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| Main Authors: | , , , |
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| Format: | Preprint |
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2025
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| Online Access: | https://arxiv.org/abs/2509.05495 |
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| _version_ | 1866912574148182016 |
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| author | Nugara, Vincenzo Borghini, Nicolas Greco, Vincenzo Plumari, Salvatore |
| author_facet | Nugara, Vincenzo Borghini, Nicolas Greco, Vincenzo Plumari, Salvatore |
| contents | We investigate the role of the Knudsen number (Kn) as a scaling parameter governing the emergence of collective behavior in relativistic heavy-ion collisions. Using the Relativistic Boltzmann Transport approach, we explore different initial conditions for both conformal (massless) and non-conformal (massive) systems with a constant specific shear viscosity $η/s$. Observables such as the time evolution of anisotropic flow coefficients collapse onto universal curves for fixed classes of Knudsen number, when using a scaled time variable accounting for the system size and the speed of sound $c_s$. More differential quantities, such as $v_n(p_T/\langle E_T\rangle)$, show a larger sensitivity to $c_s$. We also study events with fluctuating initial profiles from the \trento\ model, simulating collision systems from O-O to Pb-Pb at RHIC and LHC energies. Universal scaling at a given Kn value also holds in these event-by-event simulations, suggesting that the Knudsen number provides a unified criterion for classifying collectivity across different systems, including small systems where thermalisation may not be fully realised. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_05495 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Knudsen number and universal behavior of collective flows in conformal and non-conformal systems Nugara, Vincenzo Borghini, Nicolas Greco, Vincenzo Plumari, Salvatore High Energy Physics - Phenomenology Nuclear Theory We investigate the role of the Knudsen number (Kn) as a scaling parameter governing the emergence of collective behavior in relativistic heavy-ion collisions. Using the Relativistic Boltzmann Transport approach, we explore different initial conditions for both conformal (massless) and non-conformal (massive) systems with a constant specific shear viscosity $η/s$. Observables such as the time evolution of anisotropic flow coefficients collapse onto universal curves for fixed classes of Knudsen number, when using a scaled time variable accounting for the system size and the speed of sound $c_s$. More differential quantities, such as $v_n(p_T/\langle E_T\rangle)$, show a larger sensitivity to $c_s$. We also study events with fluctuating initial profiles from the \trento\ model, simulating collision systems from O-O to Pb-Pb at RHIC and LHC energies. Universal scaling at a given Kn value also holds in these event-by-event simulations, suggesting that the Knudsen number provides a unified criterion for classifying collectivity across different systems, including small systems where thermalisation may not be fully realised. |
| title | Knudsen number and universal behavior of collective flows in conformal and non-conformal systems |
| topic | High Energy Physics - Phenomenology Nuclear Theory |
| url | https://arxiv.org/abs/2509.05495 |