Harvard University Department of Physics

Harvard University Department of Physics

Faculty Publications added in April, 2008

Query Results from the Smithsonian/NASA Astrophysics Data System (ADS)
The following are Harvard Physics faculty members' publications, added to the ADS database last month. Please note that some publications which apeared in print last month may not be included in the database (and therefore may not appear on this list) until the following month.


 
Title:
Dynamics of One-Dimensional Bose Liquids: Andreev-Like Reflection at Y Junctions and the Absence of the Aharonov-Bohm Effect
Authors:
Tokuno, Akiyuki; Oshikawa, Masaki; Demler, Eugene
Publication:
Physical Review Letters, vol. 100, Issue 14, id. 140402 (PhRvL Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.140402
Bibliographic Code:
2008PhRvL.100n0402T

Abstract

We study one-dimensional Bose liquids of interacting ultracold atoms in the Y-shaped potential when each branch is filled with atoms. We find that the excitation packet incident on a single Y junction should experience a negative density reflection analogous to the Andreev reflection at normal-superconductor interfaces, although the present system does not contain fermions. In a ring-interferometer-type configuration, we find that the transport is completely insensitive to the (effective) flux contained in the ring, in contrast with the Aharonov-Bohm effect of a single particle in the same geometry.


 
Title:
Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in Two-Component Atomic Gases
Authors:
Widera, Artur; Trotzky, Stefan; Cheinet, Patrick; Fölling, Simon; Gerbier, Fabrice; Bloch, Immanuel; Gritsev, Vladimir; Lukin, Mikhail D.; Demler, Eugene
Publication:
Physical Review Letters, vol. 100, Issue 14, id. 140401 (PhRvL Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.140401
Bibliographic Code:
2008PhRvL.100n0401W

Abstract

We report on the observation of many-body spin dynamics of interacting, one-dimensional (1D) ultracold bosonic gases with two spin states. By controlling the nonlinear atomic interactions close to a Feshbach resonance we are able to induce a phase diffusive many-body spin dynamics of the relative phase between the two components. We monitor this dynamical evolution by Ramsey interferometry, supplemented by a novel, many-body echo technique, which unveils the role of quantum fluctuations in 1D. We find that the time evolution of the system is well described by a Luttinger liquid initially prepared in a multimode squeezed state. Our approach allows us to probe the nonequilibrium evolution of one-dimensional many-body quantum systems.



Title:
Search for CPT and Lorentz Violation in B0-&Bmacr;0 Oscillations with Dilepton Events
Authors:
Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J. P.; Poireau, V.;... Morii, M.;...; and 557 coauthors.
Publication:
Physical Review Letters, vol. 100, Issue 13, id. 131802 (PhRvL Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.131802
Bibliographic Code:
2008PhRvL.100m1802A

Abstract

We report the observation of the b→d penguin-dominated decay B0→K*0*0 with a sample of 383.2±4.2 million BB¯ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at the Stanford Linear Accelerator Center. The measured branching fraction is B(B0→K*0*0)=[1.28-0.30+0.35±0.11]×10-6 and the fraction of longitudinal polarization is fL(B0→K*0*0)=0.80-0.12+0.10±0.06. The first error quoted is statistical and the second systematic. We also obtain an upper limit at the 90% confidence level on the branching fraction for B(B0→K*0K*0)<0.41×10-6.


 
Title:
Coherence of an Optically Illuminated Single Nuclear Spin Qubit
Authors:
Jiang, L.; Dutt, M. V. Gurudev; Togan, E.; Childress, L.; Cappellaro, P.; Taylor, J. M.; Lukin, M. D.
blication:
Physical Review Letters, vol. 100, Issue 7, id. 073001 (PhRvL Homepage)
Publication Date:
02/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.073001
Bibliographic Code:
2008PhRvL.100g3001J

Abstract

We report results of a search for CPT and Lorentz violation in B0-&Bmacr;0 oscillations using inclusive dilepton events from 232×106 Υ(4S)→B&Bmacr; decays recorded by the BABAR detector at the PEP-II B Factory at SLAC. We find 2.8σ significance, compatible with no signal, for variations in the complex CPT violation parameter z at the Earth’s sidereal frequency and extract values for the quantities Δaμ in the general Lorentz-violating standard-model extension. The spectral powers for variations in z over the frequency range 0.26yr-1 to 2.1solarday-1 are also compatible with no signal.




