11 Dynamics of Elementary Particles

Modern Physics

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PHY251 - Elementary Particles PHY 251 Dynamics of Elementary Particles Introduction Elementary particles are everywhere around us. Apart from the standard matter particles proton, neutron and electron, hundreds of other particles have been found, produced in cosmic ray interactions in the atmosphere or by accelerators. Hundreds of charged particles traverse our bodies per second, and some will damage our DNA, one of the reasons for the existence of a sophisticated DNA repair mechanism in the cell. The data for this experiment is in the form of a bubble chamber photograph which shows bubble tracks made by elementary particles as they traverse liquid hydrogen. In the experiment under study, a beam of low-energy negative pions ( π - beam) hits a hydrogen ( p for proton) target in the form of a container with liquid hydrogen normally kept just below its boiling point ( T =20 K). As the pions enter the detector a piston slightly decompresses the liquid so it becomes ``super-critical'' and starts boiling (i.e. bubble formation) first at the ionization (protons and electrons) trails left by the charged particles traversing the liquid. photo - overview Figure 1: Photograph of the interaction between a high-energy π - - meson from the Berkeley Bevatron accelerator and a proton in a liquid hydrogen bubble chamber, which produces two neutral particles Λ 0 and K 0 , which are short-lived and decay into charged particles a bit further. definitions Figure 2: illustration of the interaction, and identification of bubble trails and variables to be measured in the photograph in Figure 3. The reaction photographed in Figure 1 shows the production of a pair of neutral particles (that do not leave a ionized trail in their wake), which after a short while decay into pairs of charged particles: π - + p Λ 0 + K 0 , where the neutrals decay as follows: Λ 0 p + π - , K 0 π + + π - .
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This lab report was uploaded on 02/05/2008 for the course PHY 251 taught by Professor Rijssenbeek during the Fall '01 term at SUNY Stony Brook.

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11 Dynamics of Elementary Particles - PHY251 - Elementary...

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