arXiv subjects

Q. Lin

Publications and source records attributed to Q. Lin.

At least 19 recordsLinked to original sources

arXiv2025

Room-temperature, continuous-wave Terahertz generation in free-space with an intersubband mid-infrared photomixer

We demonstrate a Terahertz photomixer pumped by mid-infrared photons at 10$\mu$m wavelength. The device is based on a dual-antenna architecture, in which a two-dimensional array of mid-infrared patch-antenna resonators is connected to the electrodes of a log-spiral Terahertz antenna. By exploiting intersubband absorption inside an AlGaAs-GaAs multi-quantum-well heterostructure, a photocurrent is coherently generated at the difference frequency between two quantum cascade lasers. The photocurrent drives the antenna electrodes allowing tunable, continuous-wave generation in free-space up to 1 Terahertz at room temperature. By experimentally studying the photomixer frequency response and dark impedance, we demonstrate that the observed power roll-off at high-frequency is limited by the combined effect of the photoexcited carrier's intrinsic lifetime and of the device $RC$ time constant. In the spectral range investigated we obtain, in continuous-wave, mid-infrared $\rightarrow$ Terahertz conversion efficiencies exceeding by orders of magnitude those of unipolar devices exploiting $\chi^{(2)}$ processes.

physics.optics↗

arXiv2022

A multi-cubic-kilometre neutrino telescope in the western Pacific Ocean

Next-generation neutrino telescopes with significantly improved sensitivity are required to pinpoint the sources of the diffuse astrophysical neutrino flux detected by IceCube and uncover the century-old puzzle of cosmic ray origins. A detector near the equator will provide a unique viewpoint of the neutrino sky, complementing IceCube and other neutrino telescopes in the Northern Hemisphere. Here we present results from an expedition to the north-eastern region of the South China Sea, in the western Pacific Ocean. A favorable neutrino telescope site was found on an abyssal plain at a depth of $\sim$ 3.5km. At depths below 3km, the sea current speed, water absorption and scattering lengths for Cherenkov light, were measured to be $v_{\mathrm{c}}<$10cm/s, $\lambda_{\mathrm{abs} }\simeq$ 27m and $\lambda_{\mathrm{sca} }\simeq$ 63m, respectively. Accounting for these measurements, we present the design and expected performance of a next-generation neutrino telescope, TRopIcal DEep-sea Neutrino Telescope (TRIDENT). With its advanced photon-detection technology and large dimensions, TRIDENT expects to observe the IceCube steady source candidate NGC 1068 with 5$\sigma$ significance within 1 year of operation. This level of sensitivity will open a new arena for diagnosing the origin of cosmic rays and probing fundamental physics over astronomical baselines.

astro-ph.HE↗

arXiv2022

Photometric Redshift Estimation with Convolutional Neural Networks and Galaxy Images: A Case Study of Resolving Biases in Data-Driven Methods

Deep Learning models have been increasingly exploited in astrophysical studies, yet such data-driven algorithms are prone to producing biased outputs detrimental for subsequent analyses. In this work, we investigate two major forms of biases, i.e., class-dependent residuals and mode collapse, in a case study of estimating photometric redshifts as a classification problem using Convolutional Neural Networks (CNNs) and galaxy images with spectroscopic redshifts. We focus on point estimates and propose a set of consecutive steps for resolving the two biases based on CNN models, involving representation learning with multi-channel outputs, balancing the training data and leveraging soft labels. The residuals can be viewed as a function of spectroscopic redshifts or photometric redshifts, and the biases with respect to these two definitions are incompatible and should be treated in a split way. We suggest that resolving biases in the spectroscopic space is a prerequisite for resolving biases in the photometric space. Experiments show that our methods possess a better capability in controlling biases compared to benchmark methods, and exhibit robustness under varying implementing and training conditions provided with high-quality data. Our methods have promises for future cosmological surveys that require a good constraint of biases, and may be applied to regression problems and other studies that make use of data-driven models. Nonetheless, the bias-variance trade-off and the demand on sufficient statistics suggest the need for developing better methodologies and optimizing data usage strategies.

