DOC PREVIEW
UT Arlington PHYS 3446 - Elementary Particle Properties

This preview shows page 1-2-20-21 out of 21 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 21 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 21 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 21 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 21 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 21 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

PHYS 3446 – Lecture #17Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu1PHYS 3446 – Lecture #17Monday, Nov. 6, 2006Dr. Jae Yu1. Elementary Particle Properties•Quantum Numbers•Strangeness•Isospin•Gell-Mann-Nishijima Relations•Production and Decay of ResonancesMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu2•LPCC Workshop was very successful–Tested the display with random people  worked pretty well–Follow up: Groups need to discuss within yourselves to prepare for the final push at the upcoming workshop on Dec. 2.•2nd term exam–Monday, Nov. 20–Covers: Ch 4 – whatever we finish on Nov. 15•Homework1. Reading assignments: 9.6 and 9.72. End of chapter problems 9.1, 9.2 and 9.33. Due for these assignments is next Wednesday, Nov. 15AnnouncementsMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu3•Baryon Number–An additive and conserved quantum number, Baryon number (B)–All baryons have B=1–Anti-baryons? (B=-1)–Photons, leptons and mesons have B=0•Lepton Number–Quantum number assigned to leptons–All leptons carry L=1 (particles) or L=-1 (antiparticles)–Photons or hadrons carry L=0–Total lepton number must be conserved–Lepton numbers by species must be conservedQuantum NumbersMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu4•From cosmic ray shower observations–K-mesons and  and 0 baryons are produced strongly w/ large x-sec•But their lifetime typical of weak interactions (~10-10 sec)•Are produced in pairs – a K w/ a or a K w/ a 0–Gave an indication of a new quantum number•Consider the reaction–K0 and 0 subsequently decay – and •Observations on 0– Always produced w/ K0 never w/ just a 0– Produced w/ K+ but not w/ K-Strangenesspp-+ �0L �0p Kp p- + -+ � + +L0p Kp p- - ++ � + +L0pp p p- - ++ � + +L0 0K +L0K �pp-+p p+ -+Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu5•Consider reactions and–With the subsequent decays and •Observations from +– + is always produced w/ a K+ never w/ just a +– + is also produced w/ a K0 but w/ an additional + for charge conservation•Observations from –  is always produced w/ a K+ never w/ K- •Thus,–Observed:–Not observed:StrangenessKpp+ + ++ � S +0p Kp p+ + ++ � S + +pp-+ � K+ -S +pp-+ � p- +S +( )+ -S �p Kp- - ++ � S +K pp- - ++ � S +K+�( )n p+ -+0p p++Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu6– 0 at v~0.1c decays in about 0.3cm•Lifetime of 0 baryon is•The short lifetime of these strange particles indicate weak decay•Further observation of cross section measurements–The cross section for reactions and w/ 1GeV/c pion momenta are ~ 1mb•Whereas the total pion-proton scattering cross section is ~ 30mb•The interactions are strong interactionsStrangeness01090.310 sec3 10 /cmcm st-L� =�0 0p Kp-+ � +L0p Kp p- + -+ � + +LMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu7•Strangeness quantum number–Murray Gell-Mann and Abraham Pais proposed a new additive quantum number that are carried by these particles–Conserved in strong interactions–Violated in weak decays–S=0 for all ordinary mesons and baryons as well as photons and leptons–For any strong associated-production reaction w/ the initial state S=0, the total strangeness of particles in the final state should add up to 0.StrangenessMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu8•Based on experimental observations of reactions and w/ an arbitrary choice of S(K0)=1, we obtain –S(K+)=S(K0)=1 and K)=0)=-1–S(0)=SS(0)=S(-)=-1–Does this work for the following reactions?– – •For strong production reactions and– cascade particles if StrangenessK Kp- - ++ � X +( ) ( )02S S-X = X =-( ) ( )0S K K 1S-= =-0 0K K p++ � X +0p Kp p- + -+ � + +L0 0p Kp-+ � +LMonday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu9•Let’s look at the reactions again–This is a strong interaction•Strangeness must be conserved•S: 0 + 0  +1 -1•How about the decays of the final state particles?– and –These decays are weak interactions so S is not conserved–S: -1  0 + 0 and +1  0 + 0•A not-really-elegant solution–S only conserved in Strong and EM interactions  Unique strangeness quantum numbers cannot be assigned to leptons•Leads into the necessity of strange quarksMore on Strangenesspp-+ �0pp-L � +0 0K +L0K p p+ -� +Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu10•Strong force does not depend on the charge of the particle–Nuclear properties of protons and neutrons are very similar–From the studies of mirror nuclei, the strengths of p-p, p-n and n-n strong interactions are essentially the same–If corrected by EM interactions, the x-sec between n-n and p-p are the same•Since strong force is much stronger than any other forces, we could imagine a new quantum number that applies to all particles–Protons and neutrons are two orthogonal mass eigenstates of the same particle like spin up and down statesIsospin Quantum Number1 and0p��=����0n 1��=����Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu11•Protons and neutrons are degenerate in mass because of some symmetry of the strong force–Isospin symmetry  Under the strong force these two particles appear identical–Presence of Electromagnetic or Weak forces breaks this symmetry, distinguishing p from n•Isospin works just like spins–Protons and neutrons have isospin ½  Isospin doublet–Three pions, +, - and 0, have almost the same masses–X-sec by these particles are almost the same after correcting for EM effects–Strong force does not distinguish these particles  Isospin tripletIsospin Quantum Number10 ,0p+����=������0010p����=������0and 0 1p-����=������Monday, Nov. 6, 2006 PHYS 3446, Fall 2006Jae Yu12•This QN is found to be conserved in strong interactions•But not conserved in EM or Weak interactions•Third component of the isospin QN is assigned to be positive for the particles with larger electric charge•Isospin is not a space-time symmetry•Cannot be assigned uniquely to leptons and


View Full Document

UT Arlington PHYS 3446 - Elementary Particle Properties

Documents in this Course
Symmetry

Symmetry

18 pages

Load more
Download Elementary Particle Properties
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Elementary Particle Properties and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Elementary Particle Properties 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?