Neutrino oscillation physics with a higher γ\gamma β\beta-beam

The precision measurement and discovery potential of a neutrino factory based on a storage ring of boosted radioactive ions ($\beta$-beam) is re-examined. In contrast with past designs, which assume ion $\gamma$ factors of $\sim 100$ and baselines of L=130 km, we emphasize the advantages of boosting the ions to higher $\gamma$ and increasing the baseline proportionally. In particular, we consider a medium-$\gamma$ scenario ($\gamma \sim 500$, L=730 km) and a high-$\gamma$ scenario ($\gamma \sim 2000$, L = 3000 km).The increase in statistics, which grow linearly with the average beam energy, the ability to exploit the energy dependence of the signal and the sizable matter effects at this longer baseline all increase the discovery potential of such a machine very significantly.Comment: An error corrected, conclusions unchanged. Revised version to appear in Nuclear Physics

Optimal β\beta-beam at the CERN-SPS

A $\beta$-beam with maximum $\gamma=150$ (for \helio ions) or $\gamma=250$ (for \neon) could be achieved at the CERN-SPS. We study the sensitivity to $\theta_{13}$ and $\delta$ of such a beam as function of $\gamma$, optimizing with the baseline constrained to CERN-Frejus (130 km), and also with simultaneous variation of the baseline. These results are compared to the {\it standard} scenario previously considered, with lower $\gamma=60/100$, and also with a higher $\gamma\sim 350$ option that requires a more powerful accelerator. Although higher $\gamma$ is better, loss of sensitivity to $\theta _{13}$ and $\delta$ is most pronounced for $\gamma$ below 100.Comment: 22 page

Secondary scintillation yield in high-pressure xenon gas for neutrinoless double beta decay (0νββ) search

AbstractThe search for neutrinoless double beta decay (0νββ) is an important topic in contemporary physics with many active experiments. New projects are planning to use high-pressure xenon gas as both source and detection medium. The secondary scintillation processes available in noble gases permit large amplification with negligible statistical fluctuations, offering the prospect of energy resolution approaching the Fano factor limit. This Letter reports results for xenon secondary scintillation yield, at room temperature, as a function of electric field in the gas scintillation gap for pressures ranging from 2 to 10 bar. A Large Area Avalanche Photodiode (LAAPD) collected the VUV secondary scintillation produced in the gas. X-rays directly absorbed in the LAAPD are used as a reference for determining the number of charge carriers produced by the scintillation pulse and, hence, the number of photons impinging the LAAPD. The number of photons produced per drifting electron and per kilovolt, the so-called scintillation amplification parameter, displays a small increase with pressure, ranging from 141±6 at 2 bar to 170±10 at 8 bar. In our setup, this parameter does not increase above 8 bar due to non-negligible electron attachment. The results are in good agreement with those presented in the literature in the 1 to 3 bar range. The increase of the scintillation amplification parameter with pressure for high gas densities has been also observed in former work at cryogenic temperatures

Measurement of CP violation at a Neutrino Factory

The prospects of measuring CP violation in the leptonic sector using the intense neutrino beams arising from muon decay in the straight sections of a muon accumulator ring (the so-called neutrino factory) are discussed.Comment: Invited talk given at the CP2000 Conference in Ferrara, September, 200

