Experimental Neutrino Physics
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Research
The experimental neutrino physics group at Drexel is actively involved in the
two state-of-the-art international experiments and one future project, all dedicated to the studies of
fundamental properties of neutrinos. Neutrinos are among the most elusive and least known elementary particles. It's been known for a long time that neutrinos are very light particles,
perhaps even massless particles that travel at the speed of light. But there's never been a compelling reason _why_
they should be massless, unlike the vast majority of subatomic particles, and yet no evidence that they actually had mass.
Before the discovery of neutrino oscillation, the lightest particles
known to have mass was the electron, about 2000 times lighter than
the proton or neutron. Neutrino oscillation showed that neutrinos
do have some mass (without mass, they don't oscillate), and while the
oscillation gives mass differences, the results make clear that
neutrinos are much lighter than even electrons; perhaps a million times
lighter. It is still a puzzle how neutrinos got a mass that is so close
to zero, yet not quite zero. Neutrino mass may provide answers to some of the most fundamental questions of the physics today: from the contribution to the missing mass of the universe to the explanation of the dominance of matter over antimatter in the universe.
Our group is involved
in the KamLAND experiment in Japan that made a high precision measurement of neutrino oscillation parameters with antineutrinos coming from nuclear reactors around Japan and beyond. KamLAND made the first ever experimental detection of antineutrinos of geological origin coming from beta decays in radioactive decay chains of uranium and thorium inside the Earth. In 1904, Ernest Rutherford hypothesized that radioactive decays of uranium and thorium provide a source of the internal heat of the Earth. KamLAND measurement proved that indeed large fraction of the Earth's internal heat comes from radioactivity.
We live in a matter dominated universe, although the birth of our universe was characterized by production of equal amounts of matter and antimatter in the Big Bang explosion. At some point, in early universe, matter won, and became dominant in the cooling, expanding universe due to a CP violation effect or a slightly different behavior exhibited between matter and antimatter. Although CP violation has been observed in quarks, the effect is insufficient to account for the amount of matter in the universe today. This raises a question if such an effect may exist in neutrinos. But to measure the CP-violation in neutrinos, one must first esaublish the size of the neutrino mixing angle Theta 13 that always appears as a multiplication factor along with the CP-violation phase. The size of Theta 13 will directly influence our ability to measure CP-violation in neutrinos and its role in the dominance of matter over antimatter in the universe!
The Double Chooz experiment is currently
being built in France and will get an early measurement or a limit of the remaining neutrino mixing angle Theta13 with antineutrinos coming from the Chooz nuclear reactor plant. Early measurement of Theta 13 is of the utmost importance for all future experimental searches for
the CP-violation effect in neutrinos.
Finally, group is involved in the design studies for the future Hanohano
experiment that will search for geological neutrinos originating in the
Earth's mantle. This measurement will be instrumental in learning about
the mantle composition, of which very little is known today and direct
experimental data are scarce.
Last modified on November 27, 2008 by jelena@physics.drexel.edu