Neutrino Factory Research Articles

A low energy neutrino factory with non-magnetic detectors

We show that a very precise neutrino/anti-neutrino event separation is not mandatory to cover the physics program of a low energy neutrino factory and thus non-magnetized detectors like water Cerenkov or liquid Argon detectors can be used. We point out, that oscillation itself strongly enhances the signal to noise ratio of a wrong sign muon search, provided there is sufficiently accurate neutrino energy reconstruction. Further, we argue that apart from a magnetic field, other means to distinguish neutrino from anti-neutrino events (at least statistically) can be explored. Combined with the fact that non-magnetic detectors potentially can be made very big, we show that modest neutrino/anti-neutrino separations at the level of 50% to 90% are sufficient to obtain good sensitivity to CP violation and the neutrino mass hierarchy for sin22θ13>10−3. These non-magnetized detectors have a rich physics program outside the context of a neutrino factory, including topics like supernova neutrinos and proton decay. Hence, our observation opens the possibility to use a multi-purpose detector also in a neutrino factory beam.

Neutrino factory optimization for nonstandard interactions

We study the optimization of a neutrino factory with respect to nonstandard neutral current neutrino interactions, and compare the results to those obtained without nonstandard interactions. We discuss the muon energy, baselines, and oscillation channels as degrees of freedom. Our conclusions are based on both analytical calculations and on a full numerical simulation of the neutrino factory setup proposed by the international design study (IDS-NF). We consider all possible nonstandard parameters, and include their complex phases. We identify the impact of the different parameters on the golden, silver, and disappearance channels. We come to the conclusion that, even in the presence of nonstandard interactions, the performance of the neutrino factory hardly profits from a silver channel detector, unless the muon energy is significantly increased compared to the IDS-NF setup. Apart from the dispensable silver channel detector, we demonstrate that the IDS-NF setup is close to optimal even if nonstandard interactions are considered. We find that one very long baseline is a key component in the search for nonstandard interactions, in particular, for $|{ϵ}_{\ensuremath{\mu}\ensuremath{\tau}}^{m}|$ and $|{ϵ}_{\ensuremath{\tau}\ensuremath{\tau}}^{m}|$.

Minimal neutrino beta beam for largeθ13

We discuss the minimum requirements for a neutrino beta beam if ${\ensuremath{\theta}}_{13}$ is discovered by an upcoming reactor experiment, such as Double Chooz or Daya Bay. We require that both neutrino mass hierarchy and leptonic $CP$ violation can be measured to competitive precisions with a single-baseline experiment in the entire remaining ${\ensuremath{\theta}}_{13}$ range. For example, we find that a $(^{18}\mathrm{Ne},^{6}\mathrm{He})$ beta beam from Fermilab to a water Cherenkov detector at Homestake with $\ensuremath{\gamma}\ensuremath{\gtrsim}190$ could outperform practically any other beam technology including wide-band beam and neutrino factory.

Testing nonunitarity of neutrino mixing matrices at neutrino factories

In this paper we explore the effect of nonunitary neutrino mixing on neutrino oscillation probabilities both in vacuum and matter. In particular, we consider the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ channel and, using a neutrino factory as the source for ${\ensuremath{\nu}}_{\ensuremath{\mu}}$'s, discuss the constraints that can be obtained on the moduli and phases of the parameters characterizing the violation of unitarity. We point out how the new $CP$ violation phases present in the case where the nonunitary mixings give rise to spurious ``degenerate'' solutions in the parameter space. We also discuss how the true solutions can be extricated by combining measurements at several baselines.

LONG BASELINE NEUTRINO EXPERIMENTS WITH TWO-DETECTOR SETUP

I discuss why and how powerful is the two-detector setting in neutrino oscillation experiments. I cover three concrete examples: (1) reactor θ13 experiments, (2) T2KK, Tokai-to-Kamioka-Korea two-detector complex for measuring CP violation, determining the neutrino mass hierarchy, and resolving the eight-fold parameter degeneracy, (3) two-detector setting in a neutrino factory at baselines 3000 km and 7000 km for detecting effects of non-standard interactions (NSI) of neutrinos.

