We derive constraints that must be satisfied by the sources of similar to 10 super(15) to similar to 10 super(18) eV cosmic rays, under the assumption that the sources are Galactic. We show that ...while these constraints are not satisfied by ordinary supernovae (SNe), which are believed to be the sources of unk10 super(15) eV cosmic rays, they may be satisfied by the recently discovered class of transrelativistic supernovae (TRSNe), which were observed in association with gamma-ray bursts. We define TRSNe as SNe that deposit a large fraction, integral of > 10 super(-2), of their kinetic energy in mildly relativistic, gamma beta > 1, ejecta. The high-velocity ejecta enable particle acceleration to similar to 10 super(18) eV, and the large value of f sub(R) (compared to integral of sub(R) similar to 10 super(-7) for ordinary SNe) ensures that if TRSNe produce the observed similar to 10 super(18) eV cosmic-ray flux, they do not overproduce the flux at lower energies. This, combined with the estimated rate and energy production of TRSNe, imply that Galactic TRSNe may be the sources of cosmic rays with energies up to similar to 10 super(18) eV.
The XENON1T dark matter experiment aims to detect weakly interacting massive particles (WIMPs) through low-energy interactions with xenon atoms. To detect such a rare event necessitates the use of ...radiopure materials to minimize the number of background events within the expected WIMP signal region. In this paper we report the results of an extensive material radioassay campaign for the XENON1T experiment. Using gamma-ray spectroscopy and mass spectrometry techniques, systematic measurements of trace radioactive impurities in over one hundred samples within a wide range of materials were performed. The measured activities allowed for stringent selection and placement of materials during the detector construction phase and provided the input for XENON1T detection sensitivity estimates through Monte Carlo simulations.
We present first results on the scalar coupling of weakly interacting massive particles (WIMPs) to pions from 1 t 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 nonrelativistic 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 6.4×10^{-46} cm^{2} (90% confidence level) at 30 GeV/c^{2} WIMP mass.
The XENON1T experiment aims for the direct detection of dark matter in a detector filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by ...radioactive decays inside the detector has to be sufficiently low. One major contributor is the
β
-emitter
85
Kr which is present in the xenon. For XENON1T a concentration of natural krypton in xenon
nat
Kr
/
Xe
<
200
ppq
(parts per quadrillion,
1
ppq
=
10
-
15
mol
/
mol
) is required. In this work, the design, construction and test of a novel cryogenic distillation column using the common McCabe–Thiele approach is described. The system demonstrated a krypton reduction factor of
6.4
·
10
5
with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of
nat
Kr
/
Xe
<
26
ppq
is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN.
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.
In this work, we expand on the XENON1T nuclear recoil searches to study the individual signals of dark matter interactions from operators up to dimension eight in a chiral effective field theory ...(ChEFT) and a model of inelastic dark matter (iDM). We analyze data from two science runs of the XENON1T detector totaling 1 t × yr exposure. For these analyses, we extended the region of interest from 4.9 , 40.9 keV NR to 4.9 , 54.4 keV NR to enhance our sensitivity for signals that peak at nonzero energies. We show that the data are consistent with the background-only hypothesis, with a small background overfluctuation observed peaking between 20 and 50 keV NR , resulting in a maximum local discovery significance of 1.7 σ for the Vector ⊗ Vector strange ChEFT channel for a dark matter particle of 70 GeV / c 2 and 1.8 σ for an iDM particle of 50 GeV / c 2 with a mass splitting of 100 keV / c 2 . For each model, we report 90% confidence level upper limits. We also report upper limits on three benchmark models of dark matter interaction using ChEFT where we investigate the effect of isospin-breaking interactions. We observe rate-driven cancellations in regions of the isospin-breaking couplings, leading to up to 6 orders of magnitude weaker upper limits with respect to the isospin-conserving case. Published by the American Physical Society 2024
This paper details the first application of a software tagging algorithm to reduce radon-induced backgrounds in liquid noble element time projection chambers, such as XENON1T and XENONnT. The ...convection velocity field in XENON1T was mapped out using Rn 222 and Po 218 events, and the rms convection speed was measured to be 0.30 ± 0.01 cm / s . Given this velocity field, Pb 214 background events can be tagged when they are followed by Bi 214 and Po 214 decays, or preceded by Po 218 decays. This was achieved by evolving a point cloud in the direction of a measured convection velocity field, and searching for Bi 214 and Po 214 decays or Po 218 decays within a volume defined by the point cloud. In XENON1T, this tagging system achieved a Pb 214 background reduction of 6.2 − 0.9 + 0.4 % with an exposure loss of 1.8 ± 0.2 % , despite the timescales of convection being smaller than the relevant decay times. We show that the performance can be improved in XENONnT, and that the performance of such a software-tagging approach can be expected to be further improved in a diffusion-limited scenario. Finally, a similar method might be useful to tag the cosmogenic Xe 137 background, which is relevant to the search for neutrinoless double-beta decay. Published by the American Physical Society 2024
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.
We describe the purification of xenon from traces of the radioactive noble gas radon using a cryogenic distillation column. The distillation column was integrated into the gas purification loop of ...the XENON100 detector for online radon removal. This enabled us to significantly reduce the constant Formula omittedRn background originating from radon emanation. After inserting an auxiliary Formula omittedRn emanation source in the gas loop, we determined a radon reduction factor of Formula omitted (95% C.L.) for the distillation column by monitoring the Formula omittedRn activity concentration inside the XENON100 detector.
Abstract
A low-energy electronic recoil calibration of XENON1T, a dual-phase xenon time projection chamber, with an internal
$^{37}$$
37
Ar source was performed. This calibration source features a ...35-day half-life and provides two mono-energetic lines at 2.82 keV and 0.27 keV. The photon yield and electron yield at 2.82 keV are measured to be (
$$32.3\,\pm \,0.3$$
32.3
±
0.3
) photons/keV and (
$$40.6\,\pm \,0.5$$
40.6
±
0.5
) electrons/keV, respectively, in agreement with other measurements and with NEST predictions. The electron yield at 0.27 keV is also measured and it is (
$$68.0^{+6.3}_{-3.7}$$
68
.
0
-
3.7
+
6.3
) electrons/keV. The
$^{37}$$
37
Ar calibration confirms that the detector is well-understood in the energy region close to the detection threshold, with the 2.82 keV line reconstructed at (
$$2.83\,\pm \,0.02$$
2.83
±
0.02
) keV, which further validates the model used to interpret the low-energy electronic recoil excess previously reported by XENON1T. The ability to efficiently remove argon with cryogenic distillation after the calibration proves that
$^{37}$$
37
Ar can be considered as a regular calibration source for multi-tonne xenon detectors.
PDF
![Online [Formula omitted]Rn ...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1434-6044/small "Online [Formula omitted]Rn removal by cryogenic distillation in the XENON100 experiment")
