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A bstract The Matrix Element Method (MEM) is a powerful method to extract information from measured events at collider experiments. Compared to multivariate techniques built on large sets of experimental data, the MEM does not rely on an examples-based learning phase but directly exploits our knowledge of the physics processes. This comes at a price, both in term of complexity and computing time since the required multi-dimensional integral of a rapidly varying function needs to be evaluated for every event and physics process considered. This can be mitigated by optimizing the integration, as is done in the MoMEMta package, but the computing time remains a concern, and often makes the use of the MEM in full-scale analysis unpractical or impossible. We investigate in this paper the use of a Deep Neural Network (DNN) built by regression of the MEM integral as an ansatz for analysis, especially in the search for new physics.

A measurement of the jet mass distribution in hadronic decays of Lorentz-boosted top quarks is presented. The measurement is performed in the lepton + jets channel of top quark pair production ( ) events, where the lepton is an electron or muon. The products of the hadronic top quark decay are reconstructed using a single large-radius jet with transverse momentum greater than 400 . The data were collected with the CMS detector at the LHC in proton-proton collisions and correspond to an integrated luminosity of 138 . The differential production cross section as a function of the jet mass is unfolded to the particle level and is used to extract the top quark mass. The jet mass scale is calibrated using the hadronic W boson decay within the large-radius jet. The uncertainties in the modelling of the final state radiation are reduced by studying angular correlations in the jet substructure. These developments lead to a significant increase in precision, and a top quark mass of .

The production of Z bosons associated with jets is measured in $$\\text {p}\\text {p}$$ pp collisions at $$\\sqrt{s}=13\\,\\text {Te}\\hspace{-.08em}\\text {V} $$ s = 13 Te V with data recorded with the CMS experiment at the LHC corresponding to an integrated luminosity of 36.3 $$\\,\\text {fb}^{-1}$$ fb - 1 . The multiplicity of jets with transverse momentum $$p_{\\textrm{T}} > 30\\,\\text {Ge}\\hspace{-.08em}\\text {V} $$ p T > 30 Ge V is measured for different regions of the Z boson’s $$p_{\\textrm{T}} (\\text {Z })$$ p T ( Z ) , from lower than 10 $$\\,\\text {Ge}\\hspace{-.08em}\\text {V}$$ Ge V to higher than 100 $$\\,\\text {Ge}\\hspace{-.08em}\\text {V}$$ Ge V . The azimuthal correlation $$\\varDelta \\phi $$ Δ ϕ between the Z boson and the leading jet, as well as the correlations between the two leading jets are measured in three regions of $$p_{\\textrm{T}} (\\text {Z })$$ p T ( Z ) . The measurements are compared with several predictions at leading and next-to-leading orders, interfaced with parton showers. Predictions based on transverse-momentum dependent parton distributions and corresponding parton showers give a good description of the measurement in the regions where multiple parton interactions and higher jet multiplicities are not important. The effects of multiple parton interactions are shown to be important to correctly describe the measured spectra in the low $$p_{\\textrm{T}} (\\text {Z })$$ p T ( Z ) regions.

A measurement of the inclusive jet production in proton-proton collisions at the LHC at$$ \\sqrt{s} $$s = 13 TeV is presented. The double-differential cross sections are measured as a function of the jet transverse momentum p T and the absolute jet rapidity |y| . The anti- k T clustering algorithm is used with distance parameter of 0.4 (0.7) in a phase space region with jet p T from 97 GeV up to 3.1 TeV and |y| < 2 . 0. Data collected with the CMS detector are used, corresponding to an integrated luminosity of 36.3 fb − 1 (33.5 fb − 1 ). The measurement is used in a comprehensive QCD analysis at next-to-next-to-leading order, which results in significant improvement in the accuracy of the parton distributions in the proton. Simultaneously, the value of the strong coupling constant at the Z boson mass is extracted as α S ( m Z ) = 0 . 1170 ± 0 . 0019. For the first time, these data are used in a standard model effective field theory analysis at next-to-leading order, where parton distributions and the QCD parameters are extracted simultaneously with imposed constraints on the Wilson coefficient c 1 of 4-quark contact interactions.

This paper outlines how objective measurements of both image quality, in terms of signal-to-noise ratio, and effective dose may be used as tools to find the optimum kVp range for a digital chest radiography system. Measurements were made with Thoravision, an amorphous selenium-based digital chest X-ray system. The entrance surface dose and the effective dose to an anthropomorphic chest phantom were determined demonstrating how effective dose is related to beam quality. The image quality was measured using detective quantum efficiency, threshold contrast and a radiologist preference trial involving 100 patients. The results show that, despite the fact that the entrance surface dose decreases as the kVp increases, the effective dose, a better measure of the risk, reaches a minimum value between 90 and 110 kVp; however, the image quality decreases as the kVp increases. In this study the optimum kVp for chest radiography, using a selenium-based radiography system, is in the range 90-110 kVp. This is contrary to the 120- to 150-kVp range that is commonly used. Also, this study shows how objective measurements can be used to optimise radiographic technique without prolonged patient trials.

The double differential cross sections of the Drell–Yan lepton pair ( $$\\ell ^+\\ell ^-$$ ℓ + ℓ - , dielectron or dimuon) production are measured as functions of the invariant mass $$m_{\\ell \\ell }$$ m ℓ ℓ , transverse momentum $$p_{\\textrm{T}} (\\ell \\ell )$$ p T ( ℓ ℓ ) , and $$\\varphi ^{*}_{\\eta }$$ φ η ∗ . The $$\\varphi ^{*}_{\\eta }$$ φ η ∗ observable, derived from angular measurements of the leptons and highly correlated with $$p_{\\textrm{T}} (\\ell \\ell )$$ p T ( ℓ ℓ ) , is used to probe the low- $$p_{\\textrm{T}} (\\ell \\ell )$$ p T ( ℓ ℓ ) region in a complementary way. Dilepton masses up to 1 $$\\,\\text {Te\\hspace{-.08em}V}$$ Te V are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections for various $$m_{\\ell \\ell }$$ m ℓ ℓ ranges to those in the Z mass peak interval are presented. The collected data correspond to an integrated luminosity of 36.3 $$\\,\\text {fb}^{-1}$$ fb - 1 of proton–proton collisions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13 $$\\,\\text {Te\\hspace{-.08em}V}$$ Te V . Measurements are compared with predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.

The first search for nonresonant production of Higgs boson pairs (HH) with one H decaying into four leptons and the other into a pair of b quarks is presented, using proton-proton collisions recorded at a center-of-mass energy of$$ \\sqrt{s} $$s = 13 TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 138 fb − 1 . A 95% confidence level upper limit of 32.4 is set on the signal strength modifier μ , defined as the ratio of the observed HH production rate in the$$ \\textrm{HH}\\to {\\textrm{ZZ}}^{\\ast}\\textrm{b}\\overline{\\textrm{b}}\\to 4\\ell \\textrm{b}\\overline{\\textrm{b}} $$HH → ZZ ∗ b b ¯ → 4 ℓ b b ¯ decay channel to the standard model (SM) expectation. Possible modifications of the H trilinear coupling λ HHH with respect to the SM value are investigated. The coupling modifier κ λ , defined as λ HHH divided by its SM prediction, is constrained to be within the observed (expected) range − 8 . 8 ( − 9 . 8) < κ λ < 13 . 4 (15 . 0) at 95% confidence level.

The production of prompt $$ {\\Lambda}_{\\textrm{c}}^{+} $$ Λ c + baryons is measured via the exclusive decay channel $$ {\\Lambda}_{\\textrm{c}}^{+}\\to p{\\textrm{K}}^{-}{\\pi}^{+} $$ Λ c + → p K − π + at a center-of-mass energy per nucleon pair of 5.02 TeV, using proton-proton (pp) and lead-lead (PbPb) collision data collected by the CMS experiment at the CERN LHC. The pp and PbPb data were obtained in 2017 and 2018 with integrated luminosities of 252 and 0.607 nb − 1 , respectively. The measurements are performed within the $$ {\\Lambda}_{\\textrm{c}}^{+} $$ Λ c + rapidity interval | y | < 1 with transverse momentum ( p T ) ranges of 3–30 and 6–40 GeV/ c for pp and PbPb collisions, respectively. Compared to the yields in pp collisions scaled by the expected number of nucleon-nucleon interactions, the observed yields of $$ {\\Lambda}_{\\textrm{c}}^{+} $$ Λ c + with p T > 10 GeV/ c are strongly suppressed in PbPb collisions. The level of suppression depends significantly on the collision centrality. The $$ {\\Lambda}_{\\textrm{c}}^{+} $$ Λ c + / D 0 production ratio is similar in PbPb and pp collisions at p T > 10 GeV/ c , suggesting that the coalescence process does not play a dominant role in prompt $$ {\\Lambda}_{\\textrm{c}}^{+} $$ Λ c + baryon production at higher p T .