Nuclear Theory·nucl-th

Thursday·September 10, 2020

11 papers—3 primary·8 cross-listed

01
Triaxial projected shell model study of $γ$ -bands in atomic nuclei
S. Jehangir · G.H. Bhat · J.A. Sheikh · S. Frauendorf · W. Li · R. Palit
A systematic study of $γ$ -bands observed in atomic nuclei is performed using the triaxial projected shell model (TPSM) approach. The staggering phase between the even and odd spin members of the $γ$ -band for most the nuclei investigated in the present work is found to have even-I-below-odd-I, which in the framework of the collective model is considered as a signature of $γ$ -softness. It is observed that out of twenty-three systems studied, only four nuclei, namely, $^{76}$ Ge, $^{112}$ Ru, $^{170}$ Er and $^{232}$ Th depict staggering phase with odd-I-below-even-I, which is regarded as an indication of the static $γ$ -deformation in the collective model picture. The inclusion of the quasiparticle excitations in the framework of configuration mixing is shown to reverse the staggering phase from odd-I-down to the even-I-down for all the studied nuclei, except for the aforementioned four nuclei. Furthermore, by fitting a collective Bohr Hamiltonian to the TPSM energies, the differences between the two models are delineated through a comparison of the transition probabilities.
nucl-thnucl-exEPJA(2021)·39 citations
02
Minimal complete sets for two pseudoscalar meson photoproduction
Philipp Kroenert🇩🇪 · Yannick Wunderlich🇩🇪 · Farah Afzal🇩🇪 · Annika Thiel🇩🇪
For photoproduction reactions with final states consisting of two pseudoscalar mesons and a spin-1/2 baryon, 8 complex amplitudes need to be determined uniquely. A modified version of Moravcsik's theorem is employed for these reactions, resulting in slightly over-complete sets of polarization observables that are able to determine the amplitudes uniquely. Further steps were taken to reduce the found sets to minimal complete sets. As a final result, multiple minimal complete sets without any remaining ambiguities are presented for the first time. These sets consist of $2 N = 16$ observables, containing only one triple polarization observable.
nucl-thPRC(2021)·12 citations
03
Photon-jet correlations in p-p and Pb-Pb collisions using JETSCAPE framework
C. Sirimanna · A. Angerami · S. A. Bass · S. Cao · Y. Chen · J. Coleman · L. Cunqueiro · T. Dai · L. Du · R. Ehlers · H. Elfner · D. Everett and 38 other authors
It is now well established that jet modification is a multistage effect; hence a single model alone cannot describe all facets of jet modification. The JETSCAPE framework is a multistage framework that uses several modules to simulate different stages of jet propagation through the QGP medium. These simulations require a set of parameters to ensure a smooth transition between stages. We fine tune these parameters to successfully describe a variety of observables, such as the nuclear modification factors of leading hadrons and jets, jet shape, and jet fragmentation function. Photons can be produced in the hard scattering or as radiation from quarks inside jets. In this work, we study photon-jet transverse momentum imbalance and azimuthal correlation for both $p - p$ and $P b - P b$ collision systems. All the photons produced in each event, including the photons from hard scattering, radiation from the parton shower, and radiation from hadronization are considered with an isolation cut to directly compare with experimental data. The simulations are conducted using the same set of tuned parameters as used for the jet analysis. No new parameters are introduced or tuned. We demonstrate a significantly improved agreement with photons from $P b - P b$ collisions compared to prior efforts. This work provides an independent, parameter free verification of the multistage evolution framework.
nucl-thhep-phPoS(2021)·1 citation
04
Effective models of a semi-quark gluon plasma
Yoshimasa Hidaka🇯🇵 · Robert D. Pisarski🇺🇸
In the deconfined regime of a non-Abelian gauge theory at nonzero temperature, previously it was argued that if a (gauge invariant) source is added to generate nonzero holonomy, that this source must be linear for small holonomy. The simplest example of this is the second Bernoulli polynomial. However, then there is a conundrum in computing the free energy to $\sim g^{3}$ in the coupling constant $g$ , as part of the free energy is discontinuous as the holonomy vanishes. In this paper we investigate two ways of generating the second Bernoulli polynomial dynamically: as a mass derivative of an auxiliary field, and from two dimensional ghosts embedded isotropically in four dimensions. Computing the holonomous hard thermal loop (HHTL) in the gluon self-energy, we find that the limit of small holonomy is only well behaved for two dimensional ghosts, with a free energy which to $\sim g^{3}$ is continuous as the holonomy vanishes.
