XENON100 exclusion limit without considering Leff as a nuisance parameter

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 10(-39) cm(2). The dependence of the exclusion limit in terms of the scintillation efficiency (L-eff) has been debated at length. To overcome possible criticisms XENON100 performed an analysis in which L-eff 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 L-eff 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 L-eff 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 L-eff as a nuisance parameter. Instead, L-eff is obtained directly from the fits to the data. This enables us to define frequentist confidence intervals by marginalizing over L-eff.