Photoproduction Processes Research Articles

Evidence for theJp=1/2+narrow state at 1650 MeV in the photoproduction ofKΛ

We have investigated the existence of the J^p=1/2^+ narrow resonance predicted by the chiral soliton model by utilizing the kaon photoproduction process gamma + p --> K^+ + Lambda. For this purpose we have constructed two phenomenological models based on our previous effective Lagrangian model, which are able to describe kaon photoproduction from threshold up to W = 1730 MeV. By varying the mass (width) of an inserted P_{11} resonance from 1620 to 1730 MeV (0.1 to 1 MeV and 1 to 10 MeV) a number of fits has been performed in order to search for the resonance mass. Our result indicates that the most promising candidate mass (width) of this resonance is 1650 MeV (5 MeV). Although our calculation does not exclude the possibility of narrow resonances with masses of 1680, 1700 and 1720 MeV, the mass of 1650 MeV is obtained for all phenomenological models used in this investigation. Variations of the resonance width and $K\Lambda$ branching ratio are found to have a mild effect on the chi^2. The possibility that the obtained result originates from other resonance states is also discussed.

New ways to access the transverse spin content of the nucleon

We first describe a new way to access the chiral odd transversity parton distribution in the proton through the photoproduction of lepton pairs. The basic ingredient is the interference of the usual Bethe-Heitler or Drell-Yan amplitudes with the amplitude of a process, where the photon couples to quarks through its chiral-odd distribution amplitude, which is normalized to the magnetic susceptibility of the QCD vacuum. We also show how the chiral-odd transversity generalized parton distributions (GPDs) of the nucleon can be accessed experimentally through the exclusive electro - or photoproduction process of a meson pair with a large invariant mass and when the final nucleon has a small transverse momentum. We calculate perturbatively the scattering amplitude at leading order, both in the high energy domain which may be accessed in electron-ion colliders and in the medium energy range. Estimated rates are encouraging.

Erratum: Photoproduction of neutral kaons on a liquid deuterium target in the threshold region [Phys. Rev. C78, 014001 (2008)

The photoproduction process of neutral kaons on a liquid deuterium target is investigated near the threshold region, Egamma = 0.8-1.1 GeV. K0 events are reconstructed from positive and negative pions, and differential cross sections are derived. Experimental momentum spectra are compared with those calculated in the spectator model using a realistic deuteron wave function. Elementary amplitudes as given by recent isobar models and a simple phenomenological model are used to study the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n(gamma,K0)Lambda process, which provides additional constraints on current models of kaon photoproduction. The present study demonstrates that the n(gamma,K0)Lambda reaction can provide key information on the mechanism of the photoproduction of strangeness.

SPECTROSCOPY OF BARYON RESONANCES AT ELSA

Current and upcoming experiments at the ELectron Stretcher Accelerator (ELSA) facility will determine polarization (or spin) observables for photoproduction processes involving baryon resonances. Differences between the predictions for these observables can be large, and so conversely they provide strong constraints in the analyses that aim at studying the properties of known resonances and at searching for hitherto unobserved states. The current effort with the Crystal Barrel/TAPS detector at ELSA is to utilize highly-polarized frozen-spin (butanol) and deuterium targets in combination with polarized photon beams. I will discuss recent spectroscopy results and present a brief status of the polarization program.

EXCLUSIVE PRODUCTION OF VECTOR MESONS IN pp AND $p\bar p$ COLLISIONS

Photoproduction process γp → Vp has been mesured recently at HERA. We compare our results with the recent data. The corresponding amplitude is used to predict the cross section for exclusive production in pp and [Formula: see text] collisions. Here we present distribution in rapidity and transverse momentum of vector mesons for Tevatron and LHC energies. The absorption effects are discussed.

Radiative corrections to neutral pion-pair production

We calculate the one-photon loop radiative corrections to the neutral pion-pair photoproduction process $\pi^-\gamma \to \pi^-\pi^0\pi^0$. At leading order this reaction is governed by the chiral pion-pion interaction. Since the chiral $\pi^+\pi^-\to\pi^0\pi^0$ contact-vertex depends only on the final-state invariant-mass it factors out of all photon-loop diagrams. We give analytical expressions for the multiplicative correction factor $R\sim \alpha/2\pi$ arising from eight classes of contributing one-photon loop diagrams. An electromagnetic counterterm has to be included in order to cancel the ultraviolet divergences generated by the photon-loops. Infrared finiteness of the virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off $\lambda$. The radiative corrections to the total cross section vary between $+2\%$ and $-2\%$ for center-of-mass energies from threshold up to $7m_\pi$. The finite part of the electromagnetic counterterm gives an additional constant contribution of about $1\%$, however with a large uncertainty.

