Naslov
Polarization of Λ and Λˉ Hyperons along the Beam Direction in Pb-Pb Collisions at √sNN = 5.02  TeV

Autori
Acharya, S. ; ... ; Erhardt, Filip ; ... ; Gotovac, Sven ; ... ; Jerčić, Marko ; ... ; Karatović, David ; ... ; Lončar, Petra ; ... ; Mudnić, Eugen ; ... ; Planinić, Mirko ; ... ; Poljak, Nikola ; ... ; Vicković, Linda ; ... ; Zurlo, N.

Kolaboracija
ALICE Collaboration

Izvornik
Physical Review Letters (0031-9007) 128 (2022); 172005, 13

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, pismo, znanstveni

Ključne riječi
Lambda: polarization ; Antilambda: polarization ; heavy ion: scattering ; quark gluon: plasma ; hyperon: transverse momentum ; model: hydrodynamics ; CERN LHC Coll ; elliptic flow ; ALICE ; thermal ; rapidity ; experimental results ; 5020 GeV-cms/nucleon

Sažetak
The polarization of the Λ and Λ¯ hyperons along the beam (z) direction, Pz, has been measured in Pb-Pb collisions at sNN=5.02 TeV recorded with ALICE at the Large Hadron Collider (LHC). The main contribution to Pz comes from elliptic flow-induced vorticity and can be characterized by the second Fourier sine coefficient Pz, s2=⟨Pzsin(2φ-2Ψ2)⟩, where φ is the hyperon azimuthal emission angle and Ψ2 is the elliptic flow plane angle. We report the measurement of Pz, s2 for different collision centralities and in the 30%–50% centrality interval as a function of the hyperon transverse momentum and rapidity. The Pz, s2 is positive similarly as measured by the STAR Collaboration in Au-Au collisions at sNN=200 GeV, with somewhat smaller amplitude in the semicentral collisions. This is the first experimental evidence of a nonzero hyperon Pz in Pb-Pb collisions at the LHC. The comparison of the measured Pz, s2 with the hydrodynamic model calculations shows sensitivity to the competing contributions from thermal and the recently found shear-induced vorticity, as well as to whether the polarization is acquired at the quark-gluon plasma or the hadronic phase.

Izvorni jezik
Engleski

Znanstvena područja
Fizika

POVEZANOST RADA