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.

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

Y. Abulaiti

Italy

United Kingdom

B.S. Acharya

A. Ackermann

C. Adam Bourdarios

Poland

L. Adamczyk

S.V. Addepalli

M.J. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A.A. Affolder

Y. Afik

Spain

M.N. 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.P.A. Åkesson

A.V. Akimov

Japan

D. Akiyama

N.N. Akolkar

S. Aktas

G.L. Alberghi

Canada

J. Albert

P. Albicocco

G.L. Albouy

S. Alderweireldt

Z.L. Alegria

Switzerland

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

Saudi Arabia

H.M.J. Ali

S. Ali

S.W. Alibocus

South Africa

M. Aliev

G. Alimonti

W. Alkakhi

C. Allaire

B.M.M. Allbrooke

J.S. Allen

J.F. Allen

P.P. Allport

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

Z.M.K. Alsolami

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

B. Amini

K. Amirie

A. Amirkhanov

Portugal

S.P. Amor Dos Santos

K.R. Amos

D. Amperiadou

S. An

V. Ananiev

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

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

This paper presents the first observation of top-quark pair production in association with two photons ( <math altimg='si1.svg'><mrow><mi>t</mi><mover accent='true'><mi>t</mi><mo>&#175;</mo></mover><mi>&#947;</mi><mi>&#947;</mi></mrow></math>). The measurement is performed in the single-lepton decay channel using proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider. The data correspond to an integrated luminosity of 140 fb <math altimg='si10.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> recorded during Run 2 at a centre-of-mass energy of 13 TeV. The <math altimg='si1.svg'><mrow><mi>t</mi><mover accent='true'><mi>t</mi><mo>&#175;</mo></mover><mi>&#947;</mi><mi>&#947;</mi></mrow></math> production cross section, measured in a fiducial phase space based on particle-level kinematic criteria for the lepton, photons, and jets, is found to be <math altimg='si11.svg'><mrow><mn>2</mn><mo>.</mo><msubsup><mn>42</mn><mrow><mo>&#8722;</mo><mn>0.53</mn></mrow><mrow><mo>+</mo><mn>0.58</mn></mrow></msubsup><mspace width='0.16em' /><mtext>fb</mtext></mrow></math>, corresponding to an observed significance of 5.2 standard deviations. Additionally, the ratio of the production cross section of <math altimg='si1.svg'><mrow><mi>t</mi><mover accent='true'><mi>t</mi><mo>&#175;</mo></mover><mi>&#947;</mi><mi>&#947;</mi></mrow></math> to top-quark pair production in association with one photon is determined, yielding <math altimg='si12.svg'><mrow><mrow><mo>(</mo><mn>3</mn><mo>.</mo><msubsup><mn>30</mn><mrow><mo>&#8722;</mo><mn>0.65</mn></mrow><mrow><mo>+</mo><mn>0.70</mn></mrow></msubsup><mo>)</mo></mrow><mo linebreak='goodbreak'>&#215;</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup></mrow></math>.

C.Adam Bourdarios

M.Ait Tamlihat

T.PA åkesson

U. Alberti

H.MJ Ali

B.MM Allbrooke

Z.MK Alsolami

A.Alvarez Fernandez

Y.Amaral Coutinho

T. Amezza

Observation of <math altimg='si1.svg'><mrow><mi>t</mi><mover accent='true'><mi>t</mi><mo>&#175;</mo></mover><mi>&#947;</mi><mi>&#947;</mi></mrow></math> production at <math altimg='si9.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13</mn></mrow></math> TeV with the ATLAS detector

A search for the dimuon decay of the Higgs boson is presented based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collision data recorded by ATLAS during Run 3 of the Large Hadron Collider, corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>165</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13.6</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>. To enhance the sensitivity, the results are combined with those from Run 2. An excess of events over the background is observed with a significance of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3.4</mn><mi>σ</mi></math> (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.5</mn><mi>σ</mi></math> expected). The best-fit signal strength is <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>μ</mi><mo>=</mo><mn>1.4</mn><mo>±</mo><mn>0.4</mn></mrow></math>. This result provides evidence for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>H</mi><mo stretchy="false">→</mo><mi>μ</mi><mi>μ</mi></mrow></math> decay with ATLAS data and offers a direct probe of the Higgs-boson Yukawa coupling to second-generation fermions.

