298 research outputs found
Probing neutral top-pion via a flavor-changing process
In the framework of topcolor-assisted-technicolor model(TC2), we study a
flavor-changing neutral top-pion production process . The study shows that there exists a resonance effect
which can enhance the cross section up to a few fb even tens fb. For a yearly
luminosity 100 at future linear colliders, there might be hundreds
even thousands events to be produced. On the other hand, the background of such
flavor-changing process is very clean due to the GIM mechanism in SM . With
such sufficient events and clean background, neutral toppion could be detected
at future linear colliders with high center of energy and luminosity. Our study
provides a possible way to test TC2 model.Comment: 10 pages, 4 figures,has been accepted by Phys.Rev.
The productions of the top-pions and top-Higgs associated with the charm quark at the hadron colliders
In the topcolor-assistant technicolor (TC2) model, the typical physical
particles, top-pions and top-Higgs, are predicted and the existence of these
particles could be regarded as the robust evidence of the model. These
particles are accessible at the Tevatron and LHC, and furthermore the
flavor-changing(FC) feature of the TC2 model can provide us a unique chance to
probe them. In this paper, we study some interesting FC production processes of
top-pions and top-Higgs at the Tevatron and LHC, i.e., and
productions. We find that the light charged top-pions
are not favorable by the Tevatron experiments and the Tevatron has a little
capability to probe neutral top-pion and top-Higgs via these FC production
processes. At the LHC, however, the cross section can reach the level of
pb for production and fb for
production. So one can expect that enough signals could be
produced at the LHC experiments. Furthermore, the SM background should be clean
due to the FC feature of the processes and the FC decay modes can provide us the typical signal to
detect the top-pions and top-Higgs. Therefore, it is hopeful to find the signal
of top-pions and top-Higgs with the running of the LHC via these FC processes.Comment: 12 pages, 6 figure
Lepton flavor violation decays in the topcolor-assisted technicolor model and the littlest Higgs model with parity
The new particles predicted by the topcolor-assisted technicolor ()
model and the littlest Higgs model with T-parity (called model) can
induce the lepton flavor violation () couplings at tree level or one loop
level, which might generate large contributions to some processes. Taking
into account the constraints of the experimental data on the relevant free
parameters, we calculate the branching ratios of the decay processes
with = , and
in the context of these two kinds of new physics models. We find
that the model and the model can indeed produce significant
contributions to some of these decay processes.Comment: 24 pages, 7 figure
The rare top quark decays in the topcolor-assisted technicolor model
We consider the rare top quark decays in the framework of topcolor-assisted
technicolor (TC2) model. We find that the contributions of top-pions and
top-Higgs predicted by the TC2 model can enhance the SM branching ratios by as
much as 6-9 orders of magnitude. i.e., in the most case, the orders of
magnitude of branching ratios are , , . With the reasonable values of the
parameters in TC2 model, such rare top quark decays may be testable in the
future experiments. So, rare top quark decays provide us a unique way to test
TC2 model.Comment: 14 pages, 4 figure
Search for Top Quark FCNC Couplings in Z' Models at the LHC and CLIC
The top quark is the heaviest particle to date discovered, with a mass close
to the electroweak symmetry breaking scale. It is expected that the top quark
would be sensitive to the new physics at the TeV scale. One of the most
important aspects of the top quark physics can be the investigation of the
possible anomalous couplings. Here, we study the top quark flavor changing
neutral current (FCNC) couplings via the extra gauge boson Z' at the Large
Hadron Collider (LHC) and the Compact Linear Collider (CLIC) energies. We
calculate the total cross sections for the signal and the corresponding
Standard Model (SM) background processes. For an FCNC mixing parameter x=0.2
and the sequential Z' mass of 1 TeV, we find the single top quark FCNC
production cross sections 0.38(1.76) fb at the LHC with sqrt{s_{pp}}=7(14) TeV,
respectively. For the resonance production of sequential Z' boson and decays to
single top quark at the Compact Linear Collider (CLIC) energies, including the
initial state radiation and beamstrahlung effects, we find the cross section
27.96(0.91) fb at sqrt{s_{e^{+}e^{-}}}=1(3) TeV, respectively. We make the
analysis to investigate the parameter space (mixing-mass) through various Z'
models. It is shown that the results benefit from the flavor tagging.Comment: 20 pages, 17 figures, 6 table
Probing Topcolor-Assisted Technicolor from Top-Charm Associated Production at LHC
We propose to probe the topcolor-assisted technicolor (TC2) model from the
top-charm associated productions at the LHC, which are highly suppressed in the
Standard Model. Due to the flavor-changing couplings of the top quark with the
scalars (top-pions and top-Higgs) in TC2 model, the top-charm associated
productions can occur via both the s-channel and t-channel parton processes by
exchanging a scalar field at the LHC. We examined these processes through Monte
Carlo simulation and found that they can reach the observable level at the LHC
in quite a large part of the parameter space of the TC2 model.Comment: Version to appear in PRD (Rapid Communication
Density pertubation of unparticle dark matter in the flat Universe
The unparticle has been suggested as a candidate of dark matter. We
investigated the growth rate of the density perturbation for the unparticle
dark matter in the flat Universe. First, we consider the model in which
unparticle is the sole dark matter and find that the growth factor can be
approximated well by , where is
the equation of state of unparticle. Our results show that the presence of
modifies the behavior of the growth factor . For the second model
where unparticle co-exists with cold dark matter, the growth factor has a new
approximation and
is a function of . Thus the growth factor of unparticle is quite
different from that of usual dark matter. These information can help us know
more about unparticle and the early evolution of the Universe.Comment: 6pages, 4 figures, accepted for publication in Eur. Phys. J.
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
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