First observation of ultra-long-range azimuthal correlations in low multiplicity pp and p-Pb collisions at the LHC
Fuente:
arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2025
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| _version_ | 1866908299135287296 |
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| author | ALICE Collaboration |
| author_facet | ALICE Collaboration |
| contents | This study presents the first observation of ultra-long-range two-particle azimuthal correlations with pseudorapidity separation of ($|Δη| > 5.0$) in proton-proton (pp) and ($|Δη| > 6.5$) in proton-lead (p-Pb) collisions at the LHC, down to and below the minimum-bias multiplicity. Two-particle correlation coefficients (${V}_{2Δ}$) are measured after removing non-flow (jets and resonance decays) contributions using the template-fit method across various multiplicity classes, providing novel insights into the origin of long-range correlations in small systems. Comparisons with the 3D-Glauber + MUSIC + UrQMD hydrodynamic model reveal significant discrepancies at low multiplicities, indicating possible dynamics beyond typical hydrodynamic behavior. Initial-state models based on the Color Glass Condensate framework generate only short-range correlations, while PYTHIA simulations implemented with the string-shoving mechanism also fail to describe these ultra-long-range correlations. The results challenge existing paradigms and question the underlying mechanisms in low-multiplicity pp and p-Pb collisions. The findings impose significant constraints on models describing collective phenomena in small collision systems and advance the understanding of origin of long-range correlations at Large Hadron Collider (LHC) energies. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_02359 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | First observation of ultra-long-range azimuthal correlations in low multiplicity pp and p-Pb collisions at the LHC ALICE Collaboration Nuclear Experiment High Energy Physics - Experiment This study presents the first observation of ultra-long-range two-particle azimuthal correlations with pseudorapidity separation of ($|Δη| > 5.0$) in proton-proton (pp) and ($|Δη| > 6.5$) in proton-lead (p-Pb) collisions at the LHC, down to and below the minimum-bias multiplicity. Two-particle correlation coefficients (${V}_{2Δ}$) are measured after removing non-flow (jets and resonance decays) contributions using the template-fit method across various multiplicity classes, providing novel insights into the origin of long-range correlations in small systems. Comparisons with the 3D-Glauber + MUSIC + UrQMD hydrodynamic model reveal significant discrepancies at low multiplicities, indicating possible dynamics beyond typical hydrodynamic behavior. Initial-state models based on the Color Glass Condensate framework generate only short-range correlations, while PYTHIA simulations implemented with the string-shoving mechanism also fail to describe these ultra-long-range correlations. The results challenge existing paradigms and question the underlying mechanisms in low-multiplicity pp and p-Pb collisions. The findings impose significant constraints on models describing collective phenomena in small collision systems and advance the understanding of origin of long-range correlations at Large Hadron Collider (LHC) energies. |
| title | First observation of ultra-long-range azimuthal correlations in low multiplicity pp and p-Pb collisions at the LHC |
| topic | Nuclear Experiment High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2504.02359 |