W7.4 - February 18, 2008 Physics for...

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Unformatted text preview: February 18, 2008 Physics for Scientists&Engineers 1 1 Physics for Scientists & Physics for Scientists & Engineers 1 Engineers 1 Spring Semester 2008 Lecture 26 February 18, 2008 Physics for Scientists&Engineers 1 2 Particle Physics Particle Physics The use of the conservation laws of momentum and energy is essential in the work of particle physicists when they analyze the products of collisions of particles at high energies, such as the ones produced at Fermilabs Tevatron, near Chicago, Illinois, currently the worlds highest energy proton/antiproton accelerator At the Tevatron particle physicists collide protons and antiprotons at total energies of 1.96 TeV (Hence the name!) Remember that 1 eV = 1.6 10-19 J; so 1.96 TeV = 1.96 10 12 eV = 3.2 10-7 J The Tevatron is set up so that the protons and antiprotons circulate in the collider ring in opposite directions with for practical purposes exactly opposite momentum vectors The main detectors, D and CDF, are located at the interaction regions, where protons and antiprotons collide February 18, 2008 Physics for Scientists&Engineers 1 3 Particle Physics (2) Particle Physics (2) In the figure below we show an example of such a collision In this computer-generated event display of the D detector and one particular collision event the protons initial momentum vector points exactly into the page and that of the antiproton exactly out of the page February 18, 2008 Physics for Scientists&Engineers 1 4 Particle Physics (3) Particle Physics (3) Thus the total initial momentum of the proton-antiproton system is zero The explosion produced by this collision produces several fragments, almost all of which are registered by the detector These measurements are indicated in gray levels in the event display shown We superimposed on this event display the momentum vectors of the corresponding particles, with their length and direction given by the information produced by the computer analysis of the detector response On the right side of this figure, we add up the momentum vectors graphically, finding a non-zero vector sum, as indicated by the thicker green arrow February 18, 2008 Physics for Scientists&Engineers 1 5 Particle Physics (4) Particle Physics (4) However, momentum conservation absolutely requires that the sum of the momentum vectors of all particles produced in this collision must be zero...
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This note was uploaded on 04/06/2008 for the course PHY 183 taught by Professor Wolf during the Spring '08 term at Michigan State University.

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W7.4 - February 18, 2008 Physics for...

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