Abstract
We report on the high statistics two-pion correlation functions from pp collisions at $\sqrt{s}=0.9$ TeV and $\sqrt{s}$=7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions, and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant non-femtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low $p_{\rm T}$. They are well reproduced by the Monte-Carlo generators and seen also in $\pi^+\pi^-$ correlations.
Highlights
Proton-proton collisionsTeV and pffiffi sExperiment (ALICE) at the Large Hadron Collider (LHC) at CERN in 2010
In our previous work [14] we reported that a multiplicity integrated measurement does not show any pair momentum dependence of the Rinv radius measured in the Pair Rest Frame (PRF)
In this study we report on the analysis of pp collisions recorded by the ALICE experiment during the 2010 run of the LHC
Summary
Experiment (ALICE) at the Large Hadron Collider (LHC) at CERN in 2010. These collisions provide a unique opportunity to probe Quantum Chromodynamics (QCD) in the new energy regime. The distinguishing feature of QCD is the mechanism of color confinement, the physics of which is not fully understood, due, in part, to its theoretical intractability [1]. The confinement mechanism has a physical scale of the order of the proton radius and is especially important at low momentum. The study presented in this work aims to measure the space-time extent of the source on this scale. Two-pion correlations at low relative momentum were first shown to be sensitive to the interaction volume of the emitting source in p" þ p collisions by G.
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