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January - December 2011

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University of Minnesota Twin Cities
College of Science and Engineering
School of Physics and Astronomy

PI: Yong-Zhong Qian

Neutrino Flavor Evolution in Supernovae

Using neutrinos produced by nuclear reactions in the sun, by interaction of cosmic rays with the earth’s atmosphere, and by accelerators and nuclear reactors on earth, a number of experiments showed that neutrinos oscillate among different flavors and therefore have mass. Yet some key parameters characterizing neutrino oscillations are unknown. New experiments such as MINOS, in which the University of Minnesota plays a prominent role, are being carried out to probe these unknown parameters. Interestingly, supernovae that signify the explosive death of massive stars are prodigious sources of neutrinos and provide another venue to study neutrino oscillations. In fact, the number density of neutrinos near the core of a supernova is so large that new phenomena of neutrino oscillations arise. In particular, the flavor evolution for neutrinos of different energies traveling in different directions may be coupled together to produce collective oscillations. This new phenomenon is extremely sensitive to the unknown neutrino oscillation parameters, thereby allowing the extraction of these parameters from the detection of neutrinos from a future supernova.

These researchers are simulating flavor evolution of supernova neutrinos taking into account the coupling among neutrinos of different energies traveling in different directions. They have successfully tested their codes at MSI. They are using these codes to study the simultaneous evolution of all three flavors of neutrinos and antineutrinos. They will also explore the effects of various neutrino energy spectra and matter density profiles in different supernova environments. The results from the study will allow the researchers to assess quantitatively the potential to probe unknown neutrino oscillation parameters with supernova neutrino signals, as well as determine the effects of neutrino oscillations on various physical processes in supernovae.

Group Member

Meng-Ru Wu, Graduate Student