Nuclear Theory·nucl-th

Wednesday·February 21, 2018

12 papers—7 primary·5 cross-listed

01
Theoretical analysis on the $K^{-}^{3} He \to Λ p n$ reaction for the $K ˉ N N$ bound-state search in the J-PARC E15 experiment
Takayasu Sekihara (1) · Eulogio Oset (2) · Angels Ramos (3) ((1) JAEA, Ibaraki, (2) Valencia U. & Valencia U., IFIC, (3) Barcelona U. & ICC, Barcelona U.)
We theoretically analyze the $K^{-}^{3} He \to Λ p n$ reaction for the $K ˉ N N$ bound-state search in the J-PARC E15 experiment. We find that, by detecting a fast and forward neutron in the final state, an almost on-shell $K ˉ$ is guaranteed, which is essential to make a bound state with two nucleons from $^{3} He$ . Then, this almost on-shell $K ˉ$ can bring a signal of the $K ˉ N N$ bound state in the $Λ p$ invariant-mass spectrum, although it inevitably brings a kinematic peak above the $K ˉ N N$ threshold as well. As a consequence, we predict two peaks across the $K ˉ N N$ threshold in the spectrum: the lower peak coming from the $K ˉ N N$ bound state, and the higher one originating from the kinematics.
nucl-thhep-phnucl-exPoS(2018)·4 citations
02
Azimuthal Anisotropies at High Momentum from Purely Non-Hydrodynamic Transport
Paul Romatschke🇺🇸
In the limit of short mean free path, relativistic kinetic theory gives rise to hydrodynamics through a systematically improvable gradient expansion. In the present work, a systematically improvable expansion in the opposite limit of large mean free path is considered, describing the dynamics of particles which are almost, but not quite, non-interacting. This non-hydrodynamic "eremitic" expansion does not break down for large gradients, and may be useful in situations where a hydrodynamic treatment is not applicable. As applications, azimuthal anisotropies at high transverse momentum in Pb+Pb and p+Pb collisions at $s = 5.02$ TeV are calculated from the first order eremitic expansion of kinetic theory in the relaxation time approximation.
nucl-thastro-ph.HEhep-phEPJC(2018)·42 citations
03
Rotational motion of triaxially deformed nuclei studied by microscopic angular-momentum-projection method I: Nuclear wobbling motion
Mitsuhiro Shimada · Yudai Fujioka · Shingo Tagami · Yoshifumi R. Shimizu
Rotation of triaxially deformed nucleus has been an interesting subject in the study of nuclear structure. In the present series of work, we investigate wobbling motion and chiral rotation by employing the microscopic framework of angular-momentum projection from cranked triaxially deformed mean-field states. In this first part the wobbling motion is studied in detail. The consequences of the three dimensional cranking are investigated. It is demonstrated that the multiple wobbling rotational bands naturally appear as a result of fully microscopic calculation. They have the characteristic properties, that are expected from the macroscopic triaxial-rotor model or the phenomenological particle-triaxial-rotor model, although quantitative agreement with the existing data is not achieved. It is also found that the excitation spectrum reflects dynamics of the angular-momentum vector in the intrinsic frame of the mean-field (transverse vs. longitudinal wobbling). The results obtained by using the Woods-Saxon potential and the schematic separable interaction are mainly discussed, while some results with the Gogny D1S interaction are also presented.
nucl-thPRC(2018)·19 citations
04
Rotational motion of triaxially deformed nuclei studied by microscopic angular-momentum-projection method II: Chiral doublet band
Mitsuhiro Shimada · Yudai Fujioka · Shingo Tagami · Yoshifumi R. Shimizu
In the sequel of the present study, we have investigated the rotational motion of triaxially deformed nucleus by using the microscopic framework of angular-momentum projection. The Woods-Saxon potential and the schematic separable-type interaction are employed as a microscopic Hamiltonian. As the first example nuclear wobbling motion was studied in detail in the part~I of the series. This second part reports on another interesting rotational mode, chiral doublet bands: two prototype examples, $^{128}$ Cs and $^{104}$ Rh, are investigated. It is demonstrated that the doublet bands naturally appear as a result of the calculation in this fully microscopic framework without any kind of core, and they have the characteristic properties of the $B (E 2)$ and $B (M 1)$ transition probabilities, which are expected from the phenomenological triaxial particle-rotor coupling model.
