A. Lehmann

Lifetime of MCP-PMTs

The main particle identification detector of the PANDA experiment will be of the DIRC type. For various reasons the favored sensors are micro-channel plate photo multipliers (MCP-PMTs). Despite many advantageous properties MCP-PMTs until recently had serious problems with aging issues at high photon rates. In this paper we present a simultaneous aging measurement for the latest MCP-PMTs of BINP, Hamamatsu (R10754X) and PHOTONIS (XP85112). In these devices specific countermeasures have been applied to reduce the loss of quantum efficiency (QE) of the photo cathode (PC) with increasing anode charge, which is the main feature of aging. We find that the new techniques show a significantly increased lifetime of the concerning MCP-PMTs. With several surface scans across the active area of the MCP-PMTs we find evidence that the loss of QE develops from the rims and corners of the PC. In addition, the spectral QE of the MCP-PMTs is given as a function of the integrated anode charge revealing that for the R10754X the QE drops faster for long wavelenghts than for short ones. At this point of the ongoing measurements the XP85112 does not show any significant aging signs after 5.6 C/cm2 which is a more than an order of magnitude improvement compared to former MCP-PMTs and corresponds to more than 10 years of running time for the PANDA Barrel DIRC. In this PMT the micro-channels are coated by an atomic layer deposition (ALD) technique which currently appears to be the most promising countermeasure against the aging of MCP-PMTs.

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.

Fast SiPM Readout of the PANDA TOF Detector

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 × 30 × 5 mm3 SciTils read out by two single 3 × 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 × 30 × 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.

A focussing disc DIRC for the PANDA experiment

The PANDA experiment at the planned facility for anti-proton and ion research (FAIR) aims at studying the strong interaction by precision spectroscopy, hunting for exotic hadronic states, hard exclusive processes and measuring Drell-Yan pairs. A detector system with excellent particle identification properties covering the full angular and momentum range is therefore mandatory. Polar angles from 5deg to 25deg will be covered by a novel detector in disc geometry using the DIRC principle. The conceptual design of this device includes dispersion correction and focussing optics. Studies are carried out on the radiation hardness of fused silica as candidate radiator material. MCP-PMTs were tested as a likely photon detector candidate. Both studies show that promising candidates for the final detector are already identified.

The Barrel TOF detector for P̅ANDA

D. Steinschaden1∗,K. Dutta2, L. Gruber1, K. Suzuki1, M. Böhm3, M. Cardinali4, M. Hoek4, K. Kalita2, K. Götzen6, H. Kumawat5, W. Lauth4, A. Lehmann3, J. Marton1, H. Orth6, A. Parmar5, B. J. Roy5, C. Sonika5, L. Schmitt7, C. Schwarz6, C. Sfienti4, M. Thiel4 1Stefan Meyer Institute for Subatomic Physics, Austrian Academy of Sciences, Vienna, Austria 2Department of Physics, Gauhati Universitiy, Guwahati, India 3Friedrich Alexander-University of Erlangen-Nuremberg, Erlangen, Germany 4Institut für Kernphysik, Johannes Gutenberg-University Mainz, Mainz, Germany 5Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai, India 6GSI Helholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany 7Facility for Antiproton and Ion Research in Europe GmbH, Darmstadt, Germany E-mail: dominik.steinschaden@oeaw.ac.at