MUST2

MUST2
Name	MUST2
Type	Arrayed detector system
Wavelength	Charged-particle spectroscopy

MUST2

MUST2 is a charged-particle detector array used in experimental nuclear physics, developed to study nuclear structure and reaction mechanisms with rare-isotope beams and stable-ion facilities. The system combines segmented silicon detectors, drift chambers, and CsI scintillators to measure energy, position, and time-of-flight for light ejectiles in inverse kinematics experiments. MUST2 has been deployed at major European and international laboratories to investigate topics ranging from single-particle states to continuum correlations.

Overview

MUST2 was conceived to follow earlier compact arrays and to complement large spectrometers at facilities such as GANIL, GSI, RIKEN, TRIUMF, and JYFL. The project involved collaborations among institutions including CEA Saclay, Institut de Physique Nucléaire d'Orsay, Università di Milano, University of Manchester, and University of Catania. The design emphasis was on angular coverage, energy resolution, and rate capability to enable experiments on reactions like (d,p), (p,d), and knockout on radioactive beams from separators such as LISE, ALTO, SPIRAL, and ISAC. MUST2 experiments have complemented measurements at magnetic spectrometers like VAMOS, PRISMA, BigRIPS, and SPEG.

Instrumentation and Design

The core of MUST2 consists of telescopes combining double-sided silicon strip detectors, single-sided silicon detectors, and CsI(Tl) crystals read out by photodiodes. Position and angle are reconstructed using segmentation akin to devices deployed at DRAGON and techniques developed for CDT-style arrays. Front-end electronics and data acquisition were adapted from systems used at CERN teststands and modules compatible with standards from FAIR-era developments. Mechanical support and vacuum integration allowed coupling with ancillary detectors such as EXOGAM, AGATA, NEDA, and time-of-flight walls used at LNS and KVI. Calibration procedures incorporated alpha sources and beam elastic scattering standards referenced to targets provided by groups at CENBG and IRFU.

Scientific Goals and Capabilities

MUST2 was optimized to address single-particle spectroscopy, transfer reaction mechanisms, resonance properties, and continuum correlations in neutron-rich and proton-rich nuclei produced at facilities like SPES and FRIB-class installations. It enables determination of spectroscopic factors, angular distributions, and Q-values for reactions studied in inverse kinematics with beam energies typical of GANIL and GSI reaccelerated beams. Sensitivity to low-energy charged particles made it suitable for investigating astrophysical reaction rates relevant to scenarios such as the r-process, rp-process, and nucleosynthesis pathways probed by experiments informed by theories from groups at Argonne National Laboratory and TRIUMF. The array's timing and granularity supported coincidence measurements with gamma-ray arrays including CLARION, MINIBALL, and TIGRESS.

Operational History and Deployments

MUST2 saw its first physics runs at GANIL and rapidly moved to campaigns at GSI and collaborations with RIKEN researchers. Major deployment periods included experiments coordinated with SPIRAL beam schedules and joint runs with AGATA commissioning. International teams from INFN, SUBATECH, IPNO, and KU Leuven executed proposals evaluated by program committees at host laboratories. The array participated in campaigns focused on neutron-rich oxygen and fluorine isotopes, proton-rich sulfur isotopes, and experiments addressing shell evolution near N=20 and N=28 shell closures. Beam-time logistics often interfaced with separator operations at LISE3 and cryogenic target systems from groups at CEA facilities.

Data Processing and Analysis

Data acquisition used modular electronics and on-line event building comparable to systems at GANIL and GSI, employing digitizers, trigger logic, and software frameworks developed with input from CERN DAQ teams. Offline analysis pipelines included energy calibration, dead-layer corrections, particle-identification via DeltaE-E matrices, and tracking algorithms adapted from silicon-array toolkits used in experiments at Oak Ridge National Laboratory and Michigan State University. Monte Carlo modeling with codes such as GEANT4 and reaction-model simulations using inputs from theoretical groups at Università di Milano-Bicocca and TU Darmstadt supported efficiency and acceptance corrections. Data products were archived in institutional repositories at host laboratories and shared among collaboration members through platforms used by IReNA-linked projects.

Major Results and Publications

MUST2-enabled experiments produced publications on single-particle strength distributions, resonance widths in unbound systems, and spectroscopic factor extractions for isotopes near shell closures investigated by collaborations including teams from CEA, INFN, CNRS, and Universidad de Sevilla. Results contributed to revisions of level schemes in light and medium-mass nuclei and informed theoretical work from groups at GANIL Theory Unit, GSI Theory Division, and RIKEN Nishina Center. Key articles appeared in journals commonly used by the nuclear physics community and were presented at conferences such as the International Nuclear Physics Conference and meetings organized by the European Physical Society nuclear physics division. The body of work influenced subsequent instrument developments and proposals at facilities including SPES and projects within the FAIR program.

Category:Particle detectors Category:Nuclear physics experiments