CERN

Evidence for the Dimuon Decay of the Higgs Boson in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> Collisions with the ATLAS Detector

This Letter reports the observation of <math altimg='si31.svg'><mrow><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>&#8722;</mo></msup><mi>&#947;</mi></mrow></math> triboson production in 140 fb <math altimg='si33.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> of data collected by the ATLAS detector from proton&#8211;proton collisions at a centre-of-mass energy of <math altimg='si32.svg'><msqrt><mi>s</mi></msqrt></math> = 13 TeV at the LHC. Events with an opposite-charge <italic>e&#956;</italic> pair, a high transverse-momentum photon, and significant missing transverse momentum are considered. The observed (expected) significance of the signal is 5.9 (6.0) standard deviations. The measured fiducial cross-section, defined for the <math altimg='si34.svg'><mrow><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>&#8722;</mo></msup><mi>&#947;</mi><mo>&#8594;</mo><msup><mi>e</mi><mo>&#177;</mo></msup><msup><mi>&#956;</mi><mo>&#8723;</mo></msup><mi>&#957;</mi><mover accent='true'><mi>&#957;</mi><mo>&#175;</mo></mover><mi>&#947;</mi></mrow></math> final state is 6.2 &#8239;&#177;&#8239; 0.8 (stat.) &#8239;&#177;&#8239; 0.6 (sys.) fb, in good agreement with the Standard Model prediction of 6.1 <math altimg='si35.svg'><msubsup><mrow /><mrow><mo>&#8722;</mo><mn>0.7</mn></mrow><mrow><mspace width='0.16em' /><mo>+</mo><mn>1.0</mn></mrow></msubsup></math> fb. Constraints on the Wilson coefficients of 13 dimension-8 operators describing physics beyond the Standard Model through anomalous quartic gauge-boson couplings are derived using the effective field theory framework.

D.R. Allen

Observation of <math altimg='si31.svg'><mrow><msup><mi>W</mi><mo>+</mo></msup><msup><mi>W</mi><mo>&#8722;</mo></msup><mi>&#947;</mi></mrow></math> production in <italic>pp</italic> collisions at <math altimg='si32.svg'><msqrt><mi>s</mi></msqrt></math> = 13 TeV with the ATLAS detector and constraints on anomalous quartic gauge-boson couplings

This article reports on a search for dijet resonances using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>132</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collision data 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> by the ATLAS detector at the Large Hadron Collider. The search is performed solely on jets reconstructed within the ATLAS trigger to overcome bandwidth limitations imposed on conventional single-jet triggers, which would otherwise reject data from decays of sub-TeV dijet resonances. Collision events with two jets satisfying transverse momentum thresholds of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>p</mi><mi mathvariant="normal">T</mi></msub><mo>≥</mo><mn>85</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and jet rapidity separation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><msup><mi>y</mi><mo>*</mo></msup><mo stretchy="false">|</mo><mo>&lt;</mo><mn>0.6</mn></math> are analysed for dijet resonances with invariant masses from 375 to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>1800</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></mrow></math>. A data-driven background estimate is used to model the dijet mass distribution from multijet processes. No significant excess above the expected background is observed. Upper limits are set at 95% confidence level on coupling values for a benchmark leptophobic axial-vector <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mo>′</mo></msup></math> model and on the production cross section for a new resonance contributing a Gaussian-distributed line-shape to the dijet mass distribution.

Search for electroweak-scale dijet resonances using trigger-level analysis with the ATLAS detector in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>132</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions 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>

Measurements of jet substructure in Pb+Pb collisions provide key insights into the mechanism of jet quenching in the hot and dense QCD medium created in these collisions.This Letter presents a measurement of the suppression of large-radius jets with a radius parameter of <math altimg='si2.svg'><mrow><mi>R</mi><mo linebreak='goodbreak'>=</mo><mn>1.0</mn></mrow></math> and its dependence on the jet substructure. The measurement uses 1.72 nb <math altimg='si10.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> of Pb+Pb data and 255 pb <math altimg='si10.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> of <italic>pp</italic> data, both at <math altimg='si11.svg'><mrow><msqrt><msub><mi>s</mi><msub><mrow /><mtext>NN</mtext></msub></msub></msqrt><mo linebreak='goodbreak'>=</mo><mn>5.02</mn></mrow></math> TeV, recorded with the ATLAS detector at the Large Hadron Collider. Large-radius jets are reconstructed by reclustering <math altimg='si6.svg'><mrow><mi>R</mi><mo linebreak='goodbreak'>=</mo><mn>0.2</mn></mrow></math> calorimetric jets and are measured for transverse momentum above 200 GeV. Jet substructure is evaluated using charged-particle tracks, and the overall level of jet suppression is quantified using the jet nuclear modification factor ( <italic>R</italic> <inf>AA</inf>). The jet <italic>R</italic> <inf>AA</inf> is measured as a function of jet <italic>p</italic> <inf>T</inf>, the charged <italic>k<inf>t</inf></italic> splitting scale ( <math altimg='si1.svg'><msqrt><msub><mi>d</mi><mn>12</mn></msub></msqrt></math>), and the angular separation (&#916; <italic>R</italic> <inf>12</inf>) of two leading sub-jets. The jet <italic>R</italic> <inf>AA</inf> gradually decreases with increasing <math altimg='si1.svg'><msqrt><msub><mi>d</mi><mn>12</mn></msub></msqrt></math>, implying significantly stronger suppression of large-radius jets with larger <italic>k<inf>t</inf></italic> splitting scale. The jet <italic>R</italic> <inf>AA</inf> gradually decreases for &#916; <italic>R</italic> <inf>12</inf> in the range <math altimg='si12.svg'><mrow><mn>0.01</mn><mo linebreak='goodbreak'>&#8722;</mo><mn>0.2</mn></mrow></math> and then remains consistent with a constant for &#916; <italic>R</italic> <inf>12</inf>&#8239;&#8819;&#8239;0.2. The observed significant dependence of jet suppression on the jet substructure will provide new insights into its role in the quenching process.

T. P A åkesson

H. M J Ali

B. M M Allbrooke

Z. M K Alsolami

Measurement of substructure-dependent suppression of large-radius jets with charged particles in Pb+Pb collisions with ATLAS

A search for events with one displaced vertex from long-lived particles using data collected by the ATLAS detector at the Large Hadron Collider is presented, using <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> of proton-proton collision data 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> recorded in 2015–2018. The search employs techniques for reconstructing vertices of long-lived particles decaying into hadronic jets in the muon spectrometer displaced between 3 m and 14 m from the primary interaction vertex. The observed number of events is consistent with the expected background and limits for several benchmark signals are determined. A scalar-portal model and a Higgs-boson-portal baryogenesis model are considered. A dedicated analysis channel is employed to target Z-boson associated long-lived particle production, including an axionlike particle and a dark photon model. For the Higgs boson model, branching fractions above 1% are excluded at 95% confidence level for long-lived particle proper decay lengths ranging from 5 cm to 40 m. For the photophobic axionlike particle model considered, this search produces the strongest limits to date for proper decay lengths greater than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>10</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><mi>cm</mi></math>.

Search for events with one displaced vertex from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions 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>

An anomaly detection search for narrow-width resonances beyond the Standard Model that decay into a pair of jets is presented. The search is based on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>139</mn><mtext> </mtext><mtext> </mtext><msup><mi>fb</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> of proton-proton collisions 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> recorded during 2015–2018 with the ATLAS detector at the Large Hadron Collider. The analysis is optimized without a particular signal model and aims to be sensitive to a broad range of new physics. It uses two different machine learning strategies to estimate the background in different signal regions. In each region, a weakly supervised classifier is trained to distinguish this background model from data. The analysis focuses on events with high transverse momentum jets reconstructed as large-radius jets. The mass and substructure of these jets are used as inputs to the classifiers. After a classifier-based selection, the distribution of the invariant mass of the two jets is used to search for potential local excesses. The model-independent results of both the anomaly detection methods show no signs of significant local excesses. In addition to model-independent results, a representative set of signal models is injected into the data, and the sensitivity of the methods to these scenarios is reported.

Weakly supervised anomaly detection for resonant new physics in the dijet final state using proton-proton collisions 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> with the ATLAS detector

A search for exotic decays of the Higgs boson <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi></math> into new scalar or pseudoscalar particles that subsequently decay into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-quarks is presented. The search considers <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Z</mi><mi>H</mi></math> production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><mn>2</mn><mi>a</mi><mo stretchy="false">→</mo><mn>4</mn><mi>b</mi></math>, second to a pair of scalars with different masses (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mrow><mi>a</mi><mn>1</mn></mrow></msub><mo>&lt;</mo><msub><mi>m</mi><mrow><mi>a</mi><mn>2</mn></mrow></msub></math>), either directly, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><msub><mi>a</mi><mn>1</mn></msub><msub><mi>a</mi><mn>2</mn></msub><mo stretchy="false">→</mo><mn>4</mn><mi>b</mi></math>, or via a longer decay chain, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>H</mi><mo stretchy="false">→</mo><msub><mi>a</mi><mn>1</mn></msub><msub><mi>a</mi><mn>2</mn></msub><mo stretchy="false">→</mo><mn>3</mn><msub><mi>a</mi><mn>1</mn></msub><mo stretchy="false">→</mo><mn>6</mn><mi>b</mi></math>. The analysis uses proton-proton collision data 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> collected with 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>. No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4</mn><mi>b</mi></math> or <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>6</mn><mi>b</mi></math>, between 4% and 25% for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>σ</mi><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>SM</mi></mrow></msub><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><mn>2</mn><mi>a</mi><mo stretchy="false">→</mo><mn>4</mn><mi>b</mi><mo stretchy="false">)</mo></mrow></math>, between 24% and 38% for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>σ</mi><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>SM</mi></mrow></msub><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mspace linebreak="goodbreak"></mspace><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy="false">→</mo><mn>4</mn><mi>b</mi><mo stretchy="false">)</mo></mrow></math>, and between 10% and 20% for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>σ</mi><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>/</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>SM</mi></mrow></msub><mo stretchy="false">(</mo><mi>Z</mi><mi>H</mi><mo stretchy="false">)</mo><mo>×</mo><mi mathvariant="script">B</mi><mo stretchy="false">(</mo><mi>H</mi><mo stretchy="false">→</mo><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>a</mi></mrow><mrow><mn>2</mn></mrow></msub><mo stretchy="false">→</mo><mn>3</mn><msub><mrow><mi>a</mi></mrow><mrow><mn>1</mn></mrow></msub><mo stretchy="false">→</mo><mn>6</mn><mi>b</mi><mo stretchy="false">)</mo></mrow></math>, depending on the masses of the scalar particles.

Search for decays of the Higgs boson into scalar particles decaying into four or six <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math> quarks using <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi><mi>p</mi></math> collisions 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> with the ATLAS detector

A measurement of off-shell Higgs boson production is performed in the <italic>H</italic>*&#8239;&#8594;&#8239; <italic>WW</italic> channel. The measurement uses a proton&#8211;proton collision dataset with an integrated luminosity of 140 fb <math altimg='si12.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math> collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Final states in which both <italic>W</italic> bosons decay leptonically are targeted, and events are categorised based on the flavour of the final-state leptons, the jet multiplicity, and the output of neural network-based classifiers. The data are found to be compatible with the Standard Model expectation. An observed (expected) upper bound on the 95 % symmetric confidence level interval is set on the rate of off-shell Higgs boson production at a value of 3.4 (4.4) times the Standard Model prediction. These results are combined with the results from the measurement of on-shell Higgs boson production in the same final states to obtain an observed (expected) upper bound at 95 % confidence level on the Higgs boson total width of 13.1 (17.3) MeV.

Constraining off-shell Higgs boson production and the Higgs boson total width using <italic>WW</italic>&#8239;&#8594;&#8239;&#8467; <italic>&#957;</italic>&#8467; <italic>&#957;</italic> final states with the ATLAS detector