Beamline specifications
| Beamline | Particles | Momentum [GeV/c] | Intensity [particles/spill] | Characteristics |
|---|---|---|---|---|
| Beamlines in the present facility | ||||
| K1.8 (A) | K±, π± | 1.0–2.0 | ∼106 K− (1.8 GeV/c) | Mass separated |
| K1.8BR (A) | K±, π± | <1.1 | ∼5×105 K− (1.0 GeV/c) | Mass separated |
| KL (A) | KL | Mean 2.1 | 107 KL | 16° extraction angle |
| high-p (B) | p | 30.9 | 1010 p | Primary protons (30 GeV) |
| π20 (B) | Mixed (π±, p±, K±, etc.) | <31 | 6×107 (final design) – 105 (current) | Secondary beam |
| COMET (C) | μ− | — | — | For μ−→e− |
| Beamlines in the extended area (future plans) | ||||
| K1.1 | K±, π± | <1.2 | ∼4×105 K− (1.1 GeV/c) | Mass separated |
| K1.1BR | K±, π± | 0.7–0.8 | ∼1.5×105 K− | Mass separated |
| HIHR | π± | <2.0 | ∼2×108 π (1.2 GeV/c) | Mass separated; 10-fold improvement in Δp/p |
| K10 | K±, π±, p̄ | <10 | ∼7×106 K− | Mass separated |
| KL2 | KL | Mean ∼5 | ∼4×107 KL | 5° extraction angle; optimized n/KL |
- Intensities for the present facility are typical values scaled to an approximately 80 kW primary beam incident on a production target with 50% beam loss. In April 2026, operation was carried out at approximately 96 kW.
- Intensities for the extended area are design values assuming approximately 50 kW for charged beams and 100 kW for neutral beams, with a production target of 50% beam loss.
- Values in parentheses in the intensity column denote the corresponding momentum in GeV/c.
- The classification and values are based on the 2021 white paper. The π20 intensity was updated in October 2026.
Overview of beams at the Hadron Experimental Facility
Experiments at the J-PARC Hadron Experimental Facility use proton beams extracted from the Main Ring (MR). These protons can either strike a production target to generate secondary particles or be used directly in experiments. The A, B, and C lines serve different roles.
A line: secondary particles produced at a target
Protons extracted from the MR with a kinetic energy of 30 GeV strike a production target. The resulting secondary particles are transported along beamlines for use in experiments. The A line includes the K1.8, K1.8BR, and KL beamlines.
K1.8 and K1.8BR are operated alternately by switching the beam between them. For example, beam can be delivered to K1.8BR while the experimental setup at K1.8 is being changed. Beam can be delivered to KL simultaneously with either K1.8 or K1.8BR.
B line: direct use of the MR proton beam or use of high-momentum secondary particles
A small fraction of the proton beam from the MR is extracted and used directly in experiments. This line is commonly known as the high-momentum beamline (high-p). The pi20 project, which uses secondary particles, is also underway.
C line: an 8 GeV proton beam
The C line uses a proton beam with a kinetic energy of 8 GeV. The COMET experiment uses this line.
Operating modes
The A and B lines can operate simultaneously. The C line is generally operated on its own, while simultaneous A+C operation is also being planned.