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D. Loomba

Publications and source records attributed to D. Loomba.

At least 19 recordsLinked to original sources
arXiv2026

Optical effects in Gaseous Electron Multipliers (GEMs)

Optical time projection chambers (OTPCs) are well suited for applications that require the highest spatial resolution for particle track reconstruction. The MIGDAL experiment uses a glass GEM-based OTPC and observes a systematic excess in both the intensity and width of particle tracks in its optical readout, when compared with charge readout simulations. One hypothesis is that scintillation light produced inside a GEM hole during the avalanche propagates through the GEM substrate and exits neighboring holes. We present lab measurements testing this hypothesized optical broadening effect in three types of GEM substrates: glass, ceramic, and FR4. Our observations quantify this optical broadening and demonstrate it to be strongest in glass GEMs. Additionally, we use Geant4 simulations to both reproduce our observations and quantify optical broadening effects in realistic charge avalanches. Applying our glass GEM effects to simulated particle tracks yields increases of track intensity and widths by up to around 26% and 31%, respectively. This may explain the larger than expected intensity and track widths observed in the MIGDAL OTPC and is expected to be an observed effect in all GEM-based OTPCs.

physics.ins-det↗
arXiv2025

Overlap-aware segmentation for topological reconstruction of obscured objects

The separation of overlapping objects presents a significant challenge in scientific imaging. While deep learning segmentation-regression algorithms can predict pixel-wise intensities, they typically treat all regions equally rather than prioritizing overlap regions where attribution is most ambiguous. Recent advances in instance segmentation show that weighting regions of pixel overlap in training can improve segmentation boundary predictions in regions of overlap, but this idea has not yet been extended to segmentation regression. We address this with Overlap-Aware Segmentation of ImageS (OASIS): a new segmentation-regression framework with a weighted loss function designed to prioritize regions of object-overlap during training, enabling extraction of pixel intensities and topological features from heavily obscured objects. We demonstrate OASIS in the context of the MIGDAL experiment, which aims to directly image the Migdal effect--a rare process where electron emission is induced by nuclear scattering--in a low-pressure optical time projection chamber. This setting poses an extreme test case, as the target for reconstruction is a faint electron recoil track which is often heavily-buried within the order(s)-of-magnitude brighter nuclear recoil track. Compared to unweighted segmentation regression, we demonstrate OASIS's novel overlap region-targeted loss function weight to be the single most important training weight for improving intensity and topological reconstructions of the low-energy electron tracks that tend to be most dominated by pixel overlap. Averaging over eight training campaigns, we further show the addition of overlap-targeted weights to improve median intensity reconstruction errors from -41.1% to -13.3% for these low-energy electrons. These performance gains demonstrate OASIS as a generalizable methodology for recovering obscured signals in overlap-dominated regions.

hep-ex↗
arXiv2024

Transforming a rare event search into a not-so-rare event search in real-time with deep learning-based object detection

Deep learning-based object detection algorithms enable the simultaneous classification and localization of any number of objects in image data. Many of these algorithms are capable of operating in real-time on high resolution images, attributing to their widespread usage across many fields. We present an end-to-end object detection pipeline designed for real-time rare event searches for the Migdal effect, using high-resolution image data from a state-of-the-art scientific CMOS camera in the MIGDAL experiment. The Migdal effect in nuclear scattering, crucial for sub-GeV dark matter searches, has yet to be experimentally confirmed, making its detection a primary goal of the MIGDAL experiment. Our pipeline employs the YOLOv8 object detection algorithm and is trained on real data to enhance the detection efficiency of nuclear and electronic recoils, particularly those exhibiting overlapping tracks that are indicative of the Migdal effect. When deployed online on the MIGDAL readout PC, we demonstrate our pipeline to process and perform the rare event search on 2D image data faster than the peak 120 frame per second acquisition rate of the CMOS camera. Applying these same steps offline, we demonstrate that we can reduce a sample of 20 million camera frames to around 1000 frames while maintaining nearly all signal that YOLOv8 is able to detect, thereby transforming a rare search into a much more manageable search. Our studies highlight the potential of pipelines similar to ours significantly improving the detection capabilities of experiments requiring rapid and precise object identification in high-throughput data environments.

hep-ex↗
arXiv2022

The MIGDAL experiment: Measuring a rare atomic process to aid the search for dark matter

We present the Migdal In Galactic Dark mAtter expLoration (MIGDAL) experiment aiming at the unambiguous observation and study of the so-called Migdal effect induced by fast-neutron scattering. It is hoped that this elusive atomic process can be exploited to enhance the reach of direct dark matter search experiments to lower masses, but it is still lacking experimental confirmation. Our goal is to detect the predicted atomic electron emission which is thought to accompany nuclear scattering with low, but calculable, probability, by deploying an Optical Time Projection Chamber filled with a low-pressure gas based on CF$_4$. Initially, pure CF$_4$ will be used, and then in mixtures containing other elements employed by leading dark matter search technologies -- including noble species, plus Si and Ge. High resolution track images generated by a Gas Electron Multiplier stack, together with timing information from scintillation and ionisation readout, will be used for 3D reconstruction of the characteristic event topology expected for this process -- an arrangement of two tracks sharing a common vertex, with one belonging to a Migdal electron and the other to a nuclear recoil. Different energy-loss rate distributions along both tracks will be used as a powerful discrimination tool against background events. In this article we present the design of the experiment, informed by extensive particle and track simulations and detailed estimations of signal and background rates. In pure CF$_4$ we expect to observe 8.9 (29.3) Migdal events per calendar day of exposure to an intense D-D (D-T) neutron generator beam at the NILE facility located at the Rutherford Appleton Laboratory (UK). With our nominal assumptions, 5$\sigma$ median discovery significance can be achieved in under one day with either generator.

hep-ex↗
arXiv2022

Snowmass2021 Cosmic Frontier Dark Matter Direct Detection to the Neutrino Fog

We present a summary of future prospects for direct detection of dark matter within the GeV/c2 to TeV/c2 mass range. This is paired with a new definition of the neutrino fog in order to better quantify the rate of diminishing returns on sensitivity due to irreducible neutrino backgrounds. A survey of dark matter candidates predicted to fall within this mass range demonstrates that fully testing multiple well-motivated theo-ries will require expanding the currently-funded generation of experiments down to and past the neutrino fog. We end with the status and plans for next-generation exper-iments and novel R&D concepts which will get us there.

hep-ex↗
arXiv2022

Recoil imaging for directional detection of dark matter, neutrinos, and physics beyond the Standard Model

Recoil imaging entails the detection of spatially resolved ionization tracks generated by particle interactions. This is a highly sought-after capability in many classes of detector, with broad applications across particle and astroparticle physics. However, at low energies, where ionization signatures are small in size, recoil imaging only seems to be a practical goal for micro-pattern gas detectors. This white paper outlines the physics case for recoil imaging, and puts forward a decadal plan to advance towards the directional detection of low-energy recoils with sensitivity and resolution close to fundamental performance limits. The science case covered includes: the discovery of dark matter into the neutrino fog, directional detection of sub-MeV solar neutrinos, the precision study of coherent-elastic neutrino-nucleus scattering, the detection of solar axions, the measurement of the Migdal effect, X-ray polarimetry, and several other applied physics goals. We also outline the R&D programs necessary to test concepts that are crucial to advance detector performance towards their fundamental limit: single primary electron sensitivity with full 3D spatial resolution at the $\sim$100 micron-scale. These advancements include: the use of negative ion drift, electron counting with high-definition electronic readout, time projection chambers with optical readout, and the possibility for nuclear recoil tracking in high-density gases such as argon. We also discuss the readout and electronics systems needed to scale-up such detectors to the ton-scale and beyond.

