18,303,408 research outputs found
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
Mixtures of fermionic atoms in an optical lattice
A mixture of light and heavy spin-polarized fermionic atoms in an optical
lattice is considered. Tunneling of the heavy atoms is neglected such that they
are only subject to thermal fluctuations. This results in a complex interplay
between light and heavy atoms caused by quantum tunneling of the light atoms.
The distribution of the heavy atoms is studied. It can be described by an
Ising-like distribution with a first-order transition from homogeneous to
staggered order. The latter is caused by an effective nonlocal interaction due
to quantum tunneling of the light atoms. A second-order transition is also
possible between an ordered and a disordered phase of the heavy atoms
Measurement of the multi-TeV neutrino cross section with IceCube using Earth absorption
Neutrinos interact only very weakly, so they are extremely penetrating.
However, the theoretical neutrino-nucleon interaction cross section rises with
energy such that, at energies above 40 TeV, neutrinos are expected to be
absorbed as they pass through the Earth. Experimentally, the cross section has
been measured only at the relatively low energies (below 400 GeV) available at
neutrino beams from accelerators \cite{Agashe:2014kda, Formaggio:2013kya}. Here
we report the first measurement of neutrino absorption in the Earth, using a
sample of 10,784 energetic upward-going neutrino-induced muons observed with
the IceCube Neutrino Observatory. The flux of high-energy neutrinos transiting
long paths through the Earth is attenuated compared to a reference sample that
follows shorter trajectories through the Earth. Using a fit to the
two-dimensional distribution of muon energy and zenith angle, we determine the
cross section for neutrino energies between 6.3 TeV and 980 TeV, more than an
order of magnitude higher in energy than previous measurements. The measured
cross section is (stat.) (syst.)
times the prediction of the Standard Model \cite{CooperSarkar:2011pa},
consistent with the expectation for charged and neutral current interactions.
We do not observe a dramatic increase in the cross section, expected in some
speculative models, including those invoking new compact dimensions
\cite{AlvarezMuniz:2002ga} or the production of leptoquarks
\cite{Romero:2009vu}.Comment: Preprint version of Nature paper 10.1038/nature2445
Clonal mixing in the soldier-producing aphid <i>Pemphigus spyrothecae</i> (Hemiptera: Aphididae)
Illuminating the genetic relationships within soldier-producing aphid colonies is an essential element of any attempt to explain the evolution of the altruistic soldier caste. Pemphigus spyrothecae is a soldier-producing aphid that induces galls on the leaf petioles of its host (trees of the genus Populus). At least a quarter of the aphids within the clonally produced gall population are morphologically and behaviourally distinct first-instar soldiers that defend the gall population from predation. Using field trapping and microsatellites, we investigated the degree of clonal mixing within natural gall populations. Field trapping in the UK showed that all the migrants of P. spyrothecae and of two other Pemphigus species were wingless first-instar soldiers. The average degree of mixing estimated from trapping P. spyrothecae migrants was 0.68% (range = 0–15%). Microsatellite genotyping of 277 aphids from 13 galls collected in Italy revealed an average mixing level of 10.4% (range = 0–59%). Six galls contained more than one clone (range = 2–5 clones). Non-kin aphids were not restricted to the soldier caste but were evenly distributed across instars. An additional gall, from which 527 occupants were genotyped, contained 12 non-kin aphids distributed among nine clones, showing that clonal diversity can be high even when mixing is very low. These observations suggest that although soldiers migrate regularly and can moult and reproduce within foreign galls, clonal mixing in this species is generally low and is unlikely to provide a barrier to the evolution of investment by the aphid clones in an altruistic soldier caste
Antimicrobials: a global alliance for optimizing their rational use in intra-abdominal infections (AGORA)
