Onset of radial flow in p plus p collisions

It has been debated for decades whether hadrons emerging from p + p collisions exhibit collective expansion. The signal of the collective motion in p + p collisions is not as clear or as clean as in heavy-ion collisions because of the low multiplicity and large fluctuation in p + p collisions. The Tsallis blast-wave (TBW) model is a thermodynamic approach, introduced to handle the overwhelming correlation and fluctuation in the hadronic processes. We have systematically studied the identified particle spectra in p + p collisions from the BNL Relativistic Heavy Ion Collider (RHIC) to the CERN Large Hadron Collider (LHC) using TBW and have found no appreciable radial flow in p + p collisions below root s = 900 GeV. At the LHC higher energy of 7 TeV in p + p collisions, the radial flow velocity achieves an average value of = 0.320 +/- 0.005. This flow velocity is comparable to that in peripheral (40-60%) Au + Au collisions at the RHIC. Breaking of the identified particle spectra mT scaling was also observed at the LHC from a model-independent test.