Observation of Associated Near-Side and Away-Side Long-Range Correlations insNN=5.02  TeVProton-Lead Collisions with the ATLAS Detector

Abstract

Two-particle correlations in relative azimuthal angle (Δø) and pseudorapidity (Δη) are measured in sqrt[s(NN)] = 5.02 TeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1 μb(-1) of data as a function of transverse momentum (p(T)) and the transverse energy (ΣE(T)(Pb)) summed over 3.1 < η < 4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2 < |Δ η | < 5) "near-side" (Δø ~ 0) correlation that grows rapidly with increasing ΣE(T)(Pb). A long-range "away-side" (Δø ~ π) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ΣE(T)(Pb), is found to match the near-side correlation in magnitude, shape (in Δη and Δø) and ΣE(T)(Pb) dependence. The resultant Δø correlation is approximately symmetric about π/2, and is consistent with a dominant cos2Δø modulation for all ΣE(T)(Pb) ranges and particle p(T).

Measurement of Long-Range Angular Correlation and Quadrupole Anisotropy of Pions and (Anti)Protons in Centrald+AuCollisions atsNNAdare1, Aidala2, Ajitanand3 et al. 2015Phys. Rev. Lett.Self Cite152131180View full textAdd to dashboardCite

“…Even if there is a 30% enhancement of jet-like correlation from p+p to central d+Au collisions, it will only raise from 10% to 13% our estimate of the jet-like contribution to the v 2 in central d+Au collisions. The present v 2 measurement is closer to that of p+Pb collisions [2,3,6]. It is about 20% higher than that of p+Pb at p T = 1 GeV/c, and the difference decreases to a few percent at p T > 2.0 GeV/c.…”

“…The d+Au and p+Pb systems have generally been considered too small to create significant quantities of hot nuclear matter. This assumption has been challenged in p+Pb at √ s N N = 5.02 TeV with the measurements of (i) near-side azimuthal correlations across a large pseudorapidity gap [1][2][3], also observed in high multiplicity p+p collisions at 7 TeV [4], and (ii)the elliptic anisotropy parameter v 2 measured by multiple particle correlations [5,6].…”

What have we learned about the quark–gluon plasma with the ATLAS detector at the LHC?

“…2 for the high p T behavior of v 2 . To suggest that the Cronin effect is a collective effect would have seemed preposterous before the observation of the "double ridge" at the LHC [8]. However, given the observation of higher-order flow harmonics and non-zero multiparticle cumulants [13], its interpretation as a possible collective effect seems more plausible at the present time.…”

“…While originally intended to isolate the effects of the nuclear wave function on hard processes, even the very first measurements of soft and semi-hard observables (e.g. multiplicity, charged particle spectra) have revealed subtle conceptual issues pertaining to both nucleon-nucleon collisions, and to the conditions under which a quark-gluon plasma can be formed [8].…”

Measurement of the D0 Meson Production in Pb–Pb and p–Pb Collisions

“…Recent studies on long-range correlations of charged hadrons in p-Pb collisions [86][87][88][89], the measured species-dependent nuclear modification factor of pions, kaons, and protons in d-Au collisions [90], and the larger suppression observed for the ψ meson with respect …”