372 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
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
A heavy quark effective field lagrangian keeping particle and antiparticle mixed sectors
We derive a tree-level heavy quark effective Lagrangian keeping
particle-antiparticle mixed sectors allowing for heavy quark-antiquark pair
annihilation and creation. However, when removing the unwanted degrees of
freedom from the effective Lagrangian one has to be careful in using the
classical equations of motion obeyed by the effective fields in order to get a
convergent expansion on the reciprocal of the heavy quark mass. Then the
application of the effective theory to such hard processes should be sensible
for special kinematic regimes as for example heavy quark pair production near
threshold.Comment: LaTeX, 14 pages, 1 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
Indirect detection of light neutralino dark matter in the NMSSM
We explore the prospects for indirect detection of neutralino dark matter in
supersymmetric models with an extended Higgs sector (NMSSM). We compute, for
the first time, one-loop amplitudes for NMSSM neutralino pair annihilation into
two photons and two gluons, and point out that extra diagrams (with respect to
the MSSM), featuring a potentially light CP-odd Higgs boson exchange, can
strongly enhance these radiative modes. Expected signals in neutrino telescopes
due to the annihilation of relic neutralinos in the Sun and in the Earth are
evaluated, as well as the prospects of detection of a neutralino annihilation
signal in space-based gamma-ray, antiproton and positron search experiments,
and at low-energy antideuteron searches. We find that in the low mass regime
the signals from capture in the Earth are enhanced compared to the MSSM, and
that NMSSM neutralinos have a remote possibility of affecting solar dynamics.
Also, antimatter experiments are an excellent probe of galactic NMSSM dark
matter. We also find enhanced two photon decay modes that make the possibility
of the detection of a monochromatic gamma-ray line within the NMSSM more
promising than in the MSSM.Comment: 26 pages, 12 figures. Updated references and corrected discussion of
Upsilon decay
Two-particle angular correlations in the search for new physics at future colliders
The analysis of angular particle correlations can yield valuable insights
into the initial state of matter in high-energy collisions, thereby potentially
revealing the existence of Beyond the Standard Model scenarios such as Hidden
Valley (HV). In this study, we focus on a QCD-like hidden sector with
relatively massive HV quarks (~GeV) which might enlarge and
strengthen azimuthal correlations of final-state SM hadrons. In particular, we
study the formation and possible observation of \textit{ridge-like} structures
in the angular two-particle correlation function at future colliders,
with a much cleaner environment than in hadron colliders, such as the LHC.Comment: Talk presented at the International Workshop on Future Linear
Colliders (LCWS 2023), 15-19 May 2023. C23-05-15.
High- production as signals for Double Parton scattering at hadron colliders
We present an analysis of the \psi\psi production from double parton (DP)
sacttering and single parton (SP) scattering in the large p_T region via
color-octet gluon fragmentation. We find that at the Tevatron the DP \psi\psi
production is at the edge of the detectability at present, and at the LHC the
DP cross section will dominate over the SP cross section in the lower p_T(min)
region (i.e., p_T(min)<7GeV). We also conclude that the color-octet mechanism
is of crucial importance to the double j/psi production at high energy hadron
colliders.Comment: Revtex, 12 pages, 3 Postscript figure
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