Tesis doctoral de María Catalina Espinoza Hernandez
Cp-violation in neutrino oscillations from ec/beta(+) decaying ion beams in this work neutrino facilities as variations of the beta beam concept have been presented and their physics reach has been studied. for heavy proton-rich nuclei, their weak decay is, in some privileged cases, dominated by atomic electron capture. The concentration of the gamow-teller strength in a single discrete level of the daughter nucleus allows the generation of an intense monochromatic neutrino beam in the forward direction of the radioactive ion boost. Such a beam is very suitable for the study of the energy dependence of neutrino oscillations. The combination of different energies for the beam, chosen judiciously in the experiment on precise physical basis, presents great potential for the measurement of the unknown neutrino parameters. In particular, cp-violation discovery in neutrino oscillations and the measurement of the cp phase, in the flavour lepton sector of weak interactions, as a phase shift in the interference pattern becomes accessible. This method does not need the results of a neutrino-antineutrino asymmetry in order to obtain evidence for cp-violation. under the assumptions of cpt invariance and absence of absorptive parts, the cp-odd probability is odd in l/e for relativistic neutrino oscillations in vacuum. For a fixed baseline l, the cp-odd term in the appearance probability is an odd function in the energy e, whereas the three cp-even terms are even in e. The energy discrimination provided by the boost of the radioactive ion is then a perfect ingredient to disentangle the cp-odd term. The cp-violation signals are particularly visible in the subdominant transition $ u_e o u_{mu}$, where the two interfering amplitudes in neutrino oscillation phenomena can be made comparable. the simulation of the experiment was made assuming a source of 10^18 ^150dy ions decaying each year in the straight section of the storage ring in the facility. We have chosen two definite boosts in order to reach the highest sensitivities to the neutrino parameters. for a baseline of 130 km, the distance between cern and the underground laboratory at frejus, we have chosen the two values: gamma=90, which corresponds to a neutrino energy somewhat below the first oscillation maximum, and $gamma=195$ corresponding to a neutrino energy above the first oscillation maximum. These boosts are achievable with the present sps facility at cern, corresponding to a proton energy of 450 gev. the statistics is accumulated during a total time of ten years, intending five years for each value of gamma. The detector is a wc detector with a fiducial mass of 440 kton. The main conclusion is that the separation between the two parameters ( heta_{13}, delta) is made possible. The combination of different energies opens up a window for the discovery of cp-violation. This particular setup has, however, a limited sensitivity to measure the cp phase with precision. for an energy upgrade of the sps accelerator up to a proton energy of 1000 gev, we made a comparison of the previous setup with a new one, associated with a five year run at gamma=195 plus a five year run at gamma=440, the maximum achievable at the upgraded sps, with the baseline l=650 km from cern to canfranc or gran sasso. In the last setup, the longer baseline for gamma=195 leads to a value of e/l well inside the second oscillation region. In this case, the associated strip in the ( heta_{13}, delta) plane has a more pronounced curvature, so that the two parameters can be better disentangled. The precision reachable for the cp phase is much better than that in the case of the shorter baseline. The sensitivity to cp-violation is significant even at $ heta_{13} = 1$~degree, or less, in certain cases, when this parameter and the cp phase delta are unknowns at the time of the experiment. if heta_{13} is previously known, as expected if $ heta_{13}geq 3-4$~ degrees, the corresponding analysis for the sensitivity to the cp phase $delta$ shows that the improvement in this sensitivity is impressive, suggesting that going step by step in the determination of parameters by means of several generation experiments is very rewarding. on general grounds, one lesson from these studies is that the best $e/l$ in order to reach a good sensitivity to the cp phase delta is not the same than that for the mixing |u(e3)|. Like the phase shifts in interference phenomena, the presence of $delta$ is apparent when the neutrino energy enters into the region of the second oscillation. instead, the best sensitivity to the mixing appears around the first oscillation maximum. within the strategy of using the energy dependence of neutrino oscillations for the discovery of cp-violation and the measurement of the cp phase, we have considered an alternative to the experimental setups with two different boosts for monochromatic neutrino beams. ytterbium, either ^{152}yb or ^{156}yb, shares its weak decay between the two channels of electron capture and $_x0008_eta^+$. Taking into account the energy gap between the neutrino energies in these two channels, for the same boost of the parent ion, we have at our disposal the presence of well separated neutrino energies in a single experiment with a unique boost. an additional advantage of these isotopes is their smaller lifetime, crucial in order to avoid the stripping of all atomic electrons in the parent ion due to vacuum collisions during acceleration and storage. we have considered the use of a neutrino beam sourced from boosted ^{156}yb ions directed to a single baseline. In the analysis we compare the results for the maximum boosts available from the current sps, gamma=166, and an upgraded sps, gamma=369, for two different baselines, 130 km versus 650 km in the low gamma case, 650 km versus 1050 km in the high gamma case. With the current sps facility, the ec spike is placed on top of the first oscillation for the baseline l=650 km, whereas the beta beam spectrum is peaking around the second oscillation maximum. The detector choice is either a 0.5 mton wc detector or a 50 kton detector based on tracking calorimeter principles (lar or tasd). the conclusion from these comparative studies is that the setup of higher $gamma$, a baseline l=650 km and a wc detector is particularly attractive for the cp-violation discovery potential. The combination of electron capture events and the $_x0008_eta^+$ events is crucial in order to reach a good sensitivity to the cp phase $delta$, even for values of $sin^2(2 heta_{13})=10^{-4}$ or less. The determination of the neutrino mass hierarchy is better obtained, however, for the longer baseline, as expected. the good resolution of the intrinsic degeneracy in the values of the (theta_{13}, delta) plane is due to the fact that the two separate channels, electron capture and beta beam, have a limited overlap in the allowed regions in this plane. This separation is a virtue of the different energy dependence of the cp-odd term from the three cp-even terms in the neutrino oscillation probability. the general conclusion is that the principle of energy dependence works for cp-violation studies, and there is no need of performing separate experiments, with different systematics and counting rates, for neutrinos and antineutrinos. The final physics reach of using proton-rich ions, including the monochromatic neutrinos from the ec decay channel, will depend on the number of events which is controlled by the useful number of ion decays and by the fiducial mass of the detector. The achievable production rate of these ions in future facilities, like eurisol, is an open and crucial ingredient, as it is for light nuclei in beta beams: ne and/or b for neutrino beams, he and/or li for antineutrino beams. In the case of our proposal, with proton-rich ions, there is an important synergy of the neutrino physics community, interested in the problem of cp-violation in neutrino oscillations, with the nuclear physics community, interested in the understanding of the missing gamow-teller strength for these allowed transitions.
Datos académicos de la tesis doctoral «Cp-violation in neutrino oscillations from ec/beta(+) decaying ion beams«
- Título de la tesis: Cp-violation in neutrino oscillations from ec/beta(+) decaying ion beams
- Autor: María Catalina Espinoza Hernandez
- Universidad: Universitat de valéncia (estudi general)
- Fecha de lectura de la tesis: 06/07/2010
Dirección y tribunal
- Director de la tesis
- José Bernabeú Alberola
- Tribunal
- Presidente del tribunal: Francisco jose Botella olcina
- María margarida Nesbitt rebelo (vocal)
- sergio Palomares ruiz (vocal)
- ferruccio Feruglio (vocal)