Measurement of long-range near-side two-particle angular correlations in pp collisions at sqrt(s) = 13 TeV (1510.03068v2)

Abstract: Results on two-particle angular correlations for charged particles produced in pp collisions at a center-of-mass energy of 13 TeV are presented. The data were taken with the CMS detector at the LHC and correspond to an integrated luminosity of about 270 inverse nanobarns. The correlations are studied over a broad range of pseudorapidity (abs(eta) < 2.4) and over the full azimuth (phi) as a function of charged particle multiplicity and transverse momentum (pt). In high-multiplicity events, a long-range (abs(Delta eta) > 2.0), near-side (Delta phi approximately 0) structure emerges in the two-particle Delta eta-Delta phi correlation functions. The magnitude of the correlation exhibits a pronounced maximum in the range 1.0 < pt < 2.0 GeV/c and an approximately linear increase with the charged particle multiplicity, with an overall correlation strength similar to that found in earlier pp data at sqrt(s) = 7 TeV. The present measurement extends the study of near-side long-range correlations up to charged particle multiplicities of N[ch] approximately 180, a region so far unexplored in pp collisions. The observed long-range correlations are compared to those seen in pp, pPb, and PbPb collisions at lower collision energies.

• The paper demonstrates the emergence of a significant long-range near-side correlation structure in high-multiplicity events.
• It employs the CMS detector to analyze charged particle pairs across a broad pseudorapidity range and full azimuth with precise momentum selection.
• The study reveals a linear increase in correlation strength with particle multiplicity, peaking at transverse momentum between 1.0 and 2.0 GeV/c.

Measurement of Long-range Near-side Two-particle Angular Correlations in Proton-proton Collisions at $\sqrt{s} = 13$ TeV

Proton-proton (pp) collisions at the Large Hadron Collider (LHC) provide valuable insight into particle production processes governed by quantum chromodynamics (QCD). This paper presents an analysis of two-particle angular correlations of charged particles produced in pp collisions at a center-of-mass energy of 13 TeV, conducted by the CMS Collaboration. The data corresponds to an integrated luminosity of approximately 270 nb$^{-1}$, and the correlations are evaluated over a broad range of pseudorapidity ($|\eta| < 2.4$) and the full azimuthal angle ($\phi$) across different particle multiplicities and transverse momentum (\pt).

The paper reveals the emergence of a long-range ($|\Delta\eta| > 2.0$), near-side ($\Delta\phi \approx 0$) correlation structure, prominently observed in high-multiplicity events. The correlation magnitude peaks in the range $1.0 < \pt < 2.0$ GeV/c, showing an approximately linear increase with charged particle multiplicity. This correlation strength mirrors results from previous pp collision measurements at $\sqrt{s} = 7$ TeV.

The experimental setup includes a sophisticated CMS detector with various calorimeters, silicon trackers, and magnetic solenoids. The trigger system selects events with interesting attributes, allowing for a precise examination of the correlation phenomena. The particle pairs used in the analysis originate from the primary vertex, and different event classes are defined based on track multiplicity, aiding in identifying systematic effects.

Numerical outcomes indicate that the observed correlation structures may arise from initial-state gluon field correlations or hydrodynamic expansions of a partonic medium, although quantitative discrepancies are noted, particularly at higher multiplicities explored in the present paper. Notably, it appears that the energy dependence is minimal, confirmed by similar correlation yields observed previously at $\sqrt{s} = 7$ TeV.

The implications of high-energy pp collision studies span both practical and theoretical realms. On a practical level, these measurements enhance our understanding of particle production and momentum correlation mechanisms, impacting the design and operation of particle accelerators. Theoretically, the observations provide essential data required for calibrating simulation models like PYTHIA or EPOS, further elucidating QCD dynamics.

This research represents an important step in comprehending complex particle interactions at unprecedented energy levels. Future investigations might focus on extending the multiplicity range and refining theoretical models to account for discrepancies observed at higher multiplicities. Moreover, comparative analyses across different collision systems and energies can trace the evolution of correlation structures, potentially leading to novel insights into fundamental QCD processes.