The XENON1T experiment is currently in the commissioning phase at the Laboratori Nazionali del Gran Sasso , Italy .
In this article we study the experiment ’ s expected sensitivity to the spin-independent WIMP-nucleon interaction cross section , based on Monte Carlo predictions of the electronic and nuclear recoil backgrounds .

The total electronic recoil background in 1 tonne fiducial volume and ( 1 , 12 ) keV electronic recoil equivalent energy region , before applying any selection to discriminate between electronic and nuclear recoils , is ( 1.80 \pm 0.15 ) \cdot 10 ^ { -4 } ( kg \cdot day \cdot keV ) ^ { -1 } , mainly due to the decay of ^ { 222 } Rn daughters inside the xenon target .
The nuclear recoil background in the corresponding nuclear recoil equivalent energy region ( 4 , 50 ) keV , is composed of ( 0.6 \pm 0.1 ) ( t \cdot y ) ^ { -1 } from radiogenic neutrons , ( 1.8 \pm 0.3 ) \cdot 10 ^ { -2 } ( t \cdot y ) ^ { -1 } from coherent scattering of neutrinos , and less than 0.01 ( t \cdot y ) ^ { -1 } from muon-induced neutrons .

The sensitivity of XENON1T is calculated with the Profile Likelihood Ratio method , after converting the deposited energy of electronic and nuclear recoils into the scintillation and ionization signals seen in the detector .
We take into account the systematic uncertainties on the photon and electron emission model , and on the estimation of the backgrounds , treated as nuisance parameters .
The main contribution comes from the relative scintillation efficiency \mathcal { L } _ { \mathrm { eff } } , which affects both the signal from WIMPs and the nuclear recoil backgrounds .
After a 2 y measurement in 1 t fiducial volume , the sensitivity reaches a minimum cross section of 1.6 \cdot 10 ^ { -47 } cm ^ { 2 } at m _ { \chi } = 50 GeV/ c ^ { 2 } .