Title:
Study of muon neutrino disappearance using the Fermilab Main Injector neutrino beam
Authors:
Adamson, P.; Andreopoulos, C.; Arms, K. E.; Armstrong, R.; Auty, D. J.; Avvakumov, S.; ... Feldman, G. J.;... and 191 coauthors.
Publication:
Physical Review D, vol. 77, Issue 7, id. 072002 (PhRvD Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevD.77.072002
Bibliographic Code:
2008PhRvD..77g2002A

Abstract

We report the results of a search for νμ disappearance by the Main Injector Neutrino Oscillation Search [D. G. Michael (MINOS), Phys. Rev. Lett. 97, 191801 (2006).PRLTAO0031-900710.1103/PhysRevLett.97.191801]. The experiment uses two detectors separated by 734 km to observe a beam of neutrinos created by the Neutrinos at the Main Injector facility at Fermi National Accelerator Laboratory. The data were collected in the first 282 days of beam operations and correspond to an exposure of 1.27×1020 protons on target. Based on measurements in the Near Detector, in the absence of neutrino oscillations we expected 336±14 νμ charged-current interactions at the Far Detector but observed 215. This deficit of events corresponds to a significance of 5.2 standard deviations. The deficit is energy dependent and is consistent with two-flavor neutrino oscillations according to |Δm2|=2.74-0.26+0.44×10-3eV2/c4 and sin⁡22θ>0.87 at 68% confidence level.



Title:
Photon storage in Λ -type optically dense atomic media. IV. Optimal control using gradient ascent
Authors:
Gorshkov, Alexey V.; Calarco, Tommaso; Lukin, Mikhail D.; Sørensen, Anders S.
Publication:
Physical Review A, vol. 77, Issue 4, id. 043806 (PhRvA Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevA.77.043806
Bibliographic Code:
2008PhRvA..77d3806G

Abstract

We use the numerical gradient ascent method from optimal control theory to extend efficient photon storage in Λ -type media to previously inaccessible regimes and to provide simple intuitive explanations for our optimization techniques. In particular, by using gradient ascent to shape classical control pulses used to mediate photon storage, we open up the possibility of high efficiency photon storage in the nonadiabatic limit, in which analytical solutions to the equations of motion do not exist. This control shaping technique enables an order-of-magnitude increase in the bandwidth of the memory. We also demonstrate that the often discussed connection between time reversal and optimality in photon storage follows naturally from gradient ascent. Finally, we discuss the optimization of controlled reversible inhomogeneous broadening.



Title:
Investigating interaction-induced chaos using time-dependent density-functional theory
Authors:
Wasserman, Adam; Maitra, Neepa T.; Heller, Eric J.
Publication:
Physical Review A, vol. 77, Issue 4, id. 042503 (PhRvA Homepage)
Publication Date:
04/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevA.77.042503
Bibliographic Code:
2008PhRvA..77d2503W

Abstract

Systems whose underlying classical dynamics are chaotic exhibit signatures of the chaos in their quantum mechanics. We investigate the possibility of using the linear response formalism of time-dependent density functional theory (TDDFT) to study the case when chaos is induced by electron-interaction alone. Nearest-neighbor level-spacing statistics are in principle exactly and directly accessible from TDDFT. We discuss how the TDDFT linear response procedure can reveal information about the mechanism of chaos induced by electron-interaction alone. A simple model of a two-electron quantum dot highlights the necessity to go beyond the adiabatic approximation in TDDFT.



