We investigate the $ϕ$ meson nuclear transparency using some recent theoretical developments on the $ϕ$ in medium self-energy. The inclusion of direct resonant $ϕN$-scattering and the kaon decay mechanisms leads to a $ϕ$ width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced $ϕ$ production from COSY finding an overall good agreement. The results support the need of a quite large direct $ϕN$-scattering contribution to the self-energy.
We investigate the early onset of pionic color transparency ($π$CT) observed at Jefferson Laboratory (JLAB) in semi--exclusive pion electroproduction reaction $A(e,e'π^+)$ off nuclei. In the present description the primary $γ^*p \to π^+ n$ interaction is described very well both for the longitudinal and the transverse polarizations. For the final state interactions a coupled--channel treatment of the interactions of transmitted hadrons allows to go beyond the Glauber approximation. We show that a proper distinction between the soft hadronic and hard partonic components of the electroproduction…
Color transparency is studied for the $K^+$ meson produced due to large four-momentum transfer in the $(e,e^\prime)$ reaction on nuclei. The variation of the $K^+$ meson color transparency ($K^+$CT) with the photon virtuality, and kaon momentum is investigated. The calculated results for $K^+$CT are compared with the data reported from Jefferson Laboratory.
A relativistic and quantum mechanical framework to compute nuclear transparencies for pion photo- and electroproduction reactions is presented. Final-state interactions for the ejected pions and nucleons are implemented in a relativistic eikonal approach. At sufficiently large ejectile energies, a relativistic Glauber model can be adopted. At lower energies, the framework possesses the flexibility to use relativistic optical potentials. The proposed model can account for the color-transparency (CT) phenomenon and short-range correlations (SRC) in the nucleus. Results are presented for kinemati…
It is found that the scattering of the fragile nucleus $^6$Li from $^{12}$C and $^{16}$O is unexpectedly transparent. It is shown that the internal-wave contribution is significantly large in the scattering, which suggests that some transparency could persist in the scattering involving the fragile nucleus $^6$He.
The transparency of the hadrons produced in the $γ(n,p) π^-$ reaction in nuclei is calculated using the Glauber model modified by including the Fermi motion of the nucleon in the nucleus. Since the calculated results underestimates the measured transparency for $^4$He nucleus, the Glauber model is further modified by incorporating the short-range correlation of the nucleon and the color transparency of the hadron in the nucleus. The nuclear transparency of the $γ(n,p) π^-$ reaction is calculated for $θ_{π^-}$(c.m.) = 50$^{\circ}$, 70$^{\circ}$ and 90$^{\circ}$. The calculated results are compa…
An unified shell model scheme to evaluate simultaneously the contribution of antibound states and Gamow resonances to the nuclear halos is presented. The calculations, performed in the complex energy plane, are applied to the case of $^{11}$Li. It is found that $^{11}$Li may develop a resonant state excitation near the breakup threshold.
A multichannel evolution equation is developed for the density matrix describing a hadronic wave packet produced by a virtual photon and propagation through a nuclear matter. This approach is dual to the quark-gluon representation, incorporates the effects of coherence and formation times and gives an exact solution for color transparency problem at any photon energy. We propose a procedure of data analysis, which provides an unambiguous way of detection of a color transparency signal even at medium energies.
Pionic quasielastic knockout of protons from nuclei at 200 GeV show very large effects of color transparency as -t increases from 0 to several GeV^2. Similar effects are expected for quasielastic photoproduction of vector mesons.
We study the electroproduction of rho mesons in nuclei at intermediate energies, deriving a treatment of the energy lost by the rho in each step of multiple-scattering. This enables a close match between calculations and the experimental kinematic conditions. A standard Glauber calculation is presented, and then the effects of color-transparency are included. The influence of poor experimental resolution on the extracted transparency is assessed. The effects of $ρ$ meson decay inside the nucleus are examined, and are typically about 5 percent at most. This effect disappears rapidly as $Q^2$ in…
We study inclusive omega photoproduction in nuclei and propose a measurement of the nuclear transparency ratio as a means to learn about the in-medium properties of the omega meson. To this end we are using the semi-classical coupled-channel BUU transport approach that allows for a consistent treatment of all nuclear effects. The conditions of our calculations are chosen such as to match the setup of existing experimental facilities at ELSA or MAMI C. We show that the observables (total production cross section and transparency) indeed are sensitive to the omega N interaction in the nuclear me…
Possible deformation of odd-N nuclei with N $\approx$ 28 towards the neutron drip line is investigated using the Nilsson diagram based on deformed Woods-Saxon potentials. Both weakly-bound and resonant one-particle levels are properly obtained by directly solving the Schrödinger equation in mesh of space coordinate with the correct boundary condition. If we use the same diffuseness of the potential as that of $β$-stable nuclei, the energy difference between the neutron 2p$_{3/2}$ and 1f$_{7/2}$ levels becomes very small or the N=28 energy gap almost disappears, as the binding energies of those…
Coherent electroproduction of vector mesons off $^2$H and $^4$He is considered in the kinematics of deep inelastic scattering. Special emphasis is given to the $-t\sim 0.8-1$ GeV$^2$ region where the cross section is dominated by the interaction of the $q\bar q$ configuration in the $γ^*$ with two nucleons. These kinematics provide the unique possibilities to study quantitatively in vector meson production the onset of Color Transparency with increasing $Q^2$ as well as its gradual disappearance at very small $x$, i.e., perturbative Color Opacity.
