301 research outputs found
The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model
Recently there has been much interest in the tauonic semileptonic meson
decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found
larger rates than what is predicted by the Standard Model. We analyze the
corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) +
antinu_tau with particular emphasis on the lepton helicity flip and scalar
contributions which vanish for zero lepton masses. We calculate the total rate,
differential decay distributions, the longitudinal and transverse polarization
of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side
forward-backward asymmetries. The nonvanishing polarization of the daughter
baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay
Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two
final state decay planes which we specify. We provide numerical results on
these observables using results of the covariant confined quark model. We find
large lepton mass effects in the q2-spectra and in the polarization
observables.Comment: 26 page
Four-quark structure of Zc(3900), Z(4430) and Xb(5568) states
We examine the four-quark structure of the recently discovered charged
, , and states. We calculate the widths of the
strong decays (, ,
), (), and
within a covariant quark model previously developed by us.
We find that the tetraquark-type current widely used in the literature for the
leads to a significant suppression of the and modes. Contrary to this a molecular-type current provides an
enhancement by a factor of 6-7 for the modes compared with the
, modes in agreement with recent
experimental data from the BESIII Collaboration. In case of the state
we test a sensitivity of the ratio of the
and decay rates to a choice of the size parameter
of the . Using upper constraint for the sum of
these two modes deduced from the LHCb Collaboration data we find that
varies from 4.64 to 4.08 when changes from 2.2 to 3.2 GeV.
Also we make the prediction for the decay rate.Comment: 14 page
Polarization effects in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi(-> l+ l-) in the covariant confined quark model
We calculate the invariant and helicity amplitudes for the nonleptonic decay
Lambda_b -> Lambda + J/psi, psi(2S) in the covariant confined quark model. We
discuss joint angular decay distributions in the cascade decay Lambda_b ->
Lambda(-> p pi-) + J/psi, psi(2S) (-> l+ l-) and calculate some of the
asymmetry parameters that characterize the joint angular decay distribution. We
confirm expectations from the naive quark model that the transitions into the
lambda_Lambda=1/2 helicity states of the daughter baryon Lambda are strongly
suppressed leading to a near maximal negative polarization of the Lambda. For
the same reason the azimuthal correlation between the two decay planes spanned
by (p pi-) and (l+ l-) is negligibly small. We provide form factor results for
the whole accessible q2-range. Our results are close to lattice results at
minimum recoil and light-cone sum rule results at maximum recoil. A new feature
of our analysis is that we include lepton mass effects in the calculation which
allows us to also describe the cascade decay Lambda_b -> Lambda(-> p pi-) +
psi(2S)(-> tau+ tau-).Comment: 18 page
Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders
The most general Lorentz-invariant decay-density-matrix for , or for , is expressed in terms
of eight helicity parameters. The parameters are physically defined in terms of
partial-width-intensities for polarized-final-states in decay.
The parameters are the partial width, the quark's chirality parameter
, the polarimetry parameter , a "pre-SSB" test parameter
, and four - interference parameters , ,
, which test for violation. They can be
used to test for non-CKM-type CP violation, anomalous 's, top
weak magnetism, weak electricity, and second-class currents. By stage-two
spin-correlation techniques, percent level statistical uncertainites are
typical for measurements at the Tevatron, and several mill level uncertainites
are typical at the LHC.Comment: Minor clarifications. Expression for r_{+-} corrected. 19 pages LaTex
+ Tables + 1 Figur
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