Spin content ofΛand its longitudinal polarization ine+e−annihilation at high energies

Abstract

Longitudinal polarization of Lambda produced in e + e − annihilation at LEP energies is calculated in a picture for the spin content of Lambda which is consistent with the polarized deep inelastic lepton-nucleon scattering data and SU(3) flavor symmetry for hyperon decay so that the spin of Lambda is not completely carried by its s-valence quark. A comparison with the recent ALEPH data and the results of earlier calculations based on the static quark model in which the spin of Lambda is completely determined by the s-quark is given. The result shows that further measurements of such polarization should provide useful information to the question of which picture is more suitable in describing the spin effects in the fragmentation processes.

Global polarization of QGP in non-central heavy-ion collisions at high energies

“…For those produced via the fragmentation q → H + X, we compare with the longitudinal polarization of hyperons in e + e − → Z 0 → qq → Λ + X which has been measured [8] and can be explained [11] by assuming that polarized hyperons contain the initial polarized leading quark in its SU (6) wave-function. Similar calculations lead to,…”

Hyperon polarization in semi-inclusive deeply inelastic lepton-nucleon scattering at high energy

“…This is partly triggered by the ALEPH and OPAL measurements 13,14 on Λ polarization in e + e − annihilation at the Z 0 pole. Compared with the theoretical calculations 4,6 , those data 13,14 seem to suggest that the simple SU (6) wave-function can be used to describe the relation between the spin of the fragmenting quark and that of the produced hyperon which contains the fragmenting quark. This is rather surprising because the energy is very high at CERN e + e − collider LEP and the initial quarks and antiquarks produced at the annihilation vertices of the initial e + e − are certainly current quarks and current antiquarks rather than the constituent quarks used in describing the static properties of hadrons using SU(6) symmetric wave-functions.…”

“…The problem has attracted much attention [1][2][3][4][5][6][7][8][9][10][11][12] recently. This is partly triggered by the ALEPH and OPAL measurements 13,14 on Λ polarization in e + e − annihilation at the Z 0 pole.…”

The quark–antiquark asymmetry of the nucleon sea from Λ and fragmentation

“…[3] that there are still large uncertainties in the quark to Λ fragmentation function, and it is practically more urgent to measure the Λ fragmentation functions before using the Λ fragmentation to probe the quark content of the nucleon. Indeed, some symplifying assumptions about the quark to Λ fragmentation functions were found to be of little predictive power when applied to Λ production in e + e − annihilation process at the Z resonance [6,7], and to semi-inclusive Λ production of polarized charged lepton DIS process on the nucleon target [8].…”

“…there are still large uncertainties in the quark to Λ fragmentation function, and it is practically more urgent to measure the Λ fragmentation functions before using the Λ fragmentation to probe the quark content of the nucleon. Indeed, some symplifying assumptions about the quark to Λ fragmentation functions were found to be of little predictive power when applied to Λ production in e + e − annihilation process at the Z resonance [6,7], and to semi-inclusive Λ production of polarized charged lepton DIS process on the nucleon target [8].However, there have been recent progress [9,10,11] in order to understand the quark to Λ fragmentation functions by connecting them with the quark distributions inside the Λ by the Gribov-Lipatov relation (GLR) [12]:where D h q (z) is the fragmentation function for a quark q splitting into a hadron h with longitudinal momentum fraction z, and q h (x) is the quark distribution for finding the quark q inside the hadron h carrying a momentum fraction x. D h q and q h depend also on the energy scale Q 2 , and this relation holds, in principle, in a certain Q 2 range and in leading order approximation.…”