↳ hep-phhep-thnucl-thPRD(2021)·17 citations
05
Empirical Consequences of Emergent Mass
Craig D. Roberts🇨🇳
The Lagrangian that defines quantum chromodynamics (QCD), the strong interaction piece of the Standard Model, appears very simple. Nevertheless, it is responsible for an astonishing array of high-level phenomena with enormous apparent complexity, e.g., the existence, number and structure of atomic nuclei. The source of all these things can be traced to emergent mass, which might itself be QCD's self-stabilising mechanism. A background to this perspective is provided, presenting, inter alia, a discussion of the gluon mass and QCD's process-independent effective charge and highlighting an array of observable expressions of emergent mass, ranging from its manifestations in pion parton distributions to those in nucleon electromagnetic form factors.
↳ hep-phhep-exhep-latnucl-ex+1Symmetry(2020)·94 citations
06
Neutral-current background induced by atmospheric neutrinos at large liquid-scintillator detectors: II. Methodology for in situ measurements
Jie Cheng🇨🇳 · Yu-Feng Li🇨🇳 · Hao-Qi Lu🇨🇳 · Liang-Jian Wen🇨🇳
Future large liquid-scintillator (LS) detectors are competitive with and complementary to the water-Cherenkov detectors on the searches for diffuse supernova neutrino background and nucleon decay. In a companion paper, we have performed a systematic calculation of the neutral-current (NC) background induced by atmospheric neutrino interactions on $^{12} C$ nuclei in LS detectors, which are expected to be crucially important for the experimental searches for the diffuse supernova neutrino background and nucleon decay. In this paper, we perform a systematic study on the measurement of the NC background and evaluate the associated uncertainties. We first exploit the characteristics of the NC background, in particular, the multiplicities of neutrons and pions, and the possible association with unstable residual nuclei. It turns out that the neutron multiplicity distribution is very powerful to discriminate among different models. Then, we develop a maximum-likelihood method to allow an {\it in situ} measurement of the NC interactions with a triple-coincidence signature. Finally, a data-driven approach is proposed to evaluate the uncertainty of the NC background in the search for the diffuse supernova neutrino background. We conclude that future large LS experiments like JUNO (Jiangmen Underground Neutrino Observatory) will be able to make a unique contribution to the worldwide data set to improve the prediction of atmospheric neutrino NC interactions on $^{12}$ C.
↳ hep-exastro-ph.HEhep-phnucl-ex+1PRD(2021)·18 citations
07
Rodeo Algorithm for Quantum Computing
Kenneth Choi🇺🇸 · Dean Lee🇺🇸 · Joey Bonitati🇺🇸 · Zhengrong Qian🇺🇸 · Jacob Watkins🇺🇸
We present a stochastic quantum computing algorithm that can prepare any eigenvector of a quantum Hamiltonian within a selected energy interval $[E - ϵ, E + ϵ]$ . In order to reduce the spectral weight of all other eigenvectors by a suppression factor $δ$ , the required computational effort scales as $O [∣ lo g δ ∣/ (p ϵ)]$ , where $p$ is the squared overlap of the initial state with the target eigenvector. The method, which we call the rodeo algorithm, uses auxiliary qubits to control the time evolution of the Hamiltonian minus some tunable parameter $E$ . With each auxiliary qubit measurement, the amplitudes of the eigenvectors are multiplied by a stochastic factor that depends on the proximity of their energy to $E$ . In this manner, we converge to the target eigenvector with exponential accuracy in the number of measurements. In addition to preparing eigenvectors, the method can also compute the full spectrum of the Hamiltonian. We illustrate the performance with several examples. For energy eigenvalue determination with error $ϵ$ , the computational scaling is $O [(lo g ϵ)^{2} / (p ϵ)]$ . For eigenstate preparation, the computational scaling is $O (lo g Δ/ p)$ , where $Δ$ is the magnitude of the orthogonal component of the residual vector. The speed for eigenstate preparation is exponentially faster than that for phase estimation or adiabatic evolution.
