First Measurements of Beam Backgrounds at SuperKEKB
Abstract
The high design luminosity of the SuperKEKB electron-positron collider is expected to result in challenging levels of beam-induced backgrounds in the interaction region. Properly simulating and mitigating these backgrounds is critical to the success of the Belle~II experiment. We report on measurements performed with a suite of dedicated beam background detectors, collectively known as BEAST II, during the so-called Phase 1 commissioning run of SuperKEKB in 2016, which involved operation of both the high energy ring (HER) of 7 GeV electrons as well as the low energy ring (LER) of 4 GeV positrons. We describe the BEAST II detector systems, the simulation of beam backgrounds, and the measurements performed. The measurements include standard ones of dose rates versus accelerator conditions, and more novel investigations, such as bunch-by-bunch measurements of injection backgrounds and measurements sensitive to the energy spectrum and angular distribution of fast neutrons. We observe beam-gas, Touschek, beam-dust, and injection backgrounds. We do not observe significant synchrotron radiation, as expected. Measured LER beam-gas backgrounds and Touschek backgrounds in both rings are slightly elevated, on average three times larger than the levels predicted by simulation. HER beam-gas backgrounds are on on average two orders of magnitude larger than predicted. Systematic uncertainties and channel-to-channel variations are large, so that these excesses constitute only 1-2 sigma level effects. Neutron background rates are higher than predicted and should be studied further. We will measure the remaining beam background processes, due to colliding beams, in the imminent commissioning Phase 2. These backgrounds are expected to be the most critical for Belle II, to the point of necessitating replacement of detector components during the Phase 3 (full-luminosity) operation of SuperKEB.
Keywords
Cite
@article{arxiv.1802.01366,
title = {First Measurements of Beam Backgrounds at SuperKEKB},
author = {P. M. Lewis and I. Jaegle and H. Nakayama and A. Aloisio and F. Ameli and M. Barrett and A. Beaulieu and L. Bosisio and P. Branchini and T. E. Browder and A. Budano and G. Cautero and C. Cecchi and Y. -T. Chen and K. -N. Chu and D. Cinabro and P. Cristaudo and S. de Jong and R. de Sangro and G. Finocchiaro and J. Flanagan and Y. Funakoshi and M. Gabriel and R. Giordano and D. Giuressi and M. T. Hedges and N. Honkanen and H. Ikeda and T. Ishibashi and H. Kaji and K. Kanazawa and C. Kiesling and S. Koirala and P. Križan and C. La Licata and L. Lanceri and J. -J. Liau and F. -H. Lin and J. -C. Lin and Z. Liptak and S. Longo and E. Manoni and C. Marinas and K. Miyabayashi and E. Mulyani and A. Morita and M. Nakao and M. Nayak and Y. Ohnishi and A. Passeri and P. Poffenberger and M. Ritzert and J M. Roney and A. Rossi and T. Röder and R. M. Seddon and I. S. Seong and J. -G. Shiu and F. Simon and Y. Soloviev and Y. Suetsugu and M. Szalay and S. Terui and G. Tortone and S. E. Vahsen and N. van der Kolk and L. Vitale and M. Z. Wang and H. Windel and S. Yokoyama},
journal= {arXiv preprint arXiv:1802.01366},
year = {2018}
}
Comments
101 pages, 127 figures