학술논문
Polarization of Λ and Λ¯ Hyperons along the Beam Direction in Pb-Pb Collisions at sNN=5.02 TeV
Document Type
article
Author
Acharya, S; Adamová, D; Adler, A; Rinella, G Aglieri; Agnello, M; Agrawal, N; Ahammed, Z; Ahmad, S; Ahn, SU; Ahuja, I; Akbar, Z; Akindinov, A; Al-Turany, M; Alam, SN; Aleksandrov, D; Alessandro, B; Alfanda, HM; Molina, R Alfaro; Ali, B; Ali, Y; Alici, A; Alizadehvandchali, N; Alkin, A; Alme, J; Alt, T; Altenkamper, L; Altsybeev, I; Anaam, MN; Andrei, C; Andreou, D; Andronic, A; Angeletti, M; Anguelov, V; Antinori, F; Antonioli, P; Anuj, C; Apadula, N; Aphecetche, L; Appelshäuser, H; Arcelli, S; Arnaldi, R; Arsene, IC; Arslandok, M; Augustinus, A; Averbeck, R; Aziz, S; Azmi, MD; Badalà, A; Baek, YW; Bai, X; Bailhache, R; Bailung, Y; Bala, R; Balbino, A; Baldisseri, A; Balis, B; Ball, M; Banerjee, D; Barbera, R; Barioglio, L; Barlou, M; Barnaföldi, GG; Barnby, LS; Barret, V; Bartels, C; Barth, K; Bartsch, E; Baruffaldi, F; Bastid, N; Basu, S; Batigne, G; Batyunya, B; Bauri, D; Alba, JL Bazo; Bearden, IG; Beattie, C; Belikov, I; Hechavarria, ADC Bell; Bellini, F; Bellwied, R; Belokurova, S; Belyaev, V; Bencedi, G; Beole, S; Bercuci, A; Berdnikov, Y; Berdnikova, A; Bergmann, L; Besoiu, MG; Betev, L; Bhaduri, PP; Bhasin, A; Bhat, IR; Bhat, MA; Bhattacharjee, B; Bhattacharya, P; Bianchi, L; Bianchi, N; Bielčík, J; Bielčíková, J
Source
Physical Review Letters. 128(17)
Subject
Language
Abstract
The polarization of the Λ and Λ[over ¯] hyperons along the beam (z) direction, P_{z}, has been measured in Pb-Pb collisions at sqrt[s_{NN}]=5.02 TeV recorded with ALICE at the Large Hadron Collider (LHC). The main contribution to P_{z} comes from elliptic flow-induced vorticity and can be characterized by the second Fourier sine coefficient P_{z,s2}=⟨P_{z}sin(2φ-2Ψ_{2})⟩, where φ is the hyperon azimuthal emission angle and Ψ_{2} is the elliptic flow plane angle. We report the measurement of P_{z,s2} for different collision centralities and in the 30%-50% centrality interval as a function of the hyperon transverse momentum and rapidity. The P_{z,s2} is positive similarly as measured by the STAR Collaboration in Au-Au collisions at sqrt[s_{NN}]=200 GeV, with somewhat smaller amplitude in the semicentral collisions. This is the first experimental evidence of a nonzero hyperon P_{z} in Pb-Pb collisions at the LHC. The comparison of the measured P_{z,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.