Spherical Proportional Counter Research Articles

Search for light WIMP recoils on methane with NEWS-G

The NEWS-G collaboration is searching for light dark matter using single-electron-threshold Spherical Proportional Counters (SPCs) filled with light gaseous targets (H, He, Ne). NEWS-G has built a new 140 cm diameter SPC equipped with a multi-anode ACHINOS sensor. Robust calibrations with a UV laser and an \mathrm{^{37}}37Ar source were performed to characterize the detector response to low energy events and achieve statistical background rejection. This work presents preliminary results from physics data taken with methane, leading to world-leading spin-dependent sensitivity under 2 \mathrm{GeV/c^{2}}GeV/c2 WIMP masses.

First operation of an ACHINOS-equipped spherical proportional counter with individual anode read-out

The multi-anode sensor ACHINOS revolutionised the capabilities of the spherical proportional counter by enabling large-size, high-pressure, operation and TPC-like reconstruction capabilities through individual anode read-out. First measurements with an individually read out ACHINOS are performed, which enables improved calibration and response homogenisation. Experimental results demonstrating the improvement in energy resolution brought by the individual anode calibration are presented. These are complemented by detailed simulation studies on the effect of sensor design and manufacturing imperfections, and how they may be corrected both in hardware and analysis.

Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory

Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory

R2D2 TPC: first Xenon results

Radial time projection chambers (TPC), already employed in the search for rare phenomena such as light Dark Matter candidate, could provide a new detection approach for the search of neutrinoless double beta decay (ββ0ν). The assessment of the performances of such a detector for ββ0ν search is indeed the goal of the Rare Decays with Radial Detector (R2D2) R&D. Promising results operating a spherical TPC with argon up to 1 bar have been published in 2021. Supplementary measurements were recently taken extending the gas pressure range up to 3 bar. In addition, a comparison between two detector geometries, namely spherical (SPC for spherical proportional counter) and cylindrical (CPC for cylindrical proportional counter), was performed. Using a relatively simple gas purification system the CPC detector was also operated with xenon at 1 bar: an energy resolution of 1.4% full-width at half-maximum was achieved for drift distances up to 17 cm. Much lower resolution was observed with the SPC. These results are presented in this article.

Probing light DM via the Migdal effect with spherical proportional counter* *Supported by the National Natural Science Foundation of China (12275134, 12275232, 12335005, 12147228), and the Natural Science Foundation of Shandong Province, China (ZR2018QA007)

Owing to its low electronic noise and flexible target materials, the Spherical Proportional Counter (SPC) with a single electron detection threshold can be utilized to search for sub-GeV dark matter (DM). In this study, we investigate the prospects for light DM direct detection via the DM-nucleus Migdal effect in the DARKSPHERE detector. We consider different DM velocity distributions and momentum-transfer effects. For Xenon and Neon targets, we find that the DM mass can be probed down to as low as (10) MeV, and the derived bounds on the DM-nucleus scattering cross section are sensitive to the high-velocity tails of the DM velocity distribution, which can be altered by orders of magnitude for the different DM velocity distributions in the region MeV.

Characterization of the Bakelite Prototype Sensor for NEWS-G

The New Experiments With Spheres - Gas (NEWS-G) group at Queen's University uses Spherical Proportional Counters (SPCs) in the search for dark matter. Incoming radiation interacts with the gas inside the SPC through ionization, producing electron/ion pairs [1]. These primary electrons drift towards the central anode under the influence of an electric field [1]. A secondary ionization, termed avalanche, occurs at distances proportional to the size of the anode resulting in the multiplication of charges [1]. The signal that is produced is proportional to the number of secondary charges created during the avalanche [1]. A 30 cm-diameter sphere was used to characterize a six anode, spherical Bakelite prototype sensor. The sensor is divided into north and south three-anode read-out channels. To study the detector's response, an Fe55 source was placed inside the sphere, which was then filled with 1 bar of 40Ar+CH4 2% gas. The source was moved around the sphere with thirty-second data-taking runs taken at each point and high voltages applied to each channel. Cuts were applied to the event properties to isolate the 5.9 keV Fe55 peak. The peak was plotted as a histogram and fit with a Gaussian function with two additional linear terms. The gain and resolution of the sensor were extracted from the fit parameters. The channel dominance change angle was calculated by interpolating the number of events recorded by each channel at each point on the sphere. The gain, number of events and the channel dominance change angle were mapped on the sphere between 20 and 40 cm arc length in the theta direction, and all the way around the sphere in the phi direction to improve the understanding of the Bakelite sensor.

Sensor Development and Testing for the NEWS-G Dark Matter Experiment

The NEWS-G collaboration utilizes Spherical Proportional Counters (SPCs) in direct detection searches for low-mass dark matter. The detectors use gasses with a high voltage sensor in the centre to collect incoming electrons ionized from particle interactions in the gas. The experiment is currently running at SNOLAB and uses its low threshold requirements to search for Weakly Interacting Massive Particles (WIMPs) with sub-GeV mass. To support charge collection from greater distances within the SPC volume, the detector uses a multi-anode achinos sensor. This style of sensor uses a resistive support structure to hold the anodes in place and correct the electric field in the volume of the detector. Previous sensor versions used support structures made from Bakelite or were 3D printed with a Diamond-Like Carbon coating.
 I worked on further development of the achinos utilizing electrostatic discharge resin to directly 3D print the support structure, allowing for increased precision and production rates. This included adding internal guide tubes to support the wires, reducing pressure points that could cause damage to the wire. These structures were then tested with increasing voltages in an argon gas mixture while being observed for discharges. The sensors were further tested in 30cm diameter sphere to monitor the stability during data-taking runs, leading to design iterations to improve the stability of the sensors and increase the maximum usable voltage. Tests were conducted considering the resistive properties of alternative structure materials, including glass capillary tubes of varying thicknesses, but the resin was further developed for its easier applications to multi-anode structures.
 I also worked to implement new methods of attaching the metal anodes to insulated wire, including the use of silver conductive paste to strengthen the electrical connection. This was measured to have a resistance of about 10Ω, where previous methods had connections too weak to observe.

Status and future prospects of the NEWS-G experiment

The NEWS-G collaboration is searching for light dark matter using spherical proportional counters. Access to the mass range from 50 MeV to 10 GeV is enabled by the combination of low energy threshold, light gaseous targets (H, He, Ne), and highly radio-pure detector construction. Several of the recent developments that have paved the way for the operation of a new 140 cm in diameter, spherical proportional counter are presented. Constructed and commissioned at LSM using 4N copper with a 500\muμxm electroplated inner layer, the detector is now installed in SNOLAB, where it has begun data taking. Building on the electroplating of the current detector, the collaboration construct its next detector directly in the underground laboratory, using ultra-pure copper electroforming. The design and construction of ECUME, a 140 cm in diameter spherical proportional counter fully electroformed underground is discussed, along with the potential to achieve sensitivity reaching the neutrino floor in light Dark Matter searches with a next-generation detector.

An R&D program for the research of 2β0ν decay with a SPC

The objective of the R2D2 R&D is to test the concept of a spherical proportional counter (SPC) for the search of the neutrinoless double beta decay (2β0ν). For this, we built a small prototype (40 cm in diameter), which was filled with an argon-based gas mixture at pressures up to 1.1 bar, and irradiated with a 210Po alpha source. We report on results obtained in terms of directional, volume, and energy responses. We performed time measurements by combining the charge readout from the SPC with the light detection provided by a SiPM. We also studied the possibilities of localizing tracks in the detector and of discriminating multiple tracks.

Fueling the search for light dark matter-electron scattering with spherical proportional counters

Dark matter (DM) detectors employing a spherical proportional counter (SPC) have demonstrated a single-electron detection threshold and are projected to have small background rates. We explore the sensitivity to DM-electron scattering with SPC detectors in the context of darksphere, a proposal for a 300 cm diameter fully electroformed SPC. SPCs can run with different gases, so we investigate the sensitivity for five targets: helium, neon, xenon, methane, and isobutane. We use tools from quantum chemistry to model the atomic and molecular systems and calculate the expected DM induced event rates. We find that darksphere has the potential to improve current exclusion limits on DM masses above 4 MeV by up to 5 orders of magnitude. Neon is the best all-round gas target and provides good sensitivity to scenarios with both light and heavy mediators. Gas mixtures, where methane or isobutane is added to a noble gas, can extend the sensitivity at lower masses. Our study highlights the currently untapped potential of SPCs to search for DM-electron scattering in the MeV-to-GeV DM mass range.

Performance of a spherical high pressure gas TPC for neutrino magnetic moment measurement

The measurement of neutrino magnetic moment larger than 10-19 μB would be a clear signature of physics beyond the standard model other than the existence of massive Dirac neutrinos. The use of a spherical proportional counter detector filled with gas at 40 bar located near a nuclear reactor would be a simple way to perform such a measurement exploiting the developments made on such a technology for the search of dark matter and neutrinoless double beta decay. Different targets can be used just by replacing the gas: xenon, CF4 and argon were compared and the sensitivity in one year of data taking could reach the level of 4.3 × 10-12 μB , 6.5 × 10-12 μB , and 8.5 × 10-12 μB , respectively.

Neutron spectroscopy with a high-pressure nitrogen-filled spherical proportional counter

The spherical proportional counter is a large volume gaseous detector which finds application in several fields, including direct Dark Matter searches. When the detector is filled with nitrogen it becomes an effective neutron spectrometer thanks to the 14N(n,α)11B and 14N(n,p)14C reactions. Nitrogen, however, is a challenging operating gas for proportional counters and requires a high electric field strength to gas pressure ratio. Benefiting from the latest advances in spherical proportional counter instrumentation and simulation techniques, we report first neutron measurements at operating pressures of up to 1.8bar. This achievement enhances the prospects of the spherical proportional counter to act as a neutron spectrometer appropriate for challenging environments, including underground laboratories, and industrial and medical settings.

The NEWS-G detector at SNOLAB

The New Experiments With Spheres-Gas (NEWS-G) collaboration intends to achieve sub-GeV/c2 Weakly Interacting Massive Particles (WIMPs) detection using Spherical Proportional Counters (SPCs). SPCs are gaseous detectors relying on ionisation with a single ionization electron energy threshold. The latest generation of SPC for direct dark matter searches has been installed at SNOLAB in Canada in 2021. This article details the different processes involved in the fabrication of the NEWS-G experiment. Also outlined in this paper are the mitigation strategies, measurements of radioactivity of the different components, and estimations of induced background event rates that were used to quantify and address detector backgrounds.

Neutron spectroscopy with N2-filled high-pressure large-volume spherical proportional counters

Precise in-situ measurements of the neutron flux in underground laboratories is crucial for direct dark matter searches, as neutron induced backgrounds can mimic the typical dark matter signal. The development of a novel neutron spectroscopy technique using Spherical Proportional Counters is investigated. The detector is operated with nitrogen and is sensitive to both fast and thermal neutrons through the 14N(n, α)11B and 14N(n, p)14C reactions. This method holds potential to be a safe, inexpensive, effective, and reliable alternative to 3He-based detectors. Measurements of fast and thermal neutrons from an Am-Be source with a Spherical Proportional Counter operated at pressures up to 2 bar at Birmingham are discussed.

Neutron spectroscopy: The case of the spherical proportional counter

Neutron spectroscopy is an invaluable tool for many scientific and industrial applications, including underground Dark Matter searches. Neutron-induced backgrounds produced by cosmic ray muons and the cavern radioactivity can mimic the expected Dark Matter signal. However, existing neutron detection methods have several drawbacks and limitations, thus measurements remain elusive. A promising new approach to neutron spectroscopy is the use of a nitrogen-filled spherical proportional counter that exploits the 14N(n,α)11B and 14N(n,p)14C reactions. This is a safe, inexpensive, effective and reliable technique. In this work, the latest instrumentation developments are incorporated in a compact detector operated at the University of Birmingham (UoB) with high gain at gas pressure up to 1.8bar. We demonstrate spectroscopic measurements of thermalised and fast neutrons respectively from an 241Am-9Be source and from the MC40 cyclotron facility at UoB. Additionally, the detector response to neutrons is simulated using a framework developed at UoB and compared with the experimental results.

ACHINOS: a multi-anode read-out for position reconstruction and tracking with spherical proportional counters

The spherical proportional counter is a versatile gaseous detector with physics applications ranging from rare event searches to fast neutron spectroscopy. In its simplest form, the detector operates with a single channel read-out, and uses pulse-shape information to reconstruct the interaction radius, which is used for background discrimination and target volume definition. Recent developments in the read-out instrumentation have enabled the use of a multi-anode read-out structure, ACHINOS. The multiple anodes provide information about the interaction position which, coupled with the radial information, can be used to reconstruct an ionisation track. This ability has implications for several applications of the detector, for example, enhanced background discrimination in rare event searches.

Quenching factor measurements of neon nuclei in neon gas

The NEWS-G collaboration uses spherical proportional counters (SPCs) to search for weakly interacting massive particles (WIMPs). In this paper, we report the first measurements of the nuclear quenching factor in neon gas at 2 bar using an SPC deployed in a neutron beam at the TUNL facility. The energy-dependence of the nuclear quenching factor is modeled using a simple power law: αEnrβ; we determine its parameters by simultaneously fitting the data collected with the detector over a range of energies. We measured the following parameters in Ne:CH4 at 2 bar: α=0.2801±0.0050 (fit) ±0.0045 (sys) and β=0.0867±0.020 (fit) ±0.006 (sys). Our measurements do not agree with expected values from SRIM or Lindhard theory. We demonstrated the feasibility of performing quenching factor measurements at sub-keV energies in gases using SPCs and a neutron beam.11 MoreReceived 8 September 2021Accepted 24 December 2021DOI:https://doi.org/10.1103/PhysRevD.105.052004© 2022 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasParticle dark matterTechniquesDark matter detectorsGravitation, Cosmology & Astrophysics

Simultaneous scintillation light and charge readout of a pure argon filled Spherical Proportional Counter

The possible use of a Spherical Proportional Counter for the search of neutrinoless double beta decay is investigated in the R2D2 R&D project. Dual charge and scintillation light readout may improve the detector performance. Tests were carried out with pure argon at 1.1 bar using a 6 × 6 mm2 silicon photomultiplier. Scintillation light was used for the first time to trigger in a spherical proportional counter. The measured drift time is in excellent agreement with the expectations from simulations. Furthermore the light signal emitted during the avalanche development exhibits features that could be exploited for event characterization.

Solar Kaluza-Klein axion search with NEWS-G

Kaluza-Klein (KK) axions appear in theories with extra dimensions as higher mass, significantly shorter lifetime, excitations of the Peccei-Quinn axion. When produced in the Sun, they would remain gravitationally trapped in the solar system, and their decay to a pair of photons could provide an explanation of the solar corona heating problem. A low-density detector would discriminate such a signal from the background, by identifying the separation of the interaction point of the two photons. The NEWS-G collaboration uses large volume Spherical Proportional Counters, gas-filled metallic spheres with a spherical anode in their centre. After observation of a single axionlike event in a 42 day long run with the SEDINE detector, a $90\%$ C.L. upper limit of $g_{a\gamma\gamma}<8.99\cdot10^{-13}\,GeV^{-1}$ is set on the axion-photon coupling for a KK axion density on Earth of $n_{a}=4.07\cdot10^{13}\,m^{-3}$ and two extra dimensions of size $R = 1\,eV^{-1}$.

The search for Light Dark Matter with NEWS-G

The NEWS-G direct dark matter search experiment uses spherical proportional counters (SPC) with light noble gases to explore low WIMP masses. The first results obtained with an SPC prototype operated with Ne gas at the Laboratoire Souterrain de Modane (LSM) have already set competitive results for low-mass WIMPs. The forthcoming next phase of the experiment consists of a large 140 cm diameter SPC installed at SNOLAB with a new sensor design, with improved detector performance and data quality. Before its installation at SNOLAB, the detector was commissioned with pure methane gas at the LSM, with a temporary water shield, offering a hydrogen-rich target and reduced backgrounds. After giving an overview of the improvements of the detector, preliminary results of this campaign will be discussed, including UV laser and Ar-37 calibration data.