So far no theoretical tool for the comprehensive description of exclusive electroproduction of vector mesons off nuclei at medium energies has been developed. We suggest a light-cone QCD formalism which is valid at any energy and incorporates formation effects (color transparency), the coherence length and the gluon shadowing. At medium energies color transparency (CT) and the onset of coherence length (CL) effects are not easily separated. Indeed, although nuclear transparency measured by the HERMES experiment rises with Q^2, it agrees with predictions of the vector dominance model (VDM) with…
A relativistic framework for computing the nuclear transparency extracted from A(p,2p) scattering processes is presented. The model accounts for the initial- and final-state interactions (IFSI) within the relativistic multiple-scattering Glauber approximation (RMSGA). For the description of color transparency, two existing models are used. The nuclear filtering mechanism is implemented as a possible explanation for the oscillatory energy dependence of the transparency. Results are presented for the target nuclei 7Li, 12C, 27Al, and 63Cu. An approximated, computationally less intensive version …
A linked cluster expansion for the calculation of ground state observables of complex nuclei with realistic interactions has been used to calculate the ground state energy, density and momentum distribution of 16O and 40Ca. Using the same cluster expansion and the wave function and correlation parameters obtained from the energy calculation, we have evaluated the semi inclusive reaction A(e,e'p)X taking final state interaction (FSI) into account by a Glauber type approach; the comparison between the distorted and undistorted momentum distributions provides an estimate of the transparency of th…
Using the one-dimensional potential well with realistic parameters for atomic nuclei, we illustrate the movement of the poles of the S-matrix, and the transmission coefficient when the well supports an anti-bound state. We calculate the phase shift of the atomic nuclei 5He using the three-dimensional potential well, and compare it with the experimental one. The paper gives a glance of some of the properties found in realistic loosely and resonant nuclear systems, using equations at the level of undergraduate students.
The systematic change of shell structure in both weakly bound and resonant neutron one-particle levels in nuclei towards the neutron drip line is exhibited, solving the coupled equations derived from the Schrödinger equation in coordinate space with the correct asymptotic behaviour of wave functions for $r \rightarrow \infty$. The change comes from the behaviour unique in the one-particle motion with low orbital angular momenta compared with that with high orbital angular momenta. The observed deformation of very neutron-rich nuclei with $N \simgeq 20$ in the island of inversion is a natural r…
Continuum effects in the weakly bound nuclei close to the drip-line are investigated using the analytically soluble Poschl-Teller-Ginocchio potential. Pairing correlations are studied within the Hartree-Fock-Bogoliubov method. We show that both resonant and non-resonant continuum phase space is active in creating the pairing field. The influence of positive-energy phase space is quantified in terms of localizations of states within the nuclear volume.
The cross sections for the deep sub-barrier fusion reaction of light nuclei are calculated within the theoretical framework of the selective resonant tunneling model. In this model, assumption of a complex square-well nuclear potential is invoked to describe the absorption inside the nuclear well. The theoretical estimates for these cross sections agree well with the experimentally measured values. The features of the astrophysical S-factor are derived in terms of this model. Present formalism appears to be particularly useful for the low energy resonant reactions between two charged nuclei.
