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| 2. |
- Antochi, Vasile Cristian, 1992-
(författare)
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Inference on Dark Matter in Effective Field Theories : From XENON1T towards XENONnT: Chiral effective field theory analysis of nuclear recoils, single electrons and uncommon background modelling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cosmological and astronomical observations show that most of the matter in the Universe is dark. This dissertation provides an overview of the dark matter evidence, and focuses on the particle dark matter hypothesis, describing possible particle candidates, concentrating on the Weakly Interactive Massive Particles (WIMPs). It describes the main WIMP detection strategies and addresses the subject of WIMP scattering in direct detection experiments. This work analyses the data from the XENON1T experiment, investigating within a Chiral Effective Field Theory (ChEFT) framework the nuclear recoils from possible WIMP interactions. It presents the XENON1T detector, the main backgrounds, the xenon signal emission model and the background studies, and describes the statistical inference adopted in the analysis.The XENON1T detector was a dual-phase Time Projection Chamber (TPC) using a ~2 tonne liquid xenon target to detect scattering particles. WIMPs with masses above ~10GeV/c2 scattering against the xenon nuclei would deposit enough energy to create an observable event.The ChEFT analysis is performed on the XENON1T data from 278.8 days of operation for a total exposure of 1 tonne×year, with a combined likelihood of two science runs. The region of interest for this analysis was extended from [4.9, 40.9] keVnr, in the Spin Independent analysis, to [4.9, 54.4] keVnr, to increase the acceptance of possible models with rates peaking at higher energies (>0keVnr). The analysis shows that the data is consistent with a background only hypothesis and provides constraints on the interaction coefficients and the physics scale for 25 different operators. The analysis is complemented by limits on three benchmark models of interaction using ChEFT. For these models we investigate the effect of isospin breaking interactions, reporting cancellation regions where the limit worsens up to 6 orders of magnitude with respect to the isospin conserving case.The dissertation is complemented with the dark matter-electron scattering study within an EFT framework, analysing the single or few electron emission signals in XENON1T. The analysis provides the first experimental limits on the dark matter-electron effective operators for the magnetic and electric dipole, and anapole interactions.Lastly, the dissertation describes an example of introducing a data-driven background model in an inference framework based on explicit multidimensional likelihood computation. The background modelling is done using calibration data from the XENONnT detector, the next iteration of a dual-phase xenon TPC in the XENON detector family, which is currently in operation.
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| 3. |
- Antochi, Vasile Cristian, 1992-
(författare)
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WIMP searches in an Effective Field Theory Framework from XENON1T to XENONnT
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Observations from cosmology and astronomy suggest that most of the matter in the Universe is comprised of dark matter. In this thesis the evidence for dark matter and the possible candidates are explored, focusing on the Weakly Interacting Massive Particles (WIMPs) hypothesis. The various ways WIMPs can be detected are shown, with particular regard to WIMP scattering in direct detection experiments.Since traditional Spin Independent (SI) and Spin Dependent (SD) searches for WIMPs have produced very tight constraints on the interaction cross section, we investigate the WIMP scattering through a model independent Effective Field Theory (EFT) framework. The chosen approach for this work is Chiral EFT (ChEFT), which studies the nuclear responses of possible WIMP interactions including quantum chromo-dynamics (QCD) effects using chiral symmetry, starting from fundamental interactions with quarks and gluons in atomic nuclei.This thesis presents the statistical analysis and the inference used in the XENON1T experiment to perform a ChEFT analysis of WIMP interactions. Furthermore it shows the work towards the upgrade of the XENON experiment, XENONnT, with particular regard to the photomultiplier tube (PMT) testing performed at Stockholm University.XENON1T was a dual-phase time projection chamber using a 2 tonne liquid xenon target to detect scattering particles. WIMPs with masses above 10 GeV scattering against the xenon nuclei would deposit enough recoil energy to create an observable event. The XENONnT detector is a new detector that will have a target volume of ~6 tonnes of liquid xenon and is now being commissioned.The ChEFT analysis is done considering the XENON1T data from 278.8 days of operation and a fiducial volume of 1.3 tonne and it uses the full XENON1T combined likelihood, constructed with background models and signal models slightly extended in the analysis space with respect to the previous XENON1T searches, to increase the signal acceptance for the various EFT models.Simulated data sets were used to validate the inference and to compute the expected sensitivities for 25 different ChEFT responses.This work shows that XENON1T can constrain the physics scale Lambda of WIMP interactions within the ChEFT framework to regions of O(10ˆ2-10ˆ5 GeV) for most of the channels.
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| 4. |
- Aprile, Elena, et al.
(författare)
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Analysis of the XENON1T data for WIMP search : Background Models and Statistical Inference
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The XENON1T experiment searches for dark matter recoils within a $2$ tonne liquid xenon target. The detector is operated as a dual-phase time projection chamber, and reconstructs the energy and position of interactions in the active volume. In the central volume of the target mass, the lowest background rate of a xenon-based direct detection experiment so far has been achieved. In this work we describe the detector response modelling, the background and signal models, and the statistical inference procedures used in a search for Weakly Interacting Massive Particles (WIMPs) using 1\,tonne$\times$year exposure of XENON1T data.
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| 5. |
- Aprile, E., et al.
(författare)
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Constraining the Spin-Dependent WIMP-Nucleon Cross Sections with XENON1T
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 122:14
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Tidskriftsartikel (refereegranskat)abstract
- 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 x 10(-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.
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| 6. |
- Aprile, E., et al.
(författare)
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First Results on the Scalar WIMP-Pion Coupling, Using the XENON1T Experiment
- 2019
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 122:7
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Tidskriftsartikel (refereegranskat)abstract
- 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 x 10(-46) cm(2) (90% confidence level) at 30 GeV/c(2) WIMP mass.
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| 7. |
- Aprile, E., et al.
(författare)
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Observation of two-neutrino double electron capture in 124Xe with XENON1T
- 2019
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 568:7753, s. 532-535
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Aprile, E., et al.
(författare)
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Search for events in XENON1T associated with gravitational waves
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 108:7
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Tidskriftsartikel (refereegranskat)abstract
- We perform a blind search for particle signals in the XENON1T dark matter detector that occur close in time to gravitational-wave signals in the LIGO and Virgo observatories. No particle signal is observed in the nuclear recoil and electronic recoil channels within ±500 seconds of observations of the gravitational-wave signals GW170104, GW170729, GW170817, GW170818, and GW170823. We use this null result to constrain monoenergetic neutrinos and axion-like particles emitted in the closest coalescence GW170817, a binary neutron star merger. We set new upper limits on the fluence (time-integrated flux) of coincident neutrinos down to 17 keV at the 90% confidence level. Furthermore, we constrain the product of the coincident fluence and cross section of axion-like particles to be less than 10−29 cm2/cm2 in the [5.5–210] keV energy range at the 90% confidence level.
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| 9. |
- Aprile, E., et al.
(författare)
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The XENON1T data acquisition system
- 2019
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- 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 by triggering each channel independently, achieving a single photoelectron acceptance of (93 +/- 3)%, and deferring the global trigger to a later, software stage. The event identification is based on MongoDB database queries and has over 98% efficiency at recognizing interactions at the analysis threshold in the center of the target. 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.
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| 10. |
- Aprile, E., et al.
(författare)
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XENON1T dark matter data analysis : Signal and background models and statistical inference
- 2019
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 99:11
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Tidskriftsartikel (refereegranskat)abstract
- 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 x 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/c(2).
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| 11. |
- Aprile, E., et al.
(författare)
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XENON1T dark matter data analysis : Signal reconstruction, calibration, and event selection
- 2019
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 100:5
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Tidskriftsartikel (refereegranskat)abstract
- 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 ton x 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.
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