The electroweak production of $Z(\nu\bar{\nu})\gamma$ in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb$^{-1}$ collected by the ATLAS detector during the 2015-2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial $Z(\nu\bar{\nu})\gamma jj$ cross section for electroweak production is measured to be 0.77$^{+0.34}_{-0.30}$ fb and is consistent with the Standard Model prediction. Evidence of electroweak $Z(\nu\bar{\nu})\gamma jj$ production is found with an observed significance of 3.2$\sigma$ for the background-only hypothesis, compared with an expected significance of 3.7$\sigma$. The combination of this result with the previously published ATLAS observation of electroweak $Z(\nu\bar{\nu})\gamma jj$ production yields an observed (expected) signal significance of 6.3$\sigma$ (6.6$\sigma$). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
These graphs indicate the effect of the main theory uncertainties, which are associated with the renormalisation and factorisation scales (dashed cyan), underlying event and parton showering (UE+PS) or generator choice (dash-dotted red), alternative PDF sets (dotted orange), combined NNPDF set variation and $\alpha_s$ uncertainty (loosely dash-dotted green). These are shown in the signal region for the $Z(\nu\bar{\nu})\gamma jj$ EWK process. The BDT classifier response was remapped into equal width bins for better representation. The uncertainty band corresponds to the uncertainty due to the limited number of MC events.
These graphs indicate the effect of the main theory uncertainties, which are associated with the renormalisation and factorisation scales (dashed cyan), underlying event and parton showering (UE+PS) or generator choice (dash-dotted red), alternative PDF sets (dotted orange), combined NNPDF set variation and $\alpha_{s}$ uncertainty (loosely dash-dotted green). These are shown in the signal region for the $Z(\nu\bar{\nu})\gamma jj$ QCD process. The BDT classifier response was remapped into equal width bins for better representation. The uncertainty band corresponds to the uncertainty due to the limited number of MC events.
The $m_{jj}$ distributions for the CRs and the BDT classifier response distribution for the SR after the fit in all regions. The dashed line shows the total background distribution before the fit. The vertical error bars on the data points correspond to the data's statistical uncertainty. Overflows are included in the last bin. The uncertainty band corresponds to the combination of the MC statistical uncertainty and systematic uncertainties obtained in the fit.
In a special run of the LHC with $\beta^\star = 2.5~$km, proton-proton elastic-scattering events were recorded at $\sqrt{s} = 13~$TeV with an integrated luminosity of $340~\mu \textrm{b}^{-1}$ using the ALFA subdetector of ATLAS in 2016. The elastic cross section was measured differentially in the Mandelstam $t$ variable in the range from $-t = 2.5 \cdot 10^{-4}~$GeV$^{2}$ to $-t = 0.46~$GeV$^{2}$ using 6.9 million elastic-scattering candidates. This paper presents measurements of the total cross section $\sigma_{\textrm{tot}}$, parameters of the nuclear slope, and the $\rho$-parameter defined as the ratio of the real part to the imaginary part of the elastic-scattering amplitude in the limit $t \rightarrow 0$. These parameters are determined from a fit to the differential elastic cross section using the optical theorem and different parameterizations of the $t$-dependence. The results for $\sigma_{\textrm{tot}}$ and $\rho$ are \begin{equation*} \sigma_{\textrm{tot}}(pp\rightarrow X) = \mbox{104.7} \pm 1.1 \; \mbox{mb} , \; \; \; \rho = \mbox{0.098} \pm 0.011 . \end{equation*} The uncertainty in $\sigma_{\textrm{tot}}$ is dominated by the luminosity measurement, and in $\rho$ by imperfect knowledge of the detector alignment and by modelling of the nuclear amplitude.
The measured total cross section. The systematic uncertainty includes experimental and theoretical uncerainties.
The rho-parameter, i.e. the ratio of the real to imaginary part of the elastic scattering amplitude extrapolated to t=0. The systematic uncertainty includes experimental and theoretical uncerainties.
The nuclear slope parameter B from a fit of the form exp(-Bt-Ct^2-Dt^3). The systematic uncertainty includes experimental and theoretical uncerainties.
