Correlation of Y meson production with the underlying event in pp collisions measured by the ATLAS experiment

The multiplicity and distributions of kinematic variables of charged particles produced in association with an $\Upsilon$ meson are measured in proton-proton collisions using the data collected by the ATLAS experiment at the LHC. The analysis uses a full Run 2 data set at $\sqrt{s}=13$ TeV, corresponding to the integrated luminosity of 139 fb$^{-1}$. The measurement is performed separately for the first three $\Upsilon\left(n\mathrm{S}\right)$ states in several intervals of $\Upsilon$ transverse momenta. At $\Upsilon$ transverse momentum close to zero, the associated charged-particle multiplicity is measured to be smaller by $12\pm1$\% in collisions where $\Upsilon\left(2\mathrm{S}\right)$ is observed compared to the collisions with $\Upsilon\left(1\mathrm{S}\right)$. For $\Upsilon\left(3\mathrm{S}\right)$ this difference is $17\pm4$\%. These differences decrease with increasing transverse momentum of the $\Upsilon$ states

ATLAS measurements of correlations between Υ mesons and inclusive charged particles

This talk presents a new measurement studying the relationship between the production of hard and soft particles through the correlation of Upsilon meson states with the inclusive-charged particle yields in 13 TeV pp collisions. Measurements are made differentially for Upsilon momentum and for different Upsilon states. The analysis is performed using the full-luminosity ATLAS Run-2 13 TeV pp data. This measurement benefits from the heavy-ion style approach to remove the combinatorial and pileup backgrounds leading to increased sensitivity. A description of the technical challenges associated with a heavy-ion style analysis in high-pileup pp data will be shown, as well as the results and their physics implications

Search for the Heavy Ion Physics Signatures in Small Collision Systems with the ATLAS Detector at the LHC

Quark-Gluon Plasma is the state of matter in which the quarks and gluons are not bound into hadrons. This form of matter is observed in large systems of particles that can be produced in collisions of relativistic Heavy Ions, for example, at the LHC at CERN. Recent measurements reveal the effects which are considered the signatures of the QGP also in much smaller proton-proton collisions, where they have no clear explanation. The thesis includes two independent analyses that may shed light on this novel phenomenon. The analysis of the multiplicity and kinematic distributions of charged particles produced in association with an $\Upsilon$ meson measured in proton-proton collisions uses the data collected by the ATLAS experiment at the LHC. The analysis uses a full Run-2 data set obtained at $\sqrt{s} = 13 TeV$, corresponding to the integrated luminosity of 139 $\mathrm{fb}^{−1}$. At zero $\Upsilon$ transverse momentum, the associated charged-particle multiplicity drastically differs for different $\Upsilon$ states. It is by $17\pm4$% fewer for $\Upsilon(3S)$ and by $12\pm1$% fewer for $\Upsilon (2S)$ than for $\Upsilon(1S)$. These differences are associated with the underlying event of collisions and decrease with increasing transverse momentum of the $\Upsilon$ states. This measurement is a direct suggestion of bottomonia suppression in $p+p$ collisions at the LHC. A global study of the momentum distributions of the mesons at LHC energies uses an empirical transverse mass scaling approach. This study demonstrates patterns in the spectral properties of mesons related to their quark content and is instrumental in working out the differences in the spectral shapes of particles with identical quark content and close masses. Based on the transverse mass scaling assumption, the excited bottomonia states are found to be suppressed with respect to the ground state by a factor of 1.6 and 2.4 for $\Upsilon (2S)$ and $\Upsilon (3S)$ respectively. The two measurements must be related to the same physics mechanism and have to be understood together

Transverse Mass Scaling of Heavy Mesons at LHC Energies

Transverse mass scaling has been observed for a wide range of particle species in proton-proton collisions at various energies from the SPS to RHIC and the LHC. The observed scaling is known to be different for baryons and mesons, and this work presents a comprehensive study of the transverse mass scaling of mesons at LHC energies with a focus on heavier mesons. The study demonstrates patterns in the scaling properties of mesons, which are related to the particle quark content. In particular, light species and ground-state quarkonia obey the same scaling, whereas open flavor particles deviate from it because their spectra are significantly harder. The magnitude of deviation depends on the flavor of the heaviest quark in the meson. By extending the transverse mass scaling assumption to the excited bottomonia states, it is observed that the measured cross-sections of $\Upsilon$(2S) and $\Upsilon$(3S) are reduced by factors of 1.6 and 2.4 compared to the expectation from the scaling.Comment: 7 pages, 3 figure

