A unified parametrization of the circular velocity, which accurately fits 850 galaxy rotation curves without needing in advance the knowledge of the luminous matter components, nor a fixed dark ...matter halo model, is proposed. A notable feature is that the associated gravitational potential increases with the distance from the galaxy centre, giving rise to a length-scale indicating a finite size of a galaxy, and after, the Keplerian fall-off of the parametrized circular velocity is recovered according to Newtonian gravity, making possible the estimation of the total mass enclosed by the galaxy.
Abstract
The stellar and gaseous mass distributions, as well as the extended rotation curve, in the nearby galaxy M33 are used to derive the radial distribution of dark matter density in the halo and ...to test cosmological models of galaxy formation and evolution. Two methods are examined to constrain the dark mass density profiles. The first method deals directly with fitting the rotation curve data in the range of galactocentric distances 0.24 ≤ r ≤ 22.72 kpc. Using the results of collisionless Λ cold dark matter numerical simulations, we confirm that the Navarro–Frenkel–White (NFW) dark matter profile provides a better fit to the rotation curve data than the cored Burkert profile (BRK) profile. The second method relies on the local equation of centrifugal equilibrium and on the rotation curve slope. In the aforementioned range of distances, we fit the observed velocity profile, using a function that has a rational dependence on the radius, and we derive the slope of the rotation curve. Then, we infer the effective matter densities. In the radial range 9.53 ≤ r ≤ 22.72 kpc, the uncertainties induced by the luminous matter (stars and gas) become negligible, because the dark matter density dominates, and we can determine locally the radial distribution of dark matter. With this second method, we tested the NFW and BRK dark matter profiles and we can confirm that both profiles are compatible with the data, even though in this case the cored BRK density profile provides a more reasonable value for the baryonic-to-dark matter ratio.
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
∼
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
β
β
≃
2.46
MeV
. For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at
1
σ
/
μ
is as low as (
0.80
±
0.02
) % in its one-ton fiducial mass, and for single-site interactions at
Q
β
β
. 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.
The XENON1T experiment searches for dark matter particles through their scattering off xenon atoms in a 2 metric ton 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 metric ton×year exposure of XENON1T data, that leads to the best limit to date on WIMP-nucleon spin-independent elastic scatter cross section for WIMP masses above 6 GeV/c2.
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/c2 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 ton×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.
Two-neutrino double electron capture (2νECEC) is a second-order weak-interaction process with a predicted half-life that surpasses the age of the Universe by many orders of magnitude. Until now, ...indications of 2νECEC decays have only been seen for two isotopes, 78Kr and 130Ba, and instruments with very low background levels are needed to detect them directly with high statistical significance. The 2νECEC half-life is an important observable for nuclear structure models and its measurement represents a meaningful step in the search for neutrinoless double electron capture-the detection of which would establish the Majorana nature of the neutrino and would give access to the absolute neutrino mass. Here we report the direct observation of 2νECEC in 124Xe with the XENON1T dark-matter detector. The significance of the signal is 4.4 standard deviations and the corresponding half-life of 1.8 × 1022 years (statistical uncertainty, 0.5 × 1022 years; systematic uncertainty, 0.1 × 1022 years) is the longest measured directly so far. This study demonstrates that the low background and large target mass of xenon-based dark-matter detectors make them well suited for measuring rare processes and highlights the broad physics reach of larger next-generation experiments.
The selection of low-radioactive construction materials is of utmost importance for the success of lowenergy 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 222Rn 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 222Rn activity concentration of 10 mu Bq/kg in 3.2 t of xenon. The knowledge of the distribution of the 222Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the 222Rn activity concentration in XENON1T. The final 222Rn activity concentration of (4.5 +/- 0.1) mu Bq/kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
Abstract 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 $$^{222}$$ 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 $$^{222}$$ 222 Rn activity concentration of $$10\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$ 10 μ Bq / kg in $$3.2\,\mathrm{t}$$ 3.2 t of xenon. The knowledge of the distribution of the $$^{222}$$ 222 Rn sources allowed us to selectively eliminate problematic components in the course of the experiment. The predictions from the emanation measurements were compared to data of the $$^{222}$$ 222 Rn activity concentration in XENON1T. The final $$^{222}$$ 222 Rn activity concentration of $$(4.5\pm 0.1)\,\mathrm{\,}\upmu \mathrm{Bq}/\mathrm{kg}$$ ( 4.5 ± 0.1 ) μ Bq / kg in the target of XENON1T is the lowest ever achieved in a xenon dark matter 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
μ
Bq
/
kg
in
3.2
t
of xenon. The knowledge of the distribution of the
222
Rn sources allowed us to selectively eliminate problematic 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
±
0.1
)
μ
Bq
/
kg
in the target of XENON1T is the lowest ever achieved in a xenon dark matter experiment.
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