1. The Search for Proton Decay at Super- Kamiokande ASTR-007 Theodore Liu

2. Proton Decay overview  Protons not infinitely stable, as once thought  Required for grand unification theories  Binds the electromagnetic, weak, and strong forces into one single force  Existed about 10 -40 seconds after Big Bang, with a temperature of around 10 27 K

3. Proton Decay specifics  If grand unification occurs, quarks would be able to transform into leptons through the exchange of a supermassive particle dubbed the X boson.  This process requires that protons decay to form the quarks, something generally not allowed by the Standard Model.

4. Search for Proton Decay  Proton decay would have to occur over extremely long time scales, or else the matter of the universe would not hold together.  Experiments to detect proton decay can only establish a lower limit for a proton’s half-life.

5. Search Methods specifics  A proton typically decays into a positron and a neutral pion.  Positron annihilates with an electron.  Pion almost immediately decays into two photons in the gamma range.  If the reaction is in water, the radiation released is known as Cerenkov radiation and can be detected.

6. Cerenkov Radiation When a particle moving faster than the speed of light in water enters water, it slows down to adjust to the local speed of light of the new medium. This produces a cone of light analogous to how a supersonic jet will produce a sonic boom. Cerenkov radiation giving off its characteristic blue glow in a UMR reactor core

7. Super-Kamiokande  Massive neutrino observatory situated insided an active zinc mine in Mount Ikenoyama, Japan  Contains 50,000 tons of ultrapure water, lined with more than 11,000 photomultiplier tubes to detect Cerenkov radiation

8. Super-Kamiokande findings  No detected proton decay yet since observations began in 1996  Does not mean that proton decay is not possible, simply that the lower bound is in the range of 10 35 years Interior of the Super-K detector

9. Works Cited http://hyperphysics.phy- astr.gsu.edu/HBASE/particles/neutrino2. html#c1 http://hyperphysics.phy- astr.gsu.edu/HBASE/particles/neutrino2. html#c1 http://hep.bu.edu/~superk/pdk.html http://en.wikipedia.org/wiki/Proton_decay Halcomb & Hawley