Skip to main content

Long- and short-range correlations and their event-scale dependence in high-multiplicity pp collisions at \( \sqrt{s} \) = 13 TeV

A preprint version of the article is available at arXiv.


Two-particle angular correlations are measured in high-multiplicity proton-proton collisions at \( \sqrt{s} \) = 13 TeV by the ALICE Collaboration. The yields of particle pairs at short-(∆η ∼ 0) and long-range (1.6 < |∆η| < 1.8) in pseudorapidity are extracted on the near-side (∆φ ∼ 0). They are reported as a function of transverse momentum (pT) in the range 1 < pT < 4 GeV/c. Furthermore, the event-scale dependence is studied for the first time by requiring the presence of high-pT leading particles or jets for varying pT thresholds. The results demonstrate that the long-range “ridge” yield, possibly related to the collective behavior of the system, is present in events with high-pT processes as well. The magnitudes of the short- and long-range yields are found to grow with the event scale. The results are compared to EPOS LHC and PYTHIA 8 calculations, with and without string-shoving interactions. It is found that while both models describe the qualitative trends in the data, calculations from EPOS LHC show a better quantitative agreement for the pT dependency, while overestimating the event-scale dependency.


  1. STAR collaboration, Experimental and theoretical challenges in the search for the quark gluon plasma: The STAR Collaboration’s critical assessment of the evidence from RHIC collisions, Nucl. Phys. A 757 (2005) 102 [nucl-ex/0501009] [INSPIRE].

  2. PHENIX collaboration, Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration, Nucl. Phys. A 757 (2005) 184 [nucl-ex/0410003] [INSPIRE].

  3. BRAHMS collaboration, Quark gluon plasma and color glass condensate at RHIC? The Perspective from the BRAHMS experiment, Nucl. Phys. A 757 (2005) 1 [nucl-ex/0410020] [INSPIRE].

  4. PHOBOS collaboration, The PHOBOS perspective on discoveries at RHIC, Nucl. Phys. A 757 (2005) 28 [nucl-ex/0410022] [INSPIRE].

  5. ALICE collaboration, Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at \( \sqrt{s_{NN}} \) = 2.76 TeV, Phys. Lett. B 719 (2013) 18 [arXiv:1205.5761] [INSPIRE].

  6. ALICE collaboration, Elliptic flow of identified hadrons in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, JHEP 06 (2015) 190 [arXiv:1405.4632] [INSPIRE].

  7. ATLAS collaboration, Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead-lead collisions at \( \sqrt{s_{NN}} \) = 2.76 TeV with the ATLAS detector, Phys. Lett. B 707 (2012) 330 [arXiv:1108.6018] [INSPIRE].

  8. P. Romatschke and U. Romatschke, Viscosity Information from Relativistic Nuclear Collisions: How Perfect is the Fluid Observed at RHIC?, Phys. Rev. Lett. 99 (2007) 172301 [arXiv:0706.1522] [INSPIRE].

    ADS  Article  Google Scholar 

  9. S. Jeon and U. Heinz, Introduction to Hydrodynamics, Int. J. Mod. Phys. E 24 (2015) 1530010 [arXiv:1503.03931] [INSPIRE].

    ADS  Article  Google Scholar 

  10. P. Romatschke and U. Romatschke, Relativistic Fluid Dynamics In and Out of Equilibrium, Cambridge Monographs on Mathematical Physics, Cambridge University Press (2019), [DOI] [arXiv:1712.05815] [INSPIRE].

  11. H. Niemi, K.J. Eskola and R. Paatelainen, Event-by-event fluctuations in a perturbative QCD + saturation + hydrodynamics model: Determining QCD matter shear viscosity in ultrarelativistic heavy-ion collisions, Phys. Rev. C 93 (2016) 024907 [arXiv:1505.02677] [INSPIRE].

    ADS  Article  Google Scholar 

  12. J.E. Bernhard, J.S. Moreland, S.A. Bass, J. Liu and U. Heinz, Applying Bayesian parameter estimation to relativistic heavy-ion collisions: simultaneous characterization of the initial state and quark-gluon plasma medium, Phys. Rev. C 94 (2016) 024907 [arXiv:1605.03954] [INSPIRE].