CPT violation in long baseline neutrino experiments: A three flavor analysis

We explore possible signals of CPT violation in neutrinos in the complete three-flavor framework. Employing a systematic expansion in small parameters, we analytically estimate the CPT violating contributions to the survival probabilities of ${\ensuremath{\nu}}_{\ensuremath{\mu}}$, ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$, ${\ensuremath{\nu}}_{e}$ and, ${\overline{\ensuremath{\nu}}}_{e}$. The results indicate that, in spite of the large number of CPT violating parameters, only a small number of combinations are relevant for oscillation experiments. We identify the combinations that can be constrained at the long baseline experiments, and show that their contribution to the neutrino Hamiltonian can be bounded to $\ensuremath{\lesssim}{10}^{\ensuremath{-}23}\text{ }\text{ }\mathrm{GeV}$, by considering the NOvA experiment for the muon sector, and neutrino factories for the electron sector. This formalism also allows us to translate the bounds on the parameters describing non-standard interactions of neutrinos into the bounds on CPT violating quantities.

Signals of CPT violation and non-locality in future neutrino oscillation experiments

We investigate the sensitivities of future neutrino oscillation experiments for measuring the neutrino mass squared differences and leptonic mixing angles independently with neutrinos and anti-neutrinos. We update the expected sensitivities of Neutrino Factories to the “atmospheric” (anti-)neutrino parameters using an optimized setup. A dedicated β-Beam facility, in combination with a SPMIN reactor experiment, could give excellent sensitivities also to the “solar” parameters, for neutrinos and anti-neutrinos respectively. A signal of a different mass matrix for neutrinos and anti-neutrinos would imply CPT violation and non-locality of the underlying particle theory.

Technical Challenges and Scientific Payoffs of Muon Beam Accelerators for Particle Physics

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Progress in particle physics has largely been determined by development of more capable particle accelerators. This trend continues today with the recent advent of high-luminosity electron-positron colliders at KEK and SLAC operating as “B factories,” the imminent commissioning of the Large Hadron Collider at CERN, and the worldwide development effort toward the International Linear Collider. Looking to the future, one of the most promising approaches is the development of muon-beam accelerators. Such machines have very high scientific potential, and would substantially advance the state-of-the-art in accelerator design. A 20–50 GeV muon storage ring could serve as a copious source of well-characterized electron neutrinos or antineutrinos (a Neutrino Factory), providing beams aimed at detectors located 3000–7500 km from the ring. Such long baseline experiments are expected to be able to observe and characterize the phenomenon of charge-conjugation-parity (CP) violation in the lepton sector, and thus provide an answer to one of the most fundamental questions in science, namely, why the matter-dominated universe in which we reside exists at all. By accelerating muons to even higher energies of several TeV, we can envision a Muon Collider. In contrast to composite particles like protons, muons are point particles. This means that the full collision energy is available to create new particles. A Muon Collider has roughly ten times the energy reach of a proton collider at the same collision energy, and has a much smaller footprint. Indeed, an energy frontier Muon Collider could fit on the site of an existing laboratory, such as Fermilab or BNL. The challenges of muon-beam accelerators are related to the facts that <emphasis emphasistype="boldital">i</emphasis>) muons are produced as a tertiary beam, with very large 6D phase space, and <emphasis emphasistype="boldital">ii</emphasis>) muons are unstable, with a lifetime at rest of only 2 <formula formulatype="inline"> <tex>$\mu{\hbox{s}}$</tex></formula>. How these challenges are accommodated in the accelerator design will be described. Both a Neutrino Factory and a Muon Collider require large numbers of challenging superconducting magnets, including large aperture solenoids, closely spaced solenoids with opposing fields, shielded solenoids, very high field (<formula formulatype="inline"> <tex>$\sim$</tex></formula>40–50 T) solenoids, and storage ring magnets with a room-temperature midplane section. Uses for the various magnets will be outlined, along with R&amp;D plans to develop these and other required components of such machines. </para>

The MICE scintillating-fibre tracker

The international Muon Ionization Cooling Experiment (MICE) collaboration will carry out a systematic investigation of the ionization cooling of a muon beam. An ionization cooling channel is required to compress the phase-space volume occupied by the muon beam prior to acceleration in the baseline conceptual designs for both the Neutrino Factory and the Muon Collider. Muons entering and leaving the cooling channel will be measured in two solenoidal spectrometers, each of which is instrumented with a scintillating-fibre tracker. Each tracker is composed of five planar scintillating fibre stations, each station being composed of three planar layers of 350 micron scintillating fibres. The devices will be read out using the Visible Light Photon Counters (VLPCs) developed for use in the D0 experiment at the Tevatron. The design of the system will be presented along with the status of the tracker-construction project. The expected performance of prototypes of the full tracker will be summarised.

