[Paper Review] Inclusive Pion Double Charge Exchange above 0.5 GeV

M. J. Vicente Vacas, M. Kh+1 more|arXiv (Cornell University)|Dec 15, 1994

High-Energy Particle Collisions Research3 citations

TL;DR

This paper develops a cascade model to study pion-induced multichannel reactions in nuclei at energies above 0.5 GeV, with a focus on inclusive double charge exchange (DCX). It finds that conventional two-step quasielastic SCX mechanisms contribute negligibly above 0.7 GeV, opening a window for exotic DCX mechanisms to dominate, especially at forward angles and high outgoing pion energies, where pion production effects are minimized.

ABSTRACT

A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SCX, DCX, absorption and pion production) at pion energies above 0.5 GeV. Special attention has been paid to pion double charge exchange. Pion production is a determinant feature in the high energy pion nucleus reactions, and the DCX signal not related to pion production is sizeable only at forward angles and for high energy outgoing pions. The contribution to DCX of the conventional mechanism, with two quasielastic SCX steps decreases very fast as a function of the energy and reaches very low values at energies above 0.7 GeV. This opens the opportunity of having sizeable contributions of exotic mechanisms that are negligible at the delta resonance energies.

Motivation & Objective

• To model multichannel pion-nucleus reactions (quasielastic, SCX, DCX, absorption, pion production) at energies above 0.5 GeV.
• To isolate and quantify the contribution of conventional two-step quasielastic SCX mechanisms to double charge exchange (DCX).
• To assess the potential for exotic DCX mechanisms to contribute significantly when conventional mechanisms become negligible.
• To identify kinematic regions—particularly forward angles and high outgoing pion energies—where DCX signals unrelated to pion production can be isolated.
• To evaluate the role of pion production as a dominant background in high-energy inclusive DCX measurements.

Proposed method

• A cascade model is constructed to simulate sequential and simultaneous processes in pion-nucleus interactions.
• The model includes multiple channels: quasielastic scattering, single charge exchange (SCX), double charge exchange (DCX), pion absorption, and pion production.
• The conventional DCX mechanism is modeled as two successive quasielastic SCX steps, each involving intermediate nucleon transitions.
• Kinematic cuts are applied to isolate DCX events not originating from pion production, focusing on forward-angle and high-energy outgoing pion configurations.
• Energy dependence of the conventional DCX mechanism is calculated and compared to experimental kinematic constraints.
• The model evaluates the relative contributions of exotic mechanisms by extrapolating from the suppression of conventional pathways.

Experimental results

Research questions

• RQ1 How does the contribution of the conventional two-step quasielastic SCX mechanism to DCX vary with pion beam energy above 0.5 GeV?
• RQ2 In which kinematic regions (angles, outgoing pion energies) can DCX signals be cleanly separated from pion production backgrounds?
• RQ3 To what extent do exotic DCX mechanisms become relevant when conventional mechanisms are suppressed at high energies?
• RQ4 What is the role of pion production as a background in inclusive DCX measurements at energies above 0.5 GeV?
• RQ5 Can forward-angle, high-energy outgoing pion configurations serve as a clean signature for non-pion-production DCX processes?

Key findings

• The conventional two-step quasielastic SCX mechanism for DCX decreases rapidly with increasing pion energy and becomes negligible above 0.7 GeV.
• At energies above 0.7 GeV, the DCX signal not related to pion production is sizeable only in forward angles and for high-energy outgoing pions.
• The suppression of conventional DCX mechanisms at high energies creates a favorable kinematic window for detecting exotic DCX mechanisms.
• Pion production remains a dominant feature in high-energy pion-nucleus reactions and constitutes a major background for inclusive DCX measurements.
• The model indicates that experimental searches for exotic DCX mechanisms should prioritize forward-angle and high-energy outgoing pion configurations to minimize contamination from pion production.
• The results suggest that future high-energy inclusive DCX experiments could isolate non-conventional mechanisms by focusing on specific kinematic regions where conventional contributions are minimal.