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Measurements of inclusive and differential fiducial cross-sections of tt¯γ production in leptonic final states at s=13TeV in ATLAS
https://repo.scoap3.org/record/32591
Inclusive and differential cross-sections for the production of a top-quark pair in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 36.1 fb-1 , collected by the ATLAS detector at the LHC in 2015 and 2016 at a centre-of-mass energy of 13 TeV . The measurements are performed in single-lepton and dilepton final states in a fiducial volume. Events with exactly one photon, one or two leptons, a channel-dependent minimum number of jets, and at least one b -jet are selected. Neural network algorithms are used to separate the signal from the backgrounds. The fiducial cross-sections are measured to be 521±9(stat.)±41(sys.)fb and 69±3(stat.)±4(sys.)fb for the single-lepton and dilepton channels, respectively. The differential cross-sections are measured as a function of photon transverse momentum, photon absolute pseudorapidity, and angular distance between the photon and its closest lepton in both channels, as well as azimuthal opening angle and absolute pseudorapidity difference between the two leptons in the dilepton channel. All measurements are in agreement with the theoretical predictions.Aaboud, M.Sat, 04 May 2019 03:53:41 GMThttps://repo.scoap3.org/record/32591urn:ISSN:1434-6052Springer/Società Italiana di Fisica2019-5-3Erratum to: Measurements of W and Z boson production in pp collisions at s=5.02 TeV with the ATLAS detector
https://repo.scoap3.org/record/32519
It has been found that the theoretical predictions for W and Z boson cross sections, and for the W boson charge asymmetry, which are labelled as NNPDF3.1 [1] have in fact been calculated using the NNPDF3.0 PDF set [2] instead.Aaboud, M.Thu, 02 May 2019 14:59:09 GMThttps://repo.scoap3.org/record/32519urn:ISSN:1434-6052Springer/Società Italiana di Fisica2019-4-30Performance of top-quark and W -boson tagging with ATLAS in Run 2 of the LHC
https://repo.scoap3.org/record/32518
The performance of identification algorithms (“taggers”) for hadronically decaying top quarks and W bosons in pp collisions at s = 13 TeV recorded by the ATLAS experiment at the Large Hadron Collider is presented. A set of techniques based on jet shape observables are studied to determine a set of optimal cut-based taggers for use in physics analyses. The studies are extended to assess the utility of combinations of substructure observables as a multivariate tagger using boosted decision trees or deep neural networks in comparison with taggers based on two-variable combinations. In addition, for highly boosted top-quark tagging, a deep neural network based on jet constituent inputs as well as a re-optimisation of the shower deconstruction technique is presented. The performance of these taggers is studied in data collected during 2015 and 2016 corresponding to 36.1 fb -1 for the tt¯ and γ+jet and 36.7 fb -1 for the dijet event topologies.Aaboud, M.Thu, 02 May 2019 14:58:50 GMThttps://repo.scoap3.org/record/32518urn:ISSN:1434-6052Springer/Società Italiana di Fisica2019-4-30Measurement of the <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>Z</mi></math> and <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>W</mi></math> cross sections in proton-proton collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> with the ATLAS detector
https://repo.scoap3.org/record/32487
A measurement of the associated production of a top-quark pair (tt¯) with a vector boson (W, Z) in proton-proton collisions at a center-of-mass energy of 13 TeV is presented, using 36.1 fb−1 of integrated luminosity collected by the ATLAS detector at the Large Hadron Collider. Events are selected in channels with two same- or opposite-sign leptons (electrons or muons), three leptons or four leptons, and each channel is further divided into multiple regions to maximize the sensitivity of the measurement. The tt¯Z and tt¯W production cross sections are simultaneously measured using a combined fit to all regions. The best-fit values of the production cross sections are σtt¯Z=0.95±0.08stat±0.10syst pb and σtt¯W=0.87±0.13stat±0.14syst pb in agreement with the Standard Model predictions. The measurement of the tt¯Z cross section is used to set constraints on effective field theory operators which modify the tt¯Z vertex.Aaboud, M.Thu, 02 May 2019 14:06:37 GMThttps://repo.scoap3.org/record/32487urn:ISSN:2470-0029APS2019-04-29First observations of <math><mrow><msub><mrow><mi>h</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>→</mo><mtext>hadrons</mtext></mrow></math>
