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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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


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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Determination of the strong coupling constant $\alpha_s$ from transverse energy-energy correlations in multijet events at $\sqrt{s} = 8$ TeV using the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J.C 77 (2017) 872, 2017.
Inspire Record 1609253 DOI 10.17182/hepdata.77269

Measurements of transverse energy-energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to $\sqrt{s} = 8$ TeV proton-proton collisions with an integrated luminosity of 20.2 fb$^{-1}$. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of $\alpha_s(\mu)$ predicted in QCD up to scales over 1 TeV. A global fit to the transverse energy-energy correlation distributions yields $\alpha_s(m_Z) = 0.1162 \pm 0.0011 \mbox{ (exp.)}^{+0.0084}_{-0.0070} \mbox{ (theo.)}$, while a global fit to the asymmetry distributions yields a value of $\alpha_s(m_Z) = 0.1196 \pm 0.0013 \mbox{ (exp.)}^{+0.0075}_{-0.0045} \mbox{ (theo.)}$.

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TEEC function for 800 GeV < HT2 < 850 GeV

ATEEC function for 800 GeV < HT2 < 850 GeV

TEEC function for 850 GeV < HT2 < 900 GeV

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Measurement of internal structure of jets in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 2.76$ TeV with the ATLAS detector at the LHC

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J.C 77 (2017) 379, 2017.
Inspire Record 1511869 DOI 10.17182/hepdata.77789

The distributions of transverse momentum and longitudinal momentum fraction of charged particles in jets are measured in Pb+Pb and pp collisions with the ATLAS detector at the LHC. The distributions are measured as a function of jet transverse momentum and rapidity. The analysis utilises an integrated luminosity of 0.14 nb$^{-1}$ of Pb+Pb data and 4.0 pb$^{-1}$ of pp data collected in 2011 and 2013, respectively, at the same centre-of-mass energy of 2.76 TeV per colliding nucleon pair. The distributions measured in pp collisions are used as a reference for those measured in Pb+Pb collisions in order to evaluate the impact on the internal structure of jets from the jet energy loss of fast partons propagating through the hot, dense medium created in heavy-ion collisions. Modest but significant centrality-dependent modifications of fragmentation functions in Pb+Pb collisions with respect to those in pp collisions are seen. No significant dependence of modifications on jet $p_{\mathrm{T}}$ and rapidity selections is observed except for the fragments with the highest transverse momenta for which some reduction of yields is observed for more forward jets.

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D(pt) distributions for pp and Pb+Pb collisions, jet rapidity |y| < 2.1.

D(pt) distributions for pp and Pb+Pb collisions, jet rapidity |y| < 0.3.

D(pt) distributions for pp and Pb+Pb collisions, jet rapidity 0.3 < |y| < 0.8.

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Version 2
Measurements of top-quark pair differential cross-sections in the lepton+jets channel in $pp$ collisions at $\sqrt{s}$=13 TeV using the ATLAS detector

The ATLAS collaboration Aaboud, M. ; Aad, Georges ; Abbott, Brad ; et al.
JHEP 11 (2017) 191, 2017.
Inspire Record 1614149 DOI 10.17182/hepdata.80041

Measurements of differential cross-sections of top-quark pair production in fiducial phase-spaces are presented as a function of top-quark and $t\bar{t}$ system kinematic observables in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$=13 TeV. The data set corresponds to an integrated luminosity of $3.2$ fb${}^{-1}$, recorded in 2015 with the ATLAS detector at the CERN Large Hadron Collider. Events with exactly one electron or muon and at least two jets in the final state are used for the measurement. Two separate selections are applied that each focus on different top-quark momentum regions, referred to as resolved and boosted topologies of the $t\bar{t}$ final state. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations by means of calculated $\chi^2$ and $p$-values.

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Covariance matrix of the absolute cross-section as function of the top quark pT, accounting for the statistical and systematic uncertainties in the resolved topology.

Covariance matrix of the absolute cross-section as function of the top quark pT, accounting for the statistical and systematic uncertainties in the resolved topology.

Covariance matrix of the relative cross-section as function of the top quark pT, accounting for the statistical and systematic uncertainties in the resolved topology.

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Version 2
Search for direct top squark pair production in events with a Higgs or $Z$ boson, and missing transverse momentum in $\sqrt{s}=13$ TeV $pp$ collisions with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
JHEP 08 (2017) 006, 2017.
Inspire Record 1604889 DOI 10.17182/hepdata.77997

A search for direct top squark pair production resulting in events with either a same-flavour opposite-sign dilepton pair with invariant mass compatible with a $Z$ boson or a pair of jets compatible with a Standard Model (SM) Higgs boson ($h$) is presented. Requirements on additional leptons, jets, jets identified as originating from $b$-quarks, and missing transverse momentum are imposed to target the other decay products of the top squark pair. The analysis is performed using proton-proton collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC in 2015--2016, corresponding to an integrated luminosity of 36.1 fb$^{-1}$. No excess is observed in the data with respect to the SM predictions. The results are interpreted in two sets of models. In the first set, direct production of pairs of lighter top squarks ($\tilde{t}_1$) with long decay chains involving $Z$ or Higgs bosons is considered. The second set includes direct pair production of the heavier top squark pairs ($\tilde{t}_2$) decaying via $\tilde{t}_2 \rightarrow Z \tilde{t}_1 $ or $\tilde{t}_2 \rightarrow h \tilde{t}_1$. The results exclude at 95\% confidence level $\tilde{t}_2$ and $\tilde{t}_1$ masses up to about 800 GeV, extending the exclusion region of supersymmetric parameter space covered by previous LHC searches.

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Jet multiplicity distributions in control regions CR$^{3\ell 1b}_{t\bar{t}Z}$, after normalising the $t\bar{t}Z$ and multi-boson background processes via the simultaneous fit described in Section 5. The contributions from all SM backgrounds are shown as a histogram stack; the bands represent the total uncertainty in the background prediction. The "Others" category contains the contributions from $t\bar{t} h$, $t\bar{t} WW$, $t\bar{t} t$, $t\bar{t} t\bar{t}$, $Wh$, and $Zh$ production.

Jet multiplicity distributions in control regions CR$^{3\ell 1b}_{t\bar{t}Z}$, after normalising the $t\bar{t}Z$ and multi-boson background processes via the simultaneous fit described in Section 5. The contributions from all SM backgrounds are shown as a histogram stack; the bands represent the total uncertainty in the background prediction. The "Others" category contains the contributions from $t\bar{t} h$, $t\bar{t} WW$, $t\bar{t} t$, $t\bar{t} t\bar{t}$, $Wh$, and $Zh$ production.

Jet multiplicity distributions in control region CR$^{3\ell 1b}_{VV}$, after normalising the $t\bar{t}Z$ and multi-boson background processes via the simultaneous fit described in Section 5. The contributions from all SM backgrounds are shown as a histogram stack; the bands represent the total uncertainty in the background prediction. The "Others" category contains the contributions from $t\bar{t} h$, $t\bar{t} WW$, $t\bar{t} t$, $t\bar{t} t\bar{t}$, $Wh$, and $Zh$ production.

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A search for pair-produced resonances in four-jet final states at $\sqrt{s}$=13 TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Eur.Phys.J.C 78 (2018) 250, 2018.
Inspire Record 1631641 DOI 10.17182/hepdata.79059

A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb$^{-1}$ of $\sqrt{s}=$ 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, $\tilde{t}$, which decays promptly into two quarks through $R$-parity-violating couplings. Top squarks with masses in the range 100 GeV < $m_{\tilde{t}}$ < 410 GeV are excluded at 95% confidence level. If the decay is into a $b$-quark and a light quark, a dedicated selection requiring two $b$-tags is used to exclude masses in the ranges 100 GeV < $m_{\tilde{t}}$ < 470 GeV and 480 GeV < $m_{\tilde{t}}$ < 610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances.

