The ATLAS experiment has performed a measurement of coherent exclusive $\textit{J/ψ}$ → $\textit{μ}$ $\textit{μ}$ production in ultraperipheral Pb+Pb collisions at $$ \sqrt{s_{\textrm{NN}}}=5.36 $$ TeV. The data was recorded at the Large Hadron Collider (LHC) during 2023, and corresponds to an integrated luminosity of 79 $\textit{μ}$b . Exclusive $\textit{J/ψ}$ candidates were selected with a dedicated track-sensitive trigger based on the ATLAS transition radiation tracker. The analysis involves reconstruction of the dimuon invariant mass based on muon tracks from the inner detector, as the muon transverse momentum range of interest precludes the use of the standard muon reconstruction and identification algorithms. Differential cross sections are measured as a function of $\textit{J/ψ}$ rapidity and are compared with theoretical predictions. After extrapolation to $$ \sqrt{s_{\textrm{NN}}}=5.02 $$ TeV, they are also compared with previous measurements performed by other experiments using data from LHC Run 2. While the results agree reasonably well with theoretical predictions, they are in tension with previous Run-2 results for the central rapidity region.

France

G. Aad

Norway

E. Aakvaag

United States

B. Abbott

United Arab Emirates

S. Abdelhameed

Germany

K. Abeling

N. Abicht

S. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

Y. Abulaiti

Italy

United Kingdom

B. Acharya

A. Ackermann

C. Adam Bourdarios

Poland

L. Adamczyk

S. Addepalli

M. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A. Affolder

Y. Afik

Spain

M. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

Azerbaijan

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

B. Aitbenchikh

M. Akbiyik

Sweden

T. Åkesson

A. Akimov

Japan

D. Akiyama

N. Akolkar

S. Aktas

G. Alberghi

Canada

J. Albert

Switzerland

U. Alberti

P. Albicocco

G. Albouy

S. Alderweireldt

Z. Alegria

M. Aleksa

C. Alexa

I. Aleksandrov

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

Saudi Arabia

H. Ali

S. Ali

S. Alibocus

South Africa

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B. Allbrooke

D. Allen

J. Allen

P. Allport

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

Z. Alsolami

A. Alvarez Fernandez

M. Alves Cardoso

M. Alviggi

M. Aly

A. Ambler

C. Amelung

M. Amerl

C. Ames

T. Amezza

D. Amidei

B. Amini

K. Amirie

A. Amirkhanov

Portugal

S. Amor Dos Santos

K. Amos

D. Amperiadou

S. An

C. Anastopoulos

T. Andeen

J. Anders

A. Anderson

A. Andreazza

S. Angelidakis

A. Angerami

A. Anisenkov

A. Annovi

C. Antel

E. Antipov

M. Antonelli

F. Anulli

Measurement of coherent exclusive $\textit{J/ψ → μ}$ + $\textit{μ}$ $\textit{−}$ production in ultraperipheral Pb+Pb collisions at $$ \sqrt{s_{\textrm{NN}}}=5.36 $$ TeV with the ATLAS detector

Understanding the late-time cosmic phenomenon of the universe commonly referred to as the dark energy problem, which is one of the prominent tension in the field of theoretical as well as observational cosmology. In this work, we attempt to analyze the nature of the missing fluid of the universe. In order to do so, we employ a polytropic equation of state consisting of free parameters rather assuming directly a particular form of the fluid. In addition, for the background geometry we consider a <italic>f</italic>( <italic>Q</italic>) cosmology exhibiting power-law assumption, which is recently proposed and found to be attractive in the study of late-time cosmology. We find exact cosmological solution along with a rigorous data analysis, utilizing the Bayesian statistics approach and the emcee ensemble sampler, to find the parameter constraints and then we interpret the parameters of physical interests such as deceleration and statefinder parameter. Also, we present status of the <italic>H</italic> <inf>0</inf> tension predicted by our polytropic <italic>f</italic>( <italic>Q</italic>) cosmological model.

India

Raja Solanki

Polytropic <italic>f</italic>( <italic>Q</italic>) cosmology and its implications for the <italic>H</italic> <inf>0</inf> tension

We carry out an Effective Field Theory (EFT) study of the $$pp \rightarrow \bar{t} t Zh$$ process in the final state. This process can uniquely probe the $$\bar{t} t Zh$$ couplings arising from higher dimensional EFT operators and can also provide bounds on $$\bar{t} t Z$$ coupling deviations. We highlight the importance of the proposed proton-proton Future Circular Collider (FCC-$\textit{hh}$) to study this process and then perform a complete collider analysis by examining the relevant background processes. This allows us to determine the FCC-$\textit{hh}$ sensitivity to probe anomalous $$\bar{t} t Zh$$ couplings.

Shankha Banerjee

Rick Gupta

Shilpi Jain

Michelangelo Mangano

Elena Venturini

An EFT study of the $$pp \rightarrow \bar{t} t Z(ll) h(bb)$$ process at the FCC- $$\varvec{hh}$$

We present a complete one-loop analysis of charged scalar boson pair production in photon-photon collisions, $\textit{γγ}$ → $\textit{H}$ $\textit{H}$ , within the framework of the Inert Doublet Model (IDM). The calculation is carried out in the on-shell renormalization scheme and incorporates both weak corrections and QED effects, including soft and hard photon radiation. Virtual loop contributions and real emission processes are computed using the Feynman diagrammatic method, ensuring the cancellation of ultraviolet and infrared divergences. To properly account for the Coulomb singularity that arises in the QED sector near threshold, we introduce the resummed cross section based on the Sommerfeld factor. The IDM parameter space is explored under theoretical consistency conditions, collider limits, and dark matter constraints, and three representative scenarios are studied in detail. We find that the magnitude of the quantum corrections is strongly controlled by the absolute value of the trilinear scalar coupling $$ {\lambda}_{h^0{H}^{+}{H}^{-}} $$ , which correlates with the charged scalar mass. When all constraints are applied, the weak corrections are typically in the range of −12% to −7% at $$ \sqrt{s}=250 $$ GeV, and between −15% and 6% at $$ \sqrt{s}=500 $$ GeV. At higher energies, such as $$ \sqrt{s}=1 $$ TeV, the corrections can become very large, ranging from about −20% up to +60%. Our findings highlight the significant role of higher-order effects in photon-photon collisions and establish $\textit{γγ}$ → $\textit{H}$ $\textit{H}$ as a promising process to investigate the charged scalar sector of the IDM at future high-energy photon colliders. Several benchmark points are proposed to facilitate future experimental searches.

Hamza Abouabid

Abdesslam Arhrib

Jaouad Falaki

Bin Gong

Qi-Shu Yan

One-loop QED and weak corrections to $\textit{γγ → H}$ $\textit{±}$ $\textit{H}$ ∓ in the Inert Doublet Model

C. Bourdarios

M. Tamlihat

A. Fernandez

M. Cardoso

Brazil

Y. Coutinho

S. Santos

M. Aoki

Erratum: The environmental impact, carbon emissions and sustainability of computing in the ATLAS experiment

Truncations of effective field theory expansions are technically necessary but inherently intertwined with the redundancies of general field redefinitions. This can be viewed as a juxtaposition of power-counting and theoretical uncertainties, which seek to estimate neglected higher-dimensional interactions through approaches based on community consensus. One can then understand the invariance of physics under field redefinitions as a data-informed validation of different power-counting schemes, or as a means of assigning theoretical errors in comparison with algebraic, equation of motion-based replacements. Such an approach generalises widely accepted procedures for estimating theoretical uncertainties within the SM to non-renormalisable interactions. We perform a case study for a representative example in Higgs Effective Field theory, focusing on universal Higgs properties tensioned against process-dependent sensitivity expectations.

Rodrigo Alonso

Christoph Englert

Wrishik Naskar

Shakeel Rahaman

Assessing (H)EFT theory errors by pitting EoM against field redefinitions

A model-agnostic search for Beyond the Standard Model physics is presented, targeting final states with at least four light leptons (electrons or muons). The search regions are separated by event topology and unsupervised machine learning is used to identify anomalous events in the full 140 fb $$^{-1}$$ of proton–proton collision data collected with the ATLAS detector during Run 2. No significant excess above the Standard Model background expectation is observed. Model-agnostic limits are presented in each topology, along with limits on several benchmark models including vector-like leptons, wino-like charginos and neutralinos, or smuons. Limits are set on the flavourful vector-like lepton model for the first time.

Y. Amaral Coutinho

Search for Beyond the Standard Model physics with anomaly detection in multilepton final states in $\textit{pp}$ collisions at $$\sqrt{s}=13~\textrm{TeV}$$ with the ATLAS detector

<p>The decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> is a characteristic signal of two-Higgs-doublet models (2HDMs), where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math> lie primarily within the same <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mi>U</mi><mo stretchy="false">(</mo><mn>2</mn><msub><mo stretchy="false">)</mo><mi>L</mi></msub></math> multiplet, leading to a coupling of order <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mn>2</mn></msub></math> to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> boson. The subsequent decay <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><msup><mi>t</mi><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup></math> is particularly promising, as it gives rise to distinct final states involving multiple leptons and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-jets. The required splitting between <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>A</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub></math> can naturally occur near the electroweak scale while being consistent with perturbative unitarity. Whereas dedicated ATLAS and CMS searches focused on the region with both top-quarks on-shell, we cover lower masses where one top quark is off-shell by recasting Standard Model <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mi>Z</mi></math> measurements of ATLAS and CMS. The obtained limits on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo></math> are between 0.12 pb and 0.62 pb. Interestingly, we observe these stringent limits despite a preference (up to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.5</mn><mi>σ</mi></math>) for a nonzero new physics signal, most pronounced around for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>A</mi></mrow></msub><mo>≈</mo><mn>450</mn><mi>–</mi><mn>460</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>H</mi></msub><mo>≈</mo><mn>290</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>, with a best-fit value of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>σ</mi><mo stretchy="false">(</mo><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi>Br</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">)</mo><mo>≈</mo><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>pb</mi></math>. This cross section can be accommodated within a top-philic 2HDM for a top-Yukawa coupling of the second Higgs doublet of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.16</mn><mo>≲</mo><msub><mi>μ</mi><mi>t</mi></msub><mo>≲</mo><mn>0.33</mn></math>.</p>

Saiyad Ashanujjaman

Guglielmo Coloretti

Andreas Crivellin

Siddharth P. Maharathy

Bruce Mellado

Constraining <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>A</mi><mo stretchy="false">→</mo><mi>Z</mi><mi>H</mi></math> with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mi>t</mi><mover accent="true"><mi>t</mi><mo stretchy="false">¯</mo></mover></math> in the low-mass region

<p>Understanding the source of the universe’s asymmetry between matter and antimatter is one of the major open questions in particle physics. In this work, the sensitivity of novel machine-learning-based inference techniques to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-odd and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-even <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>W</mi><mi>W</mi></math> anomalous couplings is studied in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>W</mi><mi>H</mi><mo stretchy="false">→</mo><mo>ℓ</mo><mi>ν</mi><mi>b</mi><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover></math> channel (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>ℓ</mo><mo>=</mo><mi>e</mi><mo>,</mo><mrow><mi>μ</mi></mrow></mrow></math>), within the standard model effective field theory framework. Two machine-learning simulation-based inference (SBI) methods are explored: a per-event likelihood-ratio estimator, which directly approximates the ratio of probability densities between competing hypotheses, is benchmarked against a per-event optimal-observable estimator optimized for sensitivity to the parameters of interest. Both approaches are also compared to traditional summary statistics, in this case histograms of kinematic and angular observables, as commonly used in experimental analyses. SBI methods provide tighter constraints than one-dimensional summary statistics, though their performance is comparable to two-dimensional histogram analysis. The optimal-observable approach remains promising for its ability to probe multiple couplings simultaneously. Restricting the analysis to a region of high <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi><mo>/</mo><mi>B</mi></math> also enhances sensitivity to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-odd operators while preserving sensitivity to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-even operators, which histogram analyses often lose. Although the likelihood-ratio estimator sometimes struggles with likelihood minima and shapes, optimizations that target its robustness could make it more sensitive than both the optimal-observable estimator and the histogram method. These results underscore the potential of advanced simulation-based inference techniques, encouraging further exploration with LHC Run 3 data to surpass current ATLAS and CMS sensitivities.</p>

Marta Silva

Ricardo Barrué

Inês Ochoa

Patricia Conde Muíño

Searching for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>W</mi><mi>W</mi></math> anomalous couplings with simulation-based inference

A search for Standard Model Higgs bosons produced in association with a high-energy photon and decaying to <math altimg='si39.svg'><mrow><mi>b</mi><mover accent='true'><mi>b</mi><mo>&#175;</mo></mover></mrow></math> is performed using 133 fb <math altimg='si40.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> of <math altimg='si41.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13</mn></mrow></math> TeV <italic>pp</italic> collision data collected with the ATLAS detector at the Large Hadron Collider at CERN. The photon requirement reduces the multijet background, and the <math altimg='si42.svg'><mrow><mi>H</mi><mo>&#8594;</mo><mi>b</mi><mover accent='true'><mi>b</mi><mo>&#175;</mo></mover></mrow></math> decay is the dominant decay mode. Event selection requirements target events produced by vector-boson fusion, the dominant production mode in this channel. Several improvements enhance the search sensitivity compared to previous measurements. These improvements include better background modelling and characterization, the use of a neural-network classifier, and an updated signal extraction strategy adopting a direct binned-likelihood fit to the classifier output. With these improvements, the Higgs boson signal strength is measured to be 0.2&#8239;&#177;&#8239;0.7 relative to the Standard Model prediction. This corresponds to an observed significance of 0.3 standard deviations, compared to an expectation of 1.5 standard deviations assuming the Standard Model.

N.J. Abicht

S.H. Abidi

B.S. Acharya

S.V. Addepalli

M.J. Addison

A.A. Affolder

M.N. Agaras

T.P.A. Åkesson

A.V. Akimov

N.N. Akolkar

G.L. Alberghi

G.L. Albouy

Z.L. Alegria

I.N. Aleksandrov

H.M.J. Ali

S.W. Alibocus

B.M.M. Allbrooke

J.S. Allen

J.F. Allen

P.P. Allport

Z.M.K. Alsolami

M.G. Alviggi

C.G. Ames

S.P. Amor Dos Santos

K.R. Amos

V. Ananiev

Search for Higgs bosons produced in association with a high-energy photon via vector-boson fusion and decaying to a pair of <italic>b</italic>-quarks in the ATLAS detector