56 research outputs found
Two Photon Contribution to Polarization in
Short distance physics involving virtual top and charm quarks contributes to
(and ) polarization in the decay . Measurement of the parity violating asymmetry , where and are the rates
to produce right and left-handed , may provide valuable information on
the unitarity triangle. The parity violating asymmetry also gets a contribution
from Feynman diagrams with two photon intermediate states. We estimate this two
photon contribution to the asymmetry and discuss briefly the two photon
contribution to time reversal odd asymmetries that involve both the and
polarizations.Comment: (19 pages, 5 figures available on request. Uses phyzzx),
CALT-68-1798, UCSD/PTH 92-2
About one long-range contribution to K+ -> pi+ l+ l- decays
We investigate the mechanism of K+ -> pi+ l+ l- (l= e, mu) decays in which a
virtual photon is emitted either from the incoming K+ or the outgoing pi+. We
point out some inconsistencies with and between two previous calculations,
discuss the possible experimental inputs, and estimate the branching fractions.
This mechanism alone fails to explain the existing experimental data by more
than one order-of-magnitude. But it may show itself by its interference with
the leading long-range mechanism dominated by the a_1^+ and rho^0 mesons.Comment: 12 pages, RevTeX, epsf.sty, 2 embedded figure
Running mass of the rho0 meson's implication for the dilepton mass spectrum and the mu+mu-/e+e- branching ratio in the K+ --> pi+l+l- decays
We make an attempt to resolve the discrepancy of the observed e+e- mass
spectrum in the K+ --> pi+e+e- decay with that predicted by meson dominance. To
this end we investigate the properties of the rho0 propagator. We use
dispersion relations to evaluate the running mass squared m_rho^2(t) of the
rho0 resonance without adjustable parameters. To improve the convergence of the
dispersion integral, the momentum dependence of strong vertices is taken from
the flux-tube-breaking model of Kokoski and Isgur. The obtained behavior of
m_rho^2(t) at small momentum squared t makes the K+ --> pi+e+e- form factor
rise faster with increasing than in the original meson-dominance
calculation and more in agreement with the published data. As a consequence,
the meson-dominance prediction of the mu+mu-/e+e- branching ratio changes
slightly, from 0.224 to 0.236. We do not see any possibility to accommodate
into the meson-dominance approach an even steeper e+e- spectrum, indicated by
the preliminary data of the E865 collaboration at BNL AGS.Comment: 13 pages, RevTeX, epsf.sty, 4 embedded figure
The centrosome and spindle as a ribonucleoprotein complex
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Chromosome Research 19 (2011): 367-376, doi:10.1007/s10577-011-9186-7.The presence of nucleic acids in centrosomes and the spindle have been proposed,
observed, and reported since the 1950s. Why did the subject remain, perhaps even until
today, such a controversial issue? The explanation is manifold, and includes legitimate
concern over contamination from other cellular compartments in biochemical
preparations. With a typically high background of cytoplasmic ribosomes, even
microscopic images of stained intact cells could be difficult to interpret. Also, evidence
for RNA and DNA in centrosomes accumulated for approximately 40 years but was
interspersed with contradictory studies, primarily regarding the presence of DNA
(reviewed in Johnson and Rosenbaum, 1991; Marshall and Rosenbaum, 2000). Perhaps
less tangible but still a likely cause for lingering controversy is that the presence of
nucleic acids in the spindle or centrosomes will require us to look differently at these
structures from a functional, and more to the point, evolutionary standpoint.This work was supported by grants from the NIH (GM088503) and NSF (MCB0843092)
to MCA
A new measurement of the properties of the rare decay K -> pi+ e+ e-
A large low-background sample of events (10300) has been collected for the
rare decay of kaons in flight K+ -> pi+ e+ e- by experiment E865 at the
Brookhaven AGS. The decay products were accepted by a broad band
high-resolution charged particle spectrometer with particle identification. The
branching ratio (2.94 +- 0.05(stat.) +- 0.13(syst.) +- 0.05(model))*10**{-7}
was determined normalizing to events from the decay chain K+ -> pi+ pi0; pi0 ->
e+ e- gamma. From the analysis of the decay distributions the vector nature of
this decay is firmly established now, and limits on scalar and tensor
contributions are deduced. From the (e+ e-) invariant mass distribution the
decay form factor f(z)=f0(1+ delta*z) (z=M(ee)**2/m(K)**2) is determined with
delta=2.14 +- 0.13 +- 0.15. Chiral QCD perturbation theory predictions for the
form factor are also tested, and terms beyond leading order O(p**4) are found
to be important.Comment: 4 pages, 5 figure
Weak Decays Beyond Leading Logarithms
We review the present status of QCD corrections to weak decays beyond the
leading logarithmic approximation including particle-antiparticle mixing and
rare and CP violating decays. After presenting the basic formalism for these
calculations we discuss in detail the effective hamiltonians for all decays for
which the next-to-leading corrections are known. Subsequently, we present the
phenomenological implications of these calculations. In particular we update
the values of various parameters and we incorporate new information on m_t in
view of the recent top quark discovery. One of the central issues in our review
are the theoretical uncertainties related to renormalization scale ambiguities
which are substantially reduced by including next-to-leading order corrections.
