NeuLAND - FAIR

counts
70
60
50
40
30
20
10
0
15 15.5 16 16.5 17
time (ns)
Figure 3.2.: The measured time difference as shown in the left part of figure 3.1, but
with a condition on central hits in order to exclude position dependencies.
time difference spectrum of bar S1 and S2 of 186 ps, thus a time resolution of σt=132 ps
for each bar, with a condition on central hits. We interpret this increase of about 50%
for the time resolution to be similar shared in between the two modifications, i.e. the
increase in length, causing a loss of light, and the read-out with the more economical
photomultiplier. The effect of the bar length was studied independently in experiments
with single-electron beams, see section 3.3. We observe about 25% degradation, when
going from 2 to 3 m length.
3.3. Studies with 31 MeV Electrons
Detailed studies of the detector response of the scintillator bars were performed using the
single-electron per bunch mode of the superconducting electron linac ELBE at HZDR
Dresden-Rossendorf. The electrons had an energy of 31 MeV. For the time reference
determination a similar technique as for the tests of resistive-plate chambers at ELBE
was applied, see appendix B for details. The energy loss of these minimum ionizing
particles (MIPs) is slightly less compared to the 500 MeV proton beams (see section 3.2).
In this experiment the two bars of sizes 200×3×3 cm 3 and 200×5×5 cm 3 were exposed
to the beam individually. As light readout we selected again the 1 inch photomultiplier
R8619, as in the second part of the proton tests. The time resolution was measured
versus the radio-frequency signal from the accelerator, which delivers a very precise
timing information. Together with the resolution of our readout electronics TacQuila,
the time resolution of this reference signal amounted to σref =30 ps, see figure 3.3.
From the measurement with the 2 m long bars we derive a time resolution of σ200×3×3 =154 ps
31