Ⅱ-4. Hadron Physics

RIKEN Accel. Prog. Rep. 56 (2023)
RIKEN
Accel. Prog. Rep. 56 (2023)

MIP measurement for mass production of sPHENIX-INTT ladderwith a positron beam
Y. Sugiyama,∗4 Y. Akiba,∗1 J. Bertaux,∗2 K. Fujiki,∗1,∗3 M. Fujiiwara,∗4 T. Hachiya,∗1,∗4 S. Hasegawa,∗1,∗5M. Hata,∗4 H. Imai,∗1,∗3 M. Kano,∗4 T. Kato,∗1,∗3 T. Kondo,∗6 C. M. Kuo,∗7 R. S. Lu,∗8 I. Nakagawa,∗1Y. Namimoto,∗1,∗4 R. Nouicer,∗9 G. Nukazuka,∗1 C. W. Shih,∗7 M. Shimomura,∗4 R. Shishikura,∗1,∗3M. Stojanovic,∗2 R. Takahama,∗1,∗4 W. C. Tang,∗7 H. Tsujibata,∗4 M. Watanabe,∗4 and X. Wei∗2The sPHENIX experiment will start in 2023 at theRelativistic Heavy Ion Collider in Brookhaven NationalLaboratory. Intermediate Tracker (INTT) is one of thethree tracking detectors used in the experiment, which
consists of 56 ladders of silicon strip detectors. A half
ladder is divided into 26 cells which consist of two typesof silicon sensors with diﬀerent strip lengths, and eachcell includes 128 read-out FPHX chips.1)
In 2021 at ELPH, Tohoku University, we performed
a test beam experiment to evaluate the performance ofmass production ladders.2) We used the γ-ray beamline
at the facility, and irradiated a positron beam with amomentum of about 1 GeV. Three halves of a ladderwere used, and two scintillators were installed upstream
and downstream of them, respectively.
We evaluated the performance of silicon sensor by detecting Minimum Ionizing Particles (MIP). The noisecontamination to the MIP region in the energy deposit
spectrum is crucial to achieve good signal-to-noise ratio. The FPHX read-out chip converts the height of thesignal generated by the sensor into a 3-bit ADC. As a
preparation of the signal AD conversion process, the 8bit DAC threshold values (called DAC value) are presetwith approximately 4 mV step. When the signal is processed, a corresponding DAC value is assigned and set
in a data stream as a 3-bit ADC data. The ADC value
relates to energy loss of a traversing charged particle. Itis important to observe the entire energy deposit spectrum with a good resolution though, it is not possible
by using the built-in 3-bit ADC of FPHX chip. A series of sequential measurements were executed to scanthrough the full DAC range by setting the DAC to cover
only narrow range but ﬁne pitch in one measurement.
In the data analysis, events which have too many hits
away from the beam spot were removed. Only hits ona single strip were analyzed. A hit with the highest
ADC value was excluded from the full ADC spectrum
reconstruction event samples because the hit could bean overﬂow value. We reconstructed ADC distribution∗1∗2∗3∗4∗5∗6∗7∗8∗9RIKEN Nishina Center
Department of Physics and Astronomy, Purdue University
Department of Physics, Rikkyo University
Department of Mathematical and Physical Sciences, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteCenter for High Energy and High Field Physics and Department of Physics, National Central University
Department of Physics, National Taiwan University
Physics Department, Brookhaven National Laboratory- 58 -of a cell in the upstream ladder obtained from 8 runs.
Then the distribution was normalized by the numberof entries in two overlapping bins, shown in Fig. 1(a).
Then we took the average over each overlapping bin,letting each ADC distributions of narrow region connect smoothly with the spectrum of adjacent region. It
was performed in order from the smallest ADC conﬁguration to obtain one energy deposit spectrum.

Fig. 1. (a) The ADC distribution obtained from 8 runs bynormalizing entries in overlapping bins. (b) The energy
deposit spectrum with the ﬁtting results.

We applied the Landau-Gaussian convolution function3) to reproduce the peak shape of the MIP region,
and an exponential function to express the noise contribution. The Landau most probable value indicatesthe peak value corresponding to the energy loss of theMIP. We ﬁtted the energy deposit spectrum with a sumof their functions and succeeded in reproducing the experimental data, shown in Fig. 1(b).
The ﬁtting result shows the Landau MPV was
71.13 ± 0.43 at the operation bias voltage of 50 V. The
noise contamination in the MIP region from 40 to 136
is estimated to be about 0.3%. Therefore the mass production ladder is almost noiseless in the MIP region.
In summary, we obtained one exact energy deposit
spectrum from measurements with 8 diﬀerent ADC conﬁgurations. The experimental spectrum was well reproduced by the sum of the convolution function and theexponential function. Also, the noise contamination in
the MIP region is about 0.3%. This means that theDAC threshold value can be set low, leading to highdetection eﬃciency.
References
1) C. Aidala et al., Nucl. Instrum. Meth. Phys. Res. A 755,
44 (2014).
2) G. Nukazuka et al., ELPH Annu. Rep. (2022).
3) S. Hancock et al., Phys. Rev. A 28, 615 (1983).