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This Conceptual Design Report describes LUXE (Laser Und XFEL Experiment), an experimental campaign that aims to combine the high-quality and high-energy electron beam of the European XFEL with a powerful laser to explore the uncharted terrain of quantum electrodynamics characterised by both high energy and high intensity. We will reach this hitherto inaccessible regime of quantum physics by analysing high-energy electron-photon and photon-photon interactions in the extreme environment provided by an intense laser focus. The physics background and its relevance are presented in the science case which in turn leads to, and justifies, the ensuing plan for all aspects of the experiment: Our choice of experimental parameters allows (i) field strengths to be probed where the coupling to charges becomes non-perturbative and (ii) a precision to be achieved that permits a detailed comparison of the measured data with calculations. In addition, the high photon flux predicted will enable a sensitive search for new physics beyond the Standard Model. The initial phase of the experiment will employ an existing 40 TW laser, whereas the second phase will utilise an upgraded laser power of 350 TW. All expectations regarding the performance of the experimental set-up as well as the expected physics results are based on detailed numerical simulations throughout.

The high accuracy $\phi $-meson photoproduction data from the CLAS experiment in Hall~B of Jefferson Laboratory allow us to determine the near-threshold total cross section of the $\gamma p\to\phi p$ reaction and use it for evaluating the $\phi p$ scattering length $\alpha_{\phi p}$. These data result in an absolute value of $|\alpha_{\phi p}| = (0.063\pm 0.010)$~fm, which is smaller than the typical hadron size. A comparative analysis of $\alpha_{\phi p}$ with the previously determined scattering lengths for $\omega p$ and $J/\psi p$ from the A2 and GlueX experiments is performed.

The probabilities of various elementary laser - photon - electron/positron interactions display in selected phase space and parameter regions typical non-perturbative dependencies such as $\propto {\cal P} \exp\{- a E_{crit} /E\}$, where ${\cal P}$ is a pre-exponential factor, $E_{crit}$ denotes the critical Sauter-Schwinger field strength, and $E$ characterizes the (laser) field strength. While the Schwinger process with $a = a_S \equiv \pi$ and the non-linear Breit-Wheeler process in the tunneling regime with $a = a_{n \ell BW} \equiv 4 m / 3 \omega'$ (with $\omega'$ the probe photon energy and $m$ the electron/positron mass) are famous results, we point out here that also the non-linear Compton scattering exhibits a similar behavior when focusing on high harmonics. Using a suitable cut-off $c > 0$, the factor $a$ becomes $a = a_{n \ell C} \equiv \frac23 c m /(p_0 + \sqrt{p_0^2 -m^2)}$. This opens the avenue towards a new signature of the boiling point of the vacuum even for field strengths $E$ below $E_{crit}$ by employing a high electron beam-energy $p_0$ to counter balance the large ratio $E_{crit} / E$ by a small factor $a$ to achieve $E / a \to E_{crit}$. In the weak-field regime, the cut-off facilitates a threshold leading to multi-photon signatures showing up in the total cross section at sub-threshold energies., Comment: 21 pages, 13 figures

We study the non-linear Breit-Wheeler process $\vec \gamma' + \vec L \to e^+ + e^-$ in the interaction of linearly polarized probe photons ($\vec \gamma'$) with a linearly polarized laser beam ($\vec L$). In particular, we consider the asymmetry of the total cross section and the azimuthal electron distributions when the polarizations of the photon and laser beams in the initial state are mutually perpendicular or parallel. Considering intense laser beams and the strong field asymptotic we explore essentially the multi-photon dynamics. The asymmetry exhibits some non-monotonic behavior depending on initial kinematic conditions; it depends sensitively on the laser pulse duration. Our results provide additional knowledge for studying non-linear multi-photon effects in quantum electrodynamics and may be used in planning experiments in upcoming laser facilities., Comment: 9 pages, 8 figures

Non-linear Breit-Wheeler $e^+e^-$ pair production and its crossing channel - the non-linear Compton process - in the multi-photon regime are analyzed for linearly and circularly polarized short laser pulses. The contribution of multi-photon processes to total cross sections is determined and we also show that (i) the azimuthal angular distributions of outgoing electrons in these processes differ on a qualitative level, and (ii) they depend on the polarization properties of the pulses. A finite carrier envelope phase (CEP) leads to a non-trivial non-monotonic behavior of the azimuthal angle distributions of the considered processes. That effect can be used for the CEP determination., 14 pages, 13 figures

This work provides an overview of our recent results in studying two most important and widely discussed quantum processes: electron-positron pairs production off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field or generalized Breit-Wheeler process, and a single a photon emission off an electron interacting with the laser pules, so-called non-linear Compton scattering. We show that the probabilities of particle production in both processes are determined by interplay of two dynamical effects, where the first one is related to the shape and duration of the pulse and the second one is non-linear dynamics of the interaction of charged fermions with a strong electromagnetic field. We elaborate suitable expressions for the production probabilities and cross sections, convenient for studying evolution of the plasma in presence of strong electromagnetic fields, Comment: 61 pages, 33 figures. arXiv admin note: text overlap with arXiv:1303.6487, arXiv:1408.1040

Physics letters / B 755, 162 - 167 (2016). doi:10.1016/j.physletb.2016.01.062, Published by North-Holland Publ., Amsterdam

The non-linear (strong-field) Breit-Wheeler $e^+e^-$ pair production by a probe photon traversing two consecutive short and ultra short (sub-cycle) laser pulses is considered within a QED framework. The temporal shape of the pulses and the distance between them are essential for the differential cross section as a function of the azimuthal angle distribution of the outgoing electron (positron). The found effect of a pronounced azimuthal anisotropy is important for sub-cycle pulses and decreases rapidly with increasing width of the individual pulses., Comment: 10 pages, 9 figures

We analyze decay spin-density matrix elements of $K^*$ and $D^*$ vector mesons and find that the corresponding vector meson decay distributions are sensitive to the production mechanisms. This suggests that the measurement of these quantities can be used to unravel the production mechanisms., Talk at 11th APCTP-BLTP(JINR)-PNPI(SPbU) Joint Workshop, Petergof, St.Petersburg, Jul 2017, 5pp

The production mechanisms of open strangeness ($K^*$) and open charm ($D^*$) vector mesons in $\pi^- p$ scattering, namely, $\pi^- +p \to K^{*0} + \Lambda$ and $\pi^- + p \to D^{*-} + \Lambda_c^+$, are investigated within the modified quark-gluon string model. In order to identify the major reaction mechanisms, we consider the subsequent decays of the produced vector mesons into two pseudoscalar mesons, i.e., $K^* \to K + \pi$ and $D^* \to D + \pi$. We found that the decay distributions and density matrix elements are sensitive to the production mechanisms and can be used to disentangle the vector trajectory and pseudoscalar trajectory exchange models. Our results for $K^*$ production are compared with the currently available experimental data and the predictions for $D^*$ production processes are presented as well. Our predictions can be tested at the present or planned experimental facilities.

Some features of the field induced phase transition accompanied by the vacuum creation of an electron-positron plasma (EPP) in strong time-dependent electric fields have been discussed in the work [1] in the domain of the tunneling mechanism ($\omega \ll m$, where $\omega$ is the characteristic frequency of the external field and $m$ is the electron mass). In the present contribution the features of the this process will be considered in the few photon domain where $\omega \sim m$. We observe a narrowing of the transient domain of the fast oscillations and, mainly, a considerable growth of the effectiveness of the EPP production. Under these circumstances, we see an increase of the effectiveness of the EPP creation in the particular case of a bifrequent excitation, where both mechanisms (tunneling and few photon) act simultaneously [2,3]., Comment: 6 pages, 4 figures, contribution to the Proceedings of the XXIII International Baldin Seminar on "High Energy Physics Problems", Dubna, Russia, September 19-24, 2016

The assistance of an intense optical laser pulse on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ significantly from transiently achieved mode occupations.

