This licentiate thesis presents contributions to the luminosity measurement from the data recorded by the ATLAS detector in 2017 using a track-counting technique, as well as a search for dark matter in the ATLAS experiment using 139 fb-1 of √s = 13 TeV pp collision data delivered by the LHC from 2015 to 2018. Track-counting luminosity measurements in low-luminosity operations are performed to study the effect of low collision rates on luminosity determination. The luminosity measured in a calibration transfer procedure using the track-counting technique is used to correct the pile-up dependence observed in ATLAS’s main luminosity detector called LUCID. A search in the final state of a lepton, jets and missing transverse energy, where the final state is produced from a pair of top quarks and a spin-0 scalar/pseudoscalar mediator, is presented. A dedicated signal region is designed to target this final state in which the mediator decays into dark matter particles. The signal region covers the search in the mass plane of the mediator and the dark matter particle. Dedicated control regions are designed to estimate the top-quark background events, as well as the events where a Zboson is produced in association with the top quarks. The signal region event counts in the data have not been unblinded yet, but expected exclusion limits at 95% confidence level as a function of mediator mass are presented. Scalar and pseudoscalar mediators are expected to be excluded up to 200 and 250 GeV, respectively, for the dark matter mass of 1 GeV, and the coupling strengths of the mediator to the dark matter and Standard Model particles of 1.

The aims of this thesis project have been to determine the feasibility of hyperon reconstruction utilizing a newly developed and implemented vertex fitter based on the Lagrange multiplier method. This was achieved through simulation and subsequent analysis of the reaction specified below, detailing the production of Λ-hyperon and K+ -meson pairs from proton-proton collisions. 𝑝(4.5𝐺𝑒𝑉)𝑝 → ΛΛ𝐾+𝐾+ This reaction channel provides a more complicated topology than previous benchmark studies of the fitter performance and is of interest as it enables studies of the strong ΛΛ interaction via the femtoscopy method. For this reason, measurements of this reaction channel were among the physics goals of the HADES beam time taking place in February 2022. As such, this study has provided insight into the feasibility of performing a femtoscopy analysis on this data by reconstructing the Λ-pair using the fitter. The obtained results provide the Λ-pair reconstruction efficiency and purities based on the lower limit of expected events collected during this beamtime. As for the fitter performance, it was found from the reconstructed kinematics of the Λ-pair that the fitter can effectively remove background over most of the kinematic region. However, for low relative momentum, combinatorial background becomes especially prominent. As this region is of interest in a femtoscopy study, it has been identified as especially challenging for the developed analysis procedure.

The purpose of this project was to design, construct, and evaluate an alpha spectrometer based on an inexpensive p-i-n photodiode as a radiation detector. The BPX-61 p-i-n photodiode was selected and calculated to have a 93 µm wide sensitive volume at 25 V reverse bias. Electronics consisting of a charge-sensitive preamplifier, a pole-zero canceling CR-(RC)4 pulse shaping amplifier, and an adjustable detector bias voltage supply were devised and assembled. Several alpha spectra were recorded from different alpha radiation sources to determine the performance of the alpha spectrometer. The results show that the alpha spectrometer could successfully and accurately measure alpha spectra, which could then be used to identify radioactive materials present in the sources. An FWHM resolution of about 230 keV was measured for 5.486 MeV alpha particles from Am-241. This resolution is inferior to most alpha spectrometers that measure under vacuum. However, because the device does not require a vacuum pump and uses USB for power and data acquisition, it is a convenient and compact option for field measurements. The low cost and reasonable performance of commercial p-i-n photodiodes as radiation detectors could be appealing for future alpha spectroscopy applications.

Until now the quantum field theory (QFT) that successfully describes the electric, weak and strong interactions (three out of the four fundamental forces) between particles is the Standard Model, but it omits gravity. The prime candidate for a quantum theory of gravity is string theory. However, recent developments in string theory suggest that a portion of the alternative quantum field theories that are being considered, are incompatible with gravity. In 2005, this led string theorists to outline the conditions an effective field theory (EFT) should satisfy in order to be consistent with a quantum theory of gravity. These conditions are the ones that separate the so-called landscape from the swampland. An EFT that satisfies these conditions is said to reside in the landscape, while EFTs that do not satisfy these conditions belong to the swampland. This mapping out of EFTs to the swampland gives rise to a number of predictions that are related to the physics of the Early universe and the nature of dark energy. The de Sitter conjecture and the Trans-Planckian censorship conjecture are some of these conditions and will be the main focus of this thesis. The main purpose behind this work is to gain a deep understanding of each criterium, as well as unravel their implications and predictions related to the dynamics of the Early Universe. We do this by writing a pedagogical introduction of the topic and by introducing some possible alternative to the inflationary scenario, cosmologies that seem to be consistent with the aforementioned constraints.

The neutron plays a central role in numerous fields of physics, a fact that entails a need for methods of measuring neutron energy spectra. In this project, a technique for neutron spectrometry through measurements of neutron-induced radioactivity in activation detectors was developed and tested. The developed technique involves irradiating element samples with neutrons, measuring activation products with a gamma spectrometer, and then performing a neutron spectrum unfolding procedure. The elements indium, iron, magnesium, aluminium, zinc, titanium, and copper were used as activation detectors and irradiated with neutrons from an americium-beryllium (AmBe) neutron source. Subsequent gamma spectrometry was performed with the UGGLA high-purity germanium detector setup at Uppsala University. The GRAVEL unfolding algorithm was implemented in MATLAB and used to unfold neutron spectra based on an initial spectrum guess. The unfolded neutron spectrum agrees well with the expected AmBe spectrum, though some difference between the spectra is attributed to neutron scattering in the irradiation environment. A possible ability to find approximate neutron spectra from inaccurate initial guesses is found, but additional work is needed to understand better how the initial guess affects the result for different neutron sources. Because activation detectors do not require electrical power when measuring neutrons, can be made sensitive to a wide range of neutron energies, and do not detect other types of radiation, future applications could find the developed neutron spectrometry method practical.

The IceCube Neutrino Observatory has sensitivity to MeV electron antineutrinos from core-collapse supernovae through an excess of the detection rate over the background. Wavelength-shifting sensors have the potential to greatly increase photon collection making it a promising candidate for improving the measurement of the supernova neutrino light curve in IceCube-Gen2. For high-energy neutrino reconstruction, the competing effect of increased photon collection and the broader time distribution necessitate detailed simulations to determine the impact. In this thesis, we investigate the sensitivity gain caused by wavelength shifters in a future IceCube-Gen2 detector regarding the detection of faint modulations of the supernova neutrino lightcurve. Furthermore, we lay the groundwork for a future high-energy reconstruction through the implementation and integration of wavelength-shifting sensors into the IceCube simulation framework.

The PANDA experiment at FAIR is an antiproton experiment and it will offer unique possibilities for the study of hadron physics including hyperon physics. With the PANDA detector, it will be possible to exclusively reconstruct hyperon-antihyperon events. Hyperons are relatively long-lived particles (10−10s), which can travel for a distance of up to a few meters before decaying into their reconstructible decay products. In this project, I focus on the reaction p̅ p → Ξ̄+ Ξ− → Λ̅ π+ Λ π− → p̅ π+π+ p π− π−. The Ξ− (cascade) hyperons take a special role as they are the lightest hyperons to introduce a sequential decay topology, i.e., Ξ− → Λ π− → p π− π− (and c.c.). This constitutes a substantial challenge for the reconstruction algorithms. In this thesis, a Monte-Carlo simulation study of realistic track and event reconstruction of this Ξ̄+ Ξ− reaction in the region near the production threshold is done, and the event generation of the Ξ̄+ Ξ− reaction channel was performed by the EvtGen event generator in PandaRoot. For various realistic tracking algorithms, track and event reconstruction performance levels were investigated in PandaRoot.

This thesis reports the first indications of the Λ(1520) and ∆(1232)++ decay modes in the Ξc0 → pK−K−π+ decay. The obtained fractions relative the inclusive Ξc0 → pK−K−π+ decay are (6.4±0.6)% and (32.6±1.2)% for the decays through the Λ(1520) and ∆(1232)++ resonances respectively. The estimates were done on a sample of 6449±226 events of the Ξc0 baryon originating in the pure hadron Ξb− → Ξc0π− decay. The fractions presented in this thesis should be seen as an early indication rather than final estimates as more in-depth studies need to be done.

No description available.

The Swedish Nuclear Fuel and Waste Management Company (SKB) has developed a method for final disposal of spent nuclear fuel. This technique requires accurate measurement of the residual decay heat of every assembly. For this purpose, depletion codes as well as calorimetric and gamma-ray spectroscopy experimental methods have been developed and evaluated. In this work a prototype analysis tool has been developed to automate the analysis of both calorimetric and gamma-ray spectroscopy measurements. The performance of the analysis tool has been investigated by comparing its output with earlier results and calculations. Parallel to the software development, new measurements on 73 BWR assemblies were performed. The results obtained for the determination of the residual decay heat are presented. Finally, suggestions for further development are outlined and discussed.