Title:
A laser frequency comb that enables radial velocity measurements with a precision of 1cms-1
Authors:
Li, Chih-Hao; Benedick, Andrew J.; Fendel, Peter; Glenday, Alexander G.; Kärtner, Franz X.; Phillips, David F.; Sasselov, Dimitar; Szentgyorgyi, Andrew; Walsworth, Ronald L.
Publication:
Nature, Volume 452, Issue 7187, pp. 610-612 (2008). (Nature Homepage)
Publication Date:
04/2008
Origin:
NATURE
Abstract Copyright:
(c) 2008: Nature
DOI:
10.1038/nature06854
Bibliographic Code:
2008Natur.452..610L

Abstract

Searches for extrasolar planets using the periodic Doppler shift of stellar spectral lines have recently achieved a precision of 60cms-1 (ref. 1), which is sufficient to find a 5-Earth-mass planet in a Mercury-like orbit around a Sun-like star. To find a 1-Earth-mass planet in an Earth-like orbit, a precision of ~5cms-1 is necessary. The combination of a laser frequency comb with a Fabry-Pérot filtering cavity has been suggested as a promising approach to achieve such Doppler shift resolution via improved spectrograph wavelength calibration, with recent encouraging results. Here we report the fabrication of such a filtered laser comb with up to 40-GHz (~1-Å) line spacing, generated from a 1-GHz repetition-rate source, without compromising long-term stability, reproducibility or spectral resolution. This wide-line-spacing comb, or `astro-comb', is well matched to the resolving power of high-resolution astrophysical spectrographs. The astro-comb should allow a precision as high as 1cms-1 in astronomical radial velocity measurements.



Title:
Quantum foam and topological strings
Authors:
Iqbal, Amer; Vafa, Cumrun; Nekrasov, Nikita; Okounkov, Andrei
Publication:
Journal of High Energy Physics, Issue 04, pp. 011 (2008).
Publication Date:
04/2008
Origin:
IOP
DOI:
10.1088/1126-6708/2008/04/011
Bibliographic Code:
2008JHEP...04..011I

Abstract

We find an interpretation of the recent connection found between topological strings on Calabi-Yau threefolds and crystal melting: Summing over statistical mechanical configuration of melting crystal is equivalent to a quantum gravitational path integral involving fluctuations of Kähler geometry and topology. We show how the limit shape of the melting crystal emerges as the average geometry and topology of the quantum foam at the string scale. The geometry is classical at large length scales, modified to a smooth limit shape dictated by mirror geometry at string scale and is a quantum foam at area scales ~ gsα'.



Title:
Time Dilation in Type Ia Supernova Spectra at High Redshift
Authors:
Blondin, S.; Davis, T. M.; Krisciunas, K.; Schmidt, B. P.; Sollerman, J.; Wood-Vasey, W. M.;... Stubbs, C. W.; ... and 25 coauthors.
Publication:
eprint arXiv:0804.3595
Publication Date:
04/2008
Origin:
ARXIV
Keywords:
Astrophysics
Comment:
14 pages (emulateapj), 10 figures; accepted for publication in ApJ. Version with full-resolution figures available at http://www.cfa.harvard.edu/~sblondin/publications/timedilation/
Bibliographic Code:
2008arXiv0804.3595B

Abstract

We present multiepoch spectra of 13 high-redshift Type Ia supernovae (SNe Ia) drawn from the literature, the ESSENCE and SNLS projects, and our own separate dedicated program on the ESO Very Large Telescope. We use the Supernova Identification (SNID) code of Blondin & Tonry to determine the spectral ages in the supernova rest frame. Comparison with the observed elapsed time yields an apparent aging rate consistent with the 1/(1+z) factor (where z is the redshift) expected in a homogeneous, isotropic, expanding universe. These measurements thus confirm the expansion hypothesis, while unambiguously excluding models that predict no time dilation, such as Zwicky's "tired light" hypothesis. We also test for power-law dependencies of the aging rate on redshift. The best-fit exponent for these models is consistent with the expected 1/(1+z) factor.



