Design and Construction of the BESIII Detector

Abstract: This paper will discuss the design and construction of BESIII, which is designed to study physics in the tau-charm energy region utilizing the new high luminosity BEPCII double ring e+e- collider. The expected performance will be given based on Monte Carlo simulations and results of cosmic ray and beam tests. In BESIII, tracking and momentum measurements for charged particles are made by a cylindrical multilayer drift chamber in a 1 T superconducting solenoid. Charged particles are identified with a time-of-flight system based on plastic scintillators in conjunction with dE/dx (energy loss per unit pathlength) measurements in the drift chamber. Energies of electromagnetic showers are measured by a CsI(Tl) crystal calorimeter located inside the solenoid magnet. Muons are identified by arrays of resistive plate chambers in the steel magnetic flux return. The level 1 trigger system, Data Acquisition system and the event filter system based on networked computers will also be described.

• The paper introduces the BESIII detector’s design as an innovative platform for precise τ-charm physics, integrating a high-resolution drift chamber and state-of-the-art calorimetry.
• The study highlights the multilayer drift chamber achieving 0.5% momentum resolution at 1 GeV/c and the TOF system enabling pion/kaon separation up to 900 MeV/c.
• It demonstrates efficient system integration with rapid triggers and high data throughput, establishing the detector’s capability for large-scale event filtering and data management.

The Design and Development of the BESIII Detector

The paper provides a detailed exposition on the design and construction of the BESIII detector, integrated into the BEPCII, a high-luminosity electron-positron double-ring collider at the Institute of High Energy Physics in Beijing. The BESIII detector is dedicated to exploring the τ-charm energy region, aiming to enhance our understanding of the Standard Model, particularly in τ-charm physics, by leveraging the extensive data that BEPCII delivers.

Core Detector Components

The BESIII's sophisticated design encompasses several key components, each serving a critical function in data capture and particle detection.

1. Multilayer Drift Chamber (MDC): Serving as the tracking device, the MDC is designed to adeptly capture the trajectories of charged particles generated in collisions. It operates within a superconducting solenoid magnet providing a uniform magnetic field. The MDC achieves a remarkable momentum resolution of approximately 0.5% at 1 GeV/c through its 43 layers of sense wires, facilitating 3D space reconstruction of tracks.
2. Time-of-Flight (TOF) System: Utilizing plastic scintillator counters, the TOF system is integrated for particle identification. It enhances the classification of the species of charged particles by analyzing flight times. The resolution capabilities of TOF are sufficient to allow pion/kaon separation up to momenta around 900 MeV/c.
3. Electromagnetic Calorimeter (EMC): Composed of CsI(Tl) crystals, the EMC precisely measures photon energies, achieving an energy resolution of approximately 2.5% at 1 GeV. This component is critical for identifying and reconstructing neutral particles and ensuring efficient energy measurements across the interaction spectrum.
4. Muon Counter (MUC): By employing resistive plate chambers (RPCs) installed within the steel structure of the magnetic return yoke, the MUC efficiently identifies muons amidst the experimental background to a low momentum cut-off of 400 MeV/c. This function is vital for separating muonic events from other particle interactions.

System Integration and Performance

The paper presents comprehensive simulations and initial test results to affirm that the BESIII system meets or exceeds expected performance goals. The trigger system, functioning with a latency less than 6.4 µs, effectively discriminates between relevant physics events and background noise. The DAQ and event filter system handles a maximum trigger rate of 4 kHz, efficiently managing and storing large volumes of data output with a designated throughput of 50 MB/s after online filtering with L3 triggers.

Implications and Outlook

The BESIII detector's advanced configuration, leveraging cutting-edge technology in the form of CsI(Tl) calorimeter crystals, state-of-the-art DRIFT chamber design, and high-performance RPCs, sets a benchmark in precision measurement scenarios required for τ-charm physics. The acquired data promise to add valuable insights into CP violations, lepton flavor violations, and rare decay processes over an extended energy range (2 to 4.6 GeV), providing empirical tests for QCD and CKM matrix parameter estimations.

Future prospective developments might harness enhancements in superconducting technology, refined readout electronics, and upgraded computational resources, enhancing real-time data acquisition capabilities and resolution achievements. Such advancements could further push the envelope in subatomic physics, unveiling novel phenomena and garnering deeper understandings within the particle physics domain. The BESIII offers a comprehensive framework for ongoing exploratory research, with anticipated contributions to the refinement and possible extensions of the Standard Model.