Proceedings (PRO)

Proceedings for the CHEP 2018. Deadline for initial submission is October 31st, 2018.

The Endcap Disc DIRC has been developed to provide an excellent particle identification
for the future PANDA experiment by separating pions and kaons up to a momentum of 4 GeV/c with
a separation power of 3 standard deviations in the polar angle region from 5 ◦ to 22 ◦ . This goal will
be achieved using dedicated particle identification algorithms based on likelihood methods and will
be applied in an offline analysis and online event filtering. This paper evaluates the resulting PID
performance using Monte-Carlo simulations to study basic single track PID as well as the analysis
of complex physics channels. The online reconstruction algorithm has been tested with a Virtex4
FGPA card and optimized regarding the resulting constraints.

The Endcap Disc DIRC (EDD) has been developed to provide an excellent particle identification in the future PANDA experiment by separating pions and kaons up to a momentum of 4\,GeV/c with a separation power of 3\,s.d.. The detector is placed in the forward endcap of the PANDA target spectrometer. It consists of a fused silica plate and focusing elements placed at the outer rim, which focus the Cherenkov light on the photo cathodes of the attached MCP-PMTs. A compact and fast readout of the signals is realized with special ASICs. The performance has been studied and validated with different prototype setups in various testbeam facilities.

The PANDA detector at the future FAIR facility at GSI is planned as a fixed- target experiment for proton-antiproton collisions at momenta between 1.5 and 15 GeV/c. It will be used to address open questions in hadronic physics. In order to achieve a sufficient particle identification, two different DIRC detector concepts have been developed. This talk will cover the Endcap Disc DIRC detector which is placed at the forward endcap of the PANDA target spectrometer and will provide a 3σ separation of pions and kaons up to a momentum of 4 GeV/c for polar angles from 5° to 22°. The most important component of the DIRC detector is a 2 cm thin fused silica radiator plate that is divided into 4 identical quadrants. The surfaces are polished with high precision in order to guarantee little photon losses by total reflection and conserve the Cherenkov angle during propagation through the optical system. Intrinsic chromatic errors will be minimized by the implementation of an optical filter. The readout system consists of 96 readout elements with focusing optics and attached MCP-PMTs to focus the photons that are produced by the Cherenkov cone of the traversing particle and acquire their position and timing information. This new detector concept requires the development of dedicated reconstruction and particle identification algorithms which permit an efficient analysis of the measured time-correlated photon patterns. Time and event based simulations with dedicated Monte-Carlo simulation frameworks have been used to validate the PID requirements of the DIRC counter. Additionally, the Monte-Carlo simulations have been used to estimate the radiation dose in different detector volumes in order to compare these values with actual measurement results.

The PANDA experiment at FAIR will use DIRC detectors for the separation of hadrons. The compactness of the PANDA detector requires the image planes of these detectors to be placed inside the magnetic field of the solenoid. Due to this and other boundary conditions MCP-PMTs were identified as the only suitable photon sensors. Until recently the major obstacle for an application of MCP-PMTs in high rate experiments like PANDA were serious aging problems which led to damage at the photo-cathode and a fast declining quantum efficiency as the integrated anode charge (IAC) increased. With new countermeasures against the aging, in particular due to the application of an atomic layer deposition (ALD) technique to coat the MCP pores, the lifetime of MCP-PMTs has meanwhile increased by a factor >50 which is fully sufficient for PANDA. The recent results of our long-term lifetime measurements are discussed. New 2-inch MCP-PMT prototypes from Hamamatsu show an encouraging behavior. However, the currently best performing MCP-PMT is a 2-inch PHOTONIS tube with two ALD-layers which reaches an IAC of >16 C/cm2 without any visible sign of aging. In the second part of these proceedings a new data acquisition system of the PADIWA/TRB type is presented which allows a quasi-parallel measurement of many MCP-PMT performance parameters. Especially unwanted effects like dark-count rate, crosstalk, ion afterpulsing, and recoil electrons can be studied in more detail than ever before. Exemplary results for these parameters are shown. The discussed DAQ system will be used for the comprehensive data quality checks of the MCP-PMTs being built into the DIRCs.

The PANDA experiment is a fixed target experiment where antiprotons collide with stationary hydrogen atoms. The main physics program of the experiment is to study open questions in hadron physics by performing charmonium spectroscopy by precise measurements of width, mass and decay branches and investigating possible exotic states like glueballs and hybrids. The Barrel Time-of-Flight detector (Barrel TOF), which is built in the PANDA target spectrometer, located between the DIRC detector and the EMC, has been designed to precisely measure the time at which a charged particle transits the detector with a resolution superior to the other sub-detectors of PANDA. A time resolution below 100 ps (sigma) is mandatory for this sub-detector to fulfill the requirements of good event separation and particle identification below the Cherenkov threshold. The implementation of the Barrel TOF is based on very fast organic scintillator tiles with a size of 87x29.5x5 mm3 coupled to Silicon Photomultipliers. The total of 1920 tiles are read out each by 8 SiPMs and cover almost the full azimuthal angular range and polar angles from 22.5 deg to 140 deg and an area of about 5 m2. The current prototypes achieve ~60 ps, well below the design goal. The detector R&D is now in a matured stage.

