A. Britting

Studies of MCP properties

Cherenkov detectors of the DIRC type will be used for the particle identification of the PANDA experiment at FAIR. Because of their advantageous properties inside a magnetic field micro-channel plate (MCP) photomultipliers (PMT) are very attractive photon sensors for the two PANDA DIRCs. Various types of MCP-PMTs were investigated. Their gains and their time resolutions were measured as a function of the magnitude and the direction of a magnetic field. It was found that with a pore size of ≤ 10 μm efficient single photon detection is possible even at 2 Tesla if the field direction is close to parallel to the PMT axis. The gain of most of the studied MCP-PMTs remains stable up to a photon density of roughly 1 MHz/cm2, while the new Hamamatsu R10754-00-L4 can stand rates of about 10 MHz/cm2 before the gain starts decreasing. The time resolution of all investigated MCP-PMTs was better than 50 ps (σ). The response of the multi-anode MCP-PMTs was scanned as a function of the position of the photo cathode plane in particular to measure the crosstalk among adjacent pixels. Most of the sensors show a satisfactory behavior.

Lifetime-issues of MCP-PMTs

Cherenkov detectors of the DIRC principle will be used at the ANDA experiment at FAIR. Attractive photo sensor candidates for these devices are micro-channel plate (MCP) photomultipliers (PMT). The reasons are their excellent time resolution and their usability inside magnetic fields, although their lifetime is problematic. Various types were investigated. This paper will concentrate on the performance of the Photonis XP85112 and especially its lifetime behavior. For this MCP-PMT a time resolution of 33ps (σ) was measured and it is stable up to photon rates of about 2 MHz/cm2. The peak quantum efficiency (QE) was determined to 24%. Before the actual lifetime measurement several studies were performed, such as scanning the surface of the detector to get the geometrical detector response function. Additionally the gain and time resolution were investigated in a magnetic field up to 2T. Afterwards the lifetime measurements were done up to an integrated charge of 305 mC/cm2, i.e. the collected charge was 1-5 mC/cm2 per day. The gain and QE were determined in irregular intervals of 1-3 days. Also QE scans as a function of the position at the photo cathode were done every 2-3 weeks.

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.

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.

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.

The PANDA DIRC detectors at FAIR

The PANDA detector at the international accelerator Facility for Antiproton and Ion Research in Europe (FAIR) addresses fundamental questions of hadron physics. An excellent hadronic particle identification (PID) will be accomplished by two DIRC (Detection of Internally Reflected Cherenkov light) counters in the target spectrometer. The design for the barrel region covering polar angles between 22o to 140o is based on the successful BABAR DIRC with several key improvements, such as fast photon timing and a compact imaging region. The novel Endcap Disc DIRC will cover the smaller forward angles between 5o (10o) to 22o in the vertical (horizontal) direction. Both DIRC counters will use lifetime-enhanced microchannel plate PMTs for photon detection in combination with fast readout electronics. Geant4 simulations and tests with several prototypes at various beam facilities have been used to evaluate the designs and validate the expected PID performance of both PANDA DIRC counters.