Counter-propagating and suitably polarized light (laser) beams can provide conditions for pair production. Here, we consider in more detail the following two situations: (i) in the homogeneity regions of anti-nodes of linearly polarized ultra-high intensity laser beams, the Schwinger process is dynamically assisted by a second high-frequency field, e.g. by an XFEL beam; and (ii) a high-energy probe photon beam colliding with a superposition of co-propagating intense laser and XFEL beams gives rise to the laser-assisted Breit–Wheeler process. The prospects of such bi-frequent field constellations with respect to the feasibility of conversion of light into matter are discussed.

The e + e − pair production by a probe photon traversing a linearly polarized laser pulse is treated as generalized nonlinear Breit–Wheeler process. For short laser pulses with very few oscillations of the electromagnetic field we find below the perturbative weak-field threshold s = 2 m a similar enhancement of the pair production rate as for circular polarization. The strong enhancement below the weak-field threshold is traced back to the finite bandwidth of the laser pulse. A folding model is developed which accounts for the interplay of the frequency spectrum and the intensity distribution in the course of the pulse.

We show that the differential cross section dσ/dt of γp → φp reaction at the threshold has a finite value and it is crucial to the mechanism of the φ meson photoproduction and for the models of φN interaction.

We analyze the impact of the carrier envelope phase on the differential cross sections of the Breit-Wheeler and the generalized Compton scattering in the interaction of a charged electron (positron) with an intensive ultra-short electromagnetic (laser) pulse. The differential cross sections as a function of the azimuthal angle of the outgoing electron have a clear bump structure, where the bump position coincides with the value of the carrier phase. This effect can be used for the carrier envelope phase determination., Comment: 7 pages, 4 figures

A multiscale approach to modeling of accumulation of radiation defects in silicon alpha detectors applied in the associated particle imaging systems is developed. The approach includes: calculation of primary knock-on atoms energy distribution, calculation of number of primary defects per one alpha particle, solution of system of kinetic equations for concentrations of all secondary defects, and calculation of leakage (dark) current of the detector. With this approach we have calculated the bulk generation current vs. alpha particle fluence for a detector irradiated with alpha particles with energy of 3.5 MeV. The results appeared to be in a good agreement with experimental data. Then we investigated how the bulk generation current of the irradiated device depends on concentrations of impurities (oxygen and carbon) and found a way to reduce the current by optimization of oxygen concentration in the semiconductor material.

The MOON (Molybdenum Observatory Of Neutrinos) project aims at high sensitive studies of the double beta ( ββ ) decays with sensitivity to Majorana ν mass of the order of m ν > ∼ 0.03 eV and the charged-current (CC) neutrino spectroscopy of the major components of the pp and 7 Be solar ν 's. The present status of MOON for the low energy solar ν experiment is briefly discussed. The inverse β rays from solar- ν captures of 100 Mo are measured in delayed coincidence with the subsequent β decay of 100 Tc. MOON's exclusive CC value by 7 Be solar ν , together with the GNO CC data, will provide the pp solar ν flux with good accuracy.

The MOON (Molybdenum Observatory Of Neutrinos) project is a hybrid ββ and solar ν experiment with 100 Mo. It aims at high sensitive studies of ββ decays with a sensitivity of m ν > ∼ 0.03 eV and real-time studies of pp and 7 Be solar ν's. The double β rays from 100 Mo are measured in prompt coincidence for the 0νββ studies, and the inverse β rays from solar-ν captures of 100 Mo are measured in delayed coincidence with the subsequent β decay of 100 Tc. Measurements with good position resolution enable one to select true signals by spatial and time correlations.

The rho - omega interference in the exclusive reaction pi N \to N' e+ e- is studied within a schematic model including the established baryon resonances up to 1720 MeV. Near threshold the interference can be used to separate the isoscalar part of the electromagnetic current. The role of various baryon resonances is highlighted., talk and contribution to PANIC02, Osaka, Japan, September 30 - October 4, 2002

At large momentum transfers, the main contribution to the φ-meson photoproduction comes from the resonant channel. Combined analysis of the ω and φ - meson photoproduction indicates for the strong OZI-rule violation in φNN ∗ - couplings. The spin observables are sensitive to this effect and, moreover, could help to distinguish between different theoretical models of the resonant channel.

We analyze a possible manifestation of f_1-trajectory in elastic J/psi photoproduction at high energy and large momentum transfer. Inspite of the small contribution of f_1-trajectory in total cross sections, it becomes significant in various spin observables. In particular, we show that the crucial test for f_1-exchange can be made by measuring the single beam- and double parity- and beam-target asymmetries at large momentum transfers, where a strong deviation from the exchange of conventional Pomerons is expected. This effect is caused by the interference of natural (Pomeron) and unnatural (f_1) parity exchange parts of amplitude in the region where their contributions become comparable to each other and might be interesting to observe in forthcoming experiments, if feasible. ., Comment: 8 pages, 10 figures. To be published in PLB

We analyze the production of φ mesons in πN and NN reactions in the near-threshold region, using throughout the conventional “non-strange” dynamics based on such processes which are allowed by the non-ideal ω-φ mixing. We show that the occurrence of the direct φNN interaction may show up in different unpolarized and polarization observables in πN→Nφ reactions. We find a strong non-trivial difference between observables in the reactions pp→ppφ and pn→pnφ caused by the different role of the spin singlet and triplet states in the entrance channel. A series of predictions for the experimental study of this effect is presented.

We study the possibility to constrain the hidden strangeness content of the nucleon by means of the polarization observables in phi meson electroproduction. We consider the OZI evading direct knockout mechanism that arises from the non-vanishing s\bar{s} sea quark admixture of the nucleon as well as the background of the dominant diffractive and the one-boson-exchange processes. Large sensitivity on the nucleon strangeness are found in several beam-target and beam-recoil double polarization observables. The small \sqrt{s} and W region, which is accesible at some of the current high-energy electron facilities, is found to be the optimal energy region for extracting out the OZI evasion process., 8 pages, LaTeX2e, elsart.cls, 3 figures (4 eps files)

The sensitivity of polarization observables in the reaction $N\stackrel{\ensuremath{\rightarrow}}{N}\mathrm{NN}\ensuremath{\varphi}$ slightly above the threshold is studied with respect to the details of the one-boson exchange model and a possible admixture of hidden strangeness in the nucleon. It is shown that the finite-energy predictions differ strongly from the threshold predictions. A measurement of the beam-target asymmetry and the \ensuremath{\varphi} decay anisotropy can help to disentangle the role of various reaction mechanisms.

Compton scattering of short and ultra short (sub-cycle) laser pulses off mildly relativistic electrons is considered within a QED framework. The temporal shape of the pulse is essential for the differential cross section as a function of the energy of the scattered photon at fixed observation angle. The partly integrated cross section is sensitive to the non-linear dynamics resulting in a large enhancement of the cross section for short and, in particular, for ultra-short flat-top pulse envelopes which can reach several orders of magnitude, as compared with the case of a long pulse. Such effects can be studied experimentally and must be taken into account in Monte-Carlo/transport simulations of %$e^+e^-$ pair production in the interaction of electrons and photons in a strong laser field., Comment: 14 pages, 12 figures

The MOON (Molybdenum Observatory Of Neutrinos) project aims at studies of double beta decays with a high sensitivity of m ν > ∼ 0.03 eV and real-time studies of low-energy solar neutrinos. Two β rays from 100Mo are measured in coincidence for the 0νββ studies. The inverse β rays from solar neutrino captures of 100Mo are measured in delayed coincidence with the following β decay of 100Tc. Measurements with good energy resolution and good position resolution enable one to select true signals. A prototype MOON detector (MOON 1) is now under development. The present report describes briefly the outline of the MOON project and the status of MOON 1.

