arXiv subjects

A. Vacheret

Publications and source records attributed to A. Vacheret.

At least 19 recordsLinked to original sources

arXiv2024

Search for Very-Short-Baseline Oscillations of Reactor Antineutrinos with the SoLid Detector

In this letter we report the first scientific result based on antineutrinos emitted from the BR2 reactor at SCK CEN. The SoLid experiment uses a novel type of highly granular detector whose basic detection unit combines two scintillators, PVT and 6LiF:ZnS(Ag), to measure antineutrinos via their inverse-beta-decay products. An advantage of PVT is its highly linear response as a function of deposited particle energy. The full-scale detector comprises 12800 voxels and operates over a very short 6.3--8.9 m baseline from the reactor core. The detector segmentation and its 3D imaging capabilities facilitate the extraction of the positron energy from the rest of the visible energy, allowing the latter to be utilised for signal-background discrimination. We present a result based on 280 reactor-on days (55 MW mean power) and 172 reactor-off days, respectively, of live data-taking. A total of 29479 $\pm$ 603 (stat.) antineutrino candidates have been selected, corresponding to an average rate of 105 events per day and a signal-to-background ratio of 0.27. A search for disappearance of antineutrinos to a sterile state has been conducted using complementary model-dependent frequentist and Bayesian fits, providing constraints on the allowed region of the Reactor Antineutrino Anomaly.

hep-ex↗

arXiv2022

Fast and Flexible Analysis of Direct Dark Matter Search Data with Machine Learning

We present the results from combining machine learning with the profile likelihood fit procedure, using data from the Large Underground Xenon (LUX) dark matter experiment. This approach demonstrates reduction in computation time by a factor of 30 when compared with the previous approach, without loss of performance on real data. We establish its flexibility to capture non-linear correlations between variables (such as smearing in light and charge signals due to position variation) by achieving equal performance using pulse areas with and without position-corrections applied. Its efficiency and scalability furthermore enables searching for dark matter using additional variables without significant computational burden. We demonstrate this by including a light signal pulse shape variable alongside more traditional inputs such as light and charge signal strengths. This technique can be exploited by future dark matter experiments to make use of additional information, reduce computational resources needed for signal searches and simulations, and make inclusion of physical nuisance parameters in fits tractable.

astro-ph.CO↗

arXiv2022

Nuclear Recoil Calibration at Sub-keV Energies in LUX and Its Impact on Dark Matter Search Sensitivity

Dual-phase xenon time projection chamber (TPC) detectors offer heightened sensitivities for dark matter detection across a spectrum of particle masses. To broaden their capability to low-mass dark matter interactions, we investigated the light and charge responses of liquid xenon (LXe) to sub-keV nuclear recoils. Using neutron events from a pulsed Adelphi Deuterium-Deuterium neutron generator, an in situ calibration was conducted on the LUX detector. We demonstrate direct measurements of light and charge yields down to 0.45 keV and 0.27 keV, respectively, both approaching single quanta production, the physical limit of LXe detectors. These results hold significant implications for the future of dual-phase xenon TPCs in detecting low-mass dark matter via nuclear recoils.

physics.ins-det↗

arXiv2022

Measurement of the generalized spin polarizabilities of the neutron in the low $Q^2$ region

Understanding the nucleon spin structure in the regime where the strong interaction becomes truly strong poses a challenge to both experiment and theory. At energy scales below the nucleon mass of about 1 GeV, the intense interaction among the quarks and gluons inside the nucleon makes them highly correlated. Their coherent behaviour causes the emergence of effective degrees of freedom, requiring the application of non-perturbative techniques, such as chiral effective field theory. Here, we present measurements of the neutron's generalized spin-polarizabilities that quantify the neutron's spin precession under electromagnetic fields at very low energy-momentum transfer squared down to 0.035 GeV$^2$. In this regime, chiral effective field theory calculations are expected to be applicable. Our data, however, show a strong discrepancy with these predictions, presenting a challenge to the current description of the neutron's spin properties.