https://repo.scoap3.org/record/32456
Based on (4.48±0.03)×108 ψ(3686) events, collected with the BESIII detector at the BEPCII storage ring, five hc hadronic decays are searched for via the process ψ(3686)→π0hc. Three of them, hc→pp¯π+π−, π+π−π0, and 2(π+π−)π0, are observed for the first time with significances of 7.4σ, 4.6σ, and 9.1σ, and their branching fractions are determined to be (2.89±0.32±0.55)×10−3, (1.60±0.40±0.32)×10−3, and (7.44±0.94±1.52)×10−3, respectively, where the first uncertainties are statistical and the second systematic. No significant signal is observed for the other two decay modes, and the corresponding upper limits of the branching fractions are determined to be B(hc→3(π+π−)π0)<8.7×10−3 and B(hc→K+K−π+π−)<5.8×10−4 at the 90% confidence level.Ablikim, M.Wed, 24 Apr 2019 20:16:35 GMThttps://repo.scoap3.org/record/32456urn:ISSN:2470-0029APS2019-04-24Model-Independent Observation of Exotic Contributions to <math><msup><mi>B</mi><mn>0</mn></msup><mo>→</mo><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi></mrow><msup><mi>K</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> Decays
https://repo.scoap3.org/record/32365
An angular analysis of B0→J/ψK+π− decays is performed, using proton-proton collision data corresponding to an integrated luminosity of 3 fb−1 collected with the LHCb detector. The m(K+π−) spectrum is divided into fine bins. In each m(K+π−) bin, the hypothesis that the three-dimensional angular distribution can be described by structures induced only by K* resonances is examined, making minimal assumptions about the K+π− system. The data reject the K*-only hypothesis with a large significance, implying the observation of exotic contributions in a model-independent fashion. Inspection of the m(J/ψπ−) vs m(K+π−) plane suggests structures near m(J/ψπ−)=4200 and 4600 MeV.Aaij, R.Thu, 18 Apr 2019 04:16:44 GMThttps://repo.scoap3.org/record/32365urn:ISSN:1079-7114APS2019-04-17Study of the rare decays of B s 0 and B 0 mesons into muon pairs using data collected during 2015 and 2016 with the ATLAS detector
https://repo.scoap3.org/record/32330
A study of the decays B s 0 → μ + μ − and B 0 → μ + μ − has been performed using 26.3 fb −1 of 13 TeV LHC proton-proton collision data collected with the ATLAS detector in 2015 and 2016. Since the detector resolution in μ + μ − invariant mass is comparable to the B s 0 - B 0 mass difference, a single fit determines the signal yields for both decay modes. This results in a measurement of the branching fraction ℬ B s 0 → μ + μ − = 3.2 − 1.0 + 1.1 × 10 − 9 $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right)=\left({3.2}_{-1.0}^{+1.1}\right)\times {10}^{-9} $$ and an upper limit ℬ B 0 → μ + μ − < 4.3 × 10 − 10 $$ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)<4.3\times {10}^{-10} $$ at 95% confidence level. The result is combined with the Run 1 ATLAS result, yielding ℬ B s 0 → μ + μ − = 2.8 − 0.7 + 0.8 × 10 − 9 $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right)=\left({2.8}_{-0.7}^{+0.8}\right)\times {10}^{-9} $$ and ℬ B 0 → μ + μ − < 2.1 × 10 − 10 $$ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)<2.1\times {10}^{-10} $$ at 95% confidence level. The combined result is consistent with the Standard Model prediction within 2.4 standard deviations in the ℬ B 0 → μ + μ − − ℬ B s 0 → μ + μ − $$ \mathrm{\mathcal{B}}\left({B}^0\to {\mu}^{+}{\mu}^{-}\right)-\mathrm{\mathcal{B}}\left({B}_s^0\to {\mu}^{+}{\mu}^{-}\right) $$ plane.Aaboud, M.Wed, 17 Apr 2019 13:19:13 GMThttps://repo.scoap3.org/record/32330urn:ISSN:1029-8479Springer/SISSA2019-04-15Search for Higgs boson pair production in the b b ¯ W W * $$ b\overline{b}W{W}^{*} $$ decay mode at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
