Proton-proton Final-state Interaction Research Articles

Resonant behaviour in double charge exchange reaction of [formula omitted]-mesons on the nuclear photoemulsion

The invariant-mass spectra of the pp π - and pp systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the pp π - invariant-mass spectrum, while the M pp spectrum exhibits a strong Migdal–Watson effect of the proton-proton final-state interaction. These findings are in favor of the NN-decoupled NN π pseudoscalar resonance with T = 0 called d ′ .

Near-Threshold Production ofϕMesons inppCollisions

The pp->pp phi reaction has been studied at the Cooler Synchrotron COSY-Juelich, using the internal beam and ANKE facility. Total cross sections have been determined at three excess energies epsilon near the production threshold. The differential cross section closest to threshold at epsilon=18.5 MeV exhibits a clear S-wave dominance as well as a noticeable effect due to the proton-proton final state interaction. Taken together with data for pp omega-production, a significant enhancement of the phi/omega ratio of a factor 8 is found compared to predictions based on the Okubo-Zweig-Iizuka rule.

Resonant behaviour in double charge exchange reaction of πmesons on the nuclear photoemulsion

The invariant mass spectra of the $pp\pi^-$ and $pp$ systems produced in the double charge exchange (DCX) of positively charged pions on photoemulsion are analysed. A pronounced peak is observed in the $pp\pi^-$ invariant mass spectrum, while the $M_{pp}$ spectrum exhibits a strong Migdal-Watson effect of the proton-proton final state interaction. These findings are in favor of the $NN$-decoupled $NN\pi$ pseudoscalar resonance with T=0 called $d'$.

Measurement of theH2(d,He2)2nreaction atEd=171 MeV and implications for the neutron-neutron scattering length

A measurement of the H-2(d,He-2)(2)n charge-exchange reaction at E-d=171 MeV has been performed in order to study the interaction of the di-neutron system. Spectroscopy of the neutron-neutron final-state interaction with a resolution of about 115 keV (FWHM) was achieved by measuring the momentum of He-2 at forward scattering angles. In the experiment the two protons of the unbound He-2 are momentum analyzed with a magnetic spectrometer and detected with the same detector. A simple reaction theory is employed in order to obtain information about the neutron-neutron interaction from the measured cross section data. The validity of the impulse approximation for the d ->He-2 transition at intermediate energies is discussed and compared to the Watson-Migdal theory of the proton-proton final-state interaction. Predictions of the impulse approximation for the analog transition d ->(2)n are confronted with experimental data. A procedure to extract the neutron-neutron scattering length a(nn) from this comparison is presented. The result is compatible with the recommended value of a(nn)=-18.6(+/- 0.4) fm.

Total and differential cross-sections for the $pp\rightarrow pp\eta^\prime$ reaction near threshold

The \(\eta^\prime\)-meson production in the reaction \(pp\rightarrow pp\eta^\prime\) has been studied at excess energies of Q = 26.5, 32.5 and 46.6 MeV using the internal beam facility COSY-11 at the cooler synchrotron COSY. The total cross-sections as well as one angular distribution for the highest Q-value are presented. The excitation function of the near-threshold data can be described by a pure s-wave phase space distribution with the inclusion of the proton-proton final-state interaction and Coulomb effects. The obtained angular distribution of the \(\eta^\prime\)-mesons is also consistent with pure s-wave production.

Near-Threshold Production ofωMesons in thepp→ppωReaction

The total cross section for $\ensuremath{\omega}$ production in the $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}\ensuremath{\omega}$ reaction has been measured at 5 c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold $\ensuremath{\varphi}$ and $\ensuremath{\omega}$ production is, to within relatively large uncertainties, consistent with the predictions of a simple one-pion-exchange model. The degree of violation of the Okubo-Zweig-Iizuka rule is similar to that found in the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}n\ensuremath{\omega}/\ensuremath{\varphi}$ reactions.

Higher partial waves in pp→ ppη near threshold

Exclusive measurements of the production of η-mesons in the pp→ ppη reaction have been carried out at excess energies of 16 and 37 MeV above threshold. The deviations from phase space are dominated by the proton-proton final state interaction and this influences particularly the energy distribution of the η-meson. However, evidence is also presented at the higher energy for the existence of an anisotropy in the angular distributions of the η-meson and also of the final proton-proton pair, probably to be associated with D-waves in this system interfering with the dominant S-wave term. The sign of the η angular anisotropy suggests that ρ-exchange is important for this reaction.

Particle decay ofBe6

The particle decay of the ground state of $^{6}\mathrm{Be}$ was observed following population in the $^{6}\mathrm{Li}(^{3}\mathrm{He}, t)^{6}\mathrm{Be}$ reaction. The $\ensuremath{\alpha}$ particle decay spectrum corresponds to the ordinary three body phase space shape for energies above about 100 keV in the $^{6}\mathrm{Be}$ center-of-mass system. At lower energies the relative yield exceeds the available phase space. It is shown that neither the phase space spectrum modified by the proton-proton final state interaction nor the spectrum corresponding to sequential decay through the $^{5}\mathrm{Li}$ ground state have shapes consistent with the data. The enhanced yield of low energy $\ensuremath{\alpha}$ particles is not accounted for by either process.RADIOACTIVITY $^{6}\mathrm{Be}$; measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}})$. NUCLEAR REACTIONS $^{6}\mathrm{Be}$; $^{6}\mathrm{Li}(^{3}\mathrm{He}, t)^{6}\mathrm{Be}\ensuremath{\rightarrow}\ensuremath{\alpha}+2p$, $E=24$ MeV measured ${E}_{t}$, ${E}_{\ensuremath{\alpha}}$ coin.

Proton-Proton Final-State Interaction in theH2(p,n)2pReaction

Neutron spectra from the $^{2}\mathrm{H}(p,n)2p$ reaction have been measured at nine proton energies between 16 and 26 MeV. The high-energy portions of the neutron spectra taken at a laboratory angle of 3.5\ifmmode^\circ\else\textdegree\fi{} have been analyzed with impulse approximation calculations of the proton-proton final-state interaction to extract the proton-proton scattering length. The average value of the scattering length determined from these measurements is within approximately 1 fm of the - 7.8-fm result of $pp$ scattering but is not independent of the details of the comparison of experimental and calculated spectra. Experimental requirements for a determination of the neutron-neutron scattering length from the $^{2}\mathrm{H}(n,p)2n$ reaction are discussed.

A simple theory of the proton-proton final-state interaction in the reaction d + p → p + p + n

The amplitude for deuteron break-up in deuteron-proton collisions including Coulomb final-state interactions (in all partial waves) is derived analytically. The calculation is based on the assumption of a two-step reaction with a break-up mechanism of zero range. The nuclear final-state interaction is taken into account under the same approximations in the s-waves. A comparison with experiment indicates a clear improvement compared to the Watson-Migdal theory.

Proton-proton final-state interaction in the 2H(p, pn)p reaction

Abstract The 2 H(p, pn) preaction has been studied under conditions suitable for the observation of the proton-proton final-state interaction at relative energies in the p-p system between 0.0 and 2.5 MeV. A kinematically complete experiment has been performed, detecting protons and neutrons in coincidence, for bombarding energies between 8 MeV and 13 MeV. Models based on the Watson-Migdal theory have been used to fit the experimental spectra and the possibility of extracting two-nucleon scattering parameters has been investigated. A value of 7.7±0.6 fm for the proton-proton scattering length has been obtained.

Proton-proton final-state interaction in the three-nucleon reaction p+d → p+p+n

The three-nucleon reaction p+d → p+n+n has been investigated at a deuteron bombarding energy of 52.3 MeV. A kinematically complete experiment was carried out with the aim to observe the proton-proton final-state interaction. By using the Watson-Migdal model a proton-proton scattering length of a pp = −7.5 ± 0.5 fm is extracted from the measurements.

Proton-proton final state interaction in the p + 3He reaction

The proton-proton final state interaction was studied using the 3He + p → d + p + p reaction both in single counter, kinematically “incomplete” ( E p = 30.2 and 46.0 MeV) and angular correlation, kinematically “complete” ( E p = 46.5 MeV) experiments. In the single counter experiment the angular dependence of the final state interaction was determined between ϑ lab = 10° and ϑ lab = 50°. A Watson-Migdal calculation was used to fit the experimental deuteron spectra near the high-energy cutoff; the calculated distributions obtained for a choice of reasonable parameters were found to be wider at the peak than the experimental data indicated. The angular correlation experiments were performed at counter settings at which the contributions from p-p final state interaction were expected to be relatively large; these particular experiments indicated: (i) that p-p final state interaction contributes significantly to the three-body process and, (ii) that the proton pair is preferentially emitted with an internal energy of E 2p ≈ 0.4 MeV. A Watson-Migdal calculation applied to the angular correlation experiments gave good agreement with the experimental results. An explanation for the difference in fitting single counter or angular correlation experiments is given.

Proton-proton final state interaction in the 3He (p, pd)p reaction

The final state p-p interaction has been observed by means of a 3He(p, pd)p angular correlation experiment. It was found that the probability of formation of the singlet state is most pronounced for an internal energy of the two-proton system of ≈ 0.4 MeV.