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Recent proton decay results from Super-Kamiokande
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Nuclear Physics B (Proc. Suppl.) 221 (2011) 387–388 www.elsevier.com/locate/npbps
Recent proton decay results from Super-Kamiokande J L Raaf for the Super-Kamiokande Collaboration Boston University, Department of Physics, 590 Commonwealth Avenue, Boston, MA 02215 E-mail: [email protected] Abstract. Recent experimental limits on the search for proton decay are presented. Data from Super-Kamiokande, a water Cherenkov detector with a fiducial volume of 22,500 tons of ultra pure water, are used in the analysis. Analyses from SK-I (40% photomultiplier coverage) plus SK-II (20% photomultiplier coverage) are reported with results from p → e+ π 0 , p → μ+ π 0 , and p → ν¯K + .
1. Introduction In the Standard Model, protons have a lifetime which is finite but unobservably long. The long lifetime arises from baryon number (B) conservation; however, the conservation of baryon number is considered an open experimental question, since it was introduced to the Standard Model empirically. Grand unified theories (GUTs) attempt to unify the three fundamental interactions in the Standard Model, motivated in part by the desire to constrain some of the seemingly arbitrary quantities in the model. An important decay mode in many GUTs is p → e+ π 0 , which can proceed via exchange of an extremely heavy X boson. Many other decay modes are also predicted; different modes are favored by different GUTs. 2. Results The Super-Kamiokande (SK) detector is well-suited to proton decay searches, with 7.5 × 1033 protons in the 22.5 kiloton fiducial volume. The backgrounds to proton decay in SK arise from atmospheric neutrino interactions; they are carefully accounted for in all proton decay searches. The results presented here are the combined results of SK-I and SK-II datasets. The main difference between SK-I and SK-II is the photocathode coverage of the detector (40% for SK-I, 20% for SK-II). Table 1 shows the limits set on the proton lifetime for recent Super-Kamiokande searches.
Table 1. Summary of recent Super-K proton decay searches. Mode e+ π 0
p→ p → μ+ π 0 p → ν¯K +
Dataset SK-I + SK-II SK-I + SK-II SK-I
Lifetime (yrs) 1033
8.4 × 6.6 × 1033 2.3 × 1033
0920-5632/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2011.10.038
Reference [1] [1] [2]
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J.L. Raaf / Nuclear Physics B (Proc. Suppl.) 221 (2011) 387–388
Acknowledgments We gratefully acknowledge the cooperation of the Kamioka Mining and Smelting Company. The Super-Kamiokande experiment was built from and has been operated with funding from the Japanese Ministry of Education, Culture, Sports, Science, and Technology, the United States Department of Energy, and the U.S. National Science Foundation. References [1] Clark S T 2006 Searches for proton decay with the Super-Kamiokande detector PhD thesis, Boston University [2] Kobayashi K et al. 2005 Search for nucleon decay via modes favored by supersymmetric grand unification models in Super-Kamiokande-I Phys. Rev. D 72 052007
Nuclear Physics B (Proc. Suppl.) 221 (2011) 387–388 www.elsevier.com/locate/npbps
Recent proton decay results from Super-Kamiokande J L Raaf for the Super-Kamiokande Collaboration Boston University, Department of Physics, 590 Commonwealth Avenue, Boston, MA 02215 E-mail: [email protected] Abstract. Recent experimental limits on the search for proton decay are presented. Data from Super-Kamiokande, a water Cherenkov detector with a fiducial volume of 22,500 tons of ultra pure water, are used in the analysis. Analyses from SK-I (40% photomultiplier coverage) plus SK-II (20% photomultiplier coverage) are reported with results from p → e+ π 0 , p → μ+ π 0 , and p → ν¯K + .
1. Introduction In the Standard Model, protons have a lifetime which is finite but unobservably long. The long lifetime arises from baryon number (B) conservation; however, the conservation of baryon number is considered an open experimental question, since it was introduced to the Standard Model empirically. Grand unified theories (GUTs) attempt to unify the three fundamental interactions in the Standard Model, motivated in part by the desire to constrain some of the seemingly arbitrary quantities in the model. An important decay mode in many GUTs is p → e+ π 0 , which can proceed via exchange of an extremely heavy X boson. Many other decay modes are also predicted; different modes are favored by different GUTs. 2. Results The Super-Kamiokande (SK) detector is well-suited to proton decay searches, with 7.5 × 1033 protons in the 22.5 kiloton fiducial volume. The backgrounds to proton decay in SK arise from atmospheric neutrino interactions; they are carefully accounted for in all proton decay searches. The results presented here are the combined results of SK-I and SK-II datasets. The main difference between SK-I and SK-II is the photocathode coverage of the detector (40% for SK-I, 20% for SK-II). Table 1 shows the limits set on the proton lifetime for recent Super-Kamiokande searches.
Table 1. Summary of recent Super-K proton decay searches. Mode e+ π 0
p→ p → μ+ π 0 p → ν¯K +
Dataset SK-I + SK-II SK-I + SK-II SK-I
Lifetime (yrs) 1033
8.4 × 6.6 × 1033 2.3 × 1033
0920-5632/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2011.10.038
Reference [1] [1] [2]
388
J.L. Raaf / Nuclear Physics B (Proc. Suppl.) 221 (2011) 387–388
Acknowledgments We gratefully acknowledge the cooperation of the Kamioka Mining and Smelting Company. The Super-Kamiokande experiment was built from and has been operated with funding from the Japanese Ministry of Education, Culture, Sports, Science, and Technology, the United States Department of Energy, and the U.S. National Science Foundation. References [1] Clark S T 2006 Searches for proton decay with the Super-Kamiokande detector PhD thesis, Boston University [2] Kobayashi K et al. 2005 Search for nucleon decay via modes favored by supersymmetric grand unification models in Super-Kamiokande-I Phys. Rev. D 72 052007