Intra-abdominal infections (IAI) are an important cause of morbidity and are frequently associated with poor prognosis, particularly in high-risk patients. The cornerstones in the management of complicated IAIs are timely effective source control with appropriate antimicrobial therapy. Empiric antimicrobial therapy is important in the management of intra-abdominal infections and must be broad enough to cover all likely organisms because inappropriate initial antimicrobial therapy is associated with poor patient outcomes and the development of bacterial resistance. The overuse of antimicrobials is widely accepted as a major driver of some emerging infections (such as C. difficile), the selection of resistant pathogens in individual patients, and for the continued development of antimicrobial resistance globally. The growing emergence of multi-drug resistant organisms and the limited development of new agents available to counteract them have caused an impending crisis with alarming implications, especially with regards to Gram-negative bacteria. An international task force from 79 different countries has joined this project by sharing a document on the rational use of antimicrobials for patients with IAIs. The project has been termed AGORA (Antimicrobials: A Global Alliance for Optimizing their Rational Use in Intra-Abdominal Infections). The authors hope that AGORA, involving many of the world's leading experts, can actively raise awareness in health workers and can improve prescribing behavior in treating IAIs
Aspects of Coulomb Dissociation and Interference in Peripheral Nucleus-Nucleus Collisions
Coherent vector meson production in peripheral nucleus-nucleus collisions is
discussed. These interactions may occur for impact parameters much larger than
the sum of the nuclear radii. Since the vector meson production is always
localized to one of the nuclei, the system acts as a two-source interferometer
in the transverse plane. By tagging the outgoing nuclei for Coulomb
dissociation it is possible to obtain a measure of the impact parameter and
thus the source separation in the interferometer. This is of particular
interest since the life-time of the vector mesons are generally much shorter
than the impact parameters of the collisions.Comment: 10 pages, 4 figures, Presented at the Workshop on Electromagnetic
Probes of Fundamental Physics, Erice, Italy, 16-21 October, 200
Wormhole Core, Extra Dimensions, and Physical Universe
We created a model of several dimensional physical universe. The extra
dimensions associated with the four dimensional physical universe is assumed to
have modified Gidding-Strominger wormhole core. This core is separated by a
flexible wall, but it allows the adiabatic pressure generated in the wormhole
to penetrate in the extra dimensions. We assume that the extra dimensions are a
contracting Robinson-Walker space. We show that the associated physical
universe accelerates under certain restriction of the parameters introduced.
The extra dimensional space is very large at the begining, however at present
time this space will be very reduced. As a result the physical universe will
appear to us four dimensional the way we observe it now.Comment: 8 pages, Festschrift Contributio
Deconfining by Winding
A model for the quantum effective description of the vacuum structure of
thermalized SU(3) Yang-Mills theory is proposed. The model is based on Abelian
projection leading to a Ginzburg-Landau theory for the magnetic sector. The
possibility of topologically non-trivial, effective monopole fields in the
deconfining phase is explored. These fields are assumed to be
Bogomol'nyi-Prasad-Sommerfield saturated solutions along the compact, euclidean
time dimension. Accordingly, a gauge invariant interaction for the monopole
fields is constructed.
Motivated by the corresponding lattice results the vacuum dynamics is assumed
to be dominated by the monopole fields. A reasonable value for the critical
temperature is obtained, and the partial persistence of non-perturbative
features in the deconfining phase of SU(3) Yang-Mills theory, as it is measured
on the lattice, follows naturally.Comment: 10 pages, 5 figures, Talk at conference "Lepton Scattering, Hadrons
and QCD, 26.3.-5.4 2001, Adelaide, Australi
Polarized Structure Functions in QCD
We review the nucleon's polarized structure functions from the viewpoint of
gauge invariant, nonlocal light-cone operators in QCD. We discuss a systematic
treatment of the polarized structure functions and the corresponding parton
distribution functions. We also address a question of what information on the
structure of Nature will be obtained from the future polarized experiments.
From this point of view, we will discuss the W gamma production at RHIC
polarized experiment.Comment: 8 pages, 5 Postscript figures, Invited talk presented at the Workshop
on Lepton Scattering, Hadrons and QCD, Adelaide, March 26 -- April 6, 200
Glueball properties in anisotropic SU(3) lattice QCD with improved action
We study the glueballs properties at finite temperature using SU(3) lattice
QCD at the quenched level with the anisotropic lattice. We use the tree-level
Symanzik O(a^2) improved action. We present our preliminary results which shows
the slight reduction of the scalar glueball mass near T_cComment: 8 pages, 13 figures, Talk given at Joint Workshop of the Special
Research Center for the Subatomic Structure of Matter and the National
Institute for Theoretical Physics (Workshop on Lepton Scattering, Hadrons and
QCD), Adelaide, Australia 26 March - 6 April 200
- …