Title:
Extended Supersymmetric Moduli Space and a SUSY/Non-SUSY Duality
Authors:
Aganagic, Mina; Beem, Christopher; Seo, Jihye; Vafa, Cumrun
Publication:
eprint arXiv:0804.2489
Publication Date:
04/2008
Origin:
ARXIV
Keywords:
High Energy Physics - Theory
Comment:
50 pages, 5 figures, harvmac; v2: references added, minor corrections
Bibliographic Code:
2008arXiv0804.2489A

Abstract

We study N=1 supersymmetric U(N) gauge theories coupled to an adjoint chiral field with superpotential. We consider the full supersymmetric moduli space of these theories obtained by adding all allowed chiral operators. These include higher-dimensional operators that introduce a field-dependence for the gauge coupling. We show how Feynman diagram/matrix model/string theoretic techniques can all be used to compute the IR glueball superpotential. Moreover, in the limit of turning off the superpotential, this leads to a deformation of N=2 Seiberg-Witten theory. In the case where the superpotential drives the squared gauge coupling to a negative value, we find that supersymmetry is spontaneously broken, which can be viewed as a novel mechanism for breaking supersymmetry. We propose a new duality between a class of N=1 supersymmetric U(N) gauge theories with field-dependent gauge couplings and a class of U(N) gauge theories where supersymmetry is softly broken by nonzero expectation values for auxiliary components of spurion superfields.



Title:
Optical bistability at low light level due to collective atomic recoil
Authors:
Vengalattore, M.; Hafezi, M.; Lukin, M. D.; Prentiss, M.
Publication:
eprint arXiv:0804.2306
Publication Date:
04/2008
Origin:
ARXIV
Keywords:
Quantum Physics
Bibliographic Code:
2008arXiv0804.2306V

Abstract

We demonstrate optical nonlinearities due to the interaction of weak optical fields with the collective motion of a strongly dispersive ultracold gas. The combination of a recoil-induced resonance (RIR) in the high gain regime and optical waveguiding within the dispersive medium enables us to achieve a collective atomic cooperativity of $275 \pm 50$ even in the absence of a cavity. As a result, we observe optical bistability at input powers as low as 20 pW. The present scheme allows for dynamic optical control of the dispersive properties of the ultracold gas using very weak pulses of light. The experimental observations are in good agreement with a theoretical model.



Title:
Magnetic trapping of silver and copper, and anomolous spin relaxation in the Ag-He system
Authors:
Brahms, N.; Newman, B.; Johnson, C.; Greytak, T.; Kleppner, D.; Doyle, J.
Publication:
eprint arXiv:0804.0766
Publication Date:
04/2008
Origin:
ARXIV
Keywords:
Physics - Atomic Physics
Comment:
4 pages, 4 figures
Bibliographic Code:
2008arXiv0804.0766B

Abstract

We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer gas cooling. Up to 3 trillion Cu atoms and 40 trillion Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are > 10^6, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag-3He collision rate displays anomolous behavior, varying as T^(5.8). Lifetimes of laser ablated gold (Au) in 3He buffer gas are too short to permit trapping.



Title:
Collision-Induced Spin Depolarization of Triplet-Sigma Molecules
Authors:
Campbell, Wesley C.; Tscherbul, Timur V.; Lu, Hsin-I; Tsikata, Edem; Krems, Roman V.; Doyle, John M.
Publication:
eprint arXiv:0804.0265
Publication Date:
04/2008
Origin:
ARXIV
Keywords:
Physics - Atomic Physics
Bibliographic Code:
2008arXiv0804.0265C

Abstract

We measure and theoretically determine the Zeeman relaxation rates in collisions of cold triplet-Sigma molecules with helium atoms in a magnetic field. All four stable isotopomers of the imidogen (NH) molecule are magnetically trapped and studied in the presence of both He-3 and He-4. The He-4 data support the predicted inverse square dependence of the collision-induced Zeeman relaxation rate coefficient on the molecular rotational constant B. The He-3 rate coefficients depend less strongly on B and are shown to be significantly affected by a shape resonance. The results demonstrate the influence of molecular structure and scattering shape resonances on collisional energy transfer at low temperatures, providing guidance for future experiments on collisional cooling of molecules.



