Final State Interactions Research Articles

Inclusive electron-nucleus cross section within the self-consistent Green's function approach

We compute inclusive electron-nucleus cross sections using ab initio spectral functions of $^4$He and $^{16}$O obtained within the Self Consistent Green's Function approach. The formalism adopted is based on the factorization of the spectral function and the nuclear transition matrix elements. This allows to provide an accurate description of nuclear dynamics and to account for relativistic effects in the interaction vertex. Our calculations use a saturating chiral Hamiltonian in order reproduce the correct nuclear sizes. When final state interactions for the struck particle are accounted for, we find nice agreement between the data and the theory for the inclusive electron-$^{16}$O cross section. The results lay the foundations for future applications of the Self Consistent Green's Function method, in both closed and open shell nuclei, to neutrino data analysis. This work also presents results for the point-proton, charge and single-nucleon momentum distribution of the same two nuclei. The center of mass can affect these quantities for light nuclei and cannot be separated cleanly in most ab initio post-Hartree-Fock methods. In order to address this, we developed a Metropolis Monte Carlo calculation in which the center of mass coordinate can be subtracted exactly from the trial wave function and the expectation values. We gauged this effect for $^4$He by removing the center of mass effect from the Optimal Reference State wave function that is generated during the Self Consistent Green's Function calculations. Our findings clearly indicate that the residual center of mass contribution strongly modifies calculated matter distributions with respect to those obtained in the intrinsic frame. Hence, its subtraction is crucial for a correct description of light nuclei.

Determination of the Polarization Observables $${{\varvec{C}}}_{{\varvec{x}}}$$, $${{\varvec{C}}}_{{\varvec{z}}}$$, and $${{\varvec{P}}}_{{\varvec{y}}}$$ for the Quasi-Free Mechanism in the Reaction $${\varvec{\overrightarrow{\gamma }}}{\varvec{d}}\varvec{\rightarrow } {\varvec{K}}^{\varvec{+}}{\varvec{\overrightarrow{\varLambda }}} {{\varvec{n}}}$$

The study of the excited-nucleon ( $$N^*$$ ) spectrum is fundamental for the quest to understand non-perturbative quantum chromodynamics. Measured kinematical evolutions of experimental observables, such as polarizations and unpolarized cross sections, for exclusive meson photoproduction off proton and neutron, are the foundation of theoretical and phenomenological analyses that identify the $$N^*$$ states excited in these reactions and determine their parameters. While free proton targets are readily available, experiments typically use bound neutrons, such as in the deuteron, to estimate observables for photoproduction off the free neutron. Even though exclusivity allows to select event samples dominated by quasi-free scattering (QF), it is not clear if the obtained observables are unbiased estimates of the observables for photoproduction off the free neutron. Studies assessing the possible sources of bias, such as the neutron binding and final-state interactions (FSI), are sparse and primarily focused on the unpolarized cross sections. The comparison between observables for production off the free and off the bound proton in high-statistics reactions, seems to be the natural way to study and to quantify these effects experimentally. Alternatively, one can map the evolution of the QF observables with target-neutron momentum and potentially extrapolate it to the “free”-neutron point of zero momentum. In this work, we determine the recoil polarization $$P_y$$ of the $$\varLambda $$ hyperon and the polarization transfers $$C_x$$ and $$C_z$$ from circularly-polarized photons to the $$\varLambda $$ for the quasi-free mechanism of the reaction $$\overrightarrow{\gamma }d\rightarrow K^+\overrightarrow{\varLambda } n$$ , i.e., for photoproduction off the bound proton. The data were taken with the CLAS detector at the Thomas Jefferson National accelerator facility (JLab) during the E06-103 (g13a) experiment and cover $$E_{\gamma }$$ between 0.9 and 2.6 GeV and $$\cos \theta _{KCM}$$ between $$-\,0.3$$ and 0.8. For several kinematic bins, the dependence of the polarizations on the target-proton momentum is studied. Our work can be used as a benchmark to develop analysis strategies to reduce potential bias due to FSI and the binding of the neutron in the deuteron in reported polarization observables for quasi-free meson photoproduction off the bound neutron.

A new method to study the number of colors in the final-state interactions of hadrons

Based on Chiral Perturbation Theory we introduce the dependence on the number of colors (NC) for the ππ→ππ scattering amplitudes. Those amplitudes are calculated from dispersion relations that respect analyticity and coupled channel unitarity, as well as accurately describing experiment. By varying NC the trajectories of the poles and residues (the couplings to ππ) of the light mesons, the σ/f0(500), f0(980), ρ(770) and f2(1270) are investigated. Our results show that the method proposed is a reliable way to study the NC dependence in hadron–hadron scattering with final-state interactions.

The Three-Pion Decays of the **Supported by the National Natural Science Foundation of China under Grant Nos. 11475227 and 11735003. It is also supported by the Youth Innovation Promotion Association CAS (No. 2016367)

We investigate the decay of with the assumption that the is dynamically generated from the coupled channel and interactions. In addition to the tree level diagrams that proceed via , we take into account also the final state interactions of and . We calculate the invariant mass distribution and also the total decay width of as a function of the mass of . The calculated total decay width of is significantly different from other model calculations and tied to the dynamical nature of the resonance. The future experimental observations could test of model calculations and would provide vary valuable information on the relevance of the component in the wave function.

Neutrino Energy Reconstruction Methods Using Electron Scattering Data

The precise measurement of neutrino properties is among the highest priorities in fundamental particle physics, involving many experiments worldwide. Since the experiments rely on the interactions of neutrinos with bound nucleons inside atomic nuclei, the planned advances in the scope and precision of these experiments requires a commensurate effort in the understanding and modeling of the hadronic and nuclear physics of these interactions, which is incorporated as a nuclear model in neutrino event generators. This model is essential to every phase of experimental analyses and its theoretical uncertainties play an important role in interpreting every result.Any nuclear model used to describe neutrino-nucleus scattering should first be validated against these data. Since the vector part of the weak response is related to the electro-magnetic response through CVC, such a test is necessary, but not sufficient, to ensure the validity of a model for given kinematics, namely given values of the transferred energy ω(= ν for neutrinos) and momentum q. The main challenges in connecting electron and neutrino reactions:• matching models used to predict neutrino-nucleus observables to electron scattering data.• expanding theory to include more semi-inclusive predictions.• provide semi-inclusive neutron, proton and pion data sets with broad angular range.The cross section for neutrino scattering from nuclei is sensitive to the same underlying structure determined by QCD, and as probed with pure electromagnetic processes, such as charged lepton scattering from nucleons and nuclei. As such, there are a number of ways that electron scattering data inform ν - A cross section modeling, as well as providing a test-bed for model validation. In contrast to past and current neutrino beams, charged lepton scattering has the distinct advantage of nearly monochromatic beams with well determined energies, allowing for a significantly cleaner kinematic separation of the various production mechanisms in inclusive scattering, such as reso- nance production and nucleon elastic scattering. In addition to providing important experimental input such as nucleon isovector elastic form factors and resonance transition form factors, electron scattering data provide critical information on the distributions of initial state momentum and energy for nucleons in nuclei, the importance of 2-body currents and final state interaction effects. In this analysis, we will give a brief overview of the experimental input provided by electron scattering data.

Photon or meson formation in J/ψ decays into pp¯

The measurements of the $J/\psi \rightarrow \gamma p \overline{p}$ decays by the BES Collaboration indicate an enhancement at the $p \overline{p}$ threshold which, however, is not present in the J/$\psi$ decays into $\omega p \overline{p}$ and into $\pi p \overline{p}$. Here, two processes for describing the decays $J/\psi \rightarrow \mathcal{B} p \overline{p}$ where $\mathcal{B} = \gamma, \omega$ are presented in some detail and the cases $\mathcal{B} =\phi, \pi $ are briefly touched on. The first one, applied not only to the radiative decay to reproduce the threshold peak but also to the $\omega p \overline{p}$ decay channel to improve the description of the spectrum, postulates a direct emission of the boson before the baryon pair is formed. The second process assumes that the boson $\mathcal{B}$ is emitted from the baryon pair following the $J/\psi$ decay and includes for the decays into $\gamma p \overline{p}$ a final state nucleon-antinucleon interaction based on the Paris $N \overline{N}$ potential. The reproduction of the $p \overline{p}$ distribution in the $J/\psi \rightarrow \omega p \overline{p}$ decays needs a final state interaction involving a $N(2050)\ 3/2^-$ resonance. The photon- and meson-emission rates are reproduced in a semi-quantitative way.

