1 / 6

Lepton and Baryon Conservation

Lepton and Baryon Conservation. Strong and EM conserve particle type. Weak can change but always lepton->lepton or quark->quark So number of quarks (#quarks-#antiquarks) conserved. Sometimes called baryon conservation B.

Download Presentation

Lepton and Baryon Conservation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Lepton and Baryon Conservation • Strong and EM conserve particle type. Weak can change but always lepton->lepton or quark->quark • So number of quarks (#quarks-#antiquarks) conserved. Sometimes called baryon conservation B. • Number of each type (e,mu,tau) conserved L conservation • Can always create particle-antiparticle pair • But universe breaks B,L conservation as there is more matter than antimatter • At small time after big bang #baryons = #antibaryons = #leptons = #antileptons (modulo spin/color/etc) • Now baryon/photon ratio 10-10 P461 - particles II

  2. Hadron production + Decay • Allowed production channels are simply quark counting • Can make/destroy quark-antiquark pairs with the total “flavor” (upness = #up-#antiup, downness, etc) staying the same • All decays allowed by mass conservation occur quickly (<10-21 sec) with a few decaying by EM with lifetimes of . 10-16 sec) Those forbidden are long-lived and decay weakly and do not conserve flavor. P461 - particles II

  3. Hadrons and QCD • Hadrons are made from quarks bound together by gluons • EM force QuantumElectroDynamics QED strong is QuantumChromoDynamics QCD • Strong force “color” is equivalent to electric charge except three different (identical) charges red-green-blue. Each type of quark has electric charge (2/3 up -1/3 down, etc) and either r g b (or antired, antiblue, antigreen) color charge • Unlike charge=0 photon, gluons can have color charge. 8 such charges(like blue-antigreen) combos, 2 are colorless. Gluon exchange usually color exchange. Can have gluon-gluon interaction P461 - particles II

  4. Pions • Use as strong interaction example • Produce in strong interactions • Measure pion spin. Mirror reactions have same matrix element but different phase space/kinematics term. “easy” part of phase space is just the 2s+1 spin degeneracy term • Find S=0 for pions P461 - particles II

  5. More Pions • Useful to think of pions as I=1isospin triplet and p,n is I=1/2 doublet (from quark plots) • Look at reactions: • p p -> d pi+ Total I ½ ½ 0 1 1 Iz ½ ½ 0 1 1 p n -> d pi0 Total I ½ ½ 0 1 0 or 1 Iz ½ - ½ 0 0 0 • in the past we combined 2 spin ½ states to form S=0 or 1 P461 - particles II

  6. More Pions • Reverse this and say eigentstate |p,n> is combination of I=1 and I=0 • reactions: • then take the “dot product” between |p,n> and |d,pi0> brings in a 1/sqrt(2) (the Clebsch-Gordon coefficient) • Square to get A/B cross section ratio of 1/2 P461 - particles II

More Related