Chiral corrections to [formula omitted] processes at low energies

We calculate in chiral perturbation theory the double-pion photoproduction processes π − γ → π − π 0 π 0 and π − γ → π + π − π − at low energies. At leading order these reactions are governed by the chiral pion-pion interaction. The next-to-leading order corrections arise from pion-loop diagrams and chiral-invariant counterterms involving the low-energy constants ℓ ¯ 1 , ℓ ¯ 2 , ℓ ¯ 3 and ℓ ¯ 4 . The pertinent production amplitudes A 1 and A 2 depending on five kinematical variables are given in closed analytical form. We find that the total cross section for neutral pion-pair production π − γ → π − π 0 π 0 gets enhanced in the region s < 7 m π by a factor 1.5 – 1.8 by the next-to-leading order corrections. In contrast to this behavior the total cross section for charged pion-pair production π − γ → π + π − π − remains almost unchanged in the region s < 6 m π in comparison to its tree-level result. Although the dynamics of the pion-pair production reactions is much richer, this observed pattern can be understood from the different influence of the chiral corrections on the pion-pion final state interaction ( π + π − → π 0 π 0 versus π − π − → π − π − ). We present also results for the complete set of two-pion invariant mass spectra. The predictions of chiral perturbation theory for the π − γ → 3 π processes can be tested by the COMPASS experiment which uses Primakoff scattering of high-energy pions in the Coulomb field of a heavy nucleus to extract cross sections for π − γ reactions with various final states.

Effect of a strong laser field on electron-positron photoproduction by relativistic nuclei

We study the influence of a strong laser field on the Bethe-Heitler photoproduction process by a relativistic nucleus. The laser field propagates in the same direction as the incoming high-energy photon and it is taken into account exactly in the calculations. Two cases are considered in detail. In the first case, the energy of the incoming photon in the nucleus rest frame is much larger than the electron's rest energy. The presence of the laser field may significantly suppress the photoproduction rate at soon available values of laser parameters. In the second case, the energy of the incoming photon in the rest frame of the nucleus is less than and close to the electron-positron pair production threshold. The presence of the laser field allows for the pair production process and the obtained electron-positron rate is much larger than in the presence of only the laser and the nuclear field. In both cases we have observed a strong dependence of the rate on the mutual polarization of the laser field and of the high-energy photon and the most favorable configuration is with laser field and high-energy photon linearly polarized in the same direction. The effects discussed are in principle measurable with presently available proton accelerators and laser systems.

Proteomic Analysis of Hydrogen Photoproduction in Sulfur-Deprived Chlamydomonas Cells

The green alga Chlamydomonas reinhardtii is a model organism to study H(2) metabolism in photosynthetic eukaryotes. To understand the molecular mechanism of H(2) metabolism, we used 2-DE coupled with MALDI-TOF and MALDI-TOF/TOF-MS to investigate proteomic changes of Chlamydomonas cells that undergo sulfur-depleted H(2) photoproduction process. In this report, we obtained 2-D PAGE soluble protein profiles of Chlamydomonas at three time points representing different phases leading to H(2) production. We found over 105 Coomassie-stained protein spots, corresponding to 82 unique gene products, changed in abundance throughout the process. Major changes included photosynthetic machinery, protein biosynthetic apparatus, molecular chaperones, and 20S proteasomal components. A number of proteins related to sulfate, nitrogen and acetate assimilation, and antioxidative reactions were also changed significantly. Other proteins showing alteration during the sulfur-depleted H(2) photoproduction process were proteins involved in cell wall and flagella metabolisms. In addition, among these differentially expressed proteins, 11 were found to be predicted proteins without functional annotation in the Chlamydomonas genome database. The results of this proteomic analysis provide new insight into molecular basis of H(2) photoproduction in Chlamydomonas under sulfur depletion.

Non-linear QCD dynamics and exclusive production in ep collisions

The exclusive processes in electron-proton ($ep$) interactions are an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of proton which is strongly subject to parton saturation effects. In this paper we compute the cross sections for the exclusive vector meson production as well as the deeply virtual Compton scattering (DVCS) relying on the color dipole approach and considering the numerical solution of the Balitsky-Kovchegov equation including running coupling corrections. We show that the small-$x$ evolution given by this evolution equation is able to describe the DESY-HERA data and is relevant for the physics of the exclusive observables in future electron-proton colliders and in photoproduction processes to be measured in coherent interactions at the LHC.

