1,894 research outputs found
Strong Coupling Constant from Scaling Violations in Fragmentation Functions
We present a new determination of the strong coupling constant alpha_s
through the scaling violations in the fragmentation functions for charged
pions, charged kaons, and protons. In our fit we include the latest e+e-
annihilation data from CERN LEP1 and SLAC SLC on the Z-boson resonance and
older, yet very precise data from SLAC PEP at center-of-mass energy sqrt(s)=29
GeV. A new world average of alpha_s is given.Comment: 10 pages, 3 eps figue
Lepton flavor conserving Z -> l^+ l^-$ decays in the general two Higgs doublet model
We calculate the new physics effects to the branching ratios of the lepton
flavor conserving decays Z -> l^+ l^- in the framework of the general two Higgs
Doublet model. We predict the upper limits for the couplings
|\bar{\xi}^{D}_{N,\mu\tau}| and |\bar{\xi}^{D}_{N,\tau\tau}| as 3\times 10^2
GeV and 1\times 10^2 GeV, respectively.Comment: 9 pages, 3 figure
The spin structure of the Lambda hyperon in quenched lattice QCD
It has been suggested to use the production of Lambda hyperons for
investigating the nucleon spin structure. The viability of this idea depends
crucially on the spin structure of the Lambda. Using nonperturbatively O(a)
improved Wilson fermions in the quenched approximation we have studied matrix
elements of two-quark operators in the Lambda. We present results for the axial
vector current, which give us the contributions of the u, d, and s quarks to
the Lambda spin.Comment: Lattice2001(matrixelement), 3 pages, 2 figure
An Upper Bound on the Higgs Boson Mass from a Positivity Condition on the Mass Matrix
We impose the condition that the eigenvalues of the mass matrix in the
shifted Lagrangian density be positive at \phi=\phi_{0}, the vacuum expectation
value of the scalar field. Using the one-loop effective potential of the
standard model, this condition leads to an upper bound on the Higgs boson mass
m_{H}: m_{H}<230GeV, for a top quark mass of 175GeV.Comment: LaTex, 5 page
A Note on the QCD Corrections to Forward--Backward Asymmetries of Heavy--Quark Jets in Z Decays
The measurement of the forward-backward asymmetries of heavy quarks provides
one of the most precise determinations of in decays. We
discuss in detail the one--loop QCD radiative corrections to these asymmetries.
Results are given for single heavy--quark jet asymmetries and asymmetries of
the thrust axis, as well as for heavy--quark two--jet final states.}Comment: 11pp, latex, 1 uuencoded eps figur
Phenomenology of the Gauge Boson
Assuming the existence of a gauge boson which couples to ,
we discuss the present experimental constraints on and from and . We also discuss the
discovery potential of at hadron colliders through its decay into pairs. In the scenario where all three charged leptons (and their
neutrinos) mix, lepton flavor nonconservation through becomes possible and
provides another experimental probe into this hypothesis.Comment: 19 pages, LaTeX, including 4 figure
Production and Two-photon Decay of the MSSM Scalar Higgs Bosons at the LHC
We consider the production and two-photon decay of the -even Higgs bosons
( and ) of the Minimal Supersymmetric Standard Model (MSSM) at the
Large Hadron Collider. We study in detail the dependence of the cross section
on various parameters of the MSSM, especially the dependence on the mixing
effects in the squark sector due to the Higgs bilinear parameter and the
soft supersymmetry breaking parameter . We find that the cross section for
the production of these Higgs bosons has a significant dependence on the
parameters which determine the chiral mixing in the squark sector. The cross
section times the two-photon branching ratio of is of the order of
15--25~fb in much of the parameter space that remains after imposing the
present experimental constraints. For the the two-photon branching ratio
is only significant if the is light, but then the cross section times the
branching ratio may exceed 200~fb. The QCD corrections due to quark loop
contributions are known to increase the cross section by 50\%. We find the
dependence of the cross section on the gluon distribution function used to be
rather insignificant.Comment: 16 pages, LaTex, plus 9 uuencoded figures attached Full ps file
available at ftp://vsfys1.fi.uib.no/anonymous/pub/ as nordita-9548.ps or
nordita-9548.ps-gz or via http://vsfys1.fi.uib.no/thpubl/publications.htm
Measurement of the electric dipole moment using longitudinal polarization of beams
Certain CP-odd momentum correlations in the production and subsequent decay
of pairs in collisions are enhanced significantly when the
and beams are longitudinally polarized. These may be used to probe
the real and imaginary parts of , the electric dipole moment of
the . Closed-form expressions for these ``vector correlations'' and the
standard deviation of the operators defining them due to standard model
interactions are presented for the two-body final states of decays. If
42\% average polarization of each beam is achieved, as proposed for the
tau-charm factories, with equal integrated luminosities for each sign of
polarization and a total yield of pairs, it is
possible to attain sensitivities for of , , cm respectively and for of , , cm respectively at the three operating center-of-mass energies of
3.67, 4.25 and 10.58 GeV. These bounds emerge when the effects of a posible
weak dipole form factor are negligible as is the case when it is of
the same order of magnitude as . Furthermore, in such a
polarization experiment where different polarizations are possible, a
model-independent disentangling of their individual effects is possible, and a
technique to achieve this is described. A strong longitudinal polarization
physics programme at the tau-charm factory appears warranted.Comment: 30 pages, latex, no figure
Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders
The most general Lorentz-invariant decay-density-matrix for , or for , is expressed in terms
of eight helicity parameters. The parameters are physically defined in terms of
partial-width-intensities for polarized-final-states in decay.
The parameters are the partial width, the quark's chirality parameter
, the polarimetry parameter , a "pre-SSB" test parameter
, and four - interference parameters , ,
, which test for violation. They can be
used to test for non-CKM-type CP violation, anomalous 's, top
weak magnetism, weak electricity, and second-class currents. By stage-two
spin-correlation techniques, percent level statistical uncertainites are
typical for measurements at the Tevatron, and several mill level uncertainites
are typical at the LHC.Comment: Minor clarifications. Expression for r_{+-} corrected. 19 pages LaTex
+ Tables + 1 Figur
Production of neutral MSSM Higgs bosons in collisions: a complete 1-loop calculation
We present the first complete 1-loop diagrammatic calculation of the cross
sections for the neutral Higgs production processes e^+e^-\ra Z^0h^0 and
e^+e^-\ra A^0h^0 in the minimal supersymmetric standard model. We compare the
results from the diagrammatic calculation with the corresponding ones of the
simpler and compact effective potential approximation and discuss the typical
size of the differences.Comment: LaTeX, 16 pages, 8 figures appended in a uuencoded file, complete
PostScript file available at
http://itpaxp1.physik.uni-karlsruhe.de/prep/KA-TP-16-1995/KA-TP-16-199
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