Search for the giant pairing vibration through ($p$,$t$) reactions around 50 and 60 MeV

The existence of the giant pairing vibration (GPV) in ${}^{120}\mathrm{Sn}$ and ${}^{208}\mathrm{Pb}$ was investigated using the ($p$,$t$) reaction at incident proton energies of 50 MeV and 60 MeV for the scattering angles 0${}^{°}$ and 7${}^{°}$. No clear signature for the GPV was found, providing an upper limit for the cross section of ${\sigma }_{\max }$ = 0.2 mb. Theoretical interpretations for the low cross section of the GPV are discussed.

Figure 1

Particle identification spectrum of the pulse height of the first scintillator versus the TOF for a 0${}^{°}$ measurement at $E_p$ = 50 MeV. Tritons and deuterons are clearly indicated. All the other events represent background at 0${}^{°}$ due to the internal beam stop.

Figure 2

Excitation energy spectrum of ${}^{118}\mathrm{Sn}$ for the 0${}^{°}$ measurement at $E_p$ = 50 MeV. The bin width is 30 keV/bin. The data acquired for various spectrometer field settings are displayed in different colors.

Figure 3

Excitation energy spectrum of ${}^{118}\mathrm{Sn}$ for the 0${}^{°}$ measurement at $E_p$ = 50 MeV (upper curve) and $E_p=60$ MeV (middle curve) and the 7${}^{°}$ measurement at $E_p$ = 60 MeV (lower curve). The bin width is 67 keV/bin. The data are taken for the 0${}^{°}$ measurement at $E_p$ = 60 MeV stops at 14 MeV excitation energy.

Figure 4

Excitation energy spectrum of ${}^{118}\mathrm{Sn}$ for the 0${}^{°}$ measurement at $E_p$ = 50 MeV. The linear background, deep-hole states (around 9 MeV), fit for a possible GPV (around 12 MeV), oxygen contaminant (around 13.5 MeV) and total fitting function are shown. The bin width is 67 keV/bin and a GPV width of $\sigma =800$ keV was assumed.