Neutrino factory for both large and smallθ13

An analysis of the neutrino oscillation physics capability of a low-energy neutrino factory is presented, including a first simulation of the detector efficiency and event energy threshold. The sensitivity of the physics reach to the presence of backgrounds is also studied. We consider a representative baseline of 1480 km, we use muons with 4.12 GeV energy and we exploit a very conservative estimate of the energy resolution of the detector. Our analysis suggests an impressive physics reach for this setup, which can eliminate degenerate solutions, for both large and small values of the mixing angle {theta}{sub 13}, and can determine leptonic CP violation and the neutrino mass hierarchy with extraordinary sensitivity.

CPviolation from the standard model to strings

A review of $\mathit{CP}$ violation from the standard model to strings is given which includes a broad landscape of particle physics models, encompassing the nonsupersymmetric four-dimensional (4D) extensions of the standard model, and models based on supersymmetry, on extra dimensions, on strings, and on branes. The supersymmetric models discussed include complex minimal supergravity unified model and its extensions, while the models based on extra dimensions include five-dimensional models including models based on warped geometry. $\mathit{CP}$ violation beyond the standard model is central to achieving the desired amount of baryon asymmetry in the Universe via baryogenesis and leptogenesis. They also affect a variety of particle physics phenomena: electric dipole moments, $g\ensuremath{-}2$, relic density and detection rates for neutralino dark matter in supersymmetric theories, Yukawa unification in grand unified and string based models, and sparticle production cross sections, and their decay patterns and signatures at hadron colliders. Additionally $\mathit{CP}$ violations can generate $\mathit{CP}$ even--$\mathit{CP}$ odd Higgs mixings, affect the neutral Higgs spectrum, and lead to phenomena detectable at colliders. Prominent among these are the $\mathit{CP}$ violation effects in decays of neutral and charged Higgs bosons. Neutrino masses introduce new sources of $\mathit{CP}$ violation which may be explored in neutrino factories in the future. Such phases can also enter in proton stability in unified models of particle interactions. The current experimental status of $\mathit{CP}$ violation is discussed and possibilities for the future outlined.

Solving the octant degeneracy with the silver channel

We study the potential of the combination of the golden (νe→νμ) and silver (νe→ντ) channels to solve the octant degeneracy affecting the measurement of θ13 and δ at future neutrino factories. To search for τ leptons produced in ντ charged-current interactions, we consider two different detectors: the Emulsion Cloud Chamber detector (ECC) and the Liquid Argon Time Projection Chamber (LAr TPC). We show that, when using similar detector masses, the upgraded version of the ECC detector (sensitive also to hadronic τ decay modes) and the LAr TPC detector have comparable sensitivities to the octant of θ23, being able to discriminate the two solutions for sin2(2θ13)≳10−3 at 3σ level if θ23=40°. We also show that the same setups are able to see deviation from maximal mixing as small as ∼ (4–6)% (at 3σ) if θ13 is close to its upper bound.

The neutrino factory and related accelerator R&D

A muon-based neutrino factory, encompassing high power proton accelerators, innovations in rapid acceleration techniques for unstable particles, and initiatives such as ionisation cooling, provides a rich and varied source of high-energy R&D. Over the last ten years, the UK has played a leading role in progress towards a large-scale neutrino facility, both at national and international level, and now seeks to move to the next phase with preparation of an International Design Study report for publication in 2010. The basic principles of the project are outlined here, with emphasis on the major problems still to be overcome. Much of the development work relates to other areas of accelerator science - such as spallation neutron sources, used for research in condensed matter physics - and the way in which such projects interact and benefit from each other is also described.

