The production of single top quarks and top antiquarks via the $\textit{t}$-channel exchange of a virtual $\textit{W}$ boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The full Run 2 data sample recorded with the ATLAS detector in the years 2015–2018 is used, corresponding to an integrated luminosity of 140 fb . The absolute and normalised production cross-sections are measured differentially as a function of the transverse momentum and absolute rapidity of the top quark and top antiquark. In addition, the ratio of top quark to top antiquark production cross-sections is measured. The measured distributions are compared with next-to-leading-order quantum chromodynamics predictions obtained with different combinations of matrix-element generators, parton-shower programs and proton parton distribution functions, as well as to next-to-next-to-leading-order calculations. Overall, good agreement is observed between the measurements and the theoretical predictions. For most measured distributions, the sensitivity to differences between the predictions is limited by the systematic uncertainties in the measurement. The measured differential distributions are also interpreted in an effective field theory approach to constrain the Wilson-Coefficient $$ {C}_{Qq}^{3,1} $$ associated with a four-quark operator. The interpretation accounts for the effect of the selection efficiency, which is altered significantly by non-zero contributions from $$ {C}_{Qq}^{3,1} $$ .

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

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

B. Aitbenchikh

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

M. Aoki

Measurement of differential $\textit{t}$-channel single top (anti)quark production cross-sections at 13 TeV with the ATLAS detector

A measurement of the associated production of a top-quark pair with the Higgs boson ( $$ t\overline{t}H $$ ) in multilepton final states is presented. The analysis is based on a data sample of proton-proton collisions at $$ \sqrt{s}=13 $$ TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 140 fb . Six final states defined by the number and flavour of reconstructed charged leptons are combined in a simultaneous likelihood fit to extract the $$ t\overline{t}H $$ signal and constrain the most relevant backgrounds. The measured $$ t\overline{t}H $$ cross-section normalised to Standard Model (SM) prediction is $$ {\sigma}_{t\overline{t}H}/{\sigma}^{\mathrm{SM}}=0.{63}_{-0.19}^{+0.20} $$ . This result corresponds to an observed (expected) significance of 3.3$\textit{σ}$ (5.3$\textit{σ}$). Additionally, two other fits are used to measure the $$ t\overline{t}H $$ cross-section differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, and to extract the associated production cross-section of a single top-quark with the Higgs boson ($\textit{tH}$) together with the $$ t\overline{t}H $$ one. The $\textit{CP}$ structure of the top quark-Higgs boson Yukawa coupling is probed through an analysis of $$ t\overline{t}H $$ and $\textit{tH}$ events. The results are compatible with the SM hypothesis, and values of the mixing angle between $\textit{CP}$-even and $\textit{CP}$-odd top-Higgs Yukawa couplings of |$\textit{α}$| $\textit{>}$ 62 are excluded at 68% confidence level.

T. Aoki

M. Aparo

L. Aperio Bella

M. Apicella

C. Appelt

Measurement of the Higgs boson production in association with top quarks in multilepton final states in $\textit{pp}$ collisions at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

The angular distributions of Drell–Yan lepton pairs provide sensitive probes of the underlying dynamics of quantum chromodynamics (QCD) effects in vector-boson production. This paper presents for the first time the measurement of the full set of angular coefficients together with the differential cross-section as a function of the transverse momentum of the $\textit{W}$ boson, in the full phase space of the decay leptons. The measurements are performed separately for the $$W^-$$ and $$W^+$$ channels. The analysis uses proton–proton collision data recorded by the ATLAS experiment at the Large Hadron Collider in 2017 and 2018, during special low-luminosity runs with a reduced number of interactions per bunch crossings (pile-up). The data correspond to an integrated luminosity of 338 pb $$^{-1}$$ at a centre-of-mass energy of $$\sqrt{s} = 13$$ TeV. The low pile-up environment provides excellent experimental conditions for high-precision measurements of $\textit{W}$-boson production. All results agree with theoretical predictions incorporating finite-order QCD corrections up to order $$\alpha _S^2$$ .

C. Bourdarios

China

M. Tamlihat

M. Akbiyik

A. Fernandez

M. Cardoso

Brazil

Y. Coutinho

S. Santos

Measurement of the $\textit{W}$-boson angular coefficients and transverse momentum in $$p\!p$$ collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector

A search is presented for long-lived particles decaying into an oppositely charged lepton pair, <math altimg='si6.svg'><mrow><msup><mi>&#956;</mi><mo>+</mo></msup><msup><mi>&#956;</mi><mo>&#8722;</mo></msup></mrow></math>, <math altimg='si5.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup></mrow></math>, or <italic>e</italic> <sup>&#8239;&#177;&#8239;</sup> <italic>&#956;</italic> <sup>&#8723;</sup>, that form a vertex within the inner tracking system of the ATLAS detector at the Large Hadron Collider, displaced from the primary proton&#8211;proton interaction region. The analysis uses the 140 <math altimg='si9.svg'><mrow><msup><mtext>fb</mtext><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></mrow></math> of Run-2 data collected at <math altimg='si8.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13</mn></mrow></math> TeV by the ATLAS experiment in 2015&#8211;2018. The results of the analysis are interpreted in the context of three benchmark models covering masses from 0.1 to 2.2 TeV and a range of mean proper lifetimes times the speed of light from 1 to 10 000 mm. The first model is a generic <italic>Z</italic>&#8242; boson pair-produced by a new heavy scalar, with the <italic>Z</italic>&#8242; decaying into lepton pairs. The remaining two models are <italic>R</italic>-parity violating supersymmetric models in which the lightest neutralino <math altimg='si1.svg'><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mn>1</mn><mn>0</mn></msubsup></math> decays into <math altimg='si10.svg'><mrow><msup><mi>&#8467;</mi><mo>+</mo></msup><msup><mi>&#8467;</mi><mrow><msup><mrow /><mo>&#8242;</mo></msup><mo>&#8722;</mo></mrow></msup><mi>&#957;</mi></mrow></math> ( <math altimg='si11.svg'><mrow><mi>&#8467;</mi><mo>,</mo><msup><mi>&#8467;</mi><msup><mrow /><mo>&#8242;</mo></msup></msup><mo linebreak='goodbreak'>=</mo><mi>e</mi></mrow></math>, <italic>&#956;</italic>). The models differ by the mode of production of the <math altimg='si1.svg'><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mn>1</mn><mn>0</mn></msubsup></math>, which can be produced via the decay of pairs of gluinos or of pairs of charginos and neutralinos ( <math altimg='si12.svg'><mrow><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>1</mn></mrow><mo>&#177;</mo></msubsup><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>1</mn></mrow><mn>0</mn></msubsup></mrow></math>, <math altimg='si13.svg'><mrow><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>1</mn></mrow><mo>&#177;</mo></msubsup><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>2</mn></mrow><mn>0</mn></msubsup></mrow></math>, or <math altimg='si14.svg'><mrow><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>2</mn></mrow><mn>0</mn></msubsup><msubsup><mover accent='true'><mi>&#967;</mi><mo>&#732;</mo></mover><mrow><mn>1</mn></mrow><mn>0</mn></msubsup></mrow></math>). Although each benchmark sample includes pair-produced LLPs, only a single vertex is required to be reconstructed. No dilepton displaced vertex candidate is observed and the results are presented as upper limits on the production cross-sections. This analysis sets leading limits on the production cross-sections for multiple models, including parameter space that has never been directly probed.

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

Y. Amaral Coutinho

C.G. Ames

S.P. Amor Dos Santos

K.R. Amos

V. Ananiev

J.K. Anders

A.C. Anderson

A.V. Anisenkov

Search for long-lived particles using displaced vertices of oppositely charged leptons in <math altimg='si7.svg'><mrow><mn>140</mn><mspace width='0.33em' /><mrow><msup><mtext>fb</mtext><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></mrow></mrow></math> of <italic>pp</italic> collisions at <math altimg='si8.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13</mn></mrow></math> TeV with the ATLAS detector

The inclusive top quark pair ( $$t\bar{t}$$ ) cross-section $$\sigma _{t\bar{t}}$$ has been measured in proton–proton collisions at $$\sqrt{s}=13\,\text {TeV}$$ , using $$140\,{\text {fb}^{-1}} $$ of data collected by the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge $$e\mu $$ pair and $\textit{b}$-tagged jets, the cross-section is measured to be: where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the proton beam energy, giving a total uncertainty of 1.3%. The result is used to determine the top quark pole mass via the dependence of the predicted cross-section on $${m_{t}^\textrm{pole}}$$ , giving $${m_{t}^\textrm{pole}}=172.8^{+1.5}_{-1.7}$$ $$\text {GeV}$$ . The same event sample is used to measure absolute and normalised differential cross-sections for the $$t\bar{t} \rightarrow e\mu \nu \bar{\nu }b\bar{b} $$ process as a function of single-lepton and dilepton kinematic variables. Complementary measurements of $$e\mu b\bar{b} $$ production, treating both $$t\bar{t}$$ and $\textit{Wt}$ events as signal, are also provided. Both sets of differential cross-sections are compared to the predictions of various Monte Carlo event generators, demonstrating that the state-of-the-art generators and $\textit{bb}$4$\textit{l}$ describe the data better than .

Precise measurement of the $$t\bar{t}$$ production cross-section and lepton differential distributions in $$ e\mu $$ dilepton events from $$\sqrt{s}=13\,\text {TeV}$$ $\textit{pp}$ collisions with the ATLAS detector

As the particle physics community has explored most of the conventional avenues for new physics, the more elusive areas are becoming increasingly appealing. One such potential region, where new physics might be hiding, involves light and weakly interacting long-lived particles (LLPs). To probe deeper into this region, where the possibility of highly displaced scenarios weakens the role of general-purpose collider detectors, dedicated LLP detectors are our best option. However, their potential can only be fully realized if we optimize their position and dimensions to suit our physics goals. This is possible at the upcoming Future Circular Collider (FCC) facility, where the feasibility and design studies are still ongoing and can accommodate new proposals focused specifically on LLP searches. We propose optimized dedicated detectors in both the transverse and forward directions, DELIGHT and FOREHUNT, significantly enhancing the sensitivity to previously uncharted regions of the new physics parameter space. Our proposed DELIGHT detector can additionally serve as a shared transverse detector during both the FCC-ee and FCC-hh runs. The concept of a shared transverse detector is novel and sustainable, utilizing the same interaction points of the lepton and hadron colliders at the FCC. This minimizes costs and boosts the LLP physics case at the FCC.

India

Biplob Bhattacherjee

Camellia Bose

Herbi K. Dreiner

Nivedita Ghosh

Shigeki Matsumoto

Swagata Mukherjee

Rhitaja Sengupta

Anand Sharma

Proposal for a shared transverse LLP detector for FCC-ee and FCC-hh and a forward detector for FCC-hh

This paper reports the observation of electroweak diboson ($\textit{WW}$/$\textit{WZ}$/$\textit{ZZ}$) production in association with a high-mass dijet system, in which final states with one boson decaying leptonically and the other boson decaying hadronically are studied. The hadronically decaying $\textit{W}$/$\textit{Z}$ boson is reconstructed as either two small-radius jets or one large-radius jet with jet substructure requirements. The data analyzed correspond to an integrated luminosity of $$140 \ \text {fb}^{-1}$$ of proton–proton collisions at a center-of-mass energy of $$\sqrt{s}=13$$ TeV collected with the ATLAS detector during the 2015-2018 data taking at the Large Hadron Collider. The electroweak production of $\textit{WW}$/$\textit{WZ}$/$\textit{ZZ}$ in association with two jets is observed in a phase space dominated by vector-boson scattering with a significance of $$7.4\sigma $$ (expected $$6.1\sigma $$ ) and the signal strength is determined to be $$1.28^{+0.23}_{-0.21}$$ . The corresponding production cross section in a fiducial phase space is measured in addition. The signal strengths of both electroweak and QCD associated diboson productions are furthermore measured in a two-dimensional fit, the result of which agrees with the Standard Model prediction. The data are interpreted in the context of a dimension-8 effective field theory to probe anomalous quartic gauge couplings resulting in the first set of exclusion limits on the Wilson coefficients in the semileptonic channel reported by the ATLAS Collaboration. The observed limits for the S02, T0 and M0 operators are $$(-\,3.96< f_{S02} / \Lambda ^4 < 3.96)$$ TeV $$^{-4}$$ , $$(-\,0.25< f_{T0} / \Lambda ^4 < 0.22)$$ TeV $$^{-4}$$ , $$(-\,1.26< f_{M0} / \Lambda ^4 < 1.25)$$ TeV $$^{-4}$$ .

Electroweak diboson production in association with a high-mass dijet system in semileptonic final states from $\textit{pp}$ collisions at $$\sqrt{s} = 13$$ TeV with the ATLAS detector

This Letter analyzes the sensitivity of event geometry estimators to the initial-state kinematics of hard scattering in proton–lead collisions. This analysis uses dijets as a proxy for the parton–parton scattering configuration, correlating it with event geometry estimators, namely the energy deposited in the Zero-Degree Calorimeter and the transverse energy recorded in the Forward Calorimeter in the Pb-going direction. The analysis uses data recorded by the ATLAS detector at the Large Hadron Collider with a nucleon–nucleon center-of-mass energy of 8.16 TeV, corresponding to an integrated luminosity of 56 nb <math altimg='si6.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math>. The jets are measured within the pseudorapidity interval &#8722;2.8 &#8239;&lt;&#8239; <italic>&#951;</italic> &#8239;&lt;&#8239; 4.5, where positive <italic>&#951;</italic> values correspond to the direction of the proton beam. Results are presented as a function of the Bjorken- <italic>x</italic> of the parton originating from the proton, <italic>x<inf>p</inf></italic>. Both event geometry estimators are found to be dependent on <italic>x<inf>p</inf></italic>, with the energy deposited in the Zero-Degree Calorimeter about six times less sensitive to <italic>x<inf>p</inf></italic> compared with the transverse energy deposited in the Forward Calorimeter.

Characterization of nuclear breakup as a function of hard-scattering kinematics using dijets measured by ATLAS in <italic>p</italic>+Pb collisions

A search for final states characterised by at least one isolated high transverse-momentum photon, jets and large missing transverse momentum is presented. Such a final state might occur in gauge-mediated supersymmetric models where a pair of binos and higgsinos mix to form neutralinos, one of which decays into a photon plus a gravitino while the other decays into a Higgs boson, a $\textit{Z}$ boson or a photon, plus a gravitino. The search is performed using the full Run-2 data sample of 140 fb of $$ \sqrt{s}=13 $$ TeV proton-proton collisions collected by the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed above the Standard Model prediction and model-dependent exclusion limits at the 95% confidence level are set. These limits are interpreted in terms of the masses of gauginos, which are excluded up to 1.2 TeV depending on their branching ratios, and on their branching ratios as a function of their mass.

Search for signatures of electroweakinos with photons, jets, and large missing transverse momentum in $$ \sqrt{s}=13 $$ TeV $\textit{pp}$ collisions with the ATLAS detector

The top-quark mass is measured using top-quark decays producing an isolated lepton and $\textit{J}$/$\textit{ψ}$ meson reconstructed in its $\textit{μ}$ $\textit{μ}$ decay mode. The data sample was recorded with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of $$ \sqrt{s}=13 $$ TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb . The measurement is based on the invariant mass $\textit{m}$($\textit{ℓμ}$ $\textit{μ}$ ) of the system made of the isolated lepton $\textit{ℓ}$ from the $\textit{W}$ boson decay and the non-isolated $\textit{μ}$ $\textit{μ}$ pair from a $\textit{J}$/$\textit{ψ}$ decay of a $\textit{b}$-hadron, exploiting its sensitivity to the top-quark mass. An unbinned maximum-likelihood fit to the $\textit{m}$($\textit{ℓμ}$ $\textit{μ}$ ) distribution is performed to extract the top-quark mass. The top-quark mass is measured to be $\textit{m}$ = 172.17 ± 0.80 (stat) ± 0.81 (syst) ± 1.07 (recoil) GeV, with a total uncertainty of 1.56 GeV. The third uncertainty arises from changing the dipole parton shower gluon-recoil scheme used in top-quark decays.

Measurement of the top-quark mass using decays with a $\textit{J/ψ}$ meson at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector