Neutrino Factory Research Articles

Improvement of the low energy neutrino factory

The low energy neutrino factory has been proposed as a very sensitive setup for future searches for CP violation and matter effects. Here we study how its performance is affected when the experimental specifications of the setup are varied. Most notably, we have considered the addition of the 'platinum' nu_{mu} -> nu_{e} channel. We find that, whilst theoretically the extra channel provides very useful complementary information and helps to lift degeneracies, its practical usefulness is lost when considering realistic background levels. Conversely, an increase in statistics in the 'golden' nu_{e} -> nu_{mu} channel and, to some extent, an improvement in the energy resolution, lead to an important increase in the performance of the facility, given the rich energy dependence of the 'golden' channel at these energies. We show that a low energy neutrino factory with a baseline of 1300 km, muon energy of 4.5 GeV, and either a 20 kton totally active scintillating detector or 100 kton liquid argon detector, can have outstanding sensitivity to the neutrino oscillation parameters theta13, delta and the mass hierarchy. For our estimated exposure of 2.8 x 10^{23} kton x decays per muon polarity, the low energy neutrino factory has sensitivity to theta13 and delta for sin^{2}(2theta13) > 10^{-4} and to the mass hierarchy for sin^{2}(2theta13) > 10^{-3}.

Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory

The impact of heavy mediators on neutrino oscillations is typically described by non-standard four-fermion interactions (NSIs) or non-unitarity (NU). We focus on leptonic dimension-six effective operators which do not produce charged lepton flavor violation. These operators lead to particular correlations among neutrino production, propagation, and detection non-standard effects. We point out that these NSIs and NU phenomenologically lead, in fact, to very similar effects for a neutrino factory, for completely different fundamental reasons. We discuss how the parameters and probabilities are related in this case, and compare the sensitivities. We demonstrate that the NSIs and NU can, in principle, be distinguished for large enough effects at the example of non-standard effects in the $\mu$-$\tau$-sector, which basically corresponds to differentiating between scalars and fermions as heavy mediators as leading order effect. However, we find that a near detector at superbeams could provide very synergistic information, since the correlation between source and matter NSIs is broken for hadronic neutrino production, while NU is a fundamental effect present at any experiment.

The production and anatomy of a tungsten powder jet

A tungsten powder jet is a potential candidate technology for a particle production target in a future high power (i.e. Multi-MW) particle accelerator based facility, such as a so-called conventional neutrino Super Beam, a proposed Neutrino Factory, or a future neutron source. To test the viability of producing a suitable powder jet a few simple experiments were performed using standard pneumatic conveying equipment and the encouraging results are presented.

Resonant Dirac leptogenesis on throats

We consider resonant Dirac leptogenesis in a geometry with three five-dimensional throats in the flat limit. The baryon asymmetry in the universe is generated by resonant decays of heavy Kaluza-Klein scalars that are copies of the standard model Higgs. Discrete exchange symmetries between the throats are responsible for establishing two key features of the model. First, they ensure a near degeneracy of the scalar masses and thus a resonant decay of the scalars. This allows for Dirac leptogenesis at low energies close to the TeV scale. Second, the discrete symmetries connect the observed baryon asymmetry with the Yukawa couplings of the low-energy theory. As a consequence, we obtain correlations between the low-energy leptonic mixing parameters and the Dirac CP phase that can be tested at future neutrino oscillation experiments such as neutrino factories.

The MICE spectrometers for the measurement of muon beam emittance

Tracking detectors based on 350‐μm scintillating fibers have been developed to measure muon-beam emittance at the Muon Ionization Cooling Experiment (MICE), the goal of which is to demonstrate ionization cooling by constructing and testing part of a cooling channel designed for a Neutrino Factory. The upstream and downstream trackers were assembled at the Rutherford Appleton Laboratory (RAL) in 2008 and 2009. The mechanical design and construction (including quality assurance) procedures used for the trackers are described in this paper. Results from the cosmic-ray test performed for the upstream tracker at RAL in 2008 are also presented.

