description of symmetry (group theory) and the relation between symmetry and conservation laws (Notther's theorem); Take up the case of rotational symmetry and its relation to angular momentum and spin; Consider ‘discrete' symmetries - parity, charge conjugation, and time reversal. 2. Keypoints and Difficulties Keypoints: Symmetries Difficulties: Flavor Symmetries 3. Contents 4.1 Symmetries. Groups. and Conservation Laws 4.2 Angular Momentum 4.2.1 Addition of Angular Momenta 4.2.2 Spin ଵ ଶ