Abstract
ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, ∆φ,
and pseudorapidity, ∆η, in √s=13 and 2.76 TeV pp collisions at the LHC using charged particles
measured in the pseudorapidity interval |η|<2.5. The correlation functions evaluated in
different intervals of measured charged-particle multiplicity show a multiplicity-dependent
enhancement at ∆φ ∼ 0 that extends over a wide range of ∆η, which has been referred to
as the “ridge”. Per-trigger-particle yields, Y(∆φ), are measured over 2<|∆η|<5. For both
collision energies, the Y(∆φ) distribution in all multiplicity intervals is found to be consistent
with a linear combination of the per-trigger-particle yields measured in collisions with
less than 20 reconstructed tracks, and a constant combinatoric contribution modulated by
cos (2∆φ). The fitted Fourier coefficient, v2,2, exhibits factorization, suggesting that the ridge
results from per-event cos (2φ) modulation of the single-particle distribution with Fourier
coefficients v2. The v2 values are presented as a function of multiplicity and transverse momentum. They are found to be approximately constant as a function of multiplicity and to
have a pT dependence similar to that measured in p+Pb and Pb+Pb collisions. The v2 values
in the 13 and 2.76 TeV data are consistent within uncertainties. These results suggest that the
ridge in pp collisions arises from the same or similar underlying physics as observed in p+Pb
collisions, and that the dynamics responsible for the ridge has no strong √
s dependence.
Original language | English |
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Journal | Physical Review Letters |
Volume | 116 |
DOIs | |
Publication status | Published - 27 Apr 2016 |
Bibliographical note
10 pages plus author list + cover pages (26 pages total), 4 figures, no tables, submitted to Physical Review Letters, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2015-09Keywords
- hep-ex
- nucl-ex