physics.ins-det↗
arXiv2021

Improved Sensitivity of the DRIFT-IId Directional Dark Matter Experiment using Machine Learning

We demonstrate a new type of analysis for the DRIFT-IId directional dark matter detector using a machine learning algorithm called a Random Forest Classifier. The analysis labels events as signal or background based on a series of selection parameters, rather than solely applying hard cuts. The analysis efficiency is shown to be comparable to our previous result at high energy but with increased efficiency at lower energies. This leads to a projected sensitivity enhancement of one order of magnitude below a WIMP mass of 15 GeV c$^{-2}$ and a projected sensitivity limit that reaches down to a WIMP mass of 9 GeV c$^{-2}$, which is a first for a directionally sensitive dark matter detector.

astro-ph.IM↗
arXiv2020

CYGNUS: Feasibility of a nuclear recoil observatory with directional sensitivity to dark matter and neutrinos

Now that conventional weakly interacting massive particle (WIMP) dark matter searches are approaching the neutrino floor, there has been a resurgence of interest in detectors with sensitivity to nuclear recoil directions. A large-scale directional detector is attractive in that it would have sensitivity below the neutrino floor, be capable of unambiguously establishing the galactic origin of a purported dark matter signal, and could serve a dual purpose as a neutrino observatory. We present the first detailed analysis of a 1000 m$^3$-scale detector capable of measuring a directional nuclear recoil signal at low energies. We propose a modular and multi-site observatory consisting of time projection chambers (TPCs) filled with helium and SF$_6$ at atmospheric pressure. Depending on the TPC readout technology, 10-20 helium recoils above 6 keVr or only 3-4 recoils above 20 keVr would suffice to distinguish a 10 GeV WIMP signal from the solar neutrino background. High-resolution charge readout also enables powerful electron background rejection capabilities well below 10 keV. We detail background and site requirements at the 1000 m$^3$-scale, and identify materials that require improved radiopurity. The final experiment, which we name CYGNUS-1000, will be able to observe 10-40 neutrinos from the Sun, depending on the final energy threshold. With the same exposure, the sensitivity to spin independent cross sections will extend into presently unexplored sub-10 GeV parameter space. For spin dependent interactions, already a 10 m$^3$-scale experiment could compete with upcoming generation-two detectors, but CYGNUS-1000 would improve upon this considerably. Larger volumes would bring sensitivity to neutrinos from an even wider range of sources, including galactic supernovae, nuclear reactors, and geological processes.

physics.ins-det↗
arXiv2019

Dark matter search in a Beam-Dump eXperiment (BDX) at Jefferson Lab -- 2018 update to PR12-16-001

This document complements and completes what was submitted last year to PAC45 as an update to the proposal PR12-16-001 "Dark matter search in a Beam-Dump eXperiment (BDX)" at Jefferson Lab submitted to JLab-PAC44 in 2016. Following the suggestions contained in the PAC45 report, in coordination with the lab, we ran a test to assess the beam-related backgrounds and validate the simulation framework used to design the BDX experiment. Using a common Monte Carlo framework for the test and the proposed experiment, we optimized the selection cuts to maximize the reach considering simultaneously the signal, cosmic-ray background (assessed in Catania test with BDX-Proto) and beam-related backgrounds (irreducible NC and CC neutrino interactions as determined by simulation). Our results confirmed what was presented in the original proposal: with 285 days of a parasitic run at 65 $μ$A (corresponding to $10^{22}$ EOT) the BDX experiment will lower the exclusion limits in the case of no signal by one to two orders of magnitude in the parameter space of dark-matter coupling versus mass.

physics.ins-det↗
arXiv2019

CYGNO: a CYGNUs Collaboration 1 m^3 Module with Optical Readout for Directional Dark Matter Search

