Solving the octant degeneracy with the silver channel

Davide Meloni

doi:10.1016/j.physletb.2008.05.031

Abstract

We study the potential of the combination of the golden (νe→νμ) and silver (νe→ντ) channels to solve the octant degeneracy affecting the measurement of θ13 and δ at future neutrino factories. To search for τ leptons produced in ντ charged-current interactions, we consider two different detectors: the Emulsion Cloud Chamber detector (ECC) and the Liquid Argon Time Projection Chamber (LAr TPC). We show that, when using similar detector masses, the upgraded version of the ECC detector (sensitive also to hadronic τ decay modes) and the LAr TPC detector have comparable sensitivities to the octant of θ23, being able to discriminate the two solutions for sin2(2θ13)≳10−3 at 3σ level if θ23=40°. We also show that the same setups are able to see deviation from maximal mixing as small as ∼ (4–6)% (at 3σ) if θ13 is close to its upper bound.

Highlights

The simultaneous measurement of the two still unknown neutrino mixing parameters θ13 and δ can be considered as one of the main neutrino-physics goal for the decade [1]
In this paper we have analyzed the potential of the combination of golden and silver transitions to solve the octant degeneracy problem, affecting the future measurement of θ13 and δ
Starting form the transition probabilities in vacuum, we have shown that, in many cases, the octant clones are located in different points of the (θ13,δ)-parameter space and that a promising synergy in solving this degeneracy exists

Summary

INTRODUCTION

The simultaneous measurement of the two still unknown neutrino mixing parameters θ13 and δ can be considered as one of the main neutrino-physics goal for the decade [1]. If one uses the parametrization of the three-family leptonic mixing matrix UP MNS [4] suggested in the PDG [5], θ13 and δ always appear in the combination sin θ13 e±i δ and a measurement of the CP-phase δ cannot be achieved independently on θ13: the two parameters have to be measured at the same time. Such a correlation stains the achievable precision on the parameter measurements since some θ13 and δ can reproduce the same ”true” physics (number of expected events) at some confidence level, a situation which is known as the degeneracy problem.

THE OCTANT DEGENERACY

COMBINING THE MIND AND ECC DETECTORS

THE LIQUID ARGON TIME PROJECTION CHAMBER

DEVIATION FROM MAXIMAL MIXING

Findings

CONCLUSIONS