Antilambda Hyperons Research Articles

Λ hyperon polarization in relativistic heavy ion collisions from a chiral kinetic approach

Based on the chiral kinetic approach using initial conditions from a multiphase transport model, we study the spin polarizations of quarks and antiquarks in non-central heavy ion collisions at the Relativistic Heavy Ion Collider. Because of the non-vanishing vorticity field in these collisions, quarks and antiquarks are found to acquire appreciable spin polarizations in the direction perpendicular to the reaction plane. Converting quarks and antiquarks to hadrons via the coalescence model, we further calculate the spin polarizations of Lambda and anti-Lambda hyperons and find their values comparable to those measured in experiments by the STAR Collaboration.

Hadronic structure functions in the [formula omitted] reaction

Cross-section distributions are calculated for the reaction e+e−→J/ψ→Λ¯(→p¯π+)Λ(→pπ−), and related annihilation reactions mediated by vector mesons. The hyperon-decay distributions depend on a number of structure functions that are bilinear in the, possibly complex, psionic form factors GMψ and GEψ of the Lambda hyperon. The relative size and relative phase of these form factors can be uniquely determined from the unpolarized joint-decay distributions of the Lambda and anti-Lambda hyperons. Also the decay-asymmetry parameters of Lambda and anti-Lambda hyperons can be determined.

Λpolarization in peripheral heavy ion collisions

We predict the polarization of Lambda and antiLambda hyperons in peripheral heavy ion collisions at ultrarelativistic energy, based on the assumption of local thermodynamical equilibrium at freeze-out. The polarization vector is proportional to the curl of the inverse temperature four-vector field and its length, of the order of percents, is maximal for particle with moderately high momentum lying on the reaction plane. A selective measurement of these particles could make Lambda polarization detectable.

Lambda and lambda production in central Pb-Pb collisions at 40, 80, and 158A GeV.

Production of Lambda and Antilambda hyperons was measured in central Pb-Pb collisions at 40, 80, and 158A GeV beam energy on a fixed target. Transverse mass spectra and rapidity distributions are given for all three energies. The Lambda/pi ratio at midrapidity and in full phase space shows a pronounced maximum between the highest BNL Alternating Gradient Synchrotron and 40A GeV CERN Super Proton Synchrotron energies, whereas the Lambda/pi ratio exhibits a monotonic increase.

Measurement of the polarization in νμ charged current interactions in the NOMAD experiment

We present a measurement of the polarization of Antilambda hyperons produced in nu_mu charged current interactions. The full data sample from the NOMAD experiment has been analyzed using the same V0 identification procedure and analysis method reported in a previous paper for the case of Lambda hyperons. The Antilambda polarization has been measured for the first time in a neutrino experiment. The polarization vector is found to be compatible with zero.

The design and performance of the FNAL high-energy polarized-beam facility

A new polarized-proton and -antiproton beam with 185 GeV/ c momentum has been built at Fermilab. The design uses the parity-nonconserving decays of lambda and antilambda hyperons to produce polarized protons and antiprotons, respectively, a beam-transport system that minimizes depolarization effects, and a set of twelve dipole magnets that rotate the beam-particle spin direction. A beam-tagging system determines the momentum and polarization of individual beam particles. This allows a selection of particles in definite intervals of momentum and polarization. Measurements performed by two different polarimeters showed that the beam is polarized and the determination of polarization by beam-particle tagging is verified. A new measurement of the analyzing power of large- x F π 0 production may lead to another beam polarimeter.

Interaction of antilambda hyperons with nucleons at intermediate energies

Cross-sections for the scattering and annihilation of antihyperons by nucleons are calculated at 75 and 150 MeV laboratory energies. The model of the anti-Λ0-nucleon interaction is an attractive potential at large interparticle separations and a black absorptive hole at separations less than ∼ 0.4 fermis. The cross-sections are obtained both with and without a spin-orbit term in the potential. The outer part of the potential is taken to be the same as the outer part of the Λ0-nucleon potential required to fit the binding energies of the Λ0 in hyperfragments. This form for the outer region follows from the assumption that this part of the potential arises from the exchange of two pions. The results indicate that about one anti-Λ0 in 50 will interact with a nucleon in a hydrogen bubble chamber at 150 MeV the others decaying in flight. There are as yet no experimental data with which to compare the calculated cross-sections.