Nuclear Theory·nucl-th

Tuesday·March 10, 2015

12 papers—5 primary·7 cross-listed

01
Nonmesonic Weak Decay Dynamics from proton spectra of $Λ$ -Hypernuclei
Franjo Krmpotic🇦🇷 · Cláudio De Conti🇧🇷
A novel comparison between the data and the theory is proposed for the nonmesonic (NM) weak decay of hypernuclei. Instead of confronting the primary decay rates, as is usually done, we focus attention on the effective decay rates that are straightforwardly related with the number of emitted particles. Proton kinetic energy spectra of $_{Λ}^{5}$ He, $_{Λ}^{7}$ Li, $_{Λ}^{9}$ Be, $_{Λ}^{11}$ B, $_{Λ}^{12}$ C, $_{Λ}^{13}$ C, $_{Λ}^{15}$ N and $_{Λ}^{16}$ O, measured by FINUDA, are evaluated theoretically. The Independent Particle Shell Model (IPSM) is used as the nuclear structure framework, while the dynamics is described by the One-Meson-Exchange (OME) potential. Only for the $_{Λ}^{5}$ He, $_{Λ}^{7}$ Li, and $_{Λ}^{12}$ C hypernuclei is it possible to make a comparison with the data, since for the rest there is no published experimental information on number of produced hypernuclei. Considering solely the one-nucleon-induced ( $1 N$ -NM) decay channel, the theory reproduces correctly the shapes of all three spectra at medium and high energies ( $E_{p} \geq 40$ MeV). Yet, it greatly overestimates their magnitudes, as well as the corresponding transition rates when the full OME ( $π + K + η + ρ + ω + K^{*}$ ) model is used. The agreement is much improved when only the $π + K$ mesons with soft dipole cutoff parameters participate in the decay process. We find that the IPSM is a fair first order approximation to disentangle the dynamics of the $1 N$ -NM decay, the knowledge of which is indispensable to inquire about the baryon-baryon strangeness-flipping interaction. It is shown that the IPSM provides very useful insights regarding the determination the $2 N$ -NM decay rate. In a new analysis of the FINUDA data, we derive two results for this quantity with one of them close to that obtained previously.
nucl-thIJMPE(2014)·2 citations
02
Periodic interference structures in the time-like proton form factor
Andrea Bianconi🇮🇹 · Egle Tomasi-Gustafsson🇫🇷
An intriguing and elusive feature of the timelike hadron form factor is the possible presence of an imaginary part associated to rescattering processes. We find evidence of that in the recent and precise data on the proton timelike form factor measured by the BABAR collaboration. By plotting these data as a function of the 3-momentum of the relative motion of the final proton and antiproton, a systematic sinusoidal modulation is highlighted in the near-threshold region. Our analysis attributes this pattern to rescattering processes at a relative distance of 0.7-1.5 fm between the centers of the forming hadrons. This distance implies a large fraction of inelastic processes in $p ˉ p$ interactions, and a large imaginary part in the related $e^{+} e^{-} \to p ˉ p$ reaction because of unitarity.
nucl-thhep-phPRL(2015)·88 citations
03
Determination of the neutrino mass by electron capture in 163 Holmium and the role of the three-hole states in 163 Dysprosium
Amand Faessler🇩🇪 · Christian Enss🇩🇪 · Loredana Gastaldo🇩🇪 · F. Simkovic🇷🇺
163 Holmium to 163 Dysprosium is probably due to the small Q value of about 2.5 keV the best case to determine the neutrino mass by electron capture. The energy of the Q value is distributed between the excitation of Dysprosium (and the neglected small recoil of Holmium) and the relativistic energy of the emitted neutrino including the restmass. The reduction of the upper end of the deexcitation spectrum of Dysprosium below the Q value allows to determine the neutrino mass. The excitation of Dysprosium can be calculated in the sudden approximation of the overlap of the electron wave functions of Holmium minus the captured electron and one-, two-, three- and multiple hole-excitations in Dysprosium. Robertson and the author have calculated the influence of the two-hole states on the Dysprosium deexitation spectrum. Here for the first time the influence of the three-hole states on the deexcitation bolometer spectrum of 163 Dysprosium is presented. The electron wave functions and the overlaps are calculated selfconsitently in a fully relativistic and antisymmetrized Dirac-Hartree-Fock approach in Holmium and in Dysprosium. The electron orbitals in Dysprosium are determined including the one-hole states in the selfconsistent iteration. The influence of the three-hole states on the deexcitation (by X-rays and Auger electrons) spectrum is hardly visible. The three-hole states seem not to be important for the determination of the neutrino mass.
nucl-thphysics.atom-phPRC(2015)·39 citations
04
Higher-rank discrete symmetries in the IBM. I Octahedral shapes: general Hamiltonian
P. Van Isacker (GANIL)🇫🇷 · A. Bouldjedri🇩🇿 · S. Zerguine🇩🇿
In the context of the interacting boson model with $s$ , $d$ and $g$ bosons, the conditions for obtaining an intrinsic shape with octahedral symmetry are derived for a general Hamiltonian with up to two-body interactions.
nucl-thNPA(2015)·8 citations
05
A study of $d^{*} (2380) \to d π π$ decay width
Yubing Dong🇨🇳 · Pengnian Shen🇨🇳 · Fei Huang🇨🇳 · Zongye Zhang🇨🇳
The decay widths of the $\ds \to d π^{0} π^{0}$ and $\ds \to d π^{+} π^{-}$ processes are explicitly calculated in terms of our chiral quark model. By using the experimental ratios of cross sections between various decay channels, the partial widths of the $\ds \to p n π^{0} π^{0}$ , $\ds \to p n π^{+} π^{-}$ , $\ds \to pp π^{0} π^{-}$ , and $\ds \to nn π^{+} π^{0}$ channels are also extracted. Further including the estimated partial width for the $\ds \to p n$ process, the total width of the $\ds$ resonance is obtained. In the first step of the practical calculation, the effect of the dynamical structure on the width of $\ds$ is studied in the single $ΔΔ$ channel approximation. It is found that the width is reduced by few tens of MeV, in comparison with the one obtained by considering the effect of the kinematics only. This presents the importance of such effect from the dynamical structure. However, the obtained width with the single $ΔΔ$ channel wave function is still too large to explain the data. It implies that the $\ds$ resonance will not consist of the $ΔΔ$ structure only, and instead there should be enough room for other structure such as the hidden-color (CC) component. Thus, in the second step, the width of $\ds$ is further evaluated by using a wave function obtained in the coupled $ΔΔ$ and CC channel calculation in the framework of the Resonating Group Method (RGM). It is shown that the resultant total width for $\ds$ is about 69 MeV, which is compatible with the experimental observation of about 75 MeV and justifies our assertion that the $\ds$ resonance is a hexaquark-dominated exotic state.
nucl-thhep-phPRC(2015)·54 citations
06
QCD description of backward vector meson hard electroproduction
B. Pire🇫🇷 · K. Semenov-Tian-Shansky🇫🇷 · L. Szymanowski🇵🇱
We consider backward vector meson exclusive electroproduction off nucleons in the framework of collinear QCD factorization. Nucleon to vector meson transition distribution amplitudes arise as building blocks for the corresponding factorized amplitudes. In the near-backward kinematics, the suggested factorization mechanism results in the dominance of the transverse cross section of vector meson production ( $σ_{T} ≫ σ_{L}$ ) and in the characteristic $1/ Q^{8}$ -scaling behavior of the cross section. We evaluate nucleon to vector meson TDAs in the cross-channel nucleon exchange model and present estimates of the differential cross section for backward $ρ^{0}$ , $ω$ and $ϕ$ meson production off protons. The resulting cross sections are shown to be measurable in the forthcoming JLab@12 GeV experiments.
↳ hep-phhep-exnucl-exnucl-thPRD(2015)·21 citations
07
Quantum-mechanical picture of peripheral chiral dynamics
C. Granados🇸🇪 · C. Weiss🇺🇸
The nucleon's peripheral transverse charge and magnetization densities are computed in chiral effective field theory. The densities are represented in first-quantized form, as overlap integrals of chiral light-front wave functions describing the transition of the nucleon to soft pion-nucleon intermediate states. The orbital motion of the pion causes a large left-right asymmetry in a transversely polarized nucleon. The effect attests to the relativistic nature of chiral dynamics [pion momenta k = O(M_pi)] and could be observed in form factor measurements at low momentum transfer.
↳ hep-phnucl-thPRC(2015)·8 citations
08
Scrutinizing the eta-eta' mixing, masses and pseudoscalar decay constants in the framework of U(3) chiral effective field theory
Xu-Kun Guo🇨🇳 · Zhi-Hui Guo🇨🇳 · Jose Antonio Oller🇪🇸 · Juan Jose Sanz-Cillero🇪🇸
We study the $η$ - $η^{'}$ mixing up to next-to-next-to-leading-order in $U (3)$ chiral perturbation theory in the light of recent lattice simulations and phenomenological inputs. A general treatment for the $η$ - $η^{'}$ mixing at higher orders, with the higher-derivative, kinematic and mass mixing terms, is addressed. The connections between the four mixing parameters in the two-mixing-angle scheme and the low energy constants in the $U (3)$ chiral effective theory are provided both for the singlet-octet and the quark-flavor bases. The axial-vector decay constants of pion and kaon are studied in the same order and confronted with the lattice simulation data as well. The quark-mass dependences of $m_{η}$ , $m_{η^{'}}$ and $m_{K}$ are found to be well described at next-to-leading order. Nonetheless, in order to simultaneously describe the lattice data and phenomenological determinations for the properties of light pseudoscalars $π, K, η$ and $η^{'}$ , the next-to-next-to-leading order study is essential. Furthermore, the lattice and phenomenological inputs are well reproduced for reasonable values of low the energy constants, compatible with previous bibliography.
