Abstract
One of the most important discoveries on last years in particle physics is the neutrino oscillation.This discovery triggered the development of new experiments to measure the neutrino oscillation parameters with better accuracy.
For these high precision experiments it is crucial to have a good knowledge of neutrino-nucleus interactions, and this is the main motivation for the work here presented.
The measurement of neutrino interaction cross sections on the few GeV regime is complicated since the neutrino interactions are so similar that kinematic observables overlaps.
In this thesis the measurement of the relative Multi-pion neutrino interaction cross section with respect to the quasielastic interaction with charged currents is presented. This measurement has been made with K2K data from the SciBar detector.
K2K is the first long-baseline neutrino oscillation experiment ever done with muon neutrino beam.
On that kind of experiment, both the source and the detection of neutrinos are controlled in the lab.
Production and detection of near neutrinos is made in Tsukuba (Japan) and 250 Km away seats the far detector, in Kamioka (Japan).
For the multi-pion measurement, data from the SciBar and MRD near detectors has been used. SciBar is a detector made off scintillating bars that is able to reconstruct the track of particles produced on neutrino interactions inside the detector. MRD is a muon detector that allows us to reconstruct muon energy and angle.
Neutrinos interacts with matter in different ways. When a neutrino interacts with a neutron producing a muon and a proton, the interaction is called quasielastic. When the interaction produces a muon and two or more pions, the interaction is called multi-pion. Both interactions are charged current interactions, since the neutrino becomes a charged particle in the interaction.
Only the events with a muon detected in MRD and starting in SciBar fiducial volume has been used for the analysis. With these events, six observables has been reconstructed to identify multi-pions and quasielastic interactions. These observables has been combined to create a likelihood asymmetry function that has the property to assign low values to quasielastic events and tend to assign high values to multi-pion events. Other interactions get middle values.
From the fit of the asymmetry function from Monte Carlo to data, the multi-pion relative cross section respect to quasielastics has been obtained for the neutrino energy regions 0.5 to 2.5 GeV and 2.5 to 5.0 GeV.
Measurement systematic errors due to neutrino flux, nuclear effects simulation, event reconstruction and detector response uncertainties has been evaluated.
The result of the multi-pion relative cross section respect to quasielastic interactions measurement is 0.30 +- 0.07 (sta.) +- 0.15 (sys.) for neutrino energies between 0.5 and 2.5 GeV and 3.9 +- 0.6 (sta.) + 1.4 - 1.2 (sys.) for neutrino energies between 2.5 and 5.0 GeV.
| Date of Award | 22 Jul 2008 |
|---|---|
| Original language | English |
| Supervisor | Federico Sánchez Nieto (Director) |