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Evidence for Quarks Quark Composition of Hadrons [Secs Dunlap]

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By 1964 Particle classification became: Gauge Bosons FERMION BOSON gigi Not substantiated until 70s and 80s LeptonsBaryons Mesons HADRONS (S+E-W)LEPTONS (E-W)

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The 1950s particle Explosion Young man, if I could remember the names of all these particles, I would have been a botanist Enrico Fermi In th 1950s the race was on to build larger and larger accelerators. Many physicists such as Fermi were alarmed to say the least. By the end of the 50s we had the: Then in 1964 the cascades were discovered The situation was getting out of hand – some solution had to be found

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The quark or “straton” model or hadrons Murray Gell-Mann and George Zweig tentatively put forth the idea of quarks. They suggested that mesons and baryons are composites of three quarks or antiquarks, called up, down, or strange (u, d, s) with spin 1/2 and fractional electric charge. u d s charges 2/3, -1/3, -1/3 Since the charges had never been observed, the introduction of quarks was treated more as a mathematical explanation. Later theoretical and experimental developments allow us to now regard the quarks as real physical objects, even though they cannot be isolated. Three Quarks for Muster Mark! James Joyce Finnegans Wake

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Evidence for quark structure [1] Neutral pi meson production: [2] Neutron and proton magnetic moments are not = the nuclear magneton as predicted by the Dirac equation for point fermions. Such reactions are difficult to explain if it is assumed that the proton is like the electron a fundamental structureless particle.

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Other evidences for quark structure Deep Inelastic Scattering of electrons The proton has excited states

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Particle classification with 3 quarks Gauge Bosons FERMION BOSON Quarks gigi Not substantiated until 70s and 80s LeptonsBaryons Mesons HADRONS (S+E-W)LEPTONS (E-W)

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Mathematics – SU(2) symmetry special unitary group Triplet Singlet Di-Nucleon Deuteron Bound

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mathematics – SU(3) symmetry plet octet Decuplet singlet The strange quark is seen as being the identical particle to the up and down quark – just in a different quantum state. Rotations in quark space do not change the strong interaction

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SU3 found in experiment PROTON FAMILY = OCTET J π = 1/2+ HEAVY PROTON FAMILY = dicuplet J π =3/2+

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PROTON OCTET FAMILYHEAVY PROTON – DECUPLET FAMILY In reality the strange quark “s” has a heavier intrinsic mass

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Discovery of the Omega Minus The bubble chamber photograph shown was taken in 1964 – It shows the production of the first observed Omega Minus

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A look quick look at all the quarks u d s c Q=+2/3 Q= -1/3 b t 1 st Gen 2 nd Gen 3 rd Gen

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SU3 symmetry for q-q system

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The Pi- Meson Family (of nine)

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The energies of the Pi-meson family The higher mass of the K- mesons and Eta meson results from the larger mass of the strange quark

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ParticleSymbol Anti- particle Makeup Rest mass MeV/c 2 SCBLifetimeDecay Modes Pion π+π+ π-π- udud x10 -8 μ+νμμ+νμ Pion π0π0 Self x γ Kaon K+K+ K-K- usus x10 -8 μ + ν μ, π + π 0 Kaon K0sK0s K0sK0s 1* x π + π -,2π 0 Kaon K0LK0L K0LK0L 1* x10 -8 π+e-νeπ+e-νe Eta η0η0 Self2* < γ, 3μ Eta prime η 0' Self2* π+π-ηπ+π-η Rho ρ+ρ+ ρ-ρ- udud x π+π0π+π0 Rho ρ0ρ0 Selfuu, dd x π+π-π+π- Omega ω0ω0 Selfuu, dd x π+π-π0π+π-π0 Phi φ Selfs x K + K -,K 0 K 0 D D+D+ D-D- cdcd x K + _, e + _ D D0D0 D0D0 cucu x [K,μ,e] + _ D D+sD+s D-sD-s cscs x K + _ MESONS

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ParticleSymbolMakeup Rest mass MeV/c 2 SpinBS Lifetime (secon ds> Decay Modes Proton p uud938.31/2+10Stable... Neutron n ddu939.61/ pe - ν e Lambda Λ0Λ0 uds / x pπ -, nπ 0 Sigma Σ+Σ+ uus / x pπ 0, nπ + Sigma Σ0Σ0 uds /2+16x Λ0γΛ0γ Sigma Σ-Σ- dds / x nπ - Delta Δ ++ uuu12323/ x pπ + Delta Δ+Δ+ uud12323/ x pπ 0 Delta Δ0Δ0 udd12323/ x nπ 0 Delta Δ-Δ- ddd12323/ x nπ - Xi Cascade Ξ0Ξ0 uss13151/ x Λ0π0Λ0π0 Xi Cascade Ξ-Ξ- dss13211/ x Λ0π-Λ0π- Omega minus Ω-Ω- sss16723/ x Ξ 0 π -, Λ 0 K - BARYONS

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Adding the charmed quark

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Particle classification became Gauge Bosons FERMION BOSON Quarks gigi Not substantiated until 70s and 80s Leptons Baryons Mesons HADRONS (S+E-W)LEPTONS (E-W)

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