Modeling neutrino-induced charged pion production on water at T2K kinematics

Pion production is a significant component of the signal in accelerator-based neutrino experiments. Over the last years, the MiniBooNE, T2K and MINERvA collaborations have reported a substantial amount of data on (anti)neutrino-induced pion production on the nucleus. However, a comprehensive and consistent description of the whole data set is still missing. We aim at improving the current understanding of neutrino-induced pion production on the nucleus. To this end, the comparison of experimental data with theoretical predictions, preferably based on microscopic models, is essential to disentangle the different reaction mechanisms involved in the process. To describe single-pion production (SPP) we use a hybrid model that combines a low- and a high-energy approach. The low-energy model (LEM) contains resonances and background terms. At high invariant masses, a high-energy model based on a Regge approach is employed. The model is implemented in the nucleus using the relativistic plane wave impulse approximation (RPWIA). We present a comparison of the hybrid-RPWIA and LEM with the recent neutrino-induced charged current $1\pi^+$ production cross section on water reported by T2K. In order to judge the impact of final-state interactions (FSI) we confront our results with those of the NuWro Monte Carlo generator. The hybrid-RPWIA model and NuWro compare favorably to the data, albeit that FSI are not included in the former. These results complement our previous work [Phys. Rev. D 97, 013004 (2018)] where we compared the models to the MINERvA and MiniBooNE $1\pi^+$ data. The hybrid-RPWIA model tends to overpredict both the T2K and MINERvA data in kinematic regions where the largest suppression due to FSI is expected, and agrees remarkably well with the data in other kinematic regions. On the contrary, the MiniBooNE data is underpredicted over the whole kinematic range.

Effect of final state interactions on neutrino energy reconstruction at DUNE

We quantitatively study the percentage of fake events present in CCQE and CCRes interactions and the impact of final state interactions on the neutrino oscillation parameters at DUNE. The effect of final-state interactions for DUNE oscillation physics is analyzed in an ideal and realistic detector scenario. Resonance interaction will be the most dominant interaction in the oscillation sensitive region of DUNE. The νμ-disappearance oscillation channel is studied using LAr detector. We find that nuclear effects and detector threshold play a significant role in CCQE and CCRes interactions and these nuclear effects induce a significant bias in the determination of atmospheric neutrino oscillation parameters. The impression of nuclear effects on the determination of θ23 is quantified in this work, which will help in reducing the systematic error at DUNE.

Photo- and Electro-excitation of Bound Neutrons and Protons

Data for pion photo-productions off the neutron ($\gamma n\to \pi N$) have been primarily extracted from deuteron-target data ($\gamma d\to \pi NN$) by applying kinematical cuts thereby isolating the quasi-free samples. We critically examine if the neutron-target data obtained through this conventional procedure can be contaminated by final state interactions (FSI) and/or the kinematical cuts. The analysis is conducted with a theoretical model for $\gamma d\to \pi NN$ that takes account of the impulse mechanisms supplemented by the $NN$ and $\pi N$ rescattering mechanisms. We show that the FSI effects still visibly remain in the extracted $\gamma$`$n$'$\to\pi N$ unpolarized cross sections and polarization asymmetries $E$ even after the kinematical cuts are applied. We also find the FSI effects on $\gamma$`$n$'$\to\pi^0n$ can be somewhat different from those on $\gamma$`$p$'$\to\pi^0p$.

Revisiting final state interaction in charmless Bq→PP decays

Various new measurements in charmless ${B}_{u,d,s}\ensuremath{\rightarrow}PP$ modes, where $P$ is a low lying pseudoscalar meson, are reported by Belle and LHCb. These include the rates of ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$, $\ensuremath{\eta}{\ensuremath{\pi}}^{0}$, ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\eta}}^{\ensuremath{'}}{\ensuremath{\eta}}^{\ensuremath{'}}$, ${B}^{0}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$ and ${B}_{s}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decays. Some of these modes are highly suppressed and are among the rarest $B$ decays. Direct $CP$ asymmetries on various modes are constantly updated. It is well known that direct $CP$ asymmetries and rates of suppressed modes are sensitive to final state interaction (FSI). As new measurements are reported and more data will be collected, it is interesting and timely to revisit the rescattering effects in ${B}_{u,d,s}\ensuremath{\rightarrow}PP$ states. We perform a ${\ensuremath{\chi}}^{2}$ analysis with all available data on $CP$-averaged rates and $CP$ asymmetries in ${\overline{B}}_{u,d,s}\ensuremath{\rightarrow}PP$ decays. Our numerical results are compared to data and those from factorization approach. The quality of the fit is improved significantly from the factorization results in the presence of rescattering. The relations on topological amplitudes and rescattering are explored and they help to provide a better understanding of the effects of FSI. As suggested by U(3) symmetry on topological amplitudes and FSI, a vanishing exchange rescattering scenario is considered. The exchange, annihilation, $u$-penguin, $u$-penguin annihilation, and some electroweak penguin amplitudes are enhanced significantly via annihilation and total annihilation rescatterings. In particular, the $u$-penguin annihilation amplitude is sizably enhanced by the tree amplitude via total annihilation rescattering. These enhancements affect rates and $CP$ asymmetries. Predictions can be checked in the near future.

Spin alignment following inelastic scattering of Ne17 , lifetime of F16 , and its constraint on the continuum coupling strength

The sequential two-proton decay of the second excited state in $^{17}\mathrm{Ne}$, produced by inelastic excitation at intermediate energy, is studied. This state is found to be highly spin aligned, providing another example of a recently discovered alignment mechanism. The fortuitous condition that the second decay step is slightly more energetic than the first, permits the lifetime of the one-proton daughter, the ground state of $^{16}\mathrm{F}$, to be determined from the magnitude of the final-state interactions between the protons. This new method gave a result [$\mathrm{\ensuremath{\Gamma}}=20.6(57)$ keV] consistent with that obtained by directly measuring the width of the state [$\mathrm{\ensuremath{\Gamma}}=21.3(51)$ keV]. This width allows one to determine the continuum coupling constant in this mass region. Real-energy continuum-shell-model studies yield a satisfactory description of both spectra and widths of low-energy resonances in $^{16}\mathrm{F}$ and suggest an unusual large ratio of proton-proton to proton-neutron continuum couplings in the vicinity of the proton drip line.

Λ N → NN EFT potentials and hypertriton non-mesonic weak decay

The potential for the Λ N → NN weak transition, the main responsible for the non-mesonic weak decay of hypernuclei, has been developed within the framework of effective field theory (EFT) up to next-to-leading order (NLO). The leading order (LO) and NLO contributions have been calculated in both momentum and coordinate space, and have been organised into the different operators which mediate the N → NN transition. We compare the ranges of the one-meson and two-pion exchanges for each operator. The non-mesonic weak decay of the hypertriton has been computed within the plane-wave approximation using the LO weak potential and modern strong EFT NN potentials. Formally, two methods to calculate the final state interactions among the decay products are presented. We briefly comment on the calculation of the mesonic weak decay.

A femtoscopic correlation analysis tool using the Schr\xf6dinger equation (CATS)

We present a new analysis framework called “Correlation Analysis Tool using the Schrödinger equation” (CATS) which computes the two-particle femtoscopy correlation function C(k), with k being the relative momentum for the particle pair. Any local interaction potential and emission source function can be used as an input and the wave function is evaluated exactly. In this paper we present a study on the sensitivity of C(k) to the interaction potential for different particle pairs: p–p, p–mathrm {Lambda }, mathrm {K^-}–p, mathrm {K^+}–p, p–mathrm {Xi }^- and mathrm {Lambda }–mathrm {Lambda }. For the p–p Argonne v_{18} and Reid Soft-Core potentials have been tested. For the other pair systems we present results based on strong potentials obtained from effective Lagrangians such as chi EFT for p–mathrm {Lambda }, Jülich models for mathrm{K}(bar{mathrm{K}})–N and Nijmegen models for mathrm {Lambda }–mathrm {Lambda }. For the p–mathrm {Xi }^- pairs we employ the latest lattice results from the HAL QCD collaboration. Our detailed study of different interacting particle pairs as a function of the source size and different potentials shows that femtoscopic measurements can be exploited in order to constrain the final state interactions among hadrons. In particular, small collision systems of the order of 1 fm, as produced in pp collisions at the LHC, seem to provide a suitable environment for quantitative studies of this kind.

Energy-resolved attosecond interferometric photoemission from Ag(111) and Au(111) surfaces

Photoelectron emission from solid surfaces induced by attosecond pulse trains into the electric field of delayed phase-coherent infrared (IR) pulses allows the surface-specific observation of energy-resolved electronic phase accumulations and photoemission delays. We quantum-mechanically modeled interferometric photoemission spectra from the (111) surfaces of Au and Ag, including background contributions from secondary electrons and direct emission by the IR pulse, and adjusted parameters of our model to energy-resolved photoelectron spectra recently measured at a synchrotron light source by Roth et al. [J. Electron Spectrosc. 224, 84 (2018)]. Our calculated spectra and photoelectron phase shifts are in fair agreement with the experimental data of Locher et al. [Optica 2, 405 (2015)]. Our model's not reproducing the measured energy-dependent oscillations of the Ag(111) photoemission phases may be interpreted as evidence for subtle band-structure effects on the final-state photoelectron-surface interaction not accounted for in our simulation.

Femtoscopy with ALICE at the LHC

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Predictions for isobaric collisions at sNN=200 GeV from a multiphase transport model

The isobaric collisions of $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr have recently been proposed to discern the charge separation signal of the chiral magnetic effect (CME). In this article, we employ the string melting version of a multiphase transport model to predict various charged-particle observables, including $dN/d\eta$, $p_T$ spectra, elliptic flow ($v_2$), and particularly possible CME signals in Ru + Ru and Zr + Zr collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. Two sets of the nuclear structure parametrization have been explored, and the difference between the two isobaric collisions appears to be small, in terms of $dN/d\eta$, $p_T$ spectra, and $v_2$ for charged particles. We mimic the CME by introducing an initial charge separation that is proportional to the magnetic field produced in the collision, and study how the final-state interactions affect the CME observables. The relative difference in the CME signal between the two isobaric collisions is found to be robust, insensitive to the final-state interactions.

Scaling within the spectral function approach

Scaling features of the nuclear electromagnetic response functions unveil aspects of nuclear dynamics that are crucial for interpretating neutrino- and electron-scattering data. In the large momentum-transfer regime, the nucleon-density response function defines a universal scaling function, which is independent of the nature of the probe. In this work, we analyze the nucleon-density response function of $^{12}$C, neglecting collective excitations. We employ particle and hole spectral functions obtained within two distinct many-body methods, both widely used to describe electroweak reactions in nuclei. We show that the two approaches provide compatible nucleon-density scaling functions that for large momentum transfers satisfy first-kind scaling. Both methods yield scaling functions characterized by an asymmetric shape, although less pronounced than that of experimental scaling functions. This asymmetry, only mildly affected by final state interactions, is mostly due to nucleon-nucleon correlations, encoded in the continuum component of the hole SF.

Electron-deuteron deep-inelastic scattering with spectator nucleon tagging and final-state interactions at intermediate x

We consider electron-deuteron deep-inelastic scattering (DIS) with detection of a proton in the nuclear fragmentation region ("spectator tagging") as a method for extracting the free neutron structure functions and studying their nuclear modifications. Such measurements could be performed at a future Electron-Ion Collider (EIC) with suitable forward detectors. The measured proton recoil momentum (~< 100 MeV in the deuteron rest frame) specifies the deuteron configuration during the high-energy process and permits a controlled theoretical treatment of nuclear effects. Nuclear and nucleonic structure are separated using methods of light-front quantum mechanics. The impulse approximation (IA) to the tagged DIS cross section contains the free neutron pole, which can be reached by on-shell extrapolation in the recoil momentum. Final-state interactions (FSI) distort the recoil momentum distribution away from the pole. In the intermediate-x region 0.1 < x < 0.5 FSI arise predominantly from interactions of the spectator proton with slow hadrons produced in the DIS process on the neutron (rest frame momenta ~< 1 GeV, target fragmentation region). We construct a schematic model describing this effect, using final-state hadron distributions measured in nucleon DIS experiments and low-energy hadron scattering amplitudes. We investigate the magnitude of FSI, their dependence on the recoil momentum (angular dependence, forward/backward regions), their analytic properties, and their effect on the on-shell extrapolation. We comment on the prospects for neutron structure extraction in tagged DIS with EIC. We discuss possible extensions of the FSI model to other kinematic regions (large/small x). In tagged DIS at x << 0.1 FSI resulting from diffractive scattering on the nucleons become important and require separate treatment.

Consistent Dalitz plot analysis of Cabibbo-favored [formula omitted] decays

We resume the study of the Cabibbo-favored charmed-meson decays D+→K¯ππ+ in a dispersive framework that satisfies unitarity, analyticity, and crossing symmetry by construction. The formalism explicitly describes the strong final-state interactions between all three decay products and relies on pion–pion and pion–kaon phase shift input. For the first time, we show that the D+→KSπ0π+ Dalitz plot obtained by the BESIII collaboration as well as the D+→K−π+π+ Dalitz plot data by CLEO and FOCUS can be described consistently, exploiting the isospin relation between the two coupled decay channels that provides better constraints on the subtraction constants.

Exclusive Meson Electroweak production off Bound Nucleons

The effects of final state interaction in electroweak pion production reactions have been studied. The one loop corrections to the impulse approximation due to the nucleon and the pion rescattering is evaluated using the ANL-Osaka dynamical coupled channel model for the meson production reactions. It is found the final state interaction will affects the $$\nu N$$ cross section extracted in the previous analysis of the $$\nu d$$ data.