Measurements of integrated and differential cross sections for isolated photon pair production in pp collisions at $\sqrt{s}=8$ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev.D 95 (2017) 112005, 2017.
Inspire Record 1591327 DOI 10.17182/hepdata.77381

A measurement of the production cross section for two isolated photons in proton-proton collisions at a center-of-mass energy of $\sqrt{s}=8$ TeV is presented. The results are based on an integrated luminosity of 20.2 fb$^{-1}$ recorded by the ATLAS detector at the Large Hadron Collider. The measurement considers photons with pseudorapidities satisfying $|\eta^{\gamma}|<1.37$ or ${1.56<|\eta^{\gamma}|<2.37}$ and transverse energies of respectively $E_{\mathrm{T,1}}^{\gamma}>40$ GeV and $E_{\mathrm{T,2}}^{\gamma}>30$ GeV for the two leading photons ordered in transverse energy produced in the interaction.The background due to hadronic jets and electrons is subtracted using data-driven techniques. The fiducial cross sections are corrected for detector effects and measured differentially as a function of six kinematic observables. The measured cross section integrated within the fiducial volume is $16.8 \pm 0.8$ pb. The data are compared to fixed-order QCD calculations at next-to-leading-order and next-to-next-to-leading-order accuracy as well as next-to-leading-order computations including resummation of initial-state gluon radiation at next-to-next-to-leading logarithm or matched to a parton shower, with relative uncertainties varying from 5% to 20%.

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The measured fiducial (total xs).

The measured differential as a function of Mgg.

The measured differential as a function of pTgg.

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Search for heavy resonances decaying to a $W$ or $Z$ boson and a Higgs boson in the $q\bar{q}^{(\prime)}b\bar{b}$ final state in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Lett.B 774 (2017) 494-515, 2017.
Inspire Record 1611039 DOI 10.17182/hepdata.77272

A search for heavy resonances decaying to a $W$ or $Z$ boson and a Higgs boson in the $q\bar{q}^{(\prime)}b\bar{b}$ final state is described. The search uses 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s} =$ 13 TeV collected by the ATLAS detector at the CERN Large Hadron Collider in 2015 and 2016. The data are in agreement with the Standard Model expectations, with the largest excess found at a resonance mass of 3.0 TeV with a local (global) significance of 3.3 (2.1) $\sigma$. The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching ratio for resonances decaying to a $W$ ($Z$) boson and a Higgs boson, itself decaying to $b\bar{b}$, in the mass range between 1.1 and 3.8 TeV; the limits range between 83 and 1.6 fb (77 and 1.1 fb) at 95% confidence level.

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The observed and expected cross-section upper limits at the 95% confidence level for pp -> V prime -> VH -> qq(bb+cc) in the WH signal region.

The observed and expected cross-section upper limits at the 95% confidence level for pp -> V prime -> VH -> qq(bb+cc) in the ZH signal region.

Signal acceptance x efficiency as a function of resonance mass.


Studies of $Z\gamma$ production in association with a high-mass dijet system in $pp$ collisions at $\sqrt{s}$ = 8 TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
JHEP 07 (2017) 107, 2017.
Inspire Record 1598259 DOI 10.17182/hepdata.77542

The production of a $Z$ boson and a photon in association with a high-mass dijet system is studied using 20.2fb$^{-1}$ of proton-proton collision data at a centre-of-mass energy of $\sqrt{s}$ = 8 TeV recorded with the ATLAS detector in 2012 at the Large Hadron Collider. Final states with a photon and a Z boson decaying into a pair of either electrons, muons, or neutrinos are analysed. Electroweak and total $pp \to Z\gamma j j$ cross-sections are extracted in two fiducial regions with different sensitivities to electroweak production processes. Quartic couplings of vector bosons are studied in regions of phase space with an enhanced contribution from pure electroweak production, sensitive to vector-boson scattering processes $VV \to Z\gamma$. No deviations from Standard Model predictions are observed and constraints are placed on anomalous couplings parameterized by higher-dimensional operators using effective field theory.

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The measured fiducial sections of Zyjj in the charged-leptonic channel. In the measured cross-sections, the first uncertainty is the statistical uncertainty, and the second one is the combined systematic uncertainty.

95% confidence level cross-section upper limits on the $Z\gamma jj$ processes in both charged-leptonic and neutrino channels. The reconstruction efficiencies are provided as C-factors.

95% confidence level interval (expected and observed) on aQGC parameters (VBFNLO formalism) provided for different values of unitarity scale (Form Factor).


Measurement of the cross-section for electroweak production of dijets in association with a $Z$ boson in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration Aaboud, M. ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Lett.B 775 (2017) 206-228, 2017.
Inspire Record 1627873 DOI 10.17182/hepdata.77267

The cross-section for the production of two jets in association with a leptonically decaying Z boson ($Zjj$) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb$^{-1}$. The electroweak $Zjj$ cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan $Zjj$ process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is $\sigma^{Zjj}_{EW}= 119\pm 16 (\mathrm{stat.}) \pm 20 (\mathrm{syst.})\pm 2 (\mathrm{lumi.})$ for dijet invariant mass greater than 250 GeV, and $34.2\pm 5.8 (\mathrm{stat.})\pm 5.5 (\mathrm{syst.})\pm 0.7 (\mathrm{lumi.})$ for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive $Zjj$ cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan $Zjj$ production.

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Fiducial regions definitions

Measured and predicted inclusive Zjj production cross-sections in the six fiducial regions

Measured and predicted EW-Zjj production cross-sections in the EW-enriched fiducial regions with and without an additional kinematic requirement of $m_{jj} > $ 1 TeV

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Search for dark matter at $\sqrt{s}=13$ TeV in final states containing an energetic photon and large missing transverse momentum with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J.C 77 (2017) 393, 2017.
Inspire Record 1591328 DOI 10.17182/hepdata.77382

Results of a search for physics beyond the Standard Model in events containing an energetic photon and large missing transverse momentum with the ATLAS detector at the Large Hadron Collider are reported. As the number of events observed in data, corresponding to an integrated luminosity of 36.1 $\textrm fb^{-1}$ of proton-proton collisions at a centre-of-mass energy of 13 TeV, is in agreement with the Standard Model expectations, exclusion limits in models where dark-matter candidates are pair-produced are determined. For dark-matter production via an axial-vector or a vector mediator in the s-channel, this search excludes mediator masses below 750-1200 GeV for dark-matter candidate masses below 230-480 GeV at 95% confidence level, depending on the couplings. In an effective theory of dark-matter production, the limits restrict the value of the suppression scale $M_{*}$ to be above 790 GeV at 95% confidence level. A limit is also reported on the production of a high-mass scalar resonance by processes beyond the Standard Model, in which the resonance decays to $Z\gamma$ and the Z boson subsequently decays into neutrinos.

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Observed event yields in 36.1 fb$^{-1}$ of data compared to expected yields from SM backgrounds in all signal regions, as predicted from the simultaneous fit to their respective CRs. The first three lines report the yields obtained from the inclusive-SR fit, while the two last lines report the yields obtained from the multiple-bin fit. The uncertainty includes both the statistical and systematic uncertainties.

The observed 95% CL exclusion contour for a simplified model of dark-matter production involving an axial-vector operator, Dirac DM and couplings $g_{q}$ = 0.25, $g_{\chi}$ = 1 and $g_{l}$ = 0 as a function of the dark-matter mass $m_{\chi}$ and the mediator mass $m_{\mathrm{med}}$. The plane under the limit curve is excluded.

The expected 95% CL exclusion contour (+1$\sigma$) for a simplified model of dark-matter production involving an axial-vector operator, Dirac DM and couplings $g_{q}$ = 0.25, $g_{\chi}$ = 1 and $g_{l}$ = 0 as a function of the dark-matter mass $m_{\chi}$ and the mediator mass $m_{\mathrm{med}}$. The plane under the limit curve is excluded.