↳ hep-phhep-exhep-latnucl-thJHEP(2015)·73 citations
09
Neutron skin and centrality classification in high-energy heavy-ion collisions at the LHC
Hannu Paukkunen🇫🇮
The concept of centrality in high-energy nuclear collisions has recently become a subject of an active debate. In particular, the experimental methods to determine the centrality that have given reasonable results for many observables in high-energy lead-lead collisions at the LHC have led to surprising behaviour in the case of proton-lead collisions. In this letter, we discuss the possibility to calibrate the experimental determination of centrality by asymmetries caused by mutually different spatial distributions of protons and neutrons inside the nuclei --- a well-known phenomenon in nuclear physics known as the neutron-skin effect.
↳ hep-phhep-exnucl-exnucl-thPLB(2015)·32 citations
10
Study of the $f_{2} (1270)$ , $f_{2}^{'} (1525)$ , $K ˉ_{2}^{*} (1430)$ , $f_{0} (1370)$ and $f_{0} (1710)$ production from $ψ (n S)$ and $Υ (n S)$ decays
Lian-Rong Dai🇨🇳 · Ju-Jun Xie🇨🇳 · E. Oset🇨🇳
Based on previous studies that support the important role of the $f_{2} (1270)$ , $f_{2}^{'} (1525)$ , and $K ˉ_{2}^{*} (1430)$ resonances in the $J / ψ [ψ (2 S)] \to ϕ (ω) V V$ decays, we make an analysis of the analogous decays of $Υ (1 S)$ and $Υ (2 S)$ , taking into account recent experimental data. In addition, we study the $J / ψ$ and $ψ (2 S)$ radiative decays and we also made predictions for the radiative decay of $Υ (1 S)$ and $Υ (2 S)$ into $γ f_{2} (1270)$ , $γ f_{2}^{'} (1525)$ , $γ f_{0} (1370)$ and $γ f_{0} (1710)$ , comparing with the recent results of a CLEO experiment. We can compare our results for ratios of decay rates with eight experimental ratios and find agreement in all but one case, where experimental problems are discussed.
↳ hep-phhep-exnucl-thPRD(2015)·18 citations
11
Energy Dependence of Moments of Net-Proton and Net-Charge Multiplicity Distributions at STAR
Xiaofeng Luo (for the STAR Collaboration)🇨🇳
We present the energy dependence of moments of net-proton and net-charge multiplicity distributions in Au+Au collisions measured by the STAR experiment in the first phase of the Beam Energy Scan (BES) at the Relativistic Heavy Ion Collider (RHIC). By using the time of flight detector for particle identification, the upper transverse momentum ( $p_{T}$ ) limit for proton and anti-proton is extended from 0.8 GeV/c up to 2 GeV/c. The $p_{T}$ and rapidity acceptance dependence study for the moments of net-proton distribution show that the larger the acceptance is, the greater the deviation from unity. The most pronounced structure is found in the energy dependence of {\KV} of net-proton distributions from the $0 \sim 5$ most central collisions within $0.4 < p_{T} < 2$ GeV/c and at mid-rapidity $∣ y ∣ < 0.5$ . At energies above 39 GeV, the values of {\KV} are close to unity and for energies below 39 GeV, it shows significant deviation below unity around 19.6 and 27 GeV, then a large increase above unity is observed at 7.7 GeV.
↳ nucl-exhep-exhep-phnucl-thPoS(2015)·188 citations
12
Parity violating effects in an exotic perturbation of the rigid rotator
A. Pallares Rivera🇲🇽 · M. Kirchbach🇲🇽
The perturbation of the free rigid rotator by the trigonometric Scarf potential is shown to conserve its energy excitation patterns and change only the wave functions towards spherical harmonics rescaled by a function of an unspecified parity, or mixtures of such rescaled harmonics of equal magnetic quantum numbers and different angular momenta. In effect, no parity can be assigned to the states of the rotational bands emerging in this exotic way, and the electric dipole operator is allowed to acquire non-vanishing expectation values.
↳ quant-phhep-phnucl-thEur.Phys.J.Plus(2015)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE