Precision Neutrino Research Articles

Electron-antineutrino Disappearance Observed by the Daya Bay Reactor Neutrino Experiment

The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle θ13 with a significance of 7.7 standard deviations. Antineutrinos from six 2.9 GWth reactors were detected by six 20-ton target-mass detectors of identical design, deployed in two near and one far underground experimental halls. With a 116.8 kton-GWth-day live-time exposure in 139 days, 28,909 and 205,308 electron-antineutrino candidates were detected at the far hall and near halls respectively. The ratio of the observed to expected number of antineutrinos at the far hall is R=0.944±0.007(stat)±0.003(syst). A rate-only analysis finds sin22θ13=0.089±0.010(stat)±0.005(syst) in a three-neutrino framework. The experiments will continue for several years and a more precise neutrino mixing angle θ13 will be given in the future.

Testing atmospheric mixing sum rules at precision neutrino facilities

We study the prospects for testing classes of atmospheric mixing sum rules at precision neutrino facilities. Such sum rules, which correlate the atmospheric mixing angle theta23 with the recently measured reactor angle theta13 and the cosine of the oscillation phase delta, are predicted by a variety of semi-direct models based on discrete family symmetry, classified in terms of finite von Dyck groups. We perform a detailed simulation of the performance of the next generation of oscillation experiments, including the wide band superbeam and low-energy neutrino factory proposals, and compare their discriminating power for testing atmospheric mixing sum rules.

Cyclotrons as Drivers for Precision Neutrino Measurements

As we enter the age of precision measurement in neutrino physics, improved flux sources are required. These must have a well defined flavor content with energies in ranges where backgrounds are low and cross-section knowledge is high. Very few sources of neutrinos can meet these requirements. However, pion/muon and isotope decay-at-rest sources qualify. The ideal drivers for decay-at-rest sources are cyclotron accelerators, which are compact and relatively inexpensive. This paper describes a scheme to produce decay-at-rest sources driven by such cyclotrons, developed within the DAEδALUS program. Examples of the value of the high precision beams for pursuing Beyond Standard Model interactions are reviewed. New results on a combined DAEδALUS—Hyper-K search for CP violation that achieve errors on the mixing matrix parameter of 4° to 12° are presented.

Probing the radiative zones of stars: Present status and developments

Seismology of Sun and stars associated to precise solar neutrino detections reveals microscopic and macroscopic behaviors of radiative zones that were not anticipated by stellar modeling predictions. These results allow us to check the hypotheses of the equations used in stellar evolution for long. In this review, I list some of the problems which emerge from these confrontations both on the description of the Sun or solar-like stars and on the envelopes of intermediate-type stars, then I summarize the cases at least partly solved in using 3D MHD simulations, new opacity calculations and laboratory experiments. This review shows also how we hope to progress on the others inside our OPAC consortium or in using the coming detection of neutrino fluxes.

The trigger and timing system of the Double Chooz experiment

Modern precision neutrino experiments like Double Chooz require a highly efficient trigger system in order to reduce systematic uncertainties. The trigger and timing system of the Double Chooz experiment was designed according to this goal. The Double Chooz trigger system is driven by the basic idea of triggering on multiple thresholds according to the total visible energy and additionally triggering on the number of active photomultiplier tubes (PMTs) in the detector. To do so, the trigger system continuously monitors the analogue signals from all PMTs in the detector. The amplitudes of these PMT-signals are summed for groups of certain PMTs (group signals) and for all PMTs (sum signal), respectively. The group signals are discriminated by two thresholds for each input channel and four thresholds for the sum signal. The resulting signals are processed by the trigger logic unit which is implemented in a FPGA. In addition to the proper trigger, the trigger system provides a common clock signal for all subsequent data acquisition systems to guarantee a synchronous readout of the Double Chooz detectors. The present design of the system provides a high flexibility for the applied logic and settings, making it useful for experiments other than Double Chooz. The Double Chooz trigger and timing system was installed and commissioned in 2011. This article describes the hardware of the trigger and timing system. Furthermore the setup, implemented trigger logic and performance of the trigger and timing system for the Double Chooz experiment is presented.

The MINOS Experiment: Results and Prospects

The MINOS experiment has used the world’s most powerful neutrino beam to make precision neutrino oscillation measurements. By observing the disappearance of muon neutrinos, MINOS has made the world’s most precise measurement of the larger neutrino mass splitting and has measured the neutrino mixing angleθ23. Using a dedicated antineutrino beam, MINOS has made the first direct precision measurements of the corresponding antineutrino parameters. A search forνeandν-eappearance has enabled a measurement of the mixing angleθ13. A measurement of the neutral-current interaction rate has confirmed oscillation between three active neutrino flavours. MINOS will continue as MINOS+ in an upgraded beam with higher energy and intensity, allowing precision tests of the three-flavour neutrino oscillation picture, in particular a very sensitive search for the existence of sterile neutrinos.

Toward precision neutrino physics with DeepCore and beyond

DeepCore, the fully contained low energy extension to IceCube, extends IceCube's sensitivity for indirect dark matter searches and atmospheric neutrino oscillation physics as well as astrophysical neutrino sources in the southern sky. With the first year of DeepCore data we observe a significant sample of atmospheric neutrino-induced cascades, confirming the scientific potential of this approach. We discuss ideas for PINGU, a further IceCube infill array which aims for an energy threshold of around 1GeV to support a precision IceCube neutrino physics program. In the longer term, we are exploring the feasibility of a precision neutrino physics program with a multi-megaton, sub-GeV detector in the Antarctic ice cap.

Making the sneutrino a Higgs particle with aU(1)Rlepton number

We present a supersymmetric extension of the Standard Model that posseses a continuous $ U(1)_R$ symmetry, which is identified with one of three lepton numbers, and where a sneutrino vev gives mass to the down type quark and leptons. This idea allows for a smaller particle content than the minimal $R$-symmetric supersymmetry extension of the standard model (MRSSM). We explore bounds on this model coming from electroweak precision measurements, neutrino masses and gravitino decay. Bounds from electroweak precision measurements lead to a two-sided bound on $\tan \beta$ while gravitino decay forces a low reheating temperature. Finally, the generation of neutrino masses from $R$-symmetry violation put an upper bound on the SUSY breaking scale. Despite all of this, we find that the allowed parameter space is still large and would lead to a distinctive phenomenology at the LHC.

CP violation in the neutrino sector: The new frontier

Abstract The discovery of neutrino masses has revealed a new flavour sector in the Standard Model. Just like the quark flavour sector, it contains a seed of CP violation, resulting in an asymmetric behaviour of matter and antimatter. It is argued that this new source of leptonic CP violation may be discovered in more precise neutrino oscillation experiments involving neutrino beams with energies in the GeV range that will be sent to distances of a few thousand kilometres.

Precision Neutrino Oscillation Physics with MINOS

MINOS is a long-baseline neutrino oscillation experiment utilising Fermilabʼs NuMI beam and two functionally identical steel/scintillator calorimeter detectors. Here we describe the short and long term physics goals of MINOS and we give a brief overview of the beam and detector technology used to achieve them.