Measurements of Higgs boson production cross-sections are carried out in the diphoton decay channel using 139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 13$ TeV collected by the ATLAS experiment at the LHC. The analysis is based on the definition of 101 distinct signal regions using machine-learning techniques. The inclusive Higgs boson signal strength in the diphoton channel is measured to be $1.04^{+0.10}_{-0.09}$. Cross-sections for gluon-gluon fusion, vector-boson fusion, associated production with a $W$ or $Z$ boson, and top associated production processes are reported. An upper limit of 10 times the Standard Model prediction is set for the associated production process of a Higgs boson with a single top quark, which has a unique sensitivity to the sign of the top quark Yukawa coupling. Higgs boson production is further characterized through measurements of Simplified Template Cross-Sections (STXS). In total, cross-sections of 28 STXS regions are measured. The measured STXS cross-sections are compatible with their Standard Model predictions, with a $p$-value of $93\%$. The measurements are also used to set constraints on Higgs boson coupling strengths, as well as on new interactions beyond the Standard Model in an effective field theory approach. No significant deviations from the Standard Model predictions are observed in these measurements, which provide significant sensitivity improvements compared to the previous ATLAS results.
Cross-sections times H->yy branching ratio for ggF +bbH, VBF, VH, ttH, and tH production, normalized to their SM predictions. The values are obtained from a simultaneous fit to all categories. The theory uncertainties in the predictions include uncertainties due to missing higher-order terms in the perturbative QCD calculations and choices of parton distribution functions and value of alpha_s, as well as the H->yy branching ratio uncertainty.
Correlation matrix for the measurement of production cross-sections of the Higgs boson times the H->yy branching ratio.
Best-fit values and uncertainties for STXS parameters in each of the 28 regions considered, normalized to their SM predictions. The values for the gg->H process also include the contributions from bbH production.
A precision measurement of the $Z$ boson production cross-section at $\sqrt{s} = 13$ TeV in the forward region is presented, using $pp$ collision data collected by the LHCb detector, corresponding to an integrated luminosity of 5.1 fb$^{-1}$. The production cross-section is measured using $Z\rightarrow\mu^+\mu^-$ events within the fiducial region defined as pseudorapidity $2.0<\eta<4.5$ and transverse momentum $p_{T}>20$ GeV/$c$ for both muons and dimuon invariant mass $60<M_{\mu\mu}<120$ GeV/$c^2$. The integrated cross-section is determined to be $\sigma (Z \rightarrow \mu^+ \mu^-)$ = 196.4 $\pm$ 0.2 $\pm$ 1.6 $\pm$ 3.9~pb, where the first uncertainty is statistical, the second is systematic, and the third is due to the luminosity determination. The measured results are in agreement with theoretical predictions within uncertainties.
Relative uncertainty for the integrated $Z -> \mu^{+} \mu^{-}$ cross-section measurement. The total uncertainty is the quadratic sum of uncertainties from statistical, systematic and luminosity contributions.
Final state radiation correction used in the $y^{Z}$ cross-section measurement. The first uncertainty is statistical and the second is systematic.
Final state radiation correction used in the $p_{T}^{Z}$ cross-section measurement. The first uncertainty is statistical and the second is systematic.
A search for a heavy resonance decaying into a top quark and a W boson in proton-proton collisions at $\sqrt{s} =$ 13 TeV is presented. The data analyzed were recorded with the CMS detector at the LHC and correspond to an integrated luminosity of 138 fb$^{-1}$. The top quark is reconstructed as a single jet and the W boson, from its decay into an electron or muon and the corresponding neutrino. A top quark tagging technique based on jet clustering with a variable distance parameter and simultaneous jet grooming is used to identify jets from the collimated top quark decay. The results are interpreted in the context of two benchmark models, where the heavy resonance is either an excited bottom quark b$^*$ or a vector-like quark B. A statistical combination with an earlier search by the CMS Collaboration in the all-hadronic final state is performed to place upper cross section limits on these two models. The new analysis extends the lower range of resonance mass probed from 1.4 down to 0.7 TeV. For left-handed, right-handed, and vector-like couplings, b$^*$ masses up to 3.0, 3.0, and 3.2 TeV are excluded at 95% confidence level, respectively. The observed upper limits represent the most stringent constraints on the b$^*$ model to date.
Distributions of MtW in the 1b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for a LH b* with mb∗ = 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty on the predicted background displayed as the gray band.
Distributions of MtW in the 2b category. The data are shown by filled markers, where the horizontal bars indicate the bin widths. The individual background contributions are given by filled histograms. The expected signal for a LH b* with mb∗ = 2.4 TeV is shown by a dashed line. The shaded region is the uncertainty in the total background estimate. The lower panel shows the ratio of data to the background estimate, with the total uncertainty on the predicted background displayed as the gray band.
