Formation time dependence of femtoscopic $\pi \pi$ correlations in p+p   collisions at $\sqrt{s_{NN}}$=7 TeV
  We investigate femtoscopic $\pi \pi$ correlations using the UrQMD approach combined with a correlation afterburner. The dependence of $\pi \pi$ correlations on the charged particle multiplicity and formation time in p+p collisions at $\sqrt{s_{NN}}$= 7 TeV is explored and compared to present ALICE data. The data allows to constrain the formation time in the string fragmentation to $\tau_f \leq 0.8$ fm/c. 
Gunnar Graef, Qingfeng Li, Marcus Bleicher
nucl-th