We argue that the observation of the color transparency effect in the semiexclusive $A(π^-,l^+ l^-)$ process is important for determining whether it is possible to extract the generalized parton distributions of the nucleon from the elementary reaction $π^- p \to l^+ l^- n$ at $p_{\rm lab}=15-20$ GeV/c at small $|t|$ and large invariant mass of the dilepton pair $l^+ l^-$. Assuming that the transverse size of the pionic $q \bar q$ pair in the hard interaction point is similar to the one in the reaction $γ^* p\to π^+ n$ studied at JLab we predict large color transparency effects in the discusse…
Using Woods-Saxon potentials and the eigenphase formalism for one-particle resonances, one-particle bound and resonant levels for neutrons as a function of quadrupole deformation are presented, which are supposed to be useful for the interpretation of spectroscopic properties of some light neutron-rich nuclei with weakly-bound neutrons. Compared with Nilsson diagrams in text books which are constructed using modified oscillator potentials, we point out a systematic change of the shell structure in connection with both weakly-bound and resonant one-particle levels related to small orbital angul…
The complex scaling method (CSM) is one of the most powerful methods of describing the resonances with complex energy eigenstates, based on non-Hermitian quantum mechanics. We present the basic application of CSM to the properties of the unbound phenomena of light nuclei. In particular, we focus on many-body resonant and non-resonant continuum states observed in unstable nuclei. We also investigate the continuum level density (CLD) in the scattering problem in terms of the Green's function with CSM. We discuss the explicit effects of resonant and non-resonant contributions in CLD and transitio…
This paper presents, for the first time, measurements of neutron transparency ratios for nuclei relative to C measured using the (e,e'n) reaction, spanning measured neutron momenta of 1.4 to 2.4 GeV/c. The transparency ratios were extracted in two kinematical regions, corresponding to knockout of mean-field nucleons and to the breakup of Short-Range Correlated nucleon pairs. The extracted neutron transparency ratios are consistent with each other for the two measured kinematical regions and agree with the proton transparencies extracted from new and previous (e,e'p) measurements, including tho…
We develop a complex scaling method for describing the resonances of deformed nuclei and present a theoretical formalism for the bound and resonant states on the same footing. With $^{31}$Ne as an illustrated example, we have demonstrated the utility and applicability of the extended method and have calculated the energies and widths of low-lying neutron resonances in $^{31}$Ne. The bound and resonant levels in the deformed potential are in full agreement with those from the multichannel scattering approach. The width of the two lowest-lying resonant states shows a novel evolution with deforma…
Nuclear transparency in (e,e'p) reactions is evaluated in a fully relativistic distorted wave impulse approximation model. The relativistic mean field theory is used for the bound state and the Pauli reduction for the scattering state, which is calculated from a relativistic optical potential. Results for selected nuclei are displayed in a Q^2 range between 0.3 and 1.8 (GeV/c)^2 and compared with recent electron scattering data. For Q^2 = 0.3 (GeV/c)^2 the results are lower than data; for higher Q^2 they are in reasonable agreement with data. The sensitivity of the model to different prescript…
The Relativistic Continuum Hartree-Bogoliubov (RCHB) theory, which properly takes into account the pairing correlation and the coupling to (discretized) continuum via Bogoliubov transformation in a microscopic and self-consistent way, has been reviewed together with its new interpretation of the halo phenomena observed in light nuclei as the scattering of particle pairs into the continuum, the prediction of the exotic phenomena -- giant halos in nuclei near neutron drip line, the reproduction of interaction cross sections and charge-changing cross sections in light exotic nuclei in combination…
In the annihilation of a positron with a bound atomic electron, the virtual gamma photon created may excite the atomic nucleus. We put forward this effect as a spectroscopic tool for an energy-selective excitation of nuclear transitions. This scheme can efficiently populate nuclear levels of arbitrary multipolarities in the MeV regime, including monopole transitions and giant resonances. In certain cases, it may have a higher cross sections than the conventionally used Coulomb excitation.
The complex scaling method (CSM) is a useful similarity transformation of the Schrödinger equation, in which bound-state spectra are not changed but continuum spectra are separated into resonant and non-resonant continuum ones. Because the asymptotic wave functions of the separated resonant states are regularized by the CSM, many-body resonances can be obtained by solving an eigenvalue problem with the $L^2$ basis functions. Applying this method to a system consisting of a core and valence nucleons, we investigate many-body resonant states in weakly bound nuclei very far from the stability lin…
A technique for describing scattering states within the nuclear shell model is proposed. This technique is applied to scattering of nucleons by $α$ particles based on ab initio No-Core Shell Model calculations of $^5$He and $^5$Li nuclei with JISP16 NN interaction.
