We investigate the quantum correlated $Λ\barΛ $ production in the reaction $e^{+}e^{-} \to J/ψ\to Λ\barΛ$. Since the $Λ$ or $\barΛ$ has a nonzero magnetic moment, its spin will undergo a Larmor precession in the magnetic field of the detector, such as the BESIII experiment. Because of the spin precession, the angular distribution of the $Λ$ and $\barΛ$ is slightly modified. Therefore, we obtain the corresponding term of the modified angular distribution due to the effect of the Larmor precession. We also estimate its potential effect on the measurements of $CP$ violation, as well as the decay asymmetry parameter and polarization of $Λ$. The polarization of the $Λ$ or $\barΛ$ at the production vertex will rotate around the $B$-field axis, over an angle depending on the flight length in, but it still could be measured by fit to the corrected angular distribution. Of important, We conclude that a nonzero $CP$ asymmetry of order $10^{-4}$ will be caused once neglecting spin precession of the $Λ$ and $\barΛ$ in the $e^{+}e^{-} \to J/ψ\to Λ\barΛ$ process. The size of this $CP$ asymmetry is several times that of predicted within Standard Model in the hyperon decay. Although this effect is small, it will play an important role in future high precision experiments, such as the super-tau-charm factory.
The global polarization of the $Λ$ and $\barΛ$ hyperons ($P_{\rm H}$) has been measured in Pb--Pb collisions at $\sNN=$ 2.76 TeV and 5.02 TeV in ALICE at the Large Hadron Collider (LHC). The hyperon global polarization is found to be consistent with zero at both collision energies. The local polarization of the $Λ$ and $\barΛ$ hyperons along the beam ($z$) direction, $P_{\rm z}$, has also been measured in Pb--Pb collisions at $\sNN=5.02$ TeV. The $P_{\rm z}$, measured as a function of the hyperon emission angle relative to the second harmonic symmetry plane, exhibits a second harmonic sine mod…
Using the largest $J/ψ$ and $ψ(3686)$ data samples collected at the BESIII experiment, the hyperon anti-hyperon pairs are generated in their quantum entangle system. The polarization of hyperon has been observed, which makes it possible to measure the decay parameters of hyperon and anti-hyperon precisely. The CP conservation observables have been estimated which is important to test the Standard Model. In the meanwhile, the branching fractions and angular distributions related to hyperon pair production have been measured.
Charge-Odd Hyperon Polarization from Magnetic Spin Precession
Instituto de Ciencias Nucleares, UNAM（墨西哥国立自治大学核科学研究所）；School of Physical Sciences, National Institute of Science Education and Research（印度科学技术教育研究学院物理科学学院）
We make a systematic study of $Λ$ hyperon polarizations in unpolarized lepton induced semi-inclusive reactions such as $e^-N\to e^-ΛX$ and $e^+e^-\toΛh X$. We present the general form of cross sections in terms of structure functions obtained from a general kinematic analysis. This already shows that the produced hyperons can be polarized in three orthogonal directions, i.e., the longitudinal direction along the hyperon momentum, the normal direction of the production plane, and the transverse direction in the production plane. We present the parton model results at the leading twist and leadi…
We briefly review the thermal model predictions related to longitudinal spin polarization of $Λ-$hyperons emitted from a hot and rotating hadronic medium produced in the non-central relativistic heavy ion collisions.
Spin polarization and entanglement are utilized by the BESIII experiment to learn more about the production and decay properties of hyperon-antihyperon pairs in a series of recent analyses of its unprecedented datasets at the $J/ψ$ and $ψ'$ resonances. This has lead to the observation of significant transverse polarisation in decays of $J/ψ$ or $ψ'$ into $Λ\barΛ$, $Σ\barΣ$, $Ξ\barΞ$, and $Ω\barΩ$. Because of the non-zero polarization, the decay parameters for the most common hadronic weak decays of both hyperons and antihyperons could be determined independently for the first time. Comparing t…
INFN-Sezione di Catania（意大利国家核物理研究所卡塔尼亚分部）；University of Catania（卡塔尼亚大学）；University of Science and Technology of China（中国科学技术大学）；Anhui University of Science and Technology（安徽理工大学）；Central China Normal University（华中师范大学）；Johann Wolfgang Goethe Universitaet（约翰·沃尔夫冈·歌德法兰克福大学）
We derive the twist-3 gluon fragmentation function (FF) contribution to the transversely polarized hyperon production in semi-inclusive deep inelastic scattering, $ep\to eΛ^\uparrow X$, in the leading order (LO) with respect to the QCD coupling in the framework of the collinear twist-3 factorization. Together with the known result for the contribution from the twist-3 distribution in the proton and the twist-3 quark FFs for the hyperon, this completes the LO cross section for this process. The constraint relations among the twist-3 FFs are taken into account. The formula is relevant to large-$…
Only a fraction of all $Λ$ and $\barΛ$ hyperons detected in heavy ion collisions are produced from the hot and dense matter directly at the hadronization. These hyperons are called the {\em primary} hyperons. The rest of the hyperons are products of the decays of heavier hyperon states, which in turn are produced at the hadronization. As such, the polarization of only primary hyperons can be described with the formulae introduced in Sect. 8. For the rest of the hyperons, the polarization transfer in the decays has to be computed, and convoluted with the polarization of the mother hyperon. In t…
We argue that the enhancement in the spin polarization of anti-hyperons compared to the polarization of the hyperons in noncentral relativistic heavy-ion collisions arises as a result of an interplay between the chiral and helical vortical effects. The chiral vortical effect generates the axial current of quarks along the vorticity axis while the recently found helical vortical effect generates the helicity flow -- the projection of the quark's polarization vector onto its momentum -- along the same axis. For massless fermions, the helical charge corresponds to a difference in the contribution…
We study the transverse polarization of hyperons produced in semi-inclusive deep inelastic scattering, $ep\to eΛ^\uparrow X$, in the framework of the collinear twist-3 factorization. The cross section from the twist-3 distribution functions and the twist-3 quark fragmentation functions is computed in the leading order with respect to the QCD coupling constant. The constraint relations among the twist-3 FFs are taken into account to simplify the formula. The formula is relevant to large-$P_T$ hyperon production in the future Electron-Ion-Collider experiment.
We investigate the transverse polarization of the $Λ$ hyperon in the processes $e^+e^-\toΛ^\uparrow π^\pm X$ and $e^+e^-\toΛ^\uparrow K^\pm X$ within the framework of the transverse momentum dependent~(TMD) factorization. The transverse polarization is contributed by the convolution of the transversely polarizing fragmentation function~(PFF) $D_{1T}^\perp$ of the lambda hyperon and the unpolarized fragmentation function $D_1$ of pion/kaon. We adopt the spectator diquark model result for $D_{1T}^{\perp}$ to numerically estimate the transverse polarization in $e^+e^-\toΛ^\uparrow h X$ process at…
Polarization observables in the processes $p+p\to Θ^+ +Σ^+$ and $n+p\to Θ^+ +Λ^0$, for any spin and parity of the $Θ^+$-hyperon in the threshold region