Measurements of the Higgs boson inclusive and differential fiducial cross-sections in the diphoton decay channel with collisions at 13TeV with the ATLAS detector

A measurement of inclusive and differential fiducial cross-sections for the production of the Higgs boson decaying into two photons is performed using 139 fb-1 of proton–proton collision data recorded at 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio, in a fiducial region closely matching the experimental selection, is measured to be 67   6 fb, which is in agreement with the state-of-the-art Standard Model prediction of 64 +_4 fb. Extrapolating this result to the full phase space and correcting for the branching ratio, the total cross-section for Higgs boson production is estimated to be 58 +- 6 pb. In addition, the cross-sections in four fiducial regions sensitive to various Higgs boson production modes and differential cross-sections as a function of either one or two of several observables are measured. All the measurements are found to be in agreement with the Standard Model predictions. The measured transverse momentum distribution of the Higgs boson is used as an indirect probe of the Yukawa coupling of the Higgs boson to the bottom and charm quarks. In addition, five differential cross-section measurements are used to constrain anomalous Higgs boson couplings to vector bosons in the Standard Model effective field theory framework.Fil: The ATLAS Collaboration. The ATLAS Collaboration; ArgentinaFil: Dova, Maria Teresa. Atlas Experiment, Cern; Suiza. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Aad, Georges. Centre National de la Recherche Scientifique; FranciaFil: Abbott, Braden. Oklahoma State University; Estados UnidosFil: Abed Abud, Adam. Cern - European Organization For Nuclear Research. The Cern Council; SuizaFil: Abeling, Kira. Universität Göttingen; AlemaniaFil: Abidi, Syed Haider. Brookhaven National Laboratory; Estados UnidosFil: Aboulhorma, Asmaa. Universite Mohammed V. Rabat; Otros paises de ÁfricaFil: Abramowicz, Halina. Universitat Tel Aviv; IsraelFil: Abreu, Henso. Technion - Israel Institute of Technology; IsraelFil: Abulaiti, Yiming. University of New York; Estados UnidosFil: Achkar, Baida. Universität Göttingen; AlemaniaFil: Adam, Lennart. Johannes Gutenberg Universitat Mainz; AlemaniaFil: Adamczyk, Leszek. AGH University of Science and Technology; PoloniaFil: Adamek, Lukas. University of Toronto; CanadáFil: Adelman, Jahred. Northeastern Illinois University (northeastern Illinois);Fil: Adye, Tim. Rutherford Appleton Laboratory; Reino UnidoFil: Afik, Yoav. Cern - European Organization For Nuclear Research. The Cern Council; SuizaFil: Agapopoulou, Christina. Universite Paris-saclay (universite Paris-saclay);Fil: Agaras, Merve Nazlim. Institut de Fisica D Altes Energies (ifae);Fil: Agarwala, Jinky. Istituto Nazionale di Fisica Nucleare; ItaliaFil: Aggarwal, Anamika. Radboud Universiteit Nijmegen; Países BajosFil: Aguilar Saavedra, Juan Antonio. Universidad de Granada; EspañaFil: Ahmed, Waleed Syed. McGill University. Montreal Neurological Institute and Hospital; CanadáFil: Aizenberg, Iakov. Weizmann Institute of Science; IsraelFil: Akatsuka, Shunichi. Kyoto University; JapónFil: Akbiyik, Melike. Johannes Gutenberg Universitat Mainz; AlemaniaFil: Akesson, Torsten. Lund University; SueciaFil: Akimov, Andrey. Russian Academy of Sciences; RusiaFil: Al Khoury, Konie. Columbia University; Estados UnidosFil: Alberghi, Gian Luigi. Istituto Nazionale di Fisica Nucleare; Itali

Observation of electroweak production of W+W−W^+W^- in association with jets in proton-proton collisions at s=13\sqrt{s}=13 TeV with the ATLAS Detector

