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Dilepton polarization as a signature of plasma anisotropy

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arxiv 2309.00555 v2 pith:KMKV2GBJ submitted 2023-09-01 nucl-th hep-exhep-phnucl-ex

classification nucl-thhep-exhep-phnucl-ex
keywords distributionleptonplasmaangularearlyinvariantlongitudinalquark-gluon
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

We propose the angular distribution of lepton pairs produced in ultrarelativistic heavy-ion collisions as a probe of thermalization of the quark-gluon plasma. We focus on dileptons with invariant masses large enough that they are produced through quark-antiquark annihilation in the early stages of the collision. The angular distribution of the lepton in the rest frame of the pair then reflects the angular distribution of quark momenta. At early times, the transverse pressure of the quark-gluon plasma is larger than its longitudinal pressure as a result of the fast longitudinal expansion, which results in an oblate lepton distribution. By contrast, direct (Drell-Yan) production by quarks and antiquarks from incoming nuclei, whose momenta are essentially longitudinal, results in a prolate distribution. As the invariant mass increases, Drell-Yan gradually becomes the dominant source of dilepton production, and the lepton distribution evolves from oblate to prolate. The invariant mass at which the transition occurs is highly sensitive to the equilibration time of the quark-gluon plasma or, equivalently, the shear viscosity over entropy ratio $\eta/s$ in the early stages of the collision.

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Cited by 5 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Thermal dilepton polarization and dynamics of the QCD plasma in relativistic heavy-ion collisions

    nucl-th 2024-12 conditional novelty 7.0 of 10

    Using next-to-leading-order rates, the paper predicts that dilepton polarization changes sign and magnitude in low and intermediate invariant-mass ranges, making it a sensitive probe of gluonic processes and pre-equil...

  2. Thermal Dilepton Polarization under Rotation or Magnetic Field in Heavy-ion Collisions

    hep-ph 2026-07 conditional novelty 6.5 of 10

    Vorticity and magnetic fields induce characteristically different dilepton polarization spectra via modified quark propagators, with λ_θ decreasing monotonically under rotation but oscillating under magnetic fields du...

  3. Effective temperatures of the QGP from thermal photon and dilepton production

    nucl-th 2024-12 conditional novelty 6.0 of 10

    In the Trajectum model, dilepton effective temperatures reliably track the quark-gluon plasma temperature, while photon effective temperatures are biased by flow and stay near 250-300 MeV.

  4. Thermal dilepton production within conformal viscous Gubser flow

    hep-ph 2025-06 conditional novelty 5.0 of 10

    Thermal dilepton yields and effective temperatures are computed for conformal viscous Gubser flow, showing larger yields for lower q (larger systems) and higher effective temperatures for smaller systems.

  5. Theory Summary

    nucl-th 2025-09 unverdicted

    A conference summary paper reports selected theory results from Quark Matter 2025 in heavy-ion physics, with no new original research.

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