Title:
Invited Article: Development of high-field superconducting Ioffe magnetic traps
Authors:
Yang, L.; Brome, C. R.; Butterworth, J. S.; Dzhosyuk, S. N.; Mattoni, C. E. H.; McKinsey, D. N.;... Doyle, J. M.; ... and 12 coauthors.
Publication:
Review of Scientific Instruments, Volume 79, Issue 3, pp. 031301-031301-11 (2008). (RScI Homepage)
Publication Date:
03/2008
Origin:
AIP
Keywords:
magnetic field effects, superconducting magnets
Abstract Copyright:
(c) 2008: American Institute of Physics
DOI:
10.1063/1.2897133
Bibliographic Code:
2008RScI...79c1301Y

Abstract

We describe the design, construction, and performance of three generations of superconducting Ioffe magnetic traps. The first two are low current traps, built from four racetrack shaped quadrupole coils and two solenoid assemblies. Coils are wet wound with multifilament NbTi superconducting wires embedded in epoxy matrices. The magnet bore diameters are 51 and 105 mm with identical trap depths of 1.0 T at their operating currents and at 4.2 K. A third trap uses a high current accelerator-type quadrupole magnet and two low current solenoids. This trap has a bore diameter of 140 mm and tested trap depth of 2.8 T. Both low current traps show signs of excessive training. The high current hybrid trap, on the other hand, exhibits good training behavior and is amenable to quench protection.



Title:
Spin Order in Paired Quantum Hall States
Authors:
Dimov, Ivailo; Halperin, Bertrand I.; Nayak, Chetan
Affiliation:
AA(Department of Physics and Astronomy, University of California, Los Angeles, California 90095-1547, USA), AB(Physics Department, Harvard University, Cambridge, Massachusetts 02138, USA), AC(Microsoft Station Q, CNSI Building, University of California, Santa Barbara, California 93106-4030, USA)
Publication:
Physical Review Letters, vol. 100, Issue 12, id. 126804 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.126804
Bibliographic Code:
2008PhRvL.100l6804D

Abstract

We consider quantum Hall states at even-denominator filling fractions, especially ν=5/2, in the limit of small Zeeman energy. Assuming that a paired quantum Hall state forms, we study spin ordering and its interplay with pairing. We give numerical evidence that at ν=5/2 an incompressible ground state will exhibit spontaneous ferromagnetism. The Ginzburg-Landau (GL) theory for the spin degrees of freedom of paired Hall states is a perturbed CP2 model. We compute the coefficients in the GL theory by a BCS Stoner mean-field theory for coexisting order parameters, and show that even if repulsion is smaller than that required for a Stoner instability, ferromagnetic fluctuations can induce a partially or fully polarized superconducting state.



Title:
Measurement of Lifetime and Decay-Width Difference in Bs0→J/ψϕ Decays
Authors:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.;... Franklin, M.; ... Guimaraes da Costa, J....; and 607 coauthors.
Publication:
Physical Review Letters, vol. 100, Issue 12, id. 121803 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.121803
Bibliographic Code:
2008PhRvL.100l1803A

Abstract

We measure the mean lifetime τ=2/(ΓLH) and the decay-width difference ΔΓ=ΓLH of the light and heavy mass eigenstates of the Bs0 meson, BsL0 and BsH0, in Bs0→J/ψϕ decays using 1.7fb-1 of data collected with the CDF II detector at the Fermilab Tevatron p&pmacr; collider. Assuming CP conservation, a good approximation for the Bs0 system in the standard model, we obtain ΔΓ=0.076-0.063+0.059(stat)±0.006(syst)ps-1 and τ=1.52±0.04(stat)±0.02(syst)ps, the most precise measurements to date. Our constraints on the weak phase and ΔΓ are consistent with CP conservation.



