We present results of a signature-based search for new physics using a dijet plus missing transverse energy (E(T)) data sample collected in 2 fb⁻¹ of pp collisions at √s=1.96 TeV with the CDF II ...detector at the Fermilab Tevatron. We observe no significant event excess with respect to the standard model prediction and extract a 95% C.L. upper limit on the cross section times acceptance for a potential contribution from a nonstandard model process. The search is made by using novel, data-driven techniques for estimating backgrounds that are applicable to first searches at the LHC.
Simultaneous measurements of the t$\bar{t}$, W+W–, and Z/γ*→ττ production cross-sections using an integrated luminosity of 4.6 fb–1 of pp collisions at √s=7 TeV collected by the ATLAS detector at the ...LHC are presented. Events are selected with two high transverse momentum leptons consisting of an oppositely charged electron and muon pair. The three processes are separated using the distributions of the missing transverse momentum of events with zero and greater than zero jet multiplicities. Measurements of the fiducial cross-section are presented along with results that quantify for the first time the underlying correlations in the predicted and measured cross-sections due to proton parton distribution functions. The results indicate that the correlated next-to-leading-order predictions for t$\bar{t}$ and Z/γ*→ττ underestimate the data, while those at next-to-next-to-leading-order generally describe the data well. The full cross-sections are measured to be σ(t$\bar{t}$)=181.2 ± 2.8$+9.7\atop{–9.5}$ ± 3.3 ± 3.3 pb, σ(W+W–) = 53.3 ± 2.7$+7.3\atop{–8.0}$ ± 1.0 ± 0.5 pb, and σ(Z/γ*→ττ) = 1174 ± 24$+72\atop{–87}$ ± 21 ± 9 pb, where the cited uncertainties are due to statistics, systematic effects, luminosity and the LHC beam energy measurement, respectively. The W+W– measurement includes the small contribution from Higgs boson decays, H → W+W–.
Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum with the ATLAS experiment at the LHC are reported. Data were collected in proton-proton ...collisions at a center-of-mass energy of 8 TeV and correspond to an integrated luminosity of 20.3 fb-1. The observed data are well described by the expected Standard Model backgrounds. The expected (observed) upper limit on the fiducial cross section for the production of events with a photon and large missing transverse momentum is 6.1 (5.3) fb at 95% confidence level. The exclusion limits are presented on models of new phenomena with large extra spatial dimensions, super-symmetric quarks, and direct pair production of dark-matter candidates.
This article presents measurements of the t-channel single top-quark (t) and top-antiquark ($ \bar{t} $) total production cross sections σ(tq) and σ($ \bar{t}q $), their ratio Rt=σ(tq)/σ($ \bar{t}q ...$), and a measurement of the inclusive production cross section σ(tq+$ \bar{t}q $) in proton-proton collisions at $ \sqrt{s} $=7 TeV at the LHC. Differential cross sections for the tq and $ \bar{t}q $ processes are measured as a function of the transverse momentum and the absolute value of the rapidity of t and $ \bar{t} $, respectively. The analyzed data set was recorded with the ATLAS detector and corresponds to an integrated luminosity of 4.59 fb-1. Selected events contain one charged lepton, large missing transverse momentum, and two or three jets. The cross sections are measured by performing a binned maximum-likelihood fit to the output distributions of neural networks. The resulting measurements are σ(tq)=46±1(stat)±6(syst) pb, σ($ \bar{t}q $)=23±1(stat)±3(syst) pb, Rt=2.04±0.13(stat)±0.12(syst), and σ(tq+$ \bar{t}q $)=68±2(stat)±8(syst) pb, consistent with the Standard Model expectation. The uncertainty on the measured cross sections is dominated by systematic uncertainties, while the uncertainty on Rt is mainly statistical. Using the ratio of σ(tq+$ \bar{t}q $) to its theoretical prediction, and assuming that the top-quark-related CKM matrix elements obey the relation |Vtb| |Vts|,|Vtd|, we determine |Vtb| = 1.02±0.07.
