Scott Oser

Professor

Research Classification

Elementary Particles

Research Interests

particle physics
neutrinos
dark matter
statistical methods for physics

Relevant Degree Programs

 

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Master's students
Doctoral students
Postdoctoral Fellows
2020

dark matter, SuperCDMS

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Searching for multi-nucleon processes in neutrino interactions by proton identification in the fine-grained detectors for T2K (2018)

T2K is an accelerator-based neutrino experiment designed to observe neutrino oscillations with a baseline of 295 km across Japan from Tokai to Kamioka. Its main goal is to measure oscillation parameters (θ₂₃, Δm²₃₂ and θ₁₃) through νμ (overline{νμ}) disappearance and νe (overline{νe}) appearance channels. It has also begun to provide measurements of CP violation in the neutrino sector combining all four neutrino oscillation channels. However, the precision required for these experiments has resulted in the need to reduce challenging systematic uncertainties. Among all the uncertainties, the largest contribution comes from the neutrino interaction model, where nuclear effects are poorly understood. As neutrinos typically interact on nucleons that are almost always contained within nuclei, one immediately has to confront nuclear effects. Nuclear effects alter the kinematics of out-going particles from neutrino scatterings, and hence affect the neutrino oscillation measurements. Therefore it is crucial to understand the nuclear effects in these neutrino interactions.This dissertation describes the measurement of neutrino-nucleus interactions with no final state pion and at least one final state proton. Differential cross sections are measured as a function of kinematic variables, which utilize both muon and protons. An iterative unfolding technique is used to extract the cross sections. By providing unfolded and efficiency corrected results, this measurement can be more readily compared to theoretical models to allow a better understanding of nuclear effects in neutrino interactions, thereby providing valuable constraints on the systematic uncertainties associated with neutrino oscillation measurements for both T2K and other accelerator-based neutrino experiments.

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An analysis of the oscillation of atmospheric neutrinos (2017)

This thesis presents an analysis of the oscillation of atmospheric neutrinos observed in Super-Kamiokande, a large underground water Cherenkov detector in Japan. The observed atmospheric neutrino events are reconstructed and selected using a newly developed maximum likelihood event reconstruction algorithm, and a Markov chain Monte Carlo technique is employed to present the results on neutrino oscillation parameters as marginalized Bayesian posterior probabilities. The result of analyzing the SK-IV data of 2520 days exposure shows a preference for normal mass hierarchy with the posterior probability of 85.9%, and the mode and the 68% credible interval of each oscillation parameter’s marginalized 1D posterior probability distribution for normal hierarchy are sin² θ₂₃=0.606⁺⁰·⁰⁴⁴₋₀.₁₁₈ and Δm²₃₂=2.13⁺⁰·¹⁷₋₀.₃₈ ×10-³ eV².

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Constraining the flux and cross section models using carbon and oxygen targets in the off-axis near detector for the 2016 joint oscillation analysis at T2K (2017)

The T2K experiment is a long baseline neutrino experiment designed to measure various neutrino oscillation parameters, particularly θ₁₃ and θ₂₃, at world-leading precisions. T2K uses muon neutrino and antineutrino beams produced at the Japan Proton Accelerator Research Complex. The off-axis beam strikes near detectors 280 m from the source (ND280) and the water Cherenkov detector, Super-Kamiokande, 295 km away. The far detector performs the primary oscillation analysis, while ND280 provides cross-section and flux constraints to reduce uncertainties in the oscillation analyses. ND280 consists of several different detectors, with the main target mass being the Fine Grained Detectors, one of which provides an active carbon target and one which provides a combined water-carbon target. This thesis describes the fitting methods used for T2K's oscillation analyses and near detector constraints, with a focus on the near detector fit. The addition of water target data in the near detector fit improves cross-section uncertainties at both near and far detectors. The near detector fit is a maximum likelihood fit to observed neutrino interaction rates in ND280 to constrain the cross-section and flux at the far detector. Event cuts identify and separate charged-current neutrino interactions into topology-based samples, with selection uncertainties and correlations handled through extensive detector systematic studies. The near detector fit to data including a water target shows consistent fitted cross-section and flux with previous ND280 fits, and significantly reduces the uncertainty on the neutrino energy spectrum predictions at the far detector. In addition, nuclear model dependencies in the cross-section model used at T2K were investigated using the near detector fit, and the T2K model was shown to be sufficient in accounting for nuclear effects.

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Measurement of an off-axis neutrino beam energy spectrum (2012)

The T2K long baseline neutrino oscillation experiment is designed to measure the neutrino flavour mixing parameter θ₁₃, as well as θ₂₃ and Δm²₂₃ with twenty times greater precision than previous measurements. A neutrino beam is produced using the Japan Proton Accelerator Research Complex (J-PARC) proton accelerator in Tokai, Japan and is incident on the Super-Kamiokande water Cherenkov detector 295 km away beam at an off-axis angle of 2.5°. A suite of near detectors 280 m away from the proton target (ND280) provides additional constraints on beam flux estimates as well as measures neutrino interaction cross sections. A critical component of ND280 is a Fine Grained Detector (FGD) that provides an active target for neutrino interactions, with sufficient granularity to reconstruct short ranged particle tracks. This thesis describes the T2K experiment, the design and calibration of the FGD, and its online data reduction system. A cut-based selection for charged current neutrino interactions is used to produce quasi-elastic and non-quasi-elastic enhanced samples. These samples are used in a maximum likelihood fit to measure the T2K neutrino beam energy spectrum. The fit determines the flux scale factors that best reproduce the kinematic distribution of muons produced in selected interactions, and accounts for all relevant neutrino interaction model and detector systematic uncertainties. The fitted flux factors f(Eν) in the energy ranges defined for the analysis are as follows:f(0 3.5GeV ) = 0.92⁺⁰·²⁸₋₀.₂₃. These flux factors are consistent with the default neutrino beam flux prediction and the flux measurement used in the primary oscillation analysis of the T2K collaboration, and provide an independent confirmation that the neutrino beam flux model is reliable.

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Measurements of neutrino interactions on water using a fine-grained scintillator detector with water targets (2012)

Measurements of neutrino interaction cross-sections are important for the study of neutrino oscillations. For the T2K experiment, which has a near detector with a primarily carbon target and a far detector withan oxygen target, the cross-section difference is important for correctly comparing the neutrino fluxes at the two detectors. This dissertation presents a first measurement of the ratio between oxygen and carbon of the muon neutrino charge-current inclusive cross-section using the T2K near detector, ND280. The design and construction methods of the water target system in the ND280 Fine-Grained Detector (FGD) will be discussed, as will a new algorithm for reconstructing particle tracks contained within the FGD. The data analysis leading to the cross-section ratio measurement will be described. It is based on a statistical subtraction method which extracts the contribution of the FGD water mass to the total interaction rate for the FGD with water targets. We find an oxygen/carbon ratio of 1.129 ± 0.114 (stat) ± 0.044 (syst) from the ND280 data, a 1.39σ difference from the Monte Carlo prediction of 0.954 ± 0.029.

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Master's Student Supervision (2010 - 2018)
Calibration of SuperCDMS dark matter detectors for low-mass WIMPs (2018)

Observational evidence suggests that the majority of mass in the universe takes the form of non-luminous "dark matter". The Super Cryogenic Dark Matter Search (SuperCDMS) is a direct-detection dark matter experiment that searches primarily for a well-motivated dark matter candidate known as the weakly-interacting massive particle (WIMP). The experiment looks for an above-background excess of nuclear recoil events in cryogenic solid-state detectors that could be attributed to WIMP-nucleon collisions. The most recent SuperCDMS run at the Soudan underground laboratory set a world-leading limit on the spin-independent WIMP-nucleon cross section for a WIMP mass as low as ~3 GeV/c², and the next installation of the experiment at SNOLAB aims to be sensitive to WIMP masses below 1 GeV/c². To better understand the response of solid-state germanium detectors to low-mass WIMPs, "photoneutron" calibration data was taken at the Soudan laboratory in Minnesota by passing quasi-monoenergetic neutrons through SuperCDMS detectors. Gamma rays used in the photoneutron production process create an overwhelmingly dominant background of electron recoil events in the detector. This gamma background is measured directly with regular "neutron-off" data-taking periods during which the neutron production mechanism is removed. We compare the observed electron and nuclear recoil spectra with Geant4-simulated spectra to obtain a model-dependent calibration of the nuclear recoil energy scale of the detectors. The calibration is performed using a negative log likelihood fit to a parameterized Lindhard ionization yield model. The fit includes a semi-analytical model of the gamma background component obtained from the neutron-off data.

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Hadron production measurements of the EMPATHIC group (2018)

Long-baseline neutrino experiments produce neutrinos by colliding a beam onto atarget. Hadrons produced in the target can be magnetically focused into a beam thatdecays in flight, yielding a collimated beam of neutrinos. Neutrino flux predictionsare used to constrain the uncertainties of the detected neutrino flux and its uncertaintyis dominated by the uncertainties in hadronic interactions. The reductionof this uncertainty would further the physics goals for these experiments. Theseuncertainties can be sourced to the production cross section uncertainty which hasbeen set to a conservative value due to previous discrepancies in the estimated productioncross section seen in the NA61/SHINE 2cm and 90cm carbon target data,used by the T2K collaboration. In addition, untuned secondary interactions withinthe horn and decay volume contribute to the uncertainty.The EMPHATIC group has taken data using the Fermilab test beam on carbon,aluminum, and steel targets for hadrons ranging from 2GeV/c to 120GeV/c.EMPHATIC uses gas Cherenkov and lead glass calorimeters for particle identification,semiconductor tracking detectors for position and timing information, andemulsion situated on a moving table for precise position measurements. In addition,an aerogel Cherenkov detector was constructed at TRIUMF which was usedfor testing at the Fermilab Test Beam Facility. The silicon strip tracking detectorswere instrumental in the data acquisition of the EMPHATIC experiment. The dataacquired by the silicon strip detector for 30GeV/c protons impinging on a carbontarget was fit with the Bellettini et al. model [1]. The parameters of the total cross section, the black body radius, and the nuclear transparency term were fit and agreewithin one standard deviation with previous measurements of Bellettini et al. Theelastic cross section agrees within two standard deviations.

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Data acquisition for SuperCDMS SNOLAB (2015)

The SuperCDMS SNOLAB experiment will use solid state Germanium and Silicon detectors to search for Weakly Interacting Massive Particles (WIMPs), a leading candidate to explain dark matter. WIMPs are thought to exist in halos around galaxies and therefore thought to be constantly streaming through the earth. The CDMS detectors have been developed to measure the energy deposited by a WIMP-nucleon collision in terrestrial calorimeters.This thesis focusses on the Data Acquisition (DAQ) system that uses Detector Control and Readout Cards (DCRCs) and is designed to be dead- time-less. The DCRCs read in the data stream from the detector’s 12 phonon and 4 ionization energy channels. The DCRCs also control detector settings, and we develop interactive codes to allow users to easily change detector settings through the DCRC. The DAQ is designed to decide which events to write to disk in order to keep data throughput under a limit yet never miss an event that will be useful in the subsequent analysis. In this effort we develop different readout methods of the detector array for the different calibration runs and WIMP search runs. We also develop fast algorithms for rejecting events that fail a certain criteria for being usable. We also present a novel data compression method that reduces the total data volume by a factor of ∼ 16 yet retains all important information. This method involves a large covariance matrix inversion, and we show that this inversion can be consistently computed given that a sufficient amount of data has been used to build the covariance matrix. We also develop a GUI that is a critical element of the detector testing program for SuperCDMS SNOLAB. The GUI accesses the data stream as it is being written to disk, efficiently reads in the waveforms, and displays them in a user-friendly, oscilloscope-like, format. By making use of Fast Fourier Transform technology, the GUI is also capable of displaying incoming data in the frequency domain. This tool will enable a new degree of real-time analysis of detector performance, specifically noise characteristics, at the test facilities in the next stage of detector testing.

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Likelihood based reconstruction algorithm for finding short tracks within the T2K experiment's fine-grained detectors (2015)

The T2K experiment is a long baseline neutrino experiment. Rates of different types of neutrino interactions are compared at a near detector and a detector 295 km from the neutrino source which enables neutrino oscillation and cross-section measurements. Understanding the activity near the neutrino interaction vertex in the near detector is crucial to identifying how a neutrino interacted. Current reconstruction algorithms for T2K's Fine Grained Detectors (FGD) have a decreased sensitivity to short tracks (
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