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Register a new userClassifying near-threshold enhancement using deep neural network
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One of the main issues in hadron spectroscopy is to identify the origin of threshold or near-threshold enhancement. Prior to our study, there is no straightforward way of distinguishing even the lowest channel threshold-enhancement of the nucleon-nucleon system using only the cross-sections. The difficulty lies in the proximity of either a bound or virtual state pole to the threshold which creates an almost identical structure in the scattering region. Identifying the nature of the pole causing the enhancement falls under the general classification problem and supervised machine learning using a feed-forward neural network is known to excel in this task. In this study, we discuss the basic idea behind deep neural network and how it can be used to identify the nature of the pole causing the enhancement. The applicability of the trained network can be explored by using an exact separable potential model to generate a validation dataset. We find that within some acceptable range of the cut-off parameter, the neural network gives high accuracy of inference. The result also reveals the important role played by the background singularities in the training dataset. Finally, we apply the method to nucleon-nucleon scattering data and show that the network was able to give the correct nature of pole, i.e. virtual pole for ${}^1S_0$ partial cross-section and bound state pole for ${}^3S_0$.
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Most of exotic resonances observed in the past decade appear as peak structure near some threshold. These near-threshold phenomena can be interpreted as genuine resonant states or enhanced threshold cusps. Apparently, there is no straightforward way of distinguishing the two structures. In this work, we employ the strength of deep feed-forward neural network in classifying objects with almost similar features. We construct a neural network model with scattering amplitude as input and nature of pole causing the enhancement as output. The training data is generated by an S-matrix satisfying the unitarity and analyticity requirements. Using the separable potential model, we generate a validation data set to measure the networks predictive power. We find that our trained neural network model gives high accuracy when the cut-off parameter of the validation data is within $400$-$800mbox{ MeV}$. As a final test, we use the Nijmegen partial wave and potential models for nucleon-nucleon scattering and show that the network gives the correct nature of pole.
The observed enhancement of $pbar p$-production near the threshold in radiative decays of $J/psi$ and $e^+e^-$-annihilations can be explained with final state interactions among the produced $Nbar N$ system, where the enhancement is essentially determined by $Nbar N$ elastic scattering amplitudes. We propose to use an effective theory for interactions in a $Nbar N$ system near its threshold. The effective theory is similar to the well-known one for interactions in a $NN$ system but with distinctions. It is interesting to note that in the effective theory some corrections to scattering amplitudes at tree-level can systematically be summed into a simple form. These corrections are from rescattering processes. With these corrected amplitudes we are able to describe the enhancement near the threshold in radiative decays of $J/psi$ and $e^+e^-$-annihilations, and the $pbar p$ elastic scattering near the threshold.
We develop a non-perturbative analysis of the electro-production of heavy vector mesons ($phi$, $J/Psi$) from threshold to high energy. We use the holographic construction with bulk confinement enforced through a soft wall. Using Witten diagrams, we evaluate the pertinent cross sections for heavy vector mesons ($phi$, $J/Psi$) production and study their dependence on both the incoming virtual photon polarization as well as the outgoing polarization of the heavy meson. Our results for $J/Psi$ electro-production compares well with the available HERA data at low and intermediate $Q^2$, and for a wide range of momentum transfer. We also predict the quasi-real electro-production of $J/Psi$ near threshold.
We apply perturbative QCD to investigate the near threshold heavy quarkonium photoproduction at large momentum transfer. From an explicit calculation, we show that the conventional power counting method will be modified and the three quark Fock state with nonzero orbital angular momentum dominates the near threshold production. It carries a power behavior of $1/(-t)^5$ for the differential cross section. We further comment on the impact of our results on the interpretation of the experiment measurement in terms of the gluonic gravitational form factors of the proton.
We study the observed enhancement of a $pbar p$ system near the threshold in the process $J/psi to gamma pbar p$ and $e^+ e^- to pbar p$. From early studies the enhancement can be explained by final state interactions, which are in general taken into account with some potential models. In this work we offer a simple approach within quantum field theory to explain the observed enhancement. We point out that among different final state interactions the rescattering in a $Nbar N$ system though exchange of $pi$ is the most important. The effects of the rescattering is completely fixed by the well-known coupling $g_{pi NN}$. Our results show that the enhancement in $J/psi to gamma pbar p$ and $e^+ e^- to pbar p$ can be well described with the rescattering effects.
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