astro-ph.IM↗

arXiv2021

Recommended conventions for reporting results from direct dark matter searches

The field of dark matter detection is a highly visible and highly competitive one. In this paper, we propose recommendations for presenting dark matter direct detection results particularly suited for weak-scale dark matter searches, although we believe the spirit of the recommendations can apply more broadly to searches for other dark matter candidates, such as very light dark matter or axions. To translate experimental data into a final published result, direct detection collaborations must make a series of choices in their analysis, ranging from how to model astrophysical parameters to how to make statistical inferences based on observed data. While many collaborations follow a standard set of recommendations in some areas, for example the expected flux of dark matter particles (to a large degree based on a paper from Lewin and Smith in 1995), in other areas, particularly in statistical inference, they have taken different approaches, often from result to result by the same collaboration. We set out a number of recommendations on how to apply the now commonly used Profile Likelihood Ratio method to direct detection data. In addition, updated recommendations for the Standard Halo Model astrophysical parameters and relevant neutrino fluxes are provided. The authors of this note include members of the DAMIC, DarkSide, DARWIN, DEAP, LZ, NEWS-G, PandaX, PICO, SBC, SENSEI, SuperCDMS, and XENON collaborations, and these collaborations provided input to the recommendations laid out here. Wide-spread adoption of these recommendations will make it easier to compare and combine future dark matter results.

hep-ex↗

arXiv2020

Search for inelastic scattering of WIMP dark matter in XENON1T

We report the results of a search for the inelastic scattering of weakly interacting massive particles (WIMPs) in the XENON1T dark matter experiment. Scattering off $^{129}$Xe is the most sensitive probe of inelastic WIMP interactions, with a signature of a 39.6 keV de-excitation photon detected simultaneously with the nuclear recoil. Using an exposure of 0.89 tonne-years, we find no evidence of inelastic WIMP scattering with a significance of more than 2$\sigma$. A profile-likelihood ratio analysis is used to set upper limits on the cross-section of WIMP-nucleus interactions. We exclude new parameter space for WIMPs heavier than 100 GeV/c${}^2$, with the strongest upper limit of $3.3 \times 10^{-39}$ cm${}^2$ for 130 GeV/c${}^2$ WIMPs at 90\% confidence level.

hep-ex↗

arXiv2020

$^{222}$Rn emanation measurements for the XENON1T experiment

The selection of low-radioactive construction materials is of utmost importance for the success of low-energy rare event search experiments. Besides radioactive contaminants in the bulk, the emanation of radioactive radon atoms from material surfaces attains increasing relevance in the effort to further reduce the background of such experiments. In this work, we present the $^{222}$Rn emanation measurements performed for the XENON1T dark matter experiment. Together with the bulk impurity screening campaign, the results enabled us to select the radio-purest construction materials, targeting a $^{222}$Rn activity concentration of 10 $\mu$Bq/kg in 3.2 t of xenon. The knowledge of the distribution of the $^{222}$Rn sources allowed us to selectively eliminate critical components in the course of the experiment. The predictions from the emanation measurements were compared to data of the $^{222}$Rn activity concentration in XENON1T. The final $^{222}$Rn activity concentration of (4.5 $\pm$ 0.1) $\mu$Bq/kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.

physics.ins-det↗

arXiv2020

Projected WIMP Sensitivity of the XENONnT Dark Matter Experiment

XENONnT is a dark matter direct detection experiment, utilizing 5.9 t of instrumented liquid xenon, located at the INFN Laboratori Nazionali del Gran Sasso. In this work, we predict the experimental background and project the sensitivity of XENONnT to the detection of weakly interacting massive particles (WIMPs). The expected average differential background rate in the energy region of interest, corresponding to (1, 13) keV and (4, 50) keV for electronic and nuclear recoils, amounts to $12.3 \pm 0.6$ (keV t y)$^{-1}$ and $(2.2\pm 0.5)\times 10^{-3}$ (keV t y)$^{-1}$, respectively, in a 4 t fiducial mass. We compute unified confidence intervals using the profile construction method, in order to ensure proper coverage. With the exposure goal of 20 t$\,$y, the expected sensitivity to spin-independent WIMP-nucleon interactions reaches a cross-section of $1.4\times10^{-48}$ cm$^2$ for a 50 GeV/c$^2$ mass WIMP at 90% confidence level, more than one order of magnitude beyond the current best limit, set by XENON1T. In addition, we show that for a 50 GeV/c$^2$ WIMP with cross-sections above $2.6\times10^{-48}$ cm$^2$ ($5.0\times10^{-48}$ cm$^2$) the median XENONnT discovery significance exceeds 3$\sigma$ (5$\sigma$). The expected sensitivity to the spin-dependent WIMP coupling to neutrons (protons) reaches $2.2\times10^{-43}$ cm$^2$ ($6.0\times10^{-42}$ cm$^2$).

