1,048 research outputs found
Isospin Breaking in Neutron -decay and SU(3) Violation in Semi-leptonic Hyperon Decays
Present precision measurements of the neutron life time lead to a CKM matrix
element which is three standard deviations off the value inferred
from heavy quark decays etc. We investigate the possibility whether
isospin-breaking effects in the neutron-to-proton vector current transition
matrix element could eventually close this gap.
For that we calculate in chiral perturbation theory the effect of pion and kaon
loops on the matrix element taking into account the mass
differences of the charged and neutral mesons. We find a negligibly small
isospin-breaking effect of . The crucial
quantity in the analysis of neutron beta-decay precision measurements is thus
the radiative correction term . Furthermore, we calculate in heavy
baryon chiral perturbation theory the SU(3) breaking effects on the vector
transition charges of weak semi-leptonic hyperon decays. We find for these
quantities channel-dependent relative deviations from the SU(3) limit which
range from -10% to .Comment: 6 pages, 1 figure, to be published in Physical Review C (brief
report
Right Handed Weak Currents in Sum Rules for Axialvector Constant Renormalization
The recent experimental results on deep inelastic polarized lepton scattering
off proton, deuteron and He together with polari% zed neutron
-decay data are analyzed. It is shown that the problem of Ellis-Jaffe
and Bjorken sum rules deficiency and the neutron paradox could be solved
simultaneously by assuming the small right handed current (RHC) admixture in
the weak interaction Lagrangian. The possible RHC impact on pion-nucleon
-term and Gamow-Teller sum rule for nuclear reactions is
pointed out.Comment: to be published in Phys. Rev. Lett. LaTeX, 8 pages, 21 k
Experiments to Find or Exclude a Long-Lived, Light Gluino
Gluinos in the mass range ~1 1/2 - 3 1/2 GeV are absolutely excluded. Lighter
gluinos are allowed, except for certain ranges of lifetime. Only small parts of
the mass-lifetime parameter space are excluded for larger masses unless the
lifetime is shorter than ~ 2 10^{-11} (m_{gluino}/ GeV) sec. Refined mass and
lifetime estimates for R-hadrons are given, present direct and indirect
experimental constraints are reviewed, and experiments to find or definitively
exclude these possibilities are suggested.Comment: 27 pp, latex with 1 uufiled figure, RU-94-35. New version amplifies
discussion of some points and corresponds to version for Phys. Rev.
Soft Photons in Hadron-Hadron Collisions: Synchrotron Radiation from the QCD Vacuum?
We discuss the production of soft photons in high energy hadron-hadron
collisions. We present a model where quarks and antiquarks in the hadrons emit
``synchrotron light'' when being deflected by the chromomagnetic fields of the
QCD vacuum, which we assume to have a nonperturbative structure. This gives a
source of prompt soft photons with frequencies in the c.m.
system of the collision in addition to hadronic bremsstrahlung. In comparing
the frequency spectrum and rate of ``synchrotron'' photons to experimental
results we find some supporting evidence for their existence. We make an
exclusive--inclusive connection argument to deduce from the ``synchrotron''
effect a behaviour of the neutron electric formfactor proportional
to for . We find this to be consistent with
available data. In our view, soft photon production in high energy
hadron-hadron and lepton-hadron collisions as well as the behaviour of
electromagnetic hadron formfactors for low are thus sensitive probes of
the nonperturbative structure of the QCD vacuum.Comment: Heidelberg preprint HD-THEP-94-36, 31 pages, LaTeX + ZJCITE.sty
(included), 12 figures appended as uuencoded compressed ps-fil
γ-Catenin-Dependent Signals Maintain BCR-ABL1<sup>+</sup> B Cell Acute Lymphoblastic Leukemia.
The BCR-ABL1 fusion protein is the cause of chronic myeloid leukemia (CML) and of a significant fraction of adult-onset B cell acute lymphoblastic leukemia (B-ALL) cases. Using mouse models and patient-derived samples, we identified an essential role for γ-catenin in the initiation and maintenance of BCR-ABL1 <sup>+</sup> B-ALL but not CML. The selectivity was explained by a partial γ-catenin dependence of MYC expression together with the susceptibility of B-ALL, but not CML, to reduced MYC levels. MYC and γ-catenin enabled B-ALL maintenance by augmenting BIRC5 and enforced BIRC5 expression overcame γ-catenin loss. Since γ-catenin was dispensable for normal hematopoiesis, these lineage- and disease-specific features of canonical Wnt signaling identified a potential therapeutic target for the treatment of BCR-ABL1 <sup>+</sup> B-ALL
Isotopic Composition of Light Nuclei in Cosmic Rays: Results from AMS-01
The variety of isotopes in cosmic rays allows us to study different aspects
of the processes that cosmic rays undergo between the time they are produced
and the time of their arrival in the heliosphere. In this paper we present
measurements of the isotopic ratios 2H/4He, 3He/4He, 6Li/7Li, 7Be/(9Be+10Be)
and 10B/11B in the range 0.2-1.4 GeV of kinetic energy per nucleon. The
measurements are based on the data collected by the Alpha Magnetic
Spectrometer, AMS-01, during the STS-91 flight in 1998 June.Comment: To appear in ApJ. 12 pages, 11 figures, 6 table
Search for Branons at LEP
We search, in the context of extra-dimension scenarios, for the possible
existence of brane fluctuations, called branons. Events with a single photon or
a single Z-boson and missing energy and momentum collected with the L3 detector
in e^+ e^- collisions at centre-of-mass energies sqrt{s}=189-209$ GeV are
analysed. No excess over the Standard Model expectations is found and a lower
limit at 95% confidence level of 103 GeV is derived for the mass of branons,
for a scenario with small brane tensions. Alternatively, under the assumption
of a light branon, brane tensions below 180 GeV are excluded
Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV
A search for charginos nearly mass-degenerate with the lightest
supersymmetric particle is performed using the 176 pb^-1 of data collected at
189 GeV in 1998 with the L3 detector. Mass differences between the chargino and
the lightest supersymmetric particle below 4 GeV are considered. The presence
of a high transverse momentum photon is required to single out the signal from
the photon-photon interaction background. No evidence for charginos is found
and upper limits on the cross section for chargino pair production are set. For
the first time, in the case of heavy scalar leptons, chargino mass limits are
obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference
Study of Spin and Decay-Plane Correlations of W Bosons in the e+e- -> W+W- Process at LEP
Data collected at LEP at centre-of-mass energies \sqrt(s) = 189 - 209 GeV are
used to study correlations of the spin of W bosons using e+e- -> W+W- -> lnqq~
events. Spin correlations are favoured by data, and found to agree with the
Standard Model predictions. In addition, correlations between the W-boson decay
planes are studied in e+e- -> W+W- -> lnqq~ and e+e- -> W+W- -> qq~qq~ events.
Decay-plane correlations, consistent with zero and with the Standard Model
predictions, are measured
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