The Event Display

The event display shows "pictures" of neutrino events, as seen by Super-K. This is like an "unrolled" soda pop can (a pretty big one). Each dot shows a photomultiplier tube that has detected something.

Here is an example of an event display:


The top circle is the top of the detector (think: top of soda can), the middle rectangle shows the cylindrical wall of the detector, while the bottom circle is the bottom of the detector. As you may have guessed, the rings of detected light are the Cerenkov light rings.

For our exercise, you will be looking at actual Super-K event displays of neutrino interactions!

How Do I Read This Thing?

• > Each dot on the display represents one phototube.
• > There are two modes of display: Charge Mode and Time Mode
• > "Charge Mode" shows you by colors how much charge each tube has. We use Charge Mode to determine what flavor neutrino interaction has occurred.
  • - There is a key toward the left of the display: red represents the highest charge, while violet represents the lowest
• > "Time Mode" shows you by colors what time each tube was hit by the photon. We use Time Mode to determine if the neutrino was up-going or down-going.
  • - There is a key toward the left of the display: red represents the earliest time, while violet represents the latest

Example 1:
Electron Neutrino

	Charge Mode This is an example of an event display in Charge Mode. As you can see, the PMTs detect a lot of scattering, and thus the Cherenkov cone appears fuzzy. The fuzziness is due to the shower of electrons that were produced, which caused the many overlapping Cherenkov rings. Thus, we can conclude that this event was caused by an electron neutrino
	Time Mode This is the same event, only in Time Mode. The PMT hits that are in red occurred earlier than those in yellow, which occurred earlier than those in blue, etc. Now let's look at the display. The top left is more red/orange, while the bottom right is more yellow/green. This tells us that this neutrino is going from the top to the bottom, or simply down-going

Example 2:
Muon Neutrino

	Charge Mode Again, this is displayed in Charge Mode. This time, the PMTs show a fairly clean, sharp-edged ring. This is evidence for a muon neutrino
	Time Mode This is the same event except displayed in Time Mode. Again, note the time scale and compare it with the hits that the PMTs show. In this display, the top is more orange and the bottom is more green. Thus, this muon neutrino is also down-going

Scanning Instructions

• > First, familiarize yourself with the event display features above. You will be doing this on the next page.
• > Don't hesitate to ask questions about anything!
• > For each event on your list:
  • » Look at the pattern of Cherenkov light in the event.
  • » First, figure out how many rings are in the event, and choose "1" for a single ring, "2" for a double ring, or "3+" if there are three or more rings. The single rings are the cleanest sample for looking at neutrino interactions, and these are the events we'll be counting up at the end.
  • » For single ring events, decide if the ring is a "mu-like" (has a sharp ring, mostly inside the Cherenkov cone) or "e-like" (has a fuzzy, diffuse ring, a lot of light outside the Cherenkov cone). For multiple rings, you can omit this step.
  • » For single ring events, try to visualize the direction of the cone. Use the timing colors to help you figure out which way the light is going. It takes as bit of practice. Tick off "up-going" or "down-going" on the sheet. For multiple rings, you can omit this step.
  • » Scroll down to get the next event.
• > The "Cheat Sheet" gives the answers that were determined by computer programs for each of the event characteristics. These answers are usually, but not always, correct. If you are stumped, take a look at the cheat sheet, but try to figure it out yourself first and then check the sheet later.
• > Go through as many events as you can. If you don't finish, dont worry.
• > After finishing, count up:
  • » The number of single-ring up-going e-like events
  • » The number of single-ring down-going e-like events
  • » The number of single-ring up-going mu-like events
  • » The number of single-ring down-going mu-like events
  and fill in the analysis sheets (there will be a link). Then we'll add up the results from the four groups and calculate the up/down asymmetry and its uncertainty, to show that muon neutrinos from below are disappearing.