Neutrino factory in stages: Low energy, high energy, off-axis

We discuss neutrino oscillation physics with a neutrino factory in stages, including the possibility of upgrading the muon energy within the same program. We point out that a detector designed for the low energy neutrino factory may be used off-axis in a high energy neutrino factory beam. We include the re-optimization of the experiment depending on the value of theta_13 found. As upgrade options, we consider muon energy, additional baselines, a detector mass upgrade, an off-axis detector, and the platinum (muon to electron neutrino) channels. In addition, we test the impact of Daya Bay data on the optimization. We find that for large theta_13 (theta_13 discovered by the next generation of experiments), a low energy neutrino factory might be the most plausible minimal version to test the unknown parameters. However, if a higher muon energy is needed for new physics searches, a high energy version including an off-axis detector may be an interesting alternative. For small theta_13 (theta_13 not discovered by the next generation), a plausible program could start with a low energy neutrino factory, followed by energy upgrade, and then baseline or detector mass upgrade, depending on the outcome of the earlier phases.

Computational algorithms for multiphase magnetohydrodynamics and applications to accelerator targets

An interface-tracking numerical algorithm for the simulation of magnetohydrodynamic multiphase / free surface flows in the low-magnetic-Reynolds-number approximation of (Samulyak R., Du J., Glimm J., Xu Z., J. Comp. Phys., 2007, 226, 1532) is described. The algorithm has been implemented in multi-physics code FronTier and used for the simulation of MHD processes in liquids and weakly ionized plasmas. In this paper, numerical simulations of a liquid mercury jet entering strong and nonuniform magnetic field and interacting with a powerful proton pulse have been performed and compared with experiments. Such a mercury jet is a prototype of the proposed Muon Collider / Neutrino Factory, a future particle accelerator. Simulations demonstrate the elliptic distortion of the mercury jet as it enters the magnetic solenoid at a small angle to the magnetic axis, jet-surface instabilities (filamentation) induced by the interaction with proton pulses, and the stabilizing effect of the magnetic field.

Resolving CP violation by standard and nonstandard interactions and parameter degeneracy in neutrino oscillations

In neutrino oscillation with non-standard interactions (NSI) the system is enriched with CP violation caused by phases due to NSI in addition to the standard lepton Kobayashi-Maskawa phase \delta. In this paper we show that it is possible to disentangle the two CP violating effects by measurement of muon neutrino appearance by a near-far two detector setting in neutrino factory experiments. Prior to the quantitative analysis we investigate in detail the various features of the neutrino oscillations with NSI, but under the assumption that only one of the NSI elements, \epsilon_{e \mu} or \epsilon_{e \tau}, is present. They include synergy between the near and the far detectors, the characteristic differences between the \epsilon_{e \mu} and \epsilon_{e\tau} systems, and in particular, the parameter degeneracy. Finally, we use a concrete setting with the muon energy of 50 GeV and magnetized iron detectors at two baselines, one at L=3000 km and the other at L=7000 km, each having a fiducial mass of 50 kton to study the discovery potential of NSI and its CP violation effects. We demonstrate, by assuming 4 \times 10^{21} useful muon decays for both polarities, that one can identify non-standard CP violation down to | epsilon_{e \mu} | \simeq \text{a few} \times 10^{-3}, and | \epsilon_{e \tau} | \simeq 10^{-2} at 3\sigma CL for \theta_{13} down to \sin^2 2\theta_{13} = 10^{-4} in most of the region of \delta. The impact of the existence of NSI on the measurement of \delta and the mass hierarchy is also worked out.

Non-standard neutrino interactions in the type-II seesaw model

Within the framework of the type-II seesaw model, we investigate in detail the non-standard neutrino interactions (NSIs). Non-trivial correlations between NSI parameters and neutrino masses and mixing parameters are established. We show that sizable NSIs can be generated as a consequence of a nearly degenerate neutrino mass spectrum. Significant zero distance effects in the near detector of a future neutrino factory, as well as characteristic decays of the doubly charged Higgs at the Large Hadron Collider are discussed.

Effect of tau neutrino contribution to muon signals at neutrino factories

We discuss precision measurements of the leading atmospheric parameters at a standard neutrino factory with a detector that is sensitive to muons alone. The oscillation of the muon and electron neutrinos in the neutrino factory beam to tau neutrinos adds to the muon events sample (both right sign and wrong sign) via leptonic decays of the taus produced through charge-current interactions in the detector. In particular, we study how this affects a precision measurement of the atmospheric mixing parameters and the deviation of ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ mixing from maximality. In spite of the enhancement of the number of events due to the additional tau contribution, the determination of the atmospheric mixing angle and the deviation from maximality will be poorer. We show that it is impossible to devise satisfactory cuts to remove this tau contamination. Neglect of these tau contributions will lead to an incorrect conclusion about the precision obtainable at a neutrino factory.

Evidence for right-handed neutrinos at a neutrino factory

We emphasize that a muon based neutrino factory could show the existence of light right-handed neutrinos, if a deficit in the number of detected events is observed at a near detector. This could be as large as ∼10% if the size of the new interactions saturates the present limits from electroweak precision data, what is not excluded by the oscillation experiments performed up to now. A simple model realizing such a scenario can be obtained adding right-handed neutrinos to the minimal Standard Model, together with an extra scalar doublet and a triplet of hypercharge 1. In this case, however, the possible deficit is reduced by a factor of ∼3, and the Yukawa couplings must be adequately chosen. This is also generically required if lepton flavour violation must be below present bounds.

Muon Colliders and Neutrino Factories

Over the past decade, there has been significant progress in developing the concepts and technologies needed to produce, capture, and accelerate O(1021) muons per year. These developments have paved the way for a new type of neutrino source (neutrino factory) and a new type of very high energy lepton-antilepton collider (muon collider). This article reviews the motivation, design, and research and development for future neutrino factories and muon colliders.

Non-standard neutrino interactions in the Zee–Babu model

We investigate non-standard neutrino interactions (NSIs) in the Zee–Babu model. The size of NSIs predicted by this model is obtained from a full scan over the parameter space, taking into account constraints from low-energy experiments such as searches for lepton flavor violation (LFV) and the requirement to obtain a viable neutrino mass matrix. The dependence on the scale of new physics as well as on the type of the neutrino mass hierarchy is discussed. We find that NSIs at the source of a future neutrino factory may be at an observable level in the νe→ντ and/or νμ→ντ channels. In particular, if the doubly charged scalar of the model has a mass in reach of the LHC and if the neutrino mass hierarchy is inverted, a highly predictive scenario is obtained with observable signals at the LHC, in upcoming neutrino oscillation experiments, in LFV processes, and for NSIs at a neutrino factory.

Short-baseline electron neutrino disappearance at a neutrino factory

We discuss short-baseline and very-short-baseline ${\ensuremath{\nu}}_{e}$ disappearance at a neutrino factory. We take into account geometric effects, such as from averaging over the decay straights, and the uncertainties of the cross sections. We follow an approach similar to reactor experiments with two detectors: we use two sets of near detectors at different distances to cancel systematics. We demonstrate that such a setup is very robust with respect to systematics, and can have excellent sensitivities to the effective mixing angle and squared-mass splitting. In addition, we allow for $CPT$ invariance violation, which can be tested (depending on the parameters) up to a 0.1% level.

Neutrino oscillation parameter sampling with MonteCUBES

We present MonteCUBES (“Monte Carlo Utility Based Experiment Simulator”), a software package designed to sample the neutrino oscillation parameter space through Markov Chain Monte Carlo algorithms. MonteCUBES makes use of the GLoBES software so that the existing experiment definitions for GLoBES, describing long baseline and reactor experiments, can be used with MonteCUBES. MonteCUBES consists of two main parts: The first is a C library, written as a plug-in for GLoBES, implementing the Markov Chain Monte Carlo algorithm to sample the parameter space. The second part is a user-friendly graphical Matlab interface to easily read, analyze, plot and export the results of the parameter space sampling. Program summary Program title: MonteCUBES (Monte Carlo Utility Based Experiment Simulator) Catalogue identifier: AEFJ_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public Licence No. of lines in distributed program, including test data, etc.: 69 634 No. of bytes in distributed program, including test data, etc.: 3 980 776 Distribution format: tar.gz Programming language: C Computer: MonteCUBES builds and installs on 32 bit and 64 bit Linux systems where GLoBES is installed Operating system: 32 bit and 64 bit Linux RAM: Typically a few MBs Classification: 11.1 External routines: GLoBES [1,2] and routines/libraries used by GLoBES Subprograms used: Cat Id ADZI_v1_0, Title GLoBES, Reference CPC 177 (2007) 439 Nature of problem: Since neutrino masses do not appear in the standard model of particle physics, many models of neutrino masses also induce other types of new physics, which could affect the outcome of neutrino oscillation experiments. In general, these new physics imply high-dimensional parameter spaces that are difficult to explore using classical methods such as multi-dimensional projections and minimizations, such as those used in GLoBES [1,2]. Solution method: MonteCUBES is written as a plug-in to the GLoBES software [1,2] and provides the necessary methods to perform Markov Chain Monte Carlo sampling of the parameter space. This allows an efficient sampling of the parameter space and has a complexity which does not grow exponentially with the parameter space dimension. The integration of the MonteCUBES package with the GLoBES software makes sure that the experimental definitions already in use by the community can also be used with MonteCUBES, while also lowering the learning threshold for users who already know GLoBES. Additional comments: A Matlab GUI for interpretation of results is included in the distribution. Running time: The typical running time varies depending on the dimensionality of the parameter space, the complexity of the experiment, and how well the parameter space should be sampled. The running time for our simulations [3] with 15 free parameters at a Neutrino Factory with O ( 10 6 ) samples varied from a few hours to tens of hours.