nucl-ex↗

arXiv2021

Constraints on Effective Field Theory Couplings Using 311.2 days of LUX Data

We report here the results of an Effective Field Theory (EFT) WIMP search analysis using LUX data. We build upon previous LUX analyses by extending the search window to include nuclear recoil energies up to $\sim$180 keV$_{nr}$, requiring a reassessment of data quality cuts and background models. In order to use a binned Profile Likelihood statistical framework, the development of new analysis techniques to account for higher-energy backgrounds was required. With a 3.14$\times10^4$ kg$\cdot$day exposure using data collected between 2014 and 2016, we set 90\% C.L. exclusion limits on non-relativistic EFT WIMP couplings to neutrons and protons, providing the most stringent constraints on a significant fraction of the possible EFT WIMP interactions. Additionally, we report world-leading exclusion limits on inelastic EFT WIMP-nucleon recoils.

astro-ph.CO↗

arXiv2020

SoLid: A short baseline reactor neutrino experiment

The SoLid experiment, short for Search for Oscillations with a Lithium-6 detector, is a new generation neutrino experiment which tries to address the key challenges for high precision reactor neutrino measurements at very short distances from a reactor core and with little or no overburden. The primary goal of the SoLid experiment is to perform a precise measurement of the electron antineutrino energy spectrum and flux and to search for very short distance neutrino oscillations as a probe of eV-scale sterile neutrinos. This paper describes the SoLid detection principle, the mechanical design and the construction of the detector. It then reports on the installation and commissioning on site near the BR2 reactor, Belgium, and finally highlights its performance in terms of detector response and calibration.

physics.ins-det↗

arXiv2020

Discrimination of electronic recoils from nuclear recoils in two-phase xenon time projection chambers

We present a comprehensive analysis of electronic recoil vs. nuclear recoil discrimination in liquid/gas xenon time projection chambers, using calibration data from the 2013 and 2014-16 runs of the Large Underground Xenon (LUX) experiment. We observe strong charge-to-light discrimination enhancement with increased event energy. For events with S1 = 120 detected photons, i.e. equivalent to a nuclear recoil energy of $\sim$100 keV, we observe an electronic recoil background acceptance of $<10^{-5}$ at a nuclear recoil signal acceptance of 50%. We also observe modest electric field dependence of the discrimination power, which peaks at a field of around 300 V/cm over the range of fields explored in this study (50-500 V/cm). In the WIMP search region of S1 = 1-80 phd, the minimum electronic recoil leakage we observe is ${(7.3\pm0.6)\times10^{-4}}$, which is obtained for a drift field of 240-290 V/cm. Pulse shape discrimination is utilized to improve our results, and we find that, at low energies and low fields, there is an additional reduction in background leakage by a factor of up to 3. We develop an empirical model for recombination fluctuations which, when used alongside the Noble Element Scintillation Technique (NEST) simulation package, correctly reproduces the skewness of the electronic recoil data. We use this updated simulation to study the width of the electronic recoil band, finding that its dominant contribution comes from electron-ion recombination fluctuations, followed in magnitude of contribution by fluctuations in the S1 signal, fluctuations in the S2 signal, and fluctuations in the total number of quanta produced for a given energy deposition.

physics.ins-det↗

arXiv2020

Improving sensitivity to low-mass dark matter in LUX using a novel electrode background mitigation technique

This paper presents a novel technique for mitigating electrode backgrounds that limit the sensitivity of searches for low-mass dark matter (DM) using xenon time projection chambers. In the LUX detector, signatures of low-mass DM interactions would be very low energy ($\sim$keV) scatters in the active target that ionize only a few xenon atoms and seldom produce detectable scintillation signals. In this regime, extra precaution is required to reject a complex set of low-energy electron backgrounds that have long been observed in this class of detector. Noticing backgrounds from the wire grid electrodes near the top and bottom of the active target are particularly pernicious, we develop a machine learning technique based on ionization pulse shape to identify and reject these events. We demonstrate the technique can improve Poisson limits on low-mass DM interactions by a factor of $2$-$7$ with improvement depending heavily on the size of ionization signals. We use the technique on events in an effective $5$ tonne$\cdot$day exposure from LUX's 2013 science operation to place strong limits on low-mass DM particles with masses in the range $m_χ\in0.15$-$10$ GeV. This machine learning technique is expected to be useful for near-future experiments, such as LZ and XENONnT, which hope to perform low-mass DM searches with the stringent background control necessary to make a discovery.