    ADS  Article  Google Scholar 

  13. J.E. Bernhard, J.S. Moreland and S.A. Bass, Bayesian estimation of the specific shear and bulk viscosity of quark-gluon plasma, Nature Phys. 15 (2019) 1113.

    ADS  Article  Google Scholar 

  14. ALICE collaboration, Correlated event-by-event fluctuations of flow harmonics in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, Phys. Rev. Lett. 117 (2016) 182301 [arXiv:1604.07663] [INSPIRE].

  15. ALICE collaboration, Systematic studies of correlations between different order flow harmonics in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, Phys. Rev. C 97 (2018) 024906 [arXiv:1709.01127] [INSPIRE].

  16. ALICE collaboration, Linear and non-linear flow modes in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, Phys. Lett. B 773 (2017) 68 [arXiv:1705.04377] [INSPIRE].

  17. ALICE collaboration, Higher harmonic non-linear flow modes of charged hadrons in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 5.02 TeV, JHEP 05 (2020) 085 [arXiv:2002.00633] [INSPIRE].

  18. ATLAS collaboration, Observation of Long-Range Elliptic Azimuthal Anisotropies in \( \sqrt{s} \) = 13 and 2.76 TeV pp Collisions with the ATLAS Detector, Phys. Rev. Lett. 116 (2016) 172301 [arXiv:1509.04776] [INSPIRE].

  19. CMS collaboration, Measurement of long-range near-side two-particle angular correlations in pp collisions at \( \sqrt{s} \) = 13 TeV, Phys. Rev. Lett. 116 (2016) 172302 [arXiv:1510.03068] [INSPIRE].

  20. CMS collaboration, Evidence for collectivity in pp collisions at the LHC, Phys. Lett. B 765 (2017) 193 [arXiv:1606.06198] [INSPIRE].

  21. ALICE collaboration, Investigations of Anisotropic Flow Using Multiparticle Azimuthal Correlations in pp, p-Pb, Xe-Xe, and Pb-Pb Collisions at the LHC, Phys. Rev. Lett. 123 (2019) 142301 [arXiv:1903.01790] [INSPIRE].

  22. ALICE collaboration, Long-range angular correlations on the near and away side in p-Pb collisions at \( \sqrt{s_{NN}} \) = 5.02 TeV, Phys. Lett. B 719 (2013) 29 [arXiv:1212.2001] [INSPIRE].

  23. ATLAS collaboration, Measurement of long-range pseudorapidity correlations and azimuthal harmonics in \( \sqrt{s_{NN}} \) = 5.02 TeV proton-lead collisions with the ATLAS detector, Phys. Rev. C 90 (2014) 044906 [arXiv:1409.1792] [INSPIRE].

  24. ATLAS collaboration, Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at \( \sqrt{s} \) = 5.02 and 13 TeV and p+Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 5.02 TeV with the ATLAS detector, Phys. Rev. C 96 (2017) 024908 [arXiv:1609.06213] [INSPIRE].

  25. CMS collaboration, Pseudorapidity dependence of long-range two-particle correlations in pPb collisions at \( \sqrt{s_{NN}} \) = 5.02 TeV, Phys. Rev. C 96 (2017) 014915 [arXiv:1604.05347] [INSPIRE].

  26. PHENIX collaboration, Creation of quark-gluon plasma droplets with three distinct geometries, Nature Phys. 15 (2019) 214 [arXiv:1805.02973] [INSPIRE].

  27. PHENIX collaboration, Measurements of Multiparticle Correlations in d + Au Collisions at 200, 62.4, 39, and 19.6 GeV and p + Au Collisions at 200 GeV and Implications for Collective Behavior, Phys. Rev. Lett. 120 (2018) 062302 [arXiv:1707.06108] [INSPIRE].

  28. W. Busza, K. Rajagopal and W. van der Schee, Heavy Ion Collisions: The Big Picture, and the Big Questions, Ann. Rev. Nucl. Part. Sci. 68 (2018) 339 [arXiv:1802.04801] [INSPIRE].

    ADS  Article  Google Scholar 

  29. J.L. Nagle and W.A. Zajc, Small System Collectivity in Relativistic Hadronic and Nuclear Collisions, Ann. Rev. Nucl. Part. Sci. 68 (2018) 211 [arXiv:1801.03477] [INSPIRE].

    ADS  Article  Google Scholar 

  30. M.A. Lisa, S. Pratt, R. Soltz and U. Wiedemann, Femtoscopy in relativistic heavy ion collisions, Ann. Rev. Nucl. Part. Sci. 55 (2005) 357 [nucl-ex/0505014] [INSPIRE].

  31. A.M. Poskanzer and S.A. Voloshin, Methods for analyzing anisotropic flow in relativistic nuclear collisions, Phys. Rev. C 58 (1998) 1671 [nucl-ex/9805001] [INSPIRE].

  32. S.A. Voloshin, A.M. Poskanzer and R. Snellings, Collective phenomena in non-central nuclear collisions, Landolt-Bornstein 23 (2010) 293 [arXiv:0809.2949] [INSPIRE].

    ADS  Google Scholar 

  33. B. Alver and G. Roland, Collision geometry fluctuations and triangular flow in heavy-ion collisions, Phys. Rev. C 81 (2010) 054905 [Erratum ibid. 82 (2010) 039903] [arXiv:1003.0194] [INSPIRE].

  34. B.H. Alver, C. Gombeaud, M. Luzum and J.-Y. Ollitrault, Triangular flow in hydrodynamics and transport theory, Phys. Rev. C 82 (2010) 034913 [arXiv:1007.5469] [INSPIRE].

    ADS  Article  Google Scholar 

  35. ALICE collaboration, Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at \( \sqrt{s_{NN}} \) = 2.76 TeV, Phys. Rev. Lett. 107 (2011) 032301 [arXiv:1105.3865] [INSPIRE].

  36. C. Gale, S. Jeon, B. Schenke, P. Tribedy and R. Venugopalan, Event-by-event anisotropic flow in heavy-ion collisions from combined Yang-Mills and viscous fluid dynamics, Phys. Rev. Lett. 110 (2013) 012302 [arXiv:1209.6330] [INSPIRE].

    ADS  Article  Google Scholar 

  37. C. Shen, Z. Qiu, H. Song, J. Bernhard, S. Bass and U. Heinz, The iEBE-VISHNU code package for relativistic heavy-ion collisions, Comput. Phys. Commun. 199 (2016) 61 [arXiv:1409.8164] [INSPIRE].

    ADS  MathSciNet  Article  Google Scholar 

  38. K. Dusling and R. Venugopalan, Evidence for BFKL and saturation dynamics from dihadron spectra at the LHC, Phys. Rev. D 87 (2013) 051502 [arXiv:1210.3890] [INSPIRE].

    ADS  Article  Google Scholar 

  39. A. Bzdak, B. Schenke, P. Tribedy and R. Venugopalan, Initial state geometry and the role of hydrodynamics in proton-proton, proton-nucleus and deuteron-nucleus collisions, Phys. Rev. C 87 (2013) 064906 [arXiv:1304.3403] [INSPIRE].

    ADS  Article  Google Scholar 

  40. B.A. Arbuzov, E.E. Boos and V.I. Savrin, CMS ridge effect at LHC as a manifestation of bremstralung of gluons due to the quark-anti-quark string formation, Eur. Phys. J. C 71 (2011) 1730 [arXiv:1104.1283] [INSPIRE].

    ADS  Article  Google Scholar 

  41. R.D. Weller and P. Romatschke, One fluid to rule them all: viscous hydrodynamic description of event-by-event central p+p, p+Pb and Pb+Pb collisions at \( \sqrt{s} \) = 5.02 TeV, Phys. Lett. B 774 (2017) 351 [arXiv:1701.07145] [INSPIRE].

  42. W. Zhao, Y. Zhou, H. Xu, W. Deng and H. Song, Hydrodynamic collectivity in proton-proton collisions at 13 TeV, Phys. Lett. B 780 (2018) 495 [arXiv:1801.00271] [INSPIRE].

    ADS  Article  Google Scholar 

  43. M. Greif, C. Greiner, B. Schenke, S. Schlichting and Z. Xu, Importance of initial and final state effects for azimuthal correlations in p+Pb collisions, Phys. Rev. D 96 (2017) 091504 [arXiv:1708.02076] [INSPIRE].

    ADS  Article  Google Scholar 

  44. H. Mäntysaari, B. Schenke, C. Shen and P. Tribedy, Imprints of fluctuating proton shapes on flow in proton-lead collisions at the LHC, Phys. Lett. B 772 (2017) 681 [arXiv:1705.03177] [INSPIRE].

    ADS  Article  Google Scholar 

  45. T. Pierog, I. Karpenko, J.M. Katzy, E. Yatsenko and K. Werner, EPOS LHC: Test of collective hadronization with data measured at the CERN Large Hadron Collider, Phys. Rev. C 92 (2015) 034906 [arXiv:1306.0121] [INSPIRE].

    ADS  Article  Google Scholar 

  46. B. Schenke, C. Shen and P. Tribedy, Hybrid Color Glass Condensate and hydrodynamic description of the Relativistic Heavy Ion Collider small system scan, Phys. Lett. B 803 (2020) 135322 [arXiv:1908.06212] [INSPIRE].

    Article  Google Scholar 

  47. B. Schenke, C. Shen and P. Tribedy, Running the gamut of high energy nuclear collisions, Phys. Rev. C 102 (2020) 044905 [arXiv:2005.14682] [INSPIRE].

    ADS  Article  Google Scholar 

  48. M. Strickland, Small system studies: A theory overview, Nucl. Phys. A 982 (2019) 92 [arXiv:1807.07191] [INSPIRE].

    ADS  Article  Google Scholar 

  49. C. Loizides, Experimental overview on small collision systems at the LHC, Nucl. Phys. A 956 (2016) 200 [arXiv:1602.09138] [INSPIRE].

    ADS  Article  Google Scholar 

  50. C. Bierlich, G. Gustafson and L. Lönnblad, Collectivity without plasma in hadronic collisions, Phys. Lett. B 779 (2018) 58 [arXiv:1710.09725] [INSPIRE].

    ADS  Article  Google Scholar 

  51. C. Bierlich, Soft modifications to jet fragmentation in high energy proton-proton collisions, Phys. Lett. B 795 (2019) 194 [arXiv:1901.07447] [INSPIRE].

    Article  Google Scholar 

  52. M. Gyulassy and M. Plumer, Jet Quenching in Dense Matter, Phys. Lett. B 243 (1990) 432 [INSPIRE].

    ADS  Article  Google Scholar 

  53. X.-N. Wang and M. Gyulassy, Gluon shadowing and jet quenching in A + A collisions at \( \sqrt{s} \) = 200 GeV, Phys. Rev. Lett. 68 (1992) 1480 [INSPIRE].

    ADS  Article  Google Scholar 

  54. CMS collaboration, Charged-particle nuclear modification factors in PbPb and pPb collisions at \( \sqrt{s_{\mathrm{NN}}} \) = 5.02 TeV, JHEP 04 (2017) 039 [arXiv:1611.01664] [INSPIRE].

  55. ALICE collaboration, Centrality dependence of charged jet production in p-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 5.02 TeV, Eur. Phys. J. C 76 (2016) 271 [arXiv:1603.03402] [INSPIRE].

  56. ALICE collaboration, Multiplicity dependence of charged pion, kaon, and (anti)proton production at large transverse momentum in p-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 5.02 TeV, Phys. Lett. B 760 (2016) 720 [arXiv:1601.03658] [INSPIRE].

  57. ALICE collaboration, Constraints on jet quenching in p-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 5.02 TeV measured by the event-activity dependence of semi-inclusive hadron-jet distributions, Phys. Lett. B 783 (2018) 95 [arXiv:1712.05603] [INSPIRE].

  58. ALICE collaboration, Anomalous evolution of the near-side jet peak shape in Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, Phys. Rev. Lett. 119 (2017) 102301 [arXiv:1609.06643].

  59. T. Sjöstrand and M. van Zijl, Multiple Parton-parton Interactions in an Impact Parameter Picture, Phys. Lett. B 188 (1987) 149 [INSPIRE].

    ADS  Article  Google Scholar 

  60. L. Frankfurt, M. Strikman and C. Weiss, Transverse nucleon structure and diagnostics of hard parton-parton processes at LHC, Phys. Rev. D 83 (2011) 054012 [arXiv:1009.2559] [INSPIRE].

    ADS  Article  Google Scholar 

  61. CMS collaboration, Measurement of the Underlying Event Activity in pp Collisions at \( \sqrt{s} \) = 0.9 and 7 TeV with the Novel Jet-Area/Median Approach, JHEP 08 (2012) 130 [arXiv:1207.2392] [INSPIRE].

  62. CMS collaboration, Measurement of the Underlying Event Activity at the LHC with \( \sqrt{s} \) = 7 TeV and Comparison with \( \sqrt{s} \) = 0.9 TeV, JHEP 09 (2011) 109 [arXiv:1107.0330] [INSPIRE].

  63. ATLAS collaboration, Measurement of long-range two-particle azimuthal correlations in Z-boson tagged pp collisions at \( \sqrt{s} \)=8 and 13 TeV, Eur. Phys. J. C 80 (2020) 64 [arXiv:1906.08290] [INSPIRE].

  64. ALICE collaboration, The ALICE experiment at the CERN LHC, 2008 JINST 3 S08002 [INSPIRE].

  65. ALICE collaboration, Performance of the ALICE Experiment at the CERN LHC, Int. J. Mod. Phys. A 29 (2014) 1430044 [arXiv:1402.4476] [INSPIRE].

  66. ALICE collaboration, Performance of the ALICE VZERO system, 2013 JINST 8 P10016 [arXiv:1306.3130] [INSPIRE].

  67. ALICE collaboration, Alignment of the ALICE Inner Tracking System with cosmic-ray tracks, 2010 JINST 5 P03003 [arXiv:1001.0502] [INSPIRE].

  68. J. Alme et al., The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events, Nucl. Instrum. Meth. A 622 (2010) 316 [arXiv:1001.1950] [INSPIRE].

    ADS  Article  Google Scholar 

  69. ALICE collaboration, ALICE luminosity determination for pp collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 13 TeV, ALICE-PUBLIC-2016-002 (2016).

  70. R. Santoro et al., The ALICE Silicon Pixel Detector: Readiness for the first proton beam, 2009 JINST 4 P03023 [INSPIRE].

  71. G. Contin, Performance of the present ALICE Inner Tracking System and studies for the upgrade, 2012 JINST 7 C06007 [INSPIRE].

  72. ALICE collaboration, Measurement of jet suppression in central Pb-Pb collisions at \( \sqrt{{\mathrm{s}}_{\mathrm{NN}}} \) = 2.76 TeV, Phys. Lett. B 746 (2015) 1 [arXiv:1502.01689] [INSPIRE].

  73. G.I. Kopylov, Like particle correlations as a tool to study the multiple production mechanism, Phys. Lett. B 50 (1974) 472 [INSPIRE].

    ADS  Article  Google Scholar 

  74. N.N. Ajitanand et al., Decomposition of harmonic and jet contributions to particle-pair correlations at ultra-relativistic energies, Phys. Rev. C 72 (2005) 011902 [nucl-ex/0501025] [INSPIRE].

  75. M. Cacciari, G.P. Salam and G. Soyez, The anti-kt jet clustering algorithm, JHEP 04 (2008) 063 [arXiv:0802.1189] [INSPIRE].

    ADS  Article  Google Scholar 

  76. M. Cacciari, G.P. Salam and G. Soyez, FastJet User Manual, Eur. Phys. J. C 72 (2012) 1896 [arXiv:1111.6097] [INSPIRE].

    ADS  Article  Google Scholar 

  77. ALICE collaboration, Charged jet cross section and fragmentation in proton-proton collisions at \( \sqrt{s} \) = 7 TeV, Phys. Rev. D 99 (2019) 012016 [arXiv:1809.03232] [INSPIRE].

Download references

Author information

Authors and Affiliations