The missing mass resolutions in $\gamma + d \rightarrow p + X$ and $\gamma + d \rightarrow p + \pi^- + X$

The missing mass distribution of events when a proton is required in the final state is shown in 13. As expected (see Fig.13 bottom plot), the requirement to have a hit only in a single sector, significantly reduces the background. The missing mass spectra fitted by a sum of Gaussian and exponent (for the background subtraction) is shown in Fig.14. The mean for all events (integrated over all photon and proton energies) is 0.9367 with a $\sigma = 0.0148$. Detailed dependence of the mean of the missing mass spectra for deuteron photo-disintegration events as a function of different kinematic variables is shown in Fig.15. The Fig. 16 shows the actual missing mass distributions, for low, medium and high energy protons. The mass (neutron) is clearly decreasing with the increasing of the proton energy. Similar behavior could be seen with much higher statistics in the missing mass spectra behavior from $\gamma + d \rightarrow p + \pi^- + X$.

  

Figure 13: The missing mass distribution for $\gamma + d \rightarrow p + X$. The solid line includes all events, the dashed is with additional requirement to have just one sector hit in Level 2 (TGBI) bank, and the dotted is with requirement to have just one track in the hit base (HBTR) bank. The Bottom plot shows the ratio of dashed and dotted curves from top plot to the solid one.

  

Figure 14: The missing mass resolution in $\gamma + d \rightarrow p + X$.

  

Figure 15: The missing mass mean (defined in 2$\sigma$ interval) as a function of the proton energy, polar angle, azimuthal angle and the energy of the incoming photon. The filled circles include all data and open circles only events with single sector hits (LVL2).

  

Figure 16: The missing mass distribution in $\gamma + d \rightarrow p + X$ for 3 different proton energy ranges.

  

Figure 17: The missing mass spectra for $\gamma + d \rightarrow p + \pi^- + X$.

The dependence of the mean of the missing mass spectra for slow protons in $\gamma + d \rightarrow p + \pi^- + p$(see Fig.17) as a function of different kinematic variables is shown in Fig.18 with corresponding distributions in 19. The mean of the mass is decreasing at high energies of protons. Similar behavior could be seen in the same dependence from $\pi^-$ energy and angles (see Fig 20. High energy $\pi^-$ corresponds to low energy protons.

The distributions of slow protons reconstructed using the cut on the missing mass are shown in Fig. 22. There is a reasonable amount of identified (undetected) protons to be used in the acceptance and efficiency study of proton reconstruction as a function of different kinematic variables (see Fig.23).

The missing mass distribution from reconstructed data was also compared with MC reconstructed distributions (see Fig.21). The normalization was done using the incoming photon spectra.

  

Figure 18: The mean of the missing mass spectra for slow protons in $\gamma + d \rightarrow p + \pi^- + p$ as a function of the first (fast) proton energy, polar angle, azimuthal angle and the energy of the incoming photon.

  

Figure 19: The missing mass distribution in $\gamma + d \rightarrow p + \pi^- + X$ for 4 different proton energy ranges.

  

Figure 20: The mean of the missing mass spectra for slow protons in $\gamma + d \rightarrow p + \pi^- + p$ as a function of the $\pi^-$ energy, polar angle, azimuthal angle and the energy of the incoming photon.

  

Figure 21: MC/DATA comparison of missing mass spectra for $\gamma + d \rightarrow p + \pi^- + X$

  

Figure 22: Energy, polar and azimuthal angle distributions of slow protons in $\gamma + d \rightarrow p + \pi^- + p$.

captypefigure

Energy distributions of slow protons in $\gamma + d \rightarrow p + \pi^- + p$, reconstructed from the missing mass (top) and detected directly (middle). The bottom plot shows their ratio.