Nuclear Theory·nucl-th

Tuesday·July 30, 2024

16 papers—8 primary·8 cross-listed

09
Cold nuclear matter effects on azimuthal decorrelation in heavy-ion collisions
Néstor Armesto🇪🇸 · Florian Cougoulic🇪🇸 · Bin Wu🇪🇸
The assumption of factorization lies at the core of calculations of medium effects on observables computable in perturbative Quantum Chromodynamics. In this work we examine this assumption, for which we propose a setup to study hard processes and bulk nuclear matter in heavy-ion collisions on the same footing using the Glauber modelling of heavy nuclei. To exemplify this approach, we calculate the leading-order corrections to azimuthal decorrelation in Drell-Yan and boson-jet processes due to cold nuclear matter effects, not considering radiation. At leading order in both the hard momentum scale and the nuclear size, the impact-parameter dependent cross section is found to factorize for both processes. The factorization formula involves a convolution of the hard cross section with the medium-modified parton distributions, and, for boson-jet production, the medium-modified jet function.
↳ hep-phnucl-thJHEP(2024)·2 citations
10
Magicity versus superfluidity around $^{28}$ O viewed from the study of $^{30}$ F
J. Kahlbow🇰🇷 · T. Aumann🇰🇷 · O. Sorlin🇫🇷 · Y. Kondo🇯🇵 · T. Nakamura🇯🇵 · F. Nowacki🇫🇷 · A. Revel🇫🇷 · N. L. Achouri🇫🇷 · H. Al Falou🇱🇧 · L. Atar🇰🇷 · H. Baba🇯🇵 · K. Boretzky🇩🇪 and 75 other authors
The neutron-rich unbound fluorine isotope $^{30}$ F $_{21}$ has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasi-free proton knockout reaction of $^{31}$ Ne nuclei at 235 MeV/nucleon. The mass and thus one-neutron-separation energy of $^{30}$ F has been determined to be $S_{n} = - 472 \pm 58 (stat.) \pm 33 (sys.)$ keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in $S_{n}$ ( $^{30}$ F) shows that the ``magic'' $N = 20$ shell gap is not restored close to $^{28}$ O, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron $d$ and $f p$ orbitals, with the $1 p_{3/2}$ and $1 p_{1/2}$ orbitals becoming more bound than the $0 f_{7/2}$ one. This degeneracy and reordering of orbitals has two potential consequences: $^{28}$ O behaves like a strongly superfluid nucleus with neutron pairs scattering across shells, and both $^{29, 31}$ F appear to be good two-neutron halo-nucleus candidates.
↳ nucl-exnucl-thPRL(2024)·11 citations
11
Revisiting gauge invariance and Reggeization of pion exchange
Gloria Montana🇺🇸 · Daniel Winney🇩🇪 · Lukasz Bibrzycki🇵🇱 · Cesar Fernandez-Ramirez🇪🇸 · Giorgio Foti🇮🇹 · Nadine Hammoud🇪🇸 · Vincent Mathieu🇪🇸 · Robert J. Perry🇪🇸 · Alessandro Pilloni🇮🇹 · Arkaitz Rodas🇺🇸 · Vanamali Shastry🇺🇸 · Wyatt A. Smith🇺🇸 · Adam P. Szczepaniak🇺🇸
The Reggeized pion is expected to provide the main contribution to the forward cross section in light meson photoproduction reactions with charge exchange at high energies. We discuss the Reggeization of pion exchange in charged pion photoproduction with an emphasis on consistency with current conservation. We show that the gauge-invariant amplitude for the exchange of a particle with generic even spin $J \geq 2$ in the $t$ -channel is analytic at $J = 0$ , and that it can be interpreted in terms of the nucleon electric current. This enables us to reconcile the dynamics in the $s$ - and $u$ -channel, which involves also nucleon exchanges, with the amplitude expressed in terms of $t$ -channel partial waves, as required by Regge theory.
↳ hep-phnucl-thPRD(2024)·9 citations
12
Formulating Schwinger--Dyson equations for QED propagators in Minkowski space
Shaoyang Jia🇺🇸
The Schwinger--Dyson equations (SDEs) are coupled integral equations for the Green's functions of a quantum field theory (QFT). The SDE approach is the analytic nonperturbative method for solving strongly coupled QFTs. When applied to QCD, this approach, also based on the first principle, is the analytic alternative to lattice QCD. However, the SDEs for the n-point Green's functions involves (n+1)-point Green's functions (sometimes (n+2)-point functions as well). Therefore any practical method for solving this infinitely coupled system of equations requires a truncation scheme. When considering strongly coupled QED as a modeling of QCD, naive truncation schemes violate various principles of the gauge theory. These principles include gauge invariance, gauge covariance, and multiplicative renormalizability. The combination of dimensional regularization with the spectral representation of propagators results in a tractable formulation of a truncation scheme for the SDEs of QED propagators, which has the potential to preserve the aforementioned principles and renders solutions obtainable in the Minkowski space.
↳ hep-thnucl-th1 citation
13
Study of one-step and two-step neutron transfer in the reaction $^{6}$ Li + $^{9}$ Be
Azhibekov Aidos · Lukyanov Sergey · Penionzhkevich Yuri · Urazbekov Bakytzhan · Naumenko Mikhail · Samarin Vyacheslav · Issatayev Talgat · Maslov Vladimir · Mendibayev Kayrat · Aznabayev Dauren · Temirzhanov Alisher
The paper presents the results of experiments on measuring the cross sections for elastic scattering and nucleon transfer channels in the $^{6}$ Li + $^{9}$ Be reaction at an incident energy of 68 MeV: $^{9}$ Be( $^{6}$ Li, $^{6}$ Li) $^{9}$ Be, $^{9}$ Be( $^{6}$ Li, $^{7}$ Li) $^{8}$ Be, $^{9}$ Be( $^{6}$ Li, $^{7}$ Li) $^{8}$ Be $_{2 +}$ , $^{9}$ Be( $^{6}$ Li, $^{8}$ Li) $^{7}$ Be, $^{9}$ Be( $^{6}$ Li, $^{7}$ Be) $^{8}$ Li. The aim is to reveal the manifestation of the cluster structure of $^{9}$ Be. Theoretical analysis of the contributions of one-step and two-step neutron transfer mechanisms is performed using the distorted wave Born approximation method with the Fresco code. Good agreement between the calculations and the experimental data was obtained for the channels of elastic scattering $^{9}$ Be( $^{6}$ Li, $^{6}$ Li) $^{9}$ Be, neutron $^{9}$ Be( $^{6}$ Li, $^{7}$ Li) $^{8}$ Be and proton transfer $^{9}$ Be( $^{6}$ Li, $^{7}$ Be) $^{8}$ Li, as well as the transfer of two neutrons $^{9}$ Be( $^{6}$ Li, $^{8}$ Li) $^{7}$ Be. It is shown that the dineutron cluster transfer mechanism makes a dominant contribution to the $^{9}$ Be( $^{6}$ Li, $^{8}$ Li) $^{7}$ Be reaction channel at forward angles.
↳ nucl-exnucl-thCPC(2024)·3 citations
14
QCD jets in a hot and dense medium: a study of shower formation time and collision kernels
Rouzbeh Modarresi-Yazdi🇨🇦 · Shuzhe Shi🇨🇳 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦
With the use of MARTINI, a model which considers evolving QCD jets against a fluid dynamical background, it is shown that the introduction of formation time to the parton shower after the initial hard scattering is essential for a simultaneous description of charged hadron and jet $R_{AA}$ . This inclusion also improves jet shape ratio at small angle and jet fragmentation function ratios of leading charged hadrons. The MARTINI framework is then aimed at a study of the leading order, next-to-leading-order, and non perturbative collision kernels. Sizable differences in the modification of jet substructure observables, i.e., jet shape and fragmentation functions are observed. Such differences are caused by the difference in the radiation rates of relatively soft gluons that survive in the evolution in medium.
↳ hep-phnucl-thPRC(2025)·14 citations
15
Likely existence of bound states and the Efimov effect in the triple- $J / ψ$ system
Ya-Wen Pan🇨🇳 · Zhi-Wei Liu🇨🇳 · Li-Sheng Geng🇨🇳 · Atsushi Hosaka🇯🇵 · Xiang Liu🇨🇳
The ground-breaking discovery of the first fully charmed tetraquark state $X (6900)$ in the $J / ψ J / ψ$ invariant mass distribution by the LHCb collaboration has inspired intensive theoretical studies. Various interpretations, such as molecular states, compact tetraquark states, and coupled-channel effects, have been proposed for these states. Of particular interest is the ongoing search for the triple- $J / ψ$ state--a fully-charmed hexaquark state. To deepen our understanding of the triple- $J / ψ$ state and to guide future experimental searches, we study the triple- $J / ψ$ system in this work employing the Gaussian expansion method and the $J / ψ J / ψ$ potential parameterized to yield a shallow bound state, as suggested in several theoretical works. Our results support a triple- $J / ψ$ bound state, even in cases where the attractive interaction between the two $J / ψ$ mesons is very weak. Moreover, our analysis implies the Efimov effect in the triple- $J / ψ$ system. In addition, we extend our investigation to the triple- $Υ (1 S)$ system and obtain results similar to those for the triple- $J / ψ$ system.
↳ hep-phhep-exnucl-exnucl-thPRD(2024)·3 citations
16
On the EFT of Dyon-Monopole Catalysis
S. Bogojevic🇨🇦 · C.P. Burgess🇨🇦
Monopole-fermion (and dyon-fermion) interactions provide a famous example where scattering from a compact object gives a cross section much larger than the object's geometrical size. This underlies the phenomenon of monopole catalysis of baryon-number violation because the reaction rate is much larger in the presence of a monopole than in its absence. It is sometimes claimed to violate the otherwise generic requirement that short distance physics decouples from long-distance observables -- a property that underpins the general utility of effective field theory (EFT) methods. Decoupling in this context is most simply expressed using point-particle effective field theories (PPEFTs) designed to capture systematically how small but massive objects influence their surroundings when probed only on length scales large compared to their size. These have been tested in precision calculations of how nuclear properties affect atomic energy levels for both ordinary and pionic atoms. We adapt the PPEFT formalism to describe low-energy $S$ -wave dyon-fermion scattering with a view to understanding whether large catalysis cross sections violate decoupling (and show why they do not). We also explore the related but separate issue of the long-distance complications associated with polarizing the fermion vacuum exterior to a dyon and show in some circumstances how PPEFT methods can simplify calculations of low-energy fermion-dyon scattering in their presence. We propose an effective Hamiltonian governing how dyon excitations respond to fermion scattering in terms of a time-dependent vacuum angle and outline open questions remaining in its microscopic derivation.
↳ hep-thhep-phnucl-thJHEP(2024)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE