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

G. Aad 1 S. Albrand 2 J. Collot 2 S. Crépé-Renaudin 2 P.A. Delsart 2 C. Gabaldon 2 M.H. Genest 2 J.Y. Hostachy 2 F. Ledroit-Guillon 2 A. Lleres 2 A. Lucotte 2 F. Malek 2 C. Monini 2 J. Stark 2 B. Trocmé 2 M. Wu 2 G. Rahal 3 Z. Barnovska 4 N. Berger 4 M. Delmastro 4 L. Di Ciaccio 4 S. Elles 4 C. Goy 4 T. Hryn’ova 4 S. Jézéquel 4 I. Koletsou 4 R. Lafaye 4 J. Leveque 4 N. Massol 4 P. Mastrandrea 4 G. Sauvage 4 E. Sauvan 1 O. Simard 4 T. Todorov 4 E. Yatsenko 4 I. Wingerter-Seez 4 M.K. Ayoub 5 A. Bassalat 5 C. Bécot 5 S. Binet 5 C. Bourdarios 5 D. Delgove 5 J-B. de Vivie De Regie 5 L. Duflot 5 M. Escalier 5 L. Fayard 5 D. Fournier 5 E.L. Gkougkousis 5 J-F. Grivaz 5 T. Guillemin 5 F. Hariri 5 S. Henrot-Versille 5 J. Hrivnac 5 L. Iconomidou-Fayard 5 M. Kado 5 A. Lounis 5 N. Makovec 5 N. Morange 5 C. Nellist 5 P. Petroff 5 L. Poggioli 5 P. Puzo 5 A. Renaud 5 D. Rousseau 5 G. Rybkin 5 A.C. Schaffer 5 E. Scifo 5 L. Serin 5 S. Simion 5 R. Tanaka 5 D. Zerwas 5 Zhongkai Zhang 5 Y. Zhao 5 L. Alio 1 M. Barbero 1 Y. Coadou 1 C. Diaconu 1 Sara Diglio 1 F. Djama 1 O. Duccu 1 L. Feligioni 1 J. Gao 1 G.D. Hallewell 1 F. Hubaut 1 S.J. Kahn 1 E. B. F. G. Knoops 1 E. Le Guirriec 1 J. Liu 1 K. Liu 1 D. Madaffari 1 K. Mochizuki 1 E. Monnier 1 S. Muanza 1 Y. Nagai 1 E. Nagy 1 P. Pralavorio 1 A. Rozanov 1 T. Serre 1 M. Talby 1 R.E. Ticse Torres 1 E. Tiouchichine 1 S. Tisserant 1 J. Toth 1 F. Touchard 1 L. Vacavant 1 D. Boumediene 6 E. Busato 6 D. Calvet 6 S. Calvet 6 J. Donini 6 E. Dubreuil 6 G. Gilles 6 Ph. Gris 6 H. Liao 6 R. Madar 6 D. Pallin 6 S.M. Romano Saez 6 C. Santoni 6 D. Simon 6 T. Theveneaux-Pelzer 6 F. Vazeille 6
Abstract : ATLAS has measured two-particle correlations as a function of relative azimuthal-angle, $\Delta \phi$, and pseudorapidity, $\Delta \eta$, in $\sqrt{s}$=13 and 2.76 TeV $pp$ collisions at the LHC using charged particles measured in the pseudorapidity interval $|\eta|$<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show a multiplicity-dependent enhancement at $\Delta \phi \sim 0$ that extends over a wide range of $\Delta\eta$, which has been referred to as the "ridge". Per-trigger-particle yields, $Y(\Delta \phi)$, are measured over 2<$|\Delta\eta|$<5. For both collision energies, the $Y(\Delta \phi)$ 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 $\cos{(2\Delta \phi)}$. The fitted Fourier coefficient, $v_{2,2}$, exhibits factorization, suggesting that the ridge results from per-event $\cos{(2\phi)}$ 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 $p_{\mathrm{T}}$ dependence similar to that measured in $p$+Pb and Pb+Pb collisions. The $v_2$ 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 $\sqrt{s}$ dependence.
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Contributor : Emmanuelle Vernay Connect in order to contact the contributor
Submitted on : Thursday, September 17, 2015 - 8:22:07 AM
Last modification on : Wednesday, October 27, 2021 - 9:04:02 AM

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G. Aad, S. Albrand, J. Collot, S. Crépé-Renaudin, P.A. Delsart, et al.. Observation of Long-Range Elliptic Azimuthal Anisotropies in s√=13 and 2.76 TeV pp Collisions with the ATLAS Detector. Physical Review Letters, American Physical Society, 2016, 116, pp.172301. ⟨10.1103/PhysRevLett.116.172301⟩. ⟨in2p3-01200692⟩



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