Eur. Phys. J. C (2015) 75: 546
https://doi.org/10.1140/epjc/s10052-015-3657-5

Regular Article - Experimental Physics

Lowering the radioactivity of the photomultiplier tubes for the XENON1T dark matter experiment

¹ Laboratori Nazionali del Gran Sasso, Assergi, Italy
² Physics Department, Columbia University, New York, NY, USA
³ INFN-Laboratori Nazionali del Gran Sasso and Gran Sasso Science Institute, L’Aquila, Italy
⁴ Nikhef and the University of Amsterdam, Science Park, Amsterdam, Netherlands
⁵ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, Israel
⁶ Physics and Astronomy Department, University of California, Los Angeles, CA, USA
⁷ New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
⁸ Physik-Institut, University of Zurich, Zurich, Switzerland
⁹ Department of Physics, University of Coimbra, Coimbra, Portugal
¹⁰ Institut für Physik & Exzellenzcluster PRISMA, Johannes Gutenberg-Universität Mainz, Mainz, Germany
¹¹ Department of Physics and Astronomy, Purdue University, West Lafayette, IN, USA
¹² Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY, USA
¹³ Max-Planck-Institut für Kernphysik, Heidelberg, Germany
¹⁴ Institut für Kernphysik, Wilhelms-Universität Münster, Münster, Germany
¹⁵ Albert Einstein Center for Fundamental Physics, University of Bern, Bern, Switzerland
¹⁶ Subatech, Ecole des Mines de Nantes, CNRS/In2p3, Université de Nantes, Nantes, France
¹⁷ Department of Physics and Astrophysics, University of Bologna and INFN-Bologna, Bologna, Italy
¹⁸ INFN-Torino and Osservatorio Astrofisico di Torino, Turin, Italy
¹⁹ Department of Physics and Astronomy, Rice University, Houston, TX, USA
²⁰ University of Edinburgh, Edinburgh, UK
²¹ IFIC, CSIC-Universidad de Valencia, Valencia, Spain

^* e-mail: xe-editorial@lngs.infn.it

Received: 27 March 2015
Accepted: 4 September 2015
Published online: 23 November 2015

Abstract

The low-background, VUV-sensitive 3-inch diameter photomultiplier tube R11410 has been developed by Hamamatsu for dark matter direct detection experiments using liquid xenon as the target material. We present the results from the joint effort between the XENON collaboration and the Hamamatsu company to produce a highly radio-pure photosensor (version R11410-21) for the XENON1T dark matter experiment. After introducing the photosensor and its components, we show the methods and results of the radioactive contamination measurements of the individual materials employed in the photomultiplier production. We then discuss the adopted strategies to reduce the radioactivity of the various PMT versions. Finally, we detail the results from screening 286 tubes with ultra-low background germanium detectors, as well as their implications for the expected electronic and nuclear recoil background of the XENON1T experiment.