hep-ex↗

arXiv2020

Investigation of background electron emission in the LUX detector

Dual-phase xenon detectors, as currently used in direct detection dark matter experiments, have observed elevated rates of background electron events in the low energy region. While this background negatively impacts detector performance in various ways, its origins have only been partially studied. In this paper we report a systematic investigation of the electron pathologies observed in the LUX dark matter experiment. We characterize different electron populations based on their emission intensities and their correlations with preceding energy depositions in the detector. By studying the background under different experimental conditions, we identified the leading emission mechanisms, including photoionization and the photoelectric effect induced by the xenon luminescence, delayed emission of electrons trapped under the liquid surface, capture and release of drifting electrons by impurities, and grid electron emission. We discuss how these backgrounds can be mitigated in LUX and future xenon-based dark matter experiments.

physics.ins-det↗

arXiv2020

Search for two neutrino double electron capture of $^{124}$Xe and $^{126}$Xe in the full exposure of the LUX detector

Two-neutrino double electron capture is a process allowed in the Standard Model of Particle Physics. This rare decay has been observed in $^{78}$Kr, $^{130}$Ba and more recently in $^{124}$Xe. In this publication we report on the search for this process in $^{124}$Xe and $^{126}$Xe using the full exposure of the Large Underground Xenon (LUX) experiment, in a total of of 27769.5~kg-days. No evidence of a signal was observed, allowing us to set 90\% C.L. lower limits for the half-lives of these decays of $2.0\times10^{21}$~years for $^{124}$Xe and $1.9\times10^{21}$~years for $^{126}$Xe.

nucl-ex↗

arXiv2020

Measurement of the 3He Spin-Structure Functions and of Neutron (3He) Spin-Dependent Sum Rules at 0.035<Q^2<0.24 GeV^2

The spin-structure functions $g_1$ and $g_2$, and the spin-dependent partial cross-section $σ_\mathrm{TT}$ have been extracted from the polarized cross-sections differences, $Δσ_{\parallel}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ and $Δσ_{\perp}\hspace{-0.06cm}\left(ν,Q^{2}\right)$ measured for the $\vec{^\textrm{3}\textrm{He}}(\vec{\textrm{e}},\textrm{e}')\textrm{X}$ reaction, in the E97-110 experiment at Jefferson Lab. Polarized electrons with energies from 1.147 to 4.404 GeV were scattered at angles of 6$^{\circ}$ and 9$^{\circ}$ from a longitudinally or transversely polarized $^{3}$He target. The data cover the kinematic regions of the quasi-elastic, resonance production and beyond. From the extracted spin-structure functions, the first moments $\overline{Γ_1}\hspace{-0.06cm}\left(Q^{2}\right)$, $Γ_2\hspace{-0.06cm}\left(Q^{2}\right)$ and $I_{\mathrm{TT}}\hspace{-0.06cm}\left(Q^{2}\right)$ are evaluated with high precision for the neutron in the $Q^2$ range from 0.035 to 0.24~GeV$^{2}$. The comparison of the data and the chiral effective field theory predictions reveals the importance of proper treatment of the $Δ$ degree of freedom for spin observables.

