The beyond-the-standard-model scenario presented in this work is motivated by the observations of neutrino masses, the anomalous magnetic moments of the electron and muon, and dark matter in the Universe. We explain these observations by extending the standard model with two generations of vector-like fermions and an inert scalar doublet, all of which are odd under a $Z_2$ symmetry. The light neutrino masses and mixings are generated radiatively while maintaining consistency with bounds on lepton flavor violation. Loop diagrams featuring the same fields also explain the anomalous magnetic moments. Similarly, the correct dark matter relic abundance is reproduced without conflicting with direct detection constraints, or those from big bang nucleosynthesis or cosmic microwave background observations. Finally, prospective signatures at the LHC are discussed.

India

Vandana Sahdev

Neutrino masses, anomalous magnetic moments and dark matter with vector-like fermions and an inert scalar doublet * V.S. acknowledges the support from research grant no. CRG/2018/004889 of the SERB, India; T.R. Seshadri for providing resources during the initial stages of the work; and Brajesh Choudhary for providing access to computers bought under the aegis of Grant No. SR-MF/PS-0212014-DUB (G) of the DST (India)

The first observation of a new meson state decaying into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>B</mi><mi>c</mi><mo>+</mo></msubsup></math> and a photon is presented using a dataset of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions at a center-of-mass energy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math> collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>B</mi><mi>c</mi><mo>+</mo></msubsup></math> mesons are reconstructed from a three-muon final state from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo></mrow></msubsup><mo stretchy="false">→</mo><mi>J</mi><mo>/</mo><mi>ψ</mi><mo stretchy="false">(</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo stretchy="false">)</mo><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub><mi>X</mi></mrow></math> decays, along with photons reconstructed via conversions to electron-positron pairs in the detector material. The new state is observed with a significance that exceeds 8 standard deviations. The mass difference between the new meson state and the ground-state <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></math> meson is measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>64.5</mn><mo>±</mo><mn>1.4</mn><mrow><mo stretchy="false">(</mo><mi>stat</mi><mo stretchy="false">)</mo></mrow><msubsup><mrow><mtext> </mtext></mrow><mrow><mo>−</mo><mn>1.4</mn></mrow><mrow><mo>+</mo><mn>1.0</mn></mrow></msubsup><mo stretchy="false">(</mo><mi>syst</mi><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>. This corresponds to a mass for the observed state of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>6339.0</mn><mo>±</mo><mn>1.4</mn><mrow><mo stretchy="false">(</mo><mi>stat</mi><mo stretchy="false">)</mo></mrow><msubsup><mrow><mtext> </mtext></mrow><mrow><mo>−</mo><mn>1.4</mn></mrow><mrow><mo>+</mo><mn>1.0</mn></mrow></msubsup><mrow><mo stretchy="false">(</mo><mi>syst</mi><mo stretchy="false">)</mo></mrow><mo>±</mo><mn>0.3</mn><mrow><mo stretchy="false">(</mo><msub><mrow><mi>m</mi></mrow><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo></mrow></msubsup></mrow></msub><mo stretchy="false">)</mo></mrow><mtext> </mtext><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>, where the last uncertainty is due to the precision of the best knowledge of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>B</mi><mi>c</mi><mo>+</mo></msubsup></math> meson mass. The low mass difference value matches the theory expectations for the lowest vector state of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi>b</mi><mo stretchy="false">¯</mo></mover><mi>c</mi></math> system, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>*</mo><mo>+</mo></mrow></msubsup></mrow></math> meson.

