![]() Leptons can roughly be divided into two distinct families - charged and uncharged - and within these categories, further subcategories exist. Each lepton is ‘haunted’ by its own ‘ghost particle’ neutrino (Wikipedia Commons/MissMJ/PBS NOVA/Fermilab/Particle Data Group) The particle zoo according to the standard model of particle physics. And just like electrons, neutrinos are classed as ‘leptons’ - particles with a ‘spin’ of 1/2 that do not interact with the strong force. In many respects, neutrinos are very similar to electrons in terms of the influences they feel. Only the weak force - which mitigates how atoms decay and how fundamental particles change ‘flavour’ - has any real effect on the neutrino. Likewise, the strong nuclear force - mainly at play between protons and neutrons in atomic nuclei- has no baring on neutrinos. This lack of substantial mass and charge means that of the Universe’s four fundamental forces neutrinos barely ‘feel’ gravity and aren’t influenced by electromagnetic forces at all. They are certainly far smaller than the other elementary particles. In fact, the mass of neutrinos is so tiny that for many years, scientists believed it was zero. Neutrinos are fundamental particles that, as mentioned above, are almost massless and completely chargeless. A ghost in the particle zoo: What is a neutrino? The hunt for more neutrinos was on, and it would require ever more complex and sensitive methods and equipment, pushing the limits of experimental physics. It would be another two decades, give or take, before American physicists Clyde Cowan and Frederick Reines, from Washington New York Universities respectively, would conduct an eponymous experiment to detect neutrinos being emitted from a nuclear reactor. Beta-decay actually resulted in a proton, an electron and a neutrino - more specifically an antineutrino.īeta-decay as it understood today results in three daughter particles with the anti-neutrino carrying away the missing energy that troubled Pauli. This violated the conservation laws for both properties, but Pauli postulated that if there were some non-interacting particle carrying away energy and angular momentum, that would prevent such a violation. Neutron decayed into protons and electrons - but these daughter products had less energy and angular momentum than their parent. With neutrinos, initial speculation began in the 1930s when one of the fathers of quantum physics Wolfgang Pauli noticed that in beta-decay, both energy and angular momentum were not being conserved. ![]() The discovery of a new element or phenomena in physics is usually born from the observation of a missing piece of the Universe’s overall jigsaw, the need to explain some facet of nature that defies expectation. But, the discovery of the neutrino has humble origins, merging from the need to preserve some of physics’ earliest and most important governing principles. ![]() The study of neutrinos is so vital to modern physics that it could explain lingering conundrums such as the nature of dark matter and even deliver the key to a quantum theory of gravity. Even more exotic neutrinos originate from violent cosmic events like gamma-ray bursts and supernovae outside our solar system. These neutrinos emerge from a variety of sources the majority of those that reach us here on Earth originate from the Sun, created by the nuclear processes that power our star, others are created in the upper atmosphere when it is struck by cosmic rays. ![]() The first detection of a neutrino in a bubble chamber in 1970 (Argonne National Laboratory) It’s no wonder some scientists have neutrinos on the brain, with so many constantly passing through it. Especially true when considering that this particle is so weakly interacting, that as you have been reading this opening paragraph, hundreds of billions of them have streamed through every square inch of your body. It may seem tempting to conclude that dedicating an entire week-long conference to a single particle is hyperbole at best. For one week every year, physicists from all over the globe come together to discuss the physics surrounding one particle - the neutrino. ![]()
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