Deppner, I.

Frühauf, J.

Herrmann, N.

Loizeau, P.-A.

Simon, C.

Xiang, C.

GSI Repository

RPC prototype test with cosmic irradiation∗C. Simon1, I. Deppner1, N. Herrmann1, P.-A. Loizeau1, J. Fru¨hauf 2, C. Xiang1,3, and the CBM-TOFworking group1Ruprecht-Karls-Universita¨t Heidelberg, Heidelberg, Germany; 2GSI, Darmstadt, Germany; 3Central China NormalUniversity, Wuhan, ChinaFollowing the proposal to construct the outer ToF wallbased on fully differential multi-strip MRPCs [1] the re-sponse of a new prototype RPC designed in Heidelberg tocosmic irradiation was measured throughout the year 2013.In particular, a focus was put on compatibility with theread-out electronics, i.e. PADI-6 preamplifier cards [2] andVFTX FPGA-TDC modules [3], and on refinement of theexisting calibration and correction algorithms [4].The RPC prototype implements an 8-gap single-stackconfiguration with a gap width of 220μm. It features56 read-out electrodes of length 53 cm and pitch 9.4mmthat add up to an active area of about 2800 cm2. As RPCsin the outer wall region do not have to stand incident parti-cle fluxes larger than 1 kHz, the prototype is equipped withfloat glass of resistivity 1012 Ωcm. The working voltageof the counter amounts to ±11 kV. The preamplifier cardsare placed inside the gas volume (cf. Fig. 1, right) and con-nected directly to the read-out electrodes.Figure 1: Sketched arrangement (left) of two plastic scintil-lators with respect to the RPC prototype (right) to measureits response to cosmic irradiation.The test setup in the lab comprises—besides theRPC prototype—two plastic scintillators (PLA) of dimen-sions 8 × 2 × 1 and 11 × 4 × 2 cm3 which are each readout on two sides by photomultipliers. One PLA counteris placed above, the other one below the RPC (cf. Fig. 1,left). From the coincidence of signals in both scintillatorsa trigger is built that is used to read out the RPC.To evaluate the characteristic RPC parameters time res-olution and detection efficiency of the prototype a calibra-tion algorithm needs to process the TDC raw data. In thisway, fixed time offsets due to different runtimes of the sig-nals inside the TDCs and the cables connecting the RPCand the PLA counters with the TDCs can be accounted for.Also, systematic effects varying from event to event are∗Work supported by EU/FP7-HadronPhysics3/WP19 and BMBF05PRVHFC7.corrected for, like charge walk, the velocity spectrum of theincident cosmic muons, and their angular distribution in thetest arrangement. After applying all corrections to the rawdata the algorithm proceeds with clustering RPC signals onneighboring read-out electrodes that show correlations intime and space. Here, the idea is that an avalanche triggeredby a single charged particle traversing the RPC prototypecan induce mirror charges on more than one read-out elec-trode. A typical cluster size for the prototype is 1.3 strips.In the cosmic muon setup, i.e. for the section of thecounter surface affected by the PLA coincidence (cf. Fig. 2,right), a detection efficiency of 98.5% and a system timeresolution of 67 ps were found. The term system time res-olution refers to the Gaussian standard deviation σ of thetime difference spectrum between the RPC and the PLAcounters (cf. Fig. 2, left). With a resolution of 55 ps forthe plastic reference system, this allows for an estimate ofthe counter time resolution—still including the electronicsresolution—of about 40 ps. An in-beam test of the proto-type in April 2014 at GSI/SIS-18 will demonstrate if thesevery promising results also hold under heavy-ion load.Entries  12150RMS     73.46Sigma     0.51±67.13 dt RPC-PLA cluster [ps]-400 -200 0 200 400counts110210310410cluster position x [cm]-20 -10 0 10 20cluster position y [cm]-20-15-10-505101520 Entries  12150050100150200250300350400450Figure 2: Time resolution of the PLA-RPC system (left)obtained in the trigger spot on the counter surface (right)requiring coincidence of the plastic scintillators.References[1] I. Deppner et al., CBM Progress Report 2012, Darmstadt2013, p. 64[2] M. Ciobanu et al., CBM Progress Report 2012, Darmstadt2013, p. 72[3] J. Fru¨hauf et al., CBM Progress Report 2012, Darmstadt2013, p. 71[4] C. Simon et al., CBM Progress Report 2012, Darmstadt 2013,p. 65NQM-CBM-28 GSI SCIENTIFIC REPORT 201344 doi:10.15120/GR-2014-1-NQM-CBM-28

RPC prototype test with cosmic irradiation

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RPC prototype test with cosmic irradiation

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