Photoproduction Reactions Research Articles

Overview of hadron photoproduction experiments in SPring-8 LEPS2 project

An experimental project to study hadron properties through photoproduction reactions is carried out in SPring-8 LEPS2 beamline. As an overview of this project, recent physics achievements and prospects on light baryon spectroscopy, exotic hadrons / bound states, and the origin of hadron mass are discussed with the description of experimental setups.

Extraction of polarization observables in two pion photoproduction reactions

The relevance of the study of polarization observables to gather insight on the features of baryonic resonances, and the procedure applied for the extraction of this information from the data, are illustrated. The reference reaction is the photoproduction of two charged pions with both a polarized beam and target, experimental conditions that were met in the g14 (2012) run of the CLAS experiment at Jefferson Lab. The method for the determination of the I⊙ observable is discussed and illustrated utilizing previously published data.

Measurement of the cross-section ratio σψ(2S)/σJ/ψ(1S) in exclusive photoproduction at HERA

The exclusive photoproduction reactions γp → J/ψ(1S)p and γp → ψ(2S)p have been measured at an ep centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb−1. The measurement was made in the kinematic range 30 < W < 180 GeV, Q2< 1 GeV2 and |t| < 1 GeV2, where W is the photon-proton centre-of-mass energy, Q2 is the photon virtuality and t is the squared four-momentum transfer at the proton vertex. The decay channels used were J/ψ(1S) → μ+μ−, ψ(2S) → μ+μ− and ψ(2S) → J/ψ(1S)π+π− with subsequent decay J/ψ(1S) → μ+μ−. The ratio of the production cross sections, R = σψ(2S)/σJ/ψ(1S), has been measured as a function of W and |t| and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.

Models of $$J/\varPsi $$ photo-production reactions on the nucleon

The $J/\Psi$ photo-production reactions on the nucleon can provide information on the roles of gluons in determining the $J/\Psi$-nucleon ($J/\Psi$-N) interactions and the structure of the nucleon. The information on the $J/\Psi$-N interactions is needed to test lattice QCD (LQCD) calculations and to understand the nucleon resonances such as $N^*(P_c)$ recently reported by the LHCb Collaboration. In addition, it is also needed to investigate the production of nuclei with hidden charms and to extract the gluon distributions in nuclei. The main purpose of this article is to review six reaction models of $\gamma + p \rightarrow J/\Psi +p$ reactions which have been and can be applied to analyze the data from Thomas Jefferson National Accelerator Facility (JLab). The formulae for each model are given and used to obtain the results to show the extent to which the available data can be described. The models presented include the Pomeron-exchange model of Donnachie and Landshoff (Pom-DL) and its extensions to include $J/\Psi$-N potentials extracted from LQCD (Pom-pot) and to also use the constituent quark model (CQM) to account for the quark substructure of $J/\Psi$ (Pom-CQM). The other three models are developed from applying the perturbative QCD approach to calculate the two-gluon exchange using the generalized parton distribution (GPD) of the nucleon (GPD-based), two- and three-gluon exchanges using the parton distribution of the nucleon ($2g+3g$), and the exchanges of scalar ($0^{++}$) and tensor ($2^{++}$) glueballs within the holographic formulation (holog). The results of investigating the excitation of the nucleon resonances $N^*(P_c)$ in the $\gamma + p \rightarrow J/\Psi +p$ reactions are also given.

Использование замедленной флуоресценции хлорофилла водорослей для биотестирования загрязнений

The nature of the delayed chlorophyll fluorescence (DF) in algae, which occurs already after the cessation of illumination due to the energy released during the reverse reactions of the primary photosynthesis photoproducts in the reaction center of the photosystem 2, is considered. The use of this fluorescence in algae for biotesting of contaminants is shown to be promising. The advantages of using DF for express assessment of water toxicity, especially drinking water, are short durations of tests and, accordingly, the minimized negative impact of physicochemical changes in the medium on the results, as well as the need of small amounts of test objects. The other advantage of DF is that only living cells with active photosynthetic reaction sites are measured, which increases the sensitivity of toxicity tests. This method provides additional information about the most important process in the cell - the energization of photosynthetic membranes and the formation of ATP associated with this.

Testing chiral unitary models for the Λ(1405) in K+πΣ photoproduction

We adopt a novel formalism for the low-energy analysis of the $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$ photoproduction reaction, outlined recently in [P. C. Bruns, arXiv:2012.11298.], to calculate the $\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}$ invariant mass distributions in the $\mathrm{\ensuremath{\Lambda}}(1405)$ resonance region. The approach adheres to constraints arising from unitarity, gauge invariance, and chiral perturbation theory, and is used without adjusting any model parameters. It is found that the meson-baryon rescattering in the final state has a major impact on the magnitude and structure of the generated spectra that are compared with the experimental data from the CLAS Collaboration. We demonstrate a large sensitivity of the theoretical predictions to the choice of the coupled-channel $\ensuremath{\pi}\mathrm{\ensuremath{\Sigma}}\ensuremath{-}\overline{K}N$ model amplitudes which should enable one to constrain the parameter space of these models.

Coherent photoproduction of a [formula omitted]-meson on a tensor-polarized deuteron at large momentum transfer

Measured values of the tensor analyzing power T20 for the coherent photoproduction of a π0-meson on a deuteron are analyzed in the region of large momentum transfer. The incident photons of the photoproduction reaction γd→dπ0 are the quasi-real virtual photons arising from the electron scattering in the electroproduction reaction ed→edπ0. The kinematic region of large momentum transfer is of particular interest, as it corresponds to small inter-nucleon distances in the deuteron. In this case, the amplitude of the process under study is noticeably sensitive to both the deuteron wave function at small inter-nucleon distances and the various model uncertainties arising from the description of the process for large momentum transfer. A comparison shows a significant discrepancy between the experimental data and the predictions from a number of theoretical models.

Measurement of spin density matrix elements in Λ(1520) photoproduction at 8.2–8.8 GeV

We report on the measurement of spin density matrix elements of the $\Lambda(1520)$ in the photoproduction reaction $\gamma p\rightarrow \Lambda(1520)K^+$, via its subsequent decay to $K^{-}p$. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Lab using a linearly polarized photon beam with $E_\gamma =$ 8.2-8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, $-(t-t_\text{0})$. We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in $\Lambda(1520)$ photoproduction.

On the photoproduction reactions $$\varvec{\gamma d\rightarrow \pi NN}$$

A review of our works providing a theoretical description of incoherent pion photoproduction on the deuteron is presented. The existing $\gamma d\to\pi NN$ data are analysed, especially those obtained more recently by the CLAS Collaboration at JLab, the A2 Collaboration at MAMI at Mainz, and the PION@MAX-lab Collaboration at Lund. A procedure, which accounts for the final state interactions (FSI), is applied to extract $\gamma n\to\pi N$ differential cross sections from the deuteron data. The role of FSI is discussed. We also comment on the results of other works in connection with some discrepancies seen in comparing the model with experiment. The electromagnetic properties of baryon $N^\ast$ resonances, improved using the extracted $\gamma n\to\pi N$ differential cross sections, are presented. A model description of the cross section data from charged-pion photoproduction reactions $\gamma d\to\pi^{\pm}NN$ near threshold is also given. The $\gamma d\to\pi^-pp$ data are used to extract the $E_{0+}$ multipole and total crsoss sections of the reaction $\gamma n\to\pi^-p$ near threshold.

K+Σ− photoproduction within an isobar model

We used an isobar model to study the K+Σ− photoproduction reaction on a neutron target with focus on the resonance region. In order to achieve a reasonable agreement with the data, we included spin-3/2 and spin-5/2 nucleon resonances in a consistent formalism together with a Δ resonance and two kaon resonances on top of the Born terms. The free parameters of the model were adjusted to the data from the CLAS and LEPS Collaborations on differential cross sections and photon beam asymmetry. The cornerstone of this analysis was an upgrade of the fitting method. Previously, we used only the plain χ2 minimization, which could not prevent us from overfitting the data. We, therefore, introduced a regularization method, the least absolute selection shrinkage operator (LASSO), which, together with information criteria, restricts the number of nonzero parameters and prevents us from overfitting the data. In our analysis, we arrived at two models, fit M, whose parameters were fitted with the MINUIT code only, and fit L, where we used the more advanced LASSO. Both models describe the data in a similar way and we observe only slight differences in the dσ/dΩ data description at very forward angles where the fit M is flat whereas the fit L produces two broad peaks, and in the photon beam asymmetries above 2 GeV at backward kaon angles where the fit M produces a bump. Surprisingly, no hyperon resonances are needed for the correct data description in these models. On the other hand, the N(1720)3/2+ nucleon resonance was found to be very important in both models.