It is shown that the parity--violating deep--inelastic scatterings of unpolarized charged leptons on polarized protons, $\ell^{\mp} + \vec P\to \stackrel{\scriptscriptstyle(-)}{\nu_{\ell}} + X$, could provide a sensitive test for the behavior and magnitude of the polarized strange--quark density in a proton. Below charm threshold these processes are also helpful to uniquely determine the magnitude of individual polarized parton distributions., Comment: LaTeX file, 12 pages+4 fiigures not included (available upon request)

Within an effective one-boson exchange parametrization of the T matrix of NN interactions we calculate cross sections for the reactions pp → ppγ and pn → pnγ for proton incidence energies in the order of 1 GeV. Besides bremsstrahlung processes we consider photons from Δ decays and contributions from the η → γγ process, where the η is excited via the N 1535 resonance. At beam energies above 700 MeV the Δ decay channel dominates for large photon energies, while above the η threshold the η decay photons show up only in a narrow window. The low energy photons stem from pure bremsstralung processes.

The generalized Breit-Wheeler process, i.e. the emission of $e^+e^-$ pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field, is analyzed. We show that the production probability is determined by the interplay of two dynamical effects. The first one is related to the shape and duration of the pulse and the second one is the non-linear dynamics of the interaction of $e^\pm$ with the strong electromagnetic field. The first effect manifests itself most clearly in the weak-field regime, where the small field intensity is compensated by the rapid variation of the electromagnetic field in a limited space-time region, which intensifies the few-photon events and can enhance the production probability by orders of magnitude compared to an infinitely long pulse. Therefore, short pulses may be considered as a powerful amplifier. The non-linear dynamics in the multi-photon Breit-Wheeler regime plays a decisive role at large field intensities, where effects of the pulse shape and duration are less important. In the transition regime, both effects must be taken into account simultaneously. We provide suitable expressions for the $e^+e^-$ production probability for kinematic regions which can be used in transport codes., Comment: 32 pages, 15 figures

The emission of $\nu\bar\nu$ pairs off electrons in a polarized ultra-intense electromagnetic (e.g.\ laser) wave field is analyzed. We elaborate on the significance of non-linear electrodynamics effects (i.e., multi-photon processes) and the peculiarities of neutrino production. Special attention is devoted to the convergence of the reaction probabilities as a function of the number of absorbed photons. Expressions for large field intensities are provided. The asymmetry between the probabilities of electron and $\mu+\tau$ neutrino production depends on initial conditions such as energy of the wave field photons and the field intensity. These findings differ from the lowest order perturbative calculation of the reaction $\gamma + e \to e' + \nu \bar \nu$., Comment: 24 pages, 16 figures

Estimates of elementary cross sections for dielectron production in pN and pd reactions are presented. We use the vector dominance model for all hadron-hadron-photon vertices. A dynamical suppression mechanism (off-shell behavior of the two-body T-matrix, mass dependent Δ production rate) brings the elementary rate near to previous estimates which did not use vector meson dominance. However, near to the ρ mass a characteristic shoulder appears in our approach. We consider Δ, η Dalitz decays and bremsstrahlung at 1–2 GeV as dominant sources of dielectrons. At higher energies the bremsstrahlung contribution is only a subclass of direct vector meson decays. Relying on a realistic deuteron wave function we predict the ratio of dielectron production in pd to pp reactions.

Differential cross sections and photon-beam asymmetries for the $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}(1520)$ reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at $0.6l\mathrm{cos} {\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}^{K}l1$. A new bump structure was found at $W\ensuremath{\simeq}2.11\text{ }\text{ }\mathrm{GeV}$ in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with $J\ensuremath{\le}\frac{3}{2}$. This result suggests that the bump might be produced by a nucleon resonance possibly with $J\ensuremath{\ge}\frac{5}{2}$ or by a new reaction process, for example, an interference effect with the $\ensuremath{\phi}$ photoproduction having a similar bump structure in the cross sections.

The kinetic model developed previously for soft hadron-nucleus and nucleus-nucleus collisions has been extended to describe low mass dilepton production. A fairly good description of available experimental data on dileptons created in both p+Be collisions from 12 to 1 GeV and Ca+Ca collisions at energies of 2 and 1 GeV/nucleon, is attained taking into account a variety of e + e − sources. Confirming a previous estimate of the ππ annihilation process, it has been found that the ω/ϱ→e + e − decay contributes as much as ππ annihilation does and to the same region of invariant masses, even for Ca+Ca (1 GeV/nucleon) collisions.

The MOON (Majorana/Mo Observatory Of Neutrinos) project aims at studies of the Majorana nature of the neutrino (ν) and the ν-mass spectrum by spectroscopic experiments of neutrino-less double beta decays (0νββ) with the ν-mass sensitivity of 〈m 〉 = 100−30 meV. The solid scintillator option of the MOON detector is a super ensemble of multi-layer modules, each being composed by PL scintillator plates and position-sensitive detector planes with good overall energy resolution of σ ≈ 2% at the Q ββ ≈ 3 MeV. Thin ββ source films are interleaved between the detector planes. High localization of the two β tracks enables one to select true signals and reject BG ones. The multi-layer structure of the detector makes it realistic to build a compact ton-scale detector. MOON with detector ≠ ββ source is used for studying 0νββ decays from 100Mo, 82Se and other ββ isotopes with large Q ββ . Real-time exclusive measurements of low energy solar neutrinos can be made by observing inverse β rays from solar-ν captures of 100Mo in delayed coincidence with the subsequent β decay of 100Tc.

We show that the differential cross section $d\ensuremath{\sigma}/\mathit{dt}$ of the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\phi}p$ reaction at threshold is finite and its value is crucial to the mechanism of \ensuremath{\phi}-meson photoproduction and for the models of $\ensuremath{\phi}N$ interaction.

We discuss coherent and incoherent \ensuremath{\phi} meson photoproduction off the deuteron at low energy and small momentum transfer with the aim of checking whether the recent experimental data need for their interpretation an inclusion of exotic channels. Our analysis of the differential cross section and spin-density matrix elements shows that new data on the $\ensuremath{\gamma}D\ensuremath{\rightarrow}\ensuremath{\phi}X$ reaction at ${E}_{\ensuremath{\gamma}}~2$ GeV may be understood on the basis of conventional dynamics. However, a certain ambiguity of the deviation between the model predictions and the data from the laser electron photon beamline at SPring-8 (LEPS) on the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\phi}p$ reaction still remains. To make a firm conclusion about a possible manifestation of exotic channels, one has to improve the resolution of the data by providing additional information on the channels with spin- and double-spin-flip transitions which are sensitive to the properties of the photoproduction amplitude in the $\ensuremath{\gamma}p$ and $\ensuremath{\gamma}D$ reactions. This information may be used as an additional independent test of the \ensuremath{\phi} meson photoproduction mechanism.

We analyze the possibility of producing an intermediate {theta}{sup +} via a KN{yields}{theta}{sup +} formation process in {gamma}D{yields}pK{sup -}X(X=nK{sup +},pK{sup 0}) reactions at some specific kinematical conditions, in which a pK{sup -} pair is knocked out in the forward direction and its invariant mass is close to the mass of {lambda}*[{lambda}*{identical_to}{lambda}(1520)]. The {theta}{sup +} signal may appear in the [{gamma}D,pK{sup -}] missing mass distribution. The ratio of the signal (cross section at the {theta}{sup +} peak position) to the smooth background processes varies from 0.7 to 2.5 depending on the spin and parity of {theta}{sup +}, and it decreases correspondingly if the pK{sup -} invariant mass is outside of the {lambda}*-resonance region. We analyze the recent CLAS search for the {theta}{sup +} in the {gamma}D{yields}pK{sup -}nK{sup +} reaction and show that the conditions of this experiment greatly reduce the {theta}{sup +} formation process making it difficult to extract a {theta}{sup +} peak from the data.

