A measurement is presented of the cross section for the electroweak production of a W boson in association with two jets in proton-proton collisions at a center-of-mass energy of 8 TeV. The data set was collected with the CMS detector and corresponds to an integrated luminosity of 19.3 inverse femtobarns. The measured fiducial cross section for W bosons decaying to electrons or muons and for pT(j1) > 60 GeV, pT(j2) > 50 GeV, |eta(j)| < 4.7, and m(jj) > 1000 GeV is 0.42 +/- 0.04 (stat) +/- 0.09 (syst) +/- 0.01 (lumi) pb. This result is consistent with the standard model leading-order prediction of 0.50 +/- 0.02 (scale) +/- 0.02 (PDF) pb obtained with MADGRAPH5_aMC@NLO 2.1 interfaced to PYTHIA 6.4. This is the first cross section measurement for this process.
A measurement of the W boson pair production cross section in proton-proton collisions at sqrt(s) = 8 TeV is presented. The data collected with the CMS detector at the LHC correspond to an integrated luminosity of 19.4 inverse femtobarns. The W+W- candidates are selected from events with two charged leptons, electrons or muons, and large missing transverse energy. The measured W+W- cross section is 60.1 +/- 0.9 (stat) +/- 3.2 (exp) +/- 3.1 (theo) +/- 1.6 (lum) pb = 60.1 +/- 4.8 pb, consistent with the standard model prediction. The W+W- cross sections are also measured in two different fiducial phase space regions. The normalized differential cross section is measured as a function of kinematic variables of the final-state charged leptons and compared with several perturbative QCD predictions. Limits on anomalous gauge couplings associated with dimension-six operators are also given in the framework of an effective field theory. The corresponding 95% confidence level intervals are -5.7 < c[WWW]/Lambda^2 < 5.9 TeV^{-2}, -11.4 < c[W]/Lambda^2 < 5.4 TeV^{-2}, -29.2 < c[B]/Lambda^2 < 23.9 TeV^{-2}, in the HISZ basis.
Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb$^{-1}$ recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-${k_t}$ algorithm with a radius parameter value of $R=0.4$. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to $|y|=3$. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within $|y|<3$, $y*$, up to $y*=3$. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.
Measurements are reported of the WZ and ZZ production cross sections in proton-proton collisions at $\sqrt{s}$ = 8 TeV in final states where one Z boson decays to b-tagged jets. The other gauge boson, either W or Z, is detected through its leptonic decay (either $W \to e\nu, \mu\nu$ or $Z \to e^+ e^-, \mu^+ \mu^-$, or $\nu\bar{\nu})$. The results are based on data corresponding to an integrated luminosity of 18.9 inverse-femtobarns collected with the CMS detector at the Large Hadron Collider. The measured cross sections, $\sigma(pp \to WZ)$ = 30.7 $\pm$ 9.3 (stat.) $\pm$ 7.1 (syst.) $\pm$ 4.1 (th.) $\pm$ 1.0 (lum.) pb and $\sigma(pp \to ZZ)$ = 6.5 $\pm$ 1.7 (stat.) $\pm$ 1.0 (syst.) $\pm$ 0.9 (th.) $\pm$ 0.2 (lum.) pb, are consistent with next-to-leading order quantum chromodynamics calculations.
The top-antitop quark (t t-bar) production cross section is measured in proton-proton collisions at sqrt(s) = 8 TeV with the CMS experiment at the LHC, using a data sample corresponding to an integrated luminosity of 5.3 inverse femtobarns. The measurement is performed by analysing events with a pair of electrons or muons, or one electron and one muon, and at least two jets, one of which is identified as originating from hadronisation of a bottom quark. The measured cross section is 239 +/- 2 (stat.) +/- 11 (syst.) +/- 6 (lum.) pb, for an assumed top-quark mass of 172.5 GeV, in agreement with the prediction of the standard model.
A measurement of the forward-backward asymmetry of pairs of oppositely charged leptons (dimuons and dielectrons) produced by the Drell-Yan process in proton-proton collisions is presented. The data sample corresponds to an integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC at a center-of-mass energy of 13 TeV. The asymmetry is measured as a function of lepton pair mass for masses larger than 170\GeV and compared with standard model predictions. An inclusive measurement across both channels and the full mass range yields an asymmetry of 0.599 $\pm$ 0.005 (stat) $\pm$ 0.007 (syst). As a test of lepton flavor universality, the difference between the dimuon and dielectron asymmetries is measured as well. No statistically significant deviations from standard model predictions are observed. The measurements are used to set limits on the presence of additional gauge bosons. For a Z' in the sequential standard model, a lower mass limit of 4.4 TeV is set at 95% confidence level.
The production of $\Upsilon$ mesons in Pb-Pb collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{\rm NN}}$ = 5 TeV is measured with the muon spectrometer of the ALICE detector at the LHC. The yields as well as the nuclear modification factors are determined in the forward rapidity region $2.5<y<4.0$, as a function of rapidity, transverse momentum and collision centrality. The results show that the production of the $\Upsilon$(1S) meson is suppressed by a factor of about three with respect to the production in proton-proton collisions. For the first time, a significant signal for the $\Upsilon$(2S) meson is observed at forward rapidity, indicating a suppression stronger by about a factor 2-3 with respect to the ground state. The measurements are compared with transport, hydrodynamic, comover and statistical hadronisation model calculations.
Measurements are presented of associated production of a W boson and a charm quark (W+c) in proton-proton collisions at a center-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 35.7 fb$^{-1}$ collected by the CMS experiment at the CERN LHC. The W bosons are identified by their decay into a muon and a neutrino. The charm quarks are tagged via the full reconstruction of D$^*$(2010)$^\pm$ mesons that decay via D$^*$(2010)$^\pm \to$ D$^0$ + $\pi^\pm \to$ K$^{\mp}$ + $\pi^\pm$ + $\pi^\pm$. A cross section is measured in the fiducial region defined by the muon transverse momentum $p_{T}^{\mu} >$ 26 GeV, muon pseudorapidity $|\eta^{\mu}| <$ 2.4, and charm quark transverse momentum $p_{T}^{c} >$ 5 GeV. The inclusive cross section for this kinematic range is $\sigma$(W+c) = 1026 $\pm$ 31 (stat) $\substack{+76\\-72}$ (syst) pb. The cross section is also measured differentially as a function of the pseudorapidity of the muon from the W boson decay. These measurements are compared with theoretical predictions and are used to probe the strange quark content of the proton.
This Letter presents direct searches for lepton flavour violation in Higgs boson decays, $H\rightarrow e\tau$ and $H\rightarrow\mu\tau$, performed with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of $36.1\,\mathrm{fb}^{-1}$. No significant excess is observed above the expected background from Standard Model processes. The observed (median expected) 95 % confidence-level upper limits on the lepton-flavour-violating branching ratios are $0.47\%$ ($0.34^{+0.13}_{-0.10}\,\%$) and $0.28\%$ ($0.37^{+0.14}_{-0.10}\,\%$) for $H\to e\tau$ and $H\to\mu\tau$, respectively.
The dependence of inclusive jet production in proton-proton collisions with a center-of-mass energy of 13 TeV on the distance parameter $R$ of the anti-$k_\mathrm{T}$ algorithm is studied using data corresponding to integrated luminosities up to 35.9 fb$^{-1}$ collected by the CMS experiment in 2016. The ratios of the inclusive cross sections as functions of transverse momentum $p_\mathrm{T}$ and rapidity $y$, for $R$ in the range 0.1 to 1.2 to those using $R = $ 0.4 are presented in the region 84 $\lt$ $p_\mathrm{T}$ $\lt$ 1588 GeV and $|y|$ $\lt$ 2.0. The results are compared to calculations at leading and next-to-leading order in the strong coupling constant using different parton shower models. The variation of the ratio of cross sections with $R$ is well described by calculations including a parton shower model, but not by a leading-order quantum chromodynamics calculation including nonperturbative effects. The agreement between the data and the theoretical predictions for the ratios of cross sections is significantly improved when next-to-leading order calculations with nonperturbative effects are used.
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