Photoproduction of a [formula omitted] pair with a large invariant mass and transversity generalized parton distribution

The chiral-odd transversity generalized parton distributions (GPDs) of the nucleon can be accessed experimentally through the exclusive photoproduction process γ+N→π+ρ+N′, in the kinematics where the meson pair has a large invariant mass and the final nucleon has a small transverse momentum, provided the vector meson is produced in a transversally polarized state. We calculate perturbatively the scattering amplitude at leading order in αs. We build a simple model for the dominant transversity GPD HT(x,ξ,t) based on the concept of double distribution. We estimate the unpolarized differential cross section for this process in the kinematics of the Jlab and Compass experiments. Counting rates show that the experiment looks feasible with the real photon beam characteristics expected at JLab@12 GeV, and with the quasi real photon beam in the Compass experiment.

The energy dependence of the hard exclusive diffractive processes in pQCD as the function of momentum transfer

We predict the dependence on energy of photo (electro) production processes: γ(γ*)+p→V+X with large rapidity gap at small x and large momentum −t transferred to V in pQCD. Here V is a heavy quarkonium (J/ψ,ϒ) or longitudinally polarized light vector meson (in the electroproduction processes), etc. In the kinematics of HERA we calculate the dependence on energy of cross sections of these processes as the function of momentum transfer t, photon virtuality Q2 and/or quarkonium mass. In the kinematical region \(Q_{0}^{2}\le -t\ll Q^{2}+M^{2}_{V}\) the nontrivial energy dependence of the cross section for the vector meson production due to the photon scattering off a parton follows within QCD from the summing of the double logarithmic terms. In the second regime \(-t\ge Q^{2}+M^{2}_{V}\) within DGLAP approximation in all orders of perturbation theory the \(q\bar{q}\)-parton elastic cross section is energy independent. We show that the correct account of the double logarithmic terms and of the gluon radiation including kinematical constraints removes the disagreement between pQCD calculations and recent HERA experimental data. The explicit formula for the dependence of the differential cross section \(\frac{d^{2}\sigma}{dt\,dx_{J}}\) of these processes on \(s_{\gamma^{*}N}\) is obtained. We show that perturbative Pomeron type behavior may reveal itself only at energies significantly larger than those available at HERA. In addition we evaluate the energy dependence of DVCS processes.

Study of charged pion photoproduction on deuteron

Photoproduction of charged pion on deuteron, emphasis on channels γ d → π − p p and γ d → π + π − n p , were measured with the second generation of Neutral Kaon Spectrometer. The photon beam was provided from the tagged photon facility at the Laboratory of Nuclear Science, Tohoku University. The energy range of photon is 0.8-1.1 GeV. The aim is to investigate the pion photoproduction process on the nucleus in the second and third resonance regions. The quasi-free process inside deuteron and also non-quasi-free contributions were derived individually.

10.1007/s11450-008-3011-6

The first experimental results are presented on the discovery and investigation of the η-mesic nuclei formed in the photoproduction process induced by bremsstrahlung γ rays from the 1-GeV electron synchrotron at the Lebedev Physical Institute.

Discovery potential for charmoniumlike stateY(3940)by the meson photoproduction

In this work, we investigate the discovery potential for $Y(3940)$ by the photoproduction process $\ensuremath{\gamma}p\ensuremath{\rightarrow}Y(3940)p$. The numerical result shows that the upper (lower) limit of the total cross section for $\ensuremath{\gamma}p\ensuremath{\rightarrow}Y(3940)p$ is up to the order of 1 nb ($0.1\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$). Additionally, the background analysis and the Dalitz plot relevant to the production of $Y(3940)$ are studied. The Dalitz plot analysis of $Y(3940)$ production indicates that the $Y(3940)$ signal can be distinguished from the background clearly. The lower limit of the number of events of $Y(3940)$ reaches up to $10/0.02\text{ }\text{ }{\mathrm{GeV}}^{2}$ for $1\ifmmode\times\else\texttimes\fi{}{10}^{9}$ collisions of $\ensuremath{\gamma}p$ by studying the invariant mass spectrum of $J/\ensuremath{\psi}\ensuremath{\omega}$. An experimental search for $Y(3940)$ by the meson photoproduction is suggested.

Hadro- and photo-production of η″ in quasi-free proton and neutron processes

The η″ photoproduction process on quasi-free proton and neutron and the reaction NN → η η″NN are investigated within a relativistic effective Lagrangian approach to hadronic interactions. Resonances with spins 1/2 and 3/2 are considered together with the nucleonic and t-channel meson-exchange current contributions. In photoproduction processes, the S11 resonance is found to be responsible for the sharp rise of the cross sections near threshold. In pp → η η″pp, it is found that the S11 resonance dominates the total cross section over the entire energy region considered. The spin observables, in particular the beam and target asymmetries, are shown to be very sensitive to the reaction mechanism and will help impose more stringent constraints on the model parameters.

CLAS+FROST: new generation of photoproduction experiments at Jefferson Lab.

A large part of the experimental program in Hall B of the Jefferson Lab is dedicated to baryon spectroscopy. Photoproduction experiments are essential part of this program. CEBAF Large Acceptance Spectrometer (CLAS) and availability of circularly and linearly polarized tagged photon beams provide unique conditions for this type of experiments. Recent addition of the Frozen Spin Target (FROST) gives a remarkable opportunity to measure double and triple polarization observables for different pseudo-scalar meson photoproduction processes. For the first time, a complete or nearly complete experiment becomes possible and will allow model independent extraction of the reaction amplitude. An overview of the experiment and its current status is presented.

Photoinduced charge-transfer process in rubidium manganese hexacyanoferrate probed by Raman spectroscopy

The photoinduced charge-transfer process in Rb(0.94)Mn[Fe(CN)(6)](0.98).0.2H(2)O is investigated by observing the valence states of the metal ions by Raman spectroscopy. The sample in the high-temperature phase is irradiated at the ligand to metal, CN(-)-->Fe(III) and charge-transfer band (lambda=395 nm). The Fe(III)-CN-Mn(II) pair valence state corresponding to the high-temperature configuration is totally depleted after prolonged irradiation, and the Fe(II)-CN-Mn(III) pair valence state corresponding to the low-temperature configuration appears. In addition, two kinds of CN stretching modes, ascribed to Fe(II)-CN-Mn(II) and Fe(III)-CN-Mn(III) pair valence states, are found. The photoproduction process of each pair valence states is well reproduced by a kinetic model assuming a charge transfer from Mn(II) to Fe(III). During irradiation, continuous shifts of the Raman peaks are found and ascribed to a release of the strain due to the lattice mismatching between the high-temperature and the photoinduced phases. This behavior indicates that the photoinduced phase created locally in the high-temperature-phase lattice grows up to a photoinduced phase domain. The conversion efficiency is lowered with decreasing temperature, indicating the existence of an energy barrier. We propose a model, which can explain the existence of an energy barrier in the electronic excited state.

PHOTOPRODUCTION OF THE NEUTRAL KAON IN THE THRESHOLD REGION AT LNS

The K0 photoproduction process is investigated in the threshold region, Eγ = 0.8-1.1 GeV at LNS-Tohoku. K0 events are measured via π+π- decay channel. Obtained momentum spectra for the deuteron target are compared with those calculated in the spectator model using a realistic deuteron wave function. Recent isobar models and a simple phenomenological model are used as elementary amplitudes to investigate the effect of the new data on the angular behavior of the elementary cross section. The data favor a backward-peaked angular distribution of the elementary n(γ, K0)Λ process in the center-of-mass (c.m.) system, which provides additional constraints on current models of kaon photoproduction. The present study shows that the n(γ, K0)Λ reaction can provide key information on the mechanism of the photoproduction of strangeness.

Integrated cultivation and photohydrogen production of Platymonas subcordiformis in a flat-plate photobioreactor system

this paper aimed to develop an integrated processes of microalgal cultivation and hydrogen photoproduction in a flat-plate photobioreactor system combined with alkaline fuel cell. the optimal high cell density of 8.5 x 10(6) cell/ml was achieved on 9 d when the cultivation of tetraselmis subcordiformis was supplemented with co(2) of 2%-5% (volume fraction) in the flat-plate photobioreactor. when the bioreactor system was switched to the hydrogen production condition, hydrogen evolution was induced by the addition of carbonylcyanide (m-chlorophenylhydrazone, cccp) and anaerobic condition, with a maximum hydrogen production rate of 1.1 ml/(h . l) for 60 h. the kinetics analysis of algal chlorophyll fluorescence was carried out to identify the hunting factors in both algal growth and hydrogen production at 2% co(2) supplementation. at hydrogen production phase, algal ps u activity and relative electron transfer rate(retr) decreased with the increase of time, which caused the decline and eventual stop in hydrogen production. to sustain the hydrogen production, ps h activity and retr must be maintained. the results demonstrate the feasibility of process integration of algal cultivation and hydrogen production in one single system, which will significantly improve the process economics.