CBM Progress Report 2006 - GSI

CBM Progress Report 2006 Detector Developments
Progress in the CBM-TOF wall, R&D and simulation ∗
D. González-Díaz 1 , E. Cordier 2 , and A. Semak 3
1 GSI, Darmstadt, Germany; 2 Physikalisches Institut, Universität Heidelberg, Germany; 3 IHEP, Protvino, Russia
The CBM-TOF group aims at providing high π/k separation
(more than 2-σ in the reconstructed mass) in Au+Au
central collisions at 25 GeV/A, with a coverage of midrapidity
by at least 1 unit in y and 1 GeV in p T . These PId
capabilities are needed for probing the QGP phase, through
the study of such fundamental observables as the dynamical
fluctuations of the kaon yield, kaon flow, hyperon production
close to threshold and open charm.
Based on simulation, it was shown that the mentioned
requirements can be satisfied by a tRPC (timing Resistive
Plate Chamber) wall placed at 10 m distance from the target
with 25-30 ◦ coverage in θ (∼150 m 2 ), featuring a time
resolution of 80 ps and an occupancy per cell below 5% (∼
60.000 cells). In order to cope with the high beam luminosity,
the tRPC must handle rates up to 20 kHz/cm 2 , while the
FEE must process the very fast GHz signals from the tRPC
at an interaction rate up to 10 MHz.
The CBM spectrometer benefits from the excellent overall
PId capabilities of the TOF wall: for example, the π/e
separation in time of flight is 3-σ for p=1.1 GeV, that provides
extra π suppression (apart from that of RICH and
TRD detectors) in view of di-electron spectroscopy.
Current R&D activities [1, 2, 3, 4, 5] focus on the development
of high rate capability tRPCs, aiming at extending
their working principle from few hundreds of Hz/cm 2 up to
the required rate of 20 kHz/cm 2 , for CBM usage. But also
improvements on the description of the timing properties of
the detector at high rates have been recently accomplished
[6]. As a consequence of the latter, the idea that the deterioration
of tRPC performances at high rates is mainly driven
by the DC column resistivity ρd (resistivity times the resistive
plate thickness per gap) is now more sound.
σ T [ps]
ε
150
130
110
90
70
50
1
0.95
0.9
0.85
0.8
0.75
0.7
10 −1 0.65
10 0
float glass (ionizing particles [1]
from C collisions)
semiconductive glass (10−40 MeV e−) [2]
float glass (10−40 MeV e−) [3]
AL940CD cheramics (0.511 MeV γ) [4]
Φ [kHz/cm 2 ]
Φ = 20 kHz/cm 2
10 1
σ T = 80 ps
ε = 0.95
Figure 1: Compilation of different measurements.
A number of measurements was performed at different
rates under different conditions: with ionizing particles
from carbon collisions at GSI-SIS [1], with 10-40 MeV
∗ Supported by JRA12 of EU/FP6 Hadronphysics (see annex), INTAS
Ref. Nr. 03-54-3891 and German BMBF contract 06 HD190I.
10 2
39
electrons at the ELBE LINAC [2, 3] and with γ sources
[4]. Among the more promising candidates for the resistive
plates of high rate tRPCs, semi-conductive glasses [2]
and ceramics [4] must be mentioned, whereas the possibility
of using warm thin glass deserves also consideration
[5]. A compilation of results is shown in Figure 1, together
with the dependence on rate Φ obtained in [6]:
εo
ε
1 + Ae−B/Φ , σT σo(1 + CΦ) (1)
where εo, σo, A, B, C are obtained from the fit to data.
The current theoretical and experimental understanding
of the detector has been used to better model the detector
geometry and its response. Starting from the simulation of
the gap response, a realistic description of the position resolution,
inclined tracks and multiple hits have been provided
for the first time. The studies performed after full tracking
through CBM confirm the statements of paragraph 2 (see
D. Kresan et al., this report) and open the path to a detailed
comparison between pad and strip technologies that are
currently existing for the tRPC readout. A first approach to
the final mechanical structure has also been accomplished,
where the distribution of the wall in towers looks by now
the more suited solution, providing a high flexibility and a
comfortable distribution of the weight (Figure 2).
Figure 2: Front view of the TOF wall, divided into towers.
Details on the FEE, mostly focused on ASIC design, can
be found in M. Ciobanu et al., in this report.
References
[1] H. Alvarez-Pol et al., NIM A, 535(2004)277.
[2] F. Dohrmann, talk at VIII CBM coll. meeting.
[3] R. Kotte et al. NIM A, 564(2006)155.
[4] L. Lopes et al., Nucl. Phys. B, (Proc. Suppl), 158(2006)66.
[5] P. Fonte et al., PoS(HEP2005)376.
[6] D. Gonzalez-Diaz et al., Nucl. Phys. B, (Proc. Suppl),
158(2006)111.