Hyperon Production in Bi + Bi Collisions at the Nuclotron-Based Ion Collider Facility and Angular Dependence of Hyperon Spin Polarization
The strange baryon production in Bi + Bi collisions at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi>...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2024-11-01
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| Series: | Particles |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2571-712X/7/4/60 |
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| Summary: | The strange baryon production in Bi + Bi collisions at <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>9.0</mn></mrow></semantics></math></inline-formula> GeV is studied using the PHSD transport model. Hyperon and anti-hyperon yields, transverse momentum spectra, and rapidity spectra are calculated, and their centrality dependence and the effect of rapidity and transverse momentum cuts are studied. The rapidity distributions for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover><mi mathvariant="sans-serif">Λ</mi><mo>¯</mo></mover></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Ξ</mi></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mover><mi mathvariant="sans-serif">Ξ</mi><mo>¯</mo></mover></semantics></math></inline-formula> baryons are found to be systematically narrower than for <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Λ</mi></semantics></math></inline-formula>s. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>p</mi><mi>T</mi></msub></semantics></math></inline-formula> slope parameters for anti-hyperons vary more with centrality than those for hyperons. Restricting the accepted rapidity range to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>|</mo><mi>y</mi><mo>|</mo><mo><</mo><mn>1</mn></mrow></semantics></math></inline-formula> increases the slope parameters by 13–30 MeV, depending on the centrality class and the hyperon mass. Hydrodynamic velocity and vorticity fields are calculated, and the formation of two oppositely rotating vortex rings moving in opposite directions along the collision axis is found. The hyperon spin polarization induced by the medium vorticity within the thermodynamic approach is calculated, and the dependence of the polarization on the transverse momentum and rapidity cuts and on the centrality selection is analyzed. The cuts have stronger effect on the polarization of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Λ</mi></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi mathvariant="sans-serif">Ξ</mi></semantics></math></inline-formula> hyperons than on the corresponding anti-hyperons. The polarization signal is maximal for the centrality class, 60–70%. We show that, for the considered hyperon polarization mechanism, the structure of the vorticity field makes an imprint on the polarization signal as a function of the azimuthal angle in the transverse momentum plane, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>ϕ</mi><mi>H</mi></msub></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo form="prefix">cos</mo><msub><mi>ϕ</mi><mi>H</mi></msub><mo>=</mo><msub><mi>p</mi><mi>x</mi></msub><mo>/</mo><msub><mi>p</mi><mi>T</mi></msub></mrow></semantics></math></inline-formula>. For particles with positive longitudinal momentum, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>p</mi><mi>z</mi></msub><mo>></mo><mn>0</mn></mrow></semantics></math></inline-formula>, the polarization increases with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo form="prefix">cos</mo><msub><mi>ϕ</mi><mi>H</mi></msub></mrow></semantics></math></inline-formula>, while for particles with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>p</mi><mi>z</mi></msub><mo><</mo><mn>0</mn></mrow></semantics></math></inline-formula> it decreases. |
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| ISSN: | 2571-712X |