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Physik-Institut The SHiP experiment at UZH

Sterile Neutrinos

The matter particles of the Standard Model consist of six quarks and six leptons (left figure). Quarks and leptons are organize in three families. Each family consists of the particles that differ by one unit of electric charge. For instance the "up-type" quarks have charge +2/3 and "down-type" quarks have electric charge -1/3. Charged leptons (like the electron) have electric charge -1, while neutrinos are neutral. In addition, all particles apart for neutrinos, exists in two chirality states: left-handed and right-handed. The reason why neutrinos only have one chirality state is related to the fact that in the Standard Model neutrinos are massless. However, we have now strong experimental evidences that neutrinos have a small but non-vanishing mass.

The picture of nuMSM.
A straightforward way to complete the Standard Model is to add to it 3 right-handed neutrinos (right figure). These particles are often called Sterile Neutrinos, Majorana Neutrinos or Heavy Neutral Leptons. In addition of explaining neutrino masses, right-handed neutrinos have also important cosmological and astrophysical implications. If the lightest of these neutrinos has a mass in the KeV region (about 1000 times lighter than the electron), this particle would have a lifetime much longer than the age of the Universe and it is a possible Dark Matter candidate. Moreover, right-handed neutrinos would have played a key role in the early Universe. They can explain the asymmetry between matter and anti-matter in our Universe via a process known as leptogenesys.

The  SHIP experiment, of which our group has been one of the main proponents, has been designed and optimized to search for these particles.