1,865 research outputs found
Collider Signatures of Neutrino Masses and Mixing from R-parity Violation
R-parity violation in the supersymmetric standard model can be the source of
neutrino masses and mixing. We analyze the neutrino mass matrix coming from
either bilinear or trilinear R-parity violation and its collider signatures,
assuming that the atmospheric and solar neutrino data are explained by three
active neutrino oscillations. Taking the gauge mediated supersymmetry breaking
mechanism, we show that the lightest neutralino decays well inside the detector
and the model could be tested by observing its branching ratios in the future
colliders. In the bilinear model where only the small solar neutrino mixing
angle can be accommodated, the relation, BR()
BR() BR(), serves as a
robust test of the model. The large mixing angle solution can be realized in
the trilinear model which predicts BR() BR() BR(). In either case, the
relation, BR() BR() BR(), should hold to be
consistent with the atmospheric neutrino and CHOOZ experiments.Comment: 24pages, Late
Observation of Andreev reflection in the c-axis transport of Bi_2Sr_2CaCu_2O_{8+x} single crystals near T_c and search for the preformed-pair state
We observed an enhancement of the -axis differential conductance around
the zero-bias in AuBiSrCaCuO (Bi2212) junctions near the
superconducting transition temperature . We attribute the conductance
enhancement to the Andreev reflection between the surface Cu-O bilayer with
suppressed superconductivity and the neighboring superconducting inner bilayer.
The continuous evolution from depression to an enhancement of the zero-bias
differential conductance, as the temperature approaches from below,
points to weakening of the barrier strength of the non-superconducting layer
between adjacent Cu-O bilayers. We observed that the conductance enhancement
persisted up to a few degrees above in junctions prepared on slightly
overdoped Bi2212 crystals. However, no conductance enhancement was observed
above in underdoped crystals, although recently proposed theoretical
consideration suggests an even wider temperature range of enhanced zero-bias
conductance. This seems to provide negative perspective to the existence of the
phase-incoherent preformed pairs in the pseudogap state.Comment: 17 pages including 4 figure
Activation of Peroxisome Proliferator-Activated Receptor Gamma by Rosiglitazone Increases Sirt6 Expression and Ameliorates Hepatic Steatosis in Rats
Sirt6 has been implicated in the regulation of hepatic lipid metabolism and the development of hepatic steatosis. The aim of this study was to address the potential role of Sirt6 in the protective effects of rosiglitazone (RGZ) on hepatic steatosis.) by stomach gavage for 6 weeks. The involvement of Sirt6 in the RGZ's regulation was evaluated by Sirt6 knockdown in AML12 mouse hepatocytes.RGZ treatment ameliorated hepatic lipid accumulation and increased expression of Sirt6, peroxisome proliferator-activated receptor gamma coactivtor-1-α (Ppargc1a/PGC1-α) and Forkhead box O1 (Foxo1) in rat livers. AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1. Interestingly, in free fatty acid-treated cells, Sirt6 knockdown increased hepatocyte lipid accumulation measured as increased triglyceride contents (p = 0.035), suggesting that Sirt6 may be beneficial in reducing hepatic fat accumulation. In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway. We propose Sirt6 as a possible therapeutic target for hepatic steatosis
Observation of a new charmonium state in double charmonium production in e+ e- annihilation at \sqrt{s} ~ 10.6 GeV
We report the first observation of a new charmonium state at a mass of
. This state, called X(3940), is
observed in the process in the spectrum of masses
recoiling against a reconstructed . We also observe the decay of the
X(3940) into and measure the intrinsic width of this state to be
less than at the 90% C.L. These results are obtained from a data sample collected with the Belle detector near the
resonance, at the KEKB asymmetric energy collider.Comment: BELLE-CONF-051
Search for double charmonium decays of the P-wave spin-triplet bottomonium states
Using a sample of 158 million events collected with the Belle
detector, we search for the first time for double charmonium decays of the
-wave spin-triplet bottomonium states (,
\chi_{bJ} \to \jpsi \jpsi, \jpsi \psp, \psp \psp for J=0, 1, and 2). No
significant signal is observed in the double charmonium mass
spectra, and we obtain the following upper limits, \BR(\chi_{bJ} \to \jpsi
\jpsi)<7.1\times 10^{-5}, , ,
\BR(\chi_{bJ} \to \jpsi \psp)<1.2\times 10^{-4}, ,
, \BR(\chi_{bJ} \to \psp \psp)<3.1\times 10^{-5},
, for J=0, 1, and 2, respectively, at
the 90% confidence level. These limits are significantly lower than the central
values (with uncertainties of 50% to 70%) predicted using the light cone
formalism but are consistent with calculations using the NRQCD factorization
approach.Comment: 7 pages, 4 figures, 1 tabl
Observation of B Decays to Two Kaons
Using 449 million BBbar pairs collected with the Belle detector at the KEKB
asymmetric-energy e^+e^- collider, we observe clear signals for B^+-> \bar{K}^0
K^+ and B^0-> \bar{K}^0 K^0 decays with 5.3 sigma and 6.0 sigma significance,
respectively. We measure the branching fractions Br(B^+-> \bar{K}^0 K^+ =
(1.22^{+0.32+0.13}_{-0.28-0.16})x10^{-6} and Br(B^0-> \bar{K}^0 K^0) =
(0.87^{+0.25}_{-0.20} +- 0.09)x10^{-6}, and partial-rate asymmetries
A_{CP}(B^+-> \bar{K}^0 K^+) = 0.13^{+0.23}_{-0.24}+- 0.02 and A_{CP}(B^0->
\bar{K}^0 K^0) = -0.58^{+0.73}_{-0.66}+- 0.04. From a simultaneous fit we also
obtain Br(B^+-> K^0\pi^+)= (22.8^{+0.8}_{-0.7} +- 1.3)x 10^{-6} and
A_{CP}(B^+-> K^0 \pi^+) = 0.03 +- 0.03 +- 0.01. The first and second error in
the branching fractions and the partial-rate asymmetries are statistical and
systematic, respectively. No signal is observed for B^0-> K^+ K^- decays, and
for this branching fraction we set an upper limit of 4.1x10^{-7} at the 90%
confidence level.Comment: 6 pages, 3 figure
Improved Constraints on D0-D0bar Mixing in D0 -> K+ pi- Decays from the Belle Detector
We report the results of a search for D0-D0bar mixing in D0 -> K+ pi- decays
based on 400 fb^{-1} of data accumulated by the Belle detector at KEKB. Both
assuming CP conservation and allowing for CP violation, we fit the decay-time
distribution for the mixing parameters x' and y', as well as for the parameter
R_D, the ratio of doubly-Cabibbo-suppressed decays to Cabibbo-favored decays.
The 95% confidence level region in the (x'^2,y') plane is obtained using a
frequentist method. Assuming CP conservation, we find x'^2<0.72 x 10^{-3} and
-9.9 x 10^{-3}<y'<6.8 x 10^{-3} at the 95% confidence level; these are the most
stringent constraints on the mixing parameters to date. The no-mixing point
(0,0) has a confidence level of 3.9%. Assuming no mixing, we measure
R_D=(0.377+-0.008+-0.005)%.Comment: 6 pages, 3 figures, 1 table; replaced with the version of Phys. Rev.
Let
Observation of the decay
We report the first observation of decay. These results
are obtained from a data sample that contains 449 million pairs
accumulated at the resonance with the Belle detector at the KEKB
asymmetric-energy collider. We observe a signal with a significance
of 8.1 and obtain a branching fraction of (9.5 1.7 (stat)
0.8 (syst)).Comment: 5 pages, 2 figures, submit to PRL (8 pages, 2 figures, ICHEP'06
Conference Paper
Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at Belle
The Collins effect connects transverse quark spin with a measurable azimuthal
dependence in the yield of hadronic fragments around the quark's momentum
vector. Using two different reconstruction methods we observe statistically
significant azimuthal asymmetries for charged pion pairs in e+e- annihilation
at a center-of-mass energy of 10.52 GeV, which can be attributed to a
transverse polarization of the primordial quarks. The measurement was performed
using a sample of 79 million hadronic events collected with the Belle detector.Comment: 6 pages, 4 figure
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