1,891 research outputs found
Comparison of the Geometrical Characters Inside Quark- and Gluon-jet Produced by Different Flavor Quarks
The characters of the angular distributions of quark jets and gluon jets with
different flavors are carefully studied after introducing the cone angle of
jets. The quark jets and gluon jets are identified from the 3-jet events which
are produced by Monte Carlo simulation Jetset7.4 in e+e- collisions at =91.2GeV. It turns out that the ranges of angular distributions of gluon jets
are obviously wider than that of quark jets at the same energies. The average
cone angles of gluon jets are much larger than that of quark jets. As the
multiplicity or the transverse momentum increases, the cone-angle distribution
without momentum weight of both the quark jet and gluon jet all increases, i.e
the positive linear correlation are present, but the cone-angle distribution
with momentum weight decreases at first, then increases when n > 4 or p_t > 2
GeV. The characters of cone angular distributions of gluon jets produced by
quarks with different flavors are the same, while there are obvious differences
for that of the quark jets with different flavors.Comment: 13 pages, 6 figures, to be published on the International Journal of
Modern Physics
Fragmentation Functions for Light Charged Hadrons with Complete Quark Flavour Separation
We present new sets of next-to-leading order fragmentation functions
describing the production of charged pions, kaons and protons from the gluon
and from each of the quarks, obtained by fitting to all relevant data sets from
e+ e- annihilation. The individual light quark flavour fragmentation functions
are obtained phenomenologically for the first time by including in the data the
light quark tagging probabilities obtained by the OPAL Collaboration
Four-jet Signal at LEP2 and Supersymmetry
ALEPH has reported a significant excess of four-jet events in the LEP runs
above the Z^0 resonance, which however has not been confirmed by the other LEP
collaborations. We assume here that this excess corresponds to a physics signal
and try to interpret it in the context of supersymmetric models with R-parity
violation. Associated production of a left and right selectron can explain all
the distinctive features of the ALEPH data: the value of the cross section, the
di-jet mass difference, the absence of bottom quarks in the final state, and
the di-jet charge content. Our proposed scenario makes definite predictions
which can be tested at future LEP runs at higher energies.Comment: 15 pages, LateX, 5 figures. A few typos were corrected. A reference
was adde
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
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
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
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
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 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
Tau mesonic decays and strong anomaly of PCAC
Strong anomaly of the PCAC is found in and
in the chiral limit. It originates in WZW anomaly. Theoretical
result of agrees with data well and the
measurement of will confirm the strong anomaly
of PCAC. The strong anomaly of PCAC is studied.Comment: 27 page
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