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Unformatted text preview: 1 Wed. May 1, 2007 Phy107 Lect. 38 1 From Last Time… • Discussed quarks and their interactions • Six quarks, paired in three generations • Quarks have electric charge, participate in EM interaction by exchanging photons. • Quarks also have color charge, participate in color interaction by exchanging gluons. • Color charge comes in six varieties – Red, green, blue, anti-red, anti-green, anti-blue Essay due today Wed. May 1, 2007 Phy107 Lect. 38 2 Question Quarks have color charge, and interact via the strong force. In analogy with electric charges, which of these interactions might be repulsive? A. Red-Green B. Red-AntiRed C. Red-Red D. Red-Blue Wed. May 1, 2007 Phy107 Lect. 38 3 Quark interactions • Quarks interact by exchanging gluons • Opposite colors quarks attract most strongly – Red and anti-read attract strongly to form a meson – Red and green, red and blue, etc attract, but less strongly • Like colors repel – Red and red repel – Blue and blue repel, etc. • But gluons also have a color charge – They can interact via the strong interaction Wed. May 1, 2007 Phy107 Lect. 38 4 Consequences of gluon color charge • Gluon has a color charge-> couples to the gluon field, excites more gluons - stronger force • As quarks get farther apart, gluons have more ‘room’ to interact. • Force gets stronger as quarks get further apart! • Eventually have enough energy to make more quarks. new Quark-antiQuark pair Wed. May 1, 2007 Phy107 Lect. 38 5 Pulling apart quarks Electron-positron collide an produce charm-anticharm quark pair with lots of kinetic energy. Quark pair flies apart, interaction energy increases until enough is available to excite a quark-antiquark pair....
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- Spring '08