Physics with near detectors at a neutrino factory

We discuss the impact of near detectors at a neutrino factory both on standard oscillation and nonstandard interaction measurements. Our systematics treatment includes cross section errors, flux errors, and background uncertainties, and our near detector fluxes include the geometry of the neutrino source and the detector. Instead of a specific detector concept, we introduce qualitatively different classes of near detectors with different characteristics, such as near detectors catching the whole neutrino flux (near detector limit) versus near detectors observing a spectrum similar to that of the far detector (far detector limit). We include the low energy neutrino factory in the discussion. We illustrate for which measurements near detectors are required, discuss how many are needed, and what the role of the flux monitoring is. For instance, we demonstrate that near detectors are mandatory for the leading atmospheric parameter measurements if the neutrino factory has only one baseline, whereas systematical errors partially cancel if the neutrino factory complex includes the magic baseline. Finally, near detectors with ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ detection are shown to be useful for nonstandard interactions.

Cross sections of large-angle hadron production in proton– and pion–nucleus interactions III: tantalum nuclei and beam momenta from ±3 GeV/c to ±15 GeV/c

We report on double-differential inclusive cross sections of the production of secondary protons, charged pions, and deuterons, in the interactions with a 5% λ abs thick stationary tantalum target, of proton and pion beams with momentum from ±3 GeV/c to ±15 GeV/c. Results are given for secondary particles with production angles 20°<θ<125°. They are of particular relevance for the optimization of the design parameters of the proton driver of a neutrino factory.

The discovery channel at the Neutrino Factory: νμ→ ντpointing to sterile neutrinos

We study the potential of a Neutrino Factory in constraining the parameter space of a scheme with one sterile neutrino separated from three active ones by an O(1) eV^2, mass-squared difference. We present approximated analytic expressions for the oscillation probabilities, showing that the greatest sensitivity to sterile neutrinos at a Neutrino Factory can be achieved using the \nu_\mu ->\nu_\mu and the \nu_\mu ->\nu_\tau oscillations. We have studied two setups: a Neutrino Factory with 50 GeV (20 GeV) stored muons, with two detectors of the Hybrid-MIND type (a magnetized ECC next to a magnetized iron calorimeter), located at L=3000, 7500 km (L=4000, 7500 km) from the source. Four channels have been used: \nu_e -> \nu_\mu,\nu_\tau; \nu_\mu -> \nu_\mu,\nu_\tau. The relevant backgrounds, efficiencies and systematic errors have been taken into account, and we have discussed dependence of the sensitivities on the systematic errors. We have found that the 50 GeV (20 GeV) setup can constrain \sin^2 2 \theta^{(4fam)}_{13} <= 7x10^{-5} (2x10^{-4}); \theta_{34} <= 12 deg (14 deg); and \theta_{24}<= 7.5 deg (8 deg). Our results hold for any value of \Delta m^2_{Sbl} >~ 0.1 eV^2. Eventually we have shown that, if a positive signal is found, the proposed setup is able to measure simultaneously \theta_{34} and \delta_3 with a precision of few degrees and few tens of degrees, respectively, solving the so-called "intrinsic" and "sign degeneracies". Combination of \nu_\mu disappearance and of the \nu_\mu ->\nu_\tau channel, that will be called "the discovery channel", at the two baselines is able to measure at 99% CL a new CP-violating phase \delta_3 for \sin^2 2 \theta_{34} >= 0.06.

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.

The detector system of the MICE experiment

Muon ionization cooling provides the only practical solution to prepare high brilliance beams necessary for a neutrino factory or muon colliders. The muon ionization cooling experiment (MICE) is under development at the Rutherford Appleton Laboratory (UK). It comprises a dedicated beam line to generate a range of input emittance and momentum, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. The emittance is first measured in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in liquid hydrogen and RF acceleration. A second spectrometer identical to the first one provides a measurement of the outgoing emittance. A particle identification system ensures that the measured muon has not decayed. This paper describes scope and performance of the MICE detector system.