The design of the project named CYGNO is presented. CYGNO is a new proposal supported by INFN, the Italian National Institute for Nuclear Physics, within CYGNUs proto-collaboration (CYGNUS-TPC) that aims to realize a distributed observatory in underground laboratories for directional Dark Matter (DM) search and the identification of the coherent neutrino scattering (CNS) from the Sun. CYGNO is one of the first prototypes in the road map to 100-1000 m^3 of CYGNUs and will be located at the National Laboratory of Gran Sasso (LNGS), in Italy, aiming to make significant advances in the technology of single phase gas-only time projection chambers (TPC) for the application to the detection of rare scattering events. In particular it will focus on a read-out technique based on Micro Pattern Gas Detector (MPGD) amplification of the ionization and on the visible light collection with a sub-mm position resolution sCMOS (scientific COMS) camera. This type of readout - in conjunction with a fast light detection - will allow on one hand to reconstruct 3D direction of the tracks, offering accurate sensitivity to the source directionality and, on the other hand, a high particle identification capability very useful to distinguish nuclear recoils.

physics.ins-det↗
arXiv2018

Dark matter search in a Beam-Dump eXperiment (BDX) at Jefferson Lab: an update on PR12-16-001

This document is an update to the proposal PR12-16-001 Dark matter search in a Beam-Dump eXperiment (BDX) at Jefferson Lab submitted to JLab-PAC44 in 2016 reporting progress in addressing questions raised regarding the beam-on backgrounds. The concerns are addressed by adopting a new simulation tool, FLUKA, and planning measurements of muon fluxes from the dump with its existing shielding around the dump. First, we have implemented the detailed BDX experimental geometry into a FLUKA simulation, in consultation with experts from the JLab Radiation Control Group. The FLUKA simulation has been compared directly to our GEANT4 simulations and shown to agree in regions of validity. The FLUKA interaction package, with a tuned set of biasing weights, is naturally able to generate reliable particle distributions with very small probabilities and therefore predict rates at the detector location beyond the planned shielding around the beam dump. Second, we have developed a plan to conduct measurements of the muon ux from the Hall-A dump in its current configuration to validate our simulations.

physics.ins-det↗
arXiv2017

Measurement of directional range components of nuclear recoil tracks in a fiducialised dark matter detector

We present results from the first measurement of axial range components of fiducialized neutron induced nuclear recoil tracks using the DRIFT directional dark matter detector. Nuclear recoil events are fiducialized in the DRIFT experiment using temporal charge carrier separations between different species of anions in 30:10:1 Torr of CS$_2$:CF$_4$:O$_2$ gas mixture. For this measurement, neutron-induced nuclear recoil tracks were generated by exposing the detector to $^{252}$Cf source from different directions. Using these events, the sensitivity of the detector to the expected axial directional signatures were investigated as the neutron source was moved from one detector axis to another. Results obtained from these measurements show clear sensitivity of the DRIFT detector to the axial directional signatures in this fiducialization gas mode.

physics.ins-det↗
arXiv2017

Imaging $^{55}$Fe Electron Tracks in a GEM-based TPC Using a CCD Readout

Images of resolved 5.9 keV electron tracks produced from $^{55}$Fe X-ray interactions are presented for the first time using an optical readout time projection chamber (TPC). The corresponding energy spectra are also shown, with the FWHM energy resolution in the 30-40\% range depending on gas pressure and gain. These tracks were produced in low pressure carbon tetrafluoride (CF$_4$) gas, and imaged with a fast lens and low noise CCD camera system using the secondary scintillation produced in GEM/THGEM amplification devices. The GEM/THGEMs provided effective gas gains of $\gtrsim 2 \times 10^5$ in CF$_4$ at low pressures in the 25-100 Torr range. The ability to resolve such low energy particle tracks has important applications in dark matter and other rare event searches, as well as in X-ray polarimetry. A practical application of the optical signal from $^{55}$Fe is that it provides a tool for mapping the detector gain spatial uniformity.

physics.ins-det↗
arXiv2017

Low Threshold Results and Limits from the DRIFT Directional Dark Matter Detector

We present results from a 54.7 live-day shielded run of the DRIFT-IId detector, the world's most sensitive, directional, dark matter detector. Several improvements were made relative to our previous work including a lower threshold for detection, a more robust analysis and a tenfold improvement in our gamma rejection factor. After analysis, no events remain in our fiducial region leading to an exclusion curve for spin-dependent WIMP-proton interactions which reaches 0.28 pb at 100 GeV/c^2 a fourfold improvement on our previous work. We also present results from a 45.4 live-day unshielded run of the DRIFT-IId detector during which 14 nuclear recoil-like events were observed. We demonstrate that the observed nuclear recoil rate of 0.31+/-0.08 events per day is consistent with detection of ambient, fast neutrons emanating from the walls of the Boulby Underground Science Facility.

astro-ph.IM↗
arXiv2016

First measurement of nuclear recoil head-tail sense in a fiducialised WIMP dark matter detector

Recent computational results suggest that directional dark matter detectors have potential to probe for WIMP dark matter particles below the neutrino floor. The DRIFT-IId detector used in this work is a leading directional WIMP search time projection chamber detector. We report the first measurements of the detection of the directional nuclear recoils in a fully fiducialised low-pressure time projection chamber. In this new operational mode, the distance between each event vertex and the readout plane is determined by the measurement of minority carriers produced by adding a small amount of oxygen to the nominal CS$_{2}$ + CF$_{4}$ target gas mixture. The CS$_2$ + CF$_4$ + O$_2$ mixture has been shown to enable background-free operation at current sensitivities. Sulfur, fluorine, and carbon recoils were generated using neutrons emitted from a $^{252}$Cf source positioned at different locations around the detector. Measurement of the relative energy loss along the recoil tracks allowed the track vector sense, or the so-called head-tail asymmetry parameter, to be deduced. Results show that the previously reported observation of head-tail sensitivity in pure CS$_{2}$ is well retained after the addition of oxygen to the gas mixture.

physics.ins-det↗
arXiv2016

Readout technologies for directional WIMP Dark Matter detection

The measurement of the direction of WIMP-induced nuclear recoils is a compelling but technologically challenging strategy to provide an unambiguous signature of the detection of Galactic dark matter. Most directional detectors aim to reconstruct the dark-matter-induced nuclear recoil tracks, either in gas or solid targets. The main challenge with directional detection is the need for high spatial resolution over large volumes, which puts strong requirements on the readout technologies. In this paper we review the various detector readout technologies used by directional detectors. In particular, we summarize the challenges, advantages and drawbacks of each approach, and discuss future prospects for these technologies.

physics.ins-det↗
arXiv2016

The novel properties of SF$_6$ for directional dark matter experiments

SF$_{6}$ is an inert and electronegative gas that has a long history of use in high voltage insulation and numerous other industrial applications. Although SF$_{6}$ is used as a trace component to introduce stability in tracking chambers, its highly electronegative properties have limited its use in tracking detectors. In this work we present a series of measurements with SF$_{6}$ as the primary gas in a low pressure Time Projection Chamber (TPC), with a thick GEM used as the avalanche and readout device. The first results of an $^{55}$Fe energy spectrum in SF$_{6}$ are presented. Measurements of the mobility and longitudinal diffusion confirm the negative ion drift of SF$_{6}$. However, the observed waveforms have a peculiar but interesting structure that indicates multiple drift species and a dependence on the reduced field ($E/p$), as well as on the level of water vapor contamination. The discovery of a distinct secondary peak in the waveform, together with its identification and use for fiducializing events in the TPC, are also presented. Our measurements demonstrate that SF$_{6}$ is an ideal gas for directional dark matter detection. In particular, the high fluorine content is desirable for spin-dependent sensitivity, negative ion drift ensures low diffusion over large drift distances, and the multiple species of charge carriers allow for full detector fiducialization.

physics.ins-det↗