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.
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 B
0→K
*0K¯
*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(B
0→K
*0K¯
*0)=[1.28
-0.30+0.35±0.11]×10
-6 and
the fraction of longitudinal polarization is f
L(B
0→K
*0K¯
*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(B
0→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 B
0-&Bmacr;
0 oscillations using
inclusive dilepton events from 232×10
6 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 Δa
μ 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 ν
μ 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 1.27×10
20 protons on target. Based on measurements
in the Near Detector, in the absence of neutrino oscillations
we expected 336±14 ν
μ 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 |Δm
2|=2.74
-0.26+0.44×10
-3eV
2/c
4 and
sin
22θ>0.87 at 68% confidence level.
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.
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.
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.
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/(Γ
L+Γ
H)
and the decay-width difference ΔΓ=Γ
L-Γ
H of
the light and heavy mass eigenstates of the B
s0 meson,
B
sL0 and B
sH0,
in B
s0→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 B
s0 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 D
0→K
+π
- to
the Cabibbo-favored decay D
0→K
-π
+.
A signal of 12.7×10
3 D
0→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 D
0-&Dmacr;
0 mixing
parameters (R
D,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.
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.
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.
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.
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 B
s0→μ
+μ
- and
B
0→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 B
s0 and
B
0 candidates is consistent with background
expectations. The resulting upper limits on the branching
fractions are B(B
s0→μ
+μ
-)<5.8×10
-8 and
B(B
0→μ
+μ
-)<1.8×10
-8 at
95% C.L.
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 E
Tjet≥10GeV have
been measured as a function of minimum E
Tjet.
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 J
z=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→X
sγ
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→X
sγ)=(3.66±0.85
stat±0.60
syst)×10
-4 for
photon energies E
γ 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
m
b and μ
π2. 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/c
2 to
900GeV/c
2. A topcolor leptophobic Z
' is
ruled out below 720GeV/c
2, 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 M
Z' above
700GeV/c
2.
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.
