Search

The differential cross sections of the charge exchange reaction $$dp \rightarrow (pp)n$$ has been measured at 1.75 GeV/c per nucleon for small transferred momenta using the one arm magnetic spectrometer STRELA at the Nuclotron accelerator in JINR Dubna. The ratio of the differential cross section of the charge exchange reaction $$dp \rightarrow (pp)n$$ to that of the $$np \rightarrow pn$$ elementary process is discussed in order to estimate the spin-dependent part of the $$np \rightarrow pn$$ charge exchange amplitude. The $$np \rightarrow pn$$ amplitude turned out to be predominantly spin-dependent.

The analyzing powers for neutron charge exchange nA → pX reactions on nuclei have been measured on C, CH2 and Cu targets at incident neutron momenta 3.0 - 4.2 GeV/c by detecting one charged particle in forward direction. The polarized neutron measurements are the first of their kind. The experiment was performed using the Nuclotron accelerator in JINR Dubna, where polarized neutrons and protons were obtained from breakup of a polarized deuteron beam which has a maximum momentum of 13 GeV/c. The polarimeter ALPOM2 was used to obtain the analyzing power dependence on the transverse momentum of the final-state nucleon. These data have been used to estimate the figure of merit of a proposed experiment at Jefferson Laboratory to measure the recoiling neutron polarization in the quasi-elastic 2 H(e, e′n) reaction, which yields information on the charge and magnetic elastic form factors of the neutron.

A set of differential cross-section data of the 1 H(d, pp)n breakup reaction at 130 MeV deuteron beam energy has been measured in the domain of very forward polar angles with the use of the Germanium Wall detector at the Forschungszentrum Julich. The data obtained for over 1000 kinematical points (112 geometries) are compared with the theoretical predictions based on various models of the three-nucleon (3N) dynamics. They comprise: the realistic nucleon-nucleon potentials alone or combined with the three-nucleon force (3NF), the coupled-channel calculations with the explicit treatment of the Δ-isobar excitation and finally, the potentials derived from chiral perturbation theory. In the part of the phase space studied, the Coulomb interaction between protons has a strong impact on the differential cross section of the breakup reaction. The strongest Coulomb effects are found in regions where the relative energy of the two protons is the smallest. In these regions the data are well reproduced exclusively by calculations which include the electromagnetic repulsion between protons. In spite of the dominance of the Coulomb force in the phase space studied, the contribution of 3NF effects is also observed.

Precise and large sets of cross section, vector $A_{x}, A_{y}$ and tensor$ A_{xx}, A_{xy}, A_{yy}$ analyzing power data for the $^{1}H\left ( d, pp \right )n$ breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the SALAD and BINA detectors at KVI and the Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which model the three-nucleon system dynamics. The cross section data reveal a sizable three-nucleon force (3NF) and Coulomb force influence. In case of the analyzing powers very low sensitivity to these effects was found and the data are well describe by 2N models only. For $A_{xy}$ at 130 MeV, serious disagreements were observed when 3NF models are included in the calculations.

An accurate data base for the analyzing power of thick CH2 analyzers for high energy protons has been at the basis of several research efforts in a number of laboratories. Starting in the late eighties such data were collected at SATURNE in Saclay, and with the Synchrophasotron in Dubna, and led to an extensive program of study of polarization phenomena in pd interaction, either backward elastic scattering or breakup [1–6]. At about the same time it became evident that measuring polarization observables in elastic ep was going to be the best approach to determine the form factors of the proton, GEp and GMp, as had been predicted by Akhiezer and Rekalo [7].

We have measured inclusive data on K + -meson production in pp collisions at COSY Julich close to the hyperon production threshold and determined the hyperon–nucleon invariant mass spectra. The spectra were decomposed into three parts: Λp, Σ 0 p and Σ + n . The cross section for the Σ + n channel was found to be much smaller than a previous measurement in that excess energy region. The data together with previous results at higher energies are compatible with a phase space dependence.

The reaction p p → K + + ( Λ p ) was measured at T p = 1.953 GeV and Θ = 0 ° with a high missing mass resolution in order to study the Λp final state interaction. The large final state enhancement near the Λp threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Λp invariant mass spectrum and the total cross section data of the free Λp scattering.

The extracted s-wave scattering amplitude from both the polarized and unpolarized d + d → 4He + η reaction at 2385.5 MeV/c allowed to determine the scattering length which fulfills the requirements for bound η. In the p + 27Al → 3He + p + π- + X reaction studied at recoil free kinematics the η meson is produced almost at rest and so it can be bound with enhanced probability. This state proceeds via N*(1535) resonance and the decay products proton and pion emitted into opposite direction are detected in concidence with 3He produced at zero degree. Under these conditions some hints for bound state can be observed with an upper limit of the cross section of ≈ 0.5 nb.

