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Register a new userLuminescence of water or ice as a new detection method for magnetic monopoles
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Anna Obertacke Pollmann
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Cosmic ray detectors use air as a radiator for luminescence. In water and ice, Cherenkov light is the dominant light producing mechanism when the particles velocity exceeds the Cherenkov threshold, approximately three quarters of the speed of light in vacuum. Luminescence is produced by highly ionizing particles passing through matter due to the electronic excitation of the surrounding molecules. The observables of luminescence, such as the wavelength spectrum and decay times, are highly dependent on the properties of the medium, in particular, temperature and purity. The results for the light yield of luminescence of previous measurements vary by two orders of magnitude. It will be shown that even for the lowest measured light yield, luminescence is an important signature of highly ionizing particles below the Cherenkov threshold. These could be magnetic monopoles or other massive and highly ionizing exotic particles. With the highest observed efficiencies, luminescence may even contribute significantly to the light output of standard model particles such as the PeV IceCube neutrinos. We present analysis techniques to use luminescence in neutrino telescopes and discuss experimental setups to measure the light yield of luminescence for the particular conditions in neutrino detectors.
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The IceCube neutrino observatory uses $1,mathrm{km}^{3}$ of the natural Antarctic ice near the geographic South Pole as optical detection medium. When charged particles, such as particles produced in neutrino interactions, pass through the ice with relativistic speed, Cherenkov light is emitted. This is detected by IceCubes optical modules and from all these signals a particle signature is reconstructed. A new kind of signature can be detected using light emission from luminescence. This detection channel enables searches for exotic particles (states) which do not emit Cherenkov light and currently cannot be probed by neutrino detectors. Luminescence light is induced by highly ionizing particles passing through matter due to excitation of surrounding atoms. This process is highly dependent on the ice structure, impurities, pressure and temperature which demands an in-situ measurement of the detector medium. For the measurements at IceCube, a $1.7,mathrm{km}$ deep hole was used which {vertically} overlaps with the glacial ice layers found in the IceCube volume over a range of $350,mathrm{m}$. The experiment as well as the measurement results are presented. The impact {of the results, which enable new kind of} searches for new physics with neutrino telescopes, are discussed.
The hybrid Tibet AS array was successfully constructed in 2014. It has 4500 m$^{2}$ underground water Cherenkov pools used as the muon detector (MD) and 789 scintillator detectors covering 36900 m$^{2}$ as the surface array. At 100 TeV, cosmic-ray background events can be rejected by approximately 99.99%, according to the full Monte Carlo (MC) simulation for $gamma$-ray observations. In order to use the muon detector efficiently, we propose to extend the surface array area to 72900 m$^{2}$ by adding 120 scintillator detectors around the current array to increase the effective detection area. A new prototype scintillator detector is developed via optimizing the detector geometry and its optical surface, by selecting the reflective material and adopting dynode readout. This detector can meet our physics requirements with a positional non-uniformity of the output charge within 10% (with reference to the center of the scintillator), time resolution FWHM of $sim$2.2 ns, and dynamic range from 1 to 500 minimum ionization particles.
We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiments Far Detector, a 14 kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of $2times 10^{-14} mathrm{cm^{-2}s^{-1}sr^{-1}}$ at 90% C.L. for monopole speed $6times 10^{-4} < beta < 5times 10^{-3}$ and mass greater than $5times 10^{8}$ GeV. Because of NOvAs small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.
The main characteristics of a new concept of spherical gaseous detectors, with some details on its operation are first given. The very low energy threshold of such detector has led to investigations of its potential performance for dark matter particle searches, in particular low mass WIMPs : original methods for energy and fiducial volume calibration and background rejection are described and preliminary results obtained with a low radioactivity prototype operated in Laboratoire Souterrain de Modane (Frejus lab) are presented. Typical expected sensitivities in cross section for low mass WIMPs are also shown, and other applications briefly discussed.
We present preliminary characterization of the Speedster-EXD, a new event driven hybrid CMOS detector (HCD) developed in collaboration with Penn State University and Teledyne Imaging Systems. HCDs have advantages over CCDs including lower susceptibility to radiation damage, lower power consumption, and faster read-out time to avoid pile-up. They are deeply depleted and able to detect x-rays down to approximately 0.1 keV. The Speedster-EXD has additional in-pixel features compared to previously published HCDs including: (1) an in-pixel comparator that enables read out of only the pixels with signal from an x-ray event, (2) four different gain modes to optimize either full well capacity or energy resolution, (3) in-pixel CDS subtraction to reduce read noise, and (4) a low-noise, high-gain CTIA amplifier to eliminate interpixel capacitance crosstalk. When using the comparator feature, the user can set a comparator threshold and only pixels above the threshold will be read out. This feature can be run in two modes including single pixel readout in which only pixels above the threshold are read out and 3x3 readout where a 3x3 region centered on the central pixel of the x-ray event is read out. The comparator feature of the Speedster-EXD increases the detector array effective frame rate by orders of magnitude. The new features of the Speedster-EXD hybrid CMOS x-ray detector are particularly relevant to future high throughput x-ray missions requiring large-format silicon imagers.
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