Electromagnetic Production Research Articles

Kaon electromagnetic production in Hall B

An extensive program of associated strange particle production off the proton is currently underway with the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at Jefferson Laboratory. This contribution emphasizes strangeness photo- and electro-production in the nucleon resonance region between W = 1.6 and 2.3 GeV, where indications of s-channel structure are suggestive of high-mass baryon resonances coupling to kaons and hyperons in the final state. Precision measurements of cross sections and polarization observables are being carried out with both electron and real photon beams, which are available with high polarization at energies up to 6 GeV.

Kaon electromagnetic production: constraints set by new data

The CLAS data on the photo-production of K + off the proton are utilised to study reaction mechanisms of the process using the isobaric approach. The missing D 13 resonance is shown to be important for a successful description of the data in the whole kinematical region. The constructed models provide satisfactory results for the process.

Direct observation of muon-pair production by high-energy muons in the liquid-argon calorimeter BARS

Experimental data accumulated over a long-term exposure of the big liquid-argon spectrometer BARS at the Institute for High Energy Physics (IHEP, Protvino) in a horizontal flux of cosmic rays are analyzed with the aim of selecting events that correspond to muon-pair production by muons in the sensitive volume of the detector. The results obtained in this way make it possible to perform, for the first time, a direct experimental test of various theoretical estimates of the total cross section for electromagnetic muon-pair production by high-energy muons.

Nucleon resonance excitation with CLAS

The study of the baryon spectrum is a fundamental part of the scientific program in Hall B at Jefferson Laboratory. The so called N* program indeed concerns the measurement of the electromagnetic production of exclusive hadronic final states, with the purpose of extracting information on baryon excited states. CLAS, the CEBAF Large Acceptance Spectrometer, is explicitly designed for conducting a broad experimental program in hadronic physics, using the continuous electron beam provided by the laboratory. An overview of the most recent results is presented.

Independent Speed Control of Two Six-Phase Induction Motors Using a Single Six-Phase Inverter

Split phase (Double star, six-phase) induction motors are obtained by splitting the stator windings of three-phase induction motor into two equal halves which are spatially phase separated by 30 electrical degrees. The resulting six phases can be decomposed into three orthogonal sets of phase sequences, i.e. positive sequence components and two zero sequence components. The positive sequence component consists of all the 12n ± 1 (n = 0,1, 2, 3....etc.) order harmonics. One of the two zero sequence components consists of all the 6n ± 1 (n = 1, 3, 5....etc.) order harmonics. The triplen harmonic components 3n (n = 1, 3, 5....etc.) constitute the other zero sequence component. The zero sequence components do not contribute towards air gap flux production with the existing winding disposition. Only the positive sequence components contribute for the air gap flux and electromagnetic torque production in the motor. In this paper, a scheme is proposed where one of the zero sequence components is impressed across a second six phase motor in proper sequence so that it will become a positive sequence component for the second motor and, hence, will develop air gap flux and electromagnetic torque in the second motor. By following this method of orthogonal decomposition of the harmonic voltages of the split phase sequence, two split phase (double star, six-phase) motors can be independently controlled by a single six-phase inverter.

Charge-changing interactions of ultrarelativisticPbnuclei

Experimental data and theoretical results on charge loss $\ensuremath{-}27\ensuremath{\leqslant}\ensuremath{\Delta}Z\ensuremath{\leqslant}\ensuremath{-}1$, charge pickup $\ensuremath{\Delta}Z=+1$, and total charge-changing cross sections for $158A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$ $_{82}^{208}\mathrm{Pb}$ ions on ${\mathrm{CH}}_{2}$, $\mathrm{C}$, $\mathrm{Al}$, $\mathrm{Cu}$, $\mathrm{Sn}$, and $\mathrm{Au}$ targets are presented. Calculations based on the revisited abrasion-ablation model for hadronic interaction and the relativistic electromagnetic dissociation (RELDIS) model for electromagnetic interaction describe the data. The decay of excited nuclear systems created in both types of interaction is described by the statistical multifragmentation model (SMM), which includes evaporation, fission, and multifragmentation channels. We show that at very high projectile energy the excitation energy of residual nuclei may be described on average as $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ per removed nucleon, with some increase in this value compared to fragmentation of intermediate energy heavy ions at $\ensuremath{\sim}1A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$. The importance of the electromagnetic interaction in production of $_{80}\mathrm{Hg}$, $_{81}\mathrm{Tl}$, and $_{83}\mathrm{Bi}$ projectile fragments on heavy targets is shown. A strong increase of nuclear-charge pickup cross sections, forming $_{83}\mathrm{Bi}$, is observed in comparison to similar measurements at $10.6A\phantom{\rule{0.3em}{0ex}}\mathrm{GeV}$. This process is attributed to the electromagnetic production of a negative pion by an equivalent photon, which is quantitatively described by the RELDIS model.

