$\Lambda$ and $\overline{\Lambda}$ polarization in lepton induced processes

Abstract

The study of the longitudinal polarization of Λ and Λ hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z 0 decays allows one to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Λ and Λ longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will soon provide accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms.

Quark structure ofΛfromΛpolarization inZdecays

“…There have been many proposals concerning the measurements of the Λ fragmentations functions in different processes, for different physical goals [13][14][15][18][19][20][21][22][23][24][25][26][27], and in this paper we will focus our attention on the longitudinally polarized case.…”

“…Measurements of the light-flavor quark fragmentations into Λ have been also suggested from polarized electron DIS process [23] and neutrino DIS process [25], based on the u-quark dominance assumption. It has been also suggested to determine the polarized fragmentation functions by measuring the helicity transfer asymmetry in the…”

“…The measured Λ-polarization has been compared with several theoretical calculations [25,27,28] based on simple ansatz such as ∆D Λ q (z) = C q (z)D Λ q (z) with constant coefficients C q , or Monte Carlo event generators without a clear physical motivation. It is the purpose of this paper to calculate the Λ-polarization in e + e − -annihilation at the Z-pole by using the physics results presented in Ref.…”

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

“…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

“…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.…”