The favored photon sensors for the DIRC (detection of internally reflected Cherenkov light) detectors at the PANDA (Anti-proton Annihilation at Darmstadt) experiment at FAIR (Facility for anti-proton and ion research) are microchannel-plate photomultipliers (MCP-PMTs). The main problem until a few years ago was the limited lifetime of the MCP-PMTs caused by a rapid decrease in quantum efficiency (QE) of the photo cathode (PC) with increasing integrated anode charge (IAC). These limitations are overcome by applying an atomic layer deposition (ALD) coating on the MCPs, as recently done by PHOTONIS and Hamamatsu. During the last years tests of lifetime enhanced MCP-PMTs were performed and their results were compared. For this the QE was measured in dependence of the IAC as function of the wavelength and position dependent across the PC. The best performing tubes show a lifetime increase compared to not enhanced devices by a factor > 50 with an IAC > 13 C/cm2. Additionally, performance results of new 2 inch Hamamatsu tubes and a new high QE PHOTONIS tube are presented.

Microchannel-plate (MCP) PMTs are the favored photon sensors for the DIRC detectors of the PANDA experiment at FAIR. Until recently the main drawback of MCP-PMTs were serious aging eects which led to a limited lifetime due to a rapidly decreasing quantum effciency (QE) of the photo cathode (PC) as the integrated anode charge (IAC) increased. In the latest models of PHOTONIS and Hamamatsu an innovative atomic layer deposition (ALD) technique is applied to overcome these limitations. During the last five years comprehensive aging tests with ALD coated MCP-PMTs were performed and the results were compared to tubes treated with other techniques. The QE in dependence of the IAC was measured as a function of the wavelength and the position across the PC. For the best performing tubes the lifetime improvement in comparison to the older MCP-PMTs is a factor of >50 based on an IAC of meanwhile >10 C/cm2. In addition, the performance results of a new 2-inch ALD coated MCP-PMT prototype from Hamamatsu with a very high position resolution (128x6 anode pixels) is presented and the first conclusions from investigations concerning the PC aging mechanism will be discussed.

Microchannel plate (MCP) PMTs are very attractive photon sensors for low light level applications in strong magnetic fields. However, until recently the main drawback of MCP-PMTs was their aging behavior which manifests itself in a limited lifetime due to a rapidly decreasing quantum effciency (QE) of the photo cathode (PC) as the integrated anode charge (IAC) increases. In the latest models of PHOTONIS, Hamamatsu, and BINP novel techniques are applied to avoid these aging effects which are supposed to be mainly caused by feedback ion impinging on the PC and damaging it. Since more than four years we are running a long-term aging test with new lifetime-enhanced MCP-PMT models by simultaneously illuminating various PMTs with roughly the same photon rate. This allows a fair comparison of the lifetime of all investigated MCP-PMTs and will give some insight in the best techniques to be applied for a lifetime enhancement. In this paper the results of comprehensive aging tests will be discussed. Gain, dark count rate and QE were investigated for their dependence on the IAC. The QE was measured spectrally resolved and as a function of the position across the PC to identify regions where the damage develops first. For the best performing tubes the lifetime improvement compared to former MCP-PMTs is a factor of ~50 based on an IAC of meanwhile >10 C/cm2. This breakthrough in the lifetime of MCP-PMTs was achieved by coating the MCP pores with an atomic layer deposition (ALD) technique.

For the identification of low momentum charged particles and for event timing purposes a barrel Time-of-Flight (TOF) detector surrounding the interaction point is planned for the PANDA experiment at FAIR. Since the boundary conditions in terms of available radial space and radiation length are quite strict the favored layout is a hodoscope composed of several thousand small scintillating tiles (SciTils) read out by silicon photomultipliers (SiPMs). A time resolution of well below 100 ps is aimed for. With the originally proposed 30 x 30 x 5 mm3 SciTils read out by two single 3 x 3 mm2 SiPMs at the rims of the scintillator the targeted time resolution can be just reached, but with a considerable position dependence across the scintillator surface. In this paper we discuss other design options to further improve the time resolution and its homogeneity. It will be shown that wide scintillating rods (SciRods) with a size of, e.g., 50 x 30 x 5 mm3 or longer and read out at opposite sides by a chain of four serially connected SiPMs a time resolution down to 50 ps can be reached without problems. In addition, the position dependence of the time resolution is negligible. These SciRods were tested in the laboratory with electrons of a 90Sr source and under real experimental conditions in a particle beam at CERN. The measured time resolutions using fast BC418 or BC420 plastic scintillators wrapped in aluminum foil were consistently between 45 and 75 ps dependent on the SciRod design. This is a significant improvement compared to the original SciTil layout.