Measurement of polarization observables of the associated strangeness production in proton proton interactions

TL;DR

This study measures polarization observables in proton-proton interactions producing Lambda particles at specific energies, revealing a sign change in Lambda polarization not observed before, with results aligning qualitatively with previous experiments at higher energies.

Contribution

First measurement of Lambda polarization observables below 200 MeV excess energy, providing new insights into polarization behavior in associated strangeness production.

Findings

Lambda polarization changes sign at low excess energies.

Analyzing power and spin transfer coefficient remain stable across energies.

Results qualitatively agree with the DISTO experiment at higher energies.

Abstract

The Lambda polarization, the analyzing power, and the Lambda spin transfer coefficient of the reaction pp -> p K+ Lambda were measured at beam momenta of 2.70 GeV/c and 2.95 GeV/c, corresponding to excess energies of 122 MeV and 204 MeV. While the analyzing power and the spin transfer coefficient do not change significantly with the excess energy, the Lambda polarization varies strongly and changes its sign. As this is the first measurement of polarization observables below an excess energy of 200 MeV, the change of the sign of the Lambda polarization was not observed before. The high statistics of the data (~200 k events for each momentum) enables detailed studies of the dependence of the Lambda polarization and the analyzing power on the center of mass momentum of the particles. The results of the spin transfer coefficient are in qualitative agreement with the DISTO experiment. The Lambda polarization data of 2.95 GeV/c are only conform with the DISTO experiment, while both the 2.70 GeV/c and 2.95 GeV/c data differ strongly from all previous measurements, whether exclusive or inclusive.