Committee: Or Hen, Chair ~ Daniel Harlow ~ Philip Harris
hosted by: Tracy Slatyer
Rebecca Leane, MIT
Status of the Galactic Center Gamma-Ray Excess
Abstract:
The Galactic Center Excess (GCE) is an excess of GeV gamma rays robustly detected by the Fermi Gamma-Ray Space Telescope. The GCE has garnered great interest as a possible signal of either dark matter annihilation, or a new population of gamma-ray emitting pulsars. I will discuss arguments for and against both possibilities, and present an overview of the latest developments in our understanding of this intriguing signal.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Or Hen
Alex Sushkov, Boston University
Using Nuclear Magnetic Resonance to Search for Dark Matter
Abstract:
The nature of dark matter is one of the most important open problems in modern physics. Axions and axion-like particles (ALPs) are strongly-motivated ultra-light dark matter candidates. Nuclear spins interacting with axion-like background dark matter experience a torque, oscillating at the axion Compton frequency. The Cosmic Axion Spin Precession Experiments (CASPEr) use precision magnetometry and nuclear magnetic resonance techniques to search for the effects of this interaction.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
President's Day - No Talk this Week
hosted by: Or Hen
Ronald Fernando Garcia Ruiz
Exotic Atoms and Molecules for Nuclear Science
Abstract:
Precise knowledge of the interaction between the atomic nucleus and the surrounding electrons offers a complementary insight into the atomic nucleus and the fundamental particles and forces of nature. Exotic atoms and molecules - those containing nuclei with extreme proton-to-neutron ratios - can be made to enhance a particular nuclear structure or symmetry-violating effect. Thereby offering high sensitivity to explore the emergence of nuclear phenomena, the study of fundamental symmetries, and the search for new physics. In this colloquium, I will present recent highlights from laser spectroscopy experiments of these exotic species, containing isotopes produced in extreme regions of the nuclear chart. The relevance of these results to some of the long-standing questions of nuclear science will be discussed.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Or Hen
Tyler Kutz, MIT
Nucleon Structure From A=3 Nuclei
Abstract:
Various mechanisms have been suggested to explain the breaking of SU(6) spin-flavor symmetry in QCD. As these mechanisms relate to parton dynamics, they impact the quark content of hadrons. Specifically, in the nucleon valence region (x close to 1), the ratio of down to up quarks d/u can discriminate between different symmetry-breaking mechanisms. This is accessible by deep inelastic scattering (DIS) measurements of the ratio of the neutron to proton structure functions. Due to the lack of a free neutron target, information on neutron structure is typically obtained from deuterium data, a process that leads to large uncertainties arising from nuclear corrections.
The MARATHON experiment at Jefferson Lab exploits the mirror symmetry of tritium (3H) and helium (3He) to perform a novel extraction of neutron to proton structure from the 3H/3He ratio, where nuclear effects are expected to largely cancel. Preliminary results from MARATHON will be presented. These data will be compared to predictions from a recent global analysis of DIS data using a phenomenological model where nuclear modification is attributed to short-range correlations between nucleons.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Daniel Harlow
Anson Hook, University of Maryland
A CMB Millikan Experiment with Axion Strings
Abstract:
The axion is one of the favorite candidates for dark matter as it is a dark matter candidate that can simultaneously also explain why the neutron electric dipole moment is small. Interestingly, axions can also serve as a probe of the fundamental value of the electric charge. This feature comes to the forefront in the context of axion strings, where topological effects are present and allow one to directly measure anomalies, a quantity sensitive to the charges of UV particles. We discuss how new searches utilizing CMB polarization data can simultaneously test the existence of axion strings as well as act as a Millikan experiment.
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
hosted by: Or Hen
No Talk this Week
time: 4:00 p.m.
place: Kolker Room (26-414)
(refreshments at 3:30 p.m.)
Spring Break - No Talk this Week
hosted by: Or Hen
Taritree Wongjirad, Tufts University
Applying Convolutional Neural Networks to MicroBooNE
Abstract:
The MicroBooNE experiment consists of liquid argon time projection chamber(LArTPC) situated in the path of the Booster Neutrino Beam (BNB) at Fermilab. The goals of the experiment are to (1) investigate the observation of an excess of a possible electron-neutrino and anti-neutrino events by the MiniBooNE experiment, (2) measure argon-nucleus cross sections, and (3) perform R&D for LArTPCs. The data from MicroBooNE, and other LArTPCs, can be naturally arranged as high-resolution images of particle tracks traversing the detector. This has spurred effort on MicroBooNE towards applying convolutional neural networks (CNNs), a type of deep learning algorithm shown to be extremely effective in numerous computer vision problems, to our data. I'll talk about the ways in which MicroBooNE uses CNNs with a focus on recent results demonstrating their performance on real data. I'll also discuss future directions MicroBooNE is exploring to further apply CNNs.
hosted by: Or Hen
Daniel E.M. Hoff, University of Massachusetts, Lowell
A Crack in Nuclear Mirror Symmetry
Abstract:
Symmetries are ubiquitous in nature, and the observation of symmetry breaking often leads to new insights in physics. Within nuclear physics, it is possible to consider neutrons and protons as isospin projections of a single fermion. Nuclear states can then be characterized by a total isospin (or iso-baric spin T) and this quantity is largely conserved in reactions and decays. A mirror symmetry emerges from this formalism; nuclei with exchanged numbers of neutrons and protons, or mirror nuclei, should have an identical set of states, including their ground state. Despite knowing that isospin symmetry is not perfect, it has proved to be rather robust across the chart of nuclides. In this talk, I will show evidence for mirror-symmetry violation in bound nuclear ground states between the mirror partners73Sr and 73Br. By analyzing the beta-delayed proton emission of 73Sr, a spin assignment of Jπ = 5/2− is needed to explain the proton-emission pattern observed from the T = 3/2 isobaric-analog state in 73Rb, which is identical to the ground state of 73Sr. Therefore, the ground state of 73Sr must differ from its Jπ = 1/2− mirror 73Br. This observation offers unique insights into charge-symmetry breaking forces acting in nuclei.
hosted by: Janet Conrad
Thomas Wester, Boston University
Super-Kamiokande in 2020 – Present Status and Outlook
Abstract:
Super-Kamiokande is a particle observatory located near Toyama, Japan. Throughout its over 20 years of near-continuous operation and data analysis, Super-K has contributed to our understanding of neutrino oscillations, provided the world’s most stringent limits on proton decay, and tested numerous exotic new physics scenarios. In 2018, the Super-K detector was opened for refurbishment work in preparation for its next phase. Beginning in 2020, Super-K will operate with gadolinium-loaded water, improving previous analyses and enabling new searches.
Patriot's Day - No Talk this Week
hosted by: Or Hen
Holly Szumila-Vance, MIT
Searching for the onset of color transparency
Abstract:
Color transparency (CT) is a fundamental phenomenon of QCD postulating that at high momentum transfer, one can preferentially measure hadrons that fluctuate to a small color neutral transverse size in the nucleus, and final state interactions within the nuclear medium are suppressed. Observation of the onset of CT indicates the transition between partonic and hadronic degrees of freedom in the nucleus. CT is observed experimentally as a rise in the measured nuclear transparency as a function of the momentum transferred. While a rise in the measured transparency consistent with CT models has been observed for mesons, it remains unconfirmed in baryons. Observation of CT in baryons would provide a new means to study the nuclear strong force and would be the first clear observation of baryons fluctuating to a small size in the nucleus. The most recent search for the onset of CT used the recently upgraded 12 GeV electron beam at Jefferson Lab in Hall C in the spring of 2018 and sought to observe the CT signal for baryons. This experiment used the High Momentum Spectrometer (HMS) and Super High Momentum Spectrometer (SHMS) in coincidence to measure A(e,e’p) on a carbon target and obtained four kinematic points at momentum transfer Q2 from 8-14.3 GeV/c2. Preliminary results show no increase in the transparency. This talk summarize the status of experimental searches for the onset of CT with emphasis on the most recent results from Jefferson Lab and will discuss future directions for observing CT.
hosted by: Janet Conrad
Daniel Winklener, MIT
A Fully Iron-Free Cyclotron for Proton Beam Radiotherapy Treatment
Abstract:
Superconducting cyclotrons are increasingly employed for proton beam radiotherapy treatment (PBRT). The use of superconductivity in a cyclotron design can reduce its mass by an order of magnitude and size by a factor of 3-4 over conventional resistive magnet technology, yielding significant reduction in overall cost of the device, the accelerator vault, and its infrastructure. In the presented work, we go a step further and remove the iron yoke, generating the cyclotron magnetic field with a combination of superconducting coils only. Elimination of the iron yoke has several key benefits. First and foremost, the overall weight can be reduced by another factor four. Secondly, eliminating all magnetic iron from the flux circuit results in a linear relationship between field and coil current, which allows smooth scaling of the magnetic field and thus the output energy, for example from 70 to 230 MeV, thereby removing the need for an energy degrading system. In this presentation, I describe the design of such an iron-free cyclotron, currently under development in collaboration between the Plasma Science and Fusion Center (PSFC) and LNS. I present coil and cryostat calculations as well as beam dynamics studies and treatment plan considerations.
hosted by: Lindley Winslow
Jonathan Ouellet, MIT
Latest Results from CUORE, And Other Bolometric Searches for Lepton Number Violation
Abstract:
The matter/anti-matter asymmetry of the universe is one of the most profound open questions in particle astrophysics today. Despite the Standard Model's ability to explain so much about the universe, its inability to explain why there is something rather than nothing is a pretty major deficiency. The discovery of a hypothetical and extremely rare nuclear physics process called neutrinoless double beta ($0\nu\beta\beta$) decay could provide important insights into how this matter asymmetry came about, and at the same time provide glimpses into new physics at energy scales well beyond the SM — possibly even up to the GUT scale. Cryogenic bolometers are an extremely powerful tool in the hunt for $0\nu\beta\beta$ decay, and the CUORE detector is the first running ton-scale bolometric experiment searching for this important process. CUORE has been collecting data since 2018 and will continue running for the next few years. The successor to CUORE, called CUPID, will be more sensitive by about two orders of magnitude, and will push the search for $0\nu\beta\beta$ decay into some of the most promising regions of parameter space. In this talk, I will cover the basic physics of bolometric detectors, some recent results from CUORE, and CUPID demonstrators, and touch on some of the additional physics that can be done with bolometric detectors.