https://repo.scoap3.org/record/32327
A search for Higgs boson pair production in the b b ¯ W W * $$ b\overline{b}W{W}^{*} $$ decay mode is performed in the b b ¯ ℓνqq $$ b\overline{b}\mathit{\ell \nu qq} $$ final state using 36.1 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. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.Aaboud, M.Wed, 17 Apr 2019 13:16:46 GMThttps://repo.scoap3.org/record/32327urn:ISSN:1029-8479Springer/SISSA2019-04-12Search for the Production of a Long-Lived Neutral Particle Decaying within the ATLAS Hadronic Calorimeter in Association with a <math><mi>Z</mi></math> Boson from <math><mi>p</mi><mi>p</mi></math> Collisions at <math><mrow><msqrt><mrow><mi>s</mi></mrow></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>
https://repo.scoap3.org/record/32302
This Letter presents a search for the production of a long-lived neutral particle (Zd) decaying within the ATLAS hadronic calorimeter, in association with a standard model (SM) Z boson produced via an intermediate scalar boson, where Z→ℓ+ℓ− (ℓ=e, μ). The data used were collected by the ATLAS detector during 2015 and 2016 pp collisions with a center-of-mass energy of s=13 TeV at the Large Hadron Collider and correspond to an integrated luminosity of 36.1±0.8 fb−1. No significant excess of events is observed above the expected background. Limits on the production cross section of the scalar boson times its decay branching fraction into the long-lived neutral particle are derived as a function of the mass of the intermediate scalar boson, the mass of the long-lived neutral particle, and its cτ from a few centimeters to one hundred meters. In the case that the intermediate scalar boson is the SM Higgs boson, its decay branching fraction to a long-lived neutral particle with a cτ approximately between 0.1 and 7 m is excluded with a 95% confidence level up to 10% for mZd between 5 and 15 GeV.Aaboud, M.Mon, 15 Apr 2019 20:16:38 GMThttps://repo.scoap3.org/record/32302urn:ISSN:1079-7114APS2019-04-15Observation of the doubly Cabibbo-suppressed decay Ξ c + → pϕ
https://repo.scoap3.org/record/32281
The doubly Cabibbo-suppressed decay Ξ c + → pϕ with ϕ → K + K − is observed for the first time, with a statistical significance of more than fifteen standard deviations. The data sample used in this analysis corresponds to an integrated luminosity of 2 fb −1 recorded with the LHCb detector in pp collisions at a centre-of-mass energy of 8 TeV. The ratio of branching fractions between the decay Ξ c + → pϕ and the singly Cabibbo-suppressed decay Ξ c + → pK − π + is measured to be ℬ Ξ c + → p ϕ ℬ Ξ c + → p K − π + = 19.8 ± 0.7 ± 0.9 ± 0.2 × 10 − 3 , $$ \frac{\mathrm{\mathcal{B}}\left({\varXi}_c^{+}\to p\phi \right)}{\mathrm{\mathcal{B}}\left({\varXi}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(19.8\pm 0.7\pm 0.9\pm 0.2\right)\times {10}^{-3}, $$Aaij, R.Sat, 13 Apr 2019 16:01:19 GMThttps://repo.scoap3.org/record/32281urn:ISSN:1029-8479Springer/SISSA2019-04-10Measurement of the ratio of cross sections for inclusive isolated-photon production in pp collisions at s $$ \sqrt{s} $$ = 13 and 8 TeV with the ATLAS detector
https://repo.scoap3.org/record/32279
The ratio of the cross sections for inclusive isolated-photon production in pp collisions at centre-of-mass energies of 13 and 8 TeV is measured using the ATLAS detector at the LHC. The integrated luminosities of the 13 TeV and 8 TeV datasets are 3.2 fb −1 and 20.2 fb −1 , respectively. The ratio is measured as a function of the photon transverse energy in different regions of the photon pseudorapidity. The predictions from next-to-leading-order perturbative QCD calculations are compared with the measured ratio. The experimental systematic uncertainties as well as the uncertainties affecting the predictions are evaluated taking into account the correlations between the two centre-of-mass energies, resulting