Reply to the Comments on the XENON100 First Dark Matter Results

Abstract

The recently submitted preprint on the first results from the XENON100 dark matter experiment (arxiv:1005.0380) was followed by a criticism by J.I. Collar and D.N. McKinsey (arxiv:1005.0838), focused on our extrapolation of the scintillation efficiency L_eff to the lowest nuclear recoil energies, where no data and no theoretical model exist. Here we add clarifications on our analysis and comment on their criticism.

Figures (3)

• Figure 1: All published data on ${\cal L}_{\text{eff}}$: The black datapoints -- used for the global fit in the XENON100 paper ref:xe100 -- are all published direct measurements of ${\cal L}_{\text{eff}}$. The red data (Sorensen (XENON10) ref:xe10Leff and Lebedenko (ZEPLINIII) ref:zep3) are from comparisons of data with Monte Carlo simulations. They were not used on the global fit because of their possibly larger systematic uncertainties. The three blue solid contours are the result from a global fit to all direct measurements (black) in the region from 5 -- 100 keV$_r$. The thinner contours above and below are the $\pm$90% confidence level contours. The dashed lines below 5 keV$_r$ are the extrapolations as explained in the text. For the first XENON100 data analysis, only the best fit and the lower 90% CL contour are used.
• Figure 2: Expected spectrum of a 10 GeV/$c^2$ WIMP with a cross section of $1 \times 10^{-41}$ cm$^2$ (black, solid), a benchmark case at the lower edge of the DAMA region. The red (dashed) lines show the spectrum after a convolution with a Poisson distribution, the blue (thick dashed) line is corrected for the XENON100 efficiency. The straight lines are the 3 PE and 4 PE thresholds using the lower 90% CL ${\cal L}_{\text{eff}}$ contour of the global fit as explained in the text.
• Figure 3: 90% confidence limits for the global fit of ${\cal L}_{\text{eff}}$ with a threshold of 4 PE (black), and curves for the 90% lower contour of ${\cal L}_{\text{eff}}$ at thresholds of 4 PE (yellow) and 3 PE (magenta). We used the following astrophysical parameters: galactic escape velocity = 544 km/s, WIMP density = 0.3 GeV/cm$^3$, solar velocity = 220 km/s.