Browsing by Author "Coloma, Pilar"

Now showing 1 - 9 of 9
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    Combining dark matter detectors and electron-capture sources to hunt for new physics in the neutrino sector
    Coloma, Pilar; Huber, Patrick; Link, Jonathan M. (Springer, 2014-11-10)
    In this letter we point out the possibility to study new physics in the neutrino sector using dark matter detectors based on liquid xenon. These are characterized by very good spatial resolution and extremely low thresholds for electron recoil energies. When combined with a radioactive nu e source, both features in combination allow for a very competitive sensitivity to neutrino magnetic moments and sterile neutrino oscillations. We find that, for realistic values of detector size and source strength, the bound on the neutrino magnetic moment can be improved by an order of magnitude with respect to the present value. Regarding sterile neutrino searches, we find that most of the gallium anomaly could be explored at the 95% confidence level just using shape information.
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    Comparison of the calorimetric and kinematic methods of neutrino energy reconstruction in disappearance experiments
    Ankowski, Artur M.; Benhar, Omar; Coloma, Pilar; Huber, Patrick; Jen, C. M.; Mariani, Camillo; Meloni, David; Vagnoni, E. (American Physical Society, 2015-10-22)
    To be able to achieve their physics goals, future neutrino-oscillation experiments will need to reconstruct the neutrino energy with very high accuracy. In this work, we analyze how the energy reconstruction may be affected by realistic detection capabilities, such as energy resolutions, efficiencies, and thresholds. This allows us to estimate how well the detector performance needs to be determined a priori in order to avoid a sizable bias in the measurement of the relevant oscillation parameters. We compare the kinematic and calorimetric methods of energy reconstruction in the context of two νμ &8594; νμ disappearance experiments operating in different energy regimes. For the calorimetric reconstruction method, we find that the detector performance has to be estimated with an Ο(10%) accuracy to avoid a significant bias in the extracted oscillation parameters. On the other hand, in the case of kinematic energy reconstruction, we observe that the results exhibit less sensitivity to an overestimation of the detector capabilities.
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    DUNE sensitivities to the mixing between sterile and tau neutrinos
    Coloma, Pilar; Forero, David V.; Parke, Stephen J. (Springer, 2018-07-11)
    Light sterile neutrinos can be probed in a number of ways, including electroweak decays, cosmology and neutrino oscillation experiments. At long-baseline experiments, the neutral-current data is directly sensitive to the presence of light sterile neutrinos: once the active neutrinos have oscillated into a sterile state, a depletion in the neutral-current data sample is expected since they do not interact with the Z boson. This channel offers a direct avenue to probe the mixing between a sterile neutrino and the tau neutrino, which is currently only weakly constrained by current data from SuperK, IceCube and NOvA, however, these constrains will continue to improve as more data is collected by these experiments. In this work, we study the potential of the DUNE experiment to constrain the mixing angle which parametrizes this mixing, theta(34), through the observation of neutral-current events at the far detector. We find that DUNE will be able to improve significantly over current constraints thanks to its large statistics and excellent discrimination between neutral- and charged-current events.
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    Heavy neutrino searches through double-bang events at Super-Kamiokande, DUNE, and Hyper-Kamiokande
    Atkinson, M. C.; Coloma, Pilar; Martinez-Soler, Ivan; Rocco, Noemi; Shoemaker, Ian M. (2022-04-28)
    Abstract A variety of new physics scenarios allows for neutrinos to up-scatter into a heavy neutral lepton state. For a range of couplings and neutrino energies, the heavy neutrino may travel some distance before decaying to visible final states. When both the up-scattering and decay occur within the detector volume, these “double bang” events produce distinctive phenomenology with very low background. In this work, we first consider the current sensitivity at Super-Kamiokande via the atmospheric neutrino flux, and find current data may already provide new constraints. We then examine projected future sensitivity at DUNE and Hyper-Kamiokande, including both atmospheric and beam flux contributions to double-bang signals.
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    Quantifying the sensitivity of oscillation experiments to the neutrino mass ordering
    Blennow, Mattias; Coloma, Pilar; Huber, Patrick; Schwetz, Thomas (Springer, 2014-03-05)
    Determining the type of the neutrino mass ordering ( normal versus inverted) is one of the most important open questions in neutrino physics. In this paper we clarify the statistical interpretation of sensitivity calculations for this measurement. We employ standard frequentist methods of hypothesis testing in order to precisely define terms like the median sensitivity of an experiment. We consider a test statistic T which in a certain limit will be normal distributed. We show that the median sensitivity in this limit is very close to standard sensitivities based on Delta chi(2) values from a data set without statistical fluctuations, such as widely used in the literature. Furthermore, we perform an explicit Monte Carlo simulation of the INO, JUNO, LBNE, NO nu A, and PINGU experiments in order to verify the validity of the Gaussian limit, and provide a comparison of the expected sensitivities for those experiments.
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    Reassessing the sensitivity to leptonic CP violation
    Blennow, Mattias; Coloma, Pilar; Fernandez-Martinez, Enrique (Springer, 2015-03-02)
    We address the validity of the usual procedure to determine the sensitivity of neutrino oscillation experiments to CP violation. An explicit calibration of the test statistic is performed through Monte Carlo simulations for several experimental setups. We find that significant deviations from a chi(2) distribution with one degree of freedom occur for experimental setups with low sensitivity to ffi. In particular, when the allowed region to which ffi is constrained at a given confidence level is comparable to the whole allowed range, the cyclic nature of the variable manifests and the premises of Wilk's theorem are violated. This leads to values of the test statistic significantly lower than a chi(2) distribution at that confidence level. On the other hand, for facilities which can place better constraints on ffi the cyclic nature of the variable is hidden and, as the potential of the facility improves, the values of the test statistics first become slightly higher than and then approach asymptotically a chi(2) distribution. The role of sign degeneracies is also discussed.
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    Searching for sterile neutrinos at the ESSνSB
    Blennow, Mattias; Coloma, Pilar; Fernandez-Martinez, Enrique (Springer, 2014-12-17)
    The ESS nu SB project is a proposed neutrino oscillation experiment based on the European Spallation Source with the search for leptonic CP violation as its main aim. In this letter we show that a near detector at around 1 km distance from the beamline is not only very desirable for keeping the systematic errors affecting the CP search under control, but would also provide a significant sensitivity probe for sterile neutrino oscillations in the region of the parameter space favored by the long-standing LSND anomaly. We find that the effective mixing angle theta(mu e) can be probed down to sin(2)(2 theta(mu e)) similar or equal to 2(8) . 10(-3) at 5 sigma assuming 15% bin-to-bin (un) correlated systematics.
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    Statistical interpretation of sterile neutrino oscillation searches at reactors
    Coloma, Pilar; Huber, Patrick; Schwetz, Thomas (2021-01-02)
    A considerable experimental effort is currently under way to test the persistent hints for oscillations due to an eV-scale sterile neutrino in the data of various reactor neutrino experiments. The assessment of the statistical significance of these hints is usually based on Wilks' theorem, whereby the assumption is made that the log-likelihood is chi 2-distributed. However, it is well known that the preconditions for the validity of Wilks' theorem are not fulfilled for neutrino oscillation experiments. In this work we derive a simple asymptotic form of the actual distribution of the log-likelihood based on reinterpreting the problem as fitting white Gaussian noise. From this formalism we show that, even in the absence of a sterile neutrino, the expectation value for the maximum likelihood estimate of the mixing angle remains non-zero with attendant large values of the log-likelihood. Our analytical results are then confirmed by numerical simulations of a toy reactor experiment. Finally, we apply this framework to the data of the Neutrino-4 experiment and show that the null hypothesis of no-oscillation is rejected at the 2.6 sigma level, compared to 3.2 sigma obtained under the assumption that Wilks' theorem applies.
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    Statistical significance of the sterile-neutrino hypothesis in the context of reactor and gallium data
    Berryman, Jeffrey M.; Coloma, Pilar; Huber, Patrick; Schwetz, Thomas; Zhou, Albert (Springer, 2022-02-08)
    We evaluate the statistical significance of the 3+1 sterile-neutrino hypothesis using nu(e) and (nu) over bar (e) disappearance data from reactor, solar and gallium radioactive source experiments. Concerning the latter, we investigate the implications of the recent BEST results. For reactor data we focus on relative measurements independent of flux predictions. For the problem at hand, the usual chi(2)-approximation to hypothesis testing based on Wilks' theorem has been shown in the literature to be inaccurate. We therefore present results based on Monte Carlo simulations, and find that this typically reduces the significance by roughly 1 sigma with respect to the naive expectation. We find no significant indication in favor of sterile-neutrino oscillations from reactor data. On the other hand, gallium data (dominated by the BEST result) show more than 5 sigma of evidence supporting the sterile-neutrino hypothesis, favoring oscillation parameters in agreement with constraints from reactor data. This explanation is, however, in significant tension (similar to 3 sigma) with solar neutrino experiments. In order to assess the robustness of the signal for gallium experiments we present a discussion of the impact of cross-section uncertainties on the results.