179 research outputs found
Quenching of Weak Interactions in Nucleon Matter
We have calculated the one-body Fermi and Gamow-Teller charge-current, and
vector and axial-vector neutral-current nuclear matrix elements in nucleon
matter at densities of 0.08, 0.16 and 0.24 fm and proton fractions
ranging from 0.2 to 0.5. The correlated states for nucleon matter are obtained
by operating on Fermi-gas states by a symmetrized product of pair correlation
operators determined from variational calculations with the Argonne v18 and
Urbana IX two- and three-nucleon interactions. The squares of the charge
current matrix elements are found to be quenched by 20 to 25 % by the
short-range correlations in nucleon matter. Most of the quenching is due to
spin-isospin correlations induced by the pion exchange interactions which
change the isospins and spins of the nucleons. A large part of it can be
related to the probability for a spin up proton quasi-particle to be a bare
spin up/down proton/neutron. We also calculate the matrix elements of the
nuclear Hamiltonian in the same correlated basis. These provide relatively mild
effective interactions which give the variational energies in the Hartree-Fock
approximation. The calculated two-nucleon effective interaction describes the
spin-isospin susceptibilities of nuclear and neutron matter fairly accurately.
However 3-body terms are necessary to reproduce the compressibility. All
presented results use the simple 2-body cluster approximation to calculate the
correlated basis matrix elements.Comment: submitted to PR
Can three-flavor oscillations solve the solar neutrino problem?
The most promising solution to the solar neutrino problem are neutrino
oscillations, which usually are analyzed within the reduced 2-flavor scheme,
because the solutions found therein reasonably well reproduce the recent data
of Super-Kamiokande about the recoil-electron energy spectrum, zenith-angle and
seasonal variations, and the event rate data of all the neutrino detectors. In
this work, however, a survey of the complete parameter space of 3-flavor
oscillations is performed. Basically eight new additional solutions could be
identified, where the best one with \Delta m(12)^2=2.7x10^(-10) eV^2, \Delta
m(13)^2=1.0x10^(-5) eV^2, \Theta(12)=23, and \Theta(13)=1.3 (denoted SVO) is
slightly more probable than any 2-flavor solution. However, including the
results of the atmospheric neutrino problem excludes all 3-flavour solutions
apart from the SLMA-solution (\Delta m(12)^2=7.9x10^(-6) eV^2, \Delta
m(13)^2=2.5x10^(-4) eV^2, \Theta(12)=1.4, and \Theta(13)=20). Besides, the
ability of SNO and Borexino to discriminate the various 2- and 3-flavor
solutions is investigated. Only with very good statistics in these experiments
the correct solution to the solar neutrino problem can be identified
unambiguously.Comment: 22 pages, 19 figures, REVTeX, submitted to Phys.Rev.D, article with
better resolved figures available under
http://www.mpa-garching.mpg.de/~schlattl/public.htm
Three-generation flavor transitions and decays of supernova relic neutrinos
If neutrinos have mass, they can also decay. Decay lifetimes of cosmological
interest can be probed, in principle, through the detection of the redshifted,
diffuse neutrino flux produced by all past supernovae--the so-called supernova
relic neutrino (SRN) flux. In this work, we solve the SRN kinetic equations in
the general case of three-generation flavor transitions followed by invisible
(nonradiative) two-body decays. We then use the general solution to calculate
observable SRN spectra in some representative decay scenarios. It is shown
that, in the presence of decay, the SRN event rate can basically span the whole
range below the current experimental upper bound--a range accessible to future
experimental projects. Radiative SRN decays are also briefly discussed.Comment: 25 pages, including 7 figure
Lepton Flavour Violating Leptonic/Semileptonic Decays of Charged Leptons in the Minimal Supersymmetric Standard Model
We consider the leptonic and semileptonic (SL) lepton flavour violating (LFV)
decays of the charged leptons in the minimal supersymmetric standard model
(MSSM). The formalism for evaluation of branching fractions for the SL LFV
charged-lepton decays with one or two pseudoscalar mesons, or one vector meson
in the final state, is given. Previous amplitudes for the SL LFV charged-lepton
decays in MSSM are improved, for instance the -penguin amplitude is
corrected to assure the gauge invariance. The decays are studied not only in
the model-independent formulation of the theory in the frame of MSSM, but also
within the frame of the minimal supersymmetric SO(10) model within which the
parameters of the MSSM are determined. The latter model gives predictions for
the neutrino-Dirac Yukawa coupling matrix, once free parameters in the model
are appropriately fixed to accommodate the recent neutrino oscillation data.
