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Amplitude analysis of the $\overline{N}N \to K^-K^+$ reaction  [PDF]
W. M. Kloet,F. Myhrer
Physics , 1996,
Abstract: A simple partial wave amplitude analysis of $\overline{p}p \rightarrow K^-K^+$ has been performed for data in the range $p_{\rm lab}$ = 360 -- 1000 MeV/$c$. In this low momentum interval only partial wave amplitudes with $J$ equal to 0, 1 and 2 are needed to obtain a good fit to the experimental data. This maximal $J$ = 2 value is smaller than what is required for the data of the reaction $\overline{p}p \rightarrow \pi^-\pi^+$ in the same momentum interval.
Study of the reaction pi- p --> pi- pi+ n on the polarized proton target at 1.78 GeV/c. Experiment and amplitude analysis  [PDF]
I. G. Alekseev,P. E. Budkovsky,V. P. Kanavets,L. I. Koroleva,I. I. Levintov,V. I. Martynov,B. V. Morozov,V. M. Nesterov,V. V. Ryltsov,D. N. Svirida,A. D. Sulimov,V. V. Sumachev,V. V. Zhurkin
Physics , 1998,
Abstract: We present the results of the experimental study of the reaction of dipion production by the beam of the negative pions with momentum 1.78 GeV/c on the polarized proton and liquid hydrogen targets. The experiment covers the region of dipion masses near the mass of rho-meson and small momenta transferred |t|<0.2(GeV/c)^2. The whole set of spin density matrix elements was reconstructed and model-independent and model-dependent amplitude analyses of the reaction were performed. The experiment allows to exclude the ambiguity of the amplitude analysis existing at high energies. The results contain evidences in favour of existing of narrow sigma(750). The data also allows to estimate intercept of a_1-meson Regge trajectory. The experiment was performed at the ITEP proton synchrotron, Moscow.
Comprehensive Amplitude Analysis of $γγ\rightarrow π^+π^-, π^0π^0$ and $\overline{K} K$ below 1.5 GeV  [PDF]
Ling-Yun Dai,Michael R. Pennington
Physics , 2014, DOI: 10.1103/PhysRevD.90.036004
Abstract: In this paper we perform an amplitude analysis of essentially all published pion and kaon pair production data from two photon collisions below 1.5 GeV. This includes all the high statistics results from Belle, as well as older data from Mark II at SLAC, CELLO at DESY, Crystal Ball at SLAC. The purpose of this analysis is to provide as close to a model-independent determination of the $\gamma\gamma$ to meson pair amplitudes as possible. Having data with limited angular coverage, typically $|\cos \theta| < 0.6-0.8$, and no polarization information for reactions in which spin is an essential complication, the determination of the underlying amplitudes might appear an intractable problem. However, imposing the basic constraints required by analyticity, unitarity, and crossing-symmetry makes up for the experimentally missing information. Final state interactions among the meson pairs are critical to this analysis. To fix these, we include the latest $\pi\pi\to\pi\pi$, ${\overline K}K$ scattering amplitudes given by dispersive analyses, supplemented in the ${\overline K}K$ threshold region by the recent precision Dalitz plot analysis from BaBar. With these hadronic amplitudes built into unitarity, we can constrain the overall description of $\gamma\gamma\to\pi\pi$ and $\overline{K}K$ datasets, both integrated and differential cross-sections, including the high statistics charged and neutral pion, as well as $K_sK_s$ data from Belle. Since this analysis invokes coupled hadronic channels, having data on both $\gamma\gamma\to\pi\pi$ and $\overline{K}K$ reduces the solution space to essentially a single form. We present the partial wave amplitudes, show how well they fit all the available data, and give the two photon couplings of scalar and tensor resonances that appear. These partial waves are important inputs into forthcoming dispersive calculations of hadronic light-by-light scattering.
Separation of S- wave pseudoscalar and pseudovector amplitudes in pi^- p---> pi^+ pi^- n reaction on polarized target  [PDF]
R. Kaminski,L. Lesniak,K. Rybicki
Physics , 1996, DOI: 10.1007/s002880050372
Abstract: A new analysis of S-wave production amplitudes for the reaction $\pi^- p_{\uparrow} \rightarrow \pi^+ \pi^- n$ on a transversely polarized target is performed. It is based on the results obtained by the CERN-Cracow -Munich collaboration in the pion-pion energy range from 600 MeV to 1600 MeV at 17.2 GeV/c $\pi^-$ momentum. Energy-independent separation of the S-wave pseudoscalar amplitude ($\pi$ exchange) from the pseudovector amplitude ($a_{1}$ exchange) is carried out using assumptions much weaker than those in all previous analyses. We show that, especially around 1000 MeV and around 1500 MeV, the $a_{1}$ exchange amplitude cannot be neglected. The scalar-isoscalar $\pi\pi$ phase shifts are calculated using fairly weak assumptions. Below the $K\overline{K}$ threshold we find two solutions for the $\pi-\pi$ phase shifts, for which the phases increase slower with the effective $\pi-\pi$ mass than the P-wave phases. Both solutions are consistent with a broad $f_{0}(500)$ but only one is similar to the well-known "down" solution. We find also the third solution (with a somewhat puzzling behavior of inelasticity) which exhibits a narrow $f_{0}(750)$ claimed by Svec. All the solutions undergo a rapid change at the $K\overline{K}$ threshold. Above 1420 MeV the phase shifts increase with energy faster than those obtained without the polarized-target data. This phase behavior as well as an increase of the modulus of the $a_{1}$-exchange amplitude can be due to the presence of the $f_{0}(1500)$.
Complex signal amplitude analysis for complete fusion nuclear reaction products  [PDF]
Yu. S. Tsyganov
Physics , 2015,
Abstract: A complex analysis has been performed on the energy amplitude signals corresponding to events of Z=117 element measured in the 249Bk+48Ca complete fusion nuclear reaction. These signals were detected with PIPS position sensitive detector. The significant values of pulse height defect both for recoils (ER) and fission fragments (FF) were measured. Comparison with the computer simulations and empirical formulae has been performed both for ER and FF signals.
Polarization Properties of Low Energy Amplitude for $πN \to ππ N$ Reaction  [PDF]
A. A. Bolokhov,V. A. Kozhevnikov,S. G. Sherman,D. N. Tatarkin
Physics , 1998, DOI: 10.1103/PhysRevC.61.055203
Abstract: The theoretical study of cross sections for polarized--target measurements of $ \pi N \to \pi \pi N $ reactions gives evidence that the interplay between the strong contribution from OPE mechanism and the one from isobar exchanges, which is equally strong within isobar half--widths energy region, must result in nontrivial polarization phenomena. The Monte--Carlo simulations for asymmetries in $ \pi^{-} p^{\uparrow} \to \pi^{-} \pi^{+} n $ reaction at $ P_{Lab} = 360 $~MeV/c with the use of theoretical amplitudes found as solutions for unpolarized data at $ P_{Lab} < 500 $~MeV/c provide confirmations for significant effect. The effect is capable to discriminate between the OPE and isobar exchanges and it is sensitive to the OPE parameters in question. This leads to the conclusion that the decisive $\pi N \to \pi \pi N$ analysis, aiming at determination of $ \pi \pi $--scattering lengths, must combine both unpolarized data and polarization information. The appropriate measurements are shown to be feasible at the already existing CHAOS spectrometer.
A further analysis of $Θ^+$ production in $γ+D \to Λ+n+K^{+}$ reaction  [PDF]
V. Guzey
Physics , 2006,
Abstract: We analyse Theta+ production in the gamma+D -> \Lambda+n+K+ reaction and study the dependence of the gamma+D -> \Lambda+n+K+ differential cross section on the nK+ invariant mass and on the momentum of the final neutron p_n. We examine the important role of the interference between the signal and background contributions to the gamma+D -> \Lambda+n+K+ amplitude in the extraction of the Theta+ signal from the gamma+D -> \Lambda+n+K+ cross section. We demonstrate that as a result of the cancellation between the interference and signal contributions, the Theta+ signal almost completely washes out after the integration over p_n. This is consistent with the CLAS conclusion that no statistically significant structures in the analysis of the gamma+D -> \Lambda+n+K+ reaction were observed. Therefore, there is no disagreement between the theory and the experiment and the CLAS result does not refute the existence of the Theta+.
Level Density and Radiative Strength Functions of the $^{237}$U Nucleus from the $(\overline{n},γ)$ Reaction  [PDF]
A. M. Sukhovoj,V. A. Khitrov,V. M. Maslov
Physics , 2009,
Abstract: The independent analysis of the published data on the intensities of the primary gamma-quanta following resonance neutron capture in $^{236}U$ has been performed. Distribution of these intensities about the mean value was approximated in different energy intervals of the primary gamma-transitions and neutrons. Extrapolation of the obtained functions to the zero registration threshold of the primary gamma-transition intensity allowed us to estimate (independently on the other experimental methods) expected level number of both parities for spin values J=1/2, 3/2 and sum of radiative widths for both electric and magnetic dipole gamma-transitions to levels with excitation energy up to $\approx 2.3$ MeV.
Off shell pi N amplitude and the p p->p p pi0 reaction  [PDF]
E. Hernandez,E. Oset
Physics , 1995, DOI: 10.1016/0370-2693(95)00343-J
Abstract: We have used a conventional model for the $pp \rightarrow pp \pi^{0}$ reaction consisting of the Born term plus the $s$-wave rescattering term. As a novelty we have introduced the off shell dependence of the $\pi N$ $s$-wave isoscalar amplitude. This amplitude is appreciably enhanced when one moves to the off shell situations met in the problem and, as a consequence, the $pp \rightarrow pp \pi^{0}$ cross section becomes considerably larger than with the use of the $\pi N$ on shell amplitudes. Two different models for the off shell extrapolation found in the literature have been used and the cross sections obtained are large enough to account for the experimental data, although uncertainties remain due to the incomplete knowledge of the off shell extrapolation.
Relevance of nucleon spin in amplitude analysis of reactions pi(-)p->pi(0)pi(0)n and pi(-)p->eta eta n  [PDF]
M. Svec
Physics , 1996, DOI: 10.1103/PhysRevD.55.4355
Abstract: The measurements of reactions $\pi^- p \to \pi^- \pi^+ n$ and $\pi^+ n \to \pi^+ \pi^- p$ on polarized targets at CERN found a strong dependence of pion production amplitudes on nucleon spin. Analyses of recent measurements of $\pi^- p \to \pi^0\pi^0 n$ reaction on unpolarized targets by GAMS Collaboration at 38 GeV/c and BNL E852 Collaboration at 18 GeV/c use the assumption that pion production amplitudes do not depend on nucleon spin, in conflict with the CERN results on polarized targets. We show that measurements of $\pi^- p \to \pi^0\pi^0 n$ and $\pi^- p \to \eta\eta n$ on unpolarized targets can be analysed in a model independent way in terms of 4 partial-wave intensities and 3 independent interference phases in the mass region where $S$- and $D$-wave dominate. We also describe model-independent amplitude analysis of $\pi^- p \to \pi^0\pi^0 n$ reaction measured on polarized target, both in the absence and in the presence of $G$-wave amplitudes. We suggest that high statistics measurements of reactions $\pi^- p \to \pi^0 \pi^0 n$ and $\pi^- p \to \eta\eta n$ be made on polarized targets at Protvino IHEP and at BNL, and that model-independent amplitude analyses of this polarized data be performed to advance hadron spectroscopy on the level of spin dependent production amplitudes.
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