II-9. Instrumentation

RIKEN Accel. Prog. Rep. 55 (2022)

RIKEN Accel. Prog. Rep. 55 (2022)

Detection eﬃciency of the RHIC-sPHENIX-INTT detector
M. Morita,∗1,∗4 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 H. En’yo,∗1 T. Hachiya,∗1,∗4 S. Hasegawa,∗1,∗5 M. Hata,∗4H. Imai,∗1,∗6 T. Kondo,∗7 C. Kuo,∗3 H. -S. Li,∗8 R. -S. Lu,∗9 E. Mannel,∗2 C. Miraval,∗2 I. Nakagawa,∗1Y. Nakamura,∗1,∗6 G. Nakano,∗1,∗6 Y. Namimoto,∗1,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2M. Shibata,∗1,∗4 C. Shih,∗3 M. Shimomura,∗4 M. Stojanovic,∗8 Y. Sugiyama,∗4 R. Takahama,∗1,∗4W. -C. Tang,∗3 K. Toho,∗10 K. Tsuruta,∗10 M. Watanabe,∗4 and X. Wei∗8The intermediate tracker (INTT), consisting of 56
ladders of silicon strip detectors, is a tracking detectorof charged particles for the sPHENIX experiment1) at
the Relativistic Heavy Ion Collider. So far, by using
test pulses, radiation sources, cosmic rays, and proton
test beams at Fermilab, we have conﬁrmed that theperformance required of the INTT ladders is mostly
fulﬁlled. After the completion of the research and development of INTT, mass production and detector construction are now in progress.2)
A silicon detector is expected to have a detection
eﬃciency of almost 100%; however, we obtained an efﬁciency of 96.5 ± 0.5% from a previous test beam experiment.3) This low eﬃciency may have been causedby the missing beam clock information in the experimental data because one cannot conﬁrm whether each
hit in the detectors originated from one beam particle without the beam clock information. Thus, theINTT data acquisition (DAQ) system was modiﬁed tosave the beam clock information and accept an external trigger.
In December 2021, at Research Center for Electron
Photon Science, Tohoku University, we performed a
new test beam experiment4) with the mass-produced
ladders and the new INTT DAQ system. Three ladders were collinearly placed along the beamline andsandwiched by trigger plastic scintillators. A positron
beam with an energy of 1 GeV impinged on these detectors.3)
The detection eﬃciency (Li ) of the i-th ladder Li
is calculated as(Li ) =N (Li ∩ Lj ∩ Lk ),N (Lj ∩ Lk )Fig. 1. Fired strip-ID diﬀerence between two ladders. The
events in the 2σ region (enclosed by dashed lines) areused to evaluate the detection eﬃciency of each ladder.

ﬁciency. The strip ID of the hit clusters are determined by the weighted mean of the merged hits with
their analog-to-digital conversion (ADC) value. The
events in which the beam penetrates all ladders almost perpendicularly are used to evaluate the detection eﬃciency. The ﬁred strip-ID diﬀerence between
two ladders are utilized to select such events, as shownin Fig. 1. A smaller absolute value of the diﬀerence
between the ﬁred strip IDs corresponds to a smaller
position diﬀerence in the plane perpendicular to thebeam axis. The events inside the 2σ region in the ﬁred
strip-ID distribution (the region enclosed by dashedlines in Fig. 1) are treated as the coincidence condition
in Eq. (1). The mean of the ﬁred strip-ID diﬀerence isapproximately 4, implying that the position diﬀerence
between ladders is approximately 320 μm. The widthof the distribution is governed by the angular spreadof the beam. With the coincidence condition describedabove, the detection eﬃciencies of the three ladders are
determined to be 99.53 ± 0.02%, 99.39 ± 0.03%, and99.56 ± 0.02%, respectively. The high detection efﬁciency of the INTT detector is conﬁrmed, implyingthat the detector is ready for the day-one experimentof sPHENIX.

(1)(i, j, k = 0, 1, 2)(i = j = k)where N (x) is the number of hits under a condition x.
The events from noisy strips are excluded from theanalysis. Hit clusters are formed by merging adjacenthits in a ladder before the calculation of detection ef-References
1) Conceptual Design Report of sPHENIX (2018).
2) I. Nakagawa et al., in this report.
3) A. Suzuki, Master thesis, Nara Women’s University(2019).
4) G. Nukazuka et al., in this report.

∗1

RIKEN Nishina Center∗2 Brookhaven National Laboratory∗3 Department of Physics, National Central University∗4 Department of Physics, Nara Women’s University∗5 Japan Atomic Energy Agency∗6 Department of Physics, Rikkyo University∗7 Tokyo Metropolitan Industrial Technology Research Institute∗8 Department of Physics, Purdue University∗9 Department of Physics, National Taiwan University∗10 Department of Physics, Tohoku University- 99 -1