International audienceA measurement of the production of $W$ bosons with opposite electric charges in association with two jets is presented based on 140 fb$^{-1}$ of data collected by the ATLAS detector in proton-proton collisions at $\sqrt{s}=13$ TeV. The analysis is sensitive to the scattering of $W$ bosons, which is of particular interest in the ATLAS physics programme as it can be used to probe the electroweak symmetry breaking mechanism of the Standard Model. This signal is observed with a significance of 7.1 standard deviations above the background expectation, while 6.2 standard deviations were expected. The measured cross-section is determined in a signal-enriched fiducial volume and is found to be $2.7\pm0.5$ fb, which is consistent with the theoretical prediction of $2.20^{+0.14}_{-0.13}$ fb

Search for a resonance decaying into a scalar particle and a Higgs boson in the final state with two bottom quarks and two photons in proton-proton collisions at a center of mass energy of 13 TeV with the ATLAS detector

International audienceA search for the resonant production of a heavy scalar $X$ decaying into a Higgs boson and a new lighter scalar $S$, through the process $X \to S(\to bb) H(\to \gamma\gamma)$, where the two photons are consistent with the Higgs boson decay, is performed. The search is conducted using an integrated luminosity of 140 fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The search is performed over the mass range 170 $\leq$$m_{X}$$\leq$ 1000 GeV and 15 $\leq$$m_{S}$$\leq$ 500 GeV. Parameterised neural networks are used to enhance the signal purity and to achieve continuous sensitivity in a domain of the ($m_{X}$, $m_{S}$) plane. No significant excess above the expected background is found and 95% CL upper limits are set on the cross section times branching ratio, ranging from 39 fb to 0.09 fb. The largest deviation from the background-only expectation occurs for ($m_{X}$, $m_{S}$) = (575, 200) GeV with a local (global) significance of 3.5 (2.0) standard deviations

Measurements of longitudinal flow decorrelations in pppp and Xe+Xe collisions with the ATLAS detector

Measurements of longitudinal flow decorrelations in 13 TeV $pp$ and 5.44 TeV Xe+Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within |\eta| < 2.5 with either calorimeter energy clusters or towers within 4.0<|\eta|<4.9. A template-based subtraction procedure is used to remove non-flow effects in both the $pp$ and the Xe+Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter $F_n$ for the elliptic ($n=2$) and triangular ($n=3$) harmonic moments. The results are reported as a function of charged-particle multiplicity for the $pp$ and Xe+Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in $pp$ and peripheral Xe+Xe collisions, sub-nucleonic structure and fluctuations in longitudinal energy deposition are needed to describe the data

Measurement of the total and differential cross-sections of ttˉWt\bar{t}W production in pppp collisions at s=13\sqrt{s}=13 TeV with the ATLAS detector

International audienceMeasurements of inclusive and differential production cross-sections of a top-quark-top-antiquark pair in association with a $W$ boson ($t\bar{t}W$) are presented. They are performed by targeting final states with two same-sign or three isolated leptons (electrons or muons) and are based on $\sqrt{s}=13$ TeV proton-proton collision data with an integrated luminosity of 140 fb$^{-1}$, recorded from 2015 to 2018 with the ATLAS detector at the Large Hadron Collider. The inclusive $t\bar{t}W$ production cross-section is measured to be $880 \pm 80$ fb, compared to a reference theoretical prediction of $745 \pm 50\,\textrm{(scale)} \pm 13\,\textrm{(2-loop approx.)} \pm 19\,\textrm{(PDF,} \alpha_{\textrm{S}})$ fb. Differential cross-section measurements characterise this process in detail for the first time. Several particle-level observables are compared with a variety of theoretical predictions, which generally agree well with the normalised differential cross-section results. Additionally, the relative charge asymmetry of $t\bar{t}W^{+}$ and $t\bar{t}W^{-}$ is measured inclusively to be ${A_{\mathrm{C}}^{\mathrm{rel}}} = 0.33 \pm 0.05$, in very good agreement with the theoretical prediction of $0.322 \pm 0.003\,\mathrm{(scale)} \pm 0.007\,\mathrm{(PDF)}$, as well as differentially