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 $\sqrt s$=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 τ\tau electric dipole moment using longitudinal polarization of e+e−e^+e^- beams

Certain CP-odd momentum correlations in the production and subsequent decay of $\tau$ pairs in $e^+ e^-$ collisions are enhanced significantly when the $e^+$ and $e^-$ beams are longitudinally polarized. These may be used to probe the real and imaginary parts of $d_\tau^\gamma$, the electric dipole moment of the $\tau$. 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 $\tau$ 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 $2\cdot 10^7$ $\tau^+ \tau^-$ pairs, it is possible to attain sensitivities for $\vert\delta {\rm Re} d_{\tau}^{\gamma}\vert$ of $8\cdot 10^{-19}$, $1\cdot 10^{-19}$, $1\cdot 10^{-19}$ $e$ cm respectively and for $\vert\delta {\rm Im} d_{\tau}^{\gamma}\vert$ of $4\cdot 10^{-14}$, $6\cdot 10^{-15}$, $5\cdot 10^{-16}$ $e$ 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 $d_\tau^Z$ are negligible as is the case when it is of the same order of magnitude as $d_\tau^\gamma$. 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 B−3LτB - 3 L_\tau Gauge Boson

Assuming the existence of a gauge boson $X$ which couples to $B - 3 L_\tau$, we discuss the present experimental constraints on $g_X$ and $m_X$ from $Z \to l^+ l^-$ and $Z \to \bar f f X~(f = q, \nu_\tau, \tau)$. We also discuss the discovery potential of $X$ at hadron colliders through its decay into $\tau^+ \tau^-$ pairs. In the scenario where all three charged leptons (and their neutrinos) mix, lepton flavor nonconservation through $X$ becomes possible and provides another experimental probe into this hypothesis.Comment: 19 pages, LaTeX, including 4 figure

Production of neutral MSSM Higgs bosons in e+e−e^+e^- 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 $\tau\rightarrow\omega \pi\pi\nu$ and $\omega\rho\nu$ in the chiral limit. It originates in WZW anomaly. Theoretical result of $\tau\rightarrow\omega\pi\pi\nu$ agrees with data well and the measurement of $\tau\rightarrow\omega\rho\nu$ will confirm the strong anomaly of PCAC. The strong anomaly of PCAC is studied.Comment: 27 page