Using this unambiguous neutrino-Dirac Yukawa couplings, we calculate the LFV
leptonic and SL decay processes assuming the minimal supergravity scenario. A
very detailed numerical analysis is done to constrain the MSSM parameters.
Numerical results for SL LFV processes are given, for instance for tau -> e
(mu) pi0, tau -> e (mu) eta, tau -> e (mu) eta', tau -> e (mu) rho0, tau -> e
(mu) phi, tau -> e (mu) omega, etc.Comment: 36 pages, 3 tables, 5 .eps figure
Measurements of exclusive B_s^0 decays at the Y(5S) resonance
Several exclusive decays are studied using a 1.86 fb-1 data sample
collected at the Y(5S) resonance with the Belle detector at the KEKB asymmetric
energy e^+ e^- collider. In the decay mode we find 10
candidates and measure the corresponding branching fraction. Combining
the B_s^0 -> D_s^{(*)-} \pi^+, B_s^0 -> D_s^{(*)-} \rho^+, B_s^0 -> J/\psi \phi
and B_s^0 -> J/\psi \eta decay modes, a significant signal is observed.
The ratio \sigma (e^+ e^- -> B_s^* \bar{B}_s^*) / \sigma (e^+ e^- -> B_s^{(*)}
\bar{B}_s^{(*)}) = (93^{+7}_{-9} \pm 1)% is obtained at the Y(5S) energy,
indicating that meson production proceeds predominantly through the
creation of pairs. The and meson masses are
measured to be M(B_s^0)=(5370 \pm 1 \pm 3)MeV/c^2 and M(B_s^*)=(5418 \pm 1 \pm
3)MeV/c^2. Upper limits on the B_s^0 -> \gamma \gamma, B_s^0 -> \phi \gamma,
B_s^0 -> K^+ K^- and B_s^0 -> D_s^{(*)+} D_s^{(*)-} branching fractions are
also reported.Comment: 9 pages, 5 figures, published in Phys. Rev. D76, 012002 (2007
Measurement of the near-threshold cross section using initial-state radiation
We report measurements of the exclusive cross section for , where or , in the center-of-mass energy range from the threshold to with initial-state radiation. The
analysis is based on a data sample collected with the Belle detector with an
integrated luminosity of 673 .Comment: Presented at EPS07 and LP07 conferences, published in PRD(RC
Search for Resonant Decays at Belle
We report measurements and searches for resonant decays where is a
meson or
the X(3872) particle.Comment: accepted by Physics Letters
Search for B+ -> D*+ pi0 decay
We report on a search for the doubly Cabibbo suppressed decay B+ -> D*+ pi0,
based on a data sample of 657 million BBbar pairs collected at the Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric energy e+ e- collider.
We find no significant signal and set an upper limit of Br(B+ -> D*+ pi0) < 3.6
x 10^-6 at the 90% confidence level. This limit can be used to constrain the
ratio between suppressed and favored B -> D* pi decay amplitudes, r < 0.051, at
the 90% confidence level.Comment: 5pages, 2figures, submitted to PRL (v1); PRL published version (v2:
minor corrections in the text
Study of charmonia in four-meson final states produced in two-photon collisions
We report measurements of charmonia produced in two-photon collisions and
decaying to four-meson final states, where the meson is either a charged pion
or a charged kaon. The analysis is based on a 395fb^{-1} data sample
accumulated with the Belle detector at the KEKB electron-positron collider. We
observe signals for the three C-even charmonia eta_c(1S), chi_{c0}(1P) and
chi_{c2}(1P) in the pi^+pi^-pi^+pi^-, K^+K^-pi^+pi^- and K^+K^-K^+K^- decay
modes. No clear signals for eta_c(2S) production are found in these decay
modes. We have also studied resonant structures in charmonium decays to
two-body intermediate meson resonances. We report the products of the
two-photon decay width and the branching fractions, Gamma_{gamma gamma}B, for
each of the charmonium decay modes.Comment: 22 pages, 12 figure
Moments of the Hadronic Invariant Mass Spectrum in B --> X_c l nu Decays at Belle
We present a measurement of the hadronic invariant mass squared (M^2_X)
spectrum in charmed semileptonic B meson decays B --> X_c l nu based on 140
fb^-1 of Belle data collected near the Y(4S) resonance. We determine the first,
the second central and the second non-central moments of this spectrum for
lepton energy thresholds ranging between 0.7 and 1.9 GeV. Full correlations
between these measurements are evaluated.Comment: published version of the paper (one figure added, minor changes in
the text); 16 pages, 3 figures, 10 table
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