Abstract
The global polarization of Λ hyperons has been measured in Au+Au and Ag+Ag collisions at √SNN = 2.4 and 2.55 GeV recorded with HADES. An increase of the polarization is observed following the trend measured by the STAR Collaboration. The high statistics Ag+Ag data allowed for differential measurements of the polarization. The study of acceptance effects is very important in the fixed target setup, as the phase-space coverage is not symmetric. These studies are reported together with the evaluation procedure of the systematic uncertainties.
Highlights
In non-central heavy-ion collisions, large orbital angular momenta are created [1] which might manifest itself in a global spin polarization of the produced particles [2, 3]
Such a global polarization can be accessed using weak decays of strange hyperons, where the spin direction is transferred to the momentum direction of the decay products
Measurements performed during the beam energy trend of the global polarization scan phase in Au+Au cIobllyistihoensSTdoAwRnCtooll√absoNrNat=ion7.s7hGoweVan[4i]n.cFreuarstihnegr measurements by the ALICE and STAR Collaboration confirm the decreasing trend towards hdiagtahesramcopllleissiofonretnheergreieasct[io5n, s6]A. uT+hAeuHaAt D√EsSNNex=pe2r.4im2eanntdaAt SgI+SA-1g8act o2l.l5e5ctGedeVh.igAh statistics measurement of the global polarization of the Λ hyperons at these lower collision energies provides new insights into the evolution of the angular momentum and the collective behavior of the matter created
Summary
In non-central heavy-ion collisions, large orbital angular momenta are created [1] which might manifest itself in a global spin polarization of the produced particles [2, 3]. The measurement of the global polarization is performed using the decay channel Λ → p + π− in which the proton is preferentially emitted in the spin direction of the Λ hyperon. The polarization signal is extracted with the invariant mass method.
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