arXiv subjects

P. Giampa

Publications and source records attributed to P. Giampa.

At least 19 recordsLinked to original sources

arXiv2026

Measurement of the muon flux at SNOLAB using the DEAP-3600 experiment

A direct measurement of the muon flux at SNOLAB is performed using the DEAP-3600 experiment, located 2 km underground at SNOLAB near Sudbury, Canada. Primarily designed for the direct detection of weakly interacting massive particles (WIMPs), a dark matter candidate, DEAP-3600 consists of an inner spherical acrylic vessel containing a liquid argon target; this vessel is enclosed within a steel shell which is submerged in an instrumented water tank, serving as a muon veto for the dark matter search. The muon flux measurement is performed using a cut-and-count analysis of events observed in the muon veto detector and of events which are coincident between the muon veto and the liquid argon target. The requirement that muons traverse both the water and liquid argon minimizes instrumental backgrounds and systematic uncertainties. Using data collected from November 2016 to March 2020, the muon flux is measured by this coincidence analysis to be $(3.71 \pm 0.25_{\textrm{stat}} \pm 0.09_{\textrm{sys}}) \times 10^{-10}\, \mu/$cm$^2$/s. The standalone measurement using muon veto data only is compatible within uncertainties. Both measurements agree with the previous result by the SNO experiment and with simulations carried out using the MUTE software. These results provide an important benchmark for future rare-event searches at the SNOLAB facility.

hep-ex↗

arXiv2026

A New High-Intensity Source for Ultracold Neutrons

The TRIUMF UltraCold Advanced Neutron (TUCAN) collaboration has completed a new superthermal source for ultracold neutrons (UCNs) at TRIUMF. It uses neutrons from a spallation target driven by TRIUMF's %520-MeV main cyclotron. Heavy water and liquid deuterium serve as neutron moderators, and inelastic scattering inside superfluid $^4$He at around \qty{1.1}{\kelvin} slows the neutrons down to become ultracold. During commissioning runs with the completed source, including the deuterium moderator, up to $1.47(2)\times 10^7$ UCNs were detected in the experimental area after irradiating the target and accumulating UCNs in the source for \qty{60}{\second}. Up to \qty{6.75(3)e5} UCN/s were detected during continuous operation, more than at any other source in the world.

physics.ins-det↗

arXiv2026

First evidence of neutrino absorption on argon using $^{8}$B solar neutrinos in DEAP-3600

We report experimental evidence for electron neutrino charged-current interactions (neutrino absorption, CC $\nu_e$) from $^{8}$B solar neutrinos on $^{40}$Ar using an exposure of ($7.29 \pm 0.05$) tonne$\cdot$years in the DEAP-3600 detector. A region of interest (ROI) of 10.5-13.0 MeV reconstructed energy calibrated on single-peak events, corresponding to incident neutrino energy in 12.0-14.5 MeV, is used for this measurement. We observe 5 single-peak and 1 double-peak neutrino-like events consistent with the $^{8}$B solar neutrino energy spectrum in the ROI after correcting for nonlinearities in the detector response at high energies. With an expected background of $0.48~^{+0.16}_{-0.15}$ events, the data correspond to a significance of $4.0\,\sigma$ with respect to the background-only hypothesis. We report an energy-averaged cross section of $(4.0~^{+2.0}_{-1.6}~\mathrm{(stat)}~^{+0.8}_{-0.7}~\mathrm{(sys)})\times 10^{-41}\,\mathrm{cm}^2$ in the ROI for the CC $\nu_{e}$ signal, a factor $(2.4~^{+1.3}_{-1.0})$ higher than predicted by Bhattacharya, Goodman and Garc\'ia (2009).

