246 Search Results

Conserving crop wild relatives (CWR) in their natural environments, together with the complex communities of microorganisms that live with them, could lay the foundation to unlock novel mechanisms for crop resilience and new strategies for achieving food security.

Gasoline knock resistance is characterized by the Research and Motor Octane Number (RON and MON), which are rated on the CFR octane rating engine at naturally aspirated conditions. However, modern automotive downsized boosted spark ignition (SI) engines generally operate at higher cylinder pressures and lower temperatures relative to the RON and MON tests. Using the naturally aspirated RON and MON ratings, the octane index (OI) characterizes the knock resistance of gasolines under boosted operation by linearly extrapolating into boosted “beyond RON” conditions via RON, MON, and a linear regression K factor. Using OI solely based on naturally aspirated RON andmore » MON tests to extrapolate into boosted conditions can lead to significant errors in predicting boosted knock resistance between gasolines due to non-linear changes in autoignition and knocking characteristics with increasing pressure conditions. Here, a new “Supercharged Octane Number” (SON) method was developed on the CFR engine at increased intake pressures, which improved the correlation to boosted knock-limited automotive SI engine data over RON for several surrogate fuels and gasolines, including five “Co-Optima” RON 98 fuels and an E10 regular grade gasoline. Furthermore, the conventional OI was extended to a newly introduced Supercharged Octane Index (OI_S) based on SON and RON, which significantly improved the correlation to fuel knock resistance measurements from modern boosted SI engine knock-limited spark advance tests. This demonstrated the first proof of concept of a SON and OI_S to better characterize a fuel’s knock resistance in modern boosted SI engines.« less

The strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton–proton collisions at a center-of-mass energy of 13$$\,\text {Te}\hspace{-.08em}\text {V}$$. The analysis uses a data sample corresponding to a total integrated luminosity of 138$$\,\text {fb}^{-1}$$ collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged using the presence of a muon or a secondary vertex inside the jet. The $$\hbox {W}+\hbox {c}$$ production crossmore » section and the cross section ratio $$R_\textrm{c}^{\pm }= \sigma ({\hbox {W}}^{+}+\bar{\text {c}})/\sigma (\hbox {W}^{-}+{\textrm{c}})$$ are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay. The precision of the measurements is improved with respect to previous studies, reaching 1% in $$R_\textrm{c}^{\pm }= 0.950 \pm 0.005\,\text {(stat)} \pm 0.010 \,\text {(syst)} $$. The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.« less

We present an observation of photon-photon production of $$\tau$$ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 $$\mu$$b$$^{-1}$$ collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The $$\gamma\gamma$$$$\to$$$$\tau^+\tau^-$$ process is observed for $$\tau\tau$$ events with a muon and three charged hadrons in the final state. The measured fiducial cross section is $$\sigma(\gamma\gamma$$$$\to$$$$\tau^+\tau^-)$$ = 4.8 $$\pm$$ 0.6 (stat) $$\pm$$ 0.5 (syst) $$\mu$$b, in agreement with leading-order QED predictions. Using $$\sigma(\gamma\gamma$$$$\to$$$$\tau^+\tau^-)$$, we estimate a model-dependent value of the anomalous magnetic moment of the $$\tau$$ leptonmore » of $$a_\tau$$ = 0.001 $$^{+0.055}_{-0.089}$$.« less

The first search is presented for vector-like leptons (VLLs) in the context of the “4321 model”, an ultraviolet-complete model with the potential to explain existing B physics measurements that are in tension with standard model predictions. The analyzed data, corresponding to an integrated luminosity of 96.5 ${\text{fb}}^{-1}$ , were recorded in 2017 and 2018 with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}=13\text{TeV}$ . Final states with ≥3 b -tagged jets and two third-generation leptons (ττ, $\mathrm{\tau }{more »}_{}$ ν τ , or ${\mathrm{\nu }}_{\mathrm{\tau }}{\mathrm{\nu }}_{\mathrm{\tau }}$ ) are considered. Upper limits are derived on the VLL production cross section in the VLL mass range 500–1050 GeV. The maximum likelihood fit prefers the presence of signal at the level of 2.8 standard deviations, for a representative VLL mass point of 600 GeV. As a consequence, the observed upper limits are approximately double the expected limits.« less

The Precision Proton Spectrometer (PPS) of the CMS and TOTEM experiments collected 107.7 fb$$^{-1}$$ in proton-proton (pp) collisions at the LHC at 13 TeV (Run 2). This paper describes the key features of the PPS alignment and optics calibrations, the proton reconstruction procedure, as well as the detector efficiency and the performance of the PPS simulation. The reconstruction and simulation are validated using a sample of (semi)exclusive dilepton events. The performance of PPS has proven the feasibility of continuously operating a near-beam proton spectrometer at a high luminosity hadron collider.

A data sample containing top quark pairs ($$\mathrm{t\bar{t}}$$) produced in association with a Lorentz-boosted Z or Higgs boson is used to search for signs of new physics using effective field theory. The data correspond to an integrated luminosity of 138 fb$$^{-1}$$ of proton-proton collisions produced at a center-of-mass energy of 13 TeV at the LHC and collected by the CMS experiment. Selected events contain a single lepton and hadronic jets, including two identified with the decay of bottom quarks, plus an additional large-radius jet with high transverse momentum identified as a Z or Higgs boson decaying to a bottom quarkmore » pair. Machine learning techniques are employed to discriminate between $$\mathrm{t\bar{t}}$$Z or $$\mathrm{t\bar{t}}$$H events and events from background processes, which are dominated by $$\mathrm{t\bar{t}}$$ + jets production. No indications of new physics are observed. The signal strengths of boosted $$\mathrm{t\bar{t}}$$Z and $$\mathrm{t\bar{t}}$$H production are measured, and upper limits are placed on the $$\mathrm{t\bar{t}}$$Z and $$\mathrm{t\bar{t}}$$H differential cross sections as functions of the Z or Higgs boson transverse momentum. The effects of new physics are probed using a framework in which the standard model is considered to be the low-energy effective field theory of a higher energy scale theory. Eight possible dimension-six operators are added to the standard model Lagrangian and their corresponding coefficients are constrained via fits to the data.« less

The production of a top quark-antiquark pair in association with a W boson ($$ \textrm{t}\overline{\textrm{t}}\textrm{W} $$) is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data was recorded by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb$$^{−1}$$. Events with two or three leptons (electrons and muons) and additional jets are selected. In events with two leptons, a multiclass neural network is used to distinguish between the signal and background processes. Events with three leptons are categorized based on the number of jets and of jets originating frommore » b quark hadronization, and the lepton charges. The inclusive $$ \textrm{t}\overline{\textrm{t}}\textrm{W} $$ production cross section in the full phase space is measured to be 868 ± 40(stat) ± 51(syst) fb. The $$ \textrm{t}\overline{\textrm{t}}\textrm{W} ^{+}$$ and $$ \textrm{t}\overline{\textrm{t}}\textrm{W} ^{−}$$ cross sections are also measured as 553 ± 30(stat) ± 30(syst) and 343 ± 26(stat) ± 25(syst) fb, respectively, and the corresponding ratio of the two cross sections is found to be $$ 1.61\pm 0.15{\left(\textrm{stat}\right)}_{-0.05}^{+0.07}\left(\textrm{syst}\right) $$. The measured cross sections are larger than but consistent with the standard model predictions within two standard deviations, and represent the most precise measurement of these cross sections to date.[graphic not available: see fulltext]« less

Production cross sections of the standard model Higgs boson decaying to a pair of W bosons are measured in proton-proton collisions at a center-of-mass energy of 13$$\,\text {Te\hspace{-.08em}V}$$. The analysis targets Higgs bosons produced via gluon fusion, vector boson fusion, and in association with a W or Z boson. Candidate events are required to have at least two charged leptons and moderate missing transverse momentum, targeting events with at least one leptonically decaying W boson originating from the Higgs boson. Results are presented in the form of inclusive and differential cross sections in the simplified template cross section framework, asmore » well as couplings of the Higgs boson to vector bosons and fermions. The data set collected by the CMS detector during 2016–2018 is used, corresponding to an integrated luminosity of 138$$\,\text {fb}^{-1}$$. The signal strength modifier $$\mu $$, defined as the ratio of the observed production rate in a given decay channel to the standard model expectation, is measured to be $$\mu = 0.95^{+0.10}_{-0.09}$$. All results are found to be compatible with the standard model within the uncertainties.« less

A search for nonresonant Higgs boson ($$H$$) pair production via gluon and vector boson ($$V$$) fusion is performed in the four-bottom-quark final state, using proton-proton collision data at 13 TeV corresponding to 138 fb$$^{−1}$$ collected by the CMS experiment at the LHC. The analysis targets Lorentz-boosted $$H$$ pairs identified using a graph neural network. It constrains the strengths relative to the standard model of the $$H$$ self-coupling and the quartic VVHH couplings, $$κ_{2V}$$, excluding $$κ_{2V} = 0$$ for the first time, with a significance of 6.3 standard deviations when other H couplings are fixed to their standard model values.