The electronics of the energy plane of the NEXT-White detector

[EN] This paper describes the electronics of NEXT-White (NEW) detector PMT plane, a high pressure xenon TPC with electroluminescent amplification (HPXe-EL) currently operating at the Laboratorio Subterraneo de Canfranc (LSC) in Huesca, Spain. In NEXT-White the energy of the event is measured by a plane of photomultipliers (PMTs) located behind a transparent cathode. The PMTs are Hamamatsu R11410-10 chosen due to their low radioactivity. The electronics have been designed and implemented to fulfill strict requirements: an overall energy resolution below 1% and a radiopurity budget of 20 mBq unit(-1) in the chain of Bi-214. All the components and materials have been carefully screened to assure a low radioactivity level and at the same time meet the required front-end electronics specifications. In order to reduce low frequency noise effects and enhance detector safety a grounded cathode connection has been used for the PMTs. This implies an AC-coupled readout and baseline variations in the PMT signals. A detailed description of the electronics and a novel approach based on a digital baseline restoration to obtain a linear response and handle AC coupling effects is presented. The final PMT channel design has been characterized with linearity better than 0.4% and noise below 0.4mV.We acknowledge support from the following agencies and institutions: the European Research Council (ERC), Spain under the Advanced Grant 339787-NEXT; the Ministerio de Economia y Competitividad of Spain under grants FIS2014-53371-C04, the Severo Ochoa Program, Spain SEV-2014-0398 and the Maria de Maetzu Program, Spain MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT and FEDER, Spain through the program COMPETE, projects PTDC/FIS-NUC/2525/2014 and UID/FIS/04559/2013; the U.S. Department of Energy under contracts number DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and de-sc0017721 (University of Texas at Arlington); and the University of Texas at Arlington. We acknowledge partial support from the European Union Horizon 2020 research and innovation programme, Spain under the Marie Sklodowska-Curie grant agreements No. 690575 and 674896. We also warmly acknowledge the Laboratorio Nazionale di Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.Álvarez-Puerta, V.; Herrero Bosch, V.; Esteve Bosch, R.; Laing, A.; Rodriguez-Samaniego, J.; Querol-Segura, M.; Monrabal, F.... (2019). The electronics of the energy plane of the NEXT-White detector. Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment. 917:68-76. https://doi.org/10.1016/j.nima.2018.11.126S687691

Superbeams plus Neutrino Factory: the golden path to leptonic CP violation

Superbeams (SB) and neutrino factories (NF) are not alternative facilities for exploring neutrino oscillation physics, but successive steps. The correct strategy is to contemplate the combination of their expected physics results. We show its important potential on the disappearance of fake degenerate solutions in the simultaneous measurement Of theta(13) and leptonic CP violation. Intrinsic, sign (Deltam(13)(2)) and theta(23) degeneracies are shown to be extensively eliminated when the results from one NF baseline and a SB facility are combined. A key point is the different average neutrino energy and baseline of the facilities. For values of theta(13) near its present limit, the short NF baseline, e.g., L = 732 km, becomes, after such a combination, a very interesting distance. For smaller theta(13), an intermediate NF baseline of O (3000 km) is still required

GraXe, graphene and xenon for neutrinoless double beta decay searches

We propose a new detector concept, GraXe (to be pronounced as grace), to search for neutrinoless double beta decay in Xe-136. GraXe combines a popular detection medium in rare-event searches, liquid xenon, with a new, background-free material, graphene. In our baseline design of GraXe, a sphere made of graphene-coated titanium mesh and filled with liquid xenon (LXe) enriched in the Xe-136 isotope is immersed in a large volume of natural LXe instrumented with photodetectors. Liquid xenon is an excellent scintillator, reasonably transparent to its own light. Graphene is transparent over a large frequency range, and impermeable to the xenon. Event position could be deduced from the light pattern detected in the photosensors. External backgrounds would be shielded by the buffer of natural LXe, leaving the ultra-radiopure internal volume virtually free of background. Industrial graphene can be manufactured at a competitive cost to produce the sphere. Enriching xenon in the isotope Xe-136 is easy and relatively cheap, and there is already near one ton of enriched xenon available in the world (currently being used by the EXO, KamLAND-Zen and NEXT experiments). All the cryogenic know-how is readily available from the numerous experiments using liquid xenon. An experiment using the GraXe concept appears realistic and affordable in a short time scale, and its physics potential is enormous.Comment: 17 pages, 4 figures, 2 tables. Several typos and a reference corrected. Version accepted for publication in the Journal of Cosmology and Astroparticle Physics (JCAP

On the measurement of leptonic CP violation

We show that the simultaneous determination of the leptonic CP-odd phase $\delta$ and the angle $\theta_{13}$ from the subleading transitions $\nu_e\to\nu_\mu$ and ${\bar\nu}_e\to{\bar\nu}_\mu$ results generically, at fixed neutrino energy and baseline, in two degenerate solutions. In light of this, we refine a previous analysis of the sensitivity to leptonic CP violation at a neutrino factory, in the LMA-MSW scenario, by exploring the full range of $\delta$ and $\theta_{13}$. Furthermore, we take into account the expected uncertainties on the solar and atmospheric oscillation parameters and in the average Earth matter density along the neutrino path. An intermediate baseline of O(3000) km is still the best option to tackle CP violation, although a combination of two baselines turns out to be very important in resolving degeneracies.Comment: 19 pages, 14 figures, uses epsfi