nucl-ex↗

arXiv2020

An Effective Field Theory Analysis of the First LUX Dark Matter Search

The Large Underground Xenon (LUX) dark matter search was a 250-kg active mass dual-phase time projection chamber that operated by detecting light and ionization signals from particles incident on a xenon target. In December 2015, LUX reported a minimum 90% upper C.L. of 6e-46 cm^2 on the spin-independent WIMP-nucleon elastic scattering cross section based on a 1.4e4 kg*day exposure in its first science run. Tension between experiments and the absence of a definitive positive detection suggest it would be prudent to search for WIMPs outside the standard spin-independent/spin-dependent paradigm. Recent theoretical work has identified a complete basis of 14 independent effective field theory (EFT) operators to describe WIMP-nucleon interactions. In addition to spin-independent and spin-dependent nuclear responses, these operators can produce novel responses such as angular-momentum-dependent and spin-orbit couplings. Here we report on a search for all 14 of these EFT couplings with data from LUX's first science run. Limits are placed on each coupling as a function of WIMP mass.

astro-ph.CO↗

arXiv2020

Improved Modeling of $β$ Electronic Recoils in Liquid Xenon Using LUX Calibration Data

We report here methods and techniques for creating and improving a model that reproduces the scintillation and ionization response of a dual-phase liquid and gaseous xenon time-projection chamber. Starting with the recent release of the Noble Element Simulation Technique (NEST v2.0), electronic recoil data from the $β$ decays of ${}^3$H and ${}^{14}$C in the Large Underground Xenon (LUX) detector were used to tune the model, in addition to external data sets that allow for extrapolation beyond the LUX data-taking conditions. This paper also presents techniques used for modeling complicated temporal and spatial detector pathologies that can adversely affect data using a simplified model framework. The methods outlined in this report show an example of the robust applications possible with NEST v2.0, while also providing the final electronic recoil model and detector parameters that will used in the new analysis package, the LUX Legacy Analysis Monte Carlo Application (LLAMA), for accurate reproduction of the LUX data. As accurate background reproduction is crucial for the success of rare-event searches, such as dark matter direct detection experiments, the techniques outlined here can be used in other single-phase and dual-phase xenon detectors to assist with accurate ER background reproduction.

physics.ins-det↗

arXiv2019

First direct detection constraint on mirror dark matter kinetic mixing using LUX 2013 data

We present the results of a direct detection search for mirror dark matter interactions, using data collected from the Large Underground Xenon experiment during 2013, with an exposure of 95 live-days $\times$ 118 kg. Here, the calculations of the mirror electron scattering rate in liquid xenon take into account the shielding effects from mirror dark matter captured within the Earth. Annual and diurnal modulation of the dark matter flux and atomic shell effects in xenon are also accounted for. Having found no evidence for an electron recoil signal induced by mirror dark matter interactions we place an upper limit on the kinetic mixing parameter over a range of local mirror electron temperatures between 0.1 and 0.6 keV. This limit shows significant improvement over the previous experimental constraint from orthopositronium decays and significantly reduces the allowed parameter space for the model. We exclude mirror electron temperatures above 0.3 keV at a 90% confidence level, for this model, and constrain the kinetic mixing below this temperature.

hep-ex↗

arXiv2019

Commissioning and Operation of the Readout System for the SoLid Neutrino Detector

The SoLid experiment aims to measure neutrino oscillation at a baseline of 6.4 m from the BR2 nuclear reactor in Belgium. Anti-neutrinos interact via inverse beta decay (IBD), resulting in a positron and neutron signal that are correlated in time and space. The detector operates in a surface building, with modest shielding, and relies on extremely efficient online rejection of backgrounds in order to identify these interactions. A novel detector design has been developed using 12800 5 cm cubes for high segmentation. Each cube is formed of a sandwich of two scintillators, PVT and 6LiF:ZnS(Ag), allowing the detection and identification of positrons and neutrons respectively. The active volume of the detector is an array of cubes measuring 80x80x250 cm (corresponding to a fiducial mass of 1.6 T), which is read out in layers using two dimensional arrays of wavelength shifting fibres and silicon photomultipliers, for a total of 3200 readout channels. Signals are recorded with 14 bit resolution, and at 40 MHz sampling frequency, for a total raw data rate of over 2 Tbit/s. In this paper, we describe a novel readout and trigger system built for the experiment, that satisfies requirements on: compactness, low power, high performance, and very low cost per channel. The system uses a combination of high price-performance FPGAs with a gigabit Ethernet based readout system, and its total power consumption is under 1 kW. The use of zero suppression techniques, combined with pulse shape discrimination trigger algorithms to detect neutrons, results in an online data reduction factor of around 10000. The neutron trigger is combined with a large per-channel history time buffer, allowing for unbiased positron detection. The system was commissioned in late 2017, with successful physics data taking established in early 2018.

