Time Projection Chamber “HypTPC” for the high rate beams at J-PARC

Y. Ichikawa1), J.K. Ahn2), T. Akaishi3), S. Ashikaga1,4), S.W. Choi2), K. Hicks5), H. Ekawa6),
S. Hasegawa1), S. Hayakawa1), K. Imai1), S. Ishimoto7), W. Jung2), B. Kang2), S.H. Kim2), J. Lee8),
T. Nanamura1,4), H. Sako1), K. Sasaki7), S. Sato1), K. Shirotori9), K. Suzuki4), S. Suzuki7),
T. Takahashi4), K. Tanida1), K. Tanida1), S. Yang2), J. Yoshida10),
and the J-PARC E42, 45, 72 collaborations.
1): Hadron Nuclear Physics Gr., JAEA, 2): Korea Univ., 3): Osaka Univ., 4): Kyoto Univ.,5): Ohio Univ., 6): RIKEN, 7): KEK, 8): Seoul National Univ., 9): RCNP, 10): Tohoku Univ.

J-PARC can provide secondary beams with the world’s highest
intensities such as kaon. The high intensity beam enables us tosearch for new exotic states such as a H-dibaryon with highstatistics, and the study of new exotic states helps deepen
understanding of low-energy nonperturbative phenomena inQCD.
In recent years, the hadron group in ASRC has strongly
contributed to develop a Hyperon Spectrometer (HS) bycollaborating with Korea University and so on. The HS consistsof a superconducting magnet, a time projection chamber called
as a “HypTPC”, and a time-of-flight system. HypTPC is thecentral tracker of HS. It measures the tracks of multiple charged
particles in three dimensions as a bubble chamber with excellent
momentum and special resolution, and large acceptance.
The design challenges of HypTPC are to make beam particles
with about 1M cps (counts per second) pass perpendicularly tothe TPC drift axis and make them hit an experimental target
installed inside the TPC drift volume as shown in Fig.1.
Thereby, HypTPC should have a capability for the high-particle
rate, so that we adopted a triple GEM (Gas Electron Multiplier)amplification for signal detection and the gating-wire grid tosuppress the ion backflow. The GEM is more stable against
discharge compared with wire chambers under the high particle
rates. Moreover, the P-10 (Ar : CH4 = (90:10)) gas, whose
maximum drift velocity is 5.3 cm/μs, is selected for the highparticle-rate capability. This faster drift velocity has anadvantage for the high rate operation to reduce the accidental
track rate.
By using this powerful spectrometer, we propose threeexperiments at J-PARC to search for new exotic states. The E42experiment, which aims to search for H-dibaryon, a multi-quark
baryonic states with 6-quark (uuddss) configuration. The E45
experiment, for investigating baryon excited states, such as N*
and Δ*, in (π, 2π) reactions. The E72 experiment, to search for anarrow Λ* resonance by using p(K-, Λ) reaction. In addition, we
have recently submitted a Letter of Intent to propose a newexperiment to search for the double kaonic nucleus, which is a
� and nucleus, K-K-pp. Since the HS is aquasi-bound state of 𝐾𝐾
multi-purpose large acceptance spectrometer, not only theproposed experiments but also new experiments in the near
future, it is expected to lead the hadron physics at J-PARC
facility.
We have constructed the HypTPC detectors and carried out abeam test at the Heavy-Ion Medical Accelerator Complex(HIMAC) by using 230 MeV protons with beam rates up to 1
MHz in order to confirm the basic performance and test the highrate capability of the HypTPC. This test experiment was carriedout without a magnetic field. A photograph of the experimental
setup of this experiment is displayed in Fig. 2. The result of theHIMAC data analysis is described in detail in Ref. [1].
The spatial resolutions on the pad plane without a magnetic
field were measured to be 400 – 700 μm, depending on the drift
length. The measured resolution corresponds to be 200 – 300

μm in a magnetic field of 1 T, which is consistent with ourdesign value.
Even at the 1 M cps beam rate, the track candidates can beselected correctly by using a Hough transformation method. The
measured pad efficiency of about 98% was almost unchanged
up to 1M cps beam rate. Moreover, we observed no significant
change in the transverse and longitudinal spatial resolutions
under the high rate condition. We concluded that the HypTPC
achieved the sufficient performance to carry out the actual
experiments at J-PARC. The E42 experiment, which is the firstphysics experiment employing the HS, is planned to be carriedout in June 2021.

Fig1. Schematic view of HypTPC

Fig2. Photograph of experimental setup at HIMAC. The plastic
scintillators are installed both upstream and downstream ofHypTPC as trigger counters. The silicon strip detectors are also
installed both upstream and downstream of HypTPC as positionreference detectors.
References[1] S.H. Kim, Y. Ichikawa, H. Sako, et al., Nucl. Instrum.
Methods Phys. Res. A 940, 359 (2019).