Physics

Seminars in Spring 2017

All seminars are held at 4:10 PM in Physics 123, unless otherwise noted.
Refreshments will be served at 4:00 PM.

Jan 25

Mo Copeland '82 & Owen Gross '04, Oregon Episcopal School
Perspectives on teaching high school physics

Abstract: Two graduates of the Reed College physics department return to discuss careers in secondary education. Mo Copeland is a former high school physics teacher and current Head of Oregon Episcopal school, an independent school in Portland. Owen Gross is a former visiting assistant professor at Reed College and a first year physics teacher at Oregon Episcopal School.

Feb 1

Adam Fritsch, Gonzaga University
Search for α-Cluster Structure in Exotic Nuclei with the Prototype Active-Target Time-Projection Chamber

Abstract: Some exotic nuclei appear to exhibit α-cluster structure, which may impact nucleosynthesis reaction rates. While various theoretical models currently describe such clustering, more experimental data are needed to constrain model predictions. The Prototype Active-Target Time-Projection Chamber (PAT-TPC) has low-energy thresholds for charged-particle decay and a high detection efficiency due to its thick gaseous active target volume, making it well-suited to search for low-energy α-cluster reactions. Radioactive-ion beams produced by the TwinSol facility at the University of Notre Dame were delivered to the PAT-TPC to study 14C via α-resonant scattering. Differential cross sections and excitation functions were measured and show evidence of three-body exit channels. Additional data were measured with an updated Micromegas detector more sensitive to three-body decay. Preliminary results are presented.

Feb 8

Gordan Krnjaic '05, Fermilab
Discovering or Falsifying sub-GeV Thermal Dark Matter

Abstract: This talk covers the theoretical features and experimental status of thermal dark matter (DM) with mass below the electroweak scale (MDM << 100 GeV).  In this class of models, dark and visible matter are initially in thermal equilibrium during the early universe when the DM is relativistic (Tphotons  >> MDM). During this epoch, dark and visible matter annihilate into each other at equal rates and both number densities are calculable from equilibrium thermodynamics.  However, as Hubble expansion cools the universe, the annihilation rates fall out of equilibrium and the co-moving DM number density becomes fixed to its value when equilibrium is lost. Thus, these models predict a firm relationship between the dark-visible annihilation cross section and the cosmic DM abundance, which implies a sharp sensitivity target for a variety of  novel, accelerator based search techniques. It is found that a small set of future experiments based on these new techniques can decisively discover or falsify nearly all predictive models of thermal DM below the electroweak scale. 

Feb 15

Jenne Driggers, CalTech/LIGO
Advanced LIGO's second observing run (and beyond)

Advanced LIGO made the first direct detection of gravitational waves during its first observation period, which ended in January 2016. For several months afterward, the interferometers underwent a series of upgrades with the goal of improving their sensitivity to various potential gravitational wave sources.  On November 30th, 2016, the detectors began their second observing run, which is currently ongoing.  In this talk I will discuss some of the upgrades that are now in place, and how they enhance our sensitivity to events such as massive black holes at lower frequencies and mergers involving neutron stars at higher frequencies, as well as facilitate tests of general relativity with higher signal-to-noise ratio detections. I will conclude with an outlook on future upgrades that may be added after the next observing run, to further improve our ability to detect gravitational waves.

Feb 22

Patricia Larkoski, The MITRE Corporation
Signal Processing and Detection for Radars

Abstract: Radars are complex systems that use reflected pulses of electromagnetic radiation to detect targets.  Advanced technologies from many different specializations are required to build a modern radar.  I will discuss radar concepts for receivers, signal processing, and detection to provide a physicist’s introduction to these fascinating machines.  Approved for Public Release;  Distribution Unlimited. Case Number 17-0690.  ©2017 The MITRE Corporation. ALL RIGHTS RESERVED.

Mar 1

Katherine Zaunbrecher, Colorado State University
The Physics of Photovoltaics

Photovoltaic (PV) solar cells are one of the leading sources of today’s renewable energy. They have reached grid parity in over 20 countries and the average PV production has increased about 40% per year--with cost, performance, and reliability all factoring into its success. This talk will focus on how to improve performance and further decrease costs by increasing cell efficiency. Understanding the basic principles of how a solar cell operates is an important part of doing this. There are also many electrical and optical characterization techniques that can be used to understand carrier recombination and assess material uniformity, which can in turn tell us how to build a better PV device.

Mar 8

Ragnar Stroberg, TRIUMF
Atomic nuclei from the ground up

Abstract:  The standard model of particle physics has been astoundingly successful in predicting and interpreting the results of atomic and sub-atomic experiments. However when it comes to atomic nuclei -- which make up more than 99% of the mass of visible matter -- we don't yet know how to solve the equations of the standard model to obtain predictions. Nonetheless, substantial progress towards this goal has been made in the past two decades. I will discuss some developments in nuclear many-body theory which enable the treatment of up to approximately 100 particles with controlled uncertainties. Parallel developments of nuclear interactions derived from chiral effective field theory -- a low-energy theory of quantum chromodynamics with pion and nucleon degrees of freedom -- place first-principles calculations of nuclear physics within reach. Finally, I will describe some early steps towards applications to searches for physics beyond the standard model, including neutrinoless double beta decay and dark matter detection.

Mar 22

Senior Thesis Talks

Alex Liebman-Pelaez

Benjamin Morrison

Ella Banyas

Mar 29

Senior Thesis Talks

William Ashfield

Robby Gottesman

Sabrina Appel

Apr 5

Senior Thesis Talks

Yuka Esashi

Kevin Freymiller

Kaustuv Datta

Apr 12

Senior Thesis Talks

Elias Cohen

Lara Kincheloe

Edgar Perez

Apr 19

Senior Thesis Talks

Colin Vangel

Jonathan Croom

Alex Abrahams

Apr 26

Senior Thesis Talks

Gabriel Colacion

Muldrow Etheredge

Vincent Griffith