Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 51 (2018)

A silicon vertex tracker for the 8 He(p, pα)4n reaction
F. Dufter,∗1 T. Aumann,∗2,∗3 S. Paschalis,∗4,∗2 D. M. Rossi,∗2 N. L. Achouri,∗5 D. Ahn,∗6 H. Baba,∗6C. A. Bertulani,∗7 M. Boehmer,∗1 K. Boretzky,∗3,∗6 N. Chiga,∗6 A. Corsi,∗5 D. Cortina-Gil,∗8 C. A. Douma,∗9Z. Elekes,∗10,∗6 J. Feng,∗11 B. Fernández-Domß́nguez,∗8 U. Forsberg,∗12 N. Fukuda,∗6 I. Gasparic,∗13,∗6 Z. Ge,∗6R. Gernhäuser,∗1 J. M. Gheller,∗14 J. Gibelin,∗5 A. Gillibert,∗14 Z. Halász,∗10,∗6 M. N. Harakeh,∗9A. Hirayama,∗15,∗6 N. Inabe,∗6 T. Isobe,∗6 J. Kahlbow,∗2,∗6 N. Kalantar-Nayestanaki,∗9 D. Kim,∗16,∗6 S. Kim,∗2M. A. Knösel,∗2 T. Kobayashi,∗17 Y. Kondo,∗15,∗6 D. Körper,∗3 P. Koseoglou,∗2,∗3 Y. Kubota,∗6 I. Kuti,∗10P. J. Lee,∗18 C. Lehr,∗2,∗6 S. Lindberg,∗19,∗6 Y. Liu,∗11 F. M. Marqués,∗5 S. Masuoka,∗20 M. Matsumoto,∗15,∗6J. Mayer,∗21 B. Monteagudo,∗22 T. Nakamura,∗15,∗6 A. Obertelli,∗2,∗14,∗6 N. Orr,∗5 H. Otsu,∗6 V. Panin,∗6S. Y. Park,∗16,∗6 M. Parlog,∗5 P.-M. Potlog,∗23 S. Reichert,∗1,∗6 A. Revel,∗22 A. T. Saito,∗15,∗6 M. Sasano,∗6H. Scheit,∗2 S. Shimoura,∗20 F. Schindler,∗2 H. Simon,∗3 L. Stuhl,∗20 H. Suzuki,∗6 D. Symochko,∗2 H. Takeda,∗6J. Tanaka,∗2 Y. Togano,∗24,∗6 T. Tomai,∗15,∗6 H. T. Törnqvist,∗2,∗6 T. Uesaka,∗6 V. Wagner,∗2,∗6 H. Yamada,∗15,∗6B. Yang,∗11 L. Yang,∗25 Z. H. Yang,∗6 M. Yasuda,∗15,∗6 K. Yoneda,∗6 L. Zanetti,∗2,∗6 and J. Zenihiro∗6The SAMURAI191) experiment at the RIKEN RIBF
aimed at producing 4n resonances with (p, pα) quasifree scattering of a 156 AMeV 8 He beam at large momentum transfer. A 5 cm thick liquid-hydrogen target(MINOS) with a diameter of 4 cm was used. A luminosity of ∼ 1028 cm−2 s−1 was achieved. To obtain the 4nenergy, the momenta of all outgoing particles were measured with high accuracy and the particle energy loss
in the target was determined with essential vertex reconstruction. Reaction vertex positions in the targetwere determined by a newly developed silicon vertex
tracker by TUM and RIKEN, which consists of six single
sided silicon detector layers with an active area of ∼ 5 x
8 cm2 and a thickness and pitch size of 100 µm each.2)
As shown in Fig. 1 the detectors are grouped in threeunits for X and Y determination at distances of 0.6,
12.6 and 24.6 cm with respect to the end of the target
container in a vacuum chamber. The target containeris thermally shielded from the ﬁrst detector layer by a2 um thick aluminized Mylar foil.
All 3708 detector segments are individually read out
by the ASIC chip APV25S1.3) The digital data are col∗1

Technische Universität München
Technische Universität Darmstadt∗3 GSI, Darmstadt∗4 University of York∗5 Laboratoire de Physique Corpusculaire de Caen
∗6 RIKEN, Nishina Center∗7 Texas A&M University-Commerce∗8 University of Santiago de Compostela∗9 KVI-CART, University of Groningen∗10 MTA ATOMKI, Debrecen∗11 Peking University∗12 Lund University∗13 RBI, Zagreb∗14 IRFU, CEA, Université Paris-Saclay∗15 Tokyo Institute of Technology∗16 Ewha Womans University, Seoul∗17 Tohoku University∗18 Hongkong University∗19 Chalmers University of Technology, Göteborg∗20 CNS, University of Tokyo∗21 Universität zu Köln
∗22 GANIL, Caen
∗23 Institute of Space Sciences, Magurele∗24 Rikkyo University∗25 University of Tokyo∗2

lected by a TRB3 board developed by GSI, which canhandle trigger rates of up to 50 kHz, and they are timestamped for synchronization with the BABIRL-DAQ
used for the other parts of the experiment.

Fig. 1. Installed detectors in the reaction chamber.

With a typical equivalent noise charge of ∼ 7 keV, asingle channel energy threshold of 38 keV was used to reduce event multiplicities. This is a critical parameter as
the average energy loss of the proton from the reactionis ∼ 60 keV per detector only. As the ASIC’s analogue
range is ∼ 8 MIPs (Minimum ionizing particle), signals
from α-particles may exceed the range. A sophisticatedpulse-shape algorithm can separate α-particles from thereaction from the 8 He beam particles hitting the detectors at a high rate. From the redundant position measurement of 3 points per track we deduce an averagetransverse vertex resolution of σx,y ∼ 60 µm. Owing tothe small opening angle of charged reaction residues ofinterest the resolution along the beam line is σz ∼ 1 mmwithout straggling. As next steps we will further investigate the detection eﬃciency, the tracking towards theSAMURAI detectors, hit multiplicities and transverse
momenta.
References

1) S. Paschalis, S. Shimoura et al., RIBF Proposal NP1406SAMURAI19.
2) S. Reichert et al., RIKEN Accel. Prog. Rep. 49, 167(2016).
3) M. J. French et al., Nucl. Instrm. Methods Phys. Res. A466, 359 (2001).

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