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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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