CERN-LHC. Measurements of the pseudorapidity gap and xi distributions for dijet production in diffractive events which are defined by large gaps devoid of activity seen in the ATLAS detector, based on a sample of proton-proton collisions at a centre-of-mass energy of 7 TeV of integrated luminosity of 6.8 nb-1 collected in 2010. The final state consists of two jets found by the anti-kt jet algorithm with transverse momentum greater than 20 GeV and empty regions in the acceptance of the ATLAS detector. The pseudorapidity gap variable, denoted here as DELTA(C=RAPGAP), is defined as the larger of the pseudorapidity regions extending to the limits of the ATLAS detector sensitivity at eta=+-4.8, in which no final state particles are observed above a (transverse) momentum threshold. The xi variable is calculated using M**2/S and for Single Diffraction DELTA(C=RAPGAP)~=-ln(xi). See PLBXX (2015) YY for more details. The fiducial region is defined as: The jet finding uses the anti-kt algorithm with radius R=0.6 or R=0.4 - all stable particles are used except for muons and neutrinos - at least 2 jets with ptJet1 > 20 GeV and ptJet2 > 20 GeV - at least 2 jets with |etaJet1| < 4.4 and |etaJet2| < 4.4 The selection of particles for the gap finding: - |etaParticle| < 4.8 - pParticleNeutral > 0.2 GeV - pParticleCharged > 0.5 GeV .or. ptParticleCharged > 0.2 GeV - The gap finding: two gaps are formed defined as the regions without particles from the edge of the calorimeter at eta=4.8 or eta=-4.8. The larger of the two is the final gap. The selection of particles for the xi calculation: - |etaParticle| < 4.8 - pParticleNeutral > 0.2 GeV - pParticleCharged > 0.5 GeV - The xi value is calculated as Sum [ptParticle*exp(+-etaParticle)/sqrt(S)] where the sum loops over the particles selected above and the exponential function takes the positive (negative) sign if the gap starts at eta = +4.8 (-4.8). In the tables the individual sources of systematic uncertainty are given in per cent and are described as follows: dJES = jet energy scale uncertainty dJER = jet energy resolution uncertainty dJAR = jet angular resolution uncertainty dJRE = jet reconstruction efficiency uncertainty dClustE = cluster energy scale uncertainty dCST = cell significance threshold uncertainty dJCE = jet cleaning efficiency uncertainty dUnf = unfolding procedure uncertainty dMod = model uncertainty dTrig = jet trigger efficiency uncertainty dtrack = tracking efficiency uncertainty dlum = luminosity uncertainty dmat = added material uncertainty.