![]() ![]() Luckily, proton decay is a statistical process. Unfortunately, this search would not be an easy one, as the predicted lifetime of the proton (or bound neutron) was 10 28–30 years! The observation of proton decay would therefore be evidence for grand unification, and several experimental groups were formed to attempt this search. This theory, named SU(5) after the mathematical group that it contained, predicted that the proton, until then thought to be an absolutely stable particle, would decay into other particles. It would provide a unified explanation for the electromagnetic, strong, and weak interactions. They hoped that this theory would join three of the four forces of nature together into one theoretical construct. ![]() In the 1970s theoretical physicists were hot on the trail of what they believed would be a Grand Unified Theory. There is no way to identify beam neutrinos immediately the data have to be carefully analyzed, later, to determine whether a particular event arrived during the very tiny time window when beam neutrinos passed through Super-K (half a microsecond, about once every three seconds, when the J-PARC beam is operating).CASE STUDY: SUPER-KAMIOKANDE AND THE DISCOVERY OF NEUTRINO OSCILLATIONS Also, only a few hundred out of the millions of events recorded at Super-K each year will be due to neutrinos that came from J-PARC. Physicists on duty at Super-K to babysit the experiment can switch to another map version, which shows the relative time of arrival of the light signals. The public version of the real-time event display does not show every event that is recorded at Super-K, but only a random sample every few seconds. These muons are of some interest too, since they were created along with neutrinos by the decay of pions and other short-lived subatomic particles in the upper atmosphere, and they allow us to continuously check the health of the detector. Most of the events recorded are not due to neutrinos, but to downward-going muon particles that were not stopped by the 1000 meter thickness of rock overhead. Offline (minutes or hours later) computer algorithms check the event data to see if the pattern of light observed corresponds to a neutrino interaction. The Super-K detector is equipped with sophisticated electronics to acquire data without any “dead time” after an event is recorded, so rapid sequences of events can be logged. All phototube data are logged for later analysis. A computer algorithm rates each event as e-like or muon-like - some events are ambiguous and may have to be checked by a physicist.Īn “event” is recorded whenever a significant amount of activity is observed in the phototubes within a brief time window. (If the ring were sharp-edged, the event would be identified as “muon-like”). The direction of the electron is very close to the direction of the incoming neutrino that produced it. ![]() The location and shape of the ring tell us the direction of the electron. In the example above, the electron produced by an electron neutrino scatters in the water, producing a fuzzy ring of Cherenkov light. If the info at upper left says the run is “normal” then data taking is underway sometimes you may see “calibration” or “test”, meaning physicists are working on the detector or its data acquisition electronics. The smaller map at upper right shows a similar map of the outer detector, which has only about 1800 phototubes. Each dot is one phototube, and its color represents the relative amount of light it collected, in terms of the amount of electric charge produced by the phototube, during the 1.3 microsecond time window in which the displayed data were logged. Imagine a tin can, with its top and bottom lids cut off and bent back, and its barrel slit and folded flat: that is how the event display is presented. The event display is a map of the inner detector phototube array, showing the intensity of light received by each tube in any given event. The Super-K detector is lined with over 11,000 phototubes, each 50cm in diameter. Here is an example of an electron-like neutrino “event” (interaction) in the Super-K water Cherenkov detector: How to understand the Super-K event display ![]()
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