401 research outputs found
Prospects for the extraction of from $B_c\ {\to}\ J/\psi\ {\mu}^+\ {\nu}$ decays at LHC
We discuss the possibility of extracting from the future
measurement at LHC of the decay
rate followed by the leptonic decay . We
examine in detail the influence of the measurement of the muons' momenta and
vertex reconstruction in the final uncertainty of , as well
as the required theoretical inputs at both the production and weak decay level,
and their reliability in this regard. We stress the relevance of a rigorous
description of the fragmentation contributions to inclusive production at large
transverse momentum of heavy quarkonia in collisions.Comment: Latex using psfig.sty, 19 pages including 9 uuencoded. Replaced
because of a few missprint error
Bottomonium spectroscopy with mixing of eta_b states and a light CP-odd Higgs
The mass of the eta_b(1S), measured recently by BABAR, is significantly lower
than expected from QCD predictions for the Upsilon(1S) - eta_b(1S) hyperfine
splitting. We suggest that the observed eta_b(1S) mass is shifted downwards due
to a mixing with a CP-odd Higgs scalar A with a mass m_A in the range 9.4 -
10.5 GeV compatible with LEP, CLEO and BABAR constraints. We determine the
resulting predictions for the spectrum of the eta_b(nS) - A system and the
branching ratios into tau^+ tau^- as functions of m_A.Comment: 4 pages, 4 figures, submitted to PRL, misprint correcte
Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation
In the heavy quark limit, a doubly heavy baryon is regarded as composed of a
heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations
for the heavy diquarks and the doubly heavy baryons, respectively, to leading
order in a expansion. The BS equations are solved numerically under
the covariant instantaneous approximation with the kernels containing scalar
confinement and one-gluon-exchange terms. The masses for the heavy diquarks and
the doubly heavy baryons are obtained and the non-leptonic decay widths for the
doubly heavy baryons emitting a pseudo-scalar meson are calculated within the
model.Comment: Corrections to the text, two references added, version accepted for
publication in Physical Review
Power scaling rules for charmonia production and HQEFT
We discuss the power scaling rules along the lines of a complete Heavy Quark
Effective Field Theory (HQEFT) for the description of heavy quarkonium
production through a color-octet mechanism. To this end, we firstly derive a
tree-level heavy quark effective Lagrangian keeping both particle-antiparticle
mixed sectors allowing for heavy quark-antiquark pair annihilation and
creation, but describing only low-energy modes around the heavy quark mass.
Then we show the consistency of using HQEFT fields in constructing four-fermion
local operators a la NRQCD, to be identified with standard color-octet matrix
elements. We analyze some numerical values extracted from charmonia production
by different authors and their hierarchy in the light of HQEFT.Comment: LaTeX, 19 pages, 3 EPS figure
Leptonic universality breaking in Upsilon decays as a probe of new physics
In this work we examine the possible existence of new physics beyond the
standard model which could modify the branching fractions of the leptonic
(mainly tauonic) decays of bottomonium vector resonances below the
threshold. The decay width is factorized as the product of two pieces: a) the
probability of an intermediate pseudoscalar color-singlet state
(coupling to the dominant Fock state of the Upsilon via a magnetic dipole
transition) and a soft (undetected) photon; b) the annihilation width of the
pair into two leptons, mediated by a non-standard CP-odd Higgs boson
of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in
the partial width. The process would be unwittingly ascribed to the
leptonic channel thereby (slightly) breaking lepton universality. A possible
mixing of the pseudoscalar Higgs and bottomonium resonances is also considered.
Finally, several experimental signatures to check out the validity of the
conjecture are discussed.Comment: LaTeX, 22 pages, 2 EPS figure
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