Normalised transverse emittance reduction via ionisation cooling in MICE ‘Flip Mode’

Low-emittance muon beams are central to the development of a Muon Collider and can significantly enhance the performance of a Neutrino Factory. The main challenge for muon acceleration stems from the large emittance with which the muon beam is produced. Maximising the muon yield while maintaining a suitably small aperture in the accelerator system requires that the muon beam emittance be reduced (cooled). The international Muon Ionisation Cooling Experiment (MICE) was designed to demonstrate the feasibility of the ionisation cooling technique, and provide the first measurement of normalised transverse emittance reduction in a muon beam. This work focuses on the emittance reduction analysis of 140 MeV/c MICE muon beams that passed through a liquid hydrogen or a lithium hydride absorber. During the acquisition of the studied data sets, the magnetic channel produced a field that flipped polarity at the absorber, to prevent a canonical angular momentum increase. A novel beam sampling procedure was developed to account for imperfections in beam matching at the entrance into the cooling channel, which improved the cooling signal measurement. A reduction in the muon beam normalised transverse emittance that grows linearly with input emittance was observed, which is a clear signal of ionisation cooling. The measurement is consistent with the simulation and the theoretical model. Furthermore, both the liquid hydrogen and the lithium hydride absorbers were found to induce a reduction in the mean canonical angular momentum of the beam. This effect can be attributed to energy loss at the absorber situated at the field polarity flip, combined with an increasing beam size across the absorber region. This result confirms that the field polarity flip at the absorber would maintain a low-magnitude canonical angular momentum within the cooling stage of a future muon facility.Open Acces

A comparative study of nonparametric methods for pattern recognition

The applied research discussed in this report determines and compares the correct classification percentage of the nonparametric sign test, Wilcoxon's signed rank test, and K-class classifier with the performance of the Bayes classifier. The performance is determined for data which have Gaussian, Laplacian and Rayleigh probability density functions. The correct classification percentage is shown graphically for differences in modes and/or means of the probability density functions for four, eight and sixteen samples. The K-class classifier performed very well with respect to the other classifiers used. Since the K-class classifier is a nonparametric technique, it usually performed better than the Bayes classifier which assumes the data to be Gaussian even though it may not be. The K-class classifier has the advantage over the Bayes in that it works well with non-Gaussian data without having to determine the probability density function of the data. It should be noted that the data in this experiment was always unimodal

Novel Methods for Multivariate Ordinal Data applied to Genetic Diplotypes, Genomic Pathways, Risk Profiles, and Pattern Similarity

Introduction: Conventional statistical methods for multivariate data (e.g., discriminant/regression) are based on the (generalized) linear model, i.e., the data are interpreted as points in a Euclidian space of independent dimensions. The dimensionality of the data is then reduced by assuming the components to be related by a specific function of known type (linear, exponential, etc.), which allows the distance of each point from a hyperspace to be determined. While mathematically elegant, these approaches may have shortcomings when applied to real world applications where the relative importance, the functional relationship, and the correlation among the variables tend to be unknown. Still, in many applications, each variable can be assumed to have at least an “orientation”, i.e., it can reasonably assumed that, if all other conditions are held constant, an increase in this variable is either “good” or “bad”. The direction of this orientation can be known or unknown. In genetics, for instance, having more “abnormal” alleles may increase the risk (or magnitude) of a disease phenotype. In genomics, the expression of several related genes may indicate disease activity. When screening for security risks, more indicators for atypical behavior may constitute raise more concern, in face or voice recognition, more indicators being similar may increase the likelihood of a person being identified. Methods: In 1998, we developed a nonparametric method for analyzing multivariate ordinal data to assess the overall risk of HIV infection based on different types of behavior or the overall protective effect of barrier methods against HIV infection. By using u-statistics, rather than the marginal likelihood, we were able to increase the computational efficiency of this approach by several orders of magnitude. Results: We applied this approach to assessing immunogenicity of a vaccination strategy in cancer patients. While discussing the pitfalls of the conventional methods for linking quantitative traits to haplotypes, we realized that this approach could be easily modified into to a statistically valid alternative to a previously proposed approaches. We have now begun to use the same methodology to correlate activity of anti-inflammatory drugs along genomic pathways with disease severity of psoriasis based on several clinical and histological characteristics. Conclusion: Multivariate ordinal data are frequently observed to assess semiquantitative characteristics, such as risk profiles (genetic, genomic, or security) or similarity of pattern (faces, voices, behaviors). The conventional methods require empirical validation, because the functions and weights chosen cannot be justified on theoretical grounds. The proposed statistical method for analyzing profiles of ordinal variables, is intrinsically valid. Since no additional assumptions need to be made, the often time-consuming empirical validation can be skipped.ranking; nonparametric; robust; scoring; multivariate

The Muon Ionisation Cooling Experiment

Outstanding areas of ambiguity within our present understanding of the nature and behaviour of neutrinos warrant the construction of a dedicated future facility capable of investigating the likely parameter space for the theta 1,3 mixing angle, the Dirac CP violating phase and clarifying the neutrino mass hierarchy. A number of potential discovery venues have been proposed including the beta beam, superbeam and neutrino factory accelerator facilities. Of these, the neutrino factory significantly outperforms the others. A neutrino factory will deliver intense beams of 10^21 neutrinos per year, produced from muons decaying in storage rings. This specification, coupled with the constraints of the short muon lifetime warrant the inclusion of a novel cooling channel to reduce the phase space volume of the beam to fall within the acceptance of the acceleration system. Ionisation cooling is the only viable cooling technique with efficacy over the lifetime of the muon, however, it has yet to be demonstrated in practice. In a full cooling channel, a muon beam will traverse a periodic absorber and accelerator lattice consisting of low Z absorbers enclosed by focusing coils and accelerating radio-frequency cavities. Energy loss in the absorbers reduces both transverse and longitudinal momentum. The latter is restored by the accelerating cavities providing a net reduction in transverse momentum and consequently reducing the phase space volume of the muon beam. The Muon Ionisation Cooling Experiment (MICE), under construction at the ISIS synchrotron at Rutherford Appleton Laboratory seeks to provide both a first measurement and systematic study of ionisation cooling, demonstrated within the context of a single cell prototype of a cooling channel. The experiment will evolve incrementally toward its final configuration, with construction and scientific data taking schedules proceeding in parallel. The stated goal of MICE is to measure a fractional change in emittance of order 10% to an error of 1%. This thesis constitutes research into different aspects of MICE: design and implementation of the MICE configuration database, determination of the statistical errors and alignment tolerances associated with cooling measurements made using MICE, simulations and data analysis studying the performance of the luminosity monitor and a first analysis of MICE Step I data. A sophisticated information management solution based on a bi-temporal relational database and web service suite has been designed, implemented and tested. This system will enable the experiment to record geometry, calibration and cabling information in addition to beamline settings (including but not limited to magnet and target settings) and alarm handler limits. This information is essential both to provide an experimental context to the analysis user studying data at a later time and to experimenters seeking to reinstate previous settings. The database also allows corrections to be stored, for example to the geometry, whereby a later survey may clarify an incomplete description. The old and new geometries are both stored with reference to the same period of validity, indexed by the time they are added to the configuration database. This allows MICE users to recall both the best-known geometry of the experiment at a given time by default, as well as the history of what was known about the geometry as required. Such functionality is two dimensional in time, hence the choice of a bi-temporal database paradigm, enabling the collaboration to run new analyses with the most up to date knowledge of the experimental configuration and also repeat previous analyses which were based upon incomplete information. From Step III of MICE onwards, the phase space volume, or emittance, of the beam will be measured by two scintillating fibre trackers placed before and after the cooling cell. Since the two emittance measurements are made upon a similar sample of muons, the measurement errors are influenced by correlations. This thesis will show through an empirical approach that correlations act to reduce the statistical error by an order of magnitude. In order to meet its goals MICE must also quantify its systematic errors. A misalignment study is presented which investigates the sensitivity of the scintillating fibre trackers to translational and rotational misalignment. Tolerance limits of 1 mm and 0.3 mrad respectively allow MICE to meet the requirement that systematic errors due to misalignment of the trackers contribute no more than 10% of the total error. At present, MICE is in Step I of its development: building and commissioning a muon beamline which will be presented to a cooling channel in later stages of MICE. A luminosity monitor has been built and commissioned to provide a measurement of particle production from the target, normalise particle rate at all detectors and verify the physics models which will be used throughout the lifetime of MICE and onwards through to the development of a neutrino factory. Particle identification detectors have already been installed and allow the species of particles to be distinguished according to their time of flight. This has enabled a study of particle identification, particle momenta and simulated and experimental beam profiles at each time of flight detector. The widths of the beam profiles are sensitive to multiple scattering and magnetic effects, providing an opportunity to quantify the success of the simulations in modelling these behaviours. Such a comparison was also used to detect offsets in the beam centre position which can be caused by misalignments of the detectors or relative misalignments in magnet positions causing asymmetrical skew in the magnetic axis. These effects were quantified in this analysis. Particle identification combined with the earlier statistical analysis will be used to show that the number of muons required to meet the statistical requirements of MICE can be produced within a realistic time frame for each beam configuration considered