Intermediate γ beta beams with a cluster of detectors

The acceleration of radionuclides in a beta beam provides an alternative experimental design to superbeam and neutrino factory long baseline neutrino oscillation experiments. Only single baseline beta beam scenarios have been considered thus far although a storage ring could source at least two baselines. The multitude of possible detector sites in Europe potentially allows for numerous baselines for future long baseline experiments sourced at CERN. Here, we will consider an example taking the CERN-Canfranc and CERN-Boulby baselines. We present results that indicate good sensitivity to the mass hierarchy for values of sin2 2θ13 as small as 10-3 and CP-violation discovery for sin2 2θ13 down to 10-4. These results are achieved with a single helicity since the second baseline provides the synergies usually associated with an anti-neutrino run.

International scoping study: accelerator working group report

During the past several years, an International Scoping Study (ISS) of a Neutrino Factory was carried out, with the aim of developing an internationally accepted baseline facility design. Progress toward that goal will be described. Many of the key technical aspects of a Neutrino Factory facility design are presently being investigated experimentally, and the status of these investigations will be mentioned. Plans for the recently launched International Design Study (IDS), which serves as a follow-on to the ISS, will be briefly described.

Emittance measurement in MICE

Ionisation Cooling will be an essential element of a future Neutrino Factory [1]. The Muon Ionization Cooling Experiment, MICE at RAL (UK), will be the first apparatus to demonstrate this technique. MICE will be unique in making single-particle measurements determining the amplitude of each muon in 6D phase space. It is shown how amplitude measurements can be used to quantify the increase in central phase space density due to cooling.

Latest results from HARP

The HARP experiment at CERN PS took data in 2001-2002 with a large acceptance apparatus measuring secondary particle production by protons and pion beams from 1.5 to 15 GeV/c on targets ranging from H2 to lead. A number of data are now analysed and cross-sections are presented, in particular for the K2K and MiniBooNE neutrino experiments, cosmic ray flux calculations and large angle data for optimizing the neutrino factory proton driver.

Thermal shock measurements and modelling for solid high-power targets at high temperatures

A description of lifetime shock tests on tantalum and tungsten is given and of modelling studies as part of the research into solid targets for a Neutrino Factory. A fast high current pulse is applied to a thin wire of the sample material and the number of pulses measured before the wire visibly deteriorates. These measurements are made at temperatures up to ∼2000 K. The stress on the wire is calculated and compared to the stress expected in the target using the computer code LS-DYNA. It has been found that tantalum is too weak to sustain prolonged stress at these temperatures but a tungsten wire has reached over 13 million pulses (equivalent to 10 years of operation) at the stress expected in the target. Further work is in progress to study graphite and other materials. Measurement of the surface acceleration of the wire using a VISAR are to be made, which, combined with LS-DYNA modelling, will allow the evaluation of the constitutive equations of state of the materials at high temperature and provide a more accurate model of the stresses in a number of target geometries.

The Coming Revolutions in Particle Physics

Wonderful opportunities await particle physics over the next decade, with new instruments and experiments poised to explore the frontiers of high energy, infinitesimal distances, and exquisite rarity. We look forward to the Large Hadron Collider at CERN to explore the 1-TeV scale (extending efforts at LEP and the Tevatron to unravel the nature of electroweak symmetry breaking) and many initiatives to develop our understanding of the problem of identity: what makes a neutrino a neutrino and a top quark a top quark. We suspect that the detection of proton decay is only a few orders of magnitude away in sensitivity. Astronomical observations should help to tell us what kinds of matter and energy make up the universe. We might even learn to read experiment for clues about the dimensionality of spacetime. If we are inventive enough, we may be able to follow this rich menu with the physics opportunities offered by a linear electron-positron collider and a (muon storage ring) neutrino factory. I expect a remarkable flowering of experimental particle physics, and of theoretical physics that engages with experiment.

Neutrino hierarchy from CP-blind observables with high density magnetized detectors

High density magnetized detectors are well suited to exploit the outstanding purity and intensities of novel neutrino sources like neutrino factories and beta beams. They can also provide independent measurements of leptonic mixing parameters through the observation of atmospheric muon-neutrinos. In this paper, we discuss the combination of these observables from a multi-kT iron detector and a high energy beta beam; in particular, we demonstrate that even with moderate detector granularities the neutrino mass hierarchy can be determined for θ13 values greater than 4°.