12 research outputs found
Signals from R-parity violating top quark decays at LHC
We evaluate the potential of the CERN LHC collider to observe rare decays of
the top quark in channels involving R-parity violating (RPV) interactions. We
stress the importance of calculating top quark production and decay
simultaneously as a true 2->4 process.
The process of tt-bar pair production followed by RPV decay of one of the top
quarks is analyzed with fast detector simulation. We show that intermediate
supersymmetric particles can be observed as resonances even if they are heavier
than the top quark due to the significant off-shell top-quark mass effects. The
approach where the top quark is produced on-mass-shell and then decays into 2-
or 3-body final state would in general lead to incorrect kinematical
distributions and rates. The rates of the 2 -> 4 process with top quark
production and RPV 3-body decay depend on the total width of the heavy
intermediate sfermion which could,therefore, be measured indirectly.
We find that the LHC collider offers a unique potential to study rare top
quark decays in the framework of supersymmetry with broken R-parity for
branching fractions of RPV top decays as low as 10^{-6}Comment: 23 pages, 22 figure
The Distribution of Constituent Charm Quarks in the Hadron
Using a statistical approach in the framework of non-covariant perturbation
theory the distributions for light and charmed quarks in the hadron have been
derived, taking into account the mass of the charmed quark. The parameters of
the model have been extracted from the comparison with NA3 data on
hadroproduction of J/psi particles. A reanalysis of the EMC data on charm
production in muon-nucleon scattering has been performed. It has been found in
comparison with the conventional source of charmed quarks from photon-gluon
fusion, that the EMC data indicate the presence of an additional contribution
from deep-inelastic scattering on charmed quarks at large x. The resulting
admixture of the Fock states, containing charmed quarks in the decomposition of
the proton wave function is of the order of 1%. The approach presented for the
excitation of the Fock states with charmed quarks can also be applied to states
with beauty quarks as well as to the hadronic component of the virtual photon
(resolved photon component).Comment: 23 pages, 4 PostScript figures, Latex2e. In revised version in
comparison with the original one all (?) mistypings have been corrected, one
more thank has been added and the comparison of the pion and the proton J/psi
production is described in more detai
Rate Measurement of and Constraints on Mixing
We present an observation and rate measurement of the decay D0 -> K+pi-pi0
produced in 9/fb of e+e- collisions near the Upsilon(4S) resonance. The signal
is inconsistent with an upward fluctuation of the background by 4.9 standard
deviations. We measured the rate of D0 -> K+pi-pi0 normalized to the rate of
D0bar -> K+pi-pi0 to be 0.0043 +0.0011 -0.0010 (stat) +/- 0.0007 (syst). This
decay can be produced by doubly-Cabibbo-suppressed decays or by the D0 evolving
into a D0bar through mixing, followed by a Cabibbo-favored decay to K+pi-pi0.
We also found the CP asymmetry A=(8 +25 -22)% to be consistent with zero.Comment: 10 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
A simple event weighting technique for optimizing the measurement of the forward-backward asymmetry of Drell-Yan dilepton pairs at hadron colliders
We describe a simple technique for optimizing the extraction of the
forward-backward asymmetry () of Drell-Yan lepton pairs (,) produced in and collisions at hadron colliders.
The method employs simple event weights which are functions of the rapidity and
decay angle of the lepton pair. It yields the best estimate of the
acceptance corrected parton level () forward backward asymmetry as a
function of final state dilepton mass (). Typically, when
compared to the simple count method, the technique reduces the statistical
errors by 20% for , and 40% for collisions, respectively. The
technique can be used to search for new high mass and large width Z' bosons
which may be best detected through the observation of deviations from the
Standard Model expectation for the forward-backward asymmetry. In addition, we
derive expressions for the QCD angular coefficients for Drell-Yan events.Comment: 13 pages, 1 figure, 4 tables. Accepted for publication in EPJ