II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Detection eﬃciency of the INTT test bench for sPHENIX
G. Nukazuka,∗1 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 T. Hachiya,∗1,∗4 S. Hasegawa,∗5 D. Imagawa,∗6 H. Imai,∗6T. Kondo,∗7 C. Kuo,∗3 H. -S. Li,∗8 R. -S. Lu,∗9 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1Y. Namimoto,∗4 S. Nishimori,∗4 R. Nouicer,∗2 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7W. -C. Tang,∗3 and X. Wei∗8

CAMAC crate

NIM crate

Cosmic ray
Scintillator

・Crate cntroller
・ADC
Data transfer
・TDC
and・Intterupt reg. control
・Output reg.

NIM modules for
signal processes

PMTTrigger input
Readout
Chip/Card

INTT Sillicon
module・FEM
・FEM-IB

Data transfer
Slow control

PC

VME crate
Scintillator

PMTFig. 1. Overview of the new DAQ system. See Ref. 3) forsome of the abbreviations.
∗1
∗2
∗3
∗4
∗5

∗6
∗7
∗8
∗9RIKEN Nishina Center
Physics Department, Brookhaven National Laboratory
Department of Physics, National Central UniversityDepartment of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Department of Physics, Rikkyo University
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University

1

Detection Efficiency as a function BCO phase

0.8
Efficiency

sPHENIX1) will start data acquisition in the Relativistic Heavy Ion Collider at Brookhaven National Laboratory from 2023 to study quark-gluon plasma. The Silicon Intermidiate Trackter (INTT),2) which is one of thecrucial pieces in the detector complex, enables us to perform jet ﬂavor tagging with high precision and low background. INTT inherits the readout electronics from theForward Silicon Vertex Detector of PHENIX3) so thatR&D can proceed with low cost in a short period.
In a test-beam experiment at Fermilab,4) we conﬁrmedthat the prototype of INTT satisﬁed the essential speciﬁcations for position resolution and timing resolution.
Detection eﬃciency was approximately 96%, althoughalmost 100% was expected. In these measurements,
the prototype worked using the internal clock (BCO)of 9.4 MHz while the beam arrived independently fromBCO. The lower-than-expected detection eﬃciency canbe due to timing mismatch between the beam and BCO,
because of which signals of the silicon module were occasionally not detected.
To test the hypothesis, we implemented an external
trigger system using the Nuclear Instrumentation Module (NIM) and Computer Aided Measurement And Control (CAMAC) modules and integrated it into the existing data acquisition system (DAQ) (Fig. 1). The silicon
module was set between two trigger scintillators. The
transverse dimensions of the scintillators were the sameas the active area of the silicon module. One scintillator on the top was set along the silicon module, while
the other was rotated by 90◦ longitudinally to restrictacceptance. Coincidence of signals from the two scintillators is treated as a trigger signal. The DAQ stores thefollowing parameters:• hit information on the silicon module

0.60.40.200050
100100150

BCO phase (degree)200

TDC channel

300

200

250
400

300
500

Fig. 2. Detection eﬃciency as a function of BCO phase withthe quality cuts.

• total charge and timing information of the scintillator signals• the timing diﬀerence between the coincidence signal
and a BCO pulse, i.e., a phase of BCO.
In the analysis, quality cuts for analog-to-digital converter (ADC) and time-to-digital converter (TDC) distributions of the scintillator signals reject noise-like events.
The detection eﬃciency deﬁned as a ratio of the number of trigger events with INTT hit to the number of thetrigger events is calculated after applying the quality cuts
as a function of the BCO phase (Fig. 2). Measurement
could not be performed for a sixth of the BCO period owing to technical diﬃculties. A clear drop in eﬃciency inthe ﬁrst 100 TDC channels was found as expected. The
average eﬃciency excluding and including the dropping
region was approximately 94% and 85%, respectively.
This low-eﬃciency condition can be the reason for the
96% eﬃciency obtained in the test-beam experiments.
The eﬃciency obtained in this study is lower than thatin the test-beam experiment because the acceptance restriction was not perfect; consequently cosmic rays could
activate the trigger without impingement on the siliconmodule.
We could also observe a positive correlation between
the eﬃciency and ADC for the bottom scintillator. Requiring higher ADC value to the signal may eliminate
cosmic rays, which do not penetrate the silicon sensor.
This observation suggests that optimization of the setup
can yield a higher detection eﬃciency.
In summary, we found dependency of the detection
eﬃciency on the BCO phase. It explains the lower efﬁciency observed in the test-beam experiment. Since
RHIC will provide a beam-synced trigger, this timingmismatch cannot be an issue for sPHENIX
References

1) A. Adare et al., sPHENIX proposal (2015).
2) I. Nakagawa et al., in this report.
3) C. Aidala et al., Nucl. Instrum. Methods. Phys. Res. A
755, 44 (2014).
4) A. Suzuki, Master’s thesis, Nara Women’s Univ. (2020).

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