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- - - - - - - - - - - - - - - - - - - - <p><b>Cutflows:</b><br> <a href="79059?version=1&table=CutflowTable1">Stop 100GeV</a><br> <a href="79059?version=1&table=CutflowTable2">Stop 500GeV</a><br> <a href="79059?version=1&table=CutflowTable3">Coloron 1500GeV</a><br> </p> <p><b>Event Yields:</b><br> <a href="79059?version=1&table=SRdistribution1">Inclusive stop SR</a><br> <a href="79059?version=1&table=SRdistribution2">Inclusive coloron SR </a><br> <a href="79059?version=1&table=SRdistribution3">b-tagged stop SR</a><br> </p> <p><b>Acceptances and Efficiencies:</b><br> <a href="79059?version=1&table=Acceptance1">Inclusive stop SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance2">Inclusive stop SR, after mass window</a><br> <a href="79059?version=1&table=Acceptance3">Inclusive coloron SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance4">Inclusive coloron SR, after mass window</a><br> <a href="79059?version=1&table=Acceptance5">b-tagged stop SR, before mass window</a><br> <a href="79059?version=1&table=Acceptance6">b-tagged stop SR, after mass window</a><br> </p> <p><b>Cross section upper limits:</b><br> <a href="79059?version=1&table=Limitoncrosssection1">Inclusive stop SR</a><br> <a href="79059?version=1&table=Limitoncrosssection2">Inclusive coloron SR</a><br> <a href="79059?version=1&table=Limitoncrosssection3">b-tagged stop SR</a><br> </p> <p><b>Truth Code</b> and <b>SLHA Files</b> for the cutflows are available under "Resources" (purple button on the left) </p>

Cutflow table for a pair produced top squark of 100 GeV decaying into a b- and an s-quark.

Cutflow table for a pair produced top squark of 500 GeV decaying into a b- and an s-quark.

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Search for new high-mass phenomena in the dilepton final state using 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}$ = 13 TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
JHEP 10 (2017) 182, 2017.
Inspire Record 1609250 DOI 10.17182/hepdata.79077

A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb$^{-1}$ of proton-proton collision data, collected at $\sqrt{s}$ = 13 TeV by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 for the E$_{6}$-motivated Z'$_{\chi}$. Lower limits on the $qq \ell\ell$ contact interaction scale are set between 24 TeV and 40 TeV, depending on the model.

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Product of acceptance and efficiency for the dielectron (upper curve) and dimuon (lower curve) selections as a function of the Z' (Chi) pole mass. Upper 95% CL limits on the Z' production cross-section times branching ratio to two electrons as a function of Z' pole mass.

Distribution of dielectron reconstructed invariant mass after selection, for data and the SM background estimates.

Distribution of dimuon reconstructed invariant mass after selection, for data and the SM background estimates.

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Version 2
Search for new phenomena in dijet events using 37 fb$^{-1}$ of $pp$ collision data collected at $\sqrt{s}=$13 TeV with the ATLAS detector

The ATLAS collaboration Aaboud, Morad ; Aad, Georges ; Abbott, Brad ; et al.
Phys.Rev.D 96 (2017) 052004, 2017.
Inspire Record 1519428 DOI 10.17182/hepdata.77265

Dijet events are studied in the proton--proton collision dataset recorded at $\sqrt{s}=$13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb$^{-1}$ and 33.5 fb$^{-1}$ respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The dataset is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W' bosons, W* bosons, and a range of masses and couplings in a Z' dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity.

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The number of events as a function of the dijet invariant mass, compared to background prediction from fit and corresponding uncertainties, in the region defined by |y*|<0.6

The number of events as a function of the dijet invariant mass, compared to background prediction from fit and corresponding uncertainties, in the region defined by |y*|<0.6

The number of events as a function of the dijet invariant mass, compared to background prediction from fit and corresponding uncertainties, in the region defined by |y*|<1.2 optimized for the W* search.

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