Upper limits on the production cross section times branching fraction of the b* LH hypothesis at a 95% CL. Dashed colored lines show the expected limits from the l+jets and all-hadronic channels, where the latter start at resonance masses of 1.4 TeV. The observed and expected limits from the combination are shown as solid and dashed black lines, respectively. The green and yellow bands show the 68 and 95% confidence intervals on the combined expected limits.
The cross section of the process $e^+ e^-\to\pi^+\pi^-$ has been measured in the Spherical Neutral Detector (SND) experiment at the VEPP-2000 $e^+e^-$ collider VEPP-2000 in the energy region $525 <\sqrt[]{s} <883$ MeV. The measurement is based on data with an integrated luminosity of about 4.6 pb$^{-1}$. The systematic uncertainty of the cross section determination is 0.8 % at $\sqrt{s}>0.600$ GeV. The $\rho$ meson parameters are obtained as $m_\rho = 775.3\pm 0.5\pm 0.6$ MeV, $\Gamma_\rho = 145.6\pm 0.6\pm 0.8$ MeV, $B_{\rho\to e^+ e^-}\times B_{\rho\to\pi^+\pi^-} = (4.89\pm 0.02\pm 0.04)\times 10^{-5}$, and the parameters of the $e^+ e^-\to\omega\to\pi^+\pi^-$ process, suppressed by $G$-parity, as $B_{\omega\to e^+ e^-}\times B_{\omega\to\pi^+\pi^-}= (1.32\pm 0.06\pm 0.02)\times 10^{-6} $ and $\phi_{\rho\omega} = 110.7\pm 1.5\pm1.0$ degrees.
The Born cross section of the process e+e- -> pi+pi- taking into account the radiative corrections due to the initial and final state radiation.
Measured value of the pion form factor
The bare e+e- -> pi+pi- undressed cross without vacuum polarization, but with the final state radiative correction.
The process $e^+e^-\to\omega\eta\pi^0$ is studied in the energy range $1.45-2.00$ GeV using data with an integrated luminosity of 33 pb$^{-1}$ accumulated by the SND detector at the $e^+e^-$ collider VEPP-2000. The $e^+e^-\to\omega\eta\pi^0$ cross section is measured for the first time. The cross section has a threshold near 1.75 GeV. Its value is about 2 nb in the energy range $1.8-2.0$ GeV. The dominant intermediate state for the process $e^+e^- \to \omega\eta\pi^0$ is found to be $\omega a_0(980)$.
The energy interval, integrated luminosity ($L$), number of selected events ($N$), estimated number of background events ($N_{bkg}$), detection efficiency for $e^+e^-\to\omega\eta\pi^0\to 7\gamma$ events ($\epsilon$), radiative correction ($\delta+1$), and $e^+e^-\to\omega\eta\pi^0$ Born cross section ($\sigma$). The shown cross-section errors are statistical. The systematic error is 4.2%. The 90% confidence level upper limits are listed for the first two energy intervals.
The process $e^+e^- \to \pi^0\gamma$ has been studied in the experiment with the SND detector at the VEPP-2M $e^+e^-$ collider. The $e^+e^- \to \pi^0\gamma$ cross section has been measured in the center-of-mass energy range from 0.60 to 1.38 GeV. The cross section is well described by the vector meson dominance model. From the fit to the cross section data we have determined the branching fractions $B(\rho\to\pi^0\gamma)=(4.20\pm0.52)\times10^{-4}$, $B(\omega\to\pi^0\gamma)=(8.88\pm0.18)\%$, $B(\phi\to\pi^0\gamma)=(1.367\pm0.072)\times10^{-3}$, and the relative phase between the $\rho$ and $\omega$ amplitudes $\varphi_{\rho}=(-12.7\pm4.5)^\circ$. Our data on the process $e^+e^- \to \pi^0\gamma$ are the most accurate to date.
The c.m.energy ($E$), integrated luminosity ($L$), detection efficiency ($\varepsilon$), number of selected signal events ($N_{\rm sig}$), radiative-correction factor ($1+\delta$), measured Born cross section ($\sigma$). For the cross section the first error is statistical, the second is systematic.
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The rr- + p- n + rr0 charge-exchange scattering and the rr- + p- n + 1J ( 1J- 2y) reaction were investigated in 1.55-4.5 BeVIc region in a 17-liter propane-xenon bubble chamber. The total cross sections of both reactions were measured in this region. The angular distributions of the rr0 mesons in the charge-exchange reaction were obtained. The backward exchange-scattering cross sections du( rr- + p- n + rr 0 )ldQ were estimated.
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