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Nuclear Theory·nucl-th

Wednesday·December 16, 2020

7 papers—2 primary·5 cross-listed

All7Primary2Cross-lists5
  1. 01

    [Submitted on 14 Dec 2020]

    Fluid velocity from transverse momentum spectra

    Anthony Guillen🇫🇷 · Jean-Yves Ollitrault🇫🇷

    We parametrize the transverse momentum distribution of outgoing hadrons in ultrarelativistic nucleus-nucleus collisions as a superposition of boosted thermal distributions. In this approach, which generalizes the conventional blast wave, the momentum distribution is determined by the distribution of the fluid velocity. We analyze the difference between this generalized blast-wave parametrization and a full hydrodynamic calculation. We then apply the generalized blast-wave fit to experimental data on Pb+Pb collisions at . The fit is reasonable up to , much beyond the range where hydrodynamics is usually applied, but not perfect. Based on the differences between the fit and the data, we argue that an ideal hydrodynamic calculation cannot fit simultaneously all identified particle spectra, irrespective of the specific implementation. In particular, data display a significant excess of pions at low , whose physical interpretation is discussed. Data also show that the distribution of the fluid velocity becomes broader as the collision becomes less central. This broadening is explained by event-by-event hydrodynamic calculations, where it results from the centrality dependence of initial-state fluctuations.

    Comments:
    Published version; 13 pages, 9 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2012.07898 [pdf]
    PRC(2021)·13 citations
  2. 02

    [Submitted on 15 Dec 2020]

    Theoretical calculation of nuclear reactions of interest for Big Bang Nucleosynthesis

    Alex Gnech

    Standard Big Bang Nucleosynthesis (BBN) predicts the abundances of the light elements in the early universe. Even if the overall agreement with the experimental data is good, still some discrepancies exist on the relic abundances of Li and Li. In order to exclude or confirm these scenarios, the BBN model needs precise input parameters, in particular the cross-sections of the BBN nuclear reaction network. However, the suppression of the cross-sections due to the Coulomb barrier makes the measurement very difficult and so affected by large systematic errors. Therefore, reliable theoretical calculations result fundamental in order to reduce the uncertainties. In this work we present a theoretical study of two nuclear reactions connected to Li abundance and recently the +d Li + and the p+LiBe+ radiative captures. For the first reaction we use a so-called ab-initio approach in which we solve the full six-body problem by using realistic nuclear potentials to describe the nucleon interactions. In particular we concentrate on the calculation and characterization of the final state of the reaction, the Li ground state, focusing on the electromagnetic static structure and the quantities relevant from the astrophysical point of view such as the asymptotic normalization coefficient. For doing this we use the Hyperspherical Harmonic approach developed by the Pisa group providing for the first time the possibility of using this approach beyond A = 4 nuclear systems. The second reaction is instead studied by using a two-body cluster approach where the proton and Li are considered as structureless particles. The angular distribution of the emitted photon obtained in this work were used by the LUNA Collaboration to determine the efficiency of the detector used in the measurement of the reaction.

    Comments:
    PhD Thesis
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2012.08431 [pdf]
    0 citations
  3. 03

    [Submitted on 14 Dec 2020] (cross-list from hep-ph)

    TMD Fragmentation Functions at NLO

    Markus A. Ebert🇩🇪 · Bernhard Mistlberger🇺🇸 · Gherardo Vita🇺🇸

    We compute the unpolarized quark and gluon transverse-momentum dependent fragmentation functions (TMDFFs) at next-to-next-to-next-to-leading order (NLO) in perturbative QCD. The calculation is based on a relation between the TMDFF and the limit of the semi-inclusive deep inelastic scattering cross section where all final-state radiation becomes collinear to the detected hadron. The required cross section is obtained by analytically continuing our recent computation of the Drell-Yan and Higgs boson production cross section at NLO expanded around the limit of all final-state radiation becoming collinear to one of the initial states. Our results agree with a recent independent calculation by Luo et al.

    Comments:
    20 pages + appendices, 3 figures, 6 ancillary files; v2: journal version
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2012.07853 [pdf]
    JHEP(2021)·62 citations
  4. 04

    [Submitted on 14 Dec 2020] (cross-list from hep-ph)

    The Energy-Energy Correlation in the back-to-back limit at NLO and NLL

    Markus A. Ebert🇩🇪 · Bernhard Mistlberger🇺🇸 · Gherardo Vita🇺🇸

    We present the analytic formula for the Energy-Energy Correlation (EEC) in electron-positron annihilation computed in perturbative QCD to next-to-next-to-next-to-leading order (NLO) in the back-to-back limit. In particular, we consider the EEC arising from the annihilation of an electron-positron pair into a virtual photon as well as a Higgs boson and their subsequent inclusive decay into hadrons. Our computation is based on a factorization theorem of the EEC formulated within Soft-Collinear Effective Theory (SCET) for the back-to-back limit. We obtain the last missing ingredient for our computation - the jet function - from a recent calculation of the transverse-momentum dependent fragmentation function (TMDFF) at NLO. We combine the newly obtained NLO jet function with the well known hard and soft function to predict the EEC in the back-to-back limit. The leading transcendental contribution of our analytic formula agrees with previously obtained results in supersymmetric Yang-Mills theory. We obtain the Mellin moment of the bulk region of the EEC using momentum sum rules. Finally, we obtain the first resummation of the EEC in the back-to-back limit at NLL accuracy, resulting in a factor of reduction of uncertainties in the peak region compared to NLL predictions.

    Comments:
    32 pages, many wonderful figures, 3 appendices, 7 ancillary files. v2: Journal version. Added regulator independent jet functions, comparisons with OPAL data and O(as^3) numerical fixed order results
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    2012.07859 [pdf]
    JHEP(2021)·81 citations
  5. 05

    [Submitted on 15 Dec 2020] (cross-list from hep-ph)

    Hadronic Atom as a Key to Revealing the Mystery

    Zhen-Hua Zhang🇨🇳 · Feng-Kun Guo🇨🇳

    The , whose mass coincides with the threshold, is the most extended hadron object. Since its discovery in 2003, debates have never stopped regarding its internal structure. We propose a new object, the atom, which is the composite system with positive charge parity and a mass of MeV, formed mainly due to the Coulomb force. We show that a null signal of the atom can be used to put a lower limit on the binding energy of the . From the current knowledge of the properties, the production rate for the atom relative to the in decays and at hadron colliders should be at least . New insights into the will be obtained through studying the atom.

    Comments:
    6 pages, 3 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2012.08281 [pdf]
    PRL(2021)·19 citations
  6. 06

    [Submitted on 15 Dec 2020] (cross-list from hep-th)

    All order effective action for charge diffusion from Schwinger-Keldysh holography

    Yanyan Bu🇨🇳 · Tuna Demircik🇰🇷 · Michael Lublinsky🇮🇱

    An effective action for diffusion of a conserved charge is derived to all orders in the derivative expansion within a holographic model dual to the Schwinger-Keldysh closed time path. A systematic approach to solution of the 5D Maxwell equations in a doubled Schwarzschild-AdS black brane geometry is developed. Constitutive relation for the stochastic charge current is shown to have a term induced by thermal fluctuations (coloured noise). All transport coefficient functions parameterising the effective action and constitutive relations are computed analytically in the hydrodynamic expansion, and then numerically for finite momenta.

    Comments:
    v1: 59 pages, 11 multi-figures; v2: 53 pages in JHEP style, refs added, one appendix added, revised the partially off-shell procedure based on bulk path integral
    Subjects:
    High Energy Physics — Theory (hep-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2012.08362 [pdf]
    JHEP(2021)·29 citations
  7. 07

    [Submitted on 15 Dec 2020] (cross-list from hep-ph)

    Hadronization of correlated gluon fields

    Moritz Greif🇩🇪 · Carsten Greiner🇩🇪 · Simon Plätzer🇦🇹 · Björn Schenke🇺🇸 · Sören Schlichting🇩🇪

    Following an explicit example, we present the chain of steps required for an event-by-event description of hadron production in high energy hadronic and nuclear collisions. We start from incoming nuclei, described in the Color Glass Condensate effective theory, whose collision creates the gluon fields of the glasma. Individual gluons are then sampled from the gluon fields' Husimi (smeared Wigner) distributions, and clustered using a new spacetime based algorithm. Clusters are fed into the Herwig event generator, which performs the hadronization, conserving energy and momentum. We discuss the physical implications of smearing and problems with the quasi particle picture for the studied processes. We compute spectra of charged hadrons and identified particles and their azimuthal momentum anisotropies, and address systematic uncertainties on observables, resulting from the general lack of detailed knowledge of the hadronization mechanism.

    Comments:
    12 pages, 15 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2012.08493 [pdf]
    PRD(2021)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE