A search is conducted for a new scalar boson <italic>S</italic>, with a mass distinct from that of the Higgs boson, decaying promptly into four leptons ( <math altimg='si1.svg'><mi>&#8467;</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mi>e</mi></math>, <italic>&#956;</italic>) via an intermediate state containing two on-shell, promptly decaying new spin-1 bosons <math altimg='si2.svg'><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub></math>: <math altimg='si20.svg'><mi>S</mi><mo stretchy='false'>&#8594;</mo><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub><mo stretchy='false'>&#8594;</mo><mn>4</mn><mi>&#8467;</mi></math>, where the <math altimg='si2.svg'><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub></math> boson has a mass between 15 and 300 GeV, and the <italic>S</italic> boson has a mass between either 30 and 115 GeV or 130 and 800 GeV. The search uses proton&#8211;proton collision data collected with the ATLAS detector at the Large Hadron Collider with an integrated luminosity of 139 fb <sup>&#8722;1</sup> at a centre-of-mass energy of <math altimg='si101.svg'><msqrt><mrow><mi>s</mi></mrow></msqrt><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>13</mn></math> TeV. No significant excess above the Standard Model background expectation is observed. Upper limits at 95% confidence level are set on the production cross-section times branching ratio, <math altimg='si5.svg'><mi>&#963;</mi><mo stretchy='false'>(</mo><mi>g</mi><mi>g</mi><mo stretchy='false'>&#8594;</mo><mi>S</mi><mo stretchy='false'>)</mo><mo>&#215;</mo><mi mathvariant='script'>B</mi><mo stretchy='false'>(</mo><mi>S</mi><mo stretchy='false'>&#8594;</mo><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub><msub><mrow><mi>Z</mi></mrow><mrow><mtext>d</mtext></mrow></msub><mo stretchy='false'>&#8594;</mo><mn>4</mn><mi>&#8467;</mi><mo stretchy='false'>)</mo></math>, as a function of the mass of both particles, <math altimg='si6.svg'><msub><mrow><mi>m</mi></mrow><mrow><mi>S</mi></mrow></msub></math> and <math altimg='si7.svg'><msub><mrow><mi>m</mi></mrow><mrow><mi>Z</mi><mtext>d</mtext></mrow></msub></math>.

France

G. Aad

United States

B. Abbott

Germany

K. Abeling

N.J. Abicht

S.H. Abidi

Morocco

A. Aboulhorma

Israel

H. Abramowicz

H. Abreu

Y. Abulaiti

Chile

A.C. Abusleme Hoffman

Italy

B.S. Acharya

C. Adam Bourdarios

Poland

L. Adamczyk

Canada

L. Adamek

S.V. Addepalli

United Kingdom

M.J. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A.A. Affolder

Switzerland

Y. Afik

Spain

M.N. Agaras

J. Agarwala

A. Aggarwal

Romania

C. Agheorghiesei

A. Ahmad

F. Ahmadov

W.S. Ahmed

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

B. Aitbenchikh

I. Aizenberg

M. Akbiyik

Sweden

T.P.A. Åkesson

A.V. Akimov

Japan

D. Akiyama

N.N. Akolkar

K. Al Khoury

G.L. Alberghi

J. Albert

P. Albicocco

G.L. Albouy

S. Alderweireldt

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

Netherlands

A. Alfonsi

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H.M.J. Ali

Taiwan

S. Ali

S.W. Alibocus

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B.M.M. Allbrooke

J.F. Allen

C.A. Allendes Flores

P.P. Allport

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

M. Alvarez Estevez

A. Alvarez Fernandez

M. Alves Cardoso

M.G. Alviggi

M. Aly

Brazil

Y. Amaral Coutinho

A. Ambler

C. Amelung

M. Amerl

C.G. Ames

D. Amidei

Portugal

S.P. Amor Dos Santos

K.R. Amos

Norway

V. Ananiev

C. Anastopoulos

T. Andeen

J.K. Anders

S.Y. Andrean

A. Andreazza

S. Angelidakis

A. Angerami

A.V. Anisenkov

A. Annovi

C. Antel

M.T. Anthony

E. Antipov

M. Antonelli

D.J.A. Antrim

F. Anulli

M. Aoki

T. Aoki

Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector

A search is presented for the pair production of higgsinos <math><mover><mrow><mi>χ</mi></mrow><mrow><mo>˜</mo></mrow></mover></math> in gauge-mediated supersymmetry models, where the lightest neutralinos <math><msubsup><mrow><mover><mrow><mi>χ</mi></mrow><mrow><mo>˜</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow><mrow><mn>0</mn></mrow></msubsup></math> decay into a light gravitino <math><mover><mrow><mi>G</mi></mrow><mrow><mo>˜</mo></mrow></mover></math> in association with either a Higgs h or a Z boson. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb$^{−1}$ of proton–proton collisions at a centre-of-mass energy of <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mspace width="0.2em"></mspace><mrow><mi>TeV</mi></mrow></math>. It targets final states in which a Higgs boson decays into a photon pair, while the other Higgs or Z boson decays into a <math><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> pair, with missing transverse momentum associated with the two gravitinos. Search regions dependent on the amount of missing transverse momentum are defined by the requirements that the diphoton mass should be consistent with the mass of the Higgs boson, and the <math><mi>b</mi><mover><mrow><mi>b</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> mass with the mass of the Higgs or Z boson. The main backgrounds are estimated with data-driven methods using the sidebands of the diphoton mass distribution. No excesses beyond Standard Model expectations are observed and higgsinos with masses up to <math><mn>320</mn><mspace width="0.2em"></mspace><mrow><mi>GeV</mi></mrow></math> are excluded, assuming a branching fraction of 100% for <math><msubsup><mrow><mover><mrow><mi>χ</mi></mrow><mrow><mo>˜</mo></mrow></mover></mrow><mrow><mn>1</mn></mrow><mrow><mn>0</mn></mrow></msubsup><mo>→</mo><mi>h</mi><mover><mrow><mi>G</mi></mrow><mrow><mo>˜</mo></mrow></mover></math>. This analysis excludes higgsinos with masses of <math><mn>130</mn><mspace width="0.2em"></mspace><mrow><mi>GeV</mi></mrow></math> for branching fractions to <math><mi>h</mi><mover><mrow><mi>G</mi></mrow><mrow><mo>˜</mo></mrow></mover></math> as low as 36%, thus providing complementarity to previous ATLAS searches in final states with multiple leptons or multiple b-jets, targeting different decays of the electroweak bosons.

CERN

J.A. Aparisi Pozo

M.A. Aparo

Search for pair-produced higgsinos decaying via Higgs or Bosons to Final States Containing a Pair of Photons and a Pair of -jets with the ATLAS detector

This paper reports cross-section measurements of ZZ production in pp collisions at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13.6</mn><mspace width="0.25em"></mspace><mtext>TeV</mtext></math> at the Large Hadron Collider. The data were collected by the ATLAS detector in 2022, and correspond to an integrated luminosity of 29 fb$^{−1}$. Events in the <math><mi>Z</mi><mi>Z</mi><mo>→</mo><mn>4</mn><mi>ℓ</mi></math> (<math><mi>ℓ</mi><mo>=</mo><mi>e</mi></math>, μ) final states are selected and used to measure the inclusive and differential cross-sections in a fiducial region defined close to the analysis selections. The inclusive cross-section is further extrapolated to the total phase space with a requirement of 66 <math><mo>&lt;</mo><msub><mrow><mi>m</mi></mrow><mrow><mi>Z</mi></mrow></msub><mo>&lt;</mo></math> 116 GeV for both Z bosons, yielding <math><mn>16.8</mn><mo>±</mo><mn>1.1</mn></math> pb. The results are well described by the Standard Model predictions.

S. Aktas

Z.L. Alegria

Measurement of Production Cross-sections in the Four-lepton Final State in Collisions at with the ATLAS experiment

A search is presented for the pair-production of heavy vector-like quarks in the lepton+jets final state using 140 fb$^{−1}$ of proton–proton collisions at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn></math> TeV collected with the ATLAS detector. The search is optimised for vector-like top-quarks (T) that decay into a W boson and a b-quark, with one W boson decaying leptonically and the other hadronically. Other vector-like quark flavours and decay modes are also considered. Events are selected with one high transverse-momentum electron or muon, large missing transverse momentum, a large-radius jet identified as a W boson, and multiple small-radius jets, at least one of which is b-tagged. Vector-like T-quarks with 100% branching ratio to Wb are excluded at 95% CL for masses below 1700 GeV. These limits are also applied to vector-like Y-quarks, which decay exclusively into a W boson and a b-quark. Isospin singlets with <math><mi>B</mi><mo>(</mo><mi>T</mi><mo>→</mo><mi>W</mi><mi>b</mi><mo>:</mo><mi>H</mi><mi>t</mi><mo>:</mo><mi>Z</mi><mi>t</mi><mo>)</mo><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn><mo>:</mo><mn>1</mn><mo>/</mo><mn>4</mn><mo>:</mo><mn>1</mn><mo>/</mo><mn>4</mn></math> are excluded for masses below 1360 GeV.

South Africa

Search for pair-production of vector-like quarks in lepton+jets final states containing at least one -tagged jet using the Run 2 data from the ATLAS experiment

The observation of the electroweak production of single-top-quarks is made using <math><mn>255</mn><msup><mrow><mtext> pb</mtext></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of proton-proton collision data recorded at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>5.02</mn></math> TeV with the ATLAS detector at the Large Hadron Collider. An event selection is used to identify single-top-quark candidates arising from t-channel production with the top quark decaying semi-leptonically. Events passing the selection are then used to measure the inclusive cross-section for the combined production of single-top-quarks and antiquarks, <math><mi>σ</mi><mo>(</mo><mi>t</mi><mi>q</mi><mo>+</mo><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>q</mi><mo>)</mo></math>, and the ratio <math><msub><mrow><mi>R</mi></mrow><mrow><mi>t</mi></mrow></msub></math> between these two. They are measured to be <math><mi>σ</mi><mo>(</mo><mi>t</mi><mi>q</mi><mo>+</mo><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>q</mi><mo>)</mo><mo>=</mo><msubsup><mrow><mn>27.1</mn></mrow><mrow><mo>−</mo><mn>4.1</mn></mrow><mrow><mo>+</mo><mn>4.4</mn></mrow></msubsup><msubsup><mrow><mo>(</mo><mrow><mi>stat</mi><mo>.</mo></mrow><mo>)</mo></mrow><mrow><mo>−</mo><mn>3.7</mn></mrow><mrow><mo>+</mo><mn>4.4</mn></mrow></msubsup><mo>(</mo><mrow><mi>syst</mi><mo>.</mo></mrow><mo>)</mo></math> pb and <math><msub><mrow><mi>R</mi></mrow><mrow><mi>t</mi></mrow></msub><mo>=</mo><msubsup><mrow><mn>2.73</mn></mrow><mrow><mo>−</mo><mn>0.82</mn></mrow><mrow><mo>+</mo><mn>1.43</mn></mrow></msubsup><msubsup><mrow><mo>(</mo><mrow><mi>stat</mi><mo>.</mo></mrow><mo>)</mo></mrow><mrow><mo>−</mo><mn>0.29</mn></mrow><mrow><mo>+</mo><mn>1.01</mn></mrow></msubsup><mo>(</mo><mrow><mi>syst</mi><mo>.</mo></mrow><mo>)</mo></math>. The individual single-top-quark (tq) and single-top-antiquark (<math><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>q</mi></math>) production cross-sections are measured to be <math><mi>σ</mi><mo>(</mo><mi>t</mi><mi>q</mi><mo>)</mo><mo>=</mo><msubsup><mrow><mn>19.8</mn></mrow><mrow><mo>−</mo><mn>3.1</mn></mrow><mrow><mo>+</mo><mn>3.9</mn></mrow></msubsup><msubsup><mrow><mo>(</mo><mrow><mi>stat</mi><mo>.</mo></mrow><mo>)</mo></mrow><mrow><mo>−</mo><mn>2.2</mn></mrow><mrow><mo>+</mo><mn>2.9</mn></mrow></msubsup><mo>(</mo><mrow><mi>syst</mi><mo>.</mo></mrow><mo>)</mo></math> pb and <math><mi>σ</mi><mo>(</mo><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>q</mi><mo>)</mo><mo>=</mo><msubsup><mrow><mn>7.3</mn></mrow><mrow><mo>−</mo><mn>2.1</mn></mrow><mrow><mo>+</mo><mn>3.2</mn></mrow></msubsup><msubsup><mrow><mo>(</mo><mrow><mi>stat</mi><mo>.</mo></mrow><mo>)</mo></mrow><mrow><mo>−</mo><mn>1.5</mn></mrow><mrow><mo>+</mo><mn>2.8</mn></mrow></msubsup><mo>(</mo><mrow><mi>syst</mi><mo>.</mo></mrow><mo>)</mo></math> pb. All measurements are in good agreement with the Standard Model predictions.

L. Aperio Bella

Measurement of -channel Single-top-quark Production in Collisions at TeV with the ATLAS detector

A measurement of the invisible width of the Z boson using events with jets and missing transverse momentum is presented using 37 <math><msup><mrow><mtext>fb</mtext></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of 13 TeV proton–proton data collected by the ATLAS detector in 2015 and 2016. The ratio of <math><mi>Z</mi><mo>→</mo><mtext>inv</mtext></math> to <math><mi>Z</mi><mo>→</mo><mi>ℓ</mi><mi>ℓ</mi></math> events, where inv refers to non-detected particles and ℓ is either an electron or a muon, is measured and corrected for detector effects. Events with at least one energetic central jet with <math><msub><mrow><mi>p</mi></mrow><mrow><mtext>T</mtext></mrow></msub><mo>≥</mo><mn>110</mn></math> GeV are selected for both the <math><mi>Z</mi><mo>→</mo><mtext>inv</mtext></math> and <math><mi>Z</mi><mo>→</mo><mi>ℓ</mi><mi>ℓ</mi></math> final states to obtain a similar phase space in the ratio. The invisible width is measured to be <math><mn>506</mn><mo>±</mo><mn>2</mn><mspace width="0.25em"></mspace><mtext>(stat.)</mtext><mo>±</mo><mn>12</mn><mspace width="0.25em"></mspace><mtext>(syst.)</mtext></math> MeV and is the single most precise recoil-based measurement. The result is in agreement with the most precise determination from LEP and the Standard Model prediction based on three neutrino generations.

Measurement of the Z boson invisible width at TeV with the ATLAS detector

A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn></math> TeV, corresponding to 139 fb$^{−1}$ collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the a particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the a decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to Za times the branching ratio <math><mi>a</mi><mo>→</mo><mi>γ</mi><mi>γ</mi></math> are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the a particle. The results are also interpreted in the context of ALP models.

C. Appelt

Search for the decay of the Higgs boson to a Boson and a Light Pseudoscalar Particle Decaying to two Photons

The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb$^{−1}$ of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn></math> TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, <math><mi>t</mi><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>H</mi></math>, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in <math><mi>t</mi><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover><mi>H</mi></math> and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be <math><mi>α</mi><mo>=</mo><mn>11</mn><mspace width="0.2em"></mspace><msubsup><mrow></mrow><mrow><mspace width="0.25em"></mspace><mo>−</mo><msup><mrow><mn>73</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow><mrow><mo>∘</mo><mo>+</mo><msup><mrow><mn>52</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow></msubsup></math>, compatible with the SM prediction corresponding to <math><mi>α</mi><mo>=</mo><mn>0</mn></math>.

D.C. Abbott

B. Achkar

L. Adam

S. Adorni

J.A. Aguilar-Saavedra

M.J. Alconada Verzini

E. Alunno Camelia

S. Amoroso

C.S. Amrouche

N. Andari

N. Aranzabal

V. Araujo Ferraz

C. Arcangeletti

A.T.H. Arce

E. Arena

Probing the nature of the top–Higgs Yukawa coupling in And Events With decays using the ATLAS detector at the LHC

A measurement of the charge asymmetry in top-quark pair (<math><mi>t</mi><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover></math>) production in association with a photon is presented. The measurement is performed in the single-lepton <math><mi>t</mi><mover><mrow><mi>t</mi></mrow><mrow><mo>¯</mo></mrow></mover></math> decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb$^{−1}$. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be <math><msub><mrow><mi>A</mi></mrow><mrow><mtext>C</mtext></mrow></msub><mo>=</mo><mo>−</mo><mn>0.003</mn><mo>±</mo><mn>0.029</mn></math> in agreement with the Standard Model expectation.

Australia

Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment

A search for the pair-production of vector-like quarks optimized for decays into a Z boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to <math><mn>139</mn><mspace width="0.2em"></mspace><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of pp collisions at <math><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mspace width="0.2em"></mspace><mtext>TeV</mtext></math>, collected in 2015–2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a Z boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of b-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted W, Z, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners T and B of the top and bottom quarks, respectively. The limits depend on the branching ratio configurations and, in the case of 100% branching ratio for <math><mi>T</mi><mo>→</mo><mi>Z</mi><mi>t</mi></math> and 100% branching ratio for <math><mi>B</mi><mo>→</mo><mi>Z</mi><mi>b</mi></math>, this search sets the most stringent limits to date, allowing <math><msub><mrow><mi>m</mi></mrow><mrow><mi>T</mi></mrow></msub><mo>&gt;</mo><mn>1.60</mn><mspace width="0.2em"></mspace><mtext>TeV</mtext></math> and <math><msub><mrow><mi>m</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>&gt;</mo><mn>1.42</mn><mspace width="0.2em"></mspace><mtext>TeV</mtext></math>, respectively.

A. Abed Abud

D.K. Abhayasinghe

C. Agapopoulou

S. Akatsuka

L. Ambroz

J-F. Arguin

Search for pair-production of vector-like quarks in Collision Events at TeV with at least one leptonically decaying boson and a third-generation quark with the ATLAS detector