CBM Progress Report 2006 - GSI

Detector Developments CBM Progress Report 2006
π efficiency (%)
10
1
10 -1
10
1
10 -1
p=1 GeV/c
p=1.5 GeV/c
90% e eff.
20/500/120
20/200/220
0 2 4 6 8 10
Nr. layers
Figure 3: Extrapolated electron/pion identification performance
as a function of the number of layers.
menta the e/π separation gradually degrades (a factor of
4 worse pion rejection is expected for 10 GeV/c [5]) due
to the saturation of the TR yield beyond 2 GeV/c [3] and
the pion dE/dx relativistic rise [4]. As seen in Fig. 3, the
rejection power (expressed as π efficiency at 90% electron
efficiency) is comparable for the two radiators for p=1.5
GeV/c and this is expected to be true also for higher momenta.
The radiator with larger Nf is expected to produce
a larger TR yield, but it appears that its smaller foil gap
(d2=200 µm) leads to a smaller TR yield per foil compared
to the radiator with d2=500 µm. This makes the latter option
a more suited choice, both because a lighter radiator is
prefered in a tracking TRD (as envisaged in CBM [1]) and
because of easier manufacturing and less sensitivity to foil
gap nonuniformities.
In Fig. 4 we show an example of the dependence on the
measured energy deposit spectra for hadrons and electrons
for different local rate values. From these results we could
conclude that the effect of high rates appears as pile-up, not
perfectly rejected through our segmented scintillator detectors,
rather than producing a reduction of the signal, expected
if space charge was present.
In Fig. 5 we present the rate dependence of the electron
identification with respect to hadrons as measured with one
layer at the momentum of 1.5 GeV/c. While the study
of e/π − separation could only be done at low rates (10
kHz/cm 2 ), the high rates are achieved with a positive beam.
In this case, the beam content is dominated by the protons
and, due to their larger energy loss, the electron separation
is in this case clearly worse. The separation is not much
36
Yield (keV -1 )
10 -1
10 -2
10 -3
π + +p
Xe-CO 2 (85-15)
Rate (kHz/cm 2 )
16
36
80
120
0 5 10 15 20
e +
p=1.5 GeV/c
2 mm (20/500/120)
0 5 10 15 20
Energy deposit (keV)
Figure 4: Energy deposit spectra for hadrons and electrons
for different local rate values.
Efficiency (%)
90
85
80
75
70
65
60
55
50
45
40
90% e eff., 1 layer
p+π +
π -
2mm (20/500/120)
3mm (20/200/220)
10 10 2
Rate (kHz/cm 2 )
Figure 5: Rate dependence of the electron separation with
respect to hadrons as measured with one layer.
influenced by rate, but a degradation occurs beyond 100
kHz/cm 2 . Extrapolated to 10 layers this implies a reduction
of the hadron rejection by a factor of about 3 at our
highest rates. The trend is similar for the detectors with
anode wire pitch of 2 and 3 mm.
This work is partially funded by the EU Integrated Infrastructure
Initiative Project HADRON PHYSICS under
Contract No. RII3-CT-2004-506078. We acknowledge the
help from G. Augustinski, M. Ciobanu, N. Kurz and Y.
Leifels.
References
[1] A. Andronic, Nucl. Instrum. Meth. A563 (2006) 349.
[2] H.G. Essel, N. Kurz, IEEE Trans. Nucl. Sci. 47 (2000) 337.
[3] A. Andronic et al., Nucl. Instrum. Meth. A558 (2006) 516.
[4] A. Andronic et al., Nucl. Instrum. Meth. A519 (2004) 508.
[5] R. Bailhache, C. Lippmann, Nucl. Instrum. Meth. A563
(2006) 310.