61 research outputs found
Bound state nature of the exotic Z_b states
The assumption that the newly observed charged bottomonia states Z_b(10610)
and Z_b(10650) are of molecular nature is confronted with the measured
invariant mass distributions for the transitions of the Upsilon(5S) to the
final states h_b pi^+ pi^- and h_b(2P) pi^+ pi^-. It is shown that the
assumption that the Z_b(10610) and Z_b(10650) are B\bar B^*+{\rm c.c.} and
B^*\bar B^* bound states, respectively, with very small binding energies is
consistent with the data. The calculation is based on a power counting for
bottom meson loops, which is explicitly given up to two-loop in the framework
of a nonrelativistic effective field theory. We also show that if the Z_b
states are of molecular nature, then the data should not be analyzed by using a
Breit-Wigner parametrization.Comment: 8 pages, 5 figures. Typos corrected, version appeared in Eur. Phys.
J.
Employing spin symmetry to disentangle different models for the XYZ states
In order to test different models proposed for some states discovered
recently in the charmonium mass range that do not fit into the pattern
predicted by the conventional quark model, we derive predictions for the
spectrum within the hadro-charmonium picture, the tetraquark picture as well as
the hadronic molecular approach. We exploit heavy quark spin symmetry for the
hadro-charmonium and hadronic molecule scenarios. The patterns that emerge from
the different models turn out to be quite distinct. For example, only within
the hadro-charmonium picture a pseudoscalar state emerges that is lighter than
the Y(4260). Possible discovery channels of these additional states are
discussed.Comment: 22 pages, 4 figures, version accepted by PR
Strong and radiative decays of the and
Since their discovery in 2003, the open charm states and
provide a challenge to the conventional quark model. In recent
years, theoretical evidence has been accumulated for both states in favor of a
predominantly and molecular nature, respectively. However, a direct
experimental proof of this hypothesis still needs to be found. Since radiative
decays are generally believed to be sensitive to the inner structure of the
decaying particles, we study in this work the radiative and strong decays of
both the and , as well as of their counterparts
in the bottom sector. While the strong decays are indeed strongly enhanced for
molecular states, the radiative decays are of similar order of magnitude in
different pictures. Thus, the experimental observable that allows one to
conclusively quantify the molecular components of the and
is the hadronic width, and not the radiative one, in
contradistinction to common belief. We also find that radiative decays of the
sibling states in the bottom sector are significantly more frequent than the
hadronic ones. Based on this, we identify their most promising discovery
channels
Confirming the molecular nature of the and the
The decays of the and the to ,
and (, and ) are
investigated within a nonrelativistic effective field theory. It is argued
that, while the decays to suffer from potentially large
higher order corrections, the -wave transitions of the states offer
the best possibility to confirm the nature of the states as molecular
states and to further study their properties. We give nontrivial and
parameter-free predictions for the ratios of various partial widths for final
states with and . In addition, the branching
fractions for the neutral -states to are predicted to be
of order --. This provides a fine test of the molecular
nature in future high-luminosity experiments.Comment: 18 pages, 2 figure
Effects of states and bottom meson loops on transitions
We study the dipion transitions . In particular, we consider the effects of the two
intermediate bottomoniumlike exotic states and as
well as bottom meson loops. The strong pion-pion final-state interactions,
especially including channel coupling to in the -wave, are taken
into account model-independently by using dispersion theory. Based on a
nonrelativistic effective field theory we find that the contribution from the
bottom meson loops is comparable to those from the chiral contact terms and the
-exchange terms. For the decay, the result shows that including the effects of the
-exchange and the bottom meson loops can naturally reproduce the two-hump
behavior of the mass spectra. Future angular distribution data are
decisive for the identification of different production mechanisms. For the
decay, we show that there is
a narrow dip around 1 GeV in the invariant mass distribution, caused
by the final-state interactions. The distribution is clearly different from
that in similar transitions from lower states, and needs to be
verified by future data with high statistics. Also we predict the decay width
and the dikaon mass distribution of the process.Comment: 25 pages, 8 figures, predictions of the decay width and the dikaon
mass distribution of the
process added, more discussions adde
Large scale multiplex PCR improves pathogen detection by DNA microarrays
<p>Abstract</p> <p>Background</p> <p>Medium density DNA microchips that carry a collection of probes for a broad spectrum of pathogens, have the potential to be powerful tools for simultaneous species identification, detection of virulence factors and antimicrobial resistance determinants. However, their widespread use in microbiological diagnostics is limited by the problem of low pathogen numbers in clinical specimens revealing relatively low amounts of pathogen DNA.</p> <p>Results</p> <p>To increase the detection power of a fluorescence-based prototype-microarray designed to identify pathogenic microorganisms involved in sepsis, we propose a large scale multiplex PCR (LSplex PCR) for amplification of several dozens of gene-segments of 9 pathogenic species. This protocol employs a large set of primer pairs, potentially able to amplify 800 different gene segments that correspond to the capture probes spotted on the microarray. The LSplex protocol is shown to selectively amplify only the gene segments corresponding to the specific pathogen present in the analyte. Application of LSplex increases the microarray detection of target templates by a factor of 100 to 1000.</p> <p>Conclusion</p> <p>Our data provide a proof of principle for the improvement of detection of pathogen DNA by microarray hybridization by using LSplex PCR.</p
Acceleration of the direct identification of Staphylococcus aureus versus coagulase-negative staphylococci from blood culture material: a comparison of six bacterial DNA extraction methods
To accelerate differentiation between Staphylococcus aureus and coagulase-negative staphylococci (CNS), this study aimed to compare six different DNA extraction methods from two commonly used blood culture materials, i.e. BACTEC and BacT/ALERT. Furthermore, we analysed the effect of reduced blood culture incubation for the detection of staphylococci directly from blood culture material. A real-time polymerase chain reaction (PCR) duplex assay was used to compare the six different DNA isolation protocols on two different blood culture systems. Negative blood culture material was spiked with methicillin-resistant S. aureus (MRSA). Bacterial DNA was isolated with automated extractor easyMAG (three protocols), automated extractor MagNA Pure LC (LC Microbiology Kit MGrade), a manual kit MolYsis Plus and a combination of MolYsis Plus and the easyMAG. The most optimal isolation method was used to evaluate reduced bacterial incubation times. Bacterial DNA isolation with the MolYsis Plus kit in combination with the specific B protocol on the easyMAG resulted in the most sensitive detection of S. aureus, with a detection limit of 10Â CFU/ml, in BacT/ALERT material, whereas using BACTEC resulted in a detection limit of 100Â CFU/ml. An initial S. aureus or CNS load of 1Â CFU/ml blood can be detected after 5Â h of incubation in BacT/ALERT 3D by combining the sensitive isolation method and the tuf LightCycler assay
Systematic Study of Hadronic Molecules in the Heavy-Quark Sector
In this work we study the properties of hadronic molecules in the heavy-quark sector. These have become increasingly important since from the beginning of this century a large number of states have been measured that for different reasons do not fit the predictions of simple quark models. In particular we discuss two candidates in the open charm sector, and , and two candidates in the bottomonium sector, and . Theorists have proposed different explanations for these states including tetraquarks, hybrids, hadro-quarkonia and, subject of this work, hadronic molecules. The study of these new states promises to provide insights in an important field of modern physics, the formation of matter by the strong force. Hadronic molecules are bound systems of hadrons in the same way two nucleons form the deuteron. For this the molecular states need to be located close to -wave thresholds of their constituents. The dynamics of their constituents will have a significant impact on the molecules which allows us to make predictions that are unique features of the molecular assignment
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