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Acceptance Effects on the Extracted Spin Alignment of K * 0 Mesons in Relativistic Heavy-Ion Collisions.

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Title: Acceptance Effects on the Extracted Spin Alignment of K * 0 Mesons in Relativistic Heavy-Ion Collisions.
Authors: Lan, Shaowei1 (AUTHOR) shaoweilan@pdsu.edu.cn, Liu, Qiuhua1 (AUTHOR), Ji, Pengfei1 (AUTHOR)
Source: Universe (2218-1997). May2026, Vol. 12 Issue 5, p145. 12p.
Subject Terms: *Vector mesons, *Heavy ion collisions, *Mesons, *Density matrices
Abstract: The spin alignment of vector mesons, characterized by the spin-density-matrix element ρ 00 , is an important observable for studying spin dynamics in relativistic heavy-ion collisions. Experimental measurements have reported deviations of ρ 00 from the isotropic expectation of 1 / 3 , motivating careful evaluation of possible acceptance effects. In this work, we investigate the influence of finite experimental coverage on the extracted ρ 00 of K ∗ 0 mesons using a toy model constrained by realistic kinematic distributions from the AMPT model. The reconstructed ρ 00 is examined as a function of pseudorapidity (η) and transverse momentum ( p T ) within typical experimental acceptance ranges. We find that limited pseudorapidity coverage can lead to reconstructed ρ 00 values above 1 / 3 , even when the input distribution is isotropic. This behavior originates from the selective removal of decay daughters outside the η window, which modifies the cos θ ∗ distribution. A dependence on transverse momentum is also observed, particularly at low p T where daughter particles are more sensitive to longitudinal acceptance constraints. Comparisons with STAR measurements are presented for reference, without attempting to reinterpret the experimental results. Overall, this study provides a systematic examination of acceptance-induced effects and may serve as a useful reference for future measurements of vector-meson spin alignment. [ABSTRACT FROM AUTHOR]
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Items – Name: Title
  Label: Title
  Group: Ti
  Data: Acceptance Effects on the Extracted Spin Alignment of K * 0 Mesons in Relativistic Heavy-Ion Collisions.
– Name: Author
  Label: Authors
  Group: Au
  Data: <searchLink fieldCode="AR" term="%22Lan%2C+Shaowei%22">Lan, Shaowei</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> shaoweilan@pdsu.edu.cn</i><br /><searchLink fieldCode="AR" term="%22Liu%2C+Qiuhua%22">Liu, Qiuhua</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Ji%2C+Pengfei%22">Ji, Pengfei</searchLink><relatesTo>1</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Universe+%282218-1997%29%22">Universe (2218-1997)</searchLink>. May2026, Vol. 12 Issue 5, p145. 12p.
– Name: Subject
  Label: Subject Terms
  Group: Su
  Data: *<searchLink fieldCode="DE" term="%22Vector+mesons%22">Vector mesons</searchLink><br />*<searchLink fieldCode="DE" term="%22Heavy+ion+collisions%22">Heavy ion collisions</searchLink><br />*<searchLink fieldCode="DE" term="%22Mesons%22">Mesons</searchLink><br />*<searchLink fieldCode="DE" term="%22Density+matrices%22">Density matrices</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The spin alignment of vector mesons, characterized by the spin-density-matrix element ρ 00 , is an important observable for studying spin dynamics in relativistic heavy-ion collisions. Experimental measurements have reported deviations of ρ 00 from the isotropic expectation of 1 / 3 , motivating careful evaluation of possible acceptance effects. In this work, we investigate the influence of finite experimental coverage on the extracted ρ 00 of K ∗ 0 mesons using a toy model constrained by realistic kinematic distributions from the AMPT model. The reconstructed ρ 00 is examined as a function of pseudorapidity (η) and transverse momentum ( p T ) within typical experimental acceptance ranges. We find that limited pseudorapidity coverage can lead to reconstructed ρ 00 values above 1 / 3 , even when the input distribution is isotropic. This behavior originates from the selective removal of decay daughters outside the η window, which modifies the cos θ ∗ distribution. A dependence on transverse momentum is also observed, particularly at low p T where daughter particles are more sensitive to longitudinal acceptance constraints. Comparisons with STAR measurements are presented for reference, without attempting to reinterpret the experimental results. Overall, this study provides a systematic examination of acceptance-induced effects and may serve as a useful reference for future measurements of vector-meson spin alignment. [ABSTRACT FROM AUTHOR]
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    Identifiers:
      – Type: doi
        Value: 10.3390/universe12050145
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 12
        StartPage: 145
    Subjects:
      – SubjectFull: Vector mesons
        Type: general
      – SubjectFull: Heavy ion collisions
        Type: general
      – SubjectFull: Mesons
        Type: general
      – SubjectFull: Density matrices
        Type: general
    Titles:
      – TitleFull: Acceptance Effects on the Extracted Spin Alignment of K * 0 Mesons in Relativistic Heavy-Ion Collisions.
        Type: main
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      – PersonEntity:
          Name:
            NameFull: Lan, Shaowei
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          Name:
            NameFull: Liu, Qiuhua
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          Name:
            NameFull: Ji, Pengfei
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          Dates:
            – D: 01
              M: 05
              Text: May2026
              Type: published
              Y: 2026
          Identifiers:
            – Type: issn-print
              Value: 22181997
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              Value: 12
            – Type: issue
              Value: 5
          Titles:
            – TitleFull: Universe (2218-1997)
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