  We propose a novel phenomenological model of mean transverse momentum
fluctuations based on the Geometrical Scaling hypothesis. Bose-Einstein
correlations between two gluons generated from an identical color flux tube are
taken into account as a source of the fluctuation. We calculate an
event-by-event fluctuation measure $\sqrt{C_m}/\langle p_{\rm T}\rangle$ and
show that ALICE data observed at $\sqrt s=$0.90 TeV for $p$+$p$ collisions are
reproduced. By fitting our model to the experimental data, we evaluate the
transverse size of the color flux tube as a function of the multiplicity.