Title:
Evidence for D0-&Dmacr;0 Mixing Using the CDF II Detector
Authors:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.;... Franklin, M.; ... Guimaraes da Costa, J....; and 607 coauthors.
Publication:
Physical Review Letters, vol. 100, Issue 12, id. 121802 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.121802
Bibliographic Code:
2008PhRvL.100l1802A

Abstract

We measure the time dependence of the ratio of decay rates for the rare decay D0→K+π- to the Cabibbo-favored decay D0→K-π+. A signal of 12.7×103 D0→K+π- decays was obtained using the Collider Detector at Fermilab II detector at the Fermilab Tevatron with an integrated luminosity of 1.5fb-1. We measure the D0-&Dmacr;0 mixing parameters (RD,y',x'2), and find that the data are inconsistent with the no-mixing hypothesis with a probability equivalent to 3.8 Gaussian standard deviations.



Title:
New Measurement of the Electron Magnetic Moment and the Fine Structure Constant
Authors:
Hanneke, D.; Fogwell, S.; Gabrielse, G.
Publication:
Physical Review Letters, vol. 100, Issue 12, id. 120801 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.120801
Bibliographic Code:
2008PhRvL.100l0801H

Abstract

A measurement using a one-electron quantum cyclotron gives the electron magnetic moment in Bohr magnetons, g/2=1.00115965218073(28) [0.28 ppt], with an uncertainty 2.7 and 15 times smaller than for previous measurements in 2006 and 1987. The electron is used as a magnetometer to allow line shape statistics to accumulate, and its spontaneous emission rate determines the correction for its interaction with a cylindrical trap cavity. The new measurement and QED theory determine the fine structure constant, with α-1=137.035999084(51) [0.37 ppb], and an uncertainty 20 times smaller than for any independent determination of α.



Title:
Nonequilibrium Microtubule Fluctuations in a Model Cytoskeleton
Authors:
Brangwynne, Clifford P.; Koenderink, Gijsje H.; Mackintosh, Frederick C.; Weitz, David A.
Publication:
Physical Review Letters, vol. 100, Issue 11, id. 118104 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.118104
Bibliographic Code:
2008PhRvL.100k8104B

Abstract

Biological activity gives rise to nonequilibrium fluctuations in the cytoplasm of cells; however, there are few methods to directly measure these fluctuations. Using a reconstituted actin cytoskeleton, we show that the bending dynamics of embedded microtubules can be used to probe local stress fluctuations. We add myosin motors that drive the network out of equilibrium, resulting in an increased amplitude and modified time dependence of microtubule bending fluctuations. We show that this behavior results from steplike forces on the order of 10 pN driven by collective motor dynamics.



Title:
Electron Emission in Superfluid and Low Temperature Vapor Phase Helium
Authors:
Silvera, Isaac F.; Tempere, Jacques
Publication:
Physical Review Letters, vol. 100, Issue 11, id. 117602 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.117602
Bibliographic Code:
2008PhRvL.100k7602S

Abstract

Tungsten filaments used as sources of electrons in a low-temperature liquid or gaseous helium environment have remarkable properties of operating at thousands of degrees kelvin in surroundings at temperatures of order 1 K. We provide an explanation of this performance in terms of important changes in the thermal transport mechanisms. The behavior can be cast as a first-order phase transition.



Title:
Antihydrogen Production within a Penning-Ioffe Trap
Authors:
Gabrielse, G.; Larochelle, P.; Le Sage, D.; Levitt, B.; Kolthammer, W. S.; McConnell, R.; ... and 14 coauthors.
Publication:
Physical Review Letters, vol. 100, Issue 11, id. 113001 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.113001
Bibliographic Code:
2008PhRvL.100k3001G

Abstract

Slow antihydrogen (&Hmacr;) is produced within a Penning trap that is located within a quadrupole Ioffe trap, the latter intended to ultimately confine extremely cold, ground-state &Hmacr; atoms. Observed &Hmacr; atoms in this configuration resolve a debate about whether positrons and antiprotons can be brought together to form atoms within the divergent magnetic fields of a quadrupole Ioffe trap. The number of detected &Hmacr; atoms actually increases when a 400 mK Ioffe trap is turned on.



