# Measurement of $\gamma$ rays from the giant resonances excited by $^{12}$C$(p,p')$ reaction at 392 MeV and 0$^{\circ}$

## TL;DR

This study measured gamma-ray emission probabilities from giant resonances excited by a 392 MeV proton reaction on carbon, providing new data and analysis on gamma-ray emission behavior in this energy range.

## Contribution

The paper presents the first detailed measurement of gamma-ray emission probabilities from giant resonances at this energy, calibrated with known states, and compares results with statistical model calculations.

## Key findings

- Gamma-ray emission probability peaks at 53.3% around 27 MeV excitation energy.
- Emission probability starts from zero at 16 MeV and decreases after the peak.
- Results agree with Hauser-Feshbach model predictions within uncertainties.

## Abstract

We measured both the differential cross section ($\sigma_{p,p^\prime}$ $=d^2\sigma/d\Omega dE_{x}$) and the $\gamma$-ray emission probability ($R_\gamma(E_x)$ $=\sigma_{p,p^\prime\gamma}$/$\sigma_{p,p^\prime}$) from the giant resonances excited by $\rm^{12}C$(\textit{p,p}$^\prime$) reaction at 392 MeV and 0$^\circ$, using a magnetic spectrometer and an array of NaI(Tl) counters. The absolute value of $R_\gamma(E_x)$ was calibrated by using the well-known $\gamma$-ray emission probability from $\rm^{12}C^* ( 15.11$ MeV, $ 1^+$, $T=1$) and $\rm^{16}O^* ( 6.9$ MeV, $2^+$, $T=0$) states within 5\% uncertainty. We found that $R_\gamma(E_x)$ starts from zero at $E_x=16$ MeV, increases to a maximum of 53.3$\pm$0.4$\pm$3.9\% at $E_x=27$ MeV and then decreases. We also compared the measured values of $R_\gamma(E_x)$ with statistical model calculation based on the Hauser-Feshbach formalism in the energy region $E_x=$ 16-32 MeV and discussed the features of $\gamma$-ray emission probability quantitatively.