Abstract
ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, , and pseudorapidity, , in and 2.76 TeV collisions at the LHC using charged particles measured in the pseudorapidity interval . The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at that extends over a wide range of , which has been referred to as the “ridge.” Per-trigger-particle yields, , are measured over . For both collision energies, the 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 . The fitted Fourier coefficient, , exhibits factorization, suggesting that the ridge results from per-event modulation of the single-particle distribution with Fourier coefficients . The 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 dependence similar to that measured in and collisions. The values in the 13 and 2.76 TeV data are consistent within uncertainties. These results suggest that the ridge in collisions arises from the same or similar underlying physics as observed in collisions, and that the dynamics responsible for the ridge has no strong dependence.
- Received 15 September 2015
DOI:https://doi.org/10.1103/PhysRevLett.116.172301
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© 2016 CERN, for the ATLAS Collaboration