physics.ins-det↗

arXiv2020

Excess Electronic Recoil Events in XENON1T

We report results from searches for new physics with low-energy electronic recoil data recorded with the XENON1T detector. With an exposure of 0.65 t-y and an unprecedentedly low background rate of $76\pm2$ events/(t y keV) between 1 and 30 keV, the data enables sensitive searches for solar axions, an enhanced neutrino magnetic moment, and bosonic dark matter. An excess over known backgrounds is observed at low energies and most prominent between 2 and 3 keV. The solar axion model has a 3.4$\sigma$ significance, and a 3D 90% confidence surface is reported for axion couplings to electrons, photons, and nucleons. This surface is inscribed in the cuboid defined by $g_{ae}<3.8 \times 10^{-12}$, $g_{ae}g_{an}^{eff}<4.8\times 10^{-18}$, and $g_{ae}g_{a\gamma}<7.7\times10^{-22} GeV^{-1}$, and excludes either $g_{ae}=0$ or $g_{ae}g_{a\gamma}=g_{ae}g_{an}^{eff}=0$. The neutrino magnetic moment signal is similarly favored over background at 3.2$\sigma$ and a confidence interval of $\mu_{\nu} \in (1.4,2.9)\times10^{-11}\mu_B$ (90% C.L.) is reported. Both results are in strong tension with stellar constraints. The excess can also be explained by $\beta$ decays of tritium at 3.2$\sigma$ with a trace amount that can neither be confirmed nor excluded with current knowledge of its production and reduction mechanisms. The significances of the solar axion and neutrino magnetic moment hypotheses are reduced to 2.0$\sigma$ and 0.9$\sigma$, respectively, if an unconstrained tritium component is included in the fitting. With respect to bosonic dark matter, the excess favors a monoenergetic peak at ($2.3\pm0.2$) keV (68% C.L.) with a 3.0$\sigma$ global (4.0$\sigma$ local) significance. We also consider the possibility that $^{37}$Ar may be present in the detector and yield a 2.82 keV peak. Contrary to tritium, the $^{37}$Ar concentration can be tightly constrained and is found to be negligible.

hep-ex↗

arXiv2020

The SNEMO and SUGAR Companion Datasets

The Nearby Supernova Factory has made spectrophotometric observations of Type Ia supernovae since $2004$. This work presents an interim version of the data produced, including $210$ supernovae observed between $2004$ and $2013$.

astro-ph.CO↗

arXiv2020

Energy resolution and linearity of XENON1T in the MeV energy range

Xenon dual-phase time projection chambers designed to search for Weakly Interacting Massive Particles have so far shown a relative energy resolution which degrades with energy above $\sim$200 keV due to the saturation effects. This has limited their sensitivity in the search for rare events like the neutrinoless double-beta decay of $^{136}$Xe at its $Q$-value, $Q_{\beta\beta}\simeq$ 2.46 MeV. For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at 1 $\sigma/\mu$ is as low as (0.80$\pm$0.02) % in its one-ton fiducial mass, and for single-site interactions at $Q_{\beta\beta}$. We also present a new signal correction method to rectify the saturation effects of the signal readout system, resulting in more accurate position reconstruction and indirectly improving the energy resolution. The very good result achieved in XENON1T opens up new windows for the xenon dual-phase dark matter detectors to simultaneously search for other rare events.

physics.ins-det↗

arXiv2019

Orbital-angular-momentum free-space optical communication via the azimuthal phase-shift

