XENON100 exclusion limit without considering Leff as a nuisance parameter

Jonathan H. Davis, Céline Bœhm, Niels Oppermann, Torsten Ensslin, and Thomas Lacroix
Phys. Rev. D 86, 015027 – Published 26 July 2012

Abstract

In 2011, the XENON100 experiment has set unprecedented constraints on dark matter-nucleon interactions, excluding dark matter candidates with masses down to 6 GeV if the corresponding cross section is larger than 1039cm2. The dependence of the exclusion limit in terms of the scintillation efficiency (Leff) has been debated at length. To overcome possible criticisms XENON100 performed an analysis in which Leff was considered as a nuisance parameter and its uncertainties were profiled out by using a Gaussian likelihood in which the mean value corresponds to the best fit Leff value (smoothly extrapolated to 0 below 3 keVnr). Although such a method seems fairly robust, it does not account for more extreme types of extrapolation nor does it enable us to anticipate how much the exclusion limit would vary if new data were to support a flat behavior for Leff below 3 keVnr, for example. Yet, such a question is crucial for light dark matter models which are close to the published XENON100 limit. To answer this issue, we use a maximum likelihood ratio analysis, as done by the XENON100 Collaboration, but do not consider Leff as a nuisance parameter. Instead, Leff is obtained directly from the fits to the data. This enables us to define frequentist confidence intervals by marginalizing over Leff.

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  • Received 12 April 2012

DOI:https://doi.org/10.1103/PhysRevD.86.015027

© 2012 American Physical Society

Authors & Affiliations

Jonathan H. Davis1, Céline Bœhm1,2, Niels Oppermann3, Torsten Ensslin3, and Thomas Lacroix4

  • 1Institute for Particle Physics Phenomenology, University of Durham, Durham, DH1 3LE, United Kingdom
  • 2LAPTH, U. de Savoie, CNRS, BP 110, 74941 Annecy-Le-Vieux, France
  • 3Max-Planck-Institut fur Astrophysik Karl-Schwarzschild-Str. 1. Postfach 13 17 85741 Garching, Germany
  • 4Ecole normale supérieure de Lyon, Site Jacques Monod 46 allée d’Italie, 69364 LYON cedex 07, France

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Vol. 86, Iss. 1 — 1 July 2012

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