þ ðLpÞ K þ =pþ separation abstract A new threshold Cherenkov detector has been built for the detection of charged pions in the focal plane of a magnetic spectrograph. Silica aerogel with refractive index of n ¼ 1:05 is applied as a radiator. The detector exhibits a very high detection efficiency for pions with momenta X900 MeV=c. Using two Cherenkov detectors in series a very high pion suppression factor of 10 5 was achieved.

The measurement of the η meson production in [Formula: see text] reaction has been performed at the Big Karl magnetic spectograph at COSY synchrotron in Jülich. The vector and tensor polarized deuetron beam at the excess energy of Q=16 MeV was used. The preliminary results for the unpolarized cross section are presented here.

An experiment to search for the bound state of η meson in nuclei has been performed at COSY, Juelich using the ENSTAR detector and Big Karl magnetic spectrometer. Reaction (p,3 He ) on 27 Al target has been used to search for the η-mesic nucleus 25 Mg η in the missing mass distribution from the measured 3 He particles. A preliminary figure of 1.5 nb for the upper limit of the formation cross section of η-nucleus bound state has been determined.

International audience; The reaction p + CH(2)→ forward charge particle + X is used for this aim traditionally. Analyzing power of this reaction falls off as 1/p, where p is the laboratory momentum. At the proton momenta of order 8 GeV/c, which are expected at the JLab experiment, the low analyzing power creates problems for off-line analysis of data. On the other hand, it is well known that the reaction p+p → p+p has the much more analyzing power. So, the calorimeter is predestinated for suppression of inelastic events in this reaction. In the report it is shown that the problem is solved quite well.

The positively charged pions produced in proton–proton collisions at a beam momentum of 1640 MeV/c were measured in the forward direction with a high resolution magnetic spectrograph. The missing mass distribution shows the bound state (deuteron) clearly separated from the pn continuum. Despite the very good resolution, there is no evidence for any significant

We report a new measurement of analyzing powers for the reaction p ⇒ + CH 2 → one charged particle +X, at proton momenta of 1.75, 3.8, 4.5 and 5.3 GeV / c . These results extend the existing data basis, necessary for proton polarimetry at intermediate energy, and confirm the feasibility of a large acceptance polarimeter based on this process. Particular attention was devoted to the investigation of the optimal target thickness and of the useful angular range. The experiment is performed at the accelerator complex of the JINR-VBLHE (Dubna).

Polarimeters with thick targets are a tool to measure the proton polarization. However, the question about the optimum target thickness is still the subject of discussion. An attempt to calculate the common parameters concerning this problem, in a few GeV region, is made in this paper.

We performed a series of experiments employing the two pion production reactions p + d → 3 He + π 0 and p + d → 3 H + π + . The two isopin related reactions differ by a Clebsch Gordan coefficient of 2. We searched for deviations in this ratio in complete angular distributions in the range of the Δ excitation as well as in the vicinity of the η production threshold.

One of the most important goals of modern nuclear physics is to contruct nuclear force model which properly describes the experimental data. To develop and test predictions of current models the breakup $^{1}H\left ( \vec{d}, pp \right )n$ reaction was investigated experimentally at 100 and 130 MeV deuteron beam energies. Rich set of data for cross section, vector and tensor analyzing powers was obtained with the use of the SALAD and BINA detectors at KVI and Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which describe the three-nucleon (3N) system dynamics. For correct description of the cross section data both, three-nucleon force (3NF) and Coulomb force, have to be included into calculations and influence of those ingredients is seizable at specific parts of the phase space. In case of the vector analyzing powers very low sensitivity to any effects beyond nucleon-nucleon interaction was found. At 130 MeV, the $A_{xy}$ data are not correctly described when 3NF models are included into calculations.

The problem of a complete experiment in backward elastic scattering of particles with spins of 1 and \(\) is considered. For the first time all possible effects induced by polarization of one or two initial and one final particles are touched upon. The minimal set of measurements allowing to reconstruct all of four amplitudes describing this process is proposed. Some observables are expected to be sensitive to hitherto largely unexplored deuteron properties, such as a possible P-wave component. The technique developed is a good tool to calculate easily impulse-approximation predictions for any observables. Accelerator facilities suitable for fulfilling the complete experiment are listed.

We present the results obtained at SATURNE on the measurement of the vector and tensor polarization of deuterons at high energy. A polarimeter based on d + p elastic scattering has been recently built and it has been used to measure the induced tensor deuteron polarization in the 1 H( 3 He, d )X reaction. In case of availability of a polarized 3 He beam, other polarization observables can be measured. This reaction constitutes a different approach in the study of the 3 He-structure at short distances.

The tensor analyzing power T20 for the p(d,pd) and p(d,p)pn reactions θcmp = 180° have been measured at incident deuteron momenta from 3.5 to 6.5 GeV/c. For both reactions T20 remains negative up to internal momentum k ⋍ 0.85 GeV/c and show a rich structure beyond the region where T20 is expected to be determined by the S- and D-states of the deuteron. The T20 data for deuteron breakup without pion production, close to the backward elastic kinematics, were obtained simultaneously with the elastic data.

Precise and large set of cross sections, vector A ( )x( ), A ( )y( ) and tensor A ( )xx( ), A ( )xy( ), A ( )yy( ) analyzing powers for the (1) H(d, pp)n breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the use of the SALAD and BINA detectors at KVI and Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which model the three-nucleon (3N) system dynamics. The calculations are based on different two-nucleon (2N) potentials which can be combined with models of the three-nucleon force (3NF) and other pieces of the dynamics can also be included like the Coulomb interaction and relativistic effects. The cross sections data reveal seizable 3NF and Coulomb force influence. In case of analyzing powers very low sensitivity to the effects was found and the data are well describe by 2N models only. At 130 MeV for A ( )xy( ) serious disagreements appear when 3NF models are included into calculations.

The tensor analyzing power T 20 in inclusive deuteron breakup at 9 GeV/c and 0° on hydrogen and carbon targets up to internal momenta k of the proton in the deuteron of ∼ 1 GeV/c has been measured. The analyzing power remains negative up to the highest measured values of k , and is in definite disagreement with predictions from several theoretical models. A systematic difference between T 20 for deuteron breakup on hydrogen and carbon is observed.

First results for T 20 of the inelastic ( d , d ′) X reaction above the Δ threshold are presented. It is observed that T 20 is negative; its absolute value is small in the Δ region and rises almost linearly to |T 20 | ⋍ (0.4–0.6) at energy transfers Q ⋍ 1 GeV. No significant dependence on the type of the target and on the initial energy was observed.

We report a new calibration of the polarimeter POMME for energies between 1.05 and 2.40 GeV using polarized proton beams at the Laboratoire National Saturne. A 16 parameter and a new 14 parameter empirical formula have been used to fit both the angular and energy dependencies of the inclusive proton-carbon analyzing power data between 0.80 and 2.40 GeV. Both fits have very good chi-square, 1.20 per degree of freedom for the former, and 1.05 for the latter. The parameters from these fits can be used to predict the angular distribution of the pC analyzing power at any energy within the energy range of the fits.

Recent measurements of the polarization observables in the dp → pd reaction at Dubna and Saclay have shown that a consideration of this reaction in the framework of the one nucleon exchange mechanism is inadequate. The T -odd effects due to the polarization of both colliding particles are considered. It is shown that the new polarization observable is especially sensitive to the mechanism of the reaction. The paper is inspired by the fact that a polarized proton target, which can provide a polarized deuteron beam, is now installed at the Dubna synchrophasotron. Such measurements are feasible also at COSY.

The polarization transfer κ0 and the tensor analyzing power T20 for the 1 H d p)d reaction have been measured up to an internal momentum of k = 0.58 GeV/c. Comparison of the same observables obtained in recent studies for 1 H d p)d reaction, as a function of k, show different behavior. However the data from these two reactions are almost identical when compared in T20 versus κ0 correlation plots. We discuss similarities and differences observed in the two reactions.

The differential cross sections of the charge exchange reaction dp → (pp)n has been measured at 1.75 GeV/c momentum per nucleon for small transferred momenta using the one arm magnetic spectrometer STRELA at the Nuclotron accelerator. The ratio of the differential cross section of the charge exchange reaction dp → (pp)n to that of the np → pn elementary process is discussed in order to estimate the spin-dependent part of the np → pn charge exchange amplitude on the basis of dp → (pp)n data. The np → pn amplitude turned out to be predominantly spin-dependent.

Set of vector analyzing power data of the (d) over barp elastic scattering and H-1((d) over bar, pp)n breakup reactions at 130-MeV deuteron beam energy has been measured in the domain of very forward polar angles. The results are compared with theoretical predictions originating from various approaches: realistic nucleon-nucleon (NN) potentials and the NN potentials combined with a three-nucleon force (3NF) model and with predictions based on the ChPT framework. In case of the breakup process, none of the theoretical calculations reveal sensitivity to any of the dynamical effects such as 3NF or Coulomb interaction and they describe the experimental data equally well. For the elastic scattering, the Coulomb correction appears not negligible at very small theta(c.m.)(d). The effect seems to be confirmed by the data.

The polarization transfer coefficient of the 12 C( d, p ) X reaction has been measured using a deuteron beam of the JINR synchrophasotron and the spectrometer ALPHA. The covered internal momentum range of the deuteron wave function is 0–0.51 GeV/c. The measured values compared with the ones obtained at lower energies at Saclay in term of internal momentum demonstrate the absence of essential energy and A-dependence of this observable. A comparison of the new polarization transfer data with earlier measurements of T20 demonstrates the existence of a systematic deviation from the Impulse Approximation independently of the kind of the deuteron wave function with S- and D-wave only.

The tensor polarization ${\ensuremath{\rho}}_{20}$ of deuterons emitted in the ${}^{1}\mathrm{H}{(}^{3}\mathrm{He},\stackrel{\ensuremath{\leftrightarrow}}{d})X$ reaction at ${0}^{\ensuremath{\circ}}$ in the laboratory system was measured at the Saturne National Laboratory in Saclay using the SPES-4 spectrometer with the HYPOM polarimeter located downstream from its focal plane. The momentum of the detected deuterons was kept fixed at 3.77 GeV$/c$, while the momentum of the ${}^{3}\mathrm{He}$ beam was varied from 4.60 to 5.66 GeV$/c$, thus providing a range of internal momenta $k$ of the deuteron in ${}^{3}\mathrm{He}$ from 0 up to 0.4 GeV$/c$. The data obtained are compared with theoretical predictions.

The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and \Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.

The cross section for the reaction p+{sup 6}Li{yields}{eta}+{sup 7}Be was measured at an excess energy of 11.28 MeV above threshold by detecting the recoiling {sup 7}Be nuclei. A dedicated set of focal plane detectors was built for the magnetic spectrograph Big Karl and was used for identification and four-momentum measurement of {sup 7}Be. A differential cross section of nb/(d{sigma}/d{Omega})=[0.69{+-}0.20(stat.){+-}0.20(syst.)] sr for the ground state plus 1/2{sup -} was measured. The result is compared to model calculations.

Inclusive measurements of pion production in proton-proton collisions in the forward direction were undertaken at 400 and 600 MeV at the cooler synchrotron (COSY) at Forschungszentrum Julich using the Big Karl spectrograph. The high resolution in the pi(+) momentum ensured that there was an unambiguous separation of the pp ->pi(+)d/pi(+)pn channels. Using these and earlier data, the ratio of the production cross sections could be followed through the Delta region and compared with the predictions of final state interaction theory. Deviations are strongly influenced by long-range terms in the production operator and the tensor force in the final pn system. These have been investigated in a realistic pp ->pi(+)d/pi(+)pn calculation that includes S reversible arrow D channel coupling between the final nucleons. A semiquantitative understanding of the observed effects is achieved. .

The (3He, t) charge-exchange reaction on carbon nuclei and protons, accompanied by the excitation of Δ isobars in a target, has been studied at beam momenta from 4.40 to 18.3 GeV/c. The analysis is performed to explain why the Δ-peak in the inclusive A( 3 He, t) and A(p, n) measurements is shifted towards lower energy transfers (in comparison with the reactions on free nucleons) but in the exclusive ones it is shifted towards higher transfers. An attempt is undertaken to determine the characteristics of Δ excitation in nuclei by a (3He, t) reaction that is free of the admixture of quasifree Δ production.

A polarimeter for polarized deuteron beams at the JINR synchrophasotron in the energy range of several GeV per nucleon is described. A left-right-symmetrical detector configuration is used to measure vector and tensor polarizations of deuterons in the forward scattering on a liquid hydrogen target. In this paper we present the results of various measurements to adjust optimum conditions for the working regime of the ion source.

We measured diffractive scattering cross sections of alpha-particles on carbon, aluminium, copper and lead using the beam of the Dubna synchrophasotron at 3.64 GeV/nucleon. The data are compared with model predictions of the Glauber-Sitenko multiple scattering theory. Large discrepancies between experiment and calculations appear at four-momentum transfers above ∼0.25 (GeV/c)2. Various theoretical attempts to improve the description of high-energy alpha-scattering data are discussed.

We have studied the reaction $p+{^{27}Al}\to {^3{He}}+p+\pi^-+X$ at recoil-free kinematics. An $\eta$ meson possibly produced in this reaction would be thus almost at rest in the laboratory system and could therefore be bound with high probability, if nuclear $\eta$ states exist. The decay of such a state through the $N^*(1535)$ resonance would lead to a proton-$\pi^-$ pair emitted in opposite directions. For these conditions we find some indication of such a bound state. An upper limit of $\approx$ 0.5 nb is found., Comment: 3 figures

The 0° differential cross sections of the12C(4He,p) and12C(4He,t) reactions have been measured at beam momenta of 4.52 and 2.69 GeV/c/nucleon, respectively. The proton and triton momentum distributions in4He are extracted from the cross sections using a relativistic impulse approximation. Some theoretical models based on realisticN-N potentials are examined for our data.

A large acceptance scintillator detector with wavelength shifting optical fibre readout has been designed and built to detect the decay particles of $\eta$-nucleus bound system (the so-called $\eta$-mesic nuclei), namely, protons and pions. The detector, named as ENSTAR detector, consists of 122 pieces of plastic scintillator of various shapes and sizes, which are arranged in a cylindrical geometry to provide particle identification, energy loss and coarse position information for these particles. A solid angle coverage of $\sim$95% of total 4$\pi$ is obtained in the present design of the detector. Monte Carlo phase space calculations performed to simulate the formation and decay of $\eta$-mesic nuclei suggest that its decay particles, the protons and pions are emitted with an opening angle of 150$^\circ \pm 20^\circ$, and with energies in the range of 25 to 300 MeV and 225 to 450 MeV respectively. The detailed GEANT simulations show that $\sim$ 80 % of the decay particles (protons and pions) can be detected within ENSTAR. Several test measurements using alpha source, cosmic-ray muons etc. have been carried out to study the response of ENSTAR scintillator pieces. The in-beam tests of fully assembled detector with proton beam of momentum 870 MeV/c from the Cooler synchrotron COSY have been performed. The test results show that the scintillator fiber design chosen for the detector has performed satisfactorily well. The present article describes the detector design, simulation studies, construction details and test results., Comment: accepted by Nucl. Instr. Methods in Phys. Research A

Several processes of meson production in proton-deuteron collisions have been measured simultaneously using a calibrated magnetic spectrograph. Among these processes, the $\eta$ meson is seen clearly as a sharp missing--mass peak on a slowly varying background in the $p+d\to ^3\textrm{He} +X$ reaction. Knowing the kinematics of the other reactions with well determined masses, it is possible to deduce a precise mass for the $\eta$ meson. The final result, $m(\eta)=547.311\pm 0.028 \textrm{(stat)} \pm 0.032 \textrm{(syst) MeV/c}^2$, is significantly lower than that found by the recent NA48 measurement, though it is consistent with values obtained in earlier counter experiments., Comment: 10 pages, 6 figures, Fig. 3 changed

The importance of the isospin symmetry breaking in extracting various particle physics parameters is discussed. In particular the measurement of isospin symmetry breaking in the reaction pd → 3Hπ+/3Heπ0 is presented. The energy dependence of the measured cross sections ratio indicate isospin symmetry breaking effects. Within a simple model based on π0 − η meson mixing the mixing angle of these mesons is extracted.

Experiments have been performed at COSY, Jnelich to investigate isospin symmetry breaking effects in nuclear reactions by studying simultaneously the two reactions p + d → 3H+π+and p + d 3He+π0 at beam energies close to corresponding ηproduction threshold. The beam momentum dependence of the ratio of cross section of these two reactions would be indicative of isospin symmetry breaking, if any. The present measurement reports observation of isospin symmetry breaking effect. The results are presented.of the two detection system needs further improvement. Measurements in this respect are in progress.

The characteristics of a polarimeter to measure the tensor polarization of deuterons with energy of a few GeV have been studied by Monte Carlo simulations. The analyzing reaction is forward elastic dp scattering. The results of the simulation have been verified with a prototype hydrogen cell and a recoil proton detector using drift tubes inserted in the polarimeter POMME. The test used a vector and tensor polarized deuteron beam of 1.6 GeV kinetic energy at the accelerator Saturne. The feasability of a vector and tensor deuteron high-energy polarimeter based on deuteron–proton elastic scattering reaction has been studied. We present here the prediction of a Monte Carlo simulation and the first results of a test made with a prototype, at the Saturne National Laboratory.