Free-space optical communication using the orbital angular momentum (OAM) of light has garnered significant interest lately due to the potentially vast bandwidth intrinsic to the infinite Hilbert space of OAM modes. Unfortunately, OAM light beams suffer from serious distortions due to atmospheric turbulence (AT) that has become a dominant factor limiting the advance of OAM-based free-space communication. Here we propose and demonstrate a free-space communication scheme---using OAM beams and their azimuthal-mode phase-shift for keying (OAM-APSK)---which is resilient to AT-induced distortions. Combined with a digital holographic mode sorting (DHMS) technique, the proposed approach is able to achieve high signal-to-noise ratios and to maintain low modal crosstalk, even for extremely strong turbulence conditions, with magnitudes significantly beyond existing AT mitigation methods. The demonstrated OAM-APSK and DHMS schemes may now open up a great avenue for OAM-based free-space optical communication that could elegantly resolve the long-standing challenge imposed by atmospheric turbulence.

physics.optics↗

arXiv2019

SUGAR: An improved empirical model of Type Ia Supernovae based on spectral features

Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the Universe. Improving distance measurements of SNe Ia is one technique to better constrain the acceleration of expansion and determine its physical nature. This document develops a new SNe Ia spectral energy distribution (SED) model, called the SUpernova Generator And Reconstructor (SUGAR), which improves the spectral description of SNe Ia, and consequently could improve the distance measurements. This model is constructed from SNe Ia spectral properties and spectrophotometric data from The Nearby Supernova Factory collaboration. In a first step, a PCA-like method is used on spectral features measured at maximum light, which allows us to extract the intrinsic properties of SNe Ia. Next, the intrinsic properties are used to extract the average extinction curve. Third, an interpolation using Gaussian Processes facilitates using data taken at different epochs during the lifetime of a SN Ia and then projecting the data on a fixed time grid. Finally, the three steps are combined to build the SED model as a function of time and wavelength. This is the SUGAR model. The main advancement in SUGAR is the addition of two additional parameters to characterize SNe Ia variability. The first is tied to the properties of SNe Ia ejecta velocity, the second is correlated with their calcium lines. The addition of these parameters, as well as the high quality the Nearby Supernova Factory data, makes SUGAR an accurate and efficient model for describing the spectra of normal SNe Ia as they brighten and fade. The performance of this model makes it an excellent SED model for experiments like ZTF, LSST or WFIRST.

astro-ph.CO↗

arXiv2019

Search for Light Dark Matter Interactions Enhanced by the Migdal effect or Bremsstrahlung in XENON1T

Direct dark matter detection experiments based on a liquid xenon target are leading the search for dark matter particles with masses above $\sim$ 5 GeV/c$^2$, but have limited sensitivity to lighter masses because of the small momentum transfer in dark matter-nucleus elastic scattering. However, there is an irreducible contribution from inelastic processes accompanying the elastic scattering, which leads to the excitation and ionization of the recoiling atom (the Migdal effect) or the emission of a Bremsstrahlung photon. In this letter, we report on a probe of low-mass dark matter with masses down to about 85 MeV/c$^2$ by looking for electronic recoils induced by the Migdal effect and Bremsstrahlung, using data from the XENON1T experiment. Besides the approach of detecting both scintillation and ionization signals, we exploit an approach that uses ionization signals only, which allows for a lower detection threshold. This analysis significantly enhances the sensitivity of XENON1T to light dark matter previously beyond its reach.

hep-ex↗

arXiv2019

Light Dark Matter Search with Ionization Signals in XENON1T

We report constraints on light dark matter (DM) models using ionization signals in the XENON1T experiment. We mitigate backgrounds with strong event selections, rather than requiring a scintillation signal, leaving an effective exposure of $(22 \pm 3)$ tonne-days. Above $\sim\!0.4\,\mathrm{keV}_\mathrm{ee}$, we observe $<1 \, \text{event}/(\text{tonne} \times \text{day} \times \text{keV}_\text{ee})$, which is more than one thousand times lower than in similar searches with other detectors. Despite observing a higher rate at lower energies, no DM or CEvNS detection may be claimed because we cannot model all of our backgrounds. We thus exclude new regions in the parameter spaces for DM-nucleus scattering for DM masses $m_\chi$ within $3-6\,\mathrm{GeV}/\mathrm{c}^2$, DM-electron scattering for $m_\chi > 30\,\mathrm{MeV}/\mathrm{c}^2$, and absorption of dark photons and axion-like particles for $m_\chi$ within $0.186 - 1 \, \mathrm{keV}/\mathrm{c}^2$.

