# Physics at LHC 2012

4-9 June 2012
Life Sciences Centre, UBC
<strong><font color="#cc0000">Abstract submission has closed</font></strong>

## Parameters of the neutrino sector in tau decays

4 Jun 2012, 16:00
1h
West Atrium (Life Sciences Centre, UBC)

### West Atrium

#### Life Sciences Centre, UBC

University of British Columbia Vancouver, BC Canada
Poster Standard Model & Beyond

### Speaker

Darius Jurciukonis (Vilnius University (LT))

### Description

The smallness of the neutrino masses can be well understood within the seesaw mechanism (type I). After spontaneous symmetry breaking of the Standard Model gauge group one obtains a $(n_L+n_R)\times(n_L+n_R)$ Majorana mass matrix $M_\nu$ for neutrinos. The mixing between the $n_R$ right-handed neutrino singlets and the neutral parts of the $n_L$ lepton doublets gives masses for the neutrinos which are of the size expected from neutrino oscillations. The diagonalization of the mass matrix gives rise to a split spectrum consisting of heavy and light states of neutrinos given by $U^T M_\nu U=\mathrm{diag}(m_l,m_h)$. For the case $n_R=1$ we diagonalize the neutral fermion mass matrix with a rotation matrix $U$ determined by three complex angles. For the case $n_R=2$ we parameterize the mass matrix with a rotation matrix $U$ determined by two complex angles and for the diagonalization we apply the Grimus-Lavoura ansatz. In both cases we take $n_L=3$. We calculate the 1-loop radiative corrections to the mass parameters of the neutrino sector of the seesaw extension of the Standard Model which produce mass terms for the neutral leptons. With these ingredients we plan to look at the process $W^\pm \to \tau^\pm + \nu \to h_1^\pm + h_2^\mp + h_3^\pm +\nu+\nu$ and plan to study the $\tau$ polarization coming from the decay of a $W$ boson in the data of the CMS experiment at LHC and thus determine restrictions to the parameters of the neutrino sector.

### <strong>Funding Source</strong>

The European Union Structural Funds project "Postdoctoral Fellowship Implementation in Lithuania"