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<p>Radial flow, a key collective phenomenon in heavy-ion collisions, manifests itself through event-by-event fluctuations of transverse momentum (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(p_{\textrm{T}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>p</mi> <mtext>T</mtext> </msub> </math></EquationSource> </InlineEquation>) spectra. The <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(p_{\textrm{T}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>p</mi> <mtext>T</mtext> </msub> </math></EquationSource> </InlineEquation>-differential radial-flow observable, <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(v_0(p_{\textrm{T}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>v</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mtext>T</mtext> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, was introduced to quantify local spectral-shape fluctuations, but it is unavoidably influenced by global multiplicity fluctuations. Using the HIJING model, we show that different event-activity definitions for centrality classification and different spectral-normalization schemes generate a constant vertical offset in <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(v_0(p_{\textrm{T}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>v</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mtext>T</mtext> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> without altering its shape. This offset reflects the impact of residual volume/centrality fluctuations rather than genuine dynamical radial-flow fluctuations. Accordingly, only the shape of <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(v_0(p_{\textrm{T}})\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>v</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mtext>T</mtext> </msub> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, or equivalently its derivative <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\textrm{d}v_0(p_{\textrm{T}})/\textrm{d}p_{\textrm{T}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mtext>d</mtext> <msub> <mi>v</mi> <mn>0</mn> </msub> <mrow> <mo stretchy="false">(</mo> <msub> <mi>p</mi> <mtext>T</mtext> </msub> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">/</mo> <mtext>d</mtext> <msub> <mi>p</mi> <mtext>T</mtext> </msub> </mrow> </math></EquationSource> </InlineEquation>, carries physical information about radial-flow dynamics; its zero-crossing does not. Practical implications include the need to vertically align measurements from different experiments before comparison, thereby removing normalization ambiguities when constraining QGP properties.</p>

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The shape of differential radial flow v0(pT), not its zero-crossing, carries physical information

  • 期刊论文

  • 发表日期：

    2026年6月16日

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  • Somadutta Bhatta,
  • Aman Dimri,
  • Jiangyong Jia

摘要

Radial flow, a key collective phenomenon in heavy-ion collisions, manifests itself through event-by-event fluctuations of transverse momentum ( \(p_{\textrm{T}}\) p T ) spectra. The \(p_{\textrm{T}}\) p T -differential radial-flow observable, \(v_0(p_{\textrm{T}})\) v 0 ( p T ) , was introduced to quantify local spectral-shape fluctuations, but it is unavoidably influenced by global multiplicity fluctuations. Using the HIJING model, we show that different event-activity definitions for centrality classification and different spectral-normalization schemes generate a constant vertical offset in \(v_0(p_{\textrm{T}})\) v 0 ( p T ) without altering its shape. This offset reflects the impact of residual volume/centrality fluctuations rather than genuine dynamical radial-flow fluctuations. Accordingly, only the shape of \(v_0(p_{\textrm{T}})\) v 0 ( p T ) , or equivalently its derivative \(\textrm{d}v_0(p_{\textrm{T}})/\textrm{d}p_{\textrm{T}}\) d v 0 ( p T ) / d p T , carries physical information about radial-flow dynamics; its zero-crossing does not. Practical implications include the need to vertically align measurements from different experiments before comparison, thereby removing normalization ambiguities when constraining QGP properties.