Inclusive Pion Double Charge Exchange Research Articles

Inclusive pion double charge exchange in lightp-shell nuclei

We report the results of a series of measurements of the differential cross sections for inclusive pion double charge exchange in $^{6,7}\mathrm{Li}$, $^{9}\mathrm{Be}$, and $^{12}\mathrm{C}$ for positive and negative incident pions of energies 120, 180, and 240 MeV. The data are compared with the predictions of an intranuclear cascade model and a model based on two sequential single charge exchange processes.

Inclusive pion double charge exchange inHe4at intermediate energies

A systematic experimental study of inclusive pion double charge exchange in $^{4}\mathrm{He}$ has been undertaken. The reaction $^{4}\mathrm{He}$$({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}})4p$ was observed at incident energies of 120, 150, 180, 240, and 270 MeV; the $^{4}\mathrm{He}$$({\ensuremath{\pi}}^{\ensuremath{-}},{\ensuremath{\pi}}^{+})4n$ reaction was observed at incident energies of 180 and 240 MeV. At each incident energy, the doubly differential cross section was measured at three to five outgoing pion laboratory angles between ${25}^{\ifmmode^\circ\else\textdegree\fi{}}$ and ${130}^{\ifmmode^\circ\else\textdegree\fi{}}$. At each angle, cross sections were measured over the range of outgoing pion energies from 10 MeV to the kinematic limit for the reaction in which the final state consists of the oppositely charged pion plus four free nucleons. The spectra of outgoing pions are strikingly different from those observed for the inclusive double charge exchange reaction in heavier nuclei but resemble those observed in the $({\ensuremath{\pi}}^{\ensuremath{-}},{\ensuremath{\pi}}^{+})$ reaction in $^{3}\mathrm{He}$. The forward-angle spectra in the $^{3}\mathrm{He}$ and $^{4}\mathrm{He}$ reactions exhibit a prominent peak at high outgoing pion energies. Interpretation of the peaks in $^{3}\mathrm{He}$ ($^{4}\mathrm{He}$) as a three-nucleon (four-nucleon) resonance is ruled out by kinematic analysis. The results of a calculation, wherein the double charge exchange reaction is assumed to proceed as two sequential single charge exchange interactions, suggest that the high-energy peak is naturally explained by this double scattering mechanism. Nonstatic treatment of the $\ensuremath{\pi}N$ interactions and the inclusion of nuclear binding effects appear to be important in reproducing the shape of the energy spectra at forward angles.

Inclusive pion double charge exchange onO16above the Δ resonance

The forward inclusive pion double charge exchange reaction, ^{16}O(pi^-,pi^+)X, at T_0 = 0.50 and 0.75 GeV has been studied in the kinematical region where an additional pion production is forbidden by energy-momentum conservation. The experiment was performed with the SKS spectrometer at KEK PS. The measured ratio of double charge exchange cross-section for these energies dsigma(0.50 GeV)/dOmega / dsigma(0.75 GeV)/dOmega = 1.7 +/- 0.2, disagrees with the value of 7.2 predicted within the conventional sequential single charge exchange mechanism. Possible reasons for the disagreement are discussed in connection with the Glauber inelastic rescatterings.

A dependence of inclusive pion double charge exchange

The A dependence of the forward cross section for inclusive pion double charge exchange on nine target nuclei from 6Li to 209Bi at T0 = 0.59 GeV, as well as the cross section for 6Li, 7Li, and 12C nuclei at T0 = 0.59, 0.75, and 1.1 GeV, was measured with the 3-m magnetic spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The resulting A dependence is well described within the model involving two sequential single charge exchanges and taking into account the renormalization of the amplitude for pion single charge exchange in a nucleus. A relatively weak energy dependence of the cross section for the 6Li, 7Li, and 12C nuclei agrees with the analogous dependence obtained previously for the 16O nucleus, but it contradicts the predicted sharp decrease in the cross section within the model involving two sequential single charge exchanges. This result provides an additional piece of evidence that the contribution from the mechanism of inelastic Glauber rescattering is significant at T0 ≳ 0.6 GeV.

Measurement of inclusive pion double charge exchange on 16O at T 0 ≥ 0.5 GeV with the SKS spectrometer at KEK

The inclusive cross section for pion double charge exchange on 16O at T0 = 0.5 and 0.75 GeV was measured with the superconducting kaon spectrometer (SKS) at KEK in a joint ITEP/KEK experiment. The result shows a relatively weak energy dependence of the measured cross section, which is in contradiction with its rapid drop predicted within the conventional model of two sequential single charge exchanges. The data of this experiment agree with the results that were obtained previously from similar measurements at ITEP and which are indicative of a significant contribution from the mechanism of inelastic Glauber rescatterings for T0 ≳ 0.6 GeV.

Inclusive pion double charge exchange on 16O at 0.6–1.1 GeV

The inclusive pion double charge exchange (DCX) on oxygen nuclei has been measured in the region where additional pion production is kinematically forbidden. The experiment was performed at the ITEP PS at incident π − kinetic energies T 0=0.59, 0.75 and 1.1 GeV. The integrated forward differential cross section was found to decrease with energy slowly. At 1.1 GeV it exceeds the theoretical prediction within the conventional sequential single charge exchange mechanism with a neutral pion in the intermediate state (Glauber elastic rescattering) by about a factor of five. The sequential mechanism with two pions in the intermediate state (Glauber inelastic rescatterings), which was proposed recently, seems to be able to explain the observed energy dependence and allows to predict the DCX cross section at higher energies.

Systematics of inclusive pion double charge exchange in the delta resonance region.

A systematic study of inclusive pion double charge exchange is reported for nuclei between A=16 and A=208. The doubly differential cross sections for the A(${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) and A(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{+}$) reactions in $^{16}\mathrm{O}$, $^{40}\mathrm{Ca}$, $^{103}\mathrm{Rh}$, and $^{208}\mathrm{Pb}$ were measured at incident energies between 120 and 270 MeV at three to five outgoing pion angles. Pion spectra were measured over the energy range from 10 MeV to the kinematic limit for double charge exchange. Integrating these spectra over outgoing pion energy generated angular distributions, and subsequently integrating these angular distributions generated total reaction cross sections. The shapes of the measured spectra are compared with those determined by the distribution of events in four-body phase space and with those predicted by a model in which the pion undergoes two sequential single charge exchanges on nucleons in a Fermi gas. The cross sections are compared with predictions of cascade calculations in which more than two interactions, including pion absorption and scattering without charge exchange, may occur.

Dependence of the cross section for inclusive pion double charge exchange on nuclear mass and charge.

Total reaction cross sections for inclusive pion double charge exchange have been obtained at incident pion energies of 180 and 240 MeV for /sup 4/He, /sup 6.7/Li, /sup 9/Be, /sup 12/C, /sup 16/O, /sup 40/Ca, /sup 103/Rh, and /sup 208/Pb. An explanation of the dependence of these cross sections upon the mass and charge of the target nucleus and the charge of the incident pion is suggested in terms of a phenomenological model in which successive single-charge-exchange processes compete with more probable processes such as quasifree scattering.

Inclusive pion double charge exchange in 4He.

The pion spectra observed in the inclusive double-charge-exchange reactions $^{4}\mathrm{He}$(${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$)4p and $^{4}\mathrm{He}$(${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$,${\ensuremath{\pi}}^{+}$)4n are strikingly different from those in heavier nuclei, exhibiting a prominent peak at high outgoing pion energies. The shapes of these spectra, while qualitatively consistent with two sequential single-charge-exchange processes, are not yet quantitatively understood.

Inclusive pion double charge exchange in 16O and 40Ca.

The first systematic study of inclusive pion double charge exchange in nuclei is reported. Doubly differential cross sections for the reactions $^{16}\mathrm{O}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})X$ and $^{40}\mathrm{Ca}({\ensuremath{\pi}}^{+}, {\ensuremath{\pi}}^{\ensuremath{-}})X$ have been measured at incident pion energies of 120, 150, 180, 210, 240, and 270 MeV at three to five angles in the range from 25\ifmmode^\circ\else\textdegree\fi{} to 130\ifmmode^\circ\else\textdegree\fi{} with complete coverage of the outgoing pion energy spectrum. Similarly, the reactions $^{16}\mathrm{O}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{+})X$ and $^{40}\mathrm{C}({\ensuremath{\pi}}^{\ensuremath{-}}, {\ensuremath{\pi}}^{+})X$ were studied at 180, 210, and 240 MeV at three angles.