nucl-thPRC(2018)·22 citations
05
First-order derivative of cluster size as a new signature of phase transition in heavy ion collisions at intermediate energies
P. Das🇮🇳 · S. Mallik🇮🇳 · G. Chaudhuri🇮🇳
The phenomenon of liquid-gas phase transition occurring in heavy ion collisions at intermediate energies is a subject of contemporary interest. Phase transition is usually characterized by the specific behaviour of state variables like pressure, density, energy etc. In heavy ion collisions there is no direct way of accessing these state variables and hence unambiguous detection of phase transition becomes difficult. This work establishes that signatures of phase transition can be extracted from the observables which are easily accessible in experiments and these have similar behaviour as the state variables. The temperature dependence of the first order derivative of the order parameters related to the largest and second largest cluster size (produced in heavy ion collisions) exhibit similar behavior as that of the variation of specific heat at constant volume Cv which is an established signature of first order phase transition. This motivates us to propose these derivatives as confirmatory signals of liquid-gas phase transition. The measurement of these signals in easily feasible in most experiments as compared to the other signatures like specific heat, caloric curve or bimodality. This temperature where the peak appears is designated to be the transition temperature and the effect of certain parameters on this has also been examined.
nucl-thhep-phPLB(2018)·11 citations
06
A geometry for the shell model
P. Van Isacker🇫🇷
A geometric interpretation is given of matrix elements of a short-range interaction between states that are written in terms of aligned neutron-proton pairs.
nucl-thEPJ Web Conf.(2018)·3 citations
07
Unitary Scheme Model Calculations of the Ground- and Excited-State Characteristics of 3H and 4He
S. B. Doma · H. S. El-Gendy
The ground and excited states of the 3H and 4He nuclei are studied in the framework of group-theoretical methods. Basis functions of the unitary scheme model corresponding to even numbers of quanta of excitation in the range from zero to twenty are constructed for the even-parity states of these two nuclei, and bases from one to nineteen are constructed for the odd-parity states of the 4He nucleus. The ground-state and first-excited-state energies and wave functions, the ground S-, P- and D-state probabilities, the root-mean-square radius and the magnetic dipole moment of Triton are calculated. Furthermore, for the 4He nucleus, the spectrum and the wave functions, the ground S-, P- and D-state probabilities, the root-mean-square radius and the total integral cross section of the dipole electric transition accompanying the photoabsorption of gamma quanta by this nucleus are calculated. The GPT and AV8' two-body interactions and the Urbana nine three-nucleon interaction are used in these investigations. Moreover, the convergence of the calculations is examined by incrementally extrapolating the nuclear characteristics calculated for N less than or equal to twenty to N equals thirty.
nucl-thJ.Phys.Comm.(2018)·1 citation
08
Disentangling covariant Wigner functions for chiral fermions
Jian-Hua Gao🇨🇳 · Zuo-Tang Liang🇨🇳 · Qun Wang🇨🇳 · Xin-Nian Wang🇨🇳
We develop a general formalism for the quantum kinetics of chiral fermions in a background electromagnetic field based on a semiclassical expansion of covariant Wigner functions in the Planck constant $ℏ$ . We demonstrate to any order of $ℏ$ that only the time-component of the Wigner function is independent while other components are explicit derivative. We further demonstrate to any order of $ℏ$ that a system of quantum kinetic equations for multiple-components of Wigner functions can be reduced to one chiral kinetic equation involving only the single-component distribution function. These are remarkable properties of the quantum kinetics of chiral fermions and will significantly simplify the description and simulation of chiral effects in heavy ion collisions and Dirac/Weyl semimetals. We present the unintegrated chiral kinetic equations in four-momenta up to $O (ℏ^{2})$ and the integrated ones in three-momenta up to $O (ℏ)$ . We find that some singular terms emerge in the integration over the time component of the four-momentum, which result in a new source term contributing to the chiral anomaly, in contrast to the well-known scenario of the Berry phase term. Finally we rewrite our results in any Lorentz frame with a reference four-velocity and show how the non-trivial transformation of the distribution function in different frames emerges in a natural way.
