Measurement of the azimuthal anisotropy of charged particles in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mrow> <mml:mi>N</mml:mi> <mml:mi>N</mml:mi> </mml:mrow> </mml:msub> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>5.36</mml:mn> <mml:mspace width="0.28em"/> <mml:mi>TeV</mml:mi> </mml:mrow> <mml:mo> </mml:mo> <mml:mrow> <mml:mmultiscripts> <mml:mi mathvariant="normal">O</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>16</mml:mn> </mml:mmultiscripts> <mml:mo>+</mml:mo> <mml:mmultiscripts> <mml:mi mathvariant="normal">O</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>16</mml:mn> </mml:mmultiscripts> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mmultiscripts> <mml:mi>Ne</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>20</mml:mn> </mml:mmultiscripts> <mml:mo>+</mml:mo> <mml:mmultiscripts> <mml:mi>Ne</mml:mi> <mml:mprescripts/> <mml:none/> <mml:mn>20</mml:mn> </mml:mmultiscripts> </mml:mrow> </mml:math> collisions with the ATLAS detector
Bibliographic record
Abstract
This paper presents the first measurements of the azimuthal anisotropy coefficients <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mi>v</a:mi> <a:mi>n</a:mi> </a:msub> </a:math> , which quantify the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>n</b:mi> <b:mi>th</b:mi> </b:mrow> </b:math> -order Fourier modulation of charged-particle azimuthal distributions, for <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>n</c:mi> <c:mo>=</c:mo> <c:mn>2</c:mn> <c:mo>−</c:mo> <c:mn>4</c:mn> </c:mrow> </c:math> in <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msqrt> <d:msub> <d:mi>s</d:mi> <d:mrow> <d:mi>N</d:mi> <d:mi>N</d:mi> </d:mrow> </d:msub> </d:msqrt> <d:mo>=</d:mo> <d:mn>5.36</d:mn> <d:mspace width="0.28em"/> <d:mi>TeV</d:mi> <d:mspace width="0.28em"/> <d:mmultiscripts> <d:mi mathvariant="normal">O</d:mi> <d:mprescripts/> <d:none/> <d:mn>16</d:mn> </d:mmultiscripts> <d:mo>+</d:mo> <d:mmultiscripts> <d:mi mathvariant="normal">O</d:mi> <d:mprescripts/> <d:none/> <d:mn>16</d:mn> </d:mmultiscripts> </d:mrow> </d:math> and <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mmultiscripts> <i:mi>Ne</i:mi> <i:mprescripts/> <i:none/> <i:mn>20</i:mn> </i:mmultiscripts> <i:mo>+</i:mo> <i:mmultiscripts> <i:mi>Ne</i:mi> <i:mprescripts/> <i:none/> <i:mn>20</i:mn> </i:mmultiscripts> </i:mrow> </i:math> collisions recorded with the ATLAS detector at the CERN Large Hadron Collider in 2025. The <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"> <j:msub> <j:mi>v</j:mi> <j:mi>n</j:mi> </j:msub> </j:math> coefficients are measured as a function of transverse momentum ( <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"> <k:msub> <k:mi>p</k:mi> <k:mtext>T</k:mtext> </k:msub> </k:math> ), collision centrality, and event multiplicity. They are extracted using two complementary methods: two-particle correlations with a template-fit subtraction of short-range nonflow contributions, and four-particle subevent cumulants, which intrinsically suppress nonflow effects and provide sensitivity to flow fluctuations. The results show a clear hierarchy <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mrow> <l:msub> <l:mi>v</l:mi> <l:mn>2</l:mn> </l:msub> <l:mo>></l:mo> <l:msub> <l:mi>v</l:mi> <l:mn>3</l:mn> </l:msub> <l:mo>></l:mo> <l:msub> <l:mi>v</l:mi> <l:mn>4</l:mn> </l:msub> </l:mrow> </l:math> and a nonmonotonic dependence on <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msub> <m:mi>p</m:mi> <m:mtext>T</m:mtext> </m:msub> </m:math> , reaching a maximum around <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"> <n:mrow> <n:mn>2</n:mn> <n:mspace width="0.28em"/> <n:mi>GeV</n:mi> </n:mrow> </n:math> , consistent with trends observed in heavy-ion collisions. Detailed comparisons between the two collision systems reveal an enhanced <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:msub> <p:mi>v</p:mi> <p:mn>2</p:mn> </p:msub> </p:math> in central <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mrow> <q:mmultiscripts> <q:mi>Ne</q:mi> <q:mprescripts/> <q:none/> <q:mn>20</q:mn> </q:mmultiscripts> <q:mo>+</q:mo> <q:mmultiscripts> <q:mi>Ne</q:mi> <q:mprescripts/> <q:none/> <q:mn>20</q:mn> </q:mmultiscripts> </q:mrow> </q:math> collisions, consistent with theory expectations based on the predicted prolate deformation of neon nuclei, in contrast to the slightly tetrahedral structure predicted for oxygen. The four-particle cumulant results highlight strong event-by-event fluctuations and provide the greatest sensitivity to nuclear shape effects. These measurements can place new constraints on the initial geometry and the hydrodynamic response in light-ion collisions, offering valuable input for models of nuclear structure.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.013 | 0.010 |
| Meta-epidemiology (narrow) | 0.007 | 0.013 |
| Meta-epidemiology (broad) | 0.003 | 0.013 |
| Bibliometrics | 0.005 | 0.010 |
| Science and technology studies | 0.012 | 0.013 |
| Scholarly communication | 0.010 | 0.011 |
| Open science | 0.017 | 0.016 |
| Research integrity | 0.012 | 0.014 |
| Insufficient payload (model declined to judge) | 0.383 | 0.008 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; both teacher heads agree on what is shown here.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".