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Register a new userAsymmetric Quark/Antiquark Hadronization in e+e- Annihilation
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We point out that the fragmentation of a strange quark into nucleons versus antinucleons is not necessarily identical $D_{p/s}(z,Q^2) eq D_{bar p/s}(z,Q^2)$, even though the perturbative contributions from gluon splitting and evolution are $p leftrightarrow bar p$ symmetric. The observation of such asymmetries in the hadronization of strange and other heavy quarks can provide insight into the nonperturbative mechanisms underlying jet fragmentation in QCD.
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We perform a systematic analysis of exclusive hadronic channels in e+e- collisions at centre-of-mass energies between 2.1 and 2.6 GeV within the statistical hadronization model. Because of the low multiplicities involved, calculations have been carried out in the full microcanonical ensemble, including conservation of energy-momentum, angular momentum, parity, isospin, and all relevant charges. We show that the data is in an overall good agreement with the model for an energy density of about 0.5 GeV/fm^3 and an extra strangeness suppression parameter gamma_S ~ 0.7, essentially the same values found with fits to inclusive multiplicities at higher energy.
We examine the processes $e^+ e^-longrightarrow W^+ W^-$ and $Z^0 Z^0$ in the context of the $SP(6)_Lotimes U(1)_Y$ model. We find that there are significant deviations in the total cross sections $sigma (s)$ from the standard model results due to the presence of additional gauge bosons $Z^prime$ and $W^prime$ in the model. These deviations could be detected at LEP.
We present the full O(alpha_s) longitudinal spin-spin correlations for heavy-quark pair production at e+ e- high-energy colliders in closed analytical form. In such reactions, quark and antiquark have strongly correlated spins, and the longitudinal components are dominant. For the explicit computation of the QCD bremsstrahlung contributions, new phase-space integrals are derived. Explicit numerical estimates are given for t t_bar and b b_bar production. Around the Z-peak, QCD one-loop corrections depolarize the spin-spin asymmetry for bottom quark pairs by approximately -4%. For top pair production, we find at 350GeV a 0.6% increased polarization over a value of 0.4 in the longitudinal correlation. For more than 1 TeV the O(alpha_s) corrections enhance depolarization to -2% in the top-pair case.
We study, at leading order in the large number of colours expansion and within the Resonance Chiral Theory framework, the odd-intrinsic-parity $e^+ e^- rightarrow pi^+ pi^- (pi^0, eta)$ cross-sections in the energy regime populated by hadron resonances, namely $3 , m_{pi} lsim E lsim 2 , mbox{GeV}$. In addition we implement our results in the Monte Carlo generator PHOKHARA 7.0 and we simulate hadron production through the radiative return method.
We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as $ldctoldpi^+,Sigma^0pi^+,p bar K_0$, $Xi_c^0toXi^-pi^+$ and $Omega_c^0toOmega^-pi^+$. The joint angular formulae for these processes are presented, and are used to extract the asymmetry parameters in $ee$ annihilation data. Base on the current $ldc$ data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters $alpha_{ldpi^+}$ for $ldctoldpi^+$, $alpha_{Sigma^+pi^0}$ for $ldctoSigma^+pi^0$ and $alpha_{usigpi^+}$ for $ldctousigpi^+$.
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