The Next Generation of Photo-Detectors for Particle Astrophysics

arXiv:0904.3565v1 [astro-ph.IM] 22 Apr 2009 The Next Generation of Photo-Detectors for Particle Astrophysics Robert G. Wagner1, Karen L. Byrum, Mayly Sanchez, Alexandre V. Vaniachine Argonne National Laboratory Oswald Siegmund Space Sciences Laboratory, University of California, Berkeley Nepomuk A. Otte University of California, Santa Cruz Erik Ramberg, Jeter Hall Fermi National Accelerator Laboratory and James Buckley Washington University, St. Louis ABSTRACT We advocate support of research aimed at developing alternatives to the pho- tomultiplier tube for photon detection in large astroparticle experiments such as gamma-ray and neutrino astronomy, and direct dark matter detectors. Specifi- cally, we discuss the development of large area photocathode microchannel plate photomultipliers and silicon photomultipliers. Both technologies have the poten- tial to exhibit improved photon detection efficiency compared to existing glass vacuum photomultiplier tubes. – 2 – 1. Introduction High energy physics and astroparticle physics experiments require large area photon counting detectors with high efficiency and low cost per channel cost. Currently, vacuum technology is the only way to achieve the large areas while maintaining high gains and photon-counting operation. Even as the requirements of future experiments grow, the avail- able vendors of vacuum-based photon detectors are shrinking. Companies that manufacture vacuum tube based photon counting detectors are reducing their capabilities in favor of more profitable semiconductor based technologies. This threatens to raise the costs, extend the planning required, and even compromise large scientific projects based on the detection of coherent light phenomena, especially scintillation and Cherenkov light. The most common photon detection device in use for high energy and astroparticle physics is the photomultiplier tube (PMT); first developed in the 1930s (Lubsandorzhiev 2006). In addition to particle, nuclear and astrophysics experiments, the technology is used today in a wide range of research fields such as space, medicine, biology, and chemistry. While the basic structure of PMTs remains unchanged from its inception, much development has taken place with regard to improved photocathode efficiency, precision timing characteris- tics, and multi-anode readout capability. Depending on the details of the dynode structure, amplifications of 107 can be achieved while still retaining single photoelectron sensitivity. Photocathode efficiencies presently are typically on the order of 20%, although new photo- cathode technologies can achieve twice that value. The transit time for the generation of a signal is typically < 100ns, with the transit time spread, and thus, timing resolution for single photoelectrons, on the order of a nanosecond. The cost of a phototube can be as low as $10/cm2 of photocathode coverage, with optimized detectors costing up to 10 times that. Alternative technologies to PMTs have arisen, but the superb performance and economics of phototubes is such that major innovation for vacuum photomultipliers has proceeded slowly. A promising new approach being pursued by several research groups is to combine mod- ern semiconductor technology with vacuum devices. For example, new cathode structures (in some cases semiconductor heterostructures engineered to promote efficient electron transport and other features such as intrinsic high gain or fast timing) are being combined with new kinds of electron multipliers that lend themselves to very large areas, and mass fabrication. Designs for these electron multipliers range from silicon and ceramic microchannel plates and semiconductor nanostructures to gas electron multipliers (GEMs) aimed at dramatically re- ducing the cost per unit area. New techniques for direct deposition of cathode surfaces on silicon microchannels could result in dramatic improvements. The funding for all of these developments falls short of what is required to maintain credible efforts at universities and national laboratories. Development work at U.S. research institutions is lagging compared – 3 – to similar efforts based mainly in Europe. A substantial change in the status quo is needed for new technical approaches to be developed before further shrinkage of commercial tech- nology occurs and for the U.S. to remain competitive in the development of photon detection technology. In this white paper we address two such technologies that hold the potential for replacing the PMT in many astrophysical applications: large area microchannel plate photomultipliers (MCP) and Geiger-mode avalanche photodiodes or silicon photomultipliers (SiPM). 2. Physics Motivations 2.1. Gamma-ray Astronomy TeV Gamma-ray astronomy is one of the youngest sciences, having established its first firm detection, the Crab Nebula, (Weekes et al. 1989) in 1988. In the past 3 years, the number of TeV-band sources has increased by an order of magnitude, including the remnants of supernov

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