Session T08: Particle Physics Instrumentation VI

The Mu2e Trigger Menu expected performance

The Mu2e experiment at Fermilab searches for the charged-lepton flavor violating neutrino-less conversion of a negative muon into an electron in the field of an aluminum nucleus. The dynamics of such a process is well modelled by a two-body decay, resulting in a mono-energetic electron with an energy slightly below the muon rest mass. Mu2e is designed to reach a sensitivity on the ratio between the conversion rate and the capture rate of  6x1E-17 @ 90% C.L.. This will improve the current best limit by four orders of magnitude.

A very intense pulsed muon beam 1E10 µ/s is stopped on a target inside a very long solenoid where the detector is located. The detector consists of a tracker, a crystal calorimeter and an external veto for cosmic rays surrounding the solenoid. The trigger scheme consists of a series of software filters that run over the DAQ farm where an online reconstruction of the event is performed w/o any pre-selection (no L1 trigger). 

The main physics channels are selected by track-triggers that are capable to provide a very high efficiency (~99%) while keeping a formidable rejection at the level of a few 1,000. We present the design of the Mu2e trigger Menu and the expected trigger performance evaluated with the TDAQ prototype currently installed at Fermilab.   

Building low background kton-scale liquid argon time projection chambers for physics discovery

With radiopurity controls and small design modifications a kton-scale liquid argon time projection chamber similar to DUNE could be used for enhanced low energy physics searches. This includes improved sensitivity to supernova and solar neutrinos, and even weakly interacting massive particle dark matter. This talk will present initial simulation studies to optimize the design and evaluate physics sensitivities. It will also discuss the tools being developed to support a large-scale radiopurity assay campaign necessary to construct such a detector.   

Cosmogenic Activation of Radioisotopes in NaI(Tl) Detectors

    A challenge in rare event searches that use thallium-doped sodium iodide, NaI(Tl), detectors is maintaining low background levels. A prominent application of these detectors is the dark matter direct detection field. COSINE-100, SABRE, and ANAIS-112 are NaI(Tl)-based dark matter experiments seeking improved detector sensitivity to test the DAMA/LIBRA experiment’s long-standing claim of a dark matter discovery. A primary low energy background component, below 10 keV, is tritium, one of the radioisotopes produced in NaI(Tl) by cosmic ray activation.

    We present the results of a measurement for cosmogenic isotope production rates in NaI(Tl) detectors activated at the Los Alamos Neutron Science Center which has a neutron beam energy spectrum similar to cosmic ray neutrons. After irradiation, isotope production rates are measured and extrapolated to determine production rates by cosmic rays. This enables determination of acceptable above-ground residency times for NaI(Tl) detectors, allowing future NaI(Tl)-based experiments to meet background activity goals.   

Observation of Time-Dependent Impact Ionization in a Large-Size Ge Detector Made from a Crystal Grown at USD

An experiment to understand the charge transport in a SuperCDMS-style Ge detector made from a crystal grown at USD was performed at the University of Minnesota. An Am-241 movable source was used to characterize the 59.54 keV peak in the energy spectra from each channel. This study will help to understand the charge transport, charge trapping, and charge generation processes inside the detector at a cryogenic temperature. We investigated the time-dependent impact ionization induced by holes at mK temperature and studied the charge breakdown. We observed time-dependent impact ionization, which is due to the creation of overcharged states in the detector. The binding energy of the overcharged states was determined using the data taken at different temperatures.   

Germanium ionization detector in a cryo mode at liquid helium temperature

The high-purity germanium (HPGe) detectors are well known for operating at liquid nitrogen temperature and cryogenic temperature at mK. Very little is known about Ge detector operating at liquid helium temperature. It is expected that operating Ge detectors at liquid helium temperature reduces thermal noise and hence allows the detectors to have better energy resolution in comparison to operating at liquid nitrogen temperature. We characterized Ge ionization detectors operated at liquid helium temperature at the University of South Dakota (USD) using the home-grown crystals. We measured the impurity freeze-out temperature in Ge. Using alphas from an Am-241 source, the charge collection efficiency (CCE) as a function of bias voltage was measured for three detectors with different impurity levels. Subsequently, we studied the impact of the impurity levels on the time-dependent CCE of the Ge detectors. The implication of the CCE at low temperature is discussed for Ge detectors with a-Ge contacts in searching for rare-event physics.   

Development of high-resolution InSb detectors at USD

We have been successfully growing HPGe single crystals for a decade here at University of South Dakota by using the Czochralski method. These HPGe detector-grade single crystals are fabricated into radiation detectors used in many research and application areas such as rare event physics. However, new semiconductor is still necessary especially in high resolution X-rays and g-rays spectroscopy. The most promising candidate material is Indium Antimonide (InSb), a binary semiconductor which may be developed as a future ultra-high-resolution radiation detector due to its very small band gap of 0.165 eV and its large electron mobility of around 78000 cm²V^-1s^-1. This small band gap could provide even better resolution and a higher peak-to-Compton ratios than Ge does.

Most of the previous works on the InSb crystals were concentrated on infrared applications. At this work, we present some theoretical calculations of InSb detectors compared to our own HPGe radiation detectors. And also, we present the experimental set up to grow the single crystals of InSb by Czochralski method in our lab.   

Design of sub-keV scale neutron calibrations setup using Fe and Sc filter

We will discuss recent progress in making sub-keV nuclear recoil calibrations practical in a university lab environment.  First, we will describe a method to moderate and then filter neutrons from a pulsed Deuterium-Tritium (DT) generator, enabling a pulsed keV-scale neutron source. We will discuss the design process that involves successive stages of effective moderation of neutrons for filtering and shielding of the unwanted neutrons for human safety. We will also describe work towards a large-area and affordable backing detector array employing neutron capture. The results of a prototype backing detector that has been built and characterized will be discussed.   

An Fe-shielded 124Sb9Be 24 keV photoneutron source for calibration of low threshold dark matter detectors

Direct detection dark matter searches are extending their reach to sub-GeV dark matter masses, requiring new detector technologies with low thresholds and new low-energy calibration methods.  For many detectors searching for dark matter - nucleus interactions,  the ideal calibration source is a beam of monoenergetic neutrons with ~keV energy.  We will discuss recent progress in making such neutron-based calibrations practical in a university lab environment via novel shielding of an ¹²⁴Sb⁹Be photoneutron source.  The 24 keV neutron flux is well-matched to a narrow spectral feature of neutron transparency in Fe, meaning an Fe shield can stop the ¹²⁴Sb gamma background flux while transmitting the 24 keV neutron flux with relatively little moderation. Such an Fe-shielded ¹²⁴Sb⁹Be source has been designed and assembled, and measurements of the neutron and gamma flux and energy spectrum will be presented. Additionally, the detection of the 24 keV neutrons with liquid scintillator, which would allow for tagging neutron recoil angle, will be demonstrated.