# Neutrino Physics at QMUL

The neutrino was postulated in 1930 by Pauli and discovered more than 50 years ago by Reines and Cowan.
World-wide interest in neutrinos is motivated by the many aspects of its physics spanning from the understanding of its nature in particle physics to probes of sources at cosmological distances (e.g. supernovas, active galaxies, gamma-ray bursts, etc.), to cosmology, as neutrinos can affect the evolution of the Universe. The experimental picture developed from the late 1990s, in particular through the contributions by Super-Kamiokande in Japan and SNO in Canada, is consistent with three neutrino families undergoing oscillations, i.e. neutrinos created with a specific lepton flavour can later be measured to have a different flavour, which can only happen if neutrinos have masses and mix. Such oscillations indicate that neutrinos, long thought to be massless, must have some small ammount of mass.

Incorporating neutrino oscillations means a modification of the Standard Model, which requires neutrinos to be massless particles, and it is the first direct signal of physics beyond the Standard Model. The phenomenon of neutrino oscillations can be understood by invoking quantum mechanics whereby the weak (or flavour) eigenstates through which the neutrino interacts are not aligned with the mass eigenstates via which the neutrino propagates. The phenomenon of neutrino oscillations is theoretically described via the the so-called Pontecorvo-Maki-Nakagawa-Sakata matrix (PMNS) mixing matrix. The determination of the matrix elements that determine neutrino oscillations are one of the major goals of nowdays neutrino physics.

Finally, if neutrinos are Mayorana fermions, that is a fermion that is its own antiparticles, it is possible for neutrinoless double-beta decay to occur. Neutrinoless double-beta decays have not been observed yet, but they are among the most important processes to discover in neutrino physics.

More detailed information regarding the experiments in which QMUL is involved can be found in the correspondent web pages:

• T2K is a long-baseline neutrino experiment in Japan, from J-PARC to Super-Kamiokande 295 Km away. It started data-taking in 2010, and it presented the first indication of neutrino electron appearance from a muon neutrino beam, that corresponds to the measurement of the theta13 angle in the PMNS matrix. The current goals, aparts from consolidating the measurement of the electron neutrino appearance and improving the error on the measurement of the muon neutrino disappearance, are the measurement of the neutrino mass hierarchy, solving the theta23 degeneracy and set limits on the CP violation parameter. The near detector ND280, 280m away from the neutrino source, also aims to measure neutrino cross sections at energies below 1 GeV.

• Multipurpose low energy neutrino experiment aiming primarily at the measurement of neutrino-less double beta decays, that is the golden channel to measure whether neutrinos are Dirac or Majorana particles. The experiment aims also to measure fir the first time very low energy solar neutrinos coming from the pep nuclear interactions. Other important measurements are the anti-neutrinos from nearby nuclear reactors and geoneutrinos produced by radioactive decays in the Earth's crust and mantle, plus supernova neutrinos, if a supernova explosion happens during the lifetime o fthe experiment. It will start data taking in 2014 studying neutrino-less double beta decays.

• The Hyper-Kamiokande detector is the detector that aims to replace Super-Kamiokande in the next decade as far detector for the T2K updagrade. The Hyper-Kamiokande detector is 25 times larger than Super-Kamiokande. This will be complemented by an increased beam power in the MW range. The prime physics objective of this experiment are to measure the CP violation parameter for the first time using beam and atomospheric neutrinos.

• The LAGUNA-LBNO project is a EU initiative, FP7 founded, to investigate the possibility of a very long baseline neutrino experiment in Europe, to consolidate the study of CP violation and to measure also tau neutrino oscillations. The preferred technology for the far detector is a liquid argon detector. The muin neutrino beam will star at CERN, and detector at the far detector in Finland.

### Phenomenology

• We are also involved in phenomenology work in collaboration with the University of Southampton, and the University of London through the NExT network, and with IPPP Durham, and we are both working on oscillation physics and neutrino-less double beta decays.

Last update, December 23, 2012