Session D1: Condensed Matter and Materials Physics / Nuclear, Particle and High Energy Physics I

In-situ materials characterization at high spatial resolution: A journey through liquids, low temperature and beam damage.

The last few years have seen a paradigm change in the way we characterize materials, with unprecedented improvements in both spatial and spectroscopic resolution being realized by aberration-corrected transmission electron microscopes. While spatial and energy resolutions better than 60 pm and 10 meV have been reported, aberration-correction has also enables a large variety of in-situ experiments at close to atomic resolution. Using this approach, the intercalation of Li-ions into cathode materials, the dynamics of vacancies, and the interactions between gases and nano-particles can now be directly observed, to only mention a few examples. However, the electron probe current densities required for atomic-resolution imaging are often several orders of magnitudes higher than the threshold for electron-beam damage, which will prevent us from analyzing the true structure. Therefore, understanding and controlling the effects of the electron beam on the sample materials is emerging as one of the most important areas of current electron microscopy. Here, I will explore the effects of radiolysis by examining the mechanism of bubble formation in water encapsulated between two layers of graphene and focus on how to control the electron-dose rates and the formation of unwanted radicals in a liquid.   

Dynamic Phases, Clustering, and Lane Formation for Driven Disk Systems in the Presence of Quenched Disorder

Granular systems can exhibit fluid-like and solid-like properties in the different environments. Here we examine these flow properties with numerical simulations of granular particles driven over randomly distributed pinning sites in two dimensions. By varying the number of particles and the strength of the driving force, we investigate different effects of the pinning sites on the granular particle system. We show that there is a series of distinct dynamic regimes in our simulation including a clogged or pile-up phase near depinning, a homogeneous disordered flow state, and a dynamically phase separated regime consisting of high density crystalline regions surrounded by a low density of disordered disks, which has been also observed in active matter systems. This dynamical phase separation is one of most interesting features of our granular system since it is not observed in previous studies of driven long-range repulsively interacting particles.   

Magnetic field effects in regio-regular polythiophene based devices and thermally activated delayed fluorescence organic light emitting diodes

We examine magnetic field effects in regio-regular polythiophene (P3HT) based devices and devices fabricated from a blend that exhibits thermally-activated delayed fluorescence (TADF). A sign change in magnetoresistance (MR) in regio-regular P3HT devices was observed as the bias is increased. By comparing conductance and electroluminescence measurements, as well as fabricating unipolar and bipolar devices, with disentangle two regimes of magnetic-field effects occurring in the same material system: bipolaron MR and excitonic magnetoelectroluminescence (MEL). MEL measured at a constant current demonstrates that the electroluminescence efficiency of a device can be enhanced by the application of an external magnetic field. However, the size of the effect in P3HT (and other materials that have been studied) is relatively modest, of the order of 10\% typically. Light efficiency improvement is reported at the presence of an applied magnetic field to certain TADF-based organic light-emitting diodes. We show how this drastic difference arises from fundamental differences in the spin-dependent channels that participate in the magnetic-field effects.   

Phase 1 Pixel Upgrade of the Compact Muon Solenoid

The Large Hadron Collider (LHC) has been the world's premier particle accelerator since it began operation on 10 September 2010. In order to maintain this world class performance, it is necessary to upgrade the Compact Muon Solenoid (CMS) pixel detector, to cope with increased luminosity. The instantaneous luminosity is expected to increase from $ 1\times 10^{34}cm^{-2}s^{-1}$ to $ 2\times 10^{34}cm^{-2}s^{-1}$ during Run II of the LHC. Due to data loss in the read out chip, the present pixel detector cannot handle an increase of this magnitude. The Phase 1 Pixel Upgrade will address this issue. The upgraded detector will utilize improved pixel readout chips that will minimize data loss, two-phase $CO_2$ cooling, and DC-DC power. These new components will achieve higher efficiencies, lower fake rates, lower dead-time/data loss, and extend the lifetime of the detector. The new pixel detector is scheduled to be installed during the extended technical stop between 2016 and 2017. The design of the Forward Pixel Detector and module assembly, testing, and qualification will be discussed.   

SBND Source Calibration System Test at LArIAT

Fermilab's Short Baseline Neutrino Program aims to use Liquid Argon Time Projection Chambers (LArTPCs) to study GeV-scale accelerator neutrinos produced by the Booster Neutrino Beam. While work has already begun in studying LArTPC response to high-energy events, knowledge of detector response in the 1-50 MeV scale, the range in which supernova and solar neutrinos exist, is lacking. To address this problem, development and testing of a LAr-deployable (n,gamma) radioactive source calibration system has begun utilizing the LArIAT LArTPC at Fermilab. In this talk, I will present preliminary results of test source deployments at LArIAT.   

Status of the Micro-X Microcalorimeter~X-ray~Sounding~Rocket

The~Micro-X sounding rocket is designed to use Transition Edge Sensors (TES) to make X-ray observations. The superior energy resolution of TESs compared to traditional space-based X-ray detectors brings new precision to both supernova observations and the X-ray search for sterile neutrino dark matter. Current X-ray observations disagree over the potential presence of a 3.5 keV X-ray line consistent with a sterile neutrino interaction, and Micro-X is in a unique position to establish or refute the presence of this line. The significant engineering challenges of placing sensitive cryogenic detectors on a rocket have been overcome, and testing has moved from system functionality to optimization and integration in preparation for a 2017 launch. In this talk, I will discuss the status of the instrument and expectations for flight observations, with special emphasis given to the prospects of sterile neutrino studies.~   

Fast Timing Detector R{\&}D for Forward Proton Detectors at LHC

Quartz Timing Cherenkov (QUARTIC) detectors were tested at Fermilab Test Beam Facility in order to determine the timing resolution of very forward protons from collisions at the Large Hadron Collider (LHC). The active media of the detectors are quartz and sapphire, which are radiation hard and high light-yield materials. These detectors are constructed of 20 L-shaped bars that enable one to differentiate and detect more than one proton from the same LHC bunch crossing. The QUARTIC detectors have a small active area of \textasciitilde 4cm$^{\mathrm{2}}$, which is well-matched to the acceptance of the scattered protons. Our experimental results will be presented and further testing of this design is planned.