PhyLiNO: a forward-folding likelihood-fit framework for neutrino oscillation physics

Over the last 20 years measurements of neutrino oscillation parameters have become very precise. In the standard neutrino oscillation picture most of the parameters are measured at the percent level. In this thesis we study neutrino oscillations in the standard picture and beyond. We analyze data from all types of neutrino oscillation experiments to obtain a global picture of neutrino oscillations. The remaining unknowns in the standard picture are the value of the CP-violating phase $\delta$, the octant of the atmospheric angle $\theta_{23}$ and the neutrino mass ordering. We discuss the current status of these unknowns and also comment on how well future experiments will do in measuring these quantities, where we discuss new facilities which will observe accelerator, atmossperic and reactor neutrinos. Using oscillation data it is possible to bound a possible violation of the CPT symmetry in the neutrino sector. This is done by performing a fit to neutrino and antineutrino oscillation data separately. We also address the capability of the future experiment DUNE to this scenario. We show that DUNE could improve some of the current bounds considerably. We discuss the sensitivity of DUNE together with the next generation reactor neutrino experiment JUNO to measure quasi-Dirac neutrino oscillations. We find that the future experiments will be able to bound the important quantities, mostly unbounded by current data. Finally, we discuss atmospheric neutrinos at the next generation neutrino telescope ORCA. We show that ORCA will put the best bounds on the invisible neutrino decay of $\nu_3$, coming from neutrino oscillation experiments. We also find that, a scenario like this would not affect the standard measurements of ORCA, namely the determination of the atmospheric neutrino oscillation parameters and the measurement of the neutrino mass ordering.

Determination of the neutrino mass hierarchy, octant of the mixing angle theta_{23} and the CP violating phase delta_{CP} are the unsolved problems in neutrino oscillation physics today. In this paper our aim is to obtain the minimum exposure required for the proposed Long Baseline Neutrino Oscillation (LBNO) experiment to determine the above unknowns. We emphasize on the advantage of exploiting the synergies offered by the existing and upcoming long-baseline and atmospheric neutrino experiments in economising the LBNO configuration. In particular, we do a combined analysis for LBNO, T2K, NOvA and INO. We consider three prospective LBNO setups -- CERN-Pyhasalmi (2290 km), CERN-Slanic (1500 km) and CERN-Frejus (130 km) and evaluate the adequate exposure required in each case. Our analysis shows that the exposure required from LBNO can be reduced considerably due to the synergies arising from the inclusion of the other experiments.

T2K is a long baseline neutrino oscillation experiment, located in Japan. A muon (anti)neutrino beam peaked at 0.6 GeV is produced in the J-PARC facility and measured by near detectors and the Super-Kamiokande far detector. The main goal is to measure the neutrino oscillation parameters. T2K can run in both neutrino and antineutrino mode, enhancing the sensitivity to charge-parity violation (CPV) in the lepton sector. Measuring oscillation parameters requires precise knowledge of the (anti)neutrino interaction cross sections. We present an improved cross section analysis which utilizes combined data samples of multiple detectors and in multiple beam configurations, the first of its kind. It will be used to measure the muon neutrino and antineutrino cross sections on carbon with no final state pions. This technique fully exploits the correlations between the samples' systematic uncertainties, allowing for their efficient cancellation. Since the two utilized T2K near detectors sample different neutrino energy spectra, this measurement will allow to better understand the energy dependence of neutrino interactions, thereby offering a direct probe of the processes that are responsible for the largest uncertainties in T2K oscillation analyses. In addition, by measuring both neutrino and antineutrino cross sections, it is possible not only to better tune theoretical models of nuclear effects such as multinucleon interactions, but also to properly understand the asymmetry between neutrino and antineutrino interactions, the latter being of fundamental importance for CPV experiments that measure the asymmetry between neutrino and antineutrino oscillation rates.

Encouraged by the recent results from neutrino oscillation experiments, we perform an analytical study of SO(10)-inspired models and leptogenesis with hierarchical right-handed (RH) neutrino spectrum. Under the approximation of negligible misalignment between the neutrino Yukawa basis and the charged lepton basis, we find an analytical expression for the final asymmetry directly in terms of the low energy neutrino parameters that fully reproduces previous numerical results. This expression also shows that it is possible to identify an effective leptogenesis phase for these models. When we also impose the wash-out of a large pre-existing asymmetry NB−Lp,i, the strong thermal (ST) condition, we derive analytically all those constraints on the low energy neutrino parameters that characterise the ST-SO(10)-inspired leptogenesis solution, confirming previous numerical results. In particular we show why, though neutrino masses have to be necessarily normally ordered, the solution implies an analytical lower bound on the effective neutrino-less double beta decay neutrino mass, mee≳8 meV, for NB−Lp,i=10−3, testable with next generation experiments. This, in combination with an upper bound on the atmospheric mixing angle, necessarily in the first octant, forces the lightest neutrino mass within a narrow range m1≃(10–30) meV (corresponding to ∑imi≃(75–125) meV). We also show why the solution could correctly predict a non-vanishing reactor neutrino mixing angle and requires the Dirac phase to be in the fourth quadrant, implying sin⁡δ (and JCP) negative as hinted by current global analyses. Many of the analytical results presented (expressions for the orthogonal matrix, RH neutrino mixing matrix, masses and phases) can have applications beyond leptogenesis.

Heavy neutrinos with masses below the electroweak scale can simultaneously generate the light neutrino masses via the seesaw mechanism and the baryon asymmetry of the universe via leptogenesis. The requirement to explain these phenomena imposes constraints on the mass spectrum of the heavy neutrinos, their flavour mixing pattern and their CP properties. We first combine bounds from different experiments in the past to map the viable parameter regions in which the minimal low scale seesaw model can explain the observed neutrino oscillations, while being consistent with the negative results of past searches for physics beyond the Standard Model. We then study which additional predictions for the properties of the heavy neutrinos can be made based on the requirement to explain the observed baryon asymmetry of the universe. Finally, we comment on the perspectives to find traces of heavy neutrinos in future experimental searches at the LHC, NA62, BELLE II, T2K, SHiP or a future high energy collider, such as ILC, CEPC or FCC-ee. If any heavy neutral leptons are discovered in the future, our results can be used to assess whether these particles are indeed the common origin of the light neutrino masses and the baryon asymmetry of the universe. If the magnitude of their couplings to all Standard Model flavours can be measured individually, and if the Dirac phase in the lepton mixing matrix is determined in neutrino oscillation experiments, then all model parameters can in principle be determined from this data. This makes the low scale seesaw a fully testable model of neutrino masses and baryogenesis.

Direct measurements of the core-collapse supernova rate in the redshift range 0<z 1 appear to be about a factor of two smaller than the rate inferred from the measured cosmic massive-star formation rate (SFR). We explore the possibility that one could clarify the source of this "supernova rate problem" by detecting the energy spectrum of supernova relic neutrinos with a next generation detector like Hyper-Kamiokande. We make an alternative compilation of the SFR data. We show that by only including published SFR data for which the dust obscuration has been directly determined, the ratio of the observed massive SFR to the observed supernova rate has large uncertainties$\sim 1.8^{+1.6}_{-0.6}$, and is statistically consistent with no supernova rate problem. If we consider that a significant fraction of massive stars end their lives as faint ONeMg SNe or as failed SNe, then the ratio reduces to $\sim 1.1^{+1.0}_{-0.4}$ and the rate problem is solved. We study the sources of uncertainty involved in estimates of the neutrino detection rate and analyze whether the spectrum of relic neutrinos can be used to independently identify the existence of a supernova rate problem and its source. We consider an ensemble of published and unpublished neutrino luminosities and temperatures from core collapse supernova simulation models. We illustrate how the spectrum of detector events might be used to constrain the average neutrino temperature and SN models. We study the effects of neutrino oscillations on the detected neutrino spectrum and also analyze a possible enhanced contribution from failed supernovae. We conclude that it might be possible to measure the neutrino temperature, neutrino oscillations, the EOS, and confirm this source of missing luminous supernovae.