hep-ex↗

arXiv2026

Initial Performance of the TUCAN Magnetically Shielded Room

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has commissioned a large magnetically shielded room to be used for measuring the neutron electric dipole moment (nEDM) to a precision of $10^{-27}~e\mathrm{cm}$. The room is composed of five layers of MuMetal and one layer of copper and sits within the $\lesssim 370~\mu\mathrm{T}$ ambient field produced by the TRIUMF cyclotron. Within this environment, the quasi-static shielding factor was measured to be $3.25(2) \times 10^4$ at $0.01~\mathrm{Hz}$ with an external peak-to-peak perturbation of $2~\mu\mathrm{T}$. Without the large ambient cyclotron field, the shielding factor improves to $3.75(4)\times 10^4$ at the same perturbation amplitude and frequency. After idealization in the cyclotron field, the residual field at the room center was $B = 1.8(2)~\mathrm{nT}$ and the vertical first-order gradient across the central 1~m$^3$ ($dB_{\mathrm{z}}/dz$) was $-279(64)~\mathrm{pT/m}$. With additional improvement to the idealization, and with active compensation, we expect the room to be adequate for a $10^{-27}~e\mathrm{cm}$ nEDM search.

physics.ins-det↗

arXiv2026

Dark Matter Search with the DEAP-3600 Detector using the Profile Likelihood Ratio Method

We present here a search for WIMP dark matter using 790.8 live-days of data collected with 3269 kg of liquid argon (1266 kg fiducial) by the DEAP-3600 detector at SNOLAB, using the Profile Likelihood Ratio method. The likelihood model is based on three parameters: estimated energy, pulse-shape discrimination parameter, and reconstructed position within the detector. Using this method, the expected signal sensitivity of DEAP-3600 benefits from an increased fiducial volume and improved event selection acceptance. Alpha-decays from a small number of dust particulates circulating within the liquid argon target are the dominant source of background events and limit the sensitivity of this search. This result provides improved exclusion upper limits on the WIMP-nucleon spin-independent cross section on liquid argon for WIMP masses between 20 GeV/$c^{2}$ and 100 GeV/$c^{2}$. At 100 GeV/$c^{2}$ the observed limit is 3.4 $\times$ 10$^{-45}$ cm$^2$ at 90% confidence level.

hep-ex↗

arXiv2025

Calibration Plan for the SBC 10-kg Liquid Argon Detector with 100 eV Target Threshold

The Scintillating Bubble Chamber (SBC) Collaboration is designing a new generation of low background, noble liquid bubble chamber experiments with sub-keV nuclear recoil threshold. These experiments combine the electronic recoil blindness of a bubble chamber with the energy resolution of noble liquid scintillation, and maintain electron recoil discrimination at higher degrees of superheat (lower nuclear recoil thresholds) than Freon-based bubble chambers. A 10-kg liquid argon bubble chamber has the potential to set world leading limits on the dark matter nucleon cross-section for $O(\mathrm{GeV}/c^{2})$ masses, and to perform a high statistics coherent elastic neutrino nuclear scattering measurement with reactor neutrinos. This work presents a detailed calibration plan to measure the detector response of these experiments, combining photoneutron scattering with two new techniques to induce sub-keV nuclear recoils: nuclear Thomson scattering and thermal neutron capture.

physics.ins-det↗

arXiv2025

Ultracold Neutron Guide-Coating Facility at U.Winnipeg

We report the construction and commissioning of a new ultracold neutron (UCN) guide-coating facility at the University of Winnipeg. The facility employs pulsed laser deposition (PLD) to produce diamond-like carbon (DLC) coatings on cylindrical UCN guides up to 1 m in length with a 200 mm outer diameter. DLC is a promising material for UCN transport and storage due to its high real component of the optical potential, low neutron absorption cross section, and low depolarization probabilities. First coating attempts on a full length aluminum UCN guide and matching blank flange were successfully coated with a carbon film with density of 2.3 g/cm$^3$, corresponding to optical potentials of 200 neV, as measured by X-ray reflectometry (XRR). Coating thicknesses were measured to be 90 nm for the UCN guide and 180 nm for the flange with no evidence of delamination. The implementation of a plasma plume collimator and plasma feed back control via a time of flight in vacuum ion probe produced a film with an XRR measured density of 2.8 g/cm$^3$, corresponding to an optical potential of 240 neV. This 80 nm thick film had poor adhesion to the aluminum tube substrate. These results establish a baseline for the coating facility. Ongoing and future work focuses on improving the diamond content of films and adhesion through plasma plume collimation, TOF ion probe feed back, and pre/post treatment methods with the goal of providing high quality DLC UCN guides for the TUCAN experiment at TRIUMF.

physics.ins-det↗

arXiv2025

Initial results of the TRIUMF ultracold advanced neutron source

We report the first results on ultracold neutron production from a new spallation-driven superfluid $^4$He (He-II) source at TRIUMF, which is being prepared for a new, precise measurement of the neutron electric dipole moment. A total of $(9.3 \pm 0.8)\times 10^{5}$ ultracold neutrons were observed at a proton beam current of \SI{37}{\uA}, when the target was irradiated for a period of \SI{60}{\s}. The results are in fair agreement with expectations based on a detailed simulation of neutron transport and ultracold neutron source cryogenics. There is some indication that the new source might not be as limited by the conduction of heat through the He-II as originally expected. The results indicate that the source is likely to make its ultimate production goals, once the liquid deuterium cold moderator system is completed, with the expectation that $5.7\times 10^7$~UCNs would be detected in the same experiment with full liquid levels. This would, for example, correspond to delivery of $1.4\times 10^6$~UCNs delivered to each of two nEDM measurement cells, and a statistical uncertainty of $1\times 10^{-27}~e$cm on the neutron EDM in 280 days of running.

nucl-ex↗

arXiv2025

Neutron EDM Experiment with an Advanced Ultracold Neutron Source at TRIUMF

The TRIUMF Ultracold Advanced Neutron (TUCAN) collaboration has been developing a high-intensity ultracold neutron (UCN) source aimed at searching for the neutron electric dipole moment (EDM) with a sensitivity goal of $10^{-27}\ e{\rm cm}$. This article reports on recent progress in commissioning of the UCN source and in the development of the neutron EDM spectrometer. In its final configuration, the accelerator-driven super-thermal UCN source will enable a neutron EDM experiment with two orders of magnitude improved statistics compared to the current best experiment. Substantial progress in 2024 allowed the collaboration to operate the complete source system, with the exception of the liquid deuterium cold moderator, resulting in the first production of UCNs. The status of the EDM spectrometer is also presented, with emphasis on UCN handling components and magnetic subsystems relevant to field control, shielding, and magnetometry.

physics.ins-det↗

arXiv2025

Cryogenic systems for the TUCAN EDM experiment

The TUCAN (TRIUMF UltraCold Advanced Neutron) Collaboration is completing a new ultracold neutron (UCN) source. The UCN source will deliver UCNs to a neutron electric dipole moment (EDM) experiment. The EDM experiment is projected to be capable of an uncertainty of $1\times 10^{-27}~e$cm, competitive with other planned projects, and a factor of ten more precise than the present world's best. The TUCAN source is based on a UCN production volume of superfluid helium (He-II), held at 1~K, and coupled to a proton-driven spallation target. The production rate in the source is expected to be in excess of $10^7$~UCN/s; since UCN losses can be small in superfluid helium, this should allow us to build up a large number of UCNs. The spallation-driven superfluid helium technology is the principal aspect making the TUCAN project unique. The superfluid production volume was recently cooled, for the first time, and successfully filled with superfluid helium. The design principles of the UCN source are described, along with some of the challenging cryogenic milestones that were recently passed.

physics.ins-det↗

arXiv2025

Position Reconstruction in the DEAP-3600 Dark Matter Search Experiment

In the DEAP-3600 dark matter search experiment, precise reconstruction of the positions of scattering events in liquid argon is key for background rejection and defining a fiducial volume that enhances dark matter candidate events identification. This paper describes three distinct position reconstruction algorithms employed by DEAP-3600, leveraging the spatial and temporal information provided by photomultipliers surrounding a spherical liquid argon vessel. Two of these methods are maximum-likelihood algorithms: the first uses the spatial distribution of detected photoelectrons, while the second incorporates timing information from the detected scintillation light. Additionally, a machine learning approach based on the pattern of photoelectron counts across the photomultipliers is explored.

physics.ins-det↗

arXiv2025

Characterization of external cross-talk from silicon photomultipliers in a liquid xenon detector

The Light-only Liquid Xenon experiment (LoLX) employs a small-scale detector equipped with 96 Hamamatsu VUV4 silicon photomultipliers (SiPMs) submerged in 5 kg of liquid xenon (LXe) to perform characterization measurements of light production, transport and detection in xenon. In this work, we perform a novel measurement of the "external cross-talk" (ExCT) of SiPMs, where photons produced in the avalanche process escape the device and produce correlated signals on other SiPMs. SiPMs are the photodetector technology of choice for next generation rare-event search experiments; understanding the sources and effects of correlated noise in SiPMs is critical for producing accurate estimates of detector performance and sensitivity projections. We measure the probability to observe ExCT through timing correlation of detected photons in low-light conditions within LoLX. Measurements of SiPM ExCT are highly detector dependent; thus the ExCT process is simulated and modelled using the Geant4 framework. Using the simulation, we determine the average transport and detection efficiency for ExCT photons within LoLX, a necessary input to extract the expected ExCT probability from the data. For an applied overvoltage of 4 V and 5 V, we measure a mean number of photons emitted into the LXe per avalanche of $0.5^{+0.3}_{-0.2}$ and $0.6^{+0.3}_{-0.2}$, respectively. Using an optical model to describe photon transmission through the SiPM surface, this corresponds to an estimated photon yield inside the bulk silicon of $20^{+11}_{-9}$ and $25^{+12}_{-9}$ photons per avalanche. The relative increase in intensity of SiPM ExCT emission between 4 V and 5 V is consistent with expectation for the linear increase of gain with respect to overvoltage.

physics.ins-det↗

arXiv2025

Direct Measurement of the $^{39}$Ar Half-life from 3.4 Years of Data with the DEAP-3600 Detector

The half-life of $^{39}$Ar is measured using the DEAP-3600 detector located 2 km underground at SNOLAB. Between 2016 and 2020, DEAP-3600 used a target mass of (3269 $\pm$ 24) kg of liquid argon distilled from the atmosphere in a direct-detection dark matter search. Such an argon mass also enables direct measurements of argon isotope properties. The decay of $^{39}$Ar in DEAP-3600 is the dominant source of triggers by two orders of magnitude, ensuring high statistics and making DEAP-3600 well-suited for measuring this isotope's half-life. Use of the pulse-shape discrimination technique in DEAP-3600 allows powerful discrimination between nuclear recoils and electron recoils, resulting in the selection of a clean sample of $^{39}$Ar decays. Observing over a period of 3.4 years, the $^{39}$Ar half-life is measured to be $(302 \pm 8_{\rm stat} \pm 6_{\rm sys})$ years. This new direct measurement suggests that the half-life of $^{39}$Ar is significantly longer than the accepted value, with potential implications for measurements using this isotope's half-life as input.

nucl-ex↗

arXiv2024

Low-threshold response of a scintillating xenon bubble chamber to nuclear and electronic recoils

A device filled with pure xenon first demonstrated the ability to operate simultaneously as a bubble chamber and scintillation detector in 2017. Initial results from data taken at thermodynamic thresholds down to ~4 keV showed sensitivity to ~20 keV nuclear recoils with no observable bubble nucleation by $\gamma$-ray interactions. This paper presents results from further operation of the same device at thermodynamic thresholds as low as 0.50 keV, hardware limited. The bubble chamber has now been shown to have sensitivity to ~1 keV nuclear recoils while remaining insensitive to bubble nucleation by $\gamma$-rays. A robust calibration of the chamber's nuclear recoil nucleation response, as a function of nuclear recoil energy and thermodynamic state, is presented. Stringent upper limits are established for the probability of bubble nucleation by $\gamma$-ray-induced Auger cascades, with a limit of $<1.1\times10^{-6}$ set at 0.50 keV, the lowest thermodynamic threshold explored.

physics.ins-det↗

arXiv2024

Relative Measurement and Extrapolation of the Scintillation Quenching Factor of $\alpha$-Particles in Liquid Argon using DEAP-3600 Data

The knowledge of scintillation quenching of $\alpha$-particles plays a paramount role in understanding $\alpha$-induced backgrounds and improving the sensitivity of liquid argon-based direct detection of dark matter experiments. We performed a relative measurement of scintillation quenching in the MeV energy region using radioactive isotopes ($^{222}$Rn, $^{218}$Po and $^{214}$Po isotopes) present in trace amounts in the DEAP-3600 detector and quantified the uncertainty of extrapolating the quenching factor to the low-energy region.

physics.ins-det↗

arXiv2024

Batch VUV4 Characterization for the SBC-LAr10 scintillating bubble chamber

The Scintillating Bubble Chamber (SBC) collaboration purchased 32 Hamamatsu VUV4 silicon photomultipliers (SiPMs) for use in SBC-LAr10, a bubble chamber containing 10~kg of liquid argon. A dark-count characterization technique, which avoids the use of a single-photon source, was used at two temperatures to measure the VUV4 SiPMs breakdown voltage ($V_{\text{BD}}$), the SiPM gain ($g_{\text{SiPM}}$), the rate of change of $g_{\text{SiPM}}$ with respect to voltage ($m$), the dark count rate (DCR), and the probability of a correlated avalanche (P$_{\text{CA}}$) as well as the temperature coefficients of these parameters. A Peltier-based chilled vacuum chamber was developed at Queen's University to cool down the Quads to $233.15\pm0.2$~K and $255.15\pm0.2$~K with average stability of $\pm20$~mK. An analysis framework was developed to estimate $V_{\text{BD}}$ to tens of mV precision and DCR close to Poissonian error. The temperature dependence of $V_{\text{BD}}$ was found to be $56\pm2$~mV~K$^{-1}$, and $m$ on average across all Quads was found to be $(459\pm3(\rm{stat.})\pm23(\rm{sys.}))\times 10^{3}~e^-$~PE$^{-1}$~V$^{-1}$. The average DCR temperature coefficient was estimated to be $0.099\pm0.008$~K$^{-1}$ corresponding to a reduction factor of 7 for every 20~K drop in temperature. The average temperature dependence of P$_{\text{CA}}$ was estimated to be $4000\pm1000$~ppm~K$^{-1}$. P$_{\text{CA}}$ estimated from the average across all SiPMs is a better estimator than the P$_{\text{CA}}$ calculated from individual SiPMs, for all of the other parameters, the opposite is true. All the estimated parameters were measured to the precision required for SBC-LAr10, and the Quads will be used in conditions to optimize the signal-to-noise ratio.

physics.ins-det↗

arXiv2023

Precision Measurement of the Specific Activity of $^{39}$Ar in Atmospheric Argon with the DEAP-3600 Detector

The specific activity of the beta decay of $^{39}$Ar in atmospheric argon is measured using the DEAP-3600 detector. DEAP-3600, located 2 km underground at SNOLAB, uses a total of (3269 $\pm$ 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector with very low background uses pulseshape discrimination to differentiate between nuclear recoils and electron recoils and is well-suited to measure the decay of $^{39}$Ar. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is [0.964 $\pm$ 0.001 (stat) $\pm$ 0.024 (sys)] Bq/kg$_{\rm atmAr}$ which is consistent with results from other experiments. A cross-check analysis using different event selection criteria provides a consistent result.

physics.ins-det↗

arXiv2023

Characterization of electroless nickel-phosphorus plating for ultracold-neutron storage

Electroless nickel plating is an established industrial process that provides a robust and relatively low-cost coating suitable for transporting and storing ultracold neutrons (UCN). Using roughness measurements and UCN-storage experiments we characterized UCN guides made from polished aluminum or stainless-steel tubes plated by several vendors. All electroless nickel platings were similarly suited for UCN storage with an average loss probability per wall bounce of $2.8\cdot10^{-4}$ to $4.1\cdot10^{-4}$ for energies between 90 neV and 190 neV, or a ratio of imaginary to real Fermi potential $η$ of $1.7\cdot10^{-4}$ to $3.3\cdot10^{-4}$. Measurements at different elevations indicate that the energy dependence of UCN losses is well described by the imaginary Fermi potential. Some special considerations are required to avoid an increase in surface roughness during the plating process and hence a reduction in UCN transmission. Increased roughness had only a minor impact on storage properties. Based on these findings we chose a vendor to plate the UCN-production vessel that will contain the superfluid-helium converter for the new TRIUMF UltraCold Advanced Neutron (TUCAN) source, achieving acceptable UCN-storage properties with ${η=3.5(5)\cdot10^{-4}}$.

nucl-ex↗