O. Merle

The PANDA 3D Disc DIRC

A 3D Disc DIRC detector is foreseen to provide particle identification in the endcap region of the PANDA experiment at the future FAIR facility. The 3D-DIRC is a synthesis of the previously proposed FL-DIRC and TOP-DIRC at PANDA. It is based on the measurement of the internally reflected Cherenkov light in a 2 cm thick fused silica plate. Position sensitive single photon detectors — either MCP-PMTs or a SiPMs — are placed in the focal plane of small focussing light guides and will provide a measurement of a projection of the Cherenkov angle. A precise determination of the time-of-propagation of the photons will allow to extract additional information of the Cherenkov angle and it will improve the identification of the signal pattern in a high luminosity, high background environment. Dichroic mirrors will be used to handle dispersion effects in the generation and propagation of the photons. The detector is expected to separate pions and kaons up to a momentum of ~ 4 GeV/c.

Tests and developments of the PANDA Endcap Disc DIRC

The PANDA experiment at the future Facility for Antiproton and Ion Research (FAIR) requires excellent particle identification. Two different DIRC detectors will utilize internally reflected Cherenkov light of charged particles to enable the separation of pions and kaons up to momenta of 4 GeV/c. The Endcap Disc DIRC will be placed in the forward endcap of PANDAs central spectrometer covering polar angles between 5° and 22°. Its final design is based on MCP-PMTs for the photon detection and an optical system made of fused silica. A new prototype has been investigated during a test beam at CERN in May 2015 and first results will be presented. In addition a new synthetic fused silica material by Nikon has been tested and was found to be radiation hard.

The Barrel DIRC of PANDA

Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5-15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The PANDA detector will investigate antiproton annihilations with beams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4π acceptance double spectrometer is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle.

The PANDA time-of-propagation disc DIRC

A novel Cherenkov detector, a time-of-propagation (TOP) disc DIRC, is proposed for particle identification at the PANDA experiment at the future FAIR facility. It measures Cherenkov light that is generated and internally reflected in a 2 cm thick fused silica plate. The Cherenkov angle is reconstructed from a time-of-propagation measurement at the rim of the disc of individual Cherenkov photons with a resolution of better than 50 ps. Dichroic mirrors at the rim of the disc fulfil two purposes. They allow for a selection of certain wavelength bands and thus are used to reduce dispersive smearing, and they enlarge the average photon path length by reflection and thus improve the separation power of the detector. A reconstruction algorithm has been developed to assign the detected photons to a given particle trajectory. Using a likelihood method, the algorithm calculates particle type probabilities for each track. The detector is expected to separate pions and kaons up to a momentum of ~ 4 GeV/c. Additional focussing elements at the rim of the disc are proposed to enhance the signal to background separation of the detector.

Status of the PANDA barrel DIRC

The PANDA experiment at the future Facility for Antiproton and Ion Research in Europe GmbH (FAIR) at GSI, Darmstadt will study fundamental questions of hadron physics and QCD using high-intensity cooled antiproton beams with momenta between 1.5 and 15 GeV/c. Hadronic PID in the barrel region of the PANDA detector will be provided by a DIRC (Detection of Internally Reflected Cherenkov light) counter. The design is based on the successful BABAR DIRC with several key improvements, such as fast photon timing and a compact imaging region. Detailed Monte Carlo simulation studies were performed for DIRC designs based on narrow bars or wide plates with a variety of focusing solutions. The performance of each design was characterized in terms of photon yield and single photon Cherenkov angle resolution and a maximum likelihood approach was used to determine the π/K separation. Selected design options were implemented in prototypes and tested with hadronic particle beams at GSI and CERN. This article describes the status of the design and R&D for the PANDA Barrel DIRC detector, with a focus on the performance of different DIRC designs in simulation and particle beams.

Reconstruction methods for the bar PANDA Time of Propagation Disc DIRC

The Time of Propagation (ToP) Disc DIRC is a novel type of Cherenkov detector, proposed for the particle identification system in ANDA. DIRC detectors (detection of internal reflected Cherenkov radiation) are a subtype of ring imaging Cherenkov detectors. Therefore the working principle is also based on spacial angle measurement of emitted Cherenkov photons. The ToP Disc DIRC concept involves two novel approaches. Firstly the radiator is realized in shape of a disc, what has never been done before, and secondly the Cherenkov angle is not measured by a spacial readout but reconstructed from one spacial coordinate and a fast single-photon time signal (σ < 50 ps). Photons are not only total reflected inside the radiator but also partly reflected by dielectric mirrors at the rim of the disc, leading to complicated photon tracks which have to be reconstructed. In addition, ANDA is not able to provide a useable start time for a given incident particle. Therefore measured data includes only the photons time of detection and not time of propagation. Previous approaches to DIRC reconstruction cannot be applied due to the different working principles. New specialized reconstruction methods have been developed and will be presented. Preliminary resolution studies based on Monte Carlo data (Geant4) proof that reconstruction of single tracks as well as multiple tracks is feasible.

The focussing light guide disc DIRC design

For the ANDA experiment at the future FAIR facility, charged particle identification is of major importance, and hence one foresees a DIRC detector with a circular radiator disc placing the optical elements for photon readout around the disc rim. To improve detector performance beyond the established BaBar DIRC the design presented here implements focussing optics and chromatic dispersion correction. A simplified disc DIRC at WASA shall serve a dual purpose. For the WASAatCOSY experiment itself the DIRC velocity measurement provides an improved energy resolution. For ANDA this WASA-DIRC is a real-experiment prototype validating essential design parts, and beyond the minimum design can act as a test bench for ANDA technology.

Resolution changes of MCP-PMTs in magnetic fields

Micro-channel plate photomultiplier tubes (MCP-PMTs) are chosen in many applications that have to cope with strong magnetic fields. The DIRC detectors of the PANDA experiment plan to employ them as they show excellent timing characteristics, radiation hardness, relatively low dark count rates and sufficient lifetime. This article mainly focuses on the performance of the position reconstruction of detected photons. Two different MCP-PMTs with segmented anode geometries have been tested in magnetic fields of different strengths. The variation of their performance has been studied. The measurements show improved position resolution and image shifts with increasing magnetic field strength.

A Disc-DIRC Cherenkov detector with high resolution micro channel plate photomultiplier tubes

The upcoming PANDA Experiment at FAIR in Germany will be equipped with a novel Cherenkov detector type for high-energy particle identification. This very compact Disc-DIRC detector uses a large disc-shaped fused silica plate of 2 cm thickness as its Cherenkov radiator. The internally reflected Cherenkov light is transported to the rim of the disc where it is focused by quartz light guides onto microchannel plate photomultiplier tubes (MCP-PMTs) with high spatial resolution (pitch 0.5 mm) and high time resolution (σ ≈ 100 ps). The device has an active area of about 3 m2 and will be able to identify pions and kaons with a separation power of more than 3σ in the momentum range up to 4 GeV/c. It has 32400 individual pixels and each can handle a mean photon rate of up to about 100 kHz. The presented design deals with numerous challenges that come with the very hostile environment in which the detector has to function properly, caused by the presence of high magnetic fields of up to 2 Tesla, high levels of radiation, high particle and background rates and a tight spatial volume. First test measurements have shown the performance of the design.

Simulation and reconstruction of photon patterns in the PANDA 3D Disc DIRC

The PANDA Disc DIRC is a novel type of Cherenkov detector, being developed to improve the charged particle identification of the upcoming PANDA experiment at the future FAIR facility. The detector has to cover the endcap region of the target spectrometer, resulting in a geometry that by now has never been applied to a DIRC detector. Additional complications are implied by tight space constraints at the foreseen position, interaction rates of 20 MHz up to 50 MHz and the experiments trigger-less readout scheme. To cope with the lack of experience, the development of detector concepts is driven by the development of computer simulations and dedicated reconstruction methods. The performance analysis of a preceding detector concept, presented at the DIRC workshop in 2009, showed several weaknesses which have been eliminated by revising the detector design. This publication summarizes the current status of the software, the reconstruction method and resulting detector performance of the improved design: the PANDA 3D Disc DIRC.