We analyze the problem of how to determine the parity of the ${\ensuremath{\Theta}}^{+}$ pentaquark in the reaction $\ensuremath{\gamma}N\ensuremath{\rightarrow}K\ensuremath{\Theta}\ensuremath{\rightarrow}\mathrm{NK}\overline{K}$, where $N=n,p$. Our model calculations indicate that the contribution of the nonresonant background of the reaction $\ensuremath{\gamma}N\ensuremath{\rightarrow}\mathrm{NK}\overline{K}$ cannot be neglected and that suggestions to determine the parity based solely on the initial-stage process $\ensuremath{\gamma}N\ensuremath{\rightarrow}K\ensuremath{\Theta}$ cannot be implemented cleanly. We discuss the various mechanisms that contribute to the background. Among the observables considered in this work, the triple spin asymmetry shows a kinematical ``window'' where the predictions are sensitive to the ${\ensuremath{\Theta}}^{+}$ parity and insensitive to the various reaction mechanisms considered, and thus, this observable offers a possibility of determining the parity of the ${\ensuremath{\Theta}}^{+}$.

We show that the cross sections of the ${\mathrm{\ensuremath{\Theta}}}^{+}$-pentaquark production in different processes decrease with energy faster than the cross sections of production of the conventional three-quark hyperons. Therefore, the threshold region with the initial energy of a few GeV or less seems to be more favorable for the production and experimental study of ${\mathrm{\ensuremath{\Theta}}}^{+}$ pentaquark.

The diffractive $\phi$-meson photoproduction amplitude is dominated by the Pomeron exchange process and contains the terms that govern the spin-spin and spin-orbital interactions. We show that these terms are responsible for the spin-flip transitions at forward photoproduction angles and appear in the angular distributions of $\phi\to K^+K^-$ -decay in reactions with unpolarized and polarized photon beams. At large momentum transfers, the main contribution to the $\phi$-meson photoproduction is found to be due to the excitation of nucleon resonances. Combined analysis of $\omega$ and $\phi$ photoproduction indicates strong OZI-rule violation in $\phi NN^*$ - couplings. We also show that the spin observables are sensitive to the dynamics of $\phi$-meson photoproduction at large angles and could help distinguish different theoretical models of nucleon resonances. Predictions for spin effects in $\phi$-meson photoproduction are presented for future experimental tests., Comment: 39 pages, 21 figures. Submitted to the Physical Review C

For coherent photoproduction of $\ensuremath{\varphi}$ and $\ensuremath{\omega}$ mesons from deuteron at forward angles, the isovector $\ensuremath{\pi}$-exchange amplitude is strongly suppressed. We show a possibility to study the nondiffractive channels associated with the unnatural parity exchange in $\ensuremath{\varphi}$ photoproduction and with the baryon resonance excitations in $\ensuremath{\omega}$ photoproduction by measuring the spin observables.

We apply the effective Lagrangian approach to investigate the role of the nucleon resonances in $\omega$ meson photoproduction at energies near the threshold. The resonant amplitudes are calculated from effective Lagrangians with the gamma NN* and omega NN* coupling constants fixed by the empirical helicity amplitudes and the vector meson dominance model. The contributions from the nucleon resonances are found to be significant in changing the differential cross sections in a wide interval of t and various spin observables.

Results of a combined analysis are presented for the production of $\ensuremath{\omega}$ and $\ensuremath{\varphi}$ mesons in $\ensuremath{\pi}N$ reactions in the near-threshold region using a conventional ``nonstrange'' dynamics based on processes that are allowed by the nonideal $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing. We show that the interferences of the t channel (meson exchange) and s, u channels (nucleon and nucleon-resonances) differ significantly for the $\ensuremath{\omega}$ and $\ensuremath{\varphi}$ production amplitudes. This leads to a decrease of the relative yields, in comparison with the expectations based on a one-component amplitude with standard $\ensuremath{\omega}\ensuremath{-}\ensuremath{\varphi}$ mixing. We find a strong and nontrivial difference between observables in $\ensuremath{\omega}$ and $\ensuremath{\varphi}$ production reactions caused by the different roles of the nucleon and nucleon-resonance amplitudes. A series of predictions for the experimental study of this effect is presented.