Accelerator Neutrino Experiments Research Articles

Combining accelerator and reactor measurements of θ 13: the first result

Abstract The lepton mixing angle θ 13, the only unknown angle in the standard three-flavor neutrino mixing scheme, is finally measured by the recent reactor and accelerator neutrino experiments. We perform a combined analysis of the data coming from T2K, MINOS, Double Chooz, Daya Bay and RENO experiments and find sin2 2θ 13 = 0.096 ± 0.013(±0.040) at 1 σ (3 σ) CL and that the hypothesis θ 13 = 0 is now rejected at a significance level of 7.7 σ. We also discuss the near future expectation on the precision of the θ 13 determination by using expected data from these ongoing experiments.

Constraining the (low-energy) type-I seesaw Lagrangian

The type-I seesaw Lagrangian yields a nongeneric set of active-sterile oscillation parameters---the neutrino mass eigenvalues and the physical elements of the full mixing matrix are entwined. For this reason one is able to, in principle, test the model by performing enough measurements which are sensitive to neutrino masses and lepton mixing. We point out that for light enough right-handed neutrino masses---less than 10 eV---next-generation short-baseline neutrino oscillation experiments may be able to unambiguously rule out (or ``rule in'') the low-energy seesaw as the Lagrangian that describes neutrino masses. These types of searches are already under consideration in order to address the many anomalies from accelerator neutrino experiments (LSND, MiniBooNe), reactor neutrino experiments (the ``reactor anomaly''), and others. In order to test the low-energy seesaw, it is crucial to explore different oscillation channels, including ${\ensuremath{\nu}}_{e}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ disappearance and ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ appearance.

REVIEW OF REACTOR NEUTRINO OSCILLATION EXPERIMENTS

In this document we will review the current status of reactor neutrino oscillation experiments and present their physics potentials for measuring the θ13 neutrino mixing angle. The neutrino mixing angle θ13 is currently a high-priority topic in the field of neutrino physics. There are currently three different reactor neutrino experiments, DOUBLE CHOOZ, DAYA BAY and RENO and a few accelerator neutrino experiments searching for neutrino oscillations induced by this angle. A description of the reactor experiments searching for a nonzero value of θ13 is given, along with a discussion of the sensitivities that these experiments can reach in the near future.

Investigation of neutrino oscillations in the T2k long-baseline accelerator experiment

High-sensitivity searches for transitions of muon neutrinos to electron neutrinos are the main task of the T2K (Tokai-to-Kamioka) second-generation long-baseline accelerator neutrino experiment. The present article is devoted to describing basic principles of T2K, surveying experimental apparatuses that it includes, and considering in detail the muon-range detector (SMRD) designed and manufactured by a group of physicists from the Institute of Nuclear Research (Russian Academy of Sciences, Moscow). The results of the first measurements with a neutrino beam are presented, and plans for the near future are discussed.

Long-range lepton flavor interactions and neutrino oscillations

Recent results from the MINOS accelerator neutrino experiment suggest a possible difference between ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ disappearance oscillation parameters, which one may ascribe to a new long-distance potential acting on neutrinos. As a specific example, we consider a model with gauged $B\ensuremath{-}{L}_{e}\ensuremath{-}2{L}_{\ensuremath{\tau}}$ number that contains an extremely light new vector boson ${m}_{{Z}^{\ensuremath{'}}}<{10}^{\ensuremath{-}18}\text{ }\text{ }\mathrm{eV}$ and extraordinarily weak coupling ${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\lesssim}{10}^{\ensuremath{-}52}$ (or larger ${m}_{{Z}^{\ensuremath{'}}}$ if cosmology bounds on neutrino decay apply). In that case, differences between ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ oscillations can result from a long-range potential due to neutrons in the Earth and the Sun that distinguishes ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ on Earth, with a potential difference of $\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\text{ }\text{ }\mathrm{eV}$, and changes sign for antineutrinos. We show that existing solar, reactor, accelerator, and atmospheric neutrino oscillation constraints can be largely accommodated for values of parameters that help explain the possible MINOS anomaly by this new physics, although there is some tension with atmospheric constraints. A long-range interaction, consistent with current bounds, could have very pronounced effects on atmospheric neutrino disappearance in the 15--40 GeV range that will be studied with the IceCube DeepCore array, currently in operation, and can have a significant effect on future high-precision long-baseline oscillation experiments that aim for $\ifmmode\pm\else\textpm\fi{}1%$ sensitivity, in ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$ disappearance, separately. Together, these experiments can extend the reach for new long-distance effects well beyond current bounds and test their relevance to the aforementioned MINOS anomaly. We also point out that long-range potentials originating from the Sun could lead to annual modulations of neutrino data at the percent level, due to the variation of the Earth-Sun distance. A similar phenomenology is shown to apply to other potential new gauge symmetries such as $L\ensuremath{-}3{L}_{\ensuremath{\tau}}$ and $B\ensuremath{-}3{L}_{\ensuremath{\tau}}$.

Recent status of accelerator neutrino experiments

Recent results of accelerator neutrino experiments are reviewed with emphasis on facilities and instrumentations. The progress in neutrino physics in last two decades has been made possible in large part by large underground facilities, which were motivated for the experimental search of phenomena associated with Grand Unified Theories, such as proton decay. At present, the experimental results on neutrino oscillation in atmospheric, solar, reactor and accelerator neutrinos are consistent with three generation neutrinos. The measurements of the last of the three mixing angles, CP-violation phase and mass hierarchy of the mass eigen-states will be the main topics in the next generation accelerator neutrino experiments.

Bayesian constraints onϑ13from solar and KamLAND neutrino data

We present the results of a Bayesian analysis of solar and KamLAND neutrino data in the framework of three-neutrino mixing. We adopt two approaches for the prior probability distribution of the oscillation parameters $\ensuremath{\Delta}{m}_{21}^{2}$, ${sin}^{2}{\ensuremath{\vartheta}}_{12}$, ${sin}^{2}{\ensuremath{\vartheta}}_{13}$: (1) a traditional flat uninformative prior; and (2) an informative prior which describes the limits on ${sin}^{2}{\ensuremath{\vartheta}}_{13}$ obtained in atmospheric and long-baseline accelerator and reactor neutrino experiments. In both approaches, we present the allowed regions in the ${sin}^{2}{\ensuremath{\vartheta}}_{13}\mathrm{\text{\ensuremath{-}}}\ensuremath{\Delta}{m}_{21}^{2}$ and ${sin}^{2}{\ensuremath{\vartheta}}_{12}\mathrm{\text{\ensuremath{-}}}{sin}^{2}{\ensuremath{\vartheta}}_{13}$ planes, as well as the marginal posterior probability distribution of ${sin}^{2}{\ensuremath{\vartheta}}_{13}$. We confirm the $1.2\ensuremath{\sigma}$ hint of ${\ensuremath{\vartheta}}_{13}>0$ found in [G. Fogli et al., Phys. Rev. Lett. 101, 141801 (2008).] from the analysis of solar and KamLAND neutrino data. We found that the statistical significance of the hint is reduced to about $0.8\ensuremath{\sigma}$ by the constraints on ${sin}^{2}{\ensuremath{\vartheta}}_{13}$ coming from atmospheric and long-baseline accelerator and reactor neutrino data, in agreement with [T. Schwetz, M. Tortola, and J. W. F. Valle, New J. Phys. 10, 113011 (2008).].

Searching for physics beyond the standard model with accelerator neutrino experiments

The MiniBooNE experiment at Fermilab was designed to test the LSND evidence for oscillations [1]. The first MiniBooNE oscillation result in neutrino mode [2] shows no significant excess of events at higher energies (Ev > 475 MeV), although a sizeable excess is observed at lower energies (Ev < 475 MeV). The lack of a significant excess at higher energies allows MiniBooNE to rule out simple 2 - v oscillations as an explanation of the LSND signal. However, the low-energy excess is presently unexplained. Additional antineutrino data and NuMI data may allow the collaboration to determine whether the excess is due, for example, to a neutrino neutral-current radiative interaction [3] or to neutrino oscillations involving sterile neutrinos [4, 5, 6]. If the excess is consistent with being due to sterile neutrinos, then future experiments at FNAL (MicroBooNE & BooNE) or ORNL (OscSNS) could confirm their existence.

Accelerator neutrino experiments: New results and perspectives

The current status of neutrino long-baseline accelerator experiments and new results obtained in these experiments are presented. Prospects for near-future program are also discussed.

The Main Injector Particle Production Experiment

It is currently impossible to apply the theory of strong interactions, QCD, to compute non-perturbative hadron interaction cross sections from first principles. Thus high quality hadronic particle production measurements are needed to fully understand the data from experiments that have hadronic interactions as a signal or background. This includes atmospheric and accelerator neutrino experiments, calorimetry and hadronic shower simulation. Such data can also be used to test observed regularities in particle production such as scaling relations in inclusive reactions with some precision. The spectrum of baryon resonances predicted by QCD includes many states that have not been observed. Measurements of pion, kaon, and proton beams on a liquid hydrogen target at beam momenta around 1 GeV/c will provide important input to searches for missing baryon resonances. We review status, results, and prospects of particle production measurements at Fermilab.

Long Baseline Neutrino Experiments: Present and Future Accelerator and Atmospheric Neutrino Experiments

Long Baseline Neutrino Experiments: Present and Future Accelerator and Atmospheric Neutrino Experiments Takaaki Kajita Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan (Received 21 August 2007) The present status and future prospects of experimental studies of neutrino oscillations based on atmospheric neutrinos and long baseline neutrinos are discussed. Present neutrino oscillation data are explained very well with 2avor ! oscillations. The present knowledge of the relevant oscillation parameters is summarized. However, our understanding of the neutrino oscillation parameters is still incomplete. The future direction of the neutrino oscillation experiments based on accelerator neutrino beam is discussed. PACS numbers: 14.60.Pq, 96.40.Tv

The Main Injector Particle Production experiment (MIPP) at Fermilab

The MIPP experiment at Fermilab measures particle production cross sections for a broad range of studies including a general scaling law of inclusive cross sections, meson spectroscopy, and topics in nuclear physics (y-scaling, flavor propagation in nuclei, etc.). It uses a large acceptance, open geometry detector system to measure momenta and identity of all charged particles produced in the reactions of proton, pion, kaon, and anti-proton beams from 5 to 85 GeV/c and 120 GeV/c protons on cryogenic hydrogen, various nuclei, and composite accelerator neutrino experiment targets. This paper describes detector and beam-line performance during the 2005 physics run, outlines the potential of an upgraded MIPP, and presents results from short test runs at momenta from 1 GeV/c to 5 GeV/c.

Neutrino physics at accelerators

Present and future neutrino experiments at accelerators are mainly concerned with understanding the neutrino oscillation phenomenon and its implications. Here a brief account of neutrino oscillations is given together with a description of the supporting data. Some current and planned accelerator neutrino experiments are also explained.

Bounds on heavy sterile neutrinos revisited

We revise the bounds on heavy sterile neutrinos, especially in the case of their mixing with muon neutrinos in the charged current. We summarize the present experimental limits, and we reanalyze the existing data from the accelerator neutrino experiments and from Super-Kamiokande to set new bounds on a heavy sterile neutrino in the range of masses from 8 MeV to 390 MeV. We also discuss how the future accelerator neutrino experiments can improve the present limits.

Neutrino masses from cosmological probes

There is a renewed interest in constraining the sum of the masses of the three neutrino flavours by using cosmological measurements. Solar, atmospheric, reactor and accelerator neutrino experiments have confirmed neutrino oscillations, implying that neutrinos have non-zero mass, but without pinning down their absolute masses. While it has been established that the effect of light neutrinos on the evolution of cosmic structure is small, the upper limits derived from a large-scale structure could help significantly to constrain the absolute scale of the neutrino masses. It is also important to know the sum of neutrino masses as it is degenerate with the values of other cosmological parameters, e.g. the amplitude of fluctuations and the primordial spectral index. A summary of the cosmological neutrino mass limits is given. Current results from cosmology set an upper limit on the sum of the neutrino masses at ∼1 eV, somewhat dependent on the datasets used in the analyses and assumed priors on cosmological parameters. It is important to emphasize that the total neutrino mass (‘hot dark matter’) is derived by assuming that the other components in the universe are baryons, cold dark matter and dark energy. We assessed the impact of neutrino masses on the matter power spectrum, the cosmic microwave background, peculiar velocities and gravitational lensing. We also discuss possible methods to improve the mass upper limits by an order of magnitude.

K2K and a next generation neutrino oscillation experiment

Results of K2K and a plan of the next generation long baseline neutrino experiment is described. K2K experiment has confirmed neutrino oscillation in Δ m 2 ∼ 3 × 10 −3 eV 2 region by a well controlled accelerator neutrino experiment. As a next step of understanding neutrinos, T2K (Tokai to Kamioka) experiment has been approved. The experiment will use the high intensity neutrino beam from the JPARC(Japan Proton Accelerator Research Complex) 50 GeV proton synchrotron and Super-Kamiokande. An order of magnitude improvement of the sensitivity in the search of ν μ → ν e and a high precision measurement of ν μ disappearance will be the main objectives of the first stage of the experiment. With success in observing ν μ → ν e in the first stage, CP violation in the lepton sector can be investigated with a larger water Cherenkov detector (Hyper-Kamiokande) with upgraded PS in the future.

MiniBooNE overview and status

Recent discoveries in the neutrino sector have opened a new frontier in highenergy physics and cosmology. Evidence from neutrino oscillation experiments from around the world indicate that neutrinos oscillate between their different flavours and therefore may have mass. In addition, results from solar and atmospheric neutrino experiments as well as the accelerator neutrino experiment, LSND, cannot all be explained with the three standard model neutrinos. Is this new physics or is there some other explanation? The MiniBooNE experiment presently taking data at Fermilab is designed to address the LSND signal and answer this question. Progress on the MiniBooNE experiment will be presented and prospects for the future will be discussed.

Status and prospects of neutrino oscillations: terrestrial sources

By exploring the oscillation mixing angle versus mass difference allowed regions, terrestrial-based experiments have advanced our understanding of the ν oscillation solutions proposed by the measurements of neutrinos produced in the sun and in the atmosphere. This paper reviews the contribution of reactor anti-neutrino experiments and of accelerator neutrino experiments to the development of these theories. Selected experiments are briefly described, the results are presented and the impact on our understanding of neutrino oscillations is discussed.

Constraining the absolute neutrino mass scale and MajoranaCPviolating phases by future0νββdecay experiments

Assuming that neutrinos are Majorana particles, in a three generation framework, current and future neutrino oscillation experiments can determine six out of the nine parameters which fully describe the structure of the neutrino mass matrix. We try to clarify the interplay among the remaining parameters, the absolute neutrino mass scale and two CP violating Majorana phases, and how they can be accessed by future neutrinoless double beta ($0\nu\beta\beta$) decay experiments, for the normal as well as for the inverted order of the neutrino mass spectrum. Assuming the oscillation parameters to be in the range presently allowed by atmospheric, solar, reactor and accelerator neutrino experiments, we quantitatively estimate the bounds on $m_0$, the lightest neutrino mass, that can be infered if the next generation $0\nu\beta\beta$ decay experiments can probe the effective Majorana mass ($m_{ee}$) down to $\sim$ 1 meV. In this context we conclude that in the case neutrinos are Majorana particles: (a) if $m_0 \gsim 300$ meV, {\em i.e.}, within the range directly attainable by future laboratory experiments as well as astrophysical observations, then $m_{ee} \gsim 30$ meV must be observed; (b) if $m_0 < 300$ meV, results from future $0\nu\beta\beta$ decay experiments combined with stringent bounds on the neutrino oscillation parameters, specially the solar ones, will place much stronger limits on the allowed values of $m_0$ than these direct experiments.

Neutrino mass and oscillations

Present understanding of neutrino mass and mixing are discussed based on recent neutrino experiments, including solar, atmospheric, reactor and long baseline accelerator neutrino experiments. Especially, the results from the Super-Kamiokande experiment are discussed in detail.