The three Standard Model neutrinos can have Majorana mass or strictly Dirac mass, but both scenarios are practically indistinguishable in neutrino oscillation experiments. If they are pseudo-Dirac, however, there will be new mass splittings among the pseudo-Dirac pairs, potentially leaving traces in neutrino oscillation phenomena. In this work, we use flavor ratios of astrophysical neutrinos to discriminate different possible mass spectra of pseudo-Dirac neutrinos. We show that it will be possible to impose robust bounds of order δm32≲10−12 eV2 on the new mass squared splitting involving the third pseudo-Dirac mass eigenstates (those with the least electron flavor composition) with the future experiment IceCube-Gen2. The derived sensitivity is robust because it only assumes an extragalactic origin for the astrophysical neutrinos and hierarchical pseudo-Dirac mass spectrum. In case the neutrino sources are known in the future, such bounds can potentially improve by up to five orders of magnitude, reaching δm32≲10−17 eV2.

The precise measurement of neutrino oscillation parameters is one of the highest priorities in neutrino oscillation physics. To achieve the desired precision, it is necessary to reduce the systematic uncertainties related to neutrino energy reconstruction. An error in energy reconstruction is propagated to all the oscillation parameters; hence, a careful estimation of neutrino energy is required. To increase the statistics, neutrino oscillation experiments use heavy nuclear targets like Argon (Z\(=\)18). The use of these nuclear targets introduces nuclear effects that severely impact the neutrino energy reconstruction which in turn poses influence in the determination of neutrino oscillation parameters. In this work we have tried to study the impact of nuclear effects on the determination of CP phase at DUNE using final state interactions.

Measurements of neutrino charged current scattering in K2K Fine-Grained Detector

In the presence of extra neutrino states at high scales, the low-energy effective 3×3 leptonic mixing matrix (LMM) is in general nonunitary. We revisit the question of what is our current knowledge of individual LMM matrix elements without assuming unitarity. We first demonstrate that a minimal set of experimental constraints suffices in bounding LMM nonunitarity parameters to the level of O(10−3), without the use of neutrino oscillation data. We then revisit oscillation results as a complementary cross-check, using different physics and different experimental techniques to probe a similar parameter space. We correct some common misconceptions in the neutrino nonunitarity literature resulting from an incautious treatment of input parameters. We find that neutrino oscillation experiments can constrain LMM nonclosure, but, contrary to claims in the literature, are completely insensitive to the overall normalization of the LMM. Thus, we conclude that oscillation experiments, including the future DUNE experiment, have no power in excluding nonunitarity altogether. Published by the American Physical Society 2024

CPT symmetry, the combination of Charge Conjugation, Parity and Time reversal, is a cornerstone of our model building strategy and therefore the repercussions of its potential violation will severely threaten the most extended tool we currently use to describe physics, i.e. local relativistic quantum fields. However, limits on its conservation from the Kaon system look indeed imposing. In this work we will show that neutrino oscillation experiments can improve this limit by several orders of magnitude and therefore are an ideal tool to explore the foundations of our approach to Nature.Strictly speaking testing CPT violation would require an explicit model for how CPT is broken and its effects on physics. Instead, what is presented in this paper is a test of one of the predictions of CPT conservation, i.e., the same mass and mixing parameters in neutrinos and antineutrinos. In order to do that we calculate the current CPT bound on all the neutrino mixing parameters and study the sensitivity of the DUNE experiment to such an observable. After deriving the most updated bound on CPT from neutrino oscillation data, we show that, if the recent T2K results turn out to be the true values of neutrino and antineutrino oscillations, DUNE would measure the fallout of CPT conservation at more than 3σ. Then, we study the sensitivity of the experiment to measure CPT invariance in general, finding that DUNE will be able to improve the current bounds on Δ(Δm312) by at least one order of magnitude. We also study the sensitivity to the other oscillation parameters. Finally we show that, if CPT is violated in nature, combining neutrino with antineutrino data in oscillation analysis will produce imposter solutions.

K2K is a long baseline neutrino oscillation experiment using a neutrino beam produced at the KEK 12 GeV PS, a near detector complex at KEK and a far detector (Super-Kamiokande) in Kamioka, Japan. The experiment was constructed and is being operated by an international consortium of institutions from Japan, Korea, and the US. The experiment started taking data in 1999 and has successfully taken data for about two years. K2K is the first long beseline neutrino oscillation experiment with a baseline of order hundreds of km and is the first accelerator based neutrino oscillation experiment that is sensitive to the Super-Kamiokande allowed region obtained from the atmospheric neutrino oscillation analysis. A total of 44 events have been observed in the far detector during the period of June 1999 to April 2001 corresponding to 3.85 × 1019 protons on target. The observation is consistent with the neutrino oscillation expectations based on the oscillation parameters derived from the atmospheric neutrinos, and the probability that this is a statistical fluctuation of non-oscillation expectation of [Formula: see text] is less than 3%.

In this chapter, possibility for the future neutrino experiments are discussed. The remaining issues of neutrino oscillation studies are, to measure the CP violation parameter $$\updelta $$ , to determine $$\Delta m^2_{31}$$ mass hierarchy and the $$\uptheta _{23}$$ octant degeneracy. Approximated neutrino oscillation formulas with matter effects are introduced first and then possibilities of future experiments to address the remaining issues are discussed based on them. There are anomalies in various neutrino oscillation experiments which can be explained if there is fourth neutrino that is called sterile neutrino. The search for the sterile neutrino is another important subject in the future neutrino oscillation experiments and is discussed here. In order to determine the transition amplitudes, the absolute neutrino mass is necessary in addition to the neutrino oscillation parameters. The relation between the measured neutrino oscillation parameters and possible absolute mass measurements are discussed. Finally the neutrino-less double beta decay experiment, that can determine the absolute neutrino mass and whether the neutrino is Majorana particle or Dirac particle, is explained.

These notes present a critique of the standard three-flavor neutrino oscillation framework. The design proposal of the MINOS at Fermilab based on a two-mass eigenstate framework may require serious reconsideration if there is strong mixing between all three flavors of neutrinos. For the LSND and KARMEN neutrino oscillation experiments, the amplitude of neutrino oscillation of the "one mass scale dominance" framework vanishes for certain values of mixing angles as a result of opposite signs of two equal and opposite contributions. Recent astronomical observations leave open the possibility that one of the neutrino mass eigenstates may be nonrelativistic in some instances. Neutrino oscillation phenomenology with a superposition of two relativistic, and one nonrelativistic, mass eigenstates is constructed. It is concluded that if the transition from the nonrelativistic to the relativistic regime happens for energies relevant to the reactor and the LSND neutrino oscillation experiments, then one must consider an ab initio analysis of the existing data.

This thesis explains the origins of neutrinos and their interactions, and the phenomenon of neutrino oscillations. Experiments for measuring neutrino oscillations are mentioned and the experiment investigated in this thesis, the ''Main Injector Neutrino Oscillation Search'', and its neutrino beam, the Fermi National Accelerator Laboratory's ''Neutrinos At The Main Injector'', are described. MINOS is a long baseline (735 km) neutrino oscillation experiment with a near and a far detector, intended to make precision measurements of the atmospheric sector neutrino oscillation parameters. A measurement is made of the ''atmospheric'' neutrino oscillation parameters, Δm$2\atop{23}$ and sin2(2θ23), using neutrinos from the NuMI beam. The results of this analysis are compared to measurements at MINOS using neutrinos from the atmosphere and with other experiments. A more detailed method of beam neutrino analysis is discussed, and the extra calibrations needed to perform that analysis properly are described, with special attention paid to two aspects of the calibration, which comprise the bulk of work for this thesis. The light injection calibration system uses LEDs to illuminate the detector readout and provides a normalization of the stability of the detector over time. The hardware and different modi operandi of the system are described. There is a description of installation and commissioning of the system at one of the MINOS detectors. The response normalization of each detector with cosmic ray muons is described. Special attention is paid to the explanation of necessary corrections that must be made to the muon sample in order for the sample to be used to calibrate each detector to the specified accuracy. The performance of the calibration is shown.