Title:
Search for Bs0→μ+μ- and B0→μ+μ- Decays with 2fb-1 of p&pmacr; Collisions
Authors:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.;... Franklin, M.; ... Guimaraes da Costa, J....; and 611 coauthors.
Publication:
Physical Review Letters, vol. 100, Issue 10, id. 101802 (PhRvL Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevLett.100.101802
Bibliographic Code:
2008PhRvL.100j1802A

Abstract

We have performed a search for Bs0→μ+μ- and B0→μ+μ- decays in p&pmacr; collisions at s=1.96TeV using 2fb-1 of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron Collider. The observed number of Bs0 and B0 candidates is consistent with background expectations. The resulting upper limits on the branching fractions are B(Bs0→μ+μ-)<5.8×10-8 and B(B0→μ+μ-)<1.8×10-8 at 95% C.L.



Title:
Wetting of liquid-crystal surfaces and induced smectic layering at a nematic-liquid interface: An x-ray reflectivity study
Authors:
Fukuto, Masafumi; Gang, Oleg; Alvine, Kyle J.; Ocko, Benjamin M.; Pershan, Peter S.
Publication:
Physical Review E, vol. 77, Issue 3, id. 031607 (PhRvE Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevE.77.031607
Bibliographic Code:
2008PhRvE..77c1607F

Abstract

We report the results of a synchrotron x-ray reflectivity study of bulk liquid-crystal surfaces that are coated by thin wetting films of an immiscible liquid. The liquid-crystal subphase consisted of the nematic or isotropic phase of 4-octyl- 4' -cyanobiphenyl (8CB), and the wetting film was formed by the fluorocarbon perfluoromethylcyclohexane (PFMC), a volatile liquid. The thickness of the wetting film was controlled by the temperature difference ΔTμ between the sample and a reservoir of bulk PFMC, contained within the sealed sample cell. Phase information on the interfacial electron density profiles has been extracted from the interference between the scattering from the PFMC-vapor interface and the surface-induced smectic order of the 8CB subphase. The liquid-crystal side of the nematic-liquid (8CB-PFMC) interface is characterized by a density oscillation whose period corresponds to the smectic layer spacing and whose amplitude decays exponentially toward the underlying nematic subphase. The decay length ξ of the smectic amplitude is independent of the PFMC film thickness but increases as the nematic–smectic- A transition temperature TNA is approached, in agreement with the longitudinal correlation length ξ∥∝(T‑TNA)‑0.7 for the smectic fluctuations in the bulk nematic. The results indicate that the homeotropic orientation of the 8CB molecules is preferred at the 8CB-PFMC interface and that the observed temperature dependence of the smectic layer growth is consistent with the critical adsorption mechanism. The observed ΔTμ dependence of the PFMC film thickness, L∝(ΔTμ)‑1/3 , implies that PFMC completely wets the 8CB surface and is dominated by the nonretarded dispersion interactions between hydro- and fluorocarbons. The complete wetting behavior of PFMC is nearly independent of the degree of interfacial smectic order in the subphase.



Title:
Observation of exclusive dijet production at the Fermilab Tevatron &pmacr;p collider
Authors:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.;... Franklin, M.; ... Guimaraes da Costa, J....; and 611 coauthors.
Publication:
Physical Review D, vol. 77, Issue 5, id. 052004 (PhRvD Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevD.77.052004
Bibliographic Code:
2008PhRvD..77e2004A

Abstract

We present the first observation and cross section measurement of exclusive dijet production in &pmacr;p interactions, &pmacr;p→&pmacr;+dijet+p. Using a data sample of 310pb-1 collected by the Run II Collider Detector at Fermilab at s=1.96TeV, exclusive cross sections for events with two jets of transverse energy ETjet≥10GeV have been measured as a function of minimum ETjet. The exclusive signal is extracted from fits to data distributions based on Monte Carlo simulations of expected dijet signal and background shapes. The simulated background distribution shapes are checked in a study of a largely independent data sample of 200pb-1 of b-tagged jet events, where exclusive dijet production is expected to be suppressed by the Jz=0 total angular momentum selection rule. Results obtained are compared with theoretical expectations, and implications for exclusive Higgs boson production at the pp Large Hadron Collider at s=14TeV are discussed.