France

G. Aad

Norway

E. Aakvaag

United States

B. Abbott

United Arab Emirates

S. Abdelhameed

Germany

K. Abeling

N.J. Abicht

S.H. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

Italy

B.S. Acharya

A. Ackermann

Switzerland

J. Ackerschott

C. Adam Bourdarios

Poland

L. Adamczyk

S.V. Addepalli

United Kingdom

M.J. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A.A. Affolder

Y. Afik

Spain

M.N. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

A. Ahmad

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

Sweden

T.P.A. Åkesson

Japan

D. Akiyama

N.N. Akolkar

S. Aktas

G.L. Alberghi

Canada

J. Albert

U. Alberti

P. Albicocco

S. Alderweireldt

Z.L. Alegria

CERN

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H.M.J. Ali

S. Ali

S.W. Alibocus

South Africa

M. Aliev

G. Alimonti

C. Allaire

B.M.M. Allbrooke

D.R. Allen

J.S. Allen

J.F. Allen

Australia

C.S. Alley

E.R. Almazan

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

A. Alvarez Fernandez

M. Alves Cardoso

M.G. Alviggi

Brazil

Y. Amaral Coutinho

C. Amelung

M. Amerl

T. Amezza

B. Amini

K. Amirie

A. Amirkhanov

D. Amperiadou

C. Anastopoulos

T. Andeen

J.K. Anders

A.C. Anderson

A. Andreazza

S. Angelidakis

A. Angerami

A.V. Anisenkov

A. Annovi

C. Antel

E. Antipov

M. Antonelli

F. Anulli

M. Aoki

T. Aoki

M.A. Aparo

L. Aperio Bella

M. Apicella

C. Appelt

A. Apyan

R. Arakida

M. Arampatzi

S.J. Arbiol Val

C. Arcangeletti

Observation of a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>B</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>*</mo><mo>+</mo></mrow></msubsup></mrow></math> Meson with the ATLAS Detector

This Letter presents a combination of searches for Higgs boson pair (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math>) production performed by the ATLAS and CMS Collaborations using proton-proton collision datasets recorded at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> during the Large Hadron Collider Run 2, corresponding to integrated luminosities ranging between 126 and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math>. The upper limit at the 95% confidence level on the total <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math> signal strength, defined as the ratio of the measured cross section to the standard model (SM) prediction, corresponds to 2.5, with an expected value of 1.7 (2.8) assuming the absence (presence) of the SM <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math> signal. The strength of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math> signal is measured to be <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mn>0.8</mn><mrow><mo>−</mo><mn>0.7</mn></mrow><mrow><mo>+</mo><mn>0.9</mn></mrow></msubsup></math> relative to the SM prediction. The observed significance is found to be 1.1 standard deviations whereas 1.3 are expected for the SM <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math> signal. Constraints are set on the Higgs boson trilinear self-coupling and on the couplings of two Higgs bosons to two vector bosons, both normalized to the SM predictions and denoted as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>κ</mi><mi>λ</mi></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>κ</mi><mrow><mn>2</mn><mi>V</mi></mrow></msub></math>, respectively. The observed individual constraints at the 95% confidence level are <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>−</mo><mn>0.71</mn><mo>&lt;</mo><msub><mrow><mi>κ</mi></mrow><mrow><mi>λ</mi></mrow></msub><mo>&lt;</mo><mn>6.1</mn></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.73</mn><mo>&lt;</mo><msub><mi>κ</mi><mrow><mn>2</mn><mi>V</mi></mrow></msub><mo>&lt;</mo><mn>1.3</mn></math>, while the expected constraints assuming the presence of the SM <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mi>H</mi></math> signal are <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>−</mo><mn>1.3</mn><mo>&lt;</mo><msub><mi>κ</mi><mi>λ</mi></msub><mo>&lt;</mo><mn>6.7</mn></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>0.66</mn><mo>&lt;</mo><msub><mi>κ</mi><mrow><mn>2</mn><mi>V</mi></mrow></msub><mo>&lt;</mo><mn>1.4</mn></math>.

B. Aitbenchikh

G.L. Albouy

Z.M.K. Alsolami

M. Aly

A. Ambler

Portugal

S.P. Amor Dos Santos

S. An

Combination of ATLAS and CMS Searches for Higgs Boson Pair Production at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>

This article details two studies of Higgs boson properties using the vector-boson fusion production mode and the $\textit{γγjj}$ final state. Both efforts are based on a data sample corresponding to 164 fb of $$ \sqrt{s}=13.6 $$ TeV proton-proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study employs matrix-element-based optimal observables to constrain CP-odd couplings beyond the Standard Model within the Standard Model Effective Field Theory framework, expressed in the Warsaw basis. The second study exploits angular distributions to probe the Higgs boson’s couplings to longitudinally and transversely polarised $\textit{W}$ and $\textit{Z}$ bosons in the production of the Higgs boson. To maximise the sensitivity, the constraints of the CP-odd couplings are combined with those from a previous analysis performed in $\textit{γγjj}$ events in a data sample of proton-proton collisions at $$ \sqrt{s}=13 $$ TeV, corresponding to an integrated luminosity of 140 fb . A significant improvement with respect to the previous analysis is achieved through the implementation of a new neural-network-based classification algorithm. All measurements are in agreement with the Standard Model prediction of a CP-even Higgs boson with the expected relative coupling strengths to longitudinally and transversely polarised vector bosons.