We call "projectile fragmentation" of neutron halo nuclei the elastic breakup (diffraction) reaction, when the observable studied is the neutron-core relative energy spectrum. This observable has been measured in relation to the Coulomb breakup on heavy target and recently also on light targets. Such data enlighten the effect of the neutron final state interaction with the core of origin. Projectile fragmentation is studied here by a time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final st…
This dissertation explores two main topics: 1) Color Transparency and quasi-elastic knockout reactions involving pions and $ρ$ mesons; and 2) determination of the $J/ψ$-nucleon scattering amplitude and scattering length via $J/ψ$ electroproduction on the deuteron. It is shown that at the energies available at the COMPASS experiment at CERN, Color Transparency should be detectable in the reaction $π+A\to π+p+(A-1)^*$ (proton knockout). It is also shown that Color Transparency should be detectable in the electroproduction reaction $γ^*+A\toρ+p+(A-1)^*$ at small $Q^2$ (where $Q^2$ is the virtuali…
We study the photoproduction of $η^\prime$ mesons from nuclei near the threshold within the collision model based on the nuclear spectral function. The model takes properly into account both primary photon-nucleon and secondary pion-nucleon $η^\prime$ production processes as well as the effect of the nuclear $η^\prime$ mean-field potential on these processes. We find that the secondary pion-induced reaction channel $πN \to {η^\prime}N$ plays an insignificant role in the $η^\prime$ photoproduction off nuclei. We calculate the transparency ratio for $eta^\prime$ mesons and compare it to the avai…
We study the near-threshold pion-induced production of $ϕ$ mesons off nuclei in the kinematical conditions of the HADES experiment, recently performed at GSI. The calculations have been performed within a collision model based on the nuclear spectral function. The model accounts for both the primary $π^-$ meson--proton ${π^-}p \to ϕn$ and the secondary pion--nucleon $πN \to ϕN$ $ϕ$ production processes as well as the effects of the nuclear $ϕ$ and nucleon mean-field potentials. We find that the primary reaction channel ${π^-}p \to ϕn$ dominates in the $ϕ$ production off $^{12}$C and $^{184}$W …
We study the near-threshold $J/ψ$ meson production on protons and nuclei by considering incoherent direct non-resonant $K^-p \to {J/ψ}Λ$ and two-step resonant ${K^-}p \to P_{cs}(4459)^0 \to {J/ψ}Λ$ charmonium production processes. We calculate the absolute excitation functions, energy and momentum distributions for the non-resonant, resonant and for the combined (non-resonant plus resonant) production of $J/ψ$ mesons off protons as well as off carbon and tungsten target nuclei at near-threshold incident antikaon energies by considering these elementary production channels as well as by assumin…
The integrated cross section for the incoherent photoproduction of vector mesons on nuclei $γ^* A \to VX$, $X\not=A$, is calculated within Glauber theory and as a function of the photon energy. The inverse of the longitudinal momentum transfer is called coherence length $l_c$ and depends on the virtuality and the energy of the photon. Nuclear transmission factors strongly depend on $l_c/R_A$ ($R_A$ is the nuclear radius) and this effect may interfere with the search for color transparency effects.
We study the $J/ψ$ photoproduction from nuclei in the near-threshold beam energy region of $E_γ$=5--11 GeV within the nuclear spectral function approach by considering incoherent direct ($γN \to {J/ψ}N$) and two-step ($γp \to P^+_c(4312)$, $P^+_c(4312) \to {J/ψ}p$; $γp \to P^+_c(4440)$, $P^+_c(4440) \to {J/ψ}p$; $γp \to P^+_c(4457)$, $P^+_c(4457) \to {J/ψ}p$) $J/ψ$ production processes. We calculate the absolute excitation functions for the non-resonant and resonant production of $J/ψ$ mesons off $^{12}$C and $^{208}$Pb target nuclei within the different scenarios for in-medium modification of…
This is a brief review of few relevant topics on tunneling of composite particles and how the coupling to intrinsic and external degrees of freedom affects tunneling probabilities. I discuss the phenomena of resonant tunneling, different barriers seen by subsystems, damping of resonant tunneling by level bunching and continuum effects due to particle dissociation.
Resonance is a general phenomenon which can happen in classic or quantum systems. An unbound many-body quantum system can undergo a self-resonant process. It has long been a challenge how to describe unbound many-body quantum systems in resonances. In this paper, we develop a novel first-principles method that is capable of describing resonant quantum systems. We exploit, for the first time, the advanced in-medium similarity renormalization group (IMSRG) in the complex-energy Gamow-Berggren representation with resonance and non-resonant continuum. The ab initio Gamow IMSRG has broad applicatio…
We present a simple time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final state interaction. The final state is described by an optical model S-matrix so that both resonant and non resonant states of any continuum energy can be studied as well as deeply bound initial states. It is shown that, due to the coupling between the initial and final states, the neutron-core free particle phase shifts are modified, in the exit channel, by an additional phase. The effect of the additional phase on t…
The pseudospin symmetry is a relativistic dynamical symmetry connected with the small component of the Dirac spinor. The origin of pseudospin symmetry in single particle bound states in atomic nuclei has been revealed and studied extensively. By examining the zeros of Jost functions corresponding to the small components of Dirac wave functions and phase shifts of continuum states, we show that the pseudospin symmetry in single particle resonant states in nuclei is conserved when the attractive scalar and repulsive vector potentials have the same magnitude but opposite sign. The exact conservat…
