News Article | February 20, 2017
Two physics students have shown how to levitate a variety of objects between a warm plate and a cold plate in a vacuum chamber. They levitated ceramic and polyethylene spheres, glass bubbles, ice particles, lint strands, and thistle seeds. They achieved a number of levitation breakthroughs, in terms of duration, orientation, and method. The levitation lasted for more than an hour, as opposed to a few minutes; stability was achieved radially and vertically, as opposed to just vertically; and it used a temperature gradient rather than light or a magnetic field. Their findings appear in Applied Physics Letters. “Magnetic levitation only works on magnetic particles, and optical levitation only works on objects that can be polarized by light, but with our first-of-its-kind method, we demonstrate a method to levitate generic objects,” says Cheng Chin, professor of physics, whose ultracold lab at the University of Chicago was home to the experiments. In the experiment, the bottom copper plate was kept at room temperature while a stainless steel cylinder filled with liquid nitrogen kept at negative 300 degrees Fahrenheit served as the top plate. The upward flow of heat from the warm to the cold plate kept the particles suspended indefinitely. “The large temperature gradient leads to a force that balances gravity and results in stable levitation,” says Frankie Fung, the study’s lead author. “We managed to quantify the thermophoretic force and found reasonable agreement with what is predicted by theory. This will allow us to explore the possibilities of levitating different types of objects.” Thermophoresis refers to the movement of particles by means of a temperature gradient. “Our increased understanding of the thermophoretic force will help us investigate the interactions and binding affinities between the particles we observed,” says Mykhaylo Usatyuk, a study coauthor. “We are excited about the future research directions we can follow with our system.” The key to obtaining high levitation stability is the geometrical design of the two plates. A proper ratio of their sizes and vertical spacing allows the warm air to flow around and efficiently capture the levitated objects when they drift away from the center. Another sensitivity factor is that the thermal gradient needs to be pointing upward—even a misalignment of one degree will greatly reduce the levitation stability. “Only within a narrow range of pressure, temperature gradient, and plate geometric factors can we reach stable and long levitation,” Chin says. “Different particles also require fine adjustment of the parameters.” The apparatus offers a new ground-based platform to investigate the dynamics of astrophysical, chemical and biological systems in a microgravity environment, according to the researchers. Levitation of macroscopic particles in a vacuum is of particular interest due to its wide applications in space, atmospheric, and astro-chemical research. And thermophoresis has been utilized in aerosol thermal precipitators, nuclear reactor safety, and the manufacturing of optical fibers through vacuum deposition processes, which apply progressive layers of atoms or molecules during fabrication. The new method is significant because it offers a new approach to manipulating small objects without contacting or contaminating them, says Thomas Witten, the a professor emeritus of physics. “It offers new avenues for mass assembly of tiny parts for micro-electro-mechanical systems, for example, and to measure small forces within such systems.” The National Science Foundation, Grainger Foundation, and Enrico Fermi Institute funded the work.
Carena M.,Fermi National Accelerator Laboratory |
Carena M.,Enrico Fermi Institute |
Carena M.,University of Chicago |
Ponton E.,Columbia University |
Zurita J.,University of Zürich
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012
We consider the Higgs sector in extensions of the minimal supersymmetric standard model by higher-dimension operators in the superpotential and the Kähler potential, in the context of Higgs searches at the LHC 7 TeV run. Such an effective field theory approach, also referred to as BMSSM, allows for a model-independent description that may correspond to the combined effects of additional supersymmetric sectors, such as heavy singlets, triplets or gauge bosons, in which the supersymmetry-breaking mass splittings can be treated as a perturbation. We consider the current LHC dataset, based on about 1-2fb -1 of data to set exclusion limits on a large class of BMSSM models. We also present projections for integrated luminosities of 5 and 15fb -1, assuming that the ATLAS and CMS collaborations will combine their results in each channel. Our study shows that the majority of the parameter space will be probed at the 2σ level with 15fb -1 of data. A nonobservation of a Higgs boson with about 10fb -1 of data will point towards a Higgs SUSY spectrum with intermediate tanβ (a few to10) and a light SM-like Higgs with somewhat enhanced couplings to bottom and tau pairs. We define a number of BMSSM benchmark scenarios and analyze the possible exclusion/discovery channels and the projected required luminosity to probe them. We also discuss the results of the effective field theory framework for two specific models, one with a singlet superfield and one with SU(2) L triplets. © 2012 American Physical Society.
Carena M.,Fermi National Accelerator Laboratory |
Carena M.,Enrico Fermi Institute |
Draper P.,Enrico Fermi Institute |
Shah N.R.,Fermi National Accelerator Laboratory |
And 3 more authors.
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011
We study renormalization group invariant (RGI) quantities in the minimal supersymmetric standard model and show that they are a powerful and simple instrument for testing high-scale models of supersymmetry (SUSY) breaking. For illustration, we analyze the frameworks of minimal and general gauge-mediated (MGM and GGM) SUSY breaking, with additional arbitrary soft Higgs mass parameters at the messenger scale. We show that if a gaugino and two first generation sfermion soft masses are determined at the LHC, the RGIs lead to MGM sum rules that yield accurate predictions for the other gaugino and first generation soft masses. RGIs can also be used to reconstruct the fundamental MGM parameters (including the messenger scale), calculate the hypercharge D-term, and find relationships among the third generation and Higgs soft masses. We then study the extent to which measurements of the full first generation spectrum at the LHC may distinguish different SUSY-breaking scenarios. In the case of the MGM model, although most deviations violate the sum rules by more than estimated experimental errors, we find a one-parameter family of GGM models that satisfy the constraints and produce the same first generation spectrum. The GGM-MGM degeneracy is lifted by differences in the third generation masses and the messenger scales. © 2011 American Physical Society.
News Article | November 14, 2016
A team of four theoretical physicists, Francesco Sannino from Cp3-Origins at the University of Southern Denmark, Alessandro Strumia from CERN theory division and Pisa Univ., Andrea Tesi from the Enrico Fermi Institute at the University of Chicago in US, and Elena Vigiani from Pisa University have recently published in the Journal of High Energy Physics their work "Fundamental partial compositeness, JHEP11(2016)029 ". They demonstrated that it is possible to construct fundamental theories in which the Higgs is composite and that are able to provide mass to all known particles. Differently from the standard model Higgs scenario, in which no new physics is predicted till the Planck scale, these theories predict hundreds of new composite particles to be discovered at the Large Hadron Collider at CERN or at future colliders. The new fundamental dynamics encompasses the Composite Higgs paradigm pioneered by D.B. Kaplan and H. Georgi, Phys. Lett. B136, 183 (1984), Nucl. Physics B365 (1991), 259-278.
Dauphas N.,Enrico Fermi Institute |
Chaussidon M.,University of Lorraine
Annual Review of Earth and Planetary Sciences | Year: 2011
Meteorites, which are remnants of solar system formation, provide a direct glimpse into the dynamics and evolution of a young stellar object (YSO), namely our Sun. Much of our knowledge about the astrophysical context of the birth of the Sun, the chronology of planetary growth from micrometer-sized dust to terrestrial planets, and the activity of the young Sun comes from the study of extinct radionuclides such as 26Al (t1/2=0.717 Myr). Here we review how the signatures of extinct radionuclides (short-lived isotopes that were present when the solar system formed and that have now decayed below detection level) in planetary materials influence the current paradigm of solar system formation. Particular attention is given to tying meteorite measurements to remote astronomical observations of YSOs and modeling efforts. Some extinct radionuclides were inherited from the long-term chemical evolution of the Galaxy, others were injected into the solar system by a nearby supernova, and some were produced by particle irradiation from the T-Tauri Sun. The chronology inferred from extinct radionuclides reveals that dust agglomeration to form centimeter-sized particles in the inner part of the disk was very rapid (<50 kyr), planetesimal formation started early and spanned several million years, planetary embryos (possibly like Mars) were formed in a few million years, and terrestrial planets (like Earth) completed their growths several tens of million years after the birth of the Sun. Copyright © 2011 by Annual Reviews. All rights reserved.
Ritchey A.M.,University of Washington |
Welty D.E.,University of Chicago |
Dahlstrom J.A.,Carthage College |
York D.G.,University of Chicago |
York D.G.,Enrico Fermi Institute
Astrophysical Journal | Year: 2015
We present a comprehensive analysis of interstellar absorption lines seen in moderately high resolution, high signal-to-noise ratio optical spectra of SN 2014J in M82. Our observations were acquired over the course of six nights, covering the period from 6 days before to 30 days after the supernova reached its maximum B-band brightness. We examine complex absorption from Na I, Ca II, K I, Ca I, CH+, CH, and CN, arising primarily from diffuse gas in the interstellar medium (ISM) of M82. We detect Li I absorption over a range in velocity consistent with that exhibited by the strongest Na I and K I components associated with M82; this is the first detection of interstellar Li in a galaxy outside of the Local Group. There are no significant temporal variations in the absorption-line profiles over the 37 days sampled by our observations. The relative abundances of the various interstellar species detected reveal that the ISM of M82 probed by SN 2014J consists of a mixture of diffuse atomic and molecular clouds characterized by a wide range of physical/environmental conditions. Decreasing N(Na I)/N(Ca II) ratios and increasing N(Ca I)/N(K I) ratios with increasing velocity are indicative of reduced depletion in the higher-velocity material. Significant component-to-component scatter in the N(Na I)/N(Ca II) and N(Ca I)/N(Ca II) ratios may be due to variations in the local ionization conditions. An apparent anti-correlation between the N(CH+)/N(CH) and N(Ca I)/N(Ca II) ratios can be understood in terms of an opposite dependence on gas density and radiation field strength, while the overall high CH+ abundance may be indicative of enhanced turbulence in the ISM of M82. The Li abundance also seems to be enhanced in M82, which supports the conclusions of recent gamma-ray emission studies that the cosmic-ray acceleration processes are greatly enhanced in this starburst galaxy. © 2015. The American Astronomical Society. All rights reserved..
Becker M.R.,University of Chicago |
Kravtsov A.V.,University of Chicago |
Kravtsov A.V.,Enrico Fermi Institute
Astrophysical Journal | Year: 2011
We study the bias and scatter in mass measurements of galaxy clusters resulting from fitting a spherically symmetric Navarro, Frenk, & White model to the reduced tangential shear profile measured in weak-lensing (WL) observations. The reduced shear profiles are generated for 104 cluster-sized halos formed in a ΛCDM cosmological N-body simulation of a 1h -1 Gpc box. In agreement with previous studies, we find that the scatter in the WL masses derived using this fitting method has irreducible contributions from the triaxial shapes of cluster-sized halos and uncorrelated large-scale matter projections along the line of sight. Additionally, we find that correlated large-scale structure within several virial radii of clusters contributes a smaller, but nevertheless significant, amount to the scatter. The intrinsic scatter due to these physical sources is 20% for massive clusters and can be as high as 30% for group-sized systems. For current, ground-based observations, however, the total scatter should be dominated by shape noise from the background galaxies used to measure the shear. Importantly, we find that WL mass measurements can have a small, 5%-10%, but non-negligible amount of bias. Given that WL measurements of cluster masses are a powerful way to calibrate cluster mass-observable relations for precision cosmological constraints, we strongly emphasize that a robust calibration of the bias requires detailed simulations that include more observational effects than we consider here. Such a calibration exercise needs to be carried out for each specific WL mass estimation method, as the details of the method determine in part the expected scatter and bias. We present an iterative method for estimating mass M 500c that can eliminate the bias for analyses of ground-based data. © 2011. The American Astronomical Society. All rights reserved.
Grossman L.,University of Chicago |
Grossman L.,Enrico Fermi Institute |
Fedkin A.V.,University of Chicago |
Simon S.B.,University of Chicago
Meteoritics and Planetary Science | Year: 2012
For fayalite formation times of several thousand years, and systems enriched in water by a factor of ten relative to solar composition, 1μm radius olivine grains could reach 2 mole% fayalite and 0.1μm grains 5 mole% by nebular condensation, well short of the values appropriate for precursors of most chondrules and the values found in the matrices of unequilibrated ordinary chondrites. Even 10μm olivine crystals could reach 30 mole% fayalite above 1100K in solar gas if condensation of metallic nickel-iron were delayed sufficiently by supersaturation. Consideration of the surface tensions of several phases with equilibrium condensation temperatures above that of metallic iron shows that, even if they were supersaturated, they would still nucleate homogeneously above the equilibrium condensation temperature of metallic iron. This phenomenon would have provided nuclei for heterogeneous nucleation of metallic nickel-iron, thus preventing the latter from supersaturating significantly and preventing olivine from becoming fayalitic. Unless a way is found to make nebular regions far more oxidizing than in existing models, it is unlikely that chondrule precursors or the matrix olivine grains of unequilibrated ordinary chondrites obtained their fayalite contents by condensation processes. Perhaps stabilization of FeO occurred after condensation of water ice and accretion of icy planetesimals, during heating of the planetesimals and/or in hot, dense, water-rich vapor plumes generated by impacts on them. This would imply that FeO is a relatively young feature of nebular materials. © 2012 The Meteoritical Society.
Lundgren B.F.,Yale University |
Wake D.A.,Yale University |
Padmanabhan N.,Yale University |
Coil A.,University of California at San Diego |
And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011
Strong foreground absorption features from singly ionized magnesium (Mgii) are commonly observed in the spectra of quasars and are presumed to probe a wide range of galactic environments. To date, measurements of the average dark matter (DM) halo masses of intervening Mgii absorbers by way of large-scale cross-correlations with luminous galaxies have been limited to z < 0.7. In this work, we cross-correlate 21 strong (Wλ2796 r≳ 0.6Å) Mgii absorption systems detected in quasar spectra from the Sloan Digital Sky Survey Seventh Data Release with ∼32000 spectroscopically confirmed galaxies at 0.7 ≤z≤ 1.45 from the DEEP2 galaxy redshift survey. We measure DM halo biases of bG= 1.44 ± 0.02 and bA= 1.49 ± 0.45 for the DEEP2 galaxies and Mgii absorbers respectively, indicating that their clustering amplitudes are roughly consistent. Haloes with the bias we measure for the Mgii absorbers have a corresponding mass of 1.8 ±4.2 1.6× 1012h-1M⊙, although the actual mean absorber halo mass will depend on the precise distribution of absorbers within DM haloes. This mass estimate is consistent with observations at z= 0.6, suggesting that the halo masses of typical Mgii absorbers do not significantly evolve from z∼1. We additionally measure the average Wλ2796 r≥ 0.6Å gas covering fraction to be fc= 0.5 within 60h-1kpc around the DEEP2 galaxies, and we find an absence of coincident strong Mgii absorption beyond a projected separation of ∼40h-1kpc. Although the star-forming z > 1 DEEP2 galaxies are known to exhibit ubiquitous blueshifted Mgii absorption, we find no direct evidence in our small sample linking Wλ2796 r≥ 0.6Å absorbers to galaxies with ongoing star formation. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.
Pourmand A.,Enrico Fermi Institute |
Dauphas N.,Enrico Fermi Institute
Talanta | Year: 2010
Batch equilibration experiments are conducted to measure the distribution coefficients (Kd) of a large number of elements in nitric, nitric plus hydrofluoric, and hydrochloric acids on Eichrom TODGA extraction chromatography resin. The Kds are used to devise a multi-element extraction scheme for high-precision elemental and isotopic analyses of Ca, Hf, Lu, Th and U in geological materials, using high-purity lithium metaborate (LiBO2) flux fusion that allows rapid digestion of even the most refractory materials. The fusion melt, dissolved in nitric acid, is directly loaded to a TODGA cartridge on a vacuum chamber for elemental separation. An Ln-Spec cartridge is used in tandem with TODGA for Lu purification. The entire procedure, from flux digestion to preparation for isotopic analysis, can be completed in a day. The accuracy of the proposed technique is tested by measuring the concentrations of Ca (standard bracketing), Hf, Lu, Th and U (isotope dilution), and the isotopic composition of Hf in geostandards (USNM3529, BCR-2, BHVO-1, AGV-1 and AGV-2). All measurements are in excellent agreement with recommended literature values, demonstrating the effectiveness of the proposed analytical procedure and the versatility of TODGA resin. © 2010 Elsevier B.V. All rights reserved.