↳ hep-phnucl-thPRD(2018)·85 citations
09
Landau Damping in a strong magnetic field: Dissociation of Quarkonia
Mujeeb Hasan🇮🇳 · Binoy Krishna Patra🇮🇳 · Bhaswar Chatterjee🇮🇳 · Partha Bagchi🇮🇳
We have investigated the effects of strong magnetic field on the properties of quarkonia immersed in a thermal medium of quarks and gluons and studied its quasi-free dissociation due to the Landau-damping. Thermalizing the Schwinger propagator in the lowest Landau levels for quarks and the Feynman propagator for gluons in real-time formalism, we have calculated the resummed retarded and symmetric propagators, which in turn give the real and imaginary components of dielectric permittivity, respectively. The magnetic field affects the large-distance interaction more than the short-distance interaction, as a result, the real part of potential becomes more attractive and the magnitude of imaginary part too becomes larger, compared to the thermal medium in absence of strong magnetic field. As a consequence the average size of $J / ψ$ 's and $ψ^{'}$ 's are increased but $χ_{c}$ 's get shrunk. Similarly the magnetic field affects the binding of $J / ψ$ 's and $χ_{c}$ 's discriminately, i.e. it decreases the binding of $J / ψ$ and increases for $χ_{c}$ . However, the further increase in magnetic field results in the decrease of binding energies. On contrary the magnetic field increases the width of the resonances, unless the temperature is sufficiently high. We have finally studied how the presence of magnetic field affects the dissolution of quarkonia in a thermal medium due to the Landau damping, where the dissociation temperatures are found to increase compared to the thermal medium in absence of magnetic field. However, further increase of magnetic field decreases the dissociation temperatures. For example, $J / ψ$ 's and $χ_{c}$ 's are dissociated at higher temperatures at 2 $T_{c}$ and 1.1 $T_{c}$ at a magnetic field $e B \approx 6 and 4 m_{π}^{2}$ , respectively, compared to the values 1.60 $T_{c}$ and 0.8 $T_{c}$ in the absence of magnetic field, respectively.
↳ hep-phhep-thnucl-thNPA(2020)·25 citations
10
BFKL Spectrum of N=4 SYM: non-Zero Conformal Spin
Mikhail Alfimov🇫🇷 · Nikolay Gromov🇬🇧 · Grigory Sizov🇫🇷
We developed a general non-perturbative framework for the BFKL spectrum of planar N=4 SYM, based on the Quantum Spectral Curve (QSC). It allows one to study the spectrum in the whole generality, extending previously known methods to arbitrary values of conformal spin $n$ . We show how to apply our approach to reproduce all known perturbative results for the Balitsky-Fadin-Kuraev-Lipatov (BFKL) Pomeron eigenvalue and get new predictions. In particular, we re-derived the Faddeev-Korchemsky Baxter equation for the Lipatov spin chain with non-zero conformal spin reproducing the corresponding BFKL kernel eigenvalue. We also get new non-perturbative analytic results for the Pomeron eigenvalue in the vicinity of $∣ n ∣ = 1, Δ = 0$ point and we obtained an explicit formula for the BFKL intercept function for arbitrary conformal spin up to the 3-loop order in the small coupling expansion and partial result at the 4-loop order. In addition, we implemented the numerical algorithm of arXiv:1504.06640 as an auxiliary file to this arXiv submission. From the numerical result we managed to deduce an analytic formula for the strong coupling expansion of the intercept function for arbitrary conformal spin.
↳ hep-thhep-phmath-phmath.MP+1JHEP(2018)·45 citations
11
Multiplicity distribution and normalized moments in p $-$ p collisions at LHC in forward rapidity using Weibull model
Ranjit Nayak🇮🇳 · Sadhana Dash🇮🇳
The measured charged particle multiplicity distribution in the forward rapidity region of the p $-$ p collisions at $s$ = 0.9 TeV, 7 TeV and 8 TeV at the LHC have been described using the Weibull distribution function. The higher order (up to $5^{t h}$ order ) normalized moments and the factorial moments are also calculated using the extracted parameters. The multiplicity distributions in forward region are observed to be well described by the Weibull regularity and the higher order moment calculations confirm the violation of KNO scaling that has been observed at mid-rapidity and lower energies. The Weibull parameters and moments for p $-$ p collisions at $s$ = 13 TeV are also estimated for the forward region.
↳ hep-phnucl-thJ.Phys.G(2019)·4 citations
12
Soft-photon corrections to the Bethe-Heitler process in the $γ p \to l^{+} l^{-} p$ reaction
Matthias Heller🇩🇪 · Oleksandr Tomalak🇩🇪 · Marc Vanderhaeghen🇩🇪
We report on the calculation of first-order QED corrections for the $γ p \to l^{+} l^{-} p^{'}$ process. An upcoming experiment at MAMI (Mainz) aims to compare the cross sections of muon- and electron-pair production in this reaction to test lepton universality. Precise knowledge of the electromagnetic radiative corrections is needed for these measurements. As a first step, we present the leading QED radiative corrections in the soft-photon approximation when accounting for the finite lepton mass. For the kinematics at MAMI, we find corrections of the percent level for muons, and of order $10%$ for electrons.
↳ hep-phnucl-exnucl-thPRD(2018)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE