Nuclear Theory·nucl-th

Monday·September 28, 2020

12 papers—3 primary·9 cross-listed

01
Kinetic energy dissipation and fluctuations in strongly-damped heavy-ion collisions within the stochastic mean-field approach
Sakir Ayik · Kazuyuki Sekizawa
Background: Microscopic mean-field approaches have been successful in describing the most probable reaction outcomes in low-energy heavy-ion reactions. However, those approaches are known to severely underestimate dispersions of observables around the average values that has limited their applicability. Recently it has been shown that a quantal transport approach based on the stochastic mean-field (SMF) theory significantly improves the description, while its application has been limited so far to fragment mass and charge dispersions. Purpose: In this work, we extend the quantal transport approach based on the SMF theory for relative kinetic energy dissipation and angular momentum transfer in low-energy heavy-ion reactions. Results: As the first application of the proposed formalism, we consider the radial linear momentum dispersion, neglecting the coupling between radial and angular momenta. We analyze the total kinetic energy (TKE) distribution of binary reaction products in the $^{136}$ Xe+ $^{208}$ Pb reaction at $E_{c.m.} = 526$ MeV and compare with experimental data. From time evolution of single-particle orbitals in TDHF, the radial diffusion coefficient is computed on a microscopic basis, while a phenomenological treatment is introduced for the radial friction coefficient. By solving the quantal diffusion equation for the radial linear momentum, the dispersion of the radial linear momentum is obtained, from which one can construct the TKE distribution. We find that the calculations provide a good description of the TKE distribution for large values of energy losses, TKEL $≳$ 150 MeV. However, the calculations underestimate the TKE distribution for smaller energy losses. Further studies are needed to improve the technical details of calculations. (Shortened due to the word limit)
nucl-thnucl-exPRC(2020)·15 citations
02
Chiral crossover transition from the Dyson-Schwinger equations in a sphere
Yin-Zhen Xu🇨🇳 · Chao Shi🇨🇳 · Xiao-Tao He🇨🇳 · Hong-Shi Zong🇨🇳
Within the framework of Dyson--Schwinger equations of QCD, we study the effect of finite volume on the chiral phase transition in a sphere with the MIT boundary condition. We find that the chiral quark condensate $⟨ ψ ˉ ψ ⟩$ and pseudotransition temperature $T_{p c}$ of the crossover decreases as the volume decreases, until there is no chiral crossover transition at last. We find that the system for $R = \infty$ \ fm is indistinguishable from $R = 10$ fm and there is a significant decrease in $T_{p c}$ with $R$ as $R < 4$ fm. When $R < 1.5$ fm, there is no chiral transition in the system.
nucl-thPRD(2020)·16 citations
03
SWANLOP : Scattering waves off nonlocal optical potentials in the presence of Coulomb interactions
H. F. Arellano🇨🇱 · G. Blanchon🇫🇷
We introduce the package SWANLOP to calculate scattering waves and corresponding observables for nucleon elastic collisions off spin-zero nuclei. The code is capable of handling local and nonlocal optical potentials superposed to long-range Coulomb interaction. Solutions to the implied Schrödinger integro-differential equation are obtained by solving an integral equation of Lippmann-Schwinger type for the scattering wavefunctions, $ψ = ϕ_{C} + G_{C} U_{S} ψ$ , providing and exact treatment to the Coulomb force [Phys. Lett. B 789, 256 (2019)]. The package has been developed to handle potentials either in momentum or coordinate representations, providing flexible options under each of them. The code is fully self-contained, being dimensioned to handle any $A \geq 4$ target for nucleon beam energies of up to 1.1 GeV. Accuracy and benchmark applications are presented and discussed.
nucl-thComput.Phys.Commun.(2021)·17 citations
04
Restoration of chiral symmetry in cold and dense Nambu--Jona-Lasinio model with tensor renormalization group
Shinichiro Akiyama🇯🇵 · Yoshinobu Kuramashi🇯🇵 · Takumi Yamashita🇯🇵 · Yusuke Yoshimura🇯🇵
We analyze the chiral phase transition of the Nambu--Jona-Lasinio model in the cold and dense region on the lattice developing the Grassmann version of the anisotropic tensor renormalization group algorithm. The model is formulated with the Kogut--Susskind fermion action. We use the chiral condensate as an order parameter to investigate the restoration of the chiral symmetry. The first-order chiral phase transition is clearly observed in the dense region at vanishing temperature with $μ / T \sim O (1 0^{3})$ on a large volume of $V = 102 4^{4}$ . We also present the results for the equation of state.
↳ hep-lathep-phhep-thnucl-thJHEP(2021)·38 citations
05
Joint thrust and TMD resummation in electron-positron and electron-proton collisions
Yiannis Makris🇮🇹 · Felix Ringer🇺🇸 · Wouter J. Waalewijn🇳🇱
We present the framework for obtaining precise predictions for the transverse momentum of hadrons with respect to the thrust axis in $e^{+} e^{-}$ collisions. This will enable a precise extraction of transverse momentum dependent (TMD) fragmentation functions from a recent measurement by the Belle Collaboration. Our analysis takes into account, for the first time, the nontrivial interplay between the hadron transverse momentum and the cut on the thrust event shape. To this end, we identify three different kinematic regions, derive the corresponding factorization theorems within Soft Collinear Effective Theory, and present all ingredients needed for the joint resummation of the transverse momentum and thrust spectrum at NNLL accuracy. One kinematic region can give rise to non-global logarithms (NGLs), and we describe how to include the leading NGLs. We also discuss alternative measurements in $e^{+} e^{-}$ collisions that can be used to access the TMD fragmentation function. Finally, by using crossing symmetry, we obtain a new way to constrain TMD parton distributions, by measuring the displacement of the thrust axis in $e p$ collisions.
↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·26 citations
06
Diffusion Monte Carlo calculations of fully-heavy (multiquark) bound states
M.C. Gordillo🇪🇸 · F. De Soto🇪🇸 · J. Segovia🇪🇸
We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation describing fully-heavy tetraquark systems. This approach allows to reduce the uncertainty of the numerical calculation at the percent level, accounts for multi-particle correlations in the physical observables, and avoids the usual quark-clustering assumed in other theoretical techniques applied to the same problem. The interaction between particles was modeled by the most general and accepted potential, i.e. a pairwise interaction including Coulomb, linear-confining and hyperfine spin-spin terms. This means that, in principle, our analysis should provide some rigorous statements about the mass location of the all-heavy tetraquark ground states, which is particularly timely due to the very recent observation made by the LHCb collaboration of some enhancements in the invariant mass spectra of $J / ψ$ -pairs. Our main results are: (i) the $cc c ˉ c ˉ$ , $cc b ˉ b ˉ$ ( $bb c ˉ c ˉ$ ) and $bb b ˉ b ˉ$ lowest-lying states are located well above their corresponding meson-meson thresholds; (ii) the $J^{P C} = 0^{++}$ $cc c ˉ c ˉ$ ground state with preferred quark-antiquark pair configurations is compatible with the enhancement(s) observed by the LHCb collaboration; (iii) our results for the $cc c ˉ b ˉ$ and $bb c ˉ b ˉ$ sectors seem to indicate that the $0^{+}$ and $1^{+}$ ground states are almost degenerate with the $2^{+}$ located around $100 MeV$ above them; (iv) smaller mass splittings for the $c b c ˉ b ˉ$ system are predicted, with absolute mass values in reasonable agreement with other theoretical works; (v) the $1^{++}$ $c b c ˉ b ˉ$ tetraquark ground state lies at its lowest $S$ -wave meson-meson threshold and it is compatible with a molecular configuration.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2020)·100 citations
07
Forward dijets in proton-nucleus collisions at next-to-leading order: the real corrections
Edmond Iancu🇫🇷 · Yair Mulian🇫🇮
Using the CGC effective theory together with the hybrid factorisation, we study forward dijet production in proton-nucleus collisions beyond leading order. In this paper, we compute the "real" next-to-leading order (NLO) corrections, i.e. the radiative corrections associated with a three-parton final state, out of which only two are being measured. To that aim, we start by revisiting our previous results for the three-parton cross-section presented in our previous paper. After some reshuffling of terms, we deduce new expressions for these results, which not only look considerably simpler, but are also physically more transparent. We also correct several errors in this process. The real NLO corrections to inclusive dijet production are then obtained by integrating out the kinematics of any of the three final partons. We explicitly work out the interesting limits where the unmeasured parton is either a soft gluon, or the product of a collinear splitting. We find the expected results in both limits: the B-JIMWLK evolution of the leading-order dijet cross-section in the first case (soft gluon) and, respectively, the DGLAP evolution of the initial and final states in the second case (collinear splitting). The "virtual" NLO corrections to dijet production will be presented in a subsequent publication.
↳ hep-phhep-thnucl-thJHEP(2021)·38 citations
08
Hexaquark picture for $d^{*} (2380)$
Hungchong Kim🇰🇷 · K. S. Kim🇰🇷 · Makoto Oka🇯🇵
Hexaquark wave function with the quantum numbers $I (J^{P}) = 0 (3^{+})$ , which might be relevant for $d^{*} (2380)$ , is constructed under an assumption that this is composed only of $u, d$ quarks in an $S$ -wave. By combining three diquarks of either type, ( $3 ˉ_{c}, I = 1$ ) or ( $6_{c}, I = 0$ ), we demonstrate that there are five possible configurations for the six-quark state. The fully antisymmetric wave function is constructed by linearly combining the five configurations on an equal footing. We then take this wave function as well as the five configurations to calculate the hexaquark mass using the contact type effective potential consisting of the color-spin, color electric and constant shift. The mass is found to be the same regardless of the configurations being used including the fully antisymmetric one. This result can be traced to the fact that the hexaquark system has a freedom in choosing three diquarks in the construction of its wave function. The calculated hexaquark mass using the empirical parameters independently fixed from the baryon spectroscopy is found to be around $2342$ MeV, which is indeed very close to the experimental mass of $d^{*} (2380)$ . Therefore, the hexaquark picture is promising for $d^{*} (2380)$ as far as the mass is concerned.
↳ hep-phhep-exnucl-thPRD(2020)·29 citations
09
Emergent Structure in QCD
James C. Biddle · Waseem Kamleh · Derek B. Leinweber (University of Adelaide)
The structure of the SU(3) gauge-field vacuum is explored through visualisations of centre vortices and topological charge density. Stereoscopic visualisations highlight interesting features of the vortex vacuum, especially the frequency with which singular points appear and the important connection between branching points and topological charge. This work demonstrates how visualisations of the QCD ground-state fields can reveal new perspectives of centre-vortex structure.
↳ hep-latnucl-thEPJ Web Conf.(2020)·4 citations
10
Parton distributions in radiative corrections to the cross section of electron-proton scattering
V.S. Fadin🇷🇺 · R.E. Gerasimov🇷🇺
The structure function approach and the parton picture, developed for the theoretical description of the deep inelastic electron-proton scattering, also proved to be very effective for calculation of radiative corrections in Quantum Electrodynamics. We use them to calculate radiative corrections to the cross section of electron-proton scattering due to electron-photon interaction, in the experimental setup with the recoil proton detection, proposed by A.A. Vorobev to measure the proton radius. In the one-loop approximation, explicit expressions for these corrections are obtained for arbitrary momentum transfers. It is shown that, at momentum transfers small compared with the proton mass, various contributions to the corrections mutually cancel each other with power accuracy. In two loops, the corrections are obtained in the leading logarithmic approximation.
↳ hep-phnucl-thEPJA(2021)·1 citation
11
Low-energy Scattering and Effective Interactions of Two Baryons at $m_{π} \sim 450$ MeV from Lattice Quantum Chromodynamics
Marc Illa🇪🇸 · Silas R. Beane🇺🇸 · Emmanuel Chang · Zohreh Davoudi🇺🇸 · William Detmold🇺🇸 · David J. Murphy🇺🇸 · Kostas Orginos🇺🇸 · Assumpta Parreño🇪🇸 · Martin J. Savage🇺🇸 · Phiala E. Shanahan🇺🇸 · Michael L. Wagman🇺🇸 · Frank Winter🇺🇸
The interactions between two octet baryons are studied at low energies using lattice QCD (LQCD) with larger-than-physical quark masses corresponding to a pion mass of $m_{π} \sim 450$ MeV and a kaon mass of $m_{K} \sim 596$ MeV. The two-baryon systems that are analyzed range from strangeness $S = 0$ to $S = - 4$ and include the spin-singlet and triplet $N N$ , $Σ N$ ( $I = 3/2$ ), and $ΞΞ$ states, the spin-singlet $ΣΣ$ ( $I = 2$ ) and $ΞΣ$ ( $I = 3/2$ ) states, and the spin-triplet $Ξ N$ ( $I = 0$ ) state. The $s$ -wave scattering phase shifts, low-energy scattering parameters, and binding energies when applicable, are extracted using Lüscher's formalism. While the results are consistent with most of the systems being bound at this pion mass, the interactions in the spin-triplet $Σ N$ and $ΞΞ$ channels are found to be repulsive and do not support bound states. Using results from previous studies at a larger pion mass, an extrapolation of the binding energies to the physical point is performed and is compared with experimental values and phenomenological predictions. The low-energy coefficients in pionless EFT relevant for two-baryon interactions, including those responsible for $S U (3)$ flavor-symmetry breaking, are constrained. The $S U (3)$ symmetry is observed to hold approximately at the chosen values of the quark masses, as well as the $S U (6)$ spin-flavor symmetry, predicted at large $N_{c}$ . A remnant of an accidental $S U (16)$ symmetry found previously at a larger pion mass is further observed. The $S U (6)$ -symmetric EFT constrained by these LQCD calculations is used to make predictions for two-baryon systems for which the low-energy scattering parameters could not be determined with LQCD directly in this study, and to constrain the coefficients of all leading $S U (3)$ flavor-symmetric interactions, demonstrating the predictive power of two-baryon EFTs matched to LQCD.
↳ hep-lathep-phnucl-thPRD(2021)·55 citations
12
Finite-volume energy spectrum of the $K^{-} K^{-} K^{-}$ system
Andrei Alexandru🇺🇸 · Ruairí Brett🇺🇸 · Chris Culver🇬🇧 · Michael Döring🇺🇸 · Dehua Guo🇺🇸 · Frank X. Lee🇺🇸 · Maxim Mai🇺🇸
The dynamics of multi-kaon systems are of relevance for several areas of nuclear physics. However, even the simplest systems, two and three kaons, are hard to prepare and study experimentally. Here we show how to extract this information using first-principle lattice QCD results. We (1) extend the relativistic three-body quantization condition to the strangeness sector, predicting for the first time the excited level finite-volume spectrum of three kaon systems at maximal isospin, and (2) present a first lattice QCD calculation of the excited levels of this system in a finite box. We compare our predictions with the lattice results reported here and with previous ground state calculations and find very good agreement.
↳ hep-lathep-phnucl-thPRD(2020)·84 citations

Affiliations

first authorsco-authorsvia INSPIRE