1,229 research outputs found
The Contribution of Bc Mesons to the Search for B->tau nu Decays at LEP
We study the contribution of B_c mesons to the search for B->tau nu decays.
We find that at LEP the contributions from B_u and B_c mesons can be
comparable. This observation can have a relevant impact on the extraction of
constraints on new physics (such as charged-Higgs contributions) from current
LEP limits on B->tau nu final states. Inclusion of the B_c contribution can
reduce the current L3 limit on Tan(beta)/M_H from 0.38/GeV (90%CL) down to
0.27/GeV (90%CL).Comment: 8 pages, Latex, epsfig, 1 figur
Short and long distance contributions to
We study the decay of the neutral B meson to within the
framework of the Standard Model, including long distance contributions.Comment: 14 pages, 2 figures; A sign error in the numerical estimation
corrected. Results and figures changed. Results for resonance contributions
also updated to match with the experimetal values in the narrow width
approximatio
Chiral Magnetic Effect in Hydrodynamic Approximation
We review derivations of the chiral magnetic effect (ChME) in hydrodynamic
approximation. The reader is assumed to be familiar with the basics of the
effect. The main challenge now is to account for the strong interactions
between the constituents of the fluid. The main result is that the ChME is not
renormalized: in the hydrodynamic approximation it remains the same as for
non-interacting chiral fermions moving in an external magnetic field. The key
ingredients in the proof are general laws of thermodynamics and the
Adler-Bardeen theorem for the chiral anomaly in external electromagnetic
fields. The chiral magnetic effect in hydrodynamics represents a macroscopic
manifestation of a quantum phenomenon (chiral anomaly). Moreover, one can argue
that the current induced by the magnetic field is dissipation free and talk
about a kind of "chiral superconductivity". More precise description is a
ballistic transport along magnetic field taking place in equilibrium and in
absence of a driving force. The basic limitation is exact chiral limit while
the temperature--excitingly enough- does not seemingly matter. What is still
lacking, is a detailed quantum microscopic picture for the ChME in
hydrodynamics. Probably, the chiral currents propagate through
lower-dimensional defects, like vortices in superfluid. In case of superfluid,
the prediction for the chiral magnetic effect remains unmodified although the
emerging dynamical picture differs from the standard one.Comment: 35 pages, prepared for a volume of the Springer Lecture Notes in
Physics "Strongly interacting matter in magnetic fields" edited by D.
Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Ye
CP violation in in the model III 2HDM
We have calculated the Wilson coefficients (i=1,2) in the
renormalization scheme in the model III 2HDM. Using the obtained
Wilson coefficients, we have analyzed the CP violation in decays (q=d,s) in the model. The CP asymmetry, , depends on the
parameters of models and in can be as large as 40% and
35% for and respectively. It can reach 4% for decays.
Because in SM CP violation is smaller than or equal to O() which is
unobservably small, an observation of CP asymmetry in the decays would unambiguously signal the existence of new physics.Comment: revtex4, 16 pages, 7 figure
Measurement of the Branching Fraction for B->eta' K and Search for B->eta'pi+
We report measurements for two-body charmless B decays with an eta' meson in
the final state. Using 11.1X10^6 BBbar pairs collected with the Belle detector,
we find BF(B^+ ->eta'K^+)=(79^+12_-11 +-9)x10^-6 and BF(B^0 ->
eta'K^0)=(55^+19_-16 +-8)x10^-6, where the first and second errors are
statistical and systematic, respectively. No signal is observed in the mode B^+
-> eta' pi^+, and we set a 90% confidence level upper limit of BF(B^+->
eta'pi^+) eta'K^+- decays is
investigated and a limit at 90% confidence level of -0.20<Acp<0.32 is obtained.Comment: Submitted to Physics Letters
Observation of Cabibbo-suppressed and W-exchange Lambda_c^+ baryon decays
We present measurements of the Cabibbo-suppressed decays Lambda_c^+ -->
Lambda0 K+ and Lambda_c^+ --> Sigma0 K+ (both first observations), Lambda_c^+
--> Sigma+ K+ pi- (seen with large statistics for the first time), Lambda_c^+
--> p K+ K- and Lambda_c^+ --> p phi (measured with improved accuracy).
Improved branching ratio measurements for the decays Lambda_c^+ --> Sigma+ K+
K- and Lambda_c^+ --> Sigma+ phi, which are attributed to W-exchange diagrams,
are shown. We also present the first evidence for Lambda_c^+ --> Xi(1690)^0 K+
and set an upper limit on the non-resonant decay Lambda_c^+ --> Sigma+ K+ K-.
This analysis was performed using 32.6 fb^{-1} of data collected by the Belle
detector at the asymmetric e+ e- collider KEKB.Comment: Submitted to Phys. Lett. B. v2: A small correction to the Authorlist
was made. An earlier version of this analysis was released as
BELLE-CONF-0130, hep-ex/010800
Measurements of Branching Fractions and Decay Amplitudes in B-> J/\psi K^* decays
The branching fractions and the decay amplitudes of B -> J/psi K^* decays are
measured in a 29.4/fb data sample collected with the Belle detector at the KEKB
electron-positron collider. The decay amplitudes of helicity states of the
J/psi K^* system are determined from the full angular distribution of the final
state particles in the transversity basis. The branching fractions are measured
to be (1.29\pm0.05\pm0.13) \times 10^{-3} for neutral mesons and
(1.28\pm0.07\pm0.14) \times 10^{-3} for charged mesons. The measured
longitudinal and transverse (perpendicular to the transversity plane)
amplitudes are |A_0|^2 = 0.62\pm0.02\pm0.03 and |A_{\perp}|^2 =
0.19\pm0.02\pm0.03, respectively. The value of |A_{\perp}|^2 shows that the CP
even component dominates in the B^0 \to J/\psi K^{*0}(K_S\pi^0) decay.Comment: 17 pages, 3 figures, 5 tables, to appear in Phys. Lett.
Measurement of the inclusive semileptonic branching fraction of B mesons and |Vcb|
We present a measurement of the electron spectrum from inclusive semileptonic
{\it B} decay, using 5.1 fb of data collected with the
Belle detector. A high-momentum lepton tag was used to separate the
semileptonic {\it B} decay electrons from secondary decay electrons. We
obtained the branching fraction, , with minimal model dependence.
From this measurement, we derive a value for the Cabibbo-Kobayashi-Maskawa
matrix element .Comment: 16 pages, 3 figures, 3 table
Determination of |Vcb| using the semileptonic decay \bar{B}^0 --> D^{*+}e^-\bar{\nu}
We present a measurement of the Cabibbo-Kobayashi-Maskawa (CKM) matrix
element |Vcb| using a 10.2 fb^{-1} data sample recorded at the \Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric e^+e^- storage ring.
By extrapolating the differential decay width of the \bar{B}^0 -->
D^{*+}e^-\bar{\nu} decay to the kinematic limit at which the D^{*+} is at rest
with respect to the \bar{B}^0, we extract the product of |Vcb| with the
normalization of the decay form factor F(1), |Vcb |F(1)=
(3.54+/-0.19+/-0.18)x10^{-2}, where the first error is statistical and the
second is systematic. A value of |Vcb| = (3.88+/-0.21+/-0.20+/-0.19)x10^{-2} is
obtained using a theoretical calculation of F(1), where the third error is due
to the theoretical uncertainty in the value of F(1). The branching fraction
B(\bar{B}^0 --> D^{*+}e^-\bar{\nu}) is measured to be
(4.59+/-0.23+/-0.40)x10^{-2}.Comment: 20 pages, 6 figures, elsart.cls, submitted to PL
Search for Single Top Production at LEP
Single top production in e+e- annihilations is searched for in data collected
by the L3 detector at centre-of-mass energies from 189 to 209 GeV,
corresponding to a total integrated luminosity of 634 pb-1. Investigating
hadronic and semileptonic top decays, no evidence of single top production at
LEP is obtained and upper limits on the single top cross section as a function
of the centre-of-mass energy are derived. Limits on possible anomalous
couplings, as well as on the scale of contact interactions responsible for
single top production are determined
- …