92 research outputs found
Single decay-lepton angular distributions in polarized e+e- --> t tbar and simple angular asymmetries as a measure of CP-violating top dipole couplings
In the presence of an electric dipole coupling of t-tbar to a photon, and an
analogous "weak" dipole coupling to the Z, CP violation in the process e+e- -->
t tbar results in modified polarization of the top and anti-top. This
polarization can be analyzed by studying the angular distributions of decay
charged leptons when the top or anti-top decays leptonically. Analytic
expressions are presented for these distributions when either t or tbar decays
leptonically, including O(alpha_s) QCD corrections in the soft-gluon
approximation. The angular distributions are insensitive to anomalous
interactions in top decay. Two types of simple CP-violating polar-angle
asymmetries and two azimuthal asymmetries, which do not need the full
reconstruction of the t or tbar, are studied. Independent 90% CL limits that
may be obtained on the real and imaginary parts of the electric and weak dipole
couplings at a linear collider operating at sqrt{s}=500 GeV with integrated
luminosity 500 fb^{-1} and also at sqrt{s}=1000 GeV with integrated luminosity
1000 fb^{-1} have been evaluated. The effect of longitudinal electron and/or
positron beam polarizations has been included.Comment: 26 pages, latex, figures included as latex files, version appearing
in Pramana - Journal of Physics, minor corrections and note added in proo
Effect of age, sex and gonadal hormone on brain tissue respiration of albino Rats
This article does not have an abstract
Influence of androgens on urinary excretion of 17-hydroxy steroids and amino acids in male rats
Studies were carried out in male albino rats on the influence of age, castration and substitution by testosterone on urinary amino acid excretion pattern and excretion of 17-hydroxy corticoids in the urine. While age had no effect on amino acid excretion, corticoid activity decreased with age.
Castration caused increased excretion of amino acid and slight increase in corticoid excretion, testosterone produced nitrogen retention and decrease in corticosteroid excretion
Effect of age, sex and gonadal hormone on alkaline phosphatase activity of Rat brain tissue
This article does not have an abstract
Validity of the equivalent-photon approximation for the production of massive spin-1 particles
We point out that the equivalent-photon approximation (EPA) for processes with massive spin-1 particles in the final state would have validity in a more restricted kinematic domain than for processes where it is commonly applied, viz., those with spin-½ or spin-0 particles in the final state. We obtain the criterion for the validity of EPA for the two-photon production of a pair of charged, massive, point-like spin-1 particles V ±, each of mass M and with a standard magnetic moment (κ=1). In a process in which one of the photons is real and the other virtual with four-momentum q, the condition for the validity of EPA is |q 2|« M 2, in addition to the usual condition |q 2|«W 2,W being the V+ V- invariant mass. In a process in which both photons are virtual (with four-moment aq and q'), our condition is |q 2||q'2|W 4« 16M8, in addition to |q 2| «M2, |q'2| «M 2 and |q 2| «W2, |q'2| «W 2. Even when these extra conditions permitting the use of EPA are not fulfilled, convenient approximate expressions may still be obtained assuming merely |q2| «W 2 and |q'2| «W 2. We also discuss how the extra conditions are altered when the vector bosons are incorporated in a spontaneously broken gauge theory. Examples of W boson production in Weinberg-Salam model are considered for which the condition |q2||q'2|W 4 « 16M8 is shown to be removed
Electromagnetic Interaction of Massive Spin-3 State from String Theory
In the given work we study an interaction of second massive state of an open
boson string with the constant electromagnetic field. This state contains
massive fields with spins 3 and 1. Using the method of an open string BRST
quantization, we receive gauge-invariant lagrangian, describing the
electromagnetic interaction of these fields. From the explicit view of
transformations and lagrangian it follows that the presence of external
constant e/m field leads to the mixing of the given level states. Most likely
that the presence of the external field will lead to the mixing of the states
at other mass string levels as well.Comment: 17 pages, LaTeX, no figure
QCD corrections to decay-lepton polar and azimuthal angular distributions in e+e- -> t tbar in the soft-gluon approximation
QCD corrections to order alpha_s in the soft-gluon approximation to angular
distributions of decay charged leptons in the process e+e- -> t tbar followed
by semileptonic decay of t or tbar, are obtained in the e+e- centre-of-mass
frame. As compared to distributions in the top rest frame, these have the
advantage that they would allow direct comparison with experiment without the
need to reconstruct the top rest frame. The results also do not depend on the
choice of a spin quantization axis for t or tbar. Analytic expression for the
triple distribution in the polar angle of t and polar and azimuthal angles of
the lepton is obtained. Analytic expression is also derived for the
distribution in the charged-lepton polar angle. Numerical values are discussed
for total c.m. energies of 400 GeV, 800 GeV and 1500 GeV.Comment: 21 pages, Latex, 6 figures included in the submission. To appear in
Pramana - Journal of Physics; expanded version of hep-ph/0011321, v
On measurement of top polarization as a probe of production mechanisms at the LHC
In this note we demonstrate the use of top polarization in the study of resonances at the LHC, in the possible case where the dynamics implies
a non-zero top polarization. As a probe of top polarization we construct an
asymmetry in the decay-lepton azimuthal angle distribution (corresponding to
the sign of ) in the laboratory. The asymmetry is non-vanishing
even for a symmetric collider like the LHC, where a positive axis is not
uniquely defined. The angular distribution of the leptons has the advantage of
being a faithful top-spin analyzer, unaffected by possible anomalous
couplings, to linear order. We study, for purposes of demonstration, the case
of a as might exist in the little Higgs models. We identify kinematic cuts
which ensure that our asymmetry reflects the polarization in sign and
magnitude. We investigate possibilities at the LHC with two energy options:
TeV and TeV, as well as at the Tevatron. At the
LHC the model predicts net top quark polarization of the order of a few per
cent for GeV, being as high as for a smaller mass
of the of GeV and for the largest allowed coupling in the model, the
values being higher for the TeV option. These polarizations translate to a
deviation from the standard-model value of azimuthal asymmetry of up to about
() for () TeV LHC, whereas for the Tevatron, values as high as
are attained. For the TeV LHC with an integrated luminosity of 10
fb, these numbers translate into a sensitivity over a large
part of the range GeV.Comment: 28 page, LaTeX, requires JHEP style file, 12 figures. Typos corrected
and references adde
Study of CP Property of the Higgs at a Photon Collider using
We study possible effects of CP violation in the Higgs sector on
production at a -collider. These studies are performed in a
model-independent way in terms of six form-factors which
parametrize the CP mixing in the Higgs sector, and a strategy for their
determination is developed. We observe that the angular distribution of the
decay lepton from produced in this process is independent of any CP
violation in the vertex and hence best suited for studying CP mixing in
the Higgs sector. Analytical expressions are obtained for the angular
distribution of leptons in the c.m. frame of the two colliding photons for a
general polarization state of the incoming photons. We construct combined
asymmetries in the initial state lepton (photon) polarization and the final
state lepton charge. They involve CP even ('s) and odd ('s) combinations
of the mixing parameters. We study limits up to which the values of and
, with only two of them allowed to vary at a time, can be probed by
measurements of these asymmetries, using circularly polarized photons. We use
the numerical values of the asymmetries predicted by various models to
discriminate among them. We show that this method can be sensitive to the
loop-induced CP violation in the Higgs sector in the MSSM.Comment: 15 pages, 9 figures added one referenc
Top-quark spin correlation at Linear Colliders with anomalous couplings
We investigate the feasibility of probing anomalous top-quark couplings of
, , and in terms of an effective
Lagrangian with dimension-six operators at future linear colliders
with a c. m. energy GeV. We first examine the
constraints on these anomalous couplings from the data at LEP
I and from unitarity considerations. We then consider in detail the effects of
anomalous couplings on spin correlations in the top-pair production
and decay with three spin bases: the helicity, beamline and off-diagonal bases.
Our results show that the polarized beams are more suitable for exploring the
effects of different new operators. For polarized beams, the helicity basis
yields the best sensitivity.Comment: 23 pages, 10 figures, references adde
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