The first evidence of spin alignment of vector mesons (K∗0 and φ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ00 is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at a center-of-mass energy (sNN) of 2.76 TeV with the ALICE detector. ρ00 values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum (pT<2 GeV/c) for K∗0 and φ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the KS0 meson (spin=0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

Evidence of Spin-Orbital Angular Momentum Interactions in Relativistic Heavy-Ion Collisions / Acharya, S; Adamova, D.; Adolfson, J; Aggarwal, M.; Rinella, G.; Agnello, M.; Agrawal, N; Bufalino, S.; Concas, M.; Grosa, F.; Ravasenga, I.; Catalano, F.; Fecchio, P.. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - STAMPA. - 125:1(2020), p. 012301. [10.1103/PhysRevLett.125.012301]

Evidence of Spin-Orbital Angular Momentum Interactions in Relativistic Heavy-Ion Collisions

Agnello, M.;Bufalino, S.;Concas, M.;Grosa, F.;Ravasenga, I.;Catalano, F.;Fecchio, P.
2020

Abstract

The first evidence of spin alignment of vector mesons (K∗0 and φ) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ρ00 is measured at midrapidity (|y|<0.5) in Pb-Pb collisions at a center-of-mass energy (sNN) of 2.76 TeV with the ALICE detector. ρ00 values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum (pT<2 GeV/c) for K∗0 and φ at a level of 3σ and 2σ, respectively. No significant spin alignment is observed for the KS0 meson (spin=0) in Pb-Pb collisions and for the vector mesons in pp collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/2848372