hep-ex↗

arXiv2019

XENON1T Dark Matter Data Analysis: Signal Reconstruction, Calibration and Event Selection

The XENON1T experiment at the Laboratori Nazionali del Gran Sasso is the most sensitive direct detection experiment for dark matter in the form of weakly interacting particles (WIMPs) with masses above $6\,$GeV/$c^2$ scattering off nuclei. The detector employs a dual-phase time projection chamber with 2.0 metric tons of liquid xenon in the target. A one metric $\mathrm{ton}\times\mathrm{year}$ exposure of science data was collected between October 2016 and February 2018. This article reports on the performance of the detector during this period and describes details of the data analysis that led to the most stringent exclusion limits on various WIMP-nucleon interaction models to date. In particular, signal reconstruction, event selection and calibration of the detector response to nuclear and electronic recoils in XENON1T are discussed.

physics.ins-det↗

arXiv2019

The XENON1T Data Acquisition System

The XENON1T liquid xenon time projection chamber is the most sensitive detector built to date for the measurement of direct interactions of weakly interacting massive particles with normal matter. The data acquisition system (DAQ) is constructed from commercial, open source, and custom components to digitize signals from the detector and store them for later analysis. The system achieves an extremely low signal threshold below a tenth of a photoelectron using a parallelized readout with the global trigger deferred to a later, software stage. The event identification is based on MongoDB database queries and has over 97% efficiency at recognizing interactions at the analysis energy threshold. A readout bandwidth over 300 MB/s is reached in calibration modes and is further expandable via parallelization. This DAQ system was successfully used during three years of operation of XENON1T.

physics.ins-det↗

arXiv2019

First observation of two-neutrino double electron capture in $^{124}$Xe with XENON1T

Two-neutrino double electron capture ($2\nu$ECEC) is a second-order Weak process with predicted half-lives that surpass the age of the Universe by many orders of magnitude. Until now, indications for $2\nu$ECEC decays have only been seen for two isotopes, $^{78}$Kr and $^{130}$Ba, and instruments with very low background levels are needed to detect them directly with high statistical significance. The $2\nu$ECEC half-life provides an important input for nuclear structure models and its measurement represents a first step in the search for the neutrinoless double electron capture processes ($0\nu$ECEC). A detection of the latter would have implications for the nature of the neutrino and give access to the absolute neutrino mass. Here we report on the first direct observation of $2\nu$ECEC in $^{124}$Xe with the XENON1T Dark Matter detector. The significance of the signal is $4.4\sigma$ and the corresponding half-life $T_{1/2}^{2\nu\text{ECEC}} = (1.8\pm 0.5_\text{stat}\pm 0.1_\text{sys})\times 10^{22}\;\text{y}$ is the longest ever measured directly. This study demonstrates that the low background and large target mass of xenon-based Dark Matter detectors make them well suited to measuring other rare processes as well, and it highlights the broad physics reach for even larger next-generation experiments.

nucl-ex↗

arXiv2019

XENON1T Dark Matter Data Analysis: Signal & Background Models, and Statistical Inference

The XENON1T experiment searches for dark matter particles through their scattering off xenon atoms in a 2 tonne liquid xenon target. The detector is a dual-phase time projection chamber, which measures simultaneously the scintillation and ionization signals produced by interactions in target volume, to reconstruct energy and position, as well as the type of the interaction. The background rate in the central volume of XENON1T detector is the lowest achieved so far with a liquid xenon-based direct detection experiment. In this work we describe the response model of the detector, the background and signal models, and the statistical inference procedures used in the dark matter searches with a 1 tonne$\times$year exposure of XENON1T data, that leaded to the best limit to date on WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c$^2$.

physics.ins-det↗