Nuclear Theory·nucl-th

Tuesday·December 1, 2020

17 papers—10 primary·7 cross-listed

11
Form Factors of the Nucleon Axial Current
Chen Chen🇩🇪 · Christian S. Fischer🇩🇪 · Craig D. Roberts🇨🇳 · Jorge Segovia🇪🇸
A symmetry-preserving Poincaré-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, $G_{A}$ and $G_{P}$ , respectively. The result for $G_{A}$ can reliably be represented by a dipole form factor characterised by an axial charge $g_{A} = G_{A} (0) = 1.25 (3)$ and a mass-scale $M_{A} = 1.23 (3) m_{N}$ , where $m_{N}$ is the nucleon mass; and regarding $G_{P}$ , the induced pseudoscalar charge $g_{p}^{*} = 8.80 (23)$ , the ratio $g_{p}^{*} / g_{A} = 7.04 (22)$ , and the pion pole dominance Ansatz is found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: $g_{A}^{d} / g_{A}^{u} = - 0.16 (2)$ . This value expresses a marked suppression of the size of the $d$ -quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function -- both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for $G_{A}$ should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments.
↳ hep-phhep-exhep-latnucl-ex+1PLB(2021)·32 citations
12
Charged-particle multiplicity dependence of charm-baryon-to-meson ratio in high-energy proton-proton collisions
Yu Chen🇨🇳 · Min He🇨🇳
We propose that the charged-particle multiplicity dependence of the charm-baryon-to-meson ratio observed in high-energy $pp$ collisions can be explained by canonical treatment of quantum charges in the statistical hadronization model (SHM). Taking the full particle listings of PDG complemented by additional charm-baryon states from relativistic quark model predictions, we evaluate the canonical partition function and the charm-hadron chemical factors that measure the canonical suppression arising from the requirement of strict conservation of quantum charges. We demonstrate that, while charm number conservation induces common suppression on the production of both charm-baryons and -mesons, baryon (strangeness) number conservation causes further suppression on charm-baryons (charm-strange mesons) relative to nonstrange charm-mesons, thereby resulting in a decreasing $Λ_{c} / D^{0}$ ( $D_{s} / D^{0}$ ) ratio toward smaller multiplicity events. The charm-hadron thermal densities thus computed are then used as pertinent weights to perform charm-quark fragmentation simulations yielding $p_{T}$ -dependent $Λ_{c} / D^{0}$ and $D_{s} / D^{0}$ ratios at varying multiplicities in fair agreement with ALICE measurements.
↳ hep-phhep-exnucl-exnucl-thPLB(2021)·25 citations
13
Explaining the Many Threshold Structures in the Heavy-Quark Hadron Spectrum
Xiang-Kun Dong🇨🇳 · Feng-Kun Guo🇨🇳 · Bing-Song Zou🇨🇳
Tremendous progress has been made experimentally in the hadron spectrum containing heavy quarks in the last two decades. It is surprising that many resonant structures are around thresholds of a pair of heavy hadrons. There should be a threshold cusp at any $S$ -wave threshold. By constructing a nonrelativistic effective field theory with open channels, we discuss the generalities of threshold behavior, and offer an explanation of the abundance of near-threshold peaks in the heavy quarkonium regime. We show that the threshold cusp can show up as a peak only for channels with attractive interaction, and the width of the cusp is inversely proportional to the reduced mass relevant for the threshold. We argue that there should be threshold structures at any threshold of a pair of heavy-quark and heavy-antiquark hadrons, which have attractive interaction at threshold, in the invariant mass distribution of a heavy quarkonium and light hadrons that couple to that open-flavor hadron pair. The structure becomes more pronounced if there is a near-threshold pole. Predictions of the possible pairs are also given for the ground state heavy hadrons. Precisely measuring the threshold structures will play an important role in revealing the heavy-hadron interactions, and thus understanding the puzzling hidden-charm and hidden-bottom structures.
↳ hep-phhep-exhep-latnucl-thPRL(2021)·165 citations
14
Decay: A Monte Carlo library for the decay of a particle with ROOT compatibility
R.A. Kycia🇨🇿 · P. Lebiedowicz🇵🇱 · A. Szczurek🇵🇱
Recently, there is a need for a general-purpose event generator of decays of an elementary particle or a hadron to a state of higher multiplicity ( $N > 2$ ) that is simple to use and universal. We present the structure of such a library to produce generators that generate kinematics of decay processes and can be used to integrate any matrix element squared over phase space of this decay. Some test examples are presented, and results are compared with results known from the literature. As one of examples we consider the Standard Model Higgs boson decay into four leptons. The generators discussed here are compatible with the ROOT interface.
↳ hep-phcs.CEhep-thnucl-thCommun.Comput.Phys.(2021)·2 citations
15
Spin polarization dynamics in the Gubser-expanding background
Rajeev Singh🇵🇱 · Gabriel Sophys🇵🇱 · Radoslaw Ryblewski🇵🇱
Evolution of spin polarization in the Gubser-expanding conformal perfect-fluid hydrodynamic background is studied. The analysis of the conformal transformation properties of the conservation laws is extended to the case of the angular momentum conservation. The explicit forms of equations of motion for spin components are derived and analysed, and some special solutions are found.
↳ hep-phnucl-thPRD(2021)·80 citations
16
Progress in the Glauber model at collider energies
David d'Enterria🇨🇭 · Constantin Loizides🇺🇸
We review the theoretical and experimental progress in the Glauber model of multiple nucleon and/or parton scatterings, after the last 10--15 years of operation with proton and nuclear beams at the CERN Large Hadron Collider (LHC) and with various light and heavy colliding ions at the BNL Relativistic Heavy Ion Collider (RHIC). The main developments and the state-of-the-art of the field are summarized. These encompass measurements of the inclusive inelastic proton and nuclear cross sections, advances in the description of the proton and nuclear density profiles and their fluctuations, inclusion of subnucleonic degrees of freedom, experimental procedures and issues related to the determination of the collision centrality, validation of the binary scaling prescription for hard scattering cross sections, and constraints on transport properties of quark-gluon matter from varying initial-state conditions in relativistic hydrodynamics calculations. These advances confirm the validity and usefulness of the Glauber formalism for quantitative studies of QCD matter produced in high-energy collisions of systems, from protons to uranium nuclei, of vastly different size.
↳ hep-phhep-exnucl-exnucl-thAnn.Rev.Nucl.Part.Sci.(2021)·138 citations
17
Lattice Nucleon Isovector Unpolarized Parton Distribution in the Physical-Continuum Limit
Huey-Wen Lin🇺🇸 · Jiunn-Wei Chen🇹🇼 · Rui Zhang🇺🇸
We present the first lattice-QCD calculation of the nucleon isovector unpolarized parton distribution functions (PDFs) at the physical-continuum limit using Large-Momentum Effective Theory (LaMET). The lattice results are calculated using ensembles with multiple sea pion masses with the lightest one around 135~MeV, 3 lattice spacings $a \in [0.06, 0.12]$ ~fm, and multiple volumes with $M_{π} L$ ranging 3.3 to 5.5. We perform a simultaneous chiral-continuum extrapolation to obtain RI/MOM renormalized nucleon matrix elements with various Wilson-link displacements in the continuum limit at physical pion mass. Then, we apply one-loop perturbative matching to the quasi-PDFs to obtain the lightcone PDFs. We find the lattice-spacing dependence to be much larger than the dependence on pion mass and lattice volume for these LaMET matrix elements. Our physical-continuum limit unpolarized isovector nucleon PDFs are found to be consistent with global-PDF results.
↳ hep-lathep-phnucl-th44 citations

Affiliations

first authorsco-authorsvia INSPIRE

Form Factors of the Nucleon Axial Current

Charged-particle multiplicity dependence of charm-baryon-to-meson ratio in high-energy proton-proton collisions

Explaining the Many Threshold Structures in the Heavy-Quark Hadron Spectrum

Decay: A Monte Carlo library for the decay of a particle with ROOT compatibility

Spin polarization dynamics in the Gubser-expanding background

Progress in the Glauber model at collider energies

Lattice Nucleon Isovector Unpolarized Parton Distribution in the Physical-Continuum Limit

Affiliations