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A high-precision measurement of the pion branching ratio

University of British Columbia

The pion decay branching ratio is an important observable in the Standard Model of particle physics. The value of the branching ratio has been calculated within the Standard Model to be (1.2352 ± 0.0002) ×10^−4. The PIENU experiment at TRIUMF aims to measure this quantity to a precision of < 0.1%. This tests the hypothesis that the leptons have identical weak couplings, known as lepton universality, at the 0.05% level. In addition, it provides stringent constraints on many other extensions to the Standard Model, such as R-parity violating supersymmetry, leptoquarks, and heavy neutrinos lighter than the pion. In certain cases, these constraints can far exceed the reach of direct searches at colliders. Most strikingly, a new pseudoscalar interaction whose energy scale were Ο(1000 TeV) would enhance the branching ratio by O(0.1%). The PIENU data set contains four years of data, taken between 2009 and 2012. The analysis of a subset of the 2010 data was published in 2015; the precision obtained for the branching ratio was approximately 0.25%. The 2012 data set is roughly five times larger than the 2010 data set, and its analysis is presented here. The statistical error using only 2012 data is 0.09%; incorporating the other data sets will reduce this to 0.07%. The systematic error in the 2012 analysis remains considerably larger than this, 0.27%, and the prospects for reducing it to the level needed to reach the precision goal of the experiment will be presented. The present work has been done as a blind analysis, with an unknown factor masking the branching ratio result; the final value will be obtained when the analysis is completed.

Text

2017-04-18

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/61255

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/