Photoproduction reaction γn → K *0Λ in an effective Lagrangian approach * *Supported by the National Natural Science Foundation of China (12175240, 11475181, 11635009), the Fundamental Research Funds for the Central Universities, the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (Y7292610K1), and the China Postdoctoral Science Foundation (2021M693142)

In our previous work [Phys. Rev. C 101, 014003 (2020)], the photoproduction reaction was investigated within an effective Lagrangian approach. The reaction amplitudes were constructed by including the t-channel K, , and κ exchanges, u-channel Λ, Σ, and exchanges, s-channel N, , and exchanges, and interaction current. The data on the differential cross sections and spin density matrix elements were described simultaneously. In this study, we investigate the photoproduction reaction based on the same reaction mechanism as that of to obtain a unified description of the data for and within the same model. All hadronic coupling constants, form factor cutoffs, and the resonance masses and widths in the present calculations remain the same as in our previous work for . The available differential cross-section data for are well reproduced. Further analysis shows that the cross sections of are dominated by the contributions of the t-channel K exchange, while the s-channel and exchanges also provide considerable contributions.

Photodissociation Dynamics of Nitric Oxide from N-Acetylcysteine- or N-Acetylpenicillamine-bound Roussin's Red Ester.

The photochemical release of nitric oxide (NO) from a NO precursor is advantageous in terms of spatial, temporal, and dosage control of NO delivery to target sites. To realize full control of the quantitative NO administration from photoactivated NO precursors, it is necessary to have detailed dynamical information on the photodissociation of NO from NO precursors. We synthesized two new water-soluble Roussin’s red esters (RREs), [Fe2(μ-N-acetylcysteine)2(NO)4] and [Fe2(μ-N-acetylpenicillamine)2(NO)4], which have five times longer lifetime than the well-known [Fe2(μ-cysteine)2(NO)4]. The photodissociation dynamics of NO from these RREs in water were investigated over a broad time range from 0.3 ps to 10 μs after excitation at 310 and 400 nm using femtosecond time-resolved infrared (IR) spectroscopy. When these RREs are excited, they either release one NO, producing a radical species deficient in one NO (R), [Fe2(μ-RS)2(NO)3], or relax into the ground state without photodeligation via an electronically excited intermediate state (M). R appears immediately after photoexcitation, suggesting that one NO is photodissociated faster than 0.3 ps. A certain fraction of R undergoes geminate recombination (GR) with NO with a time constant of 7–9 ps, while the remaining R competitively binds to the solvent. Solvent-bound R eventually bimolecularly recombines with NO with a rate constant of (1.3–1.6) × 108 M–1 s–1. For a given RRE molecule, the fractional yield of M (0.62–0.76) depends on the excitation wavelength (λex); however, the relaxation time of M (6 ± 1 ns) is independent of λex. Although the primary quantum yield of NO photodissociation (Φ1) was found to be 0.24–0.38, the final yield of NO suitable for other reactions (Φ2) was reduced to 0.14–0.29 due to the picosecond GR of the dissociated NO with R. Detailed photoexcitation dynamics of RRE can be utilized in the quantitative control of NO administration at a specific site and time, promoting pin-point usage of NO in chemistry and biology. We demonstrate that femtosecond IR spectroscopy combined with quantum chemical calculations is a powerful method for obtaining detailed dynamic information on photoactivated NO precursors such as Φ1 and Φ2, the GR yield, and secondary reactions of the nascent photoproducts, which are essential information for the design of efficient photoactivated NO precursors and their quantitative utilization.

Constituent counting rule and ω photoproduction

The constituent counting ruling (CCR) has been found to hold for numerous hard, exclusive processes. It predicts the differential cross section at high energies and fixed $cos{\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}$ should follow $\frac{d\ensuremath{\sigma}}{dt}\ensuremath{\sim}\frac{1}{{s}^{n\ensuremath{-}2}}$, where $n$ is the minimal number of constituents involved in the reaction. Conversely, there are hard, exclusive processes for which it has been found that the CCR does not work. The exact reasons for these have not been clearly established. One such example, for which the analysis of CLAS data deviates from the prediction of the CCR, is the omega photoproduction reaction. Here, we provide an in-depth analysis of the reaction $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\omega}p$ at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\approx}{90}^{\ensuremath{\circ}}$ using CLAS data with an energy range of $s=5\text{--}8\phantom{\rule{4pt}{0ex}}{\mathrm{GeV}}^{2}$, where the CCR has been shown to work in other reactions. We argue for a stringent method to select data to test the CCR. Na\"{\i}vely, this reaction would have $n=9$ and we would expect a scaling of ${s}^{\ensuremath{-}7}$. Instead, a scaling of ${s}^{\ensuremath{-}(9.08\ifmmode\pm\else\textpm\fi{}0.11)}$ was observed. A careful analysis of conservation of angular momentum is proposed to explain the discrepancy, supporting the validity of the CCR when applied properly.

Analysis of the differential cross section and photon beam asymmetry data for γp→η′p

The photoproduction reaction of $\gamma p \to \eta^\prime p$ is investigated based on an effective Lagrangian approach in the tree-level approximation, with the purpose being to understand the reaction mechanisms and to extract the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$-channel $\rho$ and $\omega$ exchanges, $s$- and $u$-channel nucleon exchanges, and generalized contact term, the exchanges of a minimum number of nucleon resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that a satisfactory description of the available data on both differential cross sections and photon beam asymmetries can be obtained by including in the $s$ channel the exchanges of the $N(1875)3/2^-$ and $N(2040)3/2^+$ resonances. The reaction mechanisms of $\gamma p \to \eta^\prime p$ are discussed and a prediction for the target nucleon asymmetries is presented.

The Extraction of the Near-Threshold J/ψ-Meson Photoproduction Reaction from Experimental Electroproduction Data

The Extraction of the Near-Threshold J/ψ-Meson Photoproduction Reaction from Experimental Electroproduction Data

Effects of N(2000)5/2+ on γp→K+Λ(1405)

The photoproduction reaction of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ is investigated based on an effective Lagrangian approach at the tree-level approximation with the purpose of understanding the reaction mechanism and extracting the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$-channel $K$ and ${K}^{*}$ exchanges, $s$-channel nucleon ($N$) exchange, $u$-channel $\mathrm{\ensuremath{\Sigma}}, \mathrm{\ensuremath{\Lambda}}$, and $\mathrm{\ensuremath{\Lambda}}(1405)$ exchanges, and generalized contact term, the exchanges of a minimum number of $N$ resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that by introducing the $N(2000){5/2}^{+}$ resonance exchange in the $s$ channel, one can reproduce the most recent differential cross-section data from the CLAS Collaboration quite well. Further analysis shows that the cross sections of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ at high energies are dominated by the $t$-channel $K$ exchange, while the contributions from the $s$-channel $N$ and $N(2000){5/2}^{+}$ exchanges are rather significant to the cross sections in the near-threshold energy region. Predictions for the beam and target asymmetries for $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ are given.

Minimal complete sets for two-pseudoscalar-meson photoproduction

For photoproduction reactions with final states consisting of two pseudoscalar mesons and a spin-1/2 baryon, 8 complex amplitudes need to be determined uniquely. A modified version of Moravcsik's theorem is employed for these reactions, resulting in slightly over-complete sets of polarization observables that are able to determine the amplitudes uniquely. Further steps were taken to reduce the found sets to minimal complete sets. As a final result, multiple minimal complete sets without any remaining ambiguities are presented for the first time. These sets consist of $2N=16$ observables, containing only one triple polarization observable.

The GlueX beamline and detector

The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 μs. The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation.

Installation and Commissioning of the GLUEX DIRC

The GLUEX experiment takes place in experimental Hall D at Jefferson Lab (JLab). With a linearly polarized photon beam of up to 12 GeV energy, GLUEX is a dedicated experiment to search for hybrid mesons via photoproduction reactions. The low-intensity (Phase I) of GLUEX was recently completed; the high-intensity (Phase II) started in 2020 including an upgraded particle identification system, known as the DIRC (Detection of Internally Reflected Cherenkov light), utilizing components from the decommissioned BaBar experiment. The identification and separation of the kaon final states will significantly enhance the GLUEX physics program, by adding the capability of accessing the strange quark flavor content of conventional (and potentially hybrid) mesons. In these proceedings, we report that the installation and commissioning of the DIRC detector has been successfully completed.

Threshold $$\pi ^-$$ photoproduction on the neutron

Recent data from the PIONS@MAX-lab Collaboration, measuring the total cross section of the incoherent pion photoproduction reaction, $$\gamma d\rightarrow \pi ^- pp$$ , near threshold, have been used to extract the $$E_{0+}$$ multipole and total cross section of the reaction $$\gamma n\rightarrow \pi ^-p$$ , also near threshold. These are the first measurements of the reaction $$\gamma d\rightarrow \pi ^- pp$$ in the threshold region. The value of $$E_{0+}$$ is extracted through a fit to the deuteron data in a photoproduction model accounting for final-state interactions. The model takes an S-wave approximation for the elementary reaction $$\gamma n\rightarrow \pi ^-p$$ with $$\hbox {E}_{0+} = $$ const in the threshold region. The fit over all the 6 deuteron data points gives the value $$E_{0+} = -\,31.86\pm 0.8$$ (in units $$10^{-3}/m_\pi $$ ). We explore the dependence of our results on the choice of data subsets included in the fit. The obtained values of $$E_{0+}$$ , for different subsets, have overlapping errors and agree with previous determinations.