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Register a new userThe effective radius for production of baryon-antibaryon pairs from $psi$ decays
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By using the covariant L-S Scheme for the partial wave analysis, we deduce the ratios between the S-wave and D-wave contributions from the recent data of $psi(1^-) to B_8(1/2^+) bar{B}_8(1/2^-)$ from the BESIII collaboration. For the $J/psito Lambdabar{Lambda}$ and $J/psi(psi(2S))to Sigma^{+}bar{Sigma}^{-}$, the ratios are fixed and the average angular momenta are computed to estimate the effective radii of these processes. The results show that the effective radii of these decays of $J/psi(psi(2S))$ are very small, which are around 0.04 fm. Thus, it is a nice place to search excited baryon resonances with lower spin in the decays of $J/psi(psi(2S))$. Furthermore, for the other $psi(1^-) to B_8(1/2^+) bar{B}_8(1/2^-)$ reactions, we propose some methods to get such effective radius.
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With a sample of 14 million psi(2S) events collected by the BESII detector at the Beijing Electron Positron Collider (BEPC), the decay channels psi(2S)->p p-bar, Lambda Lambda-bar, Sigma0 Sigma0-bar, Xi Xi-bar are measured, and their branching ratios are determined to be (3.36+-0.09+-0.24)*10E-4, (3.39+-0.20+-0.32)*10E-4, (2.35+-0.36+-0.32)*10E-4, (3.03+-0.40+-0.32)*10E-4, respectively. In the decay psi(2S)->p p-bar, the angular distribution parameter alpha is determined to be 0.82+-0.17+-0.04.
Using a sample of 2.59 times 10^7 psi(2S) decays collected by the CLEO--c detector, we present results of a study of chi_{cJ} (J=0,1,2) decays into baryon-antibaryon final states. We present the worlds most precise measurements of the chi_cJ -> p-pbar and chi_cJ -> Lambda-Lambdabar branching fractions, and the first measurements of chi_c0 decays to other hyperons. These results illuminate the decay mechanism of the chi_c states.
Using a sample of $1.31times 10^9$ $J/psi$ events collected with the BESIII detector, we report the first observation of spin polarization of $Lambda$ and $barLambda$ hyperons from the coherent production in the $J/psitoLambdabarLambda$ decay. We measure the phase between the hadronic form factors to be $DeltaPhi=(42.4pm0.6pm0.5)^circ$. The decay parameters for $Lambdato ppi^-$ ($alpha_-$), $barLambdatobar ppi^+$ ($alpha_+$) and $barLambdatobar npi^0$ ($baralpha_0$) are measured to be $alpha_-=0.750pm0.009pm0.004$, $alpha_+=-0.758pm0.010pm0.007$ and $baralpha_0=-0.692pm0.016pm0.006$, respectively. The obtained value of $alpha_-$ is higher by $(17pm 3)%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006pm0.012pm0.007$ is extracted with substantially improved precision. The ratio $bar{alpha}_0/alpha_{+} = 0.913pm 0.028 pm 0.012$ is also measured.
We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $cbar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.
The radiative decays of $b$-baryons facilitate the direct measurement of photon helicity in $bto sgamma$ transitions thus serving as an important test of physics beyond the Standard Model. In this paper we analyze the complete angular distribution of ground state $b$-baryon ($Lambda_{b}^{0}$ and $Xi_{b}^{-}$) radiative decays to multibody final states assuming an initially polarized $b$-baryon sample. Our sensitivity study suggests that the photon polarization asymmetry can be extracted to a good accuracy along with a simultaneous measurement of the initial $b$-baryon polarization. With higher yields of $b$-baryons, achievable in subsequent runs of the Large Hadron Collider (LHC), we find that the photon polarization measurement can play a pivotal role in constraining different new physics scenarios.
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