2. The Pion CROP: Roncalli Division Timothy Willett Roy Lehn Dwight Johns

3. Etymology of the Pion (Pi Meson) The Pion is also known as the Pi Meson Among the mesons, the pion (or pi meson) is the lightest The symbol given for the pion is very difficult to remember : <http://www.cecm.sfu.ca/projects/pihex/>

4. The Prediction of a Particle In 1935, Hideki Yukawa predicted the presence of a particle that would be “responsible for the force of the strong interactions holding the atomic nucleus together.” Hideki Yukawa <http://www.nobel.se/physics/laureates/1949/yukawa-bio.html> www.factmonster.com

5. The Discovery of the Pion 12 years later, in 1947, C. F. Powell detected a particle in cosmic rays which fit Yukawa’s hypothesis This particle became known as the pion www.factmonster.com Cecil F. Powell (1903-1969) www.siux00.physik.uni-siegen.de

6. How Did He Do It? Between 1939 and 1945, Powell developed techniques which utilized photographic emulsions to record the paths of cosmic rays He exposed plates on the tops of mountains and in high-altitude balloons His work was able to confirm the existence of this new particle, the pion Encyclopedia Britannica

7. The Characteristics of Pions Mass –charged pions have a mass 1/7 of a proton’s mass, which correlates to the mass of 273 electrons –neutral pions have 264 electron-masses Charge –pions have a positive, negative, or neutral charge –the degree of charge on the positive and negative pions is one Life-time –Charged pions have a lifetime of about 2.55 x 10 -8 seconds –Neutral pions have a lifetime of about 10 -15 seconds www.triumf.ca www.factmonster.com

8. Interactions Charged pions usually break down into muons and neutrinos Neutral pions usu. decay into a pair of photons The neutral pion is its own antiparticle