Threshold π0 photo- and electro-production in a meson-exchange model

We show that, within a meson-exchange dynamical model describing well most of the existing pion electromagnetic production data up to the second resonance region, one is also able to obtain a good agreement with the π 0 photo- and electroproduction data near threshold. In the case of π 0 production, the effects of final state interaction in the threshold region are nearly saturated by single charge exchange rescattering. This indicates that in ChPT, it might be sufficient to carry out the calculation just up to one-loop diagrams for threshold neutral pion production.

Exclusive electromagnetic production of strangeness on the nucleon: Regge analysis of recent data

In view of the numerous experimental results recently released, we provide in this paper an update on the performance of our simple Regge model for strangeness electroproduction on the nucleon. Without refitting any parameters, a decent description of all measured observables and channels is achieved. We also give predictions for spin transfer observables, recently measured at Jefferson Lab, which have high sensitivity to discriminate between different theoretical approaches.

High resolution spectroscopy of the 12Lambda B hypernucleus produced by the (e,e'K+) reaction.

High-energy, cw electron beams at new accelerator facilities allow electromagnetic production and precision study of hypernuclear structure, and we report here on the first experiment demonstrating the potential of the (e,e'K+) reaction for hypernuclear spectroscopy. This experiment is also the first to take advantage of the enhanced virtual photon flux available when electrons are scattered at approximately zero degrees. The observed energy resolution was found to be approximately 900 keV for the (12)(Lambda)B spectrum, and is substantially better than any previous hypernuclear experiment using magnetic spectrometers. The positions of the major excitations are found to be in agreement with a theoretical prediction and with a previous binding energy measurement, but additional structure is also observed in the core excited region, underlining the future promise of this technique.

PROBING Δ STRUCTURE WITH PION ELECTROMAGNETIC PRODUCTION

The Dubna-Mainz-Taipei dynamical model for pion electromagnetic production, which can describe well the existing data from threshold up to 1 GeV photon lab energy, is presented and used to analyze the recent precision data in the Δ region. We find that, within our model, the bare Δ is almost spherical while the physical Δ is oblate. The deformation is almost saturated by the pion cloud effects. We further find that up to Q2 = 4.0(GeV/c)2 the extracted helicity amplitude A3/2 and A1/2 remain comparable with each other, implying that hadronic helicity is not conserved at this range of Q2. The ratio E1+/M1+ obtained show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and to become positive with increasing Q2. This is a possible indication of a very slow approach toward the pQCD region. Finally, we find that the bare helicity amplitude A1/2 and S1/2, but not A3/2, starts exhibiting the scaling behavior at about Q2 ≥ 2.5(GeV/c)2.

Mechanism for the double-spin asymmetry in electromagnetic ρ production at HERMES

We calculate the contribution of meson and Pomeron exchanges to the double-spin asymmetry in \ensuremath{\rho}-meson electromagnetic production at HERMES energies. We show that the observed double-spin asymmetries, which are large, can be explained by the interference between the natural parity ${f}_{2}$-secondary Reggeon and the unnatural parity anomalous ${f}_{1}$ exchanges.

Microwave emission of rough ocean surfaces with full spatial spectrum based on the multilevel expansion method

Microwave emission of ocean surfaces with full spatial spectrum is studied in this paper. For ocean surfaces with full spectrum, the rms height of roughness can be many wavelengths, and the surface size must be chosen to be larger than the longest scale wave in the spectrum. Due to computer resources, it is not straightforward to conduct numerical simulations of emission from rough surfaces with large rms height and size since a large number of unknowns will be involved. In this paper, the multilevel expansion of the sparse matrix canonical grid (SMCG) method, which is available for surfaces with large rms heights, is used to study the emission of one-dimensional (1-D) ocean surfaces. The computational complexity and the memory requirement are still on the order of O(N log (N)) and O (N), respectively, as in the SMCG method. Ocean surfaces with size 1024 wavelengths (21.9 m at 14 GHz) and spatial spectrum bandwidth between 0.858 rads/m (corresponding to the longest scale of 341.3 wavelengths) and 4691.5 rads/m (corresponding to the shortest scale of 1/16 wavelengths), which is rather wide to be regarded as a full spectrum, are studied. The maximum of the electromagnetic wavenumber-surface rms height product is up to 25.18. The surface is modeled as a lossy dielectric surface with large relative permittivity rather than as a perfectly conducting surface, which is often adopted as an approximation in the active remote sensing of ocean surfaces. A relatively high sampling density is used to ensure accuracy. The effects of the low and high portions of the spectrum on the emissivity are studied numerically. Monte Carlo simulation for ocean surfaces is also performed by exploiting the efficiency of the multilevel expansion method and the use of parallel computing techniques. The convergence of the results with respect to the sampling density is also illustrated.

The [formula omitted] program with CLAS at Jefferson Laboratory

The study of the baryon spectrum is a fundamental part of the scientific program in Hall B at Jefferson Laboratory. The so called N* program indeed concerns the measurement of the electromagnetic production of exclusive baryon excited states. CLAS, the CEBAF Large Acceptance Spectrometer, is explicitly designed for conducting a broad experimental program in hadronic physics, using the continuous electron beam provided by the laboratory. Some selected issues in the N* CLAS experimental program will be outlined, then the beam and detector performance will be discussed and finally some relevant new experimental results will be reported.

π0 Photo- and electroproduction at threshold within a dynamical model

We show that, within a meson-exchange dynamical model describing most of the existing pion electromagnetic production data up to the second resonance region, one is also able to obtain a good agreement with the pi0 photo- and electroproduction data near threshold. The potentials used in the model are derived from an effective chiral Lagrangian. The only sizable discrepancy between our results and the data is in the P-wave amplitude P3 = 2M1+ + M1-, where our prediction underestimate the data by about 20%. In the case of pi0 production, the effects of final state interaction in the threshold region are nearly saturated by single charge exchange rescattering. This indicates that in ChPT it might be sufficient to carry out the calculation just up to one-loop diagrams for threshold neutral pion production.

Evidence for the flavor singlet axial anomaly related effects in φ-meson electromagnetic production at large momentum transfers

The gluonic contributions to the conventional PCAC formulas due to flavor singlet axial anomaly have been instrumental in explaining the mass of the $\eta^{\prime}$ and providing a plausible explanation for solving the spin crisis. We show that they also play an important role in the description of photo- and electroproduction of vector mesons at low energy and high momentum transfers. We calculate the contributions of this type to $\phi$ meson electromagnetic production in a model, which contains also a soft pomeron, and find agreement with recent CLAS data.

New anomalous exchange in Regge phenomenology and hard diffraction

A new mechanism for hard diffraction based on the anomalous f 1 trajectory exchange, which we identify as the odd signature partner of the Pomeron, is suggested. We calculate the contribution of the f 1 exchange to elastic and dissociative electromagnetic production of vector mesons and show that it gives a dominant contribution to the differential cross sections at large momentum transfers.

Photo- and electroproduction of strange mesons: From elementary process to hypernuclei

The general formalism for electromagnetic production of pseudoscalar mesons off nucleons is reviewed. An effective Lagrangian model for low and medium energy photo- and electroproduction of K+ mesons is introduced and compared with available experimental data. Finally, the electroproduction of K+ mesons on complex nuclear targets is investigated and it is demonstrated that planned experiments at the CEBAF electron accelerator may shed new light on the problems of the spectroscopy of hypernuclei.

電磁力による回転液層中の溶融合金ジェット流の能動制御と短繊維材の製作

電磁力による回転液層中の溶融合金ジェット流の能動制御と短繊維材の製作

Pion Cloud and theQ2Dependence ofγ*N↔ΔTransition Form Factors

Recent experiment indicates that the behavior exhibited by the ratios $E_{1^+}/M_{1^+}$ and $S_{1^+}/M_{1^+}$ of the $\gamma^* N \leftrightarrow \Delta$ transition remain small and negative for $Q^2 \le 4.0 GeV^2$. It implies that the perturbative QCD is still not applicable at these momentum transfers. We show that these data can be explained in a dynamical model for electromagnetic production of pions, together with a simple scaling assumption for the bare $\gamma^* N \Delta$ form factors. Within our model we find that the bare $\Delta$ is almost spherical and the electric E2 and Coulomb C2 quardrupole excitations of the physical $\Delta$ are nearly saturated by pion cloud contribution in $Q^2 \le 4.0 GeV^2$.

Screening effect in electromagnetic production of electron-positron pairs in relativistic nucleus-atom collisions

We study the screening effects of the atomic electrons in the electromagnetic production of electron-positron pairs in relativistic nucleus-atom collisions for fixed target experiments. Our results are contrasted with those obtained in bare collisions, with particular attention given to its dependence on the beam energy and the target atom.