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Title: Observation of long-range elliptic azimuthal anisotropies in √s = 13 and 2.76 TeV pp collisions with the ATLAS detector

In this study, ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, ΔΦ, and pseudorapidity, Δη, 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 ΔΦ~0 that extends over a wide range of Δη, which has been referred to as the “ridge.” Per-trigger-particle yields, Y(ΔΦ), are measured over 2<|Δη|<5. For both collision energies, the Y(ΔΦ) 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(2ΔΦ). The fitted Fourier coefficient, v 2 ,2, exhibits factorization, suggesting that the ridge results from per-event cos(2Φ) modulation of the single-particle distribution with Fourier coefficients v 2. The v 2 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 p T dependence similar to that measured in p+Pb and Pb+Pb collisions. The v 2 values in the 13 and 2.76more » 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.« less
Authors:
 [1]
  1. Aix-Marseille Univ., and CNRS/IN2P3, Marseille (France). et al.
Publication Date:
Grant/Contract Number:
AC02-76SF00515; AC02-05CH11231
Type:
Published Article
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 116; Journal Issue: 17; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Orgs:
ATLAS Collaboration
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 73 NUCLEAR PHYSICS AND RADIATION PHYSICS
OSTI Identifier:
1249943
Alternate Identifier(s):
OSTI ID: 1249104; OSTI ID: 1379307

Aad, G. Observation of long-range elliptic azimuthal anisotropies in √s = 13 and 2.76 TeV pp collisions with the ATLAS detector. United States: N. p., Web. doi:10.1103/PhysRevLett.116.172301.
Aad, G. Observation of long-range elliptic azimuthal anisotropies in √s = 13 and 2.76 TeV pp collisions with the ATLAS detector. United States. doi:10.1103/PhysRevLett.116.172301.
Aad, G. 2016. "Observation of long-range elliptic azimuthal anisotropies in √s = 13 and 2.76 TeV pp collisions with the ATLAS detector". United States. doi:10.1103/PhysRevLett.116.172301.
@article{osti_1249943,
title = {Observation of long-range elliptic azimuthal anisotropies in √s = 13 and 2.76 TeV pp collisions with the ATLAS detector},
author = {Aad, G.},
abstractNote = {In this study, ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, ΔΦ, and pseudorapidity, Δη, 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 ΔΦ~0 that extends over a wide range of Δη, which has been referred to as the “ridge.” Per-trigger-particle yields, Y(ΔΦ), are measured over 2<|Δη|<5. For both collision energies, the Y(ΔΦ) 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(2ΔΦ). 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.},
doi = {10.1103/PhysRevLett.116.172301},
journal = {Physical Review Letters},
number = 17,
volume = 116,
place = {United States},
year = {2016},
month = {4}
}