Forward Hemisphere Research Articles

Forward–backward multiplicity correlations in 4.5 A GeV/c16O–emulsion interactions

A detailed study of the mechanisms of the emissions of pions and protons in the forward and backward hemispheres in 4.5 A GeV/c oxygen-emulsion interactions has been carried out. The correlations between the multiplicities of secondary charged particles in the backward and forward hemispheres are investigated.

Pronounced Fluctuations of Target Fragments in ForwardHemisphere Only in Ultra Relativistic Nuclear Collision

Dynamical fluctuation of target evaporated black particles isinvestigated in both forward and backward hemispheres within theframework of multi-dimensional factorial moment methodology using thebrilliant concept of the Hurst exponent. We analyse the black particlesemitted in 32S–AgBr interactions at 200 AGeV and it isevident that the dynamical fluctuation in the backward hemisphere isself-affine. In the forward hemisphere, dynamical fluctuation isself-similar but not self-affine. However, study indicates that thefluctuation in the forward hemisphere is more pronounced than that inbackward hemisphere.

Scattering of a tightly focused beam by an optically trapped particle

Near-forward scattering of an optically trapped 5-mum-radius polystyrene latex sphere by the trapping beam was examined both theoretically and experimentally. Since the trapping beam is tightly focused, the beam fields superpose and interfere with the scattered fields in the forward hemisphere. The observed light intensity consists of a series of concentric bright and dark fringes centered about the forward-scattering direction. Both the number of fringes and their contrast depend on the position of the trapping beam focal waist with respect to the sphere. The fringes are caused by diffraction that is due to the truncation of the tail of the trapping beam as the beam is transmitted through the sphere.

String junction effects for forward and central baryon production in hadron-nucleus collisions

The process of baryon number transfer due to string junction propagation in rapidity space is considered. It leads to a significant effect in the net baryon production in pA collisions at mid-rapidities and an even more significant effect in the forward hemisphere for the cases of \pi A interactions. The results of numerical calculations in the framework of the Quark-Gluon String Model are in reasonable agreement with the data. Special consideration is given to \Lambda produced in {\pi^-}-A collisions extracted from data of WA89 Collaboration.

Publisher's Note: CoherentΘ+andΛ(1520) photoproduction off the deuteron [Phys. Rev. C 72, 035206 (2005)

We analyze an effect of the coherent $\Theta^+\Lambda(1520)$ photoproduction in $\gamma D$ interaction near the threshold. We demonstrate that the coherence effect becomes manifest in a comparison of the $nK^+$ invariant mass distribution when the $pK^-$ invariant equals the $\Lambda(1520)$ mass. Our model calculations indicate a sizeable contribution of resonant and non-resonant background processes in the $\gamma D\to np K^+K^-$ reaction which generally exceed the contribution of the coherent resonant channel. However, we find that the coherent $\Theta^+\Lambda(1520)$ photoproduction is enhanced relative to the background processes in the forward hemisphere of the $pK^-$ pair photoproduction. Moreover, the coherence effect does not depend on the $\Theta^+$ photoproduction amplitude and is defined by the probabilities of the $\Lambda(1520)$ photoproduction and the $\Theta^+\to NK$ transition. Therefore, this coherence effect may be used as an independent method for studying the mechanism of $\Theta^+$ production and $\Theta^+$ properties.

CoherentΘ+andΛ(1520)photoproduction off the deuteron

We analyze coherent ${\ensuremath{\Theta}}^{+}\ensuremath{\Lambda}(1520)$ photoproduction in the $\ensuremath{\gamma}d$ interaction near the threshold. We demonstrate that the effect of the coherent production becomes manifest in a comparison of the ${\mathit{nK}}^{+}$ invariant mass distribution when the ${\mathit{pK}}^{\ensuremath{-}}$ system is on the $\ensuremath{\Lambda}(1520)$ mass. Our model calculations indicate a sizable contribution of resonant and nonresonant background processes in the $\ensuremath{\gamma}d\ensuremath{\rightarrow}\mathit{np}{K}^{+}{K}^{\ensuremath{-}}$ reaction that generally exceeds the contribution of the coherent resonance channel. However, we find that coherent ${\ensuremath{\Theta}}^{+}\ensuremath{\Lambda}(1520)$ photoproduction is enhanced relative to the background processes in the forward hemisphere of ${\mathit{pK}}^{\ensuremath{-}}$ pair photoproduction. Moreover, the coherence effect does not depend on the ${\ensuremath{\Theta}}^{+}$ photoproduction amplitude and is defined by the probabilities of $\ensuremath{\Lambda}(1520)$ photoproduction and the ${\ensuremath{\Theta}}^{+}\ensuremath{\rightarrow}\mathit{NK}$ transition. Therefore, this effect may be used as an independent method for studying the production mechanism and properties of ${\ensuremath{\Theta}}^{+}$.

Trajectory Studies of Methyl Radical Reaction with Iodine Molecule

The reaction of methyl radical with iodine molecule on an attractive potential energy surface is studied by classical trajectory procedures. The reaction occurs over a wide range of impact parameters with the majority of reactive events occurring in the backward rebound region on a subpicosecond scale. A small fraction of reactive events take place in the forward hemisphere on a longer time scale. The ensemble average of reaction times is 0.36 ps. The occurrence of reactive events is strongly favored when the incident radical and the target molecule align in the neighborhood of collinear geometry. Since the rotational velocity of I2 is slow, the preferential occurrence of reactive events at the collinear configuration of <TEX>$CH_3{\ldots}I{\ldots}$</TEX>I leads to the reaction exhibiting an anisotropic dependence on the orientation of <TEX>$I_2$</TEX>. During the collision, there is a rapid flow of energy from the <TEX>$H_3C{\ldots}$</TEX>I interaction to the I-I bond. The <TEX>$CH_3I$</TEX> translation and <TEX>$H_3C$</TEX>-I vibration share nearly all the energy released in the reaction, and the distribution of the vibrational energy is statistical. The reaction probability is <TEX>$\cong$</TEX>0.4 at the <TEX>$CH_3$</TEX> and I2 temperatures maintained at 1000 K and 300 K, respectively. The probability is weakly dependent on the <TEX>$CH_3\;and\;I_2$</TEX> temperatures between 300 K and 1500 K.

Some special features of the momentum spectrum of protons produced in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

The momentum features of protons originating from 16Op collisions at a momentum of 3.25 GeV/c per nucleon are analyzed. It is shown that the degree of excitation of the fragmenting nucleus affects predominantly the shape of the momentum spectrum of protons emitted into the backward hemisphere in the rest frame of the projectile nucleus and partly the shape of the spectra of protons emitted into the forward hemisphere and formed via the mechanisms of Fermi breakup and evaporation.

Study of the reaction step preceding sequential fission in the nuclear interaction (16.7 MeV/u) 238U+ nat.Au

The kinematical analysis of nuclear reactions between (16.7 MeV/u) 238U and nat.Au ions has been performed by using mica solid-state track detectors (SSNTD). The reaction products emanating from each isolated collision vertex were registered in the forward hemisphere with almost 2 π angular coverage. It has been demonstrated previously that these tracks represent the second stage of a sequential fission process. In this paper the results of analysis pertaining to the first reaction step have been presented. Using a computer code based on the procedure of internal calibration it was possible to derive quantities like mass transfer, total kinetic energy loss, and scattering angles. It is shown that the mass flow and kinetic energy distribution between reacting partners interacting at different impact parameters during the first phase of the interaction decides the multiplicity of the final reaction products.

Development of wide-angle antenna pattern measurements using a probe-corrected polyplanar near-field measurement technique

The authors demonstrate through numerical simulation and experimental measurement that a polyplanar scan geometry consisting of a flat-topped pyramid provides a possible solution to the measurement of high-gain antenna patterns in the forward hemisphere using a planar scanner of size of order 1.5 times the size of the radiating aperture. The importance of correctly determining the normal field component for each partial scan data set is demonstrated and a new auxiliary rotation near-field to far-field transform algorithm is proposed. Additionally it is shown experimentally that by enclosing a medium-gain antenna (e.g. a corrugated horn) within a scan geometry formed by an imaginary box and measuring the near field on all six sides of the box using a suitable rotation of the AUT, a prediction of the full spherical radiation pattern of the antenna can be obtained.

The fast neutron component in treatment irradiations with 12C beam

Using 12C beams of 200 AMeV kinetic energy the production of secondary fragments from nuclear reactions in a thick water absorber (12.78 cm) was investigated. Fast neutrons and energetic charged particles (p-, d-, t-, α-particles) emitted in the forward hemisphere were identified by a BaF 2/plastic-scintillation detector telescope. Neutron energy spectra were recorded at various angles using time-of-flight techniques. The neutron emission is forward peaked and the energy spectrum shows a broad maximum about half the energy per nucleon of the primary 12C ions. The total yield of fast neutrons emitted into the forward hemisphere integrated over the energy range of 25 to 500 MeV was found to be 0.43±0.1 per primary ion. The dose contribution of fast neutrons in patient treatments with carbon ions is estimated to be less than 1% of the total treatment dose.

Absorption of thermal radiation in large semi-transparent particles at arbitrary illumination of the polydisperse system

An approximate theoretical model for nonuniform absorption of the external thermal radiation in a large semi-transparent spherical particle is suggested. As applied to heat transfer problems with diffuse radiation in the wide spectral range, the asymmetric illumination of single particle is considered at each spectral interval as a uniform illumination from backward and forward hemispheres (with respect to the direction of spectral radiation flux). The Mie theory is employed in calculations for particles illuminated from a hemisphere. The modified differential approximation suggested earlier by the author is used in the case of spherically symmetric illumination. Approximate analytical relations for distribution of absorbed radiation power inside a particle are obtained. Results of calculations for typical polydisperse sprays of water and diesel fuel droplets are presented.

Circular polarization in pulsar radio emission due to intrinsically relativistic effects

Observations of single pulses imply that the circular polarization (CP) at a fixed pulsar phase, in some pulsars, can be large and variable from pulse to pulse. In many cases the variations can include changes in the handedness at a fixed phase. Possible explanations for the variable CP are sought in terms of elliptical polarization of the natural wave modes. The pulsar plasma is assumed to be a highly relativistically streaming, one-dimensional, strongly magnetized, electron–positron gas with a net charge density and intrinsically relativistic random motions in its rest frame. It is shown that in such a plasma the polarization of the natural modes includes two regimes where intrinsically relativistic effects determine the CP. One regime arises from aberration causing a small cone of CP about the backward (anti-streaming) direction in the rest frame to expand into the forward hemisphere in the pulsar frame. This mechanism can lead to significant CP at relatively high frequencies. The other mechanism arises from the intrinsically relativistic random motions, which allow a new regime of CP that has no counterpart in a cold plasma; however, for typical parameters this mechanism is effective only at frequencies higher than is consistent with our neglect of the cyclotron resonance. It is suggested that the explanation for the observed CP requires that the CP arise as a propagation effect, and be determined by the properties of the wave modes at a polarization limiting region.

Search for ${\rm\Theta}(1540)^ + $ in the exclusive proton-induced reaction ${\rm p + {C(N)\to \Theta^ + \bar{K}^0 + {C}(N)}}$ at the energy of 70 GeV

A search for narrow Theta(1540)^+, a candidate for pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction p+C(N) \to Theta^+ \bar{K}^0 + C(N) on carbon nuclei or quasifree nucleons at E_{beam}=70 GeV (sqrt{s} = 11.5 GeV) studying nK^+, pK_S and pK_L decay channels of Theta(1540)^+ in four different final states of the Theta^+ \bar{K}^0 system. In order to assess the quality of the identification of the final states with neutron or K_L we reconstructed Lambda(1520)\to nK_S and phi\to K_LK_S decays in the calibration reactions p+C(N)\to Lambda(1520)K^+ + C(N) and p+C(N)\to p\phi + C(N). We found no evidence for narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the Theta^+ \bar{K^0} system are not drastically different from those of the Lambda(1520)K^+ and p\phi systems, we established upper limits on the cross section ratios sigma(Theta^+\bar{K}^0)/sigma(Lambda(1520)K^+) < 0.02 and sigma(Theta^+\bar{K}^0)/sigma(p\phi) < 0.15 at 90% CL and a preliminary upper limit for the forward hemisphere cross section sigma(Theta^+\bar{K}^0) < 30 nb/nucleon.

Baryon-number transfer in high-energy hp collisions

The process of baryon number transfer due to string junction propagation in rapidity is considered. It has a significant effect in the net baryon production in $pp$ collisions at mid-rapidities and an even larger effect in the forward hemisphere in the cases of $\pi p$ and $\gamma p$ interactions. The results of numerical calculations in the framework of the Quark-Gluon String Model are in reasonable agreement with the data with the same parameter values for different energies.

Effect of nuclear transparency from the ( p,2 p) measurements on 6Li and 12C at 1 GeV

We studied the production of protons to the backward direction in ( p,2 p) reactions on 6Li and 12C, accompanied by a proton emitted into the forward hemisphere. The momenta of the final two protons were measured in a wide range with the two-arm time-of-flight spectrometer. For each event we reconstructed the mass of the intermediate off-shell particles. We observed that the Δ(1232) is manifested in the mass spectra of intermediate baryons. A surprising angular dependence of the intermediate meson mass spectrum was revealed. Also we have discovered a strong narrow dip in the mass spectra of intermediate mesons at the mass of the real pion. We explain this effect as an abrupt decrease of the absorption probability for on-shell mesons (the pion–nuclear transparency).

Fiasco: a multidetector optimized for semiperipheral heavy ion collisions at Fermi energies

The Fiasco multidetector is a low-threshold apparatus, optimized for the investigation of peripheral to semi-central collisions in heavy ion reactions at Fermi energies. It consists of three types of detectors. The first detector layer is a shell of 24 position-sensitive Parallel Plate Avalanche Detectors (PPADs), covering about 70% of the forward hemisphere, which measure the velocity vectors of the heavy (Z≳10) reaction products. Below and around the grazing angle, behind the most forward PPADs, there are 96 ΔE–E silicon telescopes (with thickness of 200 and 500μm, respectively); they are mainly used to measure the energy of the projectile-like fragment and to identify its charge and, via the time-of-flight of the PPADs, also its mass. Finally, behind most of the PPADs there are 158 (or 182, depending on the configuration) scintillation detectors, mostly of the phoswich type, which cover 25–30% of the forward hemisphere; they identify both light charged particles (Z=1,2) and intermediate mass fragments (3⩽Z≲20), measuring also their time-of-flight.

Multifragmentation of target in 28Si–AgBr interactions at [formula omitted] GeV—self affine or self similar

Nature of dynamical fluctuations of target evaporated slow particles is investigated in both forward and backward emission angular zones in the framework of multi-dimensional factorial moment methodology using the concept of Hurst exponent. Our analysis on target fragments emitted in 28Si–AgBr interactions at 14.5 A GeV reveals the hint of self-affine dynamical fluctuations in the forward emission angular zone. However in the backward emission angular zone it cannot be unambiguously stated whether the nature of dynamical fluctuations is self affine in nature or self similar. This work further shows the presence of stronger intermittent type of fluctuations in the forward hemisphere.

Study of backward, forward shower and grey particles production from the interactions of 16O with emulsion nuclei at 4.5 A GeV/c

This paper presents the results of the study of interaction of the relativistic 16O nucleus with the momentum 4.5 A GeV/c with the photo emulsion. The average multiplicities of the different emitted hadrons (shower and grey) in the forward (FHS) and backward (BHS) hemisphere, compared with other data from the interaction of 1P, 4He, 6Li, 12C, 22Ne and 28Si at nearly the same momentum, have been studied as a function of projectile mass number, the number of interacting projectile nucleons, impact parameter and number of shower particles emitted in the backward hemisphere. The multiplicity distribution of the shower particles emitted in the forward and backward hemisphere directions using the KNO representation are represented and described by an exponential form for BHS shower particles. Another objective of this paper is to examine whether the mechanism of particle production in the BHS is significantly different from the operating in the production of particles in the FHS which can help to solve some questions connected with the role of collective phenomena in the backward emission of particles from the nuclear targets.

Selected experimental methods for determining droplet parameters from the intensity distribution of scattered light: A review

The present paper summarizes some experimental methods, which have been developed using the results of calculations based on the theory of Gustav Mie. As examples two regions of the scattered light are considered in more detail. The intensity distribution in the forward hemisphere for scattering angles 30 ≤ θ ≤ 60 shows maxima, which can be identified as regular fringes on a screen. The spacing between the fringes is a measure for the droplet size. In the intensity distribution of the backward hemisphere the region of the first rainbow can be found. In the rainbow region a main maximum, subsidiary maxima and a ripple structure can be identified. The angular position of the main maximum is a measure for the refractive index of the droplet. The angular distance between the subsidiary maxima and the angular distance between the ripples both are a function of droplet size. A comparison with other size measurement methods gives information about the sphericity of the droplet. An evaporating droplet shows for instance oscillations of the rainbow position due to morphology dependent resonances. The oscillation frequency is proportional to the evaporation rate.