The impact of this theoretical improvement on the determination of the
Cabibbo-Kobayashi-Maskawa matrix is then illustrated in various cases.Comment: 229 pages, 32 PostScript figures (included); uses RevTeX, epsf.sty,
rotate.sty, rmpbib.sty (included), times.sty (included; requires LaTeX 2e);
complete PostScript version available at
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/tum-100-95.ps.gz or
ftp://feynman.t30.physik.tu-muenchen.de/pub/preprints/tum-100-95.ps2.gz
(scaled down and rotated version to print two pages on one sheet of paper
Observation of the Decay K- -> pi- mu+ mu- and Measurements of the Branching Ratios for K+/- -> pi+/- mu+ mu-
Using data collected with the HyperCP (E871) spectrometer during the 1997
fixed-target run at Fermilab, we report the first observation of the decay K-
-> pi- mu+ mu- and new measurements of the branching ratios for K+/- -> pi+/-
mu+ mu- . By combining the branching ratios for the K+ and K- decays, we
measure the ratio (K+/- -> pi+/- mu+ mu-)/(K+/- -> all) = (9.8 +/- 1.0 +/-
0.5)x10^(-8). The CP asymmetry between the K+ and K- decay modes = -0.02 +/-
0.11 +/- 0.04.Comment: 4 pages, 4 figures, submitted to PR
Rare Decays
The rare decays of the meson have had a long tradition as a laboratory
for testing the symmetry properties of the weak interactions, and the manner in
which these symmetries are broken by higher order effects. Present--day
interest is focussed on decays that are suppressed by --symmetry or GIM
symmetry. Such decays, in the standard theory, are sensitive to effects of the
virtual top quark, and could also reveal new interactions transcending the
standard model. In addition, the radiative decays of the meson have become
a useful testing--ground for effective Lagrangians describing the low energy
interactions of pions, kaons and photons.Comment: Invited Talk at the Third Workshop on High Energy Particle Physics
(WHEPP 3) Madras, 1994, LaTex, 14 pages, 3 figures available upon reques
A New Measurement of the Rare Decay
More than 400 events were observed in a rare
decay experiment at the AGS. Normalized to the
decay, the branching ratio is determined to be
. This branching ratio
and the mass spectrum is in very good agreement with the measurement
of the decay, but deviates significantly from the
previous measurement.Comment: 4 pages, 6 figures in 7 eps files. Paper to be submitted to Phys Rev
Let
Masked mRNA is stored with aggregated nuclear speckles and its asymmetric redistribution requires a homolog of mago nashi
<p>Abstract</p> <p>Background</p> <p>Many rapidly developing systems rely on the regulated translation of stored transcripts for the formation of new proteins essential for morphogenesis. The microspores of the water fern <it>Marsilea vestita </it>dehydrate as they mature. During this process both mRNA and proteins required for subsequent development are stored within the microspores as they become fully desiccated and enter into senescence. At this point microspores become transcriptionally silent and remain so upon rehydration and for the remainder of spermatogenesis. Transcriptional silencing coupled with the translation of preformed RNA makes the microspore of <it>M. vestita </it>a useful system in which to study post-transcriptional regulation of RNA.</p> <p>Results</p> <p>We have characterized the distribution of mRNA as well as several conserved markers of subnuclear bodies within the nuclei of desiccating spores. During this period, nuclear speckles containing RNA were seen to aggregate forming a single large coalescence. We found that aggregated speckles contain several masked mRNA species known to be essential for spermatogenesis. During spermatogenesis masked mRNA and associated speckle proteins were shown to fragment and asymmetrically localize to spermatogenous but not sterile cells. This asymmetric localization was disrupted by RNAi knockdown of the <it>Marsilea </it>homolog of the Exon Junction Complex core component Mago nashi.</p> <p>Conclusions</p> <p>A subset of masked mRNA is stored in association with nuclear speckles during the dormant phase of microspore development in <it>M. vestita</it>. The asymmetric distribution of specific mRNAs to spermatogenous but not sterile cells mirrors their translational activities and appears to require the EJC or EJC components. This suggests a novel role for nuclear speckles in the post-transcriptional regulation of transcripts.</p
- …