Discovery potential of xenon-based neutrinoless double beta decay experiments in light of small angular scale CMB observations

The South Pole Telescope (SPT) has probed an expanded angular range of the CMB temperature power spectrum. Their recent analysis of the latest cosmological data prefers nonzero neutrino masses, mnu = 0.32+-0.11 eV. This result, if confirmed by the upcoming Planck data, has deep implications on the discovery of the nature of neutrinos. In particular, the values of the effective neutrino mass involved in neutrinoless double beta decay (bb0nu) are severely constrained for both the direct and inverse hierarchy, making a discovery much more likely. In this paper, we focus in xenon-based bb0nu experiments, on the double grounds of their good performance and the suitability of the technology to large-mass scaling. We show that the current generation, with effective masses in the range of 100 kg and conceivable exposures in the range of 500 kg year, could already have a sizable opportunity to observe bb0nu events, and their combined discovery potential is quite large. The next generation, with an exposure in the range of 10 ton year, would have a much more enhanced sensitivity, in particular due to the very low specific background that all the xenon technologies (liquid xenon, high-pressure xenon and xenon dissolved in liquid scintillator) can achieve. In addition, a high-pressure xenon gas TPC also features superb energy resolution. We show that such detector can fully explore the range of allowed effective Majorana masses, thus making a discovery very likely

Low-diffusion Xe-He gas mixtures for rare-event detection: electroluminescence yield

[EN] High pressure xenon Time Projection Chambers (TPC) based on secondary scintillation (electroluminescence) signal amplification are being proposed for rare event detection such as directional dark matter, double electron capture and double beta decay detection. The discrimination of the rare event through the topological signature of primary ionisation trails is a major asset for this type of TPC when compared to single liquid or double-phase TPCs, limited mainly by the high electron diffusion in pure xenon. Helium admixtures with xenon can be an attractive solution to reduce the electron diffu- sion significantly, improving the discrimination efficiency of these optical TPCs. We have measured the electroluminescence (EL) yield of Xe-He mixtures, in the range of 0 to 30% He and demonstrated the small impact on the EL yield of the addition of helium to pure xenon. For a typical reduced electric field of 2.5 kV/cm/bar in the EL region, the EL yield is lowered by similar to 2%, 3%, 6% and 10% for 10%, 15%, 20% and 30% of helium concentration, respectively. This decrease is less than what has been obtained from the most recent simulation framework in the literature. The impact of the addition of helium on EL statistical fluctuations is negligible, within the experimental uncertainties. The present results are an important benchmark for the simulation tools to be applied to future optical TPCs based on Xe-He mixtures.The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Marie Sklodowska-Curie Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economa y Competitividad of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program SEV-2014-0398 and the Mara de Maetzu Program MDM-2016-0692; the GVA of Spain under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014, under project UID/FIS/04559/2013 to fund the activities of LIBPhys, and under grants PD/BD/105921/2014, SFRH/BPD/109180/2015; the U.S. Department of Energy under contracts number DEAC02-06CH11357 (Argonne National Laboratory), DE-AC0207CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A& M) and DE-SC0019223/DESC0019054 (University of Texas at Arlington); and the University of Texas at Arlington. DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC-2015-18820. We also warmly acknowledge the Laboratori Nazionali del Gran Sasso (LNGS) and the Dark Side collaboration for their help with TPB coating of various parts of the NEXT-White TPC. Finally, we are grateful to the Laboratorio Subterraneo de Canfranc for hosting and supporting the NEXT experiment.Fernandes, A.; Henriques, C.; Mano, R.; González-Díaz, D.; Azevedo, C.; Silva, P.; Gómez-Cadenas, J.... (2020). Low-diffusion Xe-He gas mixtures for rare-event detection: electroluminescence yield. Journal of High Energy Physics (Online). (4):1-18. https://doi.org/10.1007/JHEP04(2020)034S1184D.R. Nygren, Columnar recombination: a tool for nuclear recoil directional sensitivity in a xenon-based direct detection WIMP search, J. Phys. Conf. Ser.460 (2013) 012006 [INSPIRE].G. 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