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Register a new userSearch for direct production of a2(1320) and f2(1270) mesons in e+e- annihilation
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A search for direct production of C-even resonances a2(1320) and f2(1270) in e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The upper limits of electronic widths of these mesons were obtained at 90% confidence level: Gamma(a2(1320) to e+e-) < 0.56 eV, Gamma(f2(1270) to e+e-) < 0.11 eV.
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A search for direct production of the $f_1(1285)$ resonance in $e^+e^-$ annihilation is performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The analysis is based on data with an integrated luminosity of 15.1 pb$^{-1}$ accumulated in the center-of-mass energy range 1.2--1.4 GeV. Two $e^+e^-to f_1(1285)$ candidate events are found at the peak of the resonance and zero events beyond the resonance. The significance of the $e^+e^-to f_1(1285)$ signal is $2.5sigma$. The cross section at the maximum of the resonance is found to be $sigma(e^+e^-to f_1)=45^{+33}_{-24}$ pb. The corresponding branching fraction $B(f_1(1285)to e^+e^-)=(5.1^{+3.7}_{-2.7})times 10^{-9}$. We consider this result as a first indication of the process $e^+e^-to f_1(1285)$. The measured branching fraction is consistent with the theoretical prediction.
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.
Results on Bose-Einstein correlations in e+e- ==> hadrons are reviewed.
The usual interpretation of Bose-Einstein correlations (BEC) of identical boson pairs relates the width of the peak in the correlation function at small relative four-momentum to the spatial extent of the source of the bosons. However, in the tau-model, which successfully describes BEC in hadronic Z decay, the width of the peak is related to the temporal extent of boson emission. Some new checks on the validity of both the tau-model and the usual descriptions are presented.
Within the framework of the perturbative QCD approach, we calculate the time-like $B_cB_c(B_c^*)$ form factors $F(Q^2)$ and $A_2(Q^2)$. We include relativistic corrections and QCD corrections, either of which can give about $20%$ correction to the leading-order contribution, but there are cancellation effects between them. We calculate the cross sections of the $e^+e^-to B_c^-B_c^+(B_c^{*+})$ processes. The cross sections are enhanced at the $Z$ pole to be $sigma^{PP}(Q=m_Z) sim 1.3times10^{-5}text{pb}$ and $sigma^{PV}(Q=m_Z) sim 2.5times10^{-5}text{pb}$, which are still too small to be detected by proposed $e^+e^-$ colliders such as the Circular Electron Positron Collider.
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