Universality and mX cut effects in B ->Xsl+l-

The most precise comparison between theory and experiment for the B → Xs(ell)+(ell)- rate is in the q2 < 6 GeV2 region. The hadronic uncertainties associated with an experimentally required cut on mX potentially spoil the extraction of short distance flavor-changing neutral current couplings. We compute the mX cut dependence of dΛ(B → Xs(ell)+(ell)-)/dq2 using the B → Xsγ shape function, and show that the effect is universal for all short distance contributions in the limit mX2 << mB2. This universality is not spoiled by realistic values of the mX cut, nor by αs corrections. Alternatively, normalizing the B → Xs(ell)+(ell)- rate to B → Xu(ell)(bar ν) with the same cuts removes the main uncertainties. We find that the forward-backward asymmetry vanishes near q02 = 3 GeV2