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Register a new userFour species neutrino oscillations at $ u$-Factory: sensitivity and CP-violation
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A. Donini
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The prospects of measuring the leptonic angles and CP-odd phases at a {em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino. We consider the $ u_mu raw u_e$ LSND signal. Its associated large mass difference leads to observable neutrino oscillations at short ($sim 1$ km) baseline experiments. Sensitivities to the leptonic angles down to $10^{-3}$ can be easily achieved with a 1 Ton detector. Longer baseline experiments ($sim 100$ km) with a 1 Kton detector can provide very clean tests of CP-violation especially through tau lepton detection.
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We explore the potential of several Neutrino Factory (NF) setups to constrain, discover and measure new physics effects due to Non-Standard Interactions (NSI) in propagation through Earth matter. We first study the impact of NSI in the measurement of $theta_{13}$: we find that these could be large due to strong correlations of $theta_{13}$ with NSI parameters in the golden channel, and the inclusion of a detector at the magic baseline is crucial in order to reduce them as much as possible. We present, then, the sensitivity of the considered NF setups to the NSI parameters, paying special attention to correlations arising between them and the standard oscillation parameters, when all NSI parameters are introduced at once. Off-diagonal NSI parameters could be tested down to the level of $10^{-3}$, whereas the diagonal combinations $(epsilon_{ee} - epsilon_{tautau})$ and $(epsilon_{mumu}-epsilon_{tautau})$ can be tested down to $10^{-1}$ and $10^{-2}$, respectively. The possibilities of observing CP violation in this context are also explored, by presenting a first scan of the CP discovery potential of the NF setups to the phases $phi_{emu}, phi_{etau}$ and $delta$. We study separately the case where CP violation comes only from non-standard sources, and the case where it is entangled with the standard source, $delta$. In case $delta$ turns out to be CP conserving, the interesting possibility of observing CP violation for reasonably small values of the NSI parameters emerges.
Measurements of CP--violating observables in neutrino oscillation experiments have been studied in the literature as a way to determine the CP--violating phase in the mixing matrix for leptons. Here we show that such observables also probe new neutrino interactions in the production or detection processes. Genuine CP violation and fake CP violation due to matter effects are sensitive to the imaginary and real parts of new couplings. The dependence of the CP asymmetry on source--detector distance is different from the standard one and, in particular, enhanced at short distances. We estimate that future neutrino factories will be able to probe in this way new interactions that are up to four orders of magnitude weaker than the weak interactions. We discuss the possible implications for models of new physics.
We discuss the potential of the Sudbury Neutrino Observatory (SNO) to constraint the four--neutrino mixing schemes favoured by the results of all neutrino oscillations experiments. Our results show that some information on the value of $cos^2(vartheta_{23}) cos^2(vartheta_{24})$ can be obtained by the first SNO measurement of the CC ratio, while considerable improvement on the knowledge of this mixing will be achievable after the measurement of the NC/CC ratio.
We consider a version of the low-scale type I seesaw mechanism for generating small neutrino masses, as an alternative to the standard seesaw scenario. It involves two right-handed (RH) neutrinos $ u_{1R}$ and $ u_{2R}$ having a Majorana mass term with mass $M$, which conserves the lepton charge $L$. The RH neutrino $ u_{2R}$ has lepton-charge conserving Yukawa couplings $g_{ell 2}$ to the lepton and Higgs doublet fields, while small lepton-charge breaking effects are assumed to induce tiny lepton-charge violating Yukawa couplings $g_{ell 1}$ for $ u_{1R}$, $l=e,mu,tau$. In this approach the smallness of neutrino masses is related to the smallness of the Yukawa coupling of $ u_{1R}$ and not to the large value of $M$: the RH neutrinos can have masses in the few GeV to a few TeV range. The Yukawa couplings $|g_{ell 2}|$ can be much larger than $|g_{ell 1}|$, of the order $|g_{ell 2}| sim 10^{-4} - 10^{-2}$, leading to interesting low-energy phenomenology. We consider a specific realisation of this scenario within the Froggatt-Nielsen approach to fermion masses. In this model the Dirac CP violation phase $delta$ is predicted to have approximately one of the values $delta simeq pi/4,, 3pi/4$, or $5pi/4,, 7pi/4$, or to lie in a narrow interval around one of these values. The low-energy phenomenology of the considered low-scale seesaw scenario of neutrino mass generation is also briefly discussed.
We examine the constraints on the MNS lepton mixing matrix from the present and future experimental data of the neutrino oscillation and lepton number violation processes. We introduce a graphical representation of the CP violation phases which appear in the lepton number violation processes such as neutrinoless double beta decay, the $mu^--e^+$ conversion, and the K decay, $K^-topi^+mu^-mu^-.$ Using this graphical representation, we derive the constraints on the CP violation phases in the lepton sector.
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