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Search for TeV-scale gravity signatures in high-mass final states with leptons and jets with the ATLAS detector at $\sqrt{s}=13$ TeV

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Lett.B 760 (2016) 520-537, 2016.
Inspire Record 1468067 DOI 10.17182/hepdata.77086

A search for physics beyond the Standard Model, in final states with at least one high transverse momentum charged lepton (electron or muon) and two additional high transverse momentum leptons or jets, is performed using 3.2 fb$^{-1}$ of proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider in 2015 at $\sqrt{s}=13$ TeV. The upper end of the distribution of the scalar sum of the transverse momenta of leptons and jets is sensitive to the production of high-mass objects. No excess of events beyond Standard Model predictions is observed. Exclusion limits are set for models of microscopic black holes with two to six extra dimensions.

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Background fit results for regions SR-2TeV ( sumPT > 2 TeV) and SR-3TeV ( sumPT > 3 TeV) for the electron and muons channels. The errors shown are the statistical plus systematic uncertainties. The uncertainty in the total background count includes correlations between nuisance parameters and so does not reflect a quadrature sum of the uncertainties in the individual background components.

The sumPT distribution in the W+jets control region (electron channel). Expected background yields are given along with the total background uncertainty. The ttbar, W+jets and Z+jets backgrounds are normalised by the factors 0.95, 0.81 and 1.01 as obtained from the background likelihood fit. The single-top-quark and diboson background normalisations are taken from the simulation. The multijet background is obtained using a data-driven method. Additionally, the likelihood fit may constrain nuisance parameters for certain systematic uncertainties, altering the normalisation and shape of some of the distributions.

The sumPT distribution in the W+jets control region (muon channel). Expected background yields are given along with the total background uncertainty. The ttbar, W+jets and Z+jets backgrounds are normalised by the factors 0.95, 0.81 and 1.01 as obtained from the background likelihood fit. The single-top-quark and diboson background normalisations are taken from the simulation. The multijet background is obtained using a data-driven method. Additionally, the likelihood fit may constrain nuisance parameters for certain systematic uncertainties, altering the normalisation and shape of some of the distributions.

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Evidence for light-by-light scattering in heavy-ion collisions with the ATLAS detector at the LHC

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Nature Phys. 13 (2017) 852-858, 2017.
Inspire Record 1512305 DOI 10.17182/hepdata.77761

Light-by-light scattering ($\gamma\gamma\rightarrow\gamma\gamma$) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead (Pb) ions. Using 480 $\mu$b$^{-1}$ of Pb+Pb collision data recorded at a centre-of-mass energy per nucleon pair of 5.02 TeV by the ATLAS detector, the ATLAS Collaboration reports evidence for the $\gamma\gamma\rightarrow\gamma\gamma$ reaction. A total of 13 candidate events are observed with an expected background of 2.6$\pm$0.7 events. After background subtraction and analysis corrections, the fiducial cross section of the process $\textrm{Pb+Pb}\,(\gamma\gamma)\rightarrow \textrm{Pb}^{(\ast)}\textrm{+}\textrm{Pb}^{(\ast)}\,\gamma\gamma$, for photon transverse energy $E_{\mathrm{T}}>$3 GeV, photon absolute pseudorapidity $|\eta|<$2.4, diphoton invariant mass greater than 6 GeV, diphoton transverse momentum lower than 2 GeV and diphoton acoplanarity below 0.01, is measured to be 70 $\pm$ 24 (stat.) $\pm$ 17 (syst.) nb, which is in agreement with Standard Model predictions.

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Detector-level diphoton invariant mass distribution

Detector-level diphoton acoplanarity distribution

The measured total fiducial cross section


Study of ordered hadron chains with the ATLAS detector

The ATLAS collaboration Aaboud, M. ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev.D 96 (2017) 092008, 2017.
Inspire Record 1624693 DOI 10.17182/hepdata.77268

The analysis of the momentum difference between charged hadrons in high-energy proton-proton collisions is performed in order to study coherent particle production. The observed correlation pattern agrees with a model of a helical QCD string fragmenting into a chain of ground-state hadrons. A threshold momentum difference in the production of adjacent pairs of charged hadrons is observed, in agreement with model predictions. The presence of low-mass hadron chains also explains the emergence of charge-combination-dependent two-particle correlations commonly attributed to Bose-Einstein interference. The data sample consists of 190 inverse microbarns of minimum bias events collected with proton-proton collisions at a center-of-mass energy of 7 TeV in the early low-luminosity data taking with the ATLAS detector at the LHC.

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The inclusive Delta as a function of $Q$, in the interval 0.02 GeV < Q < 2 GeV.

The Delta(3h), for 3-hadron chains with mass below 0.59 GeV, as a function of $Q$, in the interval 0.02 GeV < Q < 0.36 GeV.

The Dalitz plot, for 3-hadron chains with mass below 0.59 GeV. Coordinates X = sqrt(3)(T0-T2)/sum(T) , Y = 3T1/sum(T) - 1. T0/T1/T2 stand for kinetic energy of hadrons in the rest frame of the triplet ( hadrons 0 and 2 form like-sign pair).

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Measurement of differential $J/\psi$ production cross-sections and forward-backward ratio in p+Pb collisions with the ATLAS detector

The ATLAS collaboration Aad, Georges ; Abbott, Brad ; Abdallah, Jalal ; et al.
Phys.Rev.C 92 (2015) 034904, 2015.
Inspire Record 1373747 DOI 10.17182/hepdata.77275

Measurements of differential cross-sections for $J/\psi$ production in p+Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV at the LHC with the ATLAS detector are presented. The data set used corresponds to an integrated luminosity of 28.1 nb$^{-1}$. The $J/\psi$ mesons are reconstructed in the dimuon decay channel over the transverse momentum range $8<p_{\mathrm{T}}<30$ GeV and over the center-of-mass rapidity range $-2.87<y^{*}<1.94$. Prompt $J/\psi$ are separated from $J/\psi$ resulting from $b$-hadron decays through an analysis of the distance between the $J/\psi$ decay vertex and the event primary vertex. The differential cross-section for production of nonprompt $J/\psi$ is compared to a FONLL calculation that does not include nuclear effects. Forward-backward production ratios are presented and compared to theoretical predictions. These results constrain the kinematic dependence of nuclear modifications of charmonium and $b$-quark production in p+Pb collisions.

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Measured non-prompt fraction.

Measured non-prompt fraction.

Measured prompt J/psi differential cross-section multiplied by branching ratio. The first systematic uncertainty is the combined systematic uncertainty excluding luminosity, the second is the luminosity.

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Search for Dark Matter Produced in Association with a Higgs Boson Decaying to $b\bar b$ using 36 fb$^{-1}$ of $pp$ collisions at $\sqrt s=13$ TeV with the ATLAS Detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev.Lett. 119 (2017) 181804, 2017.
Inspire Record 1608773 DOI 10.17182/hepdata.77773

Several extensions of the Standard Model predict associated production of dark-matter particles with a Higgs boson. Such processes are searched for in final states with missing transverse momentum and a Higgs boson decaying to a $b\bar b$ pair with the ATLAS detector using 36.1 fb$^{-1}$ of $pp$ collisions at a center-of-mass energy of 13 TeV at the LHC. The observed data are in agreement with the Standard Model predictions and limits are placed on the associated production of dark-matter particles and a Higgs boson.

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Distributions of the invariant mass of the Higgs boson candidates mh=m_J with one b-tag in the SR for the fourth MET category which is used as input to the fit.

Distributions of the invariant mass of the Higgs boson candidates mh=m_jj with two b-tags in the SR for the first MET category that is used as input to the fit.

Distributions of the invariant mass of the Higgs boson candidates mh=m_jj with two b-tags in the SR for the second MET category that is used as input to the fit.

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