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Nuclear Theory·nucl-th

Wednesday·June 16, 2021

5 papers—2 primary·3 cross-listed

All5Primary2Cross-lists3
  1. 01

    [Submitted on 15 Jun 2021]

    Probing early-time longitudinal dynamics with the hyperon's spin polarization in relativistic heavy-ion collisions

    Sangwook Ryu🇺🇸 · Vahidin Jupic🇺🇸 · Chun Shen🇺🇸

    We systematically study the hyperon global polarization's sensitivity to the collision systems' initial longitudinal flow velocity in hydrodynamic simulations. By explicitly imposing local energy-momentum conservation when mapping the initial collision geometry to macroscopic hydrodynamic fields, we study the evolution of systems' orbital angular momentum (OAM) and fluid vorticity. We find that a simultaneous description of the hyperons' global polarization and the slope of pion's directed flow can strongly constrain the size of longitudinal flow at the beginning of hydrodynamic evolution. We extract the size of the initial longitudinal flow and the fraction of orbital angular momentum in the produced QGP fluid as a function of collision energy with the STAR measurements in the RHIC Beam Energy Scan program. We find that there is about 100-200 OAM that remains in the mid-rapidity fluid at the beginning of hydrodynamic evolution. We further exam the effects of different hydrodynamic gradients on the spin polarization of and . The gradients of can change the ordering between 's and 's polarization.

    Comments:
    update in accordance with the referee report
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.08125 [pdf]
    PRC(2021)·100 citations
  2. 02

    [Submitted on 15 Jun 2021]

    Imprints of high-momentum nucleons in nuclei on hard photons from heavy-ion collisions around the Fermi Energy

    Wen-Mei Guo🇨🇳 · Bao-An Li🇺🇸 · Gao-Chan Yong🇨🇳

    The short-range correlation (SRC) induced by the tensor force in the isosinglet neutron-proton interaction channel leads to a high-momentum tail (HMT) in the single-nucleon momentum distributions n(k) in nuclei. Owing to the remaining uncertainties about the tensor force, the shape of the nucleon HMT may be significantly different from the dilute interacting Fermi gas model prediction similar to the HMT in cold atoms near the unitary limit. Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck transport model incorporating approximately the nucleon HMT, we investigate hard photon emissions in N+C and Ca+Sn reactions at beam energies around the Fermi energy. Imprints of different shapes of the HMT on the energy spectrum, angular distribution and transverse momentum spectrum of hard photons are studied. While the angular distribution does not carry any information about the shape of the nucleon HMT, the energy spectra and especially the mid-rapidity transverse momentum spectra of hard photons are found to bare strong imprints of the shapes of nucleon HMTs in the two colliding nuclei.

    Comments:
    More discussions added. Physical Review C in press
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2106.08242 [pdf]
    PRC(2021)·37 citations
  3. 03

    [Submitted on 15 Jun 2021] (cross-list from hep-ph)

    Electric conductivity with the magnetic field and the chiral anomaly in a holographic QCD model

    Kenji Fukushima🇯🇵 · Akitoshi Okutsu🇯🇵

    We calculate the electric conductivity in deconfined QCD matter using a holographic QCD model, i.e., the Sakai-Sugimoto Model with varying magnetic field and chiral anomaly strength. After confirming that our estimated for is consistent with the lattice-QCD results, we study the case with in which the coefficient in the Chern-Simons term controls the chiral anomaly strength. Our results imply that the transverse conductivity, , is suppressed to be at as compared to the case when the temperature is fixed as . Since the Sakai-Sugimoto Model has massless fermions, the longitudinal conductivity, , with should diverge due to production of the matter chirality. Yet, it is possible to extract a regulated part out from with an extra condition to neutralize the matter chirality. This regulated quantity is interpreted as an Ohmic part of . We show that the longitudinal Ohmic conductivity increases with increasing for small , while it is suppressed with larger for physical due to anomaly induced interactions.

    Comments:
    9 pages, 2 figures; references added
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    2106.07968 [pdf]
    PRD(2022)·21 citations
  4. 04

    [Submitted on 15 Jun 2021] (cross-list from hep-ph)

    Application of radial basis functions neutral networks in spectral functions

    Meng Zhou🇨🇳 · Fei Gao🇩🇪 · Jingyi Chao🇨🇳 · Yu-Xin Liu🇨🇳 · Huichao Song🇨🇳

    The reconstruction of spectral function from correlation function in Euclidean space is a challenging task. In this paper, we employ the Machine Learning techniques in terms of the radial basis functions networks to reconstruct the spectral function from a finite number of correlation data. To test our method, we first generate one type of correlation data using a mock spectral function by mixing several Breit-Wigner propagators. We found that compared with other traditional methods, TSVD, Tikhonov, and MEM, our approach gives a continuous and unified reconstruction for both positive definite and negative spectral function, which is especially useful for studying the QCD phase transition. Moreover, our approach has considerably better performance in the low frequency region. This has advantages for the extraction of transport coefficients which are related to the zero frequency limit of the spectral function. With the mock data generated through a model spectral function of stress energy tensor, we find our method gives a precise and stable extraction of the transport coefficients.

    Comments:
    10 pages, 7 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2106.08168 [pdf]
    PRD(2021)·21 citations
  5. 05

    [Submitted on 15 Jun 2021] (cross-list from hep-ph)

    Constraining baryon annihilation in the hadronic phase of heavy-ion collisions via event-by-event fluctuations

    Oleh Savchuk🇩🇪 · Volodymyr Vovchenko🇺🇸 · Volker Koch🇺🇸 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪

    We point out that the variance of net-baryon distribution normalized by the Skellam distribution baseline, , is sensitive to the possible modification of (anti)baryon yields due to annihilation in the hadronic phase. The corresponding measurements can thus place stringent limits on the magnitude of the annihilation and its inverse reaction. We perform Monte Carlo simulations of the hadronic phase in Pb-Pb collisions at the LHC via the recently developed subensemble sampler + UrQMD afterburner and show that the effect survives in net-proton fluctuations, which are directly accessible experimentally. The available experimental data of the ALICE Collaboration on net-proton fluctuations disfavors a notable suppression of (anti)baryon yields in annihilations predicted by the present version of UrQMD if only global baryon conservation is incorporated. On the other hand, the annihilations improve the data description when local baryon conservation is imposed. The two effects can be disentangled by measuring , which at the LHC is notably suppressed by annihilations but virtually unaffected by baryon number conservation.

    Comments:
    6 pages, 4 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2106.08239 [pdf]
    PLB(2022)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE