|The Borexino detector at Gran Sasso: the SOX experiment will soon be using it to look for sterile neutrinos. (Courtesy: Borexino collaboration)|
Much-debated results suggesting the existence of a fourth kind of neutrino, described as sterile, are to be put to the test in a new experiment under Italy's Gran Sasso mountain. The physicists who have devised the experiment say that by using an existing solar-neutrino detector they can carry out an inexpensive yet thorough search for the hypothetical sterile neutrino.
Neutrinos are chargeless, almost massless subatomic particles that interact with ordinary matter only via the weak nuclear force. As a result they can pass through vast amounts of material undisturbed. To study them, physicists build huge detectors – the idea being that a large number of target nuclei will result in a few neutrino collisions that can be detected.
If they exist, then sterile neutrinos would be even more difficult to detect because they probably would not interact with ordinary matter at all – only with other neutrinos. They would do so via "oscillation", a well-established phenomenon in which ordinary neutrinos transform and re-transform continually from one of three flavours – electron, muon and tau – to another as they travel. Likewise, ordinary neutrinos would oscillate into sterile neutrinos and back again but probably over much shorter distances than those typical of normal neutrino oscillation.
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