Parallel readout of pathway-specific inputs to laminated brain structures

Local field potentials (LFPs) capture the electrical activity produced by principal cells during integration of converging synaptic inputs from multiple neuronal populations. However, since synaptic currents mix in the extracellular volume, LFPs have complex spatiotempo-ral structure, making them hard to exploit. Here we propose a biophysical framework to identify and separate LFP-generators. First we use a computational multineuronal model that scales up single cell electrogenesis driven by several synaptic inputs to realistic aggregate LFPs. This approach relies on the fixed but distinct locations of synaptic inputs from different presynaptic populations targeting a laminated brain structure. Thus the LFPs are contributed by several pathway-specific LFP-generators, whose electrical activity is defined by the spatial distribution of synaptic terminals and the time course of synaptic currents initiated in target cells by the corresponding presynaptic population. Then we explore the efficacy of independent component analysis to blindly separate converging sources and reconstruct pathway-specific LFP-generators. This approach can optimally locate synaptic inputs with subcellular accuracy while the reconstructed time course of pathway-specific LFP-generators is reliable in the millisecond scale. We also describe few cases where the non-linear intracellular interaction of strongly overlapping LFP-generators may lead to a significant cross-contamination and the appearance of derivative generators. We show that the approach reliably disentangle ongoing LFPs in the hippocampus into contribution of several LFP-generators.We were able to readout in parallel the pathway-specific presynap-tic activity of projection cells in the entorhinal cortex and pyramidal cells in the ipsilateral and contralateral CA3. Thus we provide formal mathematical and experimental support for parallel readout of the activity of converging presynaptic populations in working neuronal circuits from common LFPs. © 2011 Makarova, Ibarz, Makarov, Benito and Herreras.This study has been financed by grants FIS2010-20054 and BFU2010-19192 of the Spanish Ministry of Science and Innovation.Peer Reviewe

Parallel Readout of Pathway-Specific Inputs to Laminated Brain Structures

Local field potentials (LFPs) capture the electrical activity produced by principal cells during integration of converging synaptic inputs from multiple neuronal populations. However, since synaptic currents mix in the extracellular volume, LFPs have complex spatiotemporal structure, making them hard to exploit. Here we propose a biophysical framework to identify and separate LFP-generators. First we use a computational multineuronal model that scales up single cell electrogenesis driven by several synaptic inputs to realistic aggregate LFPs. This approach relies on the fixed but distinct locations of synaptic inputs from different presynaptic populations targeting a laminated brain structure. Thus the LFPs are contributed by several pathway-specific LFP-generators, whose electrical activity is defined by the spatial distribution of synaptic terminals and the time course of synaptic currents initiated in target cells by the corresponding presynaptic population. Then we explore the efficacy of independent component analysis to blindly separate converging sources and reconstruct pathway-specific LFP-generators. This approach can optimally locate synaptic inputs with subcellular accuracy while the reconstructed time course of pathway-specific LFP-generators is reliable in the millisecond scale. We also describe few cases where the non-linear intracellular interaction of strongly overlapping LFP-generators may lead to a significant cross-contamination and the appearance of derivative generators. We show that the approach reliably disentangle ongoing LFPs in the hippocampus into contribution of several LFP-generators. We were able to readout in parallel the pathway-specific presynaptic activity of projection cells in the entorhinal cortex and pyramidal cells in the ipsilateral and contralateral CA3. Thus we provide formal mathematical and experimental support for parallel readout of the activity of converging presynaptic populations in working neuronal circuits from common LFPs