Following the observation of long-range correlation signal in pp collisions with CMS collaboration, the ALICE Collaboration presented new results on observing the ridge structure, a long-range correlation of produced particles, in low-multiplicity proton-proton (pp) collisions at the Large Hadron Collider (LHC) at the 57th Rencontres de Moriond international conference.
These observations were unexpected as pp collisions were generally assumed to be too small and dilute to develop fluid-like behavior. However, the measured correlation yield represents correlated particle production related to collective effects, indicating that the signal is related to early-stage phenomena, such as in the shape of the initial collision region. These results will help identify the underlying dynamic mechanisms responsible for the emergence of collective effects in small collision systems.
In addition to presenting new results on observing the ridge structure in low-multiplicity proton-proton collisions, the ALICE Collaboration compared their findings to our published results from archived ALEPH electron-positron annihilation data. The comparison showed that the correlation strength in pp collisions is larger than that of electron-positron collisions of similar multiplicity, suggesting that the mechanisms behind the collective effects in pp collisions are distinct from those in electron-positron collisions.