Title:
Measurement of the B→Xsγ branching fraction and photon energy spectrum using the recoil method
Authors:
Aubert, B.; Bona, M.; Boutigny, D.; Karyotakis, Y.; Lees, J. P.; Poireau, V.;... Morii, M.;...; and 551 coauthors.
Publication:
Physical Review D, vol. 77, Issue 5, id. 051103 (PhRvD Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevD.77.051103
Bibliographic Code:
2008PhRvD..77e1103A

Abstract

We present a measurement of the branching fraction and photon-energy spectrum for the decay B→Xsγ using data from the BABAR experiment. The data sample corresponds to an integrated luminosity of 210fb-1, from which approximately 680 000 B&Bmacr; events are tagged by a fully reconstructed hadronic decay of one of the B mesons. In the decay of the second B meson, an isolated high-energy photon is identified. We measure B(B→Xsγ)=(3.66±0.85stat±0.60syst)×10-4 for photon energies Eγ above 1.9 GeV in the B rest frame. From the measured spectrum we calculate the first and second moments for different minimum photon energies, which are used to extract the heavy-quark parameters mb and μπ2. In addition, measurements of the direct CP asymmetry and isospin asymmetry are presented.




Title:
Limits on the production of narrow t&tmacr; resonances in p&pmacr; collisions at s=1.96TeV
Authors:
Aaltonen, T.; Adelman, J.; Akimoto, T.; Albrow, M. G.; Álvarez González, B.; Amerio, S.;... Franklin, M.; ... Guimaraes da Costa, J....; and 612coauthors.
Publication:
Physical Review D, vol. 77, Issue 5, id. 051102 (PhRvD Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevD.77.051102
Bibliographic Code:
2008PhRvD..77e1102A

Abstract

We search for evidence of resonant top quark pair production in 955 pb-1 of p&pmacr; collisions at s=1.96TeV recorded with the CDF II detector at the Fermilab Tevatron. For fully reconstructed candidate t&tmacr; events triggered on leptons with large transverse momentum and containing at least one identified b-quark jet, we compare the invariant mass spectrum of t&tmacr; pairs to the expected superposition of standard model t&tmacr;, non-t&tmacr; backgrounds, and a simple resonance model based on a sequential Z' boson. We establish upper limits for σ(p&pmacr;→Z')·Br(Z'→t&tmacr;) in the Z' mass interval from 450GeV/c2 to 900GeV/c2. A topcolor leptophobic Z' is ruled out below 720GeV/c2, and the cross section of any narrow Z'-like state decaying to t&tmacr; is found to be less than 0.64 pb at 95% C.L. for MZ' above 700GeV/c2.



Title:
Kondo screening cloud and charge staircase in one-dimensional mesoscopic devices
Authors:
Pereira, Rodrigo G.; Laflorencie, Nicolas; Affleck, Ian; Halperin, Bertrand I.
Publication:
Physical Review B, vol. 77, Issue 12, id. 125327 (PhRvB Homepage)
Publication Date:
03/2008
Origin:
APS
Abstract Copyright:
(c) 2008: The American Physical Society
DOI:
10.1103/PhysRevB.77.125327
Bibliographic Code:
2008PhRvB..77l5327P

Abstract

We propose that the finite size of the Kondo screening cloud, ξK , can be probed by measuring the charge quantization in a one-dimensional system coupled to a small quantum dot. When the chemical potential μ in the system is varied at zero temperature, one should observe charge steps whose locations are at values of μ that are controlled by the Kondo effect when the system size L is comparable to ξK . We show that, if the standard Kondo model is used, the ratio between the widths of the Coulomb blockade valleys with odd or even number of electrons is a universal scaling function of ξK/L . If we take into account electron-electron interactions in a single-channel wire, this ratio also depends on the parameters of the effective Luttinger model; in addition, the scaling is weakly violated by a marginal bulk interaction. For the geometry of a quantum dot embedded in a ring, we show that the dependence of the charge steps on a magnetic flux through the ring is controlled by the size of the Kondo screening cloud.



Title: