Physics and Astronomy Department

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In keeping with the overall missions of both Vanderbilt University and its College of Arts and Science, the Department of English strives for three primary goals. First, we provide a superb education to all students, whether for our Graduate Students embarked on a career in the academy and beyond, for our majors and minors, or for students from other majors interested in exploring the richness and complexities of literature. Our students develop their reading, writing, and analysis skills across genres of print and visual culture. Second, through published scholarship and collaborations, we explore the diversity of literary studies and creative expression. And finally, we reach out, through local, national, and international partnerships, to introduce new knowledge to the public and to join in the conversation of public humanities. Welcoming creative writers and scholars at all levels of experience into our community, we work to enrich and understand the complex cultural legacies of literary study. Welcome to our new website; it is a work in progress, and please let us know how it could be of more use to you.

Department Location:	6301 Stevenson Center Vanderbilt University Nashville, TN 37240
Mailing Address:	Vanderbilt University 6301 Stevenson Center VU Station B #351807 Nashville, TN 37235
Phone:	615-322-2828
Fax:	615-343-7263
Email:	Physics-Astronomy@vanderbilt.edu
Website:	Department of Physics & Astronomy

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Now showing 1 - 20 of 55

16TH INTERNATIONAL SYMPOSIUM ON CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS (CGS16)
(16TH Internatinal Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS16), 2018) Luo, Y. X.; Hamilton, J. H.; Rasmussen, J. O.; Ramayya, A. V.; Frauendorf, S.; Wang, E.; Hwang, J. K.; Zhu, S.J.; Liu, Y. X.; Xu, F. R.; Sun, Y.; Liu, S. H.; Oganessian, Yu; Ma, W. C.
The paper reviews the systematic studies of triaxial deformations, new mode excitations and shape evolutions with regard to triaxial deformation in the neutron-rich nuclei with Z = 41-46, A similar to 100-116.
Anapole dark matter via vector boson fusion processes at the LHC
(Physical Review D, 2019-07-29) Florez, Andres; Gurrola, Alfredo; Johns, Will; Maruri, Jessica; Sheldon, Paul; Sinha, Kuver; Starko, Savanna Rae
Dark matter that is electrically neutral but couples to the electromagnetic current through higher-dimensional operators constitutes an interesting class of models. We investigate this class of models at the Large Hadron Collider, focusing on the anapole moment operator in an effective field theory (EFT) framework, and utilizing the vector boson fusion (VBF) topology. Assuming proton-proton collisions at root s = 13 TeV, we present the VBF anapole dark matter (ADM) cross sections and kinematic distributions as functions of the free parameters of the EFT, the cutoff scale Lambda and the ADM mass m(chi). We find that the distinctive VBF topology of two forward jets and large dijet pseudorapidity gap is effective at reducing SM backgrounds, leading to a 5 sigma discovery reach for all kinematically allowed ADM masses with Lambda <= 1.62 (1.1) TeV, assuming an integrated luminosity of 3000 (100) fb(-1).
An anomalous measurement of delta m31 squared from neutrino oscillations at the Daya Bay Reactor Neutrino Experiment
(Vanderbilt University. Department of Physics and Astronomy, 2013-04-22) Burroughs, Hunter; Ernst, David
In 2012, the collaboration overseeing the Daya Bay Reactor Neutrino Experiment announced results which determined the magnitude of the mixing angle \theta_{13} with unprecedented precision. However, no attempt was made in the collaboration’s publications to predict the value of the most relevant mass-squared difference to the observed oscillation, \delta m^2_{31}. This paper presents the results of an analysis which suggests that the Daya Bay data prefers a value of \delta m^2_{31} which is far greater than its presently recognized value. Specifically, it is found that Daya Bay predicts \delta m^2_{31} = 3.53_(-1.07)^(+.74) × 10^(-3) eV^2, where the cited uncertainties correspond to the 99% confidence bounds. This measurement excludes the most precise current measurement of \delta m^2_{31}, the MINOS result, at a 99% confidence level and is in turn excluded by the MINOS data at a 10 \sigma level. The possibility that sterile neutrino effects are the cause of this anomalous result is considered and used to suggest further work.
Backscattering and Line Broadening in Orion
(Astronomical Journal, 2022-12-19) O'Dell, C. R.; ; Mendez-Delgado, J. E.
Examination of emission lines in high-velocity-resolution optical spectra of the Orion Nebula confirms that the velocity component on the red wing of the main ionization front emission line is due to backscattering in the Photon Dominated Region. This scattered light component has a weak wavelength dependence that is consistent with either general interstellar medium particles or particles in the foreground of the Orion Nebula Cluster. An anomalous line-broadening component that has been known for 60+ years is characterized in unprecedented detail. Although this extra broadening may be due to turbulence along the line of sight of our spectra, we explore the possibility that it is due to Alfven waves in conditions where the ratio of magnetic and thermal energies are about equal and constant throughout the ionized gas.
Blazar Microvariations
(Vanderbilt University. Dept. of Physics and Astronomy, 2009-04-20) Pittman, Cameron W.; Professor Robert Knop
In November 2006, the authors collected data on blazars PKS 0537-441, PKS 0447-439, and PKS 0208-5121 from the Cerra Tololo Inter-American Observatory in Chile. All three blazars are tested for microvariability, first by comparing relative magnitudes against unvarying stars, then through power spectrum analysis. The authors used GNU Scientific Library tools for the Fourier transforms needed for power spectrum analysis. Fourier transforms break down data into series of periodic functions. Running power spectra quantitatively illuminate periodicity and variability in data. The authors tested power spectra by using well-defined functions to better understand power spectra analysis. Through light curve analysis and power spectra analysis, the authors found PKS 0537-441 showed microvariability, PKS 0208-512 most likely did not show microvariability, and PKS 0447-439 did not show microvariability.
Centrality and pseudorapidity dependence of the transverse energy density in pPb collisions ats root s(NN)=5.02 TeV
(Physical Review C, 2019-08-01) Greene, S.; Gurrola, A.; Janjam, R.; Johns, W.; Maguire, C.; Melo, A.; Ni, H.; Padeken, K.; Alvarez, J. D. Ruiz; Sheldon, P.; Tuo, S.; Velkovska, J.; Verweij, M.; Xu, Q.
The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, E-T, over 13.2 units of pseudorapidity, eta, for pPb collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at -6.6 < eta < -5.2 is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias pPb collisions the maximum value of dE(T)/d eta is 22 GeV, which implies an E-T per participant nucleon pair comparable to that of peripheral PbPb collisions at root s(NN) 7 = 2.76 TeV. The increase of dE(T)/d eta with centrality is much stronger for the lead-going side than for the proton-going side. The i dependence of dE(T)/d eta is sensitive to the eta range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the eta and centrality dependence of the data and the correlations observed between different eta regions.
Combined measurements of Higgs boson couplings in proton- proton collisions at v s=13TeV
(EUROPEAN PHYSICAL JOURNAL C, 2019-05-20) Greene, S.; Gurrola, A.; Janjam, R.; Johns, W.; Maguire, C.; Melo, A.; Ni, H.; Padeken, K.; Ruiz Alvarez, J. D.; Sheldon, P.; Tuo, S.; Velkovska, J.; Verweij, M.; Xu, Q.
Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton-proton collision data set recorded with the CMS detector in 2016 at fb-1. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a W or Z boson, or a top quark-antiquark pair) and the following decay modes: H, ZZ, WW, , bb, and . Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be =1.17 +/- 0.10, assuming a Higgs boson mass of 125.09. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.
Dark Matter benchmark models for early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum
(Physics of the Dark Universe, 2020-01) Padeken, Klaas Ole
This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations. (C) 2019 The Authors. Published by Elsevier B.V.
Dark radiation from particle decays during big bang nucleosynthesis
(Vanderbilt University. Dept. of Physics and Astronomy, 2012-04) Menestrina, Justin; Scherrer, Robert J. (Robert Joseph), 1959-
Cosmic microwave background (CMB) observations suggest the possibility of an extra dark radiation component, while the current evidence from big bang nucleosynthesis (BBN) is more ambiguous. Dark radiation from a decaying particle can affect these two processes differently. Early decays add an additional radiation component to both the CMB and BBN, while late decays can alter the radiation content seen in the CMB while having a negligible effect on BBN. Here we quantify this difference and explore the intermediate regime by examining particles decaying during BBN, i.e., particle lifetimes τ_X satisfying 0.1 sec < τ_X < 1000 sec. We calculate the change in the effective number of neutrino species, Neff, as measured by the CMB, ΔN_CMB, and the change in the effective number of neutrino species as measured by BBN, ΔN_BBN, as a function of the decaying particle initial energy density and lifetime, where DNBBN is defined in terms of the number of additional two-component neutrinos needed to produce the same change in the primordial 4He abundance as our decaying particle. As expected, for short lifetimes (τ_X < 0.1 sec), the particles decay before the onset of BBN, and DNCMB = DNBBN, while for long lifetimes (τ_X >1000 sec), ΔN_BBN is dominated by the energy density of the nonrelativistic particles before they decay, so that ΔN_BBN remains nonzero and becomes independent of the particle lifetime. By varying both the particle energy density and lifetime, one can obtain any desired combination of N_BBN and ΔN_CMB, subject to the constraint that DNCMB N_BBN. We present limits on the decaying particle parameters derived from observational constraints on ΔN_CMB, and N_BBN.
Data Logistics and the CMS Analysis Model
(Vanderbilt University. Dept. of Physics and Astronomy, 2009-04-20) Managan, Julie E.
The Compact Muon Solenoid Experiment (CMS) at the Large Hadron Collider (LHC) at CERN has brilliant prospects for uncovering new information about the physical structure of our universe. Soon physicists around the world will participate together in analyzing CMS data in search of new physics phenomena and the Higgs Boson. However, they face a significant problem: with 5 Petabytes of data needing distribution each year, how will physicists get the data they need? How and where will they be able to analyze it? Computing resources and scientists are scattered around the world, while CMS data exists in localized chunks. The CMS computing model only allows analysis of locally stored data, "tethering" analysis to storage. The Vanderbilt CMS team is actively working to solve this problem with the Research and Education Data Depot Network (REDDnet), a program run by Vanderbilt's Advanced Computing Center for Research and Education (ACCRE). I participated in this effort by testing data transfers into REDDnet via the gridFTP server, a File Transfer Protocol which incorporates an LHC Computing Grid security layer. I created a test suite which helped identify and solve a large number of problems with gridFTP. Once optimized, I achieved sustained throughputs of 700-800 Megabits per second (Mbps) over a 1 Gigabit per second (Gbps) connection, with remarkably few failures. GridFTP is the gateway between REDDnet and CMS, and my tests were designed to exercise and harden this important tool. My results support other indications that the REDDnet system will be a successful solution to the limitations of data-tethering in the CMS computing model.
Density profiles of dark matter halos
(Vanderbilt University. Dept. of Physics and Astronomy, 2010-04) Robbins, Katherine; Berlind, Andreas A., 1972-
Developing High-Brightness Electron Beam Sources for Producing Quantum Degenerate Electron Beams
(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) Kohler, Jonathan; Brau, Charles A., 1938-
The Pauli Exclusion Principle places a fundamental limit on the brightness of an electron beam. Developing a cathode which can reach this limit is useful for achieving maximum operation in current applications of electron beams, but also opens new areas of physics to be explored. When the phase space of the electron beam is filled to the maximum density, the electrons will experience a degeneracy pressure, similar to that which keeps a neutron star from collapsing. One promising source for a quantum degenerate beam is field emission from adsorbates on carbon nanotubes. Adsorbates have been shown to provide several orders of magnitude enhancement to emission brightness, which approaches the degeneracy limit. We have developed experiments to test various adsorbates, in order to find those which bind tightest and provide the largest enhancement in brightness. Continuing work to discover better adsorbates should soon allow for the generation of a quantum degenerate electron beam.
The distribution of ejected stars around a super massive black hole binary due to three-body scattering
(Vanderbilt University. Dept. of Physics and Astronomy, 2010-04) Benson, Amanda; Holley-Bockelmann, Kelly
An embedding technique to determine tau tau backgrounds in proton-proton collision data
(Journal of Instrumentation, 2019-06) Greene, S.; Gurrola, A.; Janjam, R.; Johns, W.; Maguire, C.; Melo, A.; Ni, H.; Padeken, K.; Romeo, F.; Sheldon, P.; Tuo, S.; Velkovska, J.; Verweij, M.; Xu, Q.
An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).
An embedding technique to determine tau tau backgrounds in proton-proton collision data
(Journal of Instrumentation, 2019-06) Greene, S.; Gurrola, A.; Janjam, R.; Johns, W.; Maguire, C.; Melo, A.; Ni, H.; Padeken, K.; Romeo, F.; Sheldon, P.; Tuo, S.; Velkovska, J.; Verweij, M.; Xu, Q.
An embedding technique is presented to estimate standard model tau tau backgrounds from data with minimal simulation input. In the data, the muons are removed from reconstructed mu mu events and replaced with simulated tau leptons with the same kinematic properties. In this way, a set of hybrid events is obtained that does not rely on simulation except for the decay of the tau leptons. The challenges in describing the underlying event or the production of associated jets in the simulation are avoided. The technique described in this paper was developed for CMS. Its validation and the inherent uncertainties are also discussed. The demonstration of the performance of the technique is based on a sample of proton-proton collisions collected by CMS in 2017 at root s = 13 TeV corresponding to an integrated luminosity of 41.5 fb(-1).
Engineering a perfusion-enabled mechanical compressor for long-duration immobilization and microscopy of cells and small organisms
(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) Jiang, Liwei; Janetopoulos, Christopher
The study of living specimens is essential to the understanding of organismal behavior. Unfortunately, a major difficulty in the study of live organisms is that many move in and out of the field of view or focal plane during microscopy. The present work seeks to combat this considerable problem by developing a mechanical microcompressor that immobilizes living cells and small organisms for long-duration optical microscopy. The device, dubbed the "Commodore Compressor," features two key innovations: (1) the integration of a perfusion system to keep the trapped specimen alive over several hours, as well as permitting the addition of chemoattractants, drugs, and other chemicals; (2) the incorporation of an optional patterned PDMS platform to improve the efficacy of immobilization in a targeted, organism-specific manner. One application of the Commodore Compressor is in monitoring the change in protein bioluminescence intensity in many trapped Saccharomyces cerevisiae cells during synchronized cell cycles. The experiment's feasibility and key techniques have been well demonstrated, although bioluminescence cannot currently be visualized. A second application involves fluorescence imaging of the neural network development of immobilized Caenorhabditis elegans over many hours. The development of new patterned PDMS platform designs, aided by the innovative use of established techniques, has driven the present work toward accomplishing the goal, but true long-term viability remains elusive. The Commodore Compressor may be directly used or easily adapted for many other specimen types and experimental scenarios.
Exploring the Local Association : a nearby, young kinematic stream of stars in the solar neighborhood
(Vanderbilt University. Dept. of Physics & Astronomy, 2008) Saling, Chris; James, David J.
During the course of my Honors Research Project, I worked with Dr. David James to determine whether a group of target stars are members of the Local Association. I did this by reducing spectroscopic data, taken by Dr. James, in order to determine the radial velocity and lithium contents of the stars. Using the radial velocity measurements, the kinematics of each star was then defined by determining their U,V,W space motions. Lithium measurements were used to establish star youth and provide further evidence to support membership of the Local Association.
Finite-Element Analysis of Low-Power Laser Heating in Gold::Vanadium Dioxide Nanocomposites
(Vanderbilt University. Dept. of Physics and Astronomy, 2011-04) MacQuarrie, Evan; Haglund, Richard F., Jr., 1942-
Finite element modeling was performed using COMSOL Multiphysics to study the thermal dynamics of gold::vanadium dioxide (VO$_{2}$) nanocomposites. These simulations were done to understand the data from transient absorption pump probe measurements taken over the previous two years by the author. The various parameters contributing to the dynamics of the system were systematically varied within the simulation in order to understand how the various properties of the nanocomposite affect the thermodynamics of the system. It was determined that the background temperature and the optical properties of the film make the dominant contributions to the system response. The simulation was able to predict the maximum change in transmission measured in experiment fairly well but could not predict the speed at which the system responded to the pump laser. Steps to improve upon the agreement between experiment and simulation are proposed.
H-band discovery of additional second-generation stars in the Galactic bulge globular cluster NGC 6522 as observed by APOGEE and Gaia
(ASTRONOMY & ASTROPHYSICS, 2019-07-22) Majewski, S.R.
We present an elemental abundance analysis of high-resolution spectra for five giant stars spatially located within the innermost regions of the bulge globular cluster NGC 6522 and derive Fe, Mg, Al, C, N, O, Si, and Ce abundances based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea that NGC 6522 stars are formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary polluters of intra-cluster medium. The peculiar abundance signatures of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.
High-energy attosecond-width electron diffraction simulations
(Vanderbilt University. Department of Physics and Astronomy, 2013-04-22) Kidd, Daniel; Varga, Kalman
Electron microscopy has been the recent subject of molecular imaging due to the strength of the electrons' interaction with the target molecule making for a detailed pattern at a small scale.[1] To achieve the best 4D image of the target, one needs sufficient spatial and temporal resolution, the prior being an issue of using electrons in the keV regime as to achieve an optimally small deBroglie wavelength, and the latter being improved by the temporal width of the electron wave packet itself.[2] In order to image the motion of the electronic structure of the target molecule, this width must be within the attosecond regime. In this paper, we use the computational method of time-dependent density functional theory (TDDFT) to model our targets of Beryllium and the Nitrogen molecule, N2 , and an incoming electron wave packet with an energy of 1500 eV.

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