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Open Access Publications from the University of California

Scholarly Works (9 results)

  • Article
  • Peer Reviewed
Lawrence Berkeley National Laboratory (2004)

We discuss the consequence of global polarization of the produced quarks in non-central heavy-ion collisions on the spin alignment of vector mesons. We show that the alignment is quite different for different hadronization scenarios. These results can be tested directly by measuring the vector mesons' alignment through angular distributions of the decay products with respect to the reaction plane. Such angular distributions will give rise to azimuthal anisotropy v_2of the decay products in the collision frame. Constraints provided by the data on the azimuthal anisotropy of hadron spectra at RHIC points to a quark recombination scenario of hadronization.

    Cover page: Spin alignment of vector mesons in non-central A+A collisions
    • Article
    • Peer Reviewed
    Lawrence Berkeley National Laboratory (2004)

    Produced partons have large local relative orbital angular momentum along the direction opposite to the reaction plane in the early stage of non-central heavy-ion collisions. Parton scattering is shown to polarize quarks along the same direction due to spin-orbital coupling. Such global quark polarization will lead to many observable consequences, such as left-right asymmetry of hadron spectra, global transverse polarization of thermal photons, dileptons and hadrons. Hadrons from the decay of polarized resonances will have azimuthal asymmetry similar to the elliptic flow. Global hyperon polarization is predicted within different hadronization scenarios and can be easily tested.

      Cover page: Globally Polarized Quark-gluon Plasma in Non-central A+A Collisions
      • Article
      • Peer Reviewed
      Lawrence Berkeley National Laboratory (2006)

      The collinear expansion technique is generalized to the factorization of unintegrated parton distributions and other higher twist parton correlations from the corresponding collinear hard parts that involve multiple parton final state interaction. Such a generalized factorization provides a consistent approach to the calculation of inclusive and semi-inclusive cross sections of deep-inelastic lepton-nucleon scattering. As an example, the azimuthal asymmetry is calculated to the order of 1/Q in semi-inclusive deeply inelastic lepton-nucleon scattering with transversely polarized target. A non-vanishing single-spin asymmetry in the "triggered inclusive process" is predicted to be 1/Q suppressed with a part of the coefficient related to a moment of the Sivers function.

        Cover page: Azimuthal and single spin asymmetry in deep-inelastic lepton-nucleon scattering
        • Article
        • Peer Reviewed
        LBL Publications (2005)
          Cover page: Anti-Lambda Polarization in High Energy pp Collisions with Polarized Beams
          • Article
          • Peer Reviewed
          LBL Publications (2018)
          We develop a general formalism for the quantum kinetics of chiral fermions in a background electromagnetic field based on a semiclassical expansion of covariant Wigner functions in the Planck constant. We demonstrate to any order of that only the time-component of the Wigner function is independent while other components are explicit derivative. We further demonstrate to any order of that a system of quantum kinetic equations for multiple-components of Wigner functions can be reduced to one chiral kinetic equation involving only the single-component distribution function. These are remarkable properties of the quantum kinetics of chiral fermions and will significantly simplify the description and simulation of chiral effects in heavy ion collisions and Dirac/Weyl semimetals. We present the unintegrated chiral kinetic equations in four-momenta up to O(2) and the integrated ones in three-momenta up to O. We find that some singular terms emerge in the integration over the time component of the four-momentum, which result in a new source term contributing to the chiral anomaly, in contrast to the well-known scenario of the Berry phase term. Finally we rewrite our results in any Lorentz frame with a reference four-velocity and show how the non-trivial transformation of the distribution function in different frames emerges in a natural way.
            Cover page: Disentangling covariant Wigner functions for chiral fermions
            • Article
            • Peer Reviewed
            LBL Publications (2023)
            Polarized quarks and antiquarks in high-energy heavy-ion collisions can lead to the spin alignment of vector mesons formed by quark coalescence. Using the relativistic spin Boltzmann equation for vector mesons derived from Kadanoff-Baym equations with an effective quark-meson model for strong interaction and quark coalescence model for hadronizaton, we calculate the spin density matrix element ρ_{00} for ϕ mesons and show that anisotropies of local field correlations with respect to the spin quantization direction lead to ϕ meson's spin alignment. We propose that the local correlation or fluctuation of ϕ fields is the dominant mechanism for the observed ϕ meson's spin alignment and its strength can be extracted from experimental data as functions of collision energies. The calculated transverse momentum dependence of ρ_{00} agrees with STAR's data. We further predict the azimuthal angle dependence of ρ_{00} which can be tested in future experiments.
              Cover page: Spin Alignment of Vector Mesons in Heavy-Ion CollisionsCreative Commons 'BY' version 4.0 license
              • Article
              Lawrence Berkeley National Laboratory (2008)
                Cover page: Anti-Hyperon polarization in high energy pp collisions with polarized beams
                • Article
                • Peer Reviewed
                LBL Publications (2024)
                We propose a relativistic theory for spin density matrices of vector mesons based on Kadanoff-Baym equations in the closed-time-path formalism. The theory puts the calculation of spin observables such as the spin density matrix element ρ00 for vector mesons on a solid ground. Within the theory we formulate ρ00 for φ mesons into a factorization form in separation of momentum and spacetime variables. We argue that the main contribution to ρ00 at lower energies should be from the φ fields that can polarize the strange quark and antiquark in the same way as electromagnetic fields. The key observation is that there is correlation inside the φ meson wave function between the φ field that polarizes the strange quark and that polarizes the strange antiquark. This is reflected by the fact that the contributions to ρ00 are all in squares of fields that are nonvanishing even if the fields may strongly fluctuate in spacetime. The fluctuation of strong force fields can be extracted from ρ00 of unflavored vector mesons as links to fundamental properties of quantum chromodynamics.
                  Cover page: Relativistic spin dynamics for vector mesonsCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  LBL Publications (2024)
                  The observation of the vector meson's global spin alignment by the STAR Collaboration reveals that strong spin correlations may exist for quarks and antiquarks in relativistic heavy-ion collisions in the normal direction of the reaction plane. We propose a systematic method to describe such correlations in the quark matter. We classify them as local and long range quark spin correlations in the system. We show in particular that the effective quark spin correlations contain the genuine spin correlations originated directly from the dynamical process as well as those induced by averaging over other degrees of freedom. We also show that such correlations can be studied by measuring the vector meson's spin density matrix and hyperon-hyperon and hyperon-anti-hyperon spin correlations. We present the relationships between these measurable quantities and spin correlations of quarks and antiquarks.
                    Cover page: Global quark spin correlations in relativistic heavy ion collisionsCreative Commons 'BY' version 4.0 license
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