¶ Detector Concept: Silicon Tracker + LH2 target
¶ Overview
STRASSE is a compact, high-resolution silicon tracker combined with a thick liquid hydrogen (LH₂) target, designed for quasi-free scattering (QFS) experiments at the RIKEN RIBF SAMURAI spectrometer. Its primary goal is to improve the resolution of missing-mass and γ-ray spectroscopy measurements compared to existing systems like MINOS.
¶ Key Features
| Feature | Description |
|---|---|
| Silicon Tracker | Two-layer double-sided silicon strip detectors (DSSDs) in a hexagonal configuration (inner and outer barrels). |
| LH₂ Target | 150-mm thick, 15.5-mm radius target cell, optimized for luminosity and minimal angular straggling. |
| Compact Geometry | Fits inside large scintillator arrays (e.g., CATANA) or γ-ray tracking arrays (e.g., AGATA). |
| Vacuum Operation | Entire system operates in vacuum to minimize material budget and straggling. |
| High Granularity | 17,358 readout channels with 200–300 μm pitch for precise tracking. |
Figure: (a) STRASSE assembly showing the main flange, cooling base, FEBs, silicon tracker, vacuum chamber, and LH₂ target. (b) Close-up of the FEBs, STS-XYTER ASICs, and silicon layers.
¶ Innovations
-
Sub-mm Vertex Resolution:
- Target: < 1 mm (σ) to enable high-precision Doppler correction for γ-ray spectroscopy.
- Achieved via thin silicon layers (200 μm inner, 300 μm outer) and optimized geometry.
-
Missing-Mass Resolution:
- Target: < 2 MeV (σ) for (p,2p) reactions, enabled by:
- Minimized angular straggling (e.g., 3.0 mrad for LH₂ target + 200 μm Si).
- High-efficiency tracking (49% for two-proton detection).
- Target: < 2 MeV (σ) for (p,2p) reactions, enabled by:
-
Dual-Purpose Design:
- Supports both missing-mass spectroscopy and in-beam γ-ray spectroscopy in a single setup.
¶ Comparison to MINOS
| Parameter | MINOS | STRASSE |
|---|---|---|
| Target Type | LH₂ + TPC | LH₂ + Silicon Tracker |
| Angular Straggling | ~16.2 mrad | ~4.9 mrad |
| Missing-Mass Resolution | ~5 MeV (σ) | < 2 MeV (σ) |
| Vertex Resolution | ~10 mm | < 1 mm (σ) |
| γ-Ray Energy Resolution | ~10% (FWHM) | 1–2% (FWHM) with AGATA/GRETA |
¶ Schematic Diagram
Figure: STRASSE silicon tracker (inner/outer barrels) with LH₂ target and CATANA array.