Observation of Long-Range Elliptic Azimuthal Anisotropies in √s=13 and 2.76 TeV pp Collisions with the ATLAS Detector
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American Physical Society
Aad, G., Abbott, B., Abdallah, J., Aben, R., Abolins, M., AbouZeid, O. S., ... & Acharya, B. S. (2016). Observation of long-range elliptic azimuthal anisotropies in s= 13 and 2.76 TeV p p collisions with the ATLAS detector. Physical review letters, 116(17), 172301. [https://doi.org/10.1103/PhysRevLett.116.172301]
SponsorshipANPCyT; YerPhI, Armenia; Australian Research Council; BMWFW, Austria; Austrian Science Fund (FWF); Azerbaijan National Academy of Sciences (ANAS); SSTC, Belarus; National Council for Scientific and Technological Development (CNPq); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Natural Sciences and Engineering Research Council of Canada; NRC, Canada; Canada Foundation for Innovation; CERN; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT); Chinese Academy of Sciences; Ministry of Science and Technology, China; National Natural Science Foundation of China; Departamento Administrativo de Ciencia, Tecnologia e Innovacion Colciencias; Ministry of Education, Youth & Sports - Czech Republic Czech Republic Government; DNRF, Denmark; Danish Natural Science Research Council; Lundbeckfonden; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; Federal Ministry of Education & Research (BMBF); HGF, Germany; Max Planck Society; Greek Ministry of Development-GSRT; Hong Kong Research Grants Council; Israel Science Foundation; I-CORE, Israel; Benoziyo Center, Israel; Istituto Nazionale di Fisica Nucleare (INFN); Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science; CNRST, Morocco; FOM (The Netherlands) Netherlands Government; Netherlands Organization for Scientific Research (NWO) Netherlands Government; RCN, Norway; Ministry of Science and Higher Education, Poland; NCN, Poland; Portuguese Foundation for Science and Technology; MNE/IFA, Romania; Russian Federation; NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; Slovenian Research Agency - Slovenia; MIZS, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC, Sweden; Wallenberg Foundation, Sweden; SERI, Switzerland; Swiss National Science Foundation (SNSF); Canton of Bern, Switzerland; Canton of Geneva, Switzerland; Ministry of Science and Technology, Taiwan; Ministry of Energy & Natural Resources - Turkey; United States Department of Energy (DOE); National Science Foundation (NSF); BCKDF, Canada; Canada Council, Canada; CANARIE, Canada; CRC, Canada; Compute Canada, Canada; FQRNT; Ontario Innovation Trust, Canada; European Union (EU); European Union (EU) European Research Council (ERC); Horizon, European Union; French National Research Agency (ANR); Region Auvergne-Rhone-Alpes; Fondation Partager le Savoir, France; German Research Foundation (DFG); Alexander von Humboldt Foundation; Herakleitos programme - EU-ESF; Thales programme - EU-ESF; Aristeia programme - EU-ESF; Greek Ministry of Development-GSRT; US-Israel Binational Science Foundation; German-Israeli Foundation for Scientific Research and Development; Minerva, Israel; BRF, Norway; Leverhulme Trust; Royal Society of London; Science & Technology Facilities Council (STFC) GRIDPP 1366825 ST/N000463/1 PP/E000444/1; ICREA
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.