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UT Arlington PHYS 3446 - PHYS 3446 Lecture notes

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UTA McNair Scholars Program ExtendsUTA McNair Scholars Program Extends ANNUAL Application deadlineThe UTA McNair Scholars Program has extended its 2008 recruitment period through November 25. The McNair program is a federal TRIO program that offers opportunities to selected undergraduates hoping to pursue graduate studies leading to the Ph.D. and a career in the academy. We appreciate faculty recommendations of talented undergraduates to this programtalented undergraduates to this program.The McNair program works with at least 30 students each academic year from low-income/first-generation orunderrepresented (African American, Hispanic, Native American, Native Hawaiian) backgrounds. Two-thirds of our participants must be first-generation/low-income students. Applicants must be (or have):U.S. citizens or permanent residents. sophomores (by spring 2009), juniors or seniors (not graduating before at least December 2009) a minimum 2.9 GPA , able to engage in a summer of faculty-mentored research between their junior and senior years.jyAll majors are eligible, although we especially encourage those in STEM fields to apply. The program focuses on all aspects of graduate school preparation: faculty-mentored summer research (including a $3000 stipend and three credit hours of independent study) publication of research abstract in theUTA McNair Research Journalthree credit hours of independent study), publication of research abstract in the UTA McNair Research Journal, GRE prep classes, diverse seminars related to program goals, conference participation, graduate school visits, and other benefits.Application packets are available in 122 Hammond Hall, may be downloaded from http://www.uta.edu/soar/ (Click on TRIO P th M N i) t d b t l h (8172723715) iil (i@ t d)TRIO Programs, then McNair), or requested by telephone (817-272-3715) or via e-mail ([email protected]).Wednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt1Strangeness quantum numberStrangeness•Strangeness quantum number– Murray Gell-Mann and Abraham Pais proposed a new additive quantum number that are carried by these particles–Conserved in strong interactionsg– Violated in weak decaysS=0 for all ordinary mesons and baryons as well as photons–S=0 for all ordinary mesons and baryons as well as photons and leptonsFt itdd ti ti / th i iti l–For any strong associated-production reaction w/ the initial state S=0, the total strangeness of particles in the final state sho ld add p to 0should add up to 0.Wednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt2•Let’s look at the reactions againMore on Strangeness•Let s look at the reactions againThis is a strong interactionpπ−+→00K +Λ–This is a strong interaction• Strangeness must be conserved• S: 0 + 0 Æ +1 -1• How about the decays of the final state particles?–and 0pπ−Λ→ +0Kππ+−→+– These decays are weak interactions so S is not conserved–S: -1 Æ 0 + 0 and +1 Æ 0 + 0pπΛ→ +Kππ→+• A not-really-elegant solution– S only conserved in Strong and EM interactions Î Unique strangeness quantum numbers cannot be assigned to leptons• Leads to the hypothesis of strange quarksWednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt3•Strong force does not depend on the charge of the particleIsospin Quantum Number•Strong force does not depend on the charge of the particle– Nuclear properties of protons and neutrons are very similarFthtdifi lithtthfd–From the studies of mirror nuclei, the strengths of p-p, p-n and n-n strong interactions are essentially the sameIf corrected by EM interactions the xsec between nn and pp are the–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•Since strong force is much stronger than any other forces, we could imagine a new quantum number that applies to all particlesparticles– Protons and neutrons are two orthogonal mass eigenstates of the same particle like spin up and down statessame particle like spin up and down states1 and0p⎛⎞=⎜⎟⎝⎠0n 1⎛⎞=⎜⎟⎝⎠Wednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt40p⎜⎟⎝⎠1⎜⎟⎝⎠•Protons and neutrons are degenerate in mass because of someIsospin Quantum Number•Protons and neutrons are degenerate in mass because of some symmetry of the strong force–Isospin symmetryÎUnder the strong force these two particlesIsospin symmetry ÎUnder 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 spin–Protons and neutrons have isospin ½ Î Isospin doublet– Three pions, π+, π- and π0, have almost the same massesXb th ti l l t th ft ti f EM–X-sec by these particles are almost the same after correcting for EM effects–Strong force does not distinguish these particlesÎIsospin triplet–Strong force does not distinguish these particles ÎIsospin triplet10,π+⎛⎞⎜⎟=⎜⎟001π⎛⎞⎜⎟=⎜⎟0and 0 π−⎛⎞⎜⎟=⎜⎟Wednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt5,0⎜⎟⎜⎟⎝⎠0⎜⎟⎜⎟⎝⎠1⎜⎟⎜⎟⎝⎠Isospin Quantum Number• This QN is found to be conserved in strong interactions•But not conserved in EM or Weak interactions•But not conserved in EM or Weak interactions• Isospin no longer used, replaced by quark modelWednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt6Violation of Quantum Numbers• The QN we learned are conserved in strong interactions are but many of them are violated in EM or weakare but many of them are violated in EM or weak interactionsTh t f k i t ti•Three types of weak interactions–Hadronic decays: Only hadrons in the final stateyy–Semi-leptonic decays: both hadrons and leptons are present0Λ→pπ−+–Semi-leptonic decays: both hadrons and leptons are presentn →epeν−++–Leptonic decays: only leptons are presentμ−→eeμνν−++Wednesday, Nov. 12, 2008 PHYS 3446, Fall 2008 Andrew Brandt7μ→eeμνν++•Baryon NumberQuantum Numbers•Baryon Number– An additive and conserved quantum number, Baryon number (B)–This number is conserved in general but not absoluteThis number is conserved in general but not absolute• Lepton Number–Quantum number assigned to leptons–Quantum number assigned to leptons– Lepton numbers by species and the total lepton numbers must be conserved•


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UT Arlington PHYS 3446 - PHYS 3446 Lecture notes

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