physics.ins-det↗

arXiv2019

Improved Measurements of the \b{eta}-Decay Response of Liquid Xenon with the LUX Detector

We report results from an extensive set of measurements of the \b{eta}-decay response in liquid xenon.These measurements are derived from high-statistics calibration data from injected sources of both $^{3}$H and $^{14}$C in the LUX detector. The mean light-to-charge ratio is reported for 13 electric field values ranging from 43 to 491 V/cm, and for energies ranging from 1.5 to 145 keV.

physics.ins-det↗

arXiv2018

Development of a Quality Assurance Process for the SoLid Experiment

The SoLid experiment has been designed to search for an oscillation pattern induced by a light sterile neutrino state, utilising the BR2 reactor of SCK$\bullet$CEN, in Belgium. The detector leverages a new hybrid technology, utilising two distinct scintillators in a cubic array, creating a highly segmented detector volume. A combination of 5 cm cubic polyvinyltoluene cells, with $^6$LiF:ZnS(Ag) sheets on two faces of each cube, facilitate reconstruction of the neutrino signals. % The polyvinyltoluene scintillator is used as an $\overlineν_e$ target for the inverse beta decay of ($\overlineν_e + p \rightarrow e^{+}+n$), with the $^6$LiF:ZnS(Ag) sheets used for associated neutron detection. Scintillation signals are read out by a network of wavelength shifting fibres connected to multipixel photon counters. Whilst the high granularity provides a powerful toolset to discriminate backgrounds; by itself the segmentation also represents a challenge in terms of homogeneity and calibration, for a consistent detector response. The search for this light sterile neutrino implies a sensitivity to distortions of around $\mathcal{O}$(10)\% in the energy spectrum of reactor $\overlineν_e$. Hence, a very good neutron detection efficiency, light yield and homogeneous detector response are critical for data validation. The minimal requirements for the SoLid physics program are a light yield and a neutron detection efficiency larger than 40 PA/MeV/cube and 50 \% respectively. In order to guarantee these minimal requirements, the collaboration developed a rigorous quality assurance process for all 12800 cubic cells of the detector. To carry out the quality assurance process, an automated calibration system called CALIPSO was designed and constructed.

physics.ins-det↗

arXiv2018

Optimisation of the scintillation light collection and uniformity for the SoLid experiment

This paper presents a comprehensive optimisation study to maximise the light collection efficiency of scintillating cube elements used in the SoLid detector. Very short baseline reactor experiments, like SoLid, look for active to sterile neutrino oscillation signatures in the anti-neutrino energy spectrum as a function of the distance to the core and energy. Performing a precise search requires high light yield of the scintillating elements and uniformity of the response in the detector volume. The SoLid experiment uses an innovative hybrid technology with two different scintillators: polyvinyltoluene scintillator cubes and $^6$LiF:ZnS(Ag) screens. A precision test bench based on a $^{207}$Bi calibration source has been developed to study improvements on the energy resolution and uniformity of the prompt scintillation signal of antineutrino interactions. A trigger system selecting the 1~MeV conversion electrons provides a Gaussian energy peak and allows for precise comparisons of the different detector configurations that were considered to improve the SoLid detector light collection. The light collection efficiency is influenced by the choice of wrapping material, the position of the $^6$LiF:ZnS(Ag) screen, the type of fibre, the number of optical fibres and the type of mirror at the end of the fibre. This study shows that large gains in light collection efficiency are possible compared to the SoLid SM1 prototype. The light yield for the SoLid detector is expected to be at least 52$\pm$2 photo-avalanches per MeV per cube, with a relative non-uniformity of 6 %, demonstrating that the required energy resolution of at least 14 % at 1 MeV can be achieved.

physics.ins-det↗