Energy resolution

As described before, only one view of the calorimeter prototype is equipped with fibers, PMTs and electronics. This choice allows to reduce substantially the prototype cost and is justifyied by the results of the simulations. In fact Figure 15 shows that the improvement due to the second view is simply a scaling factor for the stochastic term ($1/\sqrt{2}$), independent on the energy.

The measured one-view energy resolutions shown in Figure 12 have been obtained by means of gaussian fits to the ADC spectra.

To measure the NO Ecalorimeter resolution function, taking into account both readout views, and expressing the energy in GeV, one-view data points have been fitted by the function

$$\frac{\sigma}{E} = \sqrt{ \left (\frac{a \sqrt{2}^2}{\sqrt{E}} \right ) + b^2 }$$

so that the $a$ and $b$ are the resolution coefficients referred to the fully equipped device. The results of the fits are

$$\frac{\sigma(E)}{E} = \frac{\sqrt{2} \cdot 43.3\%}{\sqrt{E}} \oplus 1.5\%$$

and

$$\frac{\sigma(E)}{E} = \frac{\sqrt{2} \cdot 20.0\%}{\sqrt{E}} \oplus 1\%$$

for pions and electrons respectively.

As shown in Figure 13 the same procedure applied to simulated data provides values of the stochastic resolution terms in good agreement with the experimental ones: $\sigma(E)/E = 0.17 /\sqrt{E}+0.002$ and $\sigma(E)/E = 0.43 /\sqrt{E}+0.033$ respectively.

The small difference between the simulated and measured electron energy resolution, can be explained as due to the underestimation of the critical energy value used in the Montecarlo discussed in the previous section. ¹