Pion-induced pion production on deuterium: a quasifree process

doi:10.1016/0375-9474(92)90642-W

Nuclear Physics A

Volume 548, Issue 4, 26 October 1992, Pages 562-578

https://doi.org/10.1016/0375-9474(92)90642-W Get rights and content

Abstract

A detailed experimental analysis of the π⁺d → π⁺π⁻pp in-plane coincidence data first presented by Rui et al. is compared to an expanded version of the Oset and Vicente-Vacas model for pion-induced pion production on a free nucleon. This extended model averages over Fermi motion to describe the assumed quasifree nature of the process occurring on the deuteron and includes nine additional diagrams to account for the $N^{∗} → N (ππ)_{p-wave}$ reaction channels. Experimental effects such as pion energy loss in the target and in the detectors, pion decay and muon detection are investigated and incorporated into the comparison of experimental data and theory. Inclusion of Fermi motion was found to be essential to provide good agreement between data and model confirming the quasifree nature of the reaction. When compared to the total-cross-section measurements of Manley et al., the free-reaction model yields a model-dependent estimate of the overall strength of the diagram containing the $N^{∗} → N (ππ)_{s-wave}$ vertex.

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The ππ interaction in nuclear matter from a study of the π+A→π+π±A′ reactions
2000, Nuclear Physics A
The pion-production reactions $π^{+} A→π^{+} π^{±} A′$ were studied on $^{2}$ H, $^{12}$ C, $^{40}$ Ca, and $^{208}$ Pb nuclei at an incident pion energy of $T_{π^{+}} =283$ MeV. Pions were detected in coincidence using the CHAOS spectrometer. The experimental results are reduced to differential cross sections and compared to both theoretical predictions and the reaction phase space. The composite ratio $C$ $_{ππ}^{A}$ between the $π^{+} π^{±}$ invariant masses on nuclei and on the nucleon is also presented. Near the $2m_{π}$ threshold pion pairs couple to $(ππ)_{I=J=0}$ when produced in the $π^{+} →π^{+} π^{−}$ reaction channel. There is a marked near-threshold enhancement of $C_{π^{+}π^{−}}^{A}$ which is consistent with theoretical predictions addressing the partial restoration of chiral symmetry in nuclear matter. Furthermore, the behaviour of $C_{π^{+}π^{−}}^{A}$ is well described when the restoration of chiral symmetry is combined with standard $P$ -wave renormalization of pions in nuclear matter. On the other hand, nuclear matter only weakly influences $C_{π^{+}π^{+}}^{A}$ , which displays a flat behaviour throughout the energy range regardless of $A$ .
The role of the Roper resonance in np → d(ππ)0
1999, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
In this work, a model for the np→d(ππ)⁰ reaction is developed. It is shown that the structure of the deuteron momentum spectra for a neutron beam momentum of 1.46 GeV/c can be explained as a consequence of the interplay of two mechanisms involving the excitation of the $N^{∗} (1440)$ resonance and its subsequent decay into N(ππ)^T=0_S-wave and Δπ respectively. The relevance of the present analysis for the study of the Roper excitation and decay properties is discussed.
π+ → π+π± on deuterium at T<inf>π+</inf> = 283 MeV: The CHAOS collaboration
1998, Nuclear Physics A
New experimental results on the π⁺d → π⁺π⁻pp and π⁺d → π⁺π⁺nn reactions at T_π¹ = 283 MeV are presented. In-plane coincidence data were taken with the CHAOS spectrometer using pions from the M11 channel at TRIUMF. Because of the quasi-free nature of the pion-production reaction, the present study is equivalent to studying the elementary π⁺N → π⁺π^±N reactions on protons and neutrons simultaneously. These exclusive measurements provide a set of many-fold differential cross sections which are an ideal testing ground for microscopic models describing the πN → ππN reaction. The interpretation of the data relies on a model which is based on effective chiral Lagrangians to describe the piece of the reaction that includes only π's and N's, and on effective Lagrangians to account for intermediate Δ's and $N^{∗}' s$ . The measured many-fold differential cross sections are used to constrain some parameters of the model (ξ, f_Δ, C, $g_{N^{∗}Δπ}$ and $g_{N^{∗}Nπ}$ ). Finally, the π⁺π^± invariant mass distributions display no evidence of strongly interacting pion pairs in either the I = J = 0 or the I = 2J = 0 channels.
Pion cloud contribution to the s-wave repulsion in pionic atoms
1995, Nuclear Physics, Section A
The nuclear pion cloud contribution to the pion self-energy for pionic atoms is evaluated and one finds large cancellations between terms involving the ππ amplitude and other terms originating from the chiral lagrangian partners. While the individual terms depend strongly on the off-shell extrapolation of the ππ amplitude, the sum is model independent within the Olson and Turner family of chiral lagrangians keeping ξ + 4η constant, as previously found for the πN → ππN and pion double-charge exchange in nuclei, and vanishes in the limit of m_π → 0. One finds a small net repulsion which is however too small to account for the “missing” s-wave repulsion. A revision of the present status of the problem of the “missing” s-wave repulsion is done at the end.
A model for the γp→ π+π-p reaction
1994, Nuclear Physics, Section A
We have studied the γp→ π⁺π⁻p reaction using a model which includes N, Δ (1232), N∗(1440) and N∗(1520) intermediate baryonic states and the ρ-meson as intermediate 2π-resonance. The model reproduces fairly well experimental cross sections below E_γ = 800 MeV and invariant-mass distributions even at higher energies. One of the interesting findings of the study is that the $γ N → N^{∗} (1520) → Δπ$ process is very important and interferes strongly with the dominant Δ Kroll-Ruderman term to produce the experimental peak of the cross section. We show that the study of the reaction can provide information on some couplings, concretely the $N^{∗} (1520) → Δπ$ . We also find that the pion energy distributions for different photon energies, which have not been measured so far, contain very valuable information on the dynamics of the reaction. Finally, the analogies and differences with respect to the πN → 2πN reaction are also discussed.
Threshold behaviour of the π+π- invariant mass in nuclei
1993, Nuclear Physics, Section A
We present π⁺π⁻ invariant-mass distributions between 300 and 380 MeV for the ²H, ⁴He, ¹⁶O, $^{208} Pb (π^{+}, π^{+} π^{−})$ reaction at an incident π⁺ energy of 280 MeV. A prominent feature is the shift of their maximum downward to the 2m_π threshold as A increases. This behaviour finds a qualitative explanation in the framework of a model that investigates the modification of the strength function for an interacting (ππ)_{I = L = 0} system embedded in the nuclear medium. Also, the π⁺π⁻ invariant-mass cross sections are compared with the predictions of an A(π⁺, π⁺π⁻) model that uses a microscopical approach for the elementary process of pion production, πN → ππ N. Four-fold differential cross sections as a function of the energy of outgoing π⁺ and p, and missing-mass distributions for the A(π⁺, pπ⁻) reaction are also presented for some of the examined nuclei. The experimental results are discussed within the framework of the two available models.

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¹: Present address: Physics Department, Carnegie Mellon University, Pittsburgh, PA 15213, USA.

²: Present affiliation: IMP/ETH, mailing address: EP-Div CERN, 1211 Geneva 23, Switzerland.

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Nuclear Physics A

Abstract

References (31)

Phys. Reports

Nucl. Phys.

Nucl. Phys.

FOWL, A general Monte Carlo phase space program

Pions and nuclei

Phys. Rev. Lett.

Current algebra and application to particle physics

Phys. Rev.

Nuovo Cim.

Phys. Rev.

Phys. Rev.

Phys. Lett.

Phys. Lett.

Sov. J. Nucl. Phys.

Phys. Rev.

Cited by (14)

The ππ interaction in nuclear matter from a study of the π<sup>+</sup>A→π<sup>+</sup>π<sup>±</sup>A′ reactions

The role of the Roper resonance in np → d(ππ)<sup>0</sup>

π<sup>+</sup> → π<sup>+</sup>π<sup>±</sup> on deuterium at T<inf>π+</inf> = 283 MeV: The CHAOS collaboration

Pion cloud contribution to the s-wave repulsion in pionic atoms

A model for the γp→ π<sup>+</sup>π<sup>-</sup>p reaction

Threshold behaviour of the π<sup>+</sup>π<sup>-</sup> invariant mass in nuclei