8,430 research outputs found
Study of sequential semileptonic decays of b hadrons produced at the Tevatron
We present a study of rates and kinematical properties of lepton pairs
contained in central jets with transverse energy E_T > 15 GeV that are produced
at the Fermilab Tevatron collider. We compare the data to a QCD prediction
based on the HERWIG and QQ Monte Carlo generator programs.We find that the data
are poorly described by the simulation, in which sequential semileptonic decays
of single b quarks (b --> l c X with c --> l s X) are the major source of such
lepton pairs.Comment: 25 pages, 8 figures. Some typos were fixed in the text and
bibliography. Submitted to Phys. Rev.
Has the anomalous single production of the fourth SM family quarks decaying into light Higgs boson been observed by CDF?
Superjet events observed by the CDF Collaboration are interpreted as
anomalous single production of the fourth SM family u_4 quark, decaying into a
new light scalar particle. The specific predictions of the proposed mechanism
are discussed.Comment: 5 pages, 1 tabl
Phenomenological study of the atypical heavy flavor production observed at the Fermilab Tevatron
We address known discrepancies between the heavy flavor properties of jets
produced at the Tevatron collider and the prediction of conventional-QCD
simulations. In this study, we entertain the possibility that these effects are
real and due to new physics. We show that all anomalies can be simultaneously
fitted by postulating the additional pair production of light bottom squarks
with a 100% semileptonic branching fraction.Comment: 30 pages, 13 figures, 3 tables. Submitted to Phys. Rev.
Spectator Effects in Inclusive Decays of Beauty Hadrons
We present a model-independent study of spectator effects, which are
responsible for the lifetime differences between beauty hadrons. These effects
can be parametrized in terms of hadronic matrix elements of four four-quark
operators. For mesons, the coefficients of the non-factorizable operators
turn out to be much larger than those of the factorizable ones, limiting
considerably the usefulness of the vacuum insertion approximation.
Non-factorizable contributions to the lifetime ratio
could naturally be of order 10--20%, and not even the sign of these
contributions can be predicted at present. In the case of the
baryon, heavy-quark symmetry is used to reduce the number of independent matrix
elements from four to two. In order to explain the large deviation from unity
in the experimental result for , it is necessary
that these baryon matrix elements be much larger than those estimated in quark
models. We have also reexamined the theoretical predictions for the
semileptonic branching ratio of mesons and charm counting, finding that,
given the present theoretical and experimental uncertainties, there is no
significant discrepancy with experiment.Comment: 32 pages, 5 postscript figures included, revised version to appear in
Nuclear Physics
Anomalous single production of the fourth SM family quarks at Tevatron
Possible single productions of fourth family u_{4} and d_{4} quarks via
anomalous q_{4}qV interactions at Tevatron are studied. Signature of such
processes are discussed and compared with the recent results from Tevatron.Comment: 6 pages, 1 figure, 4 table
Spectator effects in semileptonic decay of charmed baryons
It is shown that the absolute rate of the semileptonic decays of the
baryons can be as much as two times higher than the semileptonic decay rate of
due to the Pauli interference of the strange quark. This
interference effect is still larger in the semileptonic decay rate of
. An experimental measurement of the difference of these rates would
thus provide an important piece of information on the spectator effects in
decays of hadrons containing a heavy quark.Comment: 8 pages in LaTeX. Final journal version. To appear in Phys. Lett.
Present Limits on the Precision of SM Predictions for Jet Energies
We investigate the impact of theoretical uncertainties on the accuracy of
measurements involving hadronic jets. The analysis is performed using events
with a Z boson and a single jet observed in collisions at
= 1.96 TeV in 4.6 of data from the Collider Detector at
Fermilab (CDF). The transverse momenta (\pt) of the jet and the boson should
balance each other due to momentum conservation in the plane transverse to the
direction of the and beams. We evaluate the dependence of the
measured \pt-balance on theoretical uncertainties associated with initial and
final state radiation, choice of renormalization and factorization scales,
parton distribution functions, jet-parton matching, calculations of matrix
elements, and parton showering. We find that the uncertainty caused by parton
showering at large angles is the largest amongst the listed uncertainties. The
proposed method can be re-applied at the LHC experiments to investigate and
evaluate the uncertainties on the predicted jet energies. The distributions
produced at the CDF environment are intended for comparison to those from
modern event generators and new tunes of parton showering.Comment: Submitted to Nucl. Instr. and Meth.
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