Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector

G. Aad; B. Abbott; J. Abdallah; O. Abdinov; R. Aben; M. Abolins; O.S. AbouZeid; H. Abramowicz; H. Abreu; R. Abreu; B.S. Acharya; L. Adamczyk; David L. Adams; Mogens Dam; Jørn Dines Hansen; Jørgen Beck Hansen; Stefania Xella; Peter Henrik Hansen; Troels Christian Petersen; Lotte Ansgaard Thomsen; Almut Maria Pingel; Ask Emil Løvschall-Jensen; Alejandro Alonso Diaz; James William Monk; Lars Egholm Pedersen; Graig Wiglesworth; Gorm Aske Gram Krohn Galster

doi:10.1103/PhysRevLett.116.172301

Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector

G. Aad, B. Abbott, J. Abdallah, O. Abdinov, R. Aben, M. Abolins, O.S. AbouZeid, H. Abramowicz, H. Abreu, R. Abreu, B.S. Acharya, L. Adamczyk, David L. Adams, Mogens Dam, Jørn Dines Hansen, Jørgen Beck Hansen, Stefania Xella, Peter Henrik Hansen, Troels Christian Petersen, Lotte Ansgaard ThomsenAlmut Maria Pingel, Ask Emil Løvschall-Jensen, Alejandro Alonso Diaz, James William Monk, Lars Egholm Pedersen, Graig Wiglesworth, Gorm Aske Gram Krohn Galster

Experimental Particle Physics

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Abstract

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.

Original language	English
Article number	172301
Journal	Physical Review Letters
Volume	116
Issue number	17
ISSN	0031-9007
DOIs	https://doi.org/10.1103/PhysRevLett.116.172301
Publication status	Published - 27 Apr 2016

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Aad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M., AbouZeid, O. S., Abramowicz, H., Abreu, H., Abreu, R., Acharya, B. S., Adamczyk, L., Adams, D. L., Dam, M., Hansen, J. D., Hansen, J. B., Xella, S., Hansen, P. H., Petersen, T. C., ... Galster, G. A. G. K. (2016). Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector. Physical Review Letters, 116(17), [172301]. https://doi.org/10.1103/PhysRevLett.116.172301

Aad, G, Abbott, B, Abdallah, J, Abdinov, O, Aben, R, Abolins, M, AbouZeid, OS, Abramowicz, H, Abreu, H, Abreu, R, Acharya, BS, Adamczyk, L, Adams, DL, Dam, M , Hansen, JD , Hansen, JB , Xella, S , Hansen, PH , Petersen, TC, Thomsen, LA, Pingel, AM, Løvschall-Jensen, AE, Alonso Diaz, A, Monk, JW, Pedersen, LE, Wiglesworth, G & Galster, GAGK 2016, 'Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector', Physical Review Letters, vol. 116, no. 17, 172301. https://doi.org/10.1103/PhysRevLett.116.172301

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title = "Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector",

abstract = "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.",

author = "G. Aad and B. Abbott and J. Abdallah and O. Abdinov and R. Aben and M. Abolins and O.S. AbouZeid and H. Abramowicz and H. Abreu and R. Abreu and B.S. Acharya and L. Adamczyk and Adams, {David L.} and Mogens Dam and Hansen, {J{\o}rn Dines} and Hansen, {J{\o}rgen Beck} and Stefania Xella and Hansen, {Peter Henrik} and Petersen, {Troels Christian} and Thomsen, {Lotte Ansgaard} and Pingel, {Almut Maria} and L{\o}vschall-Jensen, {Ask Emil} and {Alonso Diaz}, Alejandro and Monk, {James William} and Pedersen, {Lars Egholm} and Graig Wiglesworth and Galster, {Gorm Aske Gram Krohn}",

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T1 - Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector

AU - Aad, G.

AU - Abbott, B.

AU - Abdallah, J.

AU - Abdinov, O.

AU - Aben, R.

AU - Abolins, M.

AU - AbouZeid, O.S.

AU - Abramowicz, H.

AU - Abreu, H.

AU - Abreu, R.

AU - Acharya, B.S.

AU - Adamczyk, L.

AU - Adams, David L.

AU - Dam, Mogens

AU - Hansen, Jørn Dines

AU - Hansen, Jørgen Beck

AU - Xella, Stefania

AU - Hansen, Peter Henrik

AU - Petersen, Troels Christian

AU - Thomsen, Lotte Ansgaard

AU - Pingel, Almut Maria

AU - Løvschall-Jensen, Ask Emil

AU - Alonso Diaz, Alejandro

AU - Monk, James William

AU - Pedersen, Lars Egholm

AU - Wiglesworth, Graig

AU - Galster, Gorm Aske Gram Krohn

PY - 2016/4/27

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N2 - 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.

AB - 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.

U2 - 10.1103/PhysRevLett.116.172301

DO - 10.1103/PhysRevLett.116.172301

M3 - Journal article

C2 - 27176515

SN - 0031-9007

VL - 116

JO - Physical Review Letters

JF - Physical Review Letters

IS - 17

M1 - 172301

ER -

Observation of Long-Range Elliptic Azimuthal Anisotropies in root s=13 and 2.76 TeV pp Collisions with the ATLAS Detector

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