59 research outputs found
Full analysis of general non-standard tbW couplings
Possible non-standard couplings which could contribute to the t -> b W
process are studied based on the effective-Lagrangian approach. The
corresponding effective Lagrangian consists of four kinds of dimension-6
effective operators, each of which has an independent coupling constant. In
this analysis, all those couplings are treated as complex numbers and
constraints on them are estimated by using recent experimental data from the
LHC. We point out that the resultant constraints on those couplings are still
not that strong because contributions from some couplings can work oppositely
with each other.Comment: One comment and two related references added. Final version to appear
in Phys.Lett.
Probing Polarized Gluon Distributions through Charmed Hadron Production in Polarized pp Collisions at BNL--RHIC Energy
In order to extract information about behavior of polarized gluons in the
nucleon, charmed hadron productions, i.e. D* meson and Lambda_c baryon
productions, are studied in polarized pp reactions at BNL-RHIC energy. For
these processes, the spin correlation asymmetry D_{LL} between the target
proton and the produced charmed hadron, and its statistical sensitivity delta
D_{LL} are calculated. From analyses on these processes, we found that the
pseudo-rapidity distribution of D_{LL} in the limited transverse momentum
region is quite effective for distinguishing the model of polarized gluons as
well as the model of spin-dependent fragmentation functions.Comment: 1+14 pages, 14 figures, added references and comments, To appear in
Int. Journal of Modern Phys.
Final charged-lepton angular distribution and possible anomalous top-quark couplings in p p -> t tbar X -> l^+ X'
Possible anomalous (or nonstandard) top-quark interactions with the gluon and
those with the W boson induced by SU(3) x SU(2) x U(1) gauge-invariant
dimension-6 effective operators are studied in p p -> t tbar X -> l^+ X' (l=e
or mu) at the Large Hadron Collider (LHC). The final charged-lepton (l^+)
angular distribution is first computed for nonvanishing nonstandard top-gluon
and top-W couplings with a cut on its transverse momentum. The
optimal-observable procedure is then applied to this distribution in order to
estimate the expected statistical uncertainties in measurements of those
couplings that contribute to this process in the leading order.Comment: latex_2e, 14 pages, 4 eps figure
Charmed Hadron Production in Polarized pp Collisions
To extract information about polarized gluons in the proton, production of
charmed hadrons, in particular, \Lambda_c^+ baryon in pp collisions was
studied. We calculated the transverse momentum distribution and the
pseudo-rapidity distribution of the spin correlation asymmetry A_{LL} between
the initial proton and the produced \Lambda_c^+. Those statistical
sensitivities were also calculated under the condition of RHIC experiment. We
found that the pseudo-rapidity distribution of A_{LL} is promising for testing
the model of polarized gluons in the proton and also the spin-dependent
fragmentation model of a charm quark decaying into \Lambda_c^+ baryon.Comment: 1+6 pages, Latex2e, 4 eps figures, Talk given at SPIN 2002,
Brookhaven National Laboratory, September 9-13, 2002, To appear in the
Proceeding
Exploring anomalous top interactions via the final lepton in ttbar productions/decays at hadron colliders
We study momentum distributions of the final-state charged lepton in ppbar/pp
--> ttbar --> l^+ X (l=e or mu) at hadron colliders, i.e., Tevatron and Large
Hadron Collider (LHC) in order to explore possible new-physics effects in the
top-quark sector. Assuming general model-independent ttbar g + ttbar gg and tbW
interactions beyond the standard model, we first derive analytical formulas for
the corresponding parton-parton processes. We then compute the lepton angular,
energy and transverse-momentum distributions in ppbar/pp collisions to clarify
how they are affected by those anomalous couplings.Comment: Journal information added. Title slightly changed in the published
version (top interaction --> top-quark interaction). One typo in
eqs.(15)-(19) corrected (dE_l c_l --> dE_l dc_l
Lambda_c^+ production in polarized pp scattering and polarized gluon distribution
To extract information about the polarized gluon distribution, \dg, in the
nucleons, we propose Lambda_c^+ productions in polarized pp scattering, p +
\vec{p} \to \vec{Lambda_c^+} + X, which will be observed at RHIC experiment
starting soon. For this process, we have calculated the spin correlation
differential cross section, d\Delta \sigma/d\pt, and the spin correlation
asymmetry defined by \A_ll \equiv [ d \Delta \sigma / d \pt ] / [ d \sigma /
d\pt ]. We have found that the \A_ll is sensitive to the polarized gluon
distribution in the nucleon and thus the process is promising for testing
\Delta G(x,Q^2).Comment: 10 pages, LaTex2e, 6 figures.(V2: typos fixed. Conclusions unchanged
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