in a reduction of up to a factor of 2.5 (5) in the experimental (theoretical) systematic uncertainties. The predictions based on several parameterisations of the proton parton distribution functions agree with the data within the reduced experimental and theoretical uncertainties. In addition, this ratio to that of the fiducial cross sections for Z boson production at 13 and 8 TeV using the decay channels Z → e + e − and Z → μ + μ − is made and compared with the theoretical predictions. In this double ratio, a further reduction of the experimental uncertainty is obtained because the uncertainties arising from the luminosity measurement cancel out. The predictions describe the measurements of the double ratio within the theoretical and experimental uncertainties.Aaboud, M.Sat, 13 Apr 2019 16:01:02 GMThttps://repo.scoap3.org/record/32279urn:ISSN:1029-8479Springer/SISSA2019-04-12Search for invisible Higgs boson decays in vector boson fusion at s=13TeV with the ATLAS detector
https://repo.scoap3.org/record/32278
We report a search for Higgs bosons that are produced via vector boson fusion and subsequently decay into invisible particles. The experimental signature is an energetic jet pair with invariant mass of O(1)TeV and O(100)GeV missing transverse momentum. The analysis uses 36.1 fb −1 of pp collision data at s=13TeV recorded by the ATLAS detector at the LHC. In the signal region the 2252 observed events are consistent with the background estimation. Assuming a 125GeV scalar particle with Standard Model cross sections, the upper limit on the branching fraction of the Higgs boson decay into invisible particles is 0.37 at 95% confidence level where 0.28 was expected. This limit is interpreted in Higgs portal models to set bounds on the wimp –nucleon scattering cross section. We also consider invisible decays of additional scalar bosons with masses up to 3TeV for which the upper limits on the cross section times branching fraction are in the range of 0.3– 1.7pb .Aaboud, M.Sat, 13 Apr 2019 03:04:32 GMThttps://repo.scoap3.org/record/32278urn:ISSN:0370-2693Elsevier2019-04-24Search for baryon and lepton number violation in <math><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><msubsup><mrow><mi>Λ</mi></mrow><mrow><mi>c</mi></mrow><mrow><mo>+</mo></mrow></msubsup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>+</mo><mi>c</mi><mo>.</mo><mi>c</mi><mo>.</mo></mrow></math>
https://repo.scoap3.org/record/32270
Using 1.31×109 J/ψ events collected by the BESIII detector at the Beijing Electron Positron Collider, we search for the process J/ψ→Λc+e−+c.c. for the first time. In this process, both baryon and lepton number conservation is violated. No signal is found and the upper limit on the branching fraction B(J/ψ→Λc+e−+c.c.) is set to be 6.9×10−8 at the 90% confidence level.Ablikim, M.Sat, 13 Apr 2019 00:17:05 GMThttps://repo.scoap3.org/record/32270urn:ISSN:2470-0029APS2019-04-12Dalitz plot analysis of the D + → K − K + K + decay
https://repo.scoap3.org/record/32245
The resonant structure of the doubly Cabibbo-suppressed decay D + → K − K + K + is studied for the first time. The measurement is based on a sample of pp -collision data, collected at a centre-of-mass energy of 8 TeV with the LHCb detector and corresponding to an integrated luminosity of 2 fb −1 . The amplitude analysis of this decay is performed with the isobar model and a phenomenological model based on an effective chiral Lagrangian. In both models the S-wave component in the K − K + system is dominant, with a small contribution of the ϕ (1020) meson and a negligible contribution from tensor resonances. The K + K − scattering amplitudes for the considered combinations of spin (0,1) and isospin (0,1) of the two-body system are obtained from the Dalitz plot fit with the phenomenological decay amplitude.Aaij, R.Fri, 12 Apr 2019 14:27:01 GMThttps://repo.scoap3.org/record/32245urn:ISSN:1029-8479Springer/SISSA2019-04-08Precision measurements of the <math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><msubsup><mrow><mi>K</mi></mrow><mrow><mi>S</mi></mrow><mrow><mn>0</mn></mrow></msubsup><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mo>∓</mo></mrow></msup></mrow></math> Born cross sections at center-of-mass energies between 3.8 and 4.6 GeV
