NEXT Collaboration(Henriques, C. A. O. et al), Benlloch-Rodriguez, J. M., Carcel, S., Carrion, J. V., Diaz, J., Felkai, R., et al. (2022). Neutral Bremsstrahlung Emission in Xenon Unveiled. Phys. Rev. X, 12(2), 021005–23pp.
Abstract: We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White time projection chamber (TPC) and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that is postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10(-2) photon/e(-) cm(-1) bar(-1) at pressure-reduced electric field values of 50 V cm(-1) bar(-1) to above 3 x 10(-1) photon/e(-) cm(-1) bar(-1) at 500 V cm(-1) bar(-1). Above 1.5 kV cm(-1) bar(-1), values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e(-) cm(-1) bar(-1), which is about 2 orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the "buffer region, where keeping the electric field below the electroluminescence threshold does not suffice to extinguish secondary scintillation. The electric field leakage in this region should be mitigated to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path toward obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e(-) cm(-1).
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NEXT Collaboration(McDonald, A. D. et al), Alvarez, V., Benlloch-Rodriguez, J. M., Botas, A., Carcel, S., Carrion, J. V., et al. (2018). Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging. Phys. Rev. Lett., 120(13), 132504–6pp.
Abstract: A new method to tag the barium daughter in the double-beta decay of Xe-136 is reported. Using the technique of single molecule fluorescent imaging (SMFI), individual barium dication (Ba++) resolution at a transparent scanning surface is demonstrated. A single-step photobleach confirms the single ion interpretation. Individual ions are localized with superresolution (similar to 2 nm), and detected with a statistical significance of 12.9 sigma over backgrounds. This lays the foundation for a new and potentially background-free neutrinoless double-beta decay technology, based on SMFI coupled to high pressure xenon gas time projection chambers.
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DUNE Collaboration(Abud, A. A. et al), Amedo, P., Antonova, M., Barenboim, G., Benitez Montiel, C., Cervera-Villanueva, A., et al. (2023). Impact of cross-section uncertainties on supernova neutrino spectral parameter fitting in the Deep Underground Neutrino Experiment. Phys. Rev. D, 107(11), 112012–25pp.
Abstract: A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is to measure the Oo10 thorn MeV neutrinos produced by a Galactic core-collapse supernova if one should occur during the lifetime of the experiment. The liquid-argon-based detectors planned for DUNE are expected to be uniquely sensitive to the & nu;e component of the supernova flux, enabling a wide variety of physics and astrophysics measurements. A key requirement for a correct interpretation of these measurements is a good understanding of the energy-dependent total cross section & sigma;oE & nu; thorn for charged-current & nu;e absorption on argon. In the context of a simulated extraction of supernova & nu;e spectral parameters from a toy analysis, we investigate the impact of & sigma;oE & nu; thorn modeling uncertainties on DUNE's supernova neutrino physics sensitivity for the first time. We find that the currently large theoretical uncertainties on & sigma;oE & nu; thorn must be substantially reduced before the & nu;e flux parameters can be extracted reliably; in the absence of external constraints, a measurement of the integrated neutrino luminosity with less than 10% bias with DUNE requires & sigma;oE & nu; thorn to be known to about 5%. The neutrino spectral shape parameters can be known to better than 10% for a 20% uncertainty on the cross-section scale, although they will be sensitive to uncertainties on the shape of & sigma;oE & nu; thorn . A direct measurement of low-energy & nu;e-argon scattering would be invaluable for improving the theoretical precision to the needed level.
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TAPS Collaboration, Piasecki, K., Matulewicz, T., Yahlali, N., Delagrange, H., Diaz, J., et al. (2010). Emission patterns of neutral pions in 40A MeV Ta plus Au reactions. Phys. Rev. C, 81(5), 054912–7pp.
Abstract: Differential cross sections of neutral pions emitted in Ta-181+Au-197 collisions at a beam energy of 39.5A Me V have been measured with the two-arm photon spectrometer (TAPS). The kinetic energy and transverse momentum spectra of neutral pions cannot be properly described in the framework of the thermal model, nor when the reabsorption of pions is accounted for in a phenomenological model. However, high energy and high momentum tails of the pion spectra can be well fitted through thermal distributions with unexpectedly soft temperature parameters below 10 MeV.
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NEXT Collaboration(Novella, P. et al), Carcel, S., Carrion, J. V., Diaz, J., Martin-Albo, J., Martinez, A., et al. (2022). Measurement of the Xe-136 two-neutrino double-beta-decay half-life via direct background subtraction in NEXT. Phys. Rev. C, 105(5), 055501–8pp.
Abstract: We report a measurement of the half-life of the Xe-136 two-neutrino double-beta decay performed with a novel direct-background-subtraction technique. The analysis relies on the data collected with the NEXT-White detector operated with Xe-136-enriched and Xe-136-depleted xenon, as well as on the topology of double-electron tracks. With a fiducial mass of only 3.5 kg of Xe, a half-life of 2.34(-0.46)(+0.80) (stat)(-0.17)(+0.30) (sys) x 10(21) yr is derived from the background-subtracted energy spectrum. The presented technique demonstrates the feasibility of unique background-model-independent neutrinoless double-beta-decay searches.
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