The KATRIN sensitivity to the neutrino mass and to right-handed currents in beta decay

The aim of the KArlsruhe TRItium Neutrino experiment KATRIN is the determination of the absolute neutrino mass scale down to 0.2 eV, with essentially smaller model dependence than from cosmology and neutrinoless double beta decay. For this purpose, the integral electron energy spectrum is measured close to the endpoint of molecular tritium beta decay. The endpoint, together with the neutrino mass, should be fitted from the KATRIN data as a free parameter. The right-handed couplings change the electron energy spectrum close to the endpoint, therefore they have some effect also to the precise neutrino mass determination. The statistical calculations show that, using the endpoint as a free parameter, the unaccounted right-handed couplings constrained by many beta decay experiments can change the fitted neutrino mass value, relative to the true neutrino mass, by not larger than about 5–10%. Using, incorrectly, the endpoint as a fixed input parameter, the above change of the neutrino mass can be much larger, order of 100%, and for some cases it can happen that for large true neutrino mass value the fitted neutrino mass squared is negative. Publications using fixed endpoint and presenting large right-handed coupling effects to the neutrino mass determination are not relevant for the KATRIN experiment.

Solitons and precision neutrino mass spectroscopy

We propose how to implement precision neutrino mass spectroscopy using radiative neutrino pair emission (RNPE) from a macro-coherent decay of a new form of target state, a large number of activated atoms interacting with static condensate field. This method makes it possible to measure still undetermined parameters of the neutrino mass matrix, two CP violating Majorana phases, the unknown mixing angle and the smallest neutrino mass which could be of order a few meV, determining at the same time the Majorana or Dirac nature of masses. The twin process of paired superradiance (PSR) is also discussed.

Neutrino mixing angles in sequential dominance to NLO and NNLO

Neutrinos with hierarchical masses and two large mixing angles may naturally originate from sequential dominance (SD). Within this framework we present analytic expressions for the neutrino mixing angles including the next-to-leading order (NLO) and next-to-next-to-leading order (NNLO) corrections arising from the second lightest and lightest neutrino masses. The analytic results for neutrino mixing angles in SD presented here, including the NLO and NNLO corrections, are applicable to a wide class of models and may provide useful insights when confronting the models with data from high precision neutrino experiments. We also point out that for special cases of SD corresponding to form dominance (FD) the NLO and NNLO corrections both vanish. For example we study tri-bimaximal (TB) mixing via constrained sequential dominance (CSD) which involves only a NNLO correction and tri-bimaximal-reactor (TBR) mixing via partially constrained sequential dominance (PCSD) which involves a NLO correction suppressed by the small reactor angle and show that the analytic results have good agreement with the numerical results for these cases.

Flavor composition of ultrahigh energy neutrinos at source and at neutrino telescopes

We parametrize the initial flux composition of high energy astrophysical neutrinos as $({\ensuremath{\Phi}}_{e}^{0}\ensuremath{\mathbin:}{\ensuremath{\Phi}}_{\ensuremath{\mu}}^{0}\ensuremath{\mathbin:}{\ensuremath{\Phi}}_{\ensuremath{\tau}}^{0})=(1\ensuremath{\mathbin:}n\ensuremath{\mathbin:}0)$, where $n$ characterizes the source. All usually assumed neutrino sources appear as limits of this simple parametrization. We investigate how precise neutrino telescopes can pin down the value of $n$. We furthermore show that there is a neutrino mixing scenario in which the ratio of muon neutrinos to the other neutrinos takes a constant value regardless of the initial flux composition. This occurs when the muon neutrino survival probability takes its minimal allowed value. The phenomenological consequences of this very predictive neutrino mixing scenario are given.

The GENIE neutrino Monte Carlo generator

GENIE [1] is a new neutrino event generator for the experimental neutrino physics community. The goal of the project is to develop a ‘canonical’ neutrino interaction physics Monte Carlo whose validity extends to all nuclear targets and neutrino flavors from MeV to PeV energy scales. Currently, emphasis is on the few-GeV energy range, the challenging boundary between the non-perturbative and perturbative regimes, which is relevant for the current and near future long-baseline precision neutrino experiments using accelerator-made beams. The design of the package addresses many challenges unique to neutrino simulations and supports the full life-cycle of simulation and generator-related analysis tasks. GENIE is a large-scale software system, consisting of ∼ 120 000 lines of C ++ code, featuring a modern object-oriented design and extensively validated physics content. The first official physics release of GENIE was made available in August 2007, and at the time of the writing of this article, the latest available version was v2.4.4.

Some radiative corrections to neutrino scattering: Neutral currents

With the advent of high precision neutrino scattering experiments comes the need for improved radiative corrections. We present a phenomenological analysis of some contributions to the production of photons in neutrino neutral current scattering that are relevant to experiments subsuming the 1% level of accuracy.

Probing nonunitary mixing andCPviolation at a neutrino factory

A low-energy nonunitary leptonic mixing matrix is a generic feature of many extensions of the standard model. In such a case, the task of future precision neutrino oscillation experiments is more ambitious than measuring the three mixing angles and the leptonic (Dirac) CP phase, i.e., the accessible parameters of a unitary leptonic mixing matrix. A nonunitary mixing matrix has 13 parameters that affect neutrino oscillations, out of which four are CP violating. In the scheme of minimal unitarity violation we analyze the potential of a neutrino factory for determining or constraining the parameters of the nonunitary leptonic mixing matrix, thereby testing the origin of CP violation in the lepton sector.

Multiple seesaw mechanisms of neutrino masses at the TeV scale

In pursuit of a balance between theoretical naturalness and experimental testability, we propose two classes of multiple seesaw mechanisms at the TeV scale to understand the origin of tiny neutrino masses. They are novel extensions of the canonical and double seesaw mechanisms, respectively, by introducing even and odd numbers of gauge-singlet fermions and scalars. It is thanks to a proper implementation of the global U(1)×Z2N symmetry that the overall neutrino mass matrix in either class has a suggestive nearest-neighbor-interaction pattern. We briefly discuss possible consequences of these TeV-scale seesaw scenarios, which can hopefully be explored in the upcoming Large Hadron Collider and precision neutrino experiments, and present a simple but instructive example of model building.

OscSNS: Precision neutrino measurements at the Spallation Neutron Source

The Spallation Neutron Source (SNS), located at Oak Ridge Laboratory [1] in the United States, will be coming online over the next few years. In addition to producing fluxes of high-intensity neutrons, the interaction of the proton beam with the liquid mercury target produces copious pions. The π+ and subsequent μ+ decay at rest, providing a neutrino beam comprising νμ, νe, and anti-νμ components. This neutrino beam is ideal for high-precision neutrino experiments. OscSNS [2] is a proposed multi-purpose experiment that will perform a search for light sterile neutrinos, search for beyond the Standard Model interactions using neutrino oscillations, and provide tests of Standard Model predictions through world-record precision neutrino cross section measurements. OscSNS plans to submit a full proposal for funding in 2009.

Correlation between the charged current interactions of light and heavy Majorana neutrinos

The evidence for neutrino oscillations implies that three neutrino flavors (νe,νμ,ντ) must have different mass states (ν1,ν2,ν3). The most popular idea of generating tiny masses of νi is to introduce three heavy Majorana neutrinos Ni (for i=1,2,3) into the Standard Model and implement the seesaw mechanism. In this approach the neutrino mixing matrix V appearing in the charged current interactions of νi is not unitary, and the strength of unitarity violation of V is associated with the matrix R which describes the strength of charged current interactions of Ni. We present an explicit parametrization of the correlation between V and R in terms of nine rotation angles and nine phase angles, which can be measured or constrained in the precision neutrino oscillation experiments and by exploring possible signatures of Ni at the LHC and ILC. Two special but viable scenarios, the type-I seesaw model with two heavy Majorana neutrinos and the type-II seesaw model with one heavy Majorana neutrino and one Higgs triplet, are taken into account to illustrate the simplified V–R correlation. The implications of R≠0 on the low-energy neutrino phenomenology are also discussed. In particular, we demonstrate that the non-unitarity of V is possible to give rise to an appreciable CP-violating asymmetry between νμ→ντ and ν¯μ→ν¯τ oscillations with short or medium baselines.