Ciobanu, M. I.

Frühauf, J.

Pietraszko, J.

Schmidt, C. J.

Träger, M.

GSI Repository

Performance of the straw tube readout based on PADI chip* M. Träger1, J. Pietraszko1, J. Frühauf1, M. Ciobanu2, C. J. Schmidt1and the FAIR@GSI division1 1GSI, Darmstadt, Germany, 2ISS Bucharest, RomaniaA prototype of the CBM MUCH straw tube detector [1]  consisting of six individual straws of 6mm inner diameter and approx. 22cm length was flushed with a gas mixture of Ar/CO2 (70/30) at ambient pressure. The straw anodes signals where connected to the PADI-6 ASIC [2] inputs via single twisted pair cables, decoupled by HV capaci-tors of 400pF and protected by PIN diodes in back-to-back orientation  The PADI have been mounted and wire bonded at GSI Detector Laboratory to the FEET-PADI6-HDa PCB [3]. For every PADI-6 with four input channels the discrimi-nator threshold could be adjusted by a dedicated potenti-ometer to ‘just above noise’-level (்ܳ௛௥ ൎ 2.2݂ܥ).  The experiment has been conducted at the COSY ac-celerator in Jülich. Protons of 2.95GeV energy at an in-tensity of ܫ ൎ 5 ∙ 10ଷݏିଵܿ݉ିଶ	in a nearly elliptical beam spot (ݔ	 ൎ 7.6݉݉, ݕ ൎ 15݉݉) where hitting two neigh-bouring straw tubes and the tracking diamond detector in about 20mm distance downstream.    Figure 1: Experiment setup with straw tubes (a), PADI readout (b) and diamond tracking detector (c).  Figure 2: PADI-6 analogue output (a) and corresponding discriminator signal (b), 200ns full scale. (right) Example histogram of proton tracks near the straw wall. Back-ground events show full range of drift times for this straw. Inefficiency hits are at the upper end of the spectrum.    The straw tubes, and as a consequence of this - their anodes, where placed horizontally and aligned in parallel to the ሺ0.09 ∙ 2.1ሻ݉݉ଶ gap between two electrodes of the diamond tracker. The trigger for the measurement was set to choose only signals with charge sharing between these electrodes. So only particles, traversing the gap were rec-ognized [4]. Additionally the tracking detector was mounted on a movable stage with micrometre precision to define the particle track distance to the anode wires. After LVDS-NIM conversion only signals of one straw detector (figure 2) and two signals (D1, D2) from the di-amond electrodes where fed into the R&S® RTO1044 (4GHz, 10GS/s) digital oscilloscope. The time difference ∆ݐ ൌ ݐ௧௥௜௚௚௘௥ െ ݐ௦௧௥௔௪	 between the trigger (ܦ1 ∩ 	ܦ2) and the PADI discriminator output was measured and analysed. ߂ݐ corresponds to the electron drift time in the straw and additional signal latencies. The main drift time peak of the ߂ݐ histogram in the range െ60݊ݏ ൑ ߂ݐ ൑ െ20݊ݏ was fitted with a Gauss function for different track positions over two straw di-ameters (figure 2). A mean drift time resolution of ߪ∆௧ ൌ 2.26݊ݏ was achieved (1.8ns...2.7ns) corresponding to a mean position resolution of 	ߪ∆௬ ൌ 157ߤ݉ with the measured electron drift velocity (see figure 3). Further analysis is needed for data taken with the self-tracking method for two straws.  Figure 3: electron drift time dependent on the track posi-tion y (error bars are smaller than symbols).  The electron drift velocity for the used detector gas was calculated.  References [1] V. Peshekhonov et al., “Straw tube subsystem of the CBM muon detector”, Physics of Particles and Nu-clei Letters, March 2012, Volume 9, Issue 2, pp 172-179. [2] M. Ciobanu et al., “PADI, an ultrafast Preamplifier - Discriminator ASIC for Time of Flight Measure-ments”, Nuclear Science, April 2014, IEEE Transac-tions ,Volume 61, Issue 2, pp 1015-1023. [3] J. Frühauf et al., “Hardware Development for CBM ToF”, GSI Report 2013-1, 292 p. [4] J. Pietraszko et al., “High resolution tracking based on scCVD diamond detector for straw tube detector tests”, this report.  ___________________________________________  * Work supported by FAIR@GSI PSP code: 1.1.1 MU-NQM-CBM-10 GSI SCIENTIFIC REPORT 201446 DOI:10.15120/GR-2015-1-MU-NQM-CBM-10

Performance of the straw tube readout based on PADI chip

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Performance of the straw tube readout based on PADI chip

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