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Quarks

Quarks. HADRON Content. 2’s or 3’s ONLY! Baryons and Mesons Quarks & Antiquarks Baryons = Three quarks (or antiquarks) of positive or neutral charge Protons Neutrons and antiprotons antineutron Mesons = One Quark plus one Antiquark Pion and Antipion. The Flavors. TOP. CHARM. UP.

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Quarks

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  1. Quarks

  2. HADRON Content • 2’s or 3’s ONLY! • Baryons and Mesons • Quarks & Antiquarks • Baryons = Three quarks (or antiquarks) of positive or neutral charge • Protons Neutrons and antiprotons antineutron • Mesons = One Quark plus one Antiquark • Pion and Antipion

  3. The Flavors. TOP CHARM UP +2/3 -1/3 BOTTOM DOWN STRANGE

  4. Protons vs Neutrons Proton Neutron Different particles are made up of different mixtures of Quarks

  5. Baryon number • Baryon numbers are assigned to the baryons • It is a quantum number • The antibaryon has the opposite baryon number to its baryon counterpart • Protons & Neutrons have +1 • Antiprotons & antineutrons have -1 • This is the same for Mesons but because they have a quark and antiquark their bryon number is 0. • BARYON NUMBERS ARE CONSERVED IN ALL REACTIONS!

  6. spin structure Each quark has a spin of ½ The spin can be spin up (+1/2) or spin down (-1/2) Baryons A particle normally has a spin of ½ Sometimes however they do have a spin of 1 ½ but these particles are more energetic and highly unstable Mesons As they consist of quark-antiquark pairs, the spins of the quarks are in the opposing sense.

  7. Pauli exclusion principle • No two fermions may occupy the same state!

  8. colours • AntiredAntigreenAntiblue • Anticolours are the only other aspect apart from charge, that is different from their quark counterparts • Red Green Blue • Colour is the quantum difference between fermions • Even though there are two up quarks in a proton their colour is different • Therefore their spin cannot be parallel • Thus giving them a different quantum state.

  9. Use of colour in forming bound quarks • Colours must combine to make white (a colour neutral combination or net colour of 0) • Combinations: • Red Blue Gree = White • AntiredAntiblueAntigreen = White • Red Antired = White • Etc.

  10. Gluon Colour • There are only 8 gluons • They exist as a combination of colours and anticolours • A Gluon has only two colours within it • And anticolour and a colour such that combinations like red – antiblue and so on. • There could be 9 combinations but the three red-antired, blue-antiblue, green-antigreenpossiblities only give two distinct behaviours. gluon

  11. strangeness • Expressed as a quantum number • Describes decay of particles in reactions • Describes strong and electromagnetic reactions. • Kept for continuity of the phrase as it predates the discovery of quarks. • Sign for antiparticles is +1 • Sign for particles is -1 • Strangeness is conserved in strong and electromagnetic interactions • S = -(ns – ns) • ns = number of strange quarks • ns = number of antistrange quarks • (the syllabus says that the equation is the other way round i.e. (ns - ns) )

  12. Confinement • It is not possible to observe isolated quarks. Quarks inside a hadron appear in colour combinations that result in a net colour number of 0. This is quark confinement or confinementof colour • The force between quark and antiquark is constant no matter the separation • Therefore the force needed to separate them gets larger the greater the separation • Complete separation would need an infinite force • Insisting on providing an ever increasing force would only result in the creation of a meson-antimeson pair.

  13. Interaction binding nucleons • The interaction between nucleons is the residual interaction between the quarks in the nucleons • This is a short-range interaction.

  14. What do sick ducks say? Qu-ark!!

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