arXiv subjects

G. Bruno

Publications and source records attributed to G. Bruno.

At least 91 records · Page 5Linked to original sources

arXiv2020

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↗

arXiv2020

The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity

Exoplanets orbiting very close to their host star are strongly irradiated. This can lead the upper atmospheric layers to expand and evaporate into space. The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We perform high-resolution transmission spectroscopy of the transiting hot Jupiter HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo, taking advantage of the simultaneous optical+near infrared spectral coverage to detect HeI in the planet's extended atmosphere and to gauge the impact of stellar magnetic activity on the planetary absorption signal. Observations were performed during five transit events of HD189733b. By comparison of the in- and out-of-transit GIANO-B observations we compute high-resolution transmission spectra, on which we perform equivalent width measurements and light-curves analyses to gauge the excess in-transit absorption in the HeI triplet. We detect an absorption signal during all five transits. The mean in-transit absorption depth amounts to 0.75+/-0.03%. We detect night-to-night variations in the HeI absorption signal likely due to the transit events occurring in presence of stellar surface inhomogeneities. We evaluate the impact of stellar-activity pseudo-signals on the true planetary absorption using a comparative analysis of the HeI and the H$α$ lines. We interpret the time-series of the HeI absorption lines in the three nights not affected by stellar contamination -exhibiting a mean in-transit absorption depth of 0.77+/-0.04%- using a 3-d atmospheric code. Our simulations suggest that the helium layers only fill part of the Roche lobe. Observations can be explained with a thermosphere heated to $\sim$12000 K, expanding up to $\sim$1.2 planetary radii, and losing $\sim$1 g/s of metastable helium.

astro-ph.EP↗

arXiv2020

The GAPS Programme at TNG -- XXIII. HD 164922 d: a close-in super-Earth discovered with HARPS-N in a system with a long-period Saturn mass companion

In the framework of the Global Architecture of Planetary Systems (GAPS) project we collected more than 300 spectra with HARPS-N at the TNG for the bright G9V star HD164922. This target is known to host one gas giant planet in a wide orbit (Pb~1200 days, semi-major axis ~2 au) and a Neptune-mass planet with a period Pc ~76 days. We searched for additional low-mass companions in the inner region of the system. We compared the radial velocities (RV) and the activity indices derived from the HARPS-N time series to measure the rotation period of the star and used a Gaussian process regression to describe the behaviour of the stellar activity. We exploited this information in a combined model of planetary and stellar activity signals in an RV time-series composed of almost 700 high-precision RVs, both from HARPS-N and literature data. We performed a dynamical analysis to evaluate the stability of the system and the allowed regions for additional potential companions. Thanks to the high sensitivity of the HARPS-N dataset, we detect an additional inner super-Earth with an RV semi-amplitude of 1.3+/-0.2 m/s, a minimum mass of ~4+/-1 M_E and a period of 12.458+/-0.003 days. We disentangle the planetary signal from activity and measure a stellar rotation period of ~42 days. The dynamical analysis shows the long term stability of the orbits of the three-planet system and allows us to identify the permitted regions for additional planets in the semi-major axis ranges 0.18-0.21 au and 0.6-1.4 au. The latter partially includes the habitable zone of the system. We did not detect any planet in these regions, down to minimum detectable masses of 5 and 18 M_E, respectively. A larger region of allowed planets is expected beyond the orbit of planet b, where our sampling rules-out bodies with minimum mass > 50 M_E.

astro-ph.EP↗

arXiv2020

Neutral Iron Emission Lines From The Day-side Of KELT-9b -- The GAPS Programme With HARPS-N At TNG XX

We present the first detection of atomic emission lines from the atmosphere of an exoplanet. We detect neutral iron lines from the day-side of KELT-9b (Teq $\sim$ 4, 000 K). We combined thousands of spectrally resolved lines observed during one night with the HARPS-N spectrograph (R $\sim$ 115, 000), mounted at the Telescopio Nazionale Galileo. We introduce a novel statistical approach to extract the planetary parameters from the binary mask cross-correlation analysis. We also adapt the concept of contribution function to the context of high spectral resolution observations, to identify the location in the planetary atmosphere where the detected emission originates. The average planetary line profile intersected by a stellar G2 binary mask was found in emission with a contrast of 84 $\pm$ 14 ppm relative to the planetary plus stellar continuum (40 $\pm$ 5$\%$ relative to the planetary continuum only). This result unambiguously indicates the presence of an atmospheric thermal inversion. Finally, assuming a modelled temperature profile previously published (Lothringer et al. 2018), we show that an iron abundance consistent with a few times the stellar value explains the data well. In this scenario, the iron emission originates at the $10^{-3}$-$10^{-5}$ bar level.

astro-ph.EP↗

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 $m_χ$ within $3-6\,\mathrm{GeV}/\mathrm{c}^2$, DM-electron scattering for $m_χ> 30\,\mathrm{MeV}/\mathrm{c}^2$, and absorption of dark photons and axion-like particles for $m_χ$ 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

Characterization of the varying flux of atmospheric muons measured with the Large Volume Detector for 24 years

The Large Volume Detector (LVD), hosted in the INFN Laboratori Nazionali del Gran Sasso, is triggered by atmospheric muons at a rate of $\sim 0.1$~Hz. The data collected over almost a quarter of century are used to study the muon intensity underground. The 50-million muon series, the longest ever exploited by an underground instrument, allows for the accurate long-term monitoring of the muon intensity underground. This is relevant as a study of the background in the Gran Sasso Laboratory, which hosts a variety of long-duration, low-background detectors. We describe the procedure to select muon-like events as well as the method used to compute the exposure. We report the value of the average muon flux measured from 1994 to 2017: $\mathrm{I_μ^0 = 3.35 \pm 0.0005^{stat}\pm 0.03^{sys} \cdot 10^{-4} ~m^{-2} s^{-1}}$. We show that the intensity is modulated around this average value due to temperature variations in the stratosphere. We quantify such a correlation by using temperature data from the European Center for Medium-range Weather Forecasts: we find an effective temperature coefficient $\mathrm{α_{T}} = 0.94\pm0.01^{stat} \pm0.01^{sys}$, in agreement with other measurements at the same depth. We scrutinise the spectral content of the time series of the muon intensity by means of the Lomb-Scargle analysis. This yields the evidence of a 1-year periodicity, as well as the indication of others, both shorter and longer, suggesting that the series is not a pure sinusoidal wave. Consequently, and for the first time, we characterise the observed modulation in terms of amplitude and position of maximum and minimum on a year-by-year basis.

astro-ph.HE↗

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

Characterisation of a CeBr$_3$(LB) detector for space application

We describe the performance of a $\mathrm{23\times 23\times30 ~mm^3}$ low background cerium bromide, CeBr$_3$(LB), scintillator crystal coupled to a Hamamatsu R11265U-200 photomultiplier. This detector will be the building block for a gamma-ray detector array designed to be the payload for a CubeSat to be launched in 2020. The aim of the mission is to study flashes of gamma rays of terrestrial origin. The design of the detector has been tuned for the detection of gamma rays in the 20 keV$-$3 MeV energy range.

physics.ins-det↗

arXiv2019

Constraining the Spin-Dependent WIMP-Nucleon Cross Sections with XENON1T

We report the first experimental results on spin-dependent elastic weakly interacting massive particle (WIMP) nucleon scattering from the XENON1T dark matter search experiment. The analysis uses the full ton year exposure of XENON1T to constrain the spin-dependent proton-only and neutron-only cases. No significant signal excess is observed, and a profile likelihood ratio analysis is used to set exclusion limits on the WIMP-nucleon interactions. This includes the most stringent constraint to date on the WIMP-neutron cross section, with a minimum of $6.3\times10^{-42}$ cm$^2$ at 30 GeV/c${}^2$ and 90% confidence level. The results are compared with those from collider searches and used to exclude new parameter space in an isoscalar theory with an axial-vector mediator.

astro-ph.CO↗

arXiv2019

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

Two-neutrino double electron capture ($2ν$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 $2ν$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 $2ν$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 ($0ν$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 $2ν$ECEC in $^{124}$Xe with the XENON1T Dark Matter detector. The significance of the signal is $4.4σ$ and the corresponding half-life $T_{1/2}^{2ν\text{ECEC}} = (1.8\pm 0.5_\text{stat}\pm 0.1_\text{sys})\times 10^{22}\;\text{y}$ 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↗

arXiv2019

First results on the scalar WIMP-pion coupling, using the XENON1T experiment

We present first results on the scalar WIMP-pion coupling from 1 t$\times$yr of exposure with the XENON1T experiment. This interaction is generated when the WIMP couples to a virtual pion exchanged between the nucleons in a nucleus. In contrast to most non-relativistic operators, these pion-exchange currents can be coherently enhanced by the total number of nucleons, and therefore may dominate in scenarios where spin-independent WIMP-nucleon interactions are suppressed. Moreover, for natural values of the couplings, they dominate over the spin-dependent channel due to their coherence in the nucleus. Using the signal model of this new WIMP-pion channel, no significant excess is found, leading to an upper limit cross section of $6.4\times10^{-46}$ cm$^2$ (90 % confidence level) at 30 GeV/c$^2$ WIMP mass.

hep-ph↗

arXiv2018

SOPHIE velocimetry of Kepler transit candidates. XIX. The transiting temperate giant planet KOI-3680b

Whereas thousands of transiting giant exoplanets are known today, only a few are well characterized with long orbital periods. Here we present KOI-3680b, a new planet in this category. First identified by the Kepler team as a promising candidate from the photometry of the Kepler spacecraft, we establish here its planetary nature from the radial velocity follow-up secured over two years with the SOPHIE spectrograph at Observatoire de Haute-Provence, France. The combined analysis of the whole dataset allows us to fully characterize this new planetary system. KOI-3680b has an orbital period of 141.2417 +/- 0.0001 days, a mass of 1.93 +/- 0.20 M_Jup, and a radius of 0.99 +/- 0.07 R_Jup. It exhibits a highly eccentric orbit (e = 0.50 +/- 0.03) around an early G dwarf. KOI-3680b is the transiting giant planet with the longest period characterized so far around a single star; it offers opportunities to extend studies which were mainly devoted to exoplanets close to their host stars, and to compare both exoplanet populations.

astro-ph.EP↗

arXiv2018

Dark Matter Search Results from a One Tonne$\times$Year Exposure of XENON1T

We report on a search for Weakly Interacting Massive Particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber with a fiducial mass of $(1.30 \pm 0.01)$ t, resulting in a 1.0 t$\times$yr exposure. The energy region of interest, [1.4, 10.6] $\mathrm{keV_{ee}}$ ([4.9, 40.9] $\mathrm{keV_{nr}}$), exhibits an ultra-low electron recoil background rate of $(82\substack{+5 \\ -3}\textrm{ (sys)}\pm3\textrm{ (stat)})$ events/$(\mathrm{t}\times\mathrm{yr}\times\mathrm{keV_{ee}})$. No significant excess over background is found and a profile likelihood analysis parameterized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c${}^2$, with a minimum of $4.1\times10^{-47}$ cm$^2$ at 30 GeV/c${}^2$ and 90% confidence level.

astro-ph.CO↗

arXiv2018

On the critical energy required for homogeneous nucleation in bubble chambers employed in dark matter searches

Two equations for the calculation of the critical energy required for homogeneous nucleation in a superheated liquid, and the related critical radius of the nucleated vapour bubble, are obtained, the former by the direct application of the first law of thermodynamics, the latter by considering that the bubble formation implies the overcoming of a barrier of the free enthalpy potential. Comparisons with the currently used relationships demonstrate that the sensitivity of the bubble chambers employed in dark matter searches can be sometimes notably overestimated.

hep-ex↗

arXiv2018

Intrinsic backgrounds from Rn and Kr in the XENON100 experiment

In this paper, we describe the XENON100 data analyses used to assess the target-intrinsic background sources radon ($^{222}$Rn), thoron ($^{220}$Rn) and krypton ($^{85}$Kr). We detail the event selections of high-energy alpha particles and decay-specific delayed coincidences. We derive distributions of the individual radionuclides inside the detector and quantify their abundances during the main three science runs of the experiment over a period of $\sim$ 4 years, from January 2010 to January 2014. We compare our results to external measurements of radon emanation and krypton concentrations where we find good agreement. We report an observed reduction in concentrations of radon daughters that we attribute to the plating-out of charged ions on the negatively biased cathode.

astro-ph.IM↗

arXiv2018

Signal Yields of keV Electronic Recoils and Their Discrimination from Nuclear Recoils in Liquid Xenon

We report on the response of liquid xenon to low energy electronic recoils below 15 keV from beta decays of tritium at drift fields of 92 V/cm, 154 V/cm and 366 V/cm using the XENON100 detector. A data-to-simulation fitting method based on Markov Chain Monte Carlo is used to extract the photon yields and recombination fluctuations from the experimental data. The photon yields measured at the two lower fields are in agreement with those from literature; additional measurements at a higher field of 366 V/cm are presented. The electronic and nuclear recoil discrimination as well as its dependence on the drift field and photon detection efficiency are investigated at these low energies. The results provide new measurements in the energy region of interest for dark matter searches using liquid xenon.

astro-ph.IM↗