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Register a new userThrust Distribution for 3-Jet Production from $e^+e^-$ Annihilation within the QCD Conformal Window and in QED
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We investigate the theoretical predictions for thrust distribution in the electron positron annihilation to three-jets process at NNLO for different values of the number of flavors, $N_f$. To determine the distribution along the entire renormalization group flow from the highest energies to zero energy we consider the number of flavors near the upper boundary of the conformal window. In this regime of number of flavors the theory develops a perturbative infrared interacting fixed point. We then consider also the QED thrust obtained as the limit $N_c rightarrow 0$ of the number of colors. In this case the low energy limit is governed by an infrared free theory. Using these quantum field theories limits as theoretical laboratories we arrive at an interesting comparison between the Conventional Scale Setting - (CSS) and the Principle of Maximum Conformality (PMC$_infty$) methods. We show that within the perturbative regime of the conformal window the two methods yield similar results while reducing the number of flavors towards the active number of flavors in the Standard Model the PMC$_infty$ method is the natural extension of the curves within the conformal window and best fits the data.
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We consider the $pi^+pi^-pi_0gamma$ final state in electron-positron annihilation at cms energies not far from the threshold. Both initial and final state radiations of the hard photon is considered but without interference between them. The amplitude for the final state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments energies are never such small that $rho$ and $omega$ mesons would have negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final state radiation amplitude to account for the vector mesons influence. Using radiative 3$pi$ production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies.
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 correct an important misprint in the journal version of our earlier work on New Jet Cluster Algorithms: Next-to-leading Order QCD..., published in Nucl. Phys. B 370 (1992) 310, which may have lead to an incorrect parametrisation of the leading order QCD coefficients for the JADE type jet cluster algorithms.
We make a detailed study on the typical production channel of double charmoniums, $e^+e^-to J/psi+eta_c$, at the center-of-mass collision energy $sqrt{s}=10.58$ GeV. The key component of the process is the form factor $F_{rm VP}(q^2)$, which has been calculated within the QCD light-cone sum rules (LCSR). To improve the accuracy of the derived LCSR, we keep the $J/psi$ light-cone distribution amplitude up to twist-4 accuracy. Total cross sections for $e^+e^-to J/psi+eta_c$ at three typical factorization scales are $sigma|_{mu_s} = 22.53^{+3.46}_{-3.49}~{rm fb}$, $sigma|_{mu_k} = 21.98^{+3.35}_{-3.38}~{rm fb}$ and $sigma|_{mu_0} = 21.74^{+3.29}_{-3.33}~{rm fb}$, respectively. The factorization scale dependence is small, and those predictions are consistent with the BABAR and Belle measurements within errors.
We present the complete leading-order results for the azimuthal dependences and polarization observables in $e^+e^-to h_1 h_2 + X$ processes, where the two hadrons are produced almost back-to-back, within a transverse momentum dependent (TMD) factorization scheme. We consider spinless (or unpolarized) and spin-1/2 hadron production and give the full set of the corresponding quark and gluon TMD fragmentation functions (TMD-FFs). By adopting the helicity formalism, which allows for a more direct probabilistic interpretation, single- and double-polarization cases are discussed in detail. Simplified expressions, useful for phenomenological analyses, are obtained by assuming a factorized Gaussian-like dependence on intrinsic transverse momenta for the TMD-FFs.
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