https://repo.scoap3.org/record/32236
Using data samples collected by the BESIII detector operating at the BEPCII storage ring, we measure the e+e−→KS0K±π∓ Born cross sections at center-of-mass energies between 3.8 and 4.6 GeV, corresponding to a luminosity of about 5.0 fb−1. The results are compatible with the BABAR measurements, but with the precision significantly improved. A simple 1/sn dependence for the continuum process can describe the measured cross sections, but a better fit is obtained by an additional resonance near 4.2 GeV, which could be an excited charmonium or a charmoniumlike state.Ablikim, M.Fri, 12 Apr 2019 00:16:50 GMThttps://repo.scoap3.org/record/32236urn:ISSN:2470-0029APS2019-04-11Cross-section measurements of the Higgs boson decaying into a pair of <math><mi>τ</mi></math>-leptons in proton-proton collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> with the ATLAS detector
https://repo.scoap3.org/record/32219
A measurement of production cross sections of the Higgs boson in proton-proton collisions is presented in the H→ττ decay channel. The analysis is performed using 36.1 fb−1 of data recorded by the ATLAS experiment at the Large Hadron Collider at a center-of-mass energy of s=13 TeV. All combinations of leptonic (τ→ℓvv¯ with ℓ=e,μ) and hadronic (τ→hadrons v) τ decays are considered. The H→ττ signal over the expected background from other Standard Model processes is established with an observed (expected) significance of 4.4 (4.1) standard deviations. Combined with results obtained using data taken at 7 and 8 TeV center-of-mass energies, the observed (expected) significance amounts to 6.4 (5.4) standard deviations and constitutes an observation of H→ττ decays. Using the data taken at s=13 TeV, the total cross section in the H→ττ decay channel is measured to be 3.77−0.59+0.60 (stat) −0.74+0.87 (syst) pb, for a Higgs boson of mass 125 GeV assuming the relative contributions of its production modes as predicted by the Standard Model. Total cross sections in the H→ττ decay channel are determined separately for vector-boson-fusion production and gluon-gluon-fusion production to be σH→ττVBF=0.28±0.09 (stat) −0.09+0.11 (syst) pb and σH→ττggF=3.1±1.0 (stat) −1.3+1.6 (syst) pb, respectively. Similarly, results of a fit are reported in the framework of simplified template cross sections. All measurements are in agreement with Standard Model expectations.Aaboud, M.Thu, 11 Apr 2019 16:16:42 GMThttps://repo.scoap3.org/record/32219urn:ISSN:2470-0029APS2019-04-10Measurements of inclusive and differential fiducial cross-sections of t t ¯ $$ t\overline{t} $$ production with additional heavy-flavour jets in proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
https://repo.scoap3.org/record/32205
This paper presents measurements of t t ¯ $$ t\overline{t} $$ production in association with additional b -jets in pp collisions at the LHC at a centre-of-mass energy of 13 TeV. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 36.1 fb −1 . Fiducial cross-section measurements are performed in the dilepton and lepton-plus-jets t t ¯ $$ t\overline{t} $$ decay channels. Results are presented at particle level in the form of inclusive cross-sections of t t ¯ $$ t\overline{t} $$ final states with three and four b -jets as well as differential cross-sections as a function of global event properties and properties of b -jet pairs. The measured inclusive fiducial cross-sections generally exceed the t t ¯ b b ¯ $$ t\overline{t}b\overline{b} $$ predictions from various next-to-leading-order matrix element calculations matched to a parton shower but are compatible within the total uncertainties. The experimental uncertainties are smaller than the uncertainties in the predictions. Comparisons of state-of-the-art theoretical predictions with the differential measurements are shown and good agreement with data is found for most of them.Aaboud, M.Thu, 11 Apr 2019 00:23:21 GMThttps://repo.scoap3.org/record/32205urn:ISSN:1029-8479Springer/SISSA2019-04-04Precision Measurement of the Branching Fractions of <math><mrow><msup><mrow><mi>η</mi></mrow><mrow><mo>′</mo></mrow></msup></mrow></math> Decays
https://repo.scoap3.org/record/32182
Based on a sample of (1310.6±7.0)×106J/ψ events collected with the BESIII detector, we present measurements of J/ψ and η′ absolute branching fractions using the process J/ψ→γη′. By analyzing events where the radiative photon converts into an e+e− pair, the branching fraction for J/ψ→γη′ is measured to be (5.27±0.03±0.05)×10−3. The absolute branching fractions of the five dominant decay channels of the η′ are then measured for the first time and are determined to be B(η′→γπ+π−)=(29.90±0.03±0.55)%, B(η′→ηπ+π−)=(41.24±0.08±1.24)%, B(η′→ηπ0π0)=(21.36±0.10±0.92)%, B(η′→γω)=(2.489±0.018±0.074)%, and B(η′→γγ)=(2.331±0.012±0.035)%, where the first uncertainties are statistical and the second systematic.Ablikim, M.Wed, 10 Apr 2019 00:17:31 GMThttps://repo.scoap3.org/record/32182urn:ISSN:1079-7114APS2019-04-09Search for the decay <math><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup><mo>→</mo><mi>γ</mi><msup><mi>e</mi><mo>+</mo></msup><msub><mi>ν</mi><mi>e</mi></msub></math>
https://repo.scoap3.org/record/32180
A search for the rare radiative leptonic decay Ds+→γe+νe is performed for the first time using electron-positron collision data corresponding to an integrated luminosity of 3.19 fb−1, collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. No evidence for the Ds+→γe+νe decay is seen, and an upper limit of B(Ds+→γe+νe)<1.3×10−4 is set on the partial branching fraction at a 90% confidence level for radiative photon energies Eγ*>0.01 GeV.Ablikim, M.Wed, 10 Apr 2019 00:16:27 GMThttps://repo.scoap3.org/record/32180urn:ISSN:2470-0029APS2019-04-09Measurement of the four-lepton invariant mass spectrum in 13 TeV proton-proton collisions with the ATLAS detector
https://repo.scoap3.org/record/32130
A measurement of the four-lepton invariant mass spectrum is made with the ATLAS detector, using an integrated luminosity of 36.1 fb −1 of proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV delivered by the Large Hadron Collider. The differential cross-section is measured for events containing two same-flavour opposite-sign lepton pairs. It exhibits a rich structure, with different mass regions dominated in the Standard Model by single Z boson production, Higgs boson production, and Z boson pair production, and non-negligible interference effects at high invariant masses. The measurement is compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. These calculations are used to interpret the data in terms of gg → ZZ → 4 ℓ and Z → 4 ℓ subprocesses, and to place constraints on a possible contribution from physics beyond the Standard Model.Aaboud, M.Tue, 09 Apr 2019 21:16:15 GMThttps://repo.scoap3.org/record/32130urn:ISSN:1029-8479Springer/SISSA2019-04-05First Measurement of Charm Production in its Fixed-Target Configuration at the LHC
https://repo.scoap3.org/record/32041
The first measurement of heavy-flavor production by the LHCb experiment in its fixed-target mode is presented. The production of J/ψ and D0 mesons is studied with beams of protons of different energies colliding with gaseous targets of helium and argon with nucleon-nucleon center-of-mass energies of sNN=86.6 and 110.4 GeV, respectively. The J/ψ and D0 production cross sections in pHe collisions in the rapidity range [2, 4.6] are found to be σJ/ψ=652±33(stat)±42(syst) nb/nucleon and σD0=80.8±2.4(stat)±6.3(syst) μb/nucleon, where the first uncertainty is statistical and the second is systematic. No evidence for a substantial intrinsic charm content of the nucleon is observed in the large Bjorken-x region.Aaij, R.Tue, 09 Apr 2019 15:06:37 GMThttps://repo.scoap3.org/record/32041urn:ISSN:1079-7114APS2019-04-02Measurement of the branching fraction of <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><mi>ω</mi><msup><mi>η</mi><mo>′</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> and search for <math><mi>J</mi><mo>/</mo><mi>ψ</mi><mo>→</mo><mi>ω</mi><mi>X</mi><mo>(</mo><mn>1835</mn><mo>)</mo></math>, <math><mi>X</mi><mo>(</mo><mn>1835</mn><mo>)</mo><mo>→</mo><msup><mi>η</mi><mo>′</mo></msup><msup><mi>π</mi><mo>+</mo></msup><msup><mi>π</mi><mo>−</mo></msup></math> decay
https://repo.scoap3.org/record/32008
Using a sample of 1.31×109 J/ψ events collected by the BESIII detector at BEPCII during 2009 and 2012, we study the J/ψ→ωη′π+π− hadronic process. For the first time, we measure the branching ratio B(J/ψ→ωη′π+π−)=(1.12±0.02±0.13)×10−3. We search for the X(1835) state in the η′π+π− invariant mass spectra. No evidence is found and we estimate the upper limit on the branching fraction at 90% confidence level to be B(J/ψ→ωX(1835),X(1835)→η′π+π−)<6.2×10−5.Ablikim, M.Tue, 09 Apr 2019 15:04:54 GMThttps://repo.scoap3.org/record/32008urn:ISSN:2470-0029APS2019-04-05Search for heavy long-lived multicharged particles in proton-proton collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> using the ATLAS detector
https://repo.scoap3.org/record/32002
A search for heavy long-lived multicharged particles is performed using the ATLAS detector at the LHC. Data with an integrated luminosity of 36.1 fb−1 collected in 2015 and 2016 from proton-proton collisions at s=13 TeV are examined. Particles producing anomalously high ionization, consistent with long-lived massive particles with electric charges from |q|=2e to |q|=7e, are searched for. No events are observed, and 95% confidence level cross-section upper limits are interpreted as lower mass limits for a Drell-Yan production model. Multicharged particles with masses between 50 and 980–1220 GeV (depending on their electric charge) are excluded.Aaboud, M.Tue, 09 Apr 2019 15:03:28 GMThttps://repo.scoap3.org/record/32002urn:ISSN:2470-0029APS2019-03-14Measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>510</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math>
https://repo.scoap3.org/record/31987
We report new STAR measurements of the single-spin asymmetries AL for W+ and W− bosons produced in polarized proton-proton collisions at s=510 GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250 pb−1. The results are combined with previous results obtained with 86 pb−1. A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the u¯ and d¯ quark helicity distributions for 0.05<x<0.25. In addition, we report new results for the double-spin asymmetries ALL for W±, as well as AL for Z/γ* production and subsequent decay into electron-positron pairs.Adam, J.Tue, 09 Apr 2019 15:03:10 GMThttps://repo.scoap3.org/record/31987urn:ISSN:2470-0029APS2019-03-14Properties of <math><mi>g</mi><mo>→</mo><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> at small opening angles in <math><mi>p</mi><mi>p</mi></math> collisions with the ATLAS detector at <math><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>
https://repo.scoap3.org/record/31986
The fragmentation of high-energy gluons at small opening angles is largely unconstrained by present measurements. Gluon splitting to b-quark pairs is a unique probe into the properties of gluon fragmentation because identified b-tagged jets provide a proxy for the quark daughters of the initial gluon. In this study, key differential distributions related to the g→bb¯ process are measured using 33 fb−1 of s=13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2016. Jets constructed from charged-particle tracks, clustered with the anti-kt jet algorithm with radius parameter R=0.2, are used to probe angular scales below the R=0.4 jet radius. The observables are unfolded to particle level in order to facilitate direct comparisons with predictions from present and future simulations. Multiple significant differences are observed between the data and parton shower Monte Carlo predictions, providing input to improve these predictions of the main source of background events in analyses involving boosted Higgs bosons decaying into b-quarks.Aaboud, M.Tue, 09 Apr 2019 15:02:10 GMThttps://repo.scoap3.org/record/31986urn:ISSN:2470-0029APS2019-03-14