N. Abicht

S. Abidi

B. Acharya

S. Addepalli

M. Addison

A. Affolder

M. Agaras

Azerbaijan

T. Åkesson

N. Akolkar

G. Alberghi

Z. Alegria

I. Aleksandrov

Saudi Arabia

H. Ali

S. Alibocus

B. Allbrooke

D. Allen

J. Allen

C. Alley

E. Almazan

M. Alviggi

J. Anders

A. Anderson

A. Anisenkov

M. Aparo

S. Arbiol Val

Search for anomalies in vector-boson fusion production of the Higgs boson in $\textit{H}$($\textit{→ γγ}$)$\textit{jj}$ events using 164 fb $\textit{−}$1 of $\textit{pp}$ collision data collected at $$ \sqrt{s}=13.6 $$ TeV with the ATLAS detector

This Letter presents a measurement of prompt charged-particle production in proton-oxygen interactions at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><msub><mi>s</mi><mi>NN</mi></msub></msqrt><mo>=</mo><mn>9.62</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> center-of-mass energy with the ATLAS detector, corresponding to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>634</mn><mtext> </mtext><mtext> </mtext><mi>μ</mi><mrow><msup><mrow><mi mathvariant="normal">b</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></mrow></math> of integrated luminosity. A total of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>246</mn><mo>×</mo><msup><mn>10</mn><mn>6</mn></msup></math> selected events have at least one track with transverse momentum <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub><mo>&gt;</mo><mn>500</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> and pseudorapidity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><mi>η</mi><mo stretchy="false">|</mo><mo>&lt;</mo><mn>2.5</mn></math>. The measured fiducial proton-oxygen cross section is <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>σ</mi><mrow><mi>fid</mi><mo>.</mo></mrow><mrow><mi>p</mi><mi mathvariant="normal">O</mi></mrow></msubsup><mo>=</mo><mn>396</mn><mo>±</mo><mn>6</mn><mo stretchy="false">(</mo><mrow><mi>exp</mi><mo>.</mo></mrow><mo stretchy="false">)</mo><mo>±</mo><mn>9</mn><mo stretchy="false">(</mo><mrow><mi>lumi</mi><mo>.</mo></mrow><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>mb</mi></math> and the extrapolated inelastic proton-air cross section is <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>σ</mi><mrow><mi>inel</mi><mo>.</mo></mrow><mrow><mi>p</mi><mo>+</mo><mi>air</mi></mrow></msubsup><mo>=</mo><mn>406</mn><mo>±</mo><mn>6</mn><mo stretchy="false">(</mo><mrow><mi>exp</mi><mo>.</mo></mrow><mo stretchy="false">)</mo><mo>±</mo><mn>9</mn><mo stretchy="false">(</mo><mrow><mi>lumi</mi><mo>.</mo></mrow><mo stretchy="false">)</mo><mo>±</mo><mn>28</mn><mo stretchy="false">(</mo><mrow><mi>th</mi><mo>.</mo></mrow><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>mb</mi></math>. Measurements of charged-particle multiplicity, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math> distributions are an order-of-magnitude more precise than differences between hadronic-interaction models. These results enable improved modeling of cosmic-ray air showers, which is important for astroparticle physics.

Measurement of Charged-Particle Production in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><msub><mi>s</mi><mrow><mi>NN</mi></mrow></msub></msqrt><mo>=</mo><mn>9.62</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> Proton-Oxygen Collisions as a Probe of Cosmic-Ray Air Showers with the ATLAS Detector

Entanglement is a key property of quantum systems. In this Letter the first measurements of quantum entanglement between spins in pairs of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math> bosons are reported, using proton-proton collision data from the Large Hadron Collider (LHC) at center-of-mass energies of 13 and 13.6 TeV, recorded with the ATLAS detector. Measurements of angular observables sensitive to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><msup><mi>Z</mi><mo>*</mo></msup></math> spin-density-matrix elements in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>H</mi><mo stretchy="false">→</mo><mi>Z</mi><msup><mrow><mi>Z</mi></mrow><mrow><mo>*</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>−</mo></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mo>ℓ</mo></mrow><mrow><mo>−</mo></mrow></msup></mrow></math> process yield coefficients <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mo>,</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo>−</mo><mn>1</mn></mrow></msub><mo>=</mo><mo>−</mo><mn>0.71</mn><mo>±</mo><mn>0.45</mn></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>C</mi><mrow><mn>2</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo>−</mo><mn>2</mn></mrow></msub><mo>=</mo><mn>0.08</mn><mo>±</mo><mn>0.44</mn></math>, consistent with their Standard Model predictions. A complementary hypothesis test using the full angular distribution, and relying on several Standard Model assumptions in the decays, provides substantially higher sensitivity to quantum correlations and disfavors the separable-state hypothesis at a significance of 4.7 standard deviations (expected <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4.9</mn><mi>σ</mi></math>) relative to the entangled Standard Model hypothesis. These results provide strong evidence of quantum entanglement between massive bosons (spin qutrits) at the electroweak scale.

J.A. Aguilar Saavedra

Measurements of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math>-Boson Pair Entanglement in Decays of Higgs Bosons at the ATLAS Experiment

A search is performed for the electroweak pair production of charginos and associated production of a chargino and neutralino, each of which decays through an <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity-violating coupling into a lepton and a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>W</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi></math>, or Higgs boson. This search targets the Higgs boson decay channel of the charginos and neutralinos, using events with three or more <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-tagged jets and one or two electrons or muons. The analyzed data corresponds to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>140</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>56</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of proton-proton collision data produced by the Large Hadron Collider at center-of-mass energies of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13.6</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>, respectively, collected by the ATLAS experiment between 2015 and 2023. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a minimal supersymmetric Standard Model with an additional <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> gauge symmetry that is spontaneously broken. Charginos and neutralinos with masses between 150 GeV and 1100 GeV are excluded at 95% confidence level for a scenario in which they decay via Higgs bosons, assuming equal decay branching fractions to each lepton flavor. Additional limits on chargino and neutralino production are derived for flavor-specific decay scenarios where the charginos decay into a single lepton flavor.

Search for charginos and neutralinos with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi><mo>−</mo><mi>L</mi></math> <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity violating decays in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> and 13.6 TeV <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions with the ATLAS detector

The Lorentz-contracted electromagnetic fields of the ions in ultra-relativistic heavy-ion collisions generate intense quasi-real photon fluxes. These lead to photon-induced interactions that are observed in ultra-peripheral collisions (UPCs), such as vector meson and lepton-pair production. The high photon flux also enables the occurrence of multiple photon-induced processes in a single collision. Presented is the first measurement of the coincident production of <math altimg='si2.svg'><mrow><mi>&#947;</mi><mi>&#947;</mi><mo>&#8594;</mo><msup><mi>&#956;</mi><mo>+</mo></msup><msup><mi>&#956;</mi><mo>&#8722;</mo></msup></mrow></math> and <math altimg='si4.svg'><mrow><mi>&#947;</mi><mo linebreak='goodbreak'>+</mo><mi>A</mi><mo>&#8594;</mo><msup><mi>&#961;</mi><mn>0</mn></msup><mo linebreak='goodbreak'>+</mo><mi>A</mi></mrow></math> in UPC Pb+Pb collisions at centre-of-mass energies of 5.02 TeV and 5.36 TeV with the ATLAS detector at the Large Hadron Collider. The coincident <italic>&#961;</italic> 0 is identified via its decay into a <math altimg='si5.svg'><mrow><msup><mi>&#960;</mi><mo>+</mo></msup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> pair, with the selected <math altimg='si5.svg'><mrow><msup><mi>&#960;</mi><mo>+</mo></msup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> sample also containing the non-resonant continuum contribution. The rate of the coincident process relative to the exclusive <math altimg='si2.svg'><mrow><mi>&#947;</mi><mi>&#947;</mi><mo>&#8594;</mo><msup><mi>&#956;</mi><mo>+</mo></msup><msup><mi>&#956;</mi><mo>&#8722;</mo></msup></mrow></math> process is measured differentially in intervals of forward event activity, quantified by the Zero Degree Calorimeters. The relative rate of coincident <italic>&#961;</italic> 0 production, including non-resonant <math altimg='si5.svg'><mrow><msup><mi>&#960;</mi><mo>+</mo></msup><msup><mi>&#960;</mi><mo>&#8722;</mo></msup></mrow></math> contributions, is measured to be <math altimg='si6.svg'><mrow><mrow><mo>(</mo><mn>9.3</mn><mspace width='0.16em' /><mo>&#177;</mo><mn>0.4</mn><mspace width='0.16em' /><mrow><mo mathvariant='normal'>(</mo><mtext>stat</mtext><mo>.</mo><mo>)</mo></mrow><mspace width='0.16em' /><mo>&#177;</mo><mn>0.2</mn><mspace width='0.16em' /><mrow><mo mathvariant='normal'>(</mo><mtext>syst</mtext><mo>.</mo><mo>)</mo></mrow><mo>)</mo></mrow><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></mrow></math>, summed over forward event activity. Correlations between the dimuon kinematic properties, such as its mass, and the coincident <italic>&#961;</italic> 0 meson production rate, are also presented. These measurements confirm the presence of multi photon-induced processes in UPC collisions, and can provide new insight into the impact parameter dependence of photon-induced vector meson production.

Y. Abulaiti

M. Akbiyik

A.V. Akimov

W. Alkakhi

P.P. Allport

C.G. Ames

D. Amidei

K.R. Amos

Measurement of coincident photon-initiated processes in ultra-peripheral Pb+Pb collisions with the ATLAS detector

A search for quantum black holes in electron+jet or muon+jet final states with high invariant mass is performed. The analysis uses data from <math altimg='si13.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13.6</mn><mspace width='0.33em' /><mtext>TeV</mtext></mrow></math> <italic>pp</italic> collisions recorded by the ATLAS detector between 2022 and 2024 during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of <math altimg='si14.svg'><mrow><mn>164</mn><mspace width='0.33em' /><msup><mrow><mtext>fb</mtext></mrow><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></mrow></math>. This search is strongly motivated by a dramatic increase of the production cross-section by up to an order of magnitude for the highest masses considered, thanks to the small increase of 0.6&#8201;TeV in centre-of-mass energy between Run 2 and Run 3. No significant excess above the Standard Model background is observed, and 95% CL upper limits are set on the production cross-section times branching ratio in several benchmark models, reaching a mass scale of 9.4&#8201;TeV. These represent the strongest exclusion limits to date on quantum black hole production.

Search for quantum black holes in lepton+jet final states using proton–proton collisions at <math altimg='si13.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13.6</mn><mspace width='0.33em' /><mtext>TeV</mtext></mrow></math> with the ATLAS detector

We present the first lattice QCD calculation of the next-to-leading order hadronic vacuum polarization contribution to the muon anomalous magnetic moment with sub-percent precision. We employ the time-momentum representation for the space-like kernel, which is combined with the spatially summed vector correlator computed on CLS ensembles with $\textit{N}$ = 2 + 1 flavors of O($\textit{a}$)-improved Wilson fermions, covering six lattice spacings between 0$\textit{.}$039 and 0$\textit{.}$097 fm and a range of pion masses including the physical value. After accounting for finite-size corrections and isospin-breaking effects, we obtain as our final, continuum-extrapolated result $$ {a}_{\mu}^{\mathrm{hvp},\kern0.30em \mathrm{nlo}} $$ = −101.57(26) (54) × 10 . It lies below the estimate provided by the 2025 White Paper of the Muon ($\textit{g}$ – 2) Theory Initiative by 1.4$\textit{σ}$ but is two times more precise. It also exhibits a strong tension of 4.6$\textit{σ}$ with data-driven evaluations based on hadronic cross section measurements excluding the recent result by CMD-3.

Arnau Beltran

Alessandro Conigli

Simon Kuberski

Harvey Meyer

Konstantin Ottnad

Hartmut Wittig

Higher-order hadronic vacuum polarization contribution to the muon $\textit{g}$ − 2 from lattice QCD