↳ quant-phnucl-thphysics.comp-phPRL(2021)·98 citations
08
Comparison of results for the electromagnetic form factors of the proton at low $Q^{2}$
Evangelos Matsinos🇬🇷
The goal in this work is the comparison of five parameterisations of the Sachs form factors of the proton $G_{E}^{p}$ (electric) and $G_{M}^{p}$ (magnetic) at low $4$ -momentum transfer $Q^{2}$ . It will be shown that a simple model, based on two dipoles which admit as parameters the rms electric charge radius $r_{E; p}$ and the rms magnetic radius $r_{M; p}$ of the proton, suffices for the purposes of the phase-shift analyses (PSAs) of the low-energy pion-nucleon ( $π N$ ) data. The replacement of the electromagnetic form factors, currently used in the ETH model of the $π N$ interaction, by the parameterisation of this work will enable the removal from the PSAs of this research programme of the largest part of the dependence on extraneous sources.
↳ hep-phnucl-th0 citations
09
Evidence of the four-quark nature of $f_{0} (980)$ and $f_{0} (500)$
N.N. Achasov🇷🇺 · J.V. Bennett🇺🇸 · A.V. Kiselev🇷🇺 · E.A. Kozyrev🇷🇺 · G.N. Shestakov🇷🇺
There exists a great deal of concrete evidence in favor of the exotic four-quark nature of light scalars. At the same time, the further expansion of the area of the $q^{2} q ˉ^{2}$ model validity for light scalars on ever new processes seems extremely interesting and important. We analyze the BESIII data on the decay $J / ψ \to γ π^{0} π^{0}$ and show that the results of this high-statistics experiment can be interpreted in favor of the four-quark nature of light scalar mesons $f_{0} (980)$ and $f_{0} (500)$ .
↳ hep-phhep-exnucl-thPRD(2021)·34 citations
10
Spectral functions from the real-time functional renormalization group
Sven Huelsmann🇩🇪 · Soeren Schlichting🇩🇪 · Philipp Scior🇩🇪
We employ the functional renormalization group approach formulated on the Schwinger-Keldysh contour to calculate real-time correlation functions in scalar field theories. We provide a detailed description of the formalism, discuss suitable truncation schemes for real-time calculations as well as the numerical procedure to self-consistently solve the flow equations for the spectral function. Subsequently, we discuss the relations to other perturbative and non-perturbative approaches to calculate spectral functions, and present a detailed comparison and benchmark in $d = 0 + 1$ dimensions.
↳ hep-phhep-thnucl-thPRD(2020)·35 citations
11
The molecular nature of some exotic hadrons
A. Ramos🇪🇸 · A. Feijoo🇨🇿 · Q. Llorens🇪🇸 · G. Montaña🇪🇸
The exciting discovery by LHCb of the $P_{c} (4312)^{+}$ and $P_{c} (4450)^{+}$ pentaquarks, or the suggestion of a tetraquark nature for the $Z_{c} (3900)$ state seen at BESIII and Belle, have triggered a lot of activity in the field of hadron physics, with new experiments planned for searching other exotic mesons and baryons, and many theoretical developments trying to disentangle the true multiquark nature from their possible molecular origin. After a brief review of the present status of these searches, this paper focusses on recently seen or yet to be discovered exotic heavy baryons that may emerge from a conveniently unitarized meson-baryon interaction model in coupled channels. In particular, we will show how interferences between the different coupled-channel amplitudes of the model may reveal the existence of a $N^{*}$ resonance around 2 GeV having a meson-baryon quasi-bound state nature. We also discuss the possible interpretation of some of the $Ω_{c}$ states recently discovered at LHCb as being hadron molecules. The model also predicts the existence of doubly-charmed quasibound meson-baryon $Ξ_{cc}$ states, which would be excited states of the ground-state $Ξ_{cc} (3621)$ MeV, whose mass has only been recently established. Extensions of these results to the bottom sector will also be presented.
↳ hep-phnucl-thFew Body Syst.(2020)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE