Future Colliders

Abstract:

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, $\eta$, corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of $\eta$ from observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range $\eta = (5.7-6.7)\times 10^{-10}$ at 95% CL (corresponding to a cosmological baryon density $\Omega_B h^2 = 0.021 - 0.025$). The D and He-4 abundances, when combined with the CMB determination of $\eta$, provide the bound $N_\nu=3.28 \pm 0.28$ on the effective number of neutrino species. Other constraints on new physics are discussed briefly.

Abstract:

The inclusive cross section for top-quark pair production measured by the CMS experiment in proton-proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, m t pole , or the strong coupling constant, α S . With the parton distribution function set NNPDF2.3, a pole mass of 176. 7 +3.8 -3.4 GeV is obtained when constraining α S at the scale of the Z boson mass, m Z , to the current world average. Alternatively, by constraining m t pole to the latest average from direct mass measurements, a value of α S (m Z ) = 0. 1151 +0.0033 -0.0032 is extracted. This is the first determination of α S using events from top-quark production. © 2013 The Authors. Published by Elsevier B.V.

Abstract:

A search for the standard model Higgs boson decaying to a W-boson pair at the LHC is reported. The event sample corresponds to an integrated luminosity of 4.9 fb-1 and 19.4 fb-1 collected with the CMS detector in pp collisions at √ s = 7 and 8 TeV, respectively. The Higgs boson candidates are selected in events with two or three charged leptons. An excess of events above background is observed, consistent with the expectation from the standard model Higgs boson with a mass of around 125 GeV. The probability to observe an excess equal or larger than the one seen, under the background-only hypothesis, corresponds to a significance of 4.3 standard deviations for m H = 125.6 GeV. The observed signal cross section times the branching fraction to WW for m H = 125.6 GeV is 0.72-0.18+0.20 times the standard model expectation. The spin-parity J P = 0+ hypothesis is favored against a narrow resonance with J P = 2+ or J P = 0- that decays to a W-boson pair. This result provides strong evidence for a Higgs-like boson decaying to a W-boson pair. [Figure not available: see fulltext.] © 2014 Cern for the benefit of the CMS collaboration.

Abstract:

Measurements are presented of the associated production of a W boson and a charm-quark jet (W + c) in pp collisions at a center-of-mass energy of 7 TeV. The analysis is conducted with a data sample corresponding to a total integrated luminosity of 5 fb−1, collected by the CMS detector at the LHC. W boson candidates are identified by their decay into a charged lepton (muon or electron) and a neutrino. The W + c measurements are performed for charm-quark jets in the kinematic region p jet T > 25 GeV, |ηjet| < 2.5, for two different thresholds for the transverse momentum of the lepton from the W-boson decay, and in the pseudorapidity range |ηℓ| < 2.1. Hadronic and inclusive semileptonic decays of charm hadrons are used to measure the following total cross sections: σ(pp → W + c + X) × B(W → ℓν) = 107.7 ± 3.3 (stat.) ± 6.9 (syst.) pb (p ℓ T > 25 GeV) and σ(pp → W + c + X)×B(W → ℓν) = 84.1 ± 2.0 (stat.) ± 4.9 (syst.) pb (p ℓ T > 35 GeV), and the cross section ratios σ(pp → W+ + ¯ c + X)/σ(pp → W− + c + X) = 0.954 ± 0.025 (stat.) ± 0.004 (syst.) (p ℓ T > 25 GeV) and σ(pp → W+ + ¯ c + X)/σ(pp → W− + c + X) = 0.938 ± 0.019 (stat.) ± 0.006 (syst.) (p ℓ T > 35 GeV). Cross sections and cross section ratios are also measured differentially with respect to the absolute value of the pseudorapidity of the lepton from the W-boson decay. These are the first measurements from the LHC directly sensitive to the strange quark and antiquark content of the proton. Results are compared with theoretical predictions and are consistent with the predictions based on global fits of parton distribution functions.