FAQ

What is "hadron"?

The most fundamental particles to constitute matters, the ingredients of starts, the earth, and ourselves, are the quarks. The quarks themselves cannot exist as a single particle, but as a composite particle formed by coupling multiple quarks via strong force. They are called "hadron". A good example of hadron is proton or neutron that consists of three quarks being tightly coupled. The pi meson is the another example which is the coupling of the two quarks. The particle called "lepton" is the other fundamental particle but not being coupled to others via "strong" force. Among them are electron, muon, and neutrino. The electro-magnetic force or the "weak" force acts on these leptons in microscopic scale.

"Why is the name of this center ""ICEHAP"" after hadron, though you are observing neutrinos which are leptons?"

Yes, the neutrinos are leptons. But they are generated by decay of hadrons or their reactions via the "weak" force. They are the only possible mechanisms to produce energetic neutrinos in our cosmos. The existence of neutrinos is indeed a solid signature of existence of high energy hadronic cosmic-rays. We use neutrinos as messengers to identify astro-sources emitting high energy hadrons.

Why the South Pole?

Neutrinos are very rarely interacting with other matters, which makes it challenging to detect them. A practical method to sense the neutrino signals is to detect light radiated from a fast-moving particle called muon initiated by this rarely occurred neutrino collisions. You need a gigantic volume of matters to cause a good number of neutrino induced events. It has to be underground to shield from other irrelevant radiations which could mimic neutrino signals. Furthermore, this volume has to be transparent because we must detect the emitted light. The water is the most inexpensive material to satisfy these demands. The glacier ice has depth of more than 2,500 meters, which brings the huge transparent volume the rare high energy neutrinos can target. This is the idea of IceCube, the world largest underground neutrino detector.

Why do you attempt detecting of high energy neutrinos whose intensity is so low?

As explained above, the high energy neutrinos are products of high energy cosmic-rays, and detecting these secondary neutrinos will allow us to study characteristics of the cosmic-ray sources. From the practical point of view, lower energy neutrinos may be plenty but indistinguishable from the atmospheric neutrinos, the neutrinos produced by radiation in the upper atmosphere. The vast energy of neutrinos, if detected, is a robust signature of astrophysical neutrinos from cosmos.

What does ARA stand for?

The ARA stands for Askaryan Radio Array. The Askaryan effect is the coherent radio emission in UHF band from a group of charged particles moving nearly at the speed of light. This emission is the extension of the Cherenkov radiation into the radio regime. A three dimensional array of radio antennas installed into the deep glacier ice will form the tremendously large neutrino detector, larger than IceCube by a factor of 30 or more.

What is "plasma"?

Plasmas are ionized matters. When the temperature of the gas increases, they are ionized, and become a plasma consisting of ions with positive charge and electrons with negative charge. Since charged particles interact by Coulomb force, the ionized gas behaves differently from the neutral gas. For example, electrons accumulate around a positive charge, and charged particles rotate around magnetic fields.