The production of single top quarks and top antiquarks via the $t$-channel exchange of a virtual $W$ boson is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV at the LHC using $140\,\mathrm{fb^{-1}}$ of ATLAS data. The total cross-sections are determined to be $\sigma(tq)=137^{+8}_{-8}\,\mathrm{pb}$ and $\sigma(\bar{t}q)=84^{+6}_{-5}\,\mathrm{pb}$ for top-quark and top-antiquark production, respectively. The combined cross-section is found to be $\sigma(tq+\bar{t}q)=221^{+13}_{-13}\,\mathrm{pb}$ and the cross-section ratio is $R_{t}=\sigma(tq)/\sigma(\bar{t}q)=1.636^{+0.036}_{-0.034}$. The predictions at next-to-next-to-leading-order in quantum chromodynamics are in good agreement with these measurements. The predicted value of $R_{t}$ using different sets of parton distribution functions is compared with the measured value, demonstrating the potential to further constrain the functions when using this result in global fits. The measured cross-sections are interpreted in an effective field theory approach, setting limits at the 95% confidence level on the strength of a four-quark operator and an operator coupling the third quark generation to the Higgs boson doublet: $-0.37 < C_{Qq}^{3,1}/\Lambda^2 < 0.06$ and $-0.87 < C_{\phi Q}^{3}/\Lambda^2 < 1.42$. The constraint $|V_{tb}|>0.95$ at the 95% confidence level is derived from the measured value of $\sigma(tq+\bar{t}q)$. In a more general approach, pairs of CKM matrix elements involving top quarks are simultaneously constrained, leading to confidence contours in the corresponding two-dimensional parameter spaces.
The 17 variables used for the training of the NN ordered by their discriminating power. The jet that is not \(b\)-tagged is referred to as the untagged jet. The charged lepton is denoted \(\ell\). The sphericity tensor \(S^{\alpha\beta}\) used to define the sphericity \(S\) is formed with the three-momenta \(\vec{p}_i\) of the reconstructed objects, namely the jets, the charged lepton and the reconstructed neutrino. The tensor is given by \(S^{\alpha\beta}=\frac{\sum_i p_i^\alpha p_i^\beta}{\sum_i |\vec{p}_i|^2}\) where \(\alpha\) and \(\beta\) correspond to the spatial components $x$, $y$ and $z$.
The impact of different groups of systematic uncertainties on the \(\sigma(tq)\) , \(\sigma(\bar t q)\), \(\sigma(tq + \bar t q)\) and \(R_t\), given in %.
The impact of the eight most important systematic uncertainties on the \(\sigma(tq)\) , \(\sigma(\bar t q)\) and \(\sigma(tq + \bar t q)\), given in %. The sequence of the uncertainties is given by the impact on \(\sigma(tq + \bar t q)\)
A measurement of the top-quark mass ($m_t$) in the $t\bar{t}\rightarrow~\textrm{lepton}+\textrm{jets}$ channel is presented, with an experimental technique which exploits semileptonic decays of $b$-hadrons produced in the top-quark decay chain. The distribution of the invariant mass $m_{\ell\mu}$ of the lepton, $\ell$ (with $\ell=e,\mu$), from the $W$-boson decay and the muon, $\mu$, originating from the $b$-hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract $m_t$. The measurement is based on data corresponding to an integrated luminosity of 36.1 fb$^{-1}$ of $\sqrt{s} = 13~\textrm{TeV}$$pp$ collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is $m_{t} = 174.41\pm0.39~(\textrm{stat.})\pm0.66~(\textrm{syst.})\pm0.25~(\textrm{recoil})~\textrm{GeV}$, where the third uncertainty arises from changing the PYTHIA8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.
Top mass measurement result.
List of all the individual sources of systematic uncertainty considered in the analysis. The individual sources, each corresponding to an independent nuisance parameter in the fit, are grouped into categories, as indicated in the first column. The second column shows the impact of each of the individual sources on the measurement, obtained as the shift on the top mass induced by a positive shift of the each of the nuisance parameters by its post-fit uncertainty. Sources for which no impact is indicated are neglected in the fit procedure as their impact on the total prediction is negligible in any of the bins. The last column shows the statistical uncertainty in each of the reported numbers as estimated with the bootstrap method.
Ranking, from top to bottom, of the main systematic uncertainties (excluding recoil) showing the pulls and the impact of the systematic uncertainties on the top mass, from the combined opposite sign (OS) and same sign (SS) binned-template profile likelihood fit to data. The OS or SS refers to the charge signs of the primary lepton and the soft muon. The gamma parameters are NPs used to describe the effect of the limited statistics of the sample.
Two samples of exclusive semileptonic decays, 579 B 0 → D ∗+ ℓ − ν ℓ events and 261 B 0 → D + ℓ − ν ℓ events, are selected from approximately 3.9 million hadronic Z decays collected by the ALEPH detector at LEP. From the reconstructed differential decay rate of each sample, the product of the hadronic form factor F (ω) at zero recoil of the D (∗)+ meson and the CKM matrix element | V cb | are measured to be F D ∗+ (1)|V cb | = (31.9 ± 1.8 stat ± 1.9 syst ) × 10 −3 , F D + (1)| V cb | = (27.8 ± 6.8 stat ± 6.5 syst ) × 10 −3 . The ratio of the form factors F D + (1) and F D ∗+ (1) is measured to be F D + (1) F D ∗+ (1) = 0.87 ± 0.22 stat ± 0.21 syst . A value of | V cb | is extracted from the two samples, using theoretical constraints on the slope and curvature of the hadronic form factors and their normalization at zero recoil, with the result | V cb | = (34.4 ± 1.6 stat ± 2.3 syst ± 1.4 th ) × 10 −3 . The branching fractions are measured from the two integrated spectra to be Br ( B 0 → D ∗+ ℓ − ν ℓ ) = (5.53 ± 0.26 stat ±0.52 syst ) %, Br ( B 0 → D ∗+ ℓ − ν ℓ ) = (2.35 ± 0.20 stat ± 0.44 syst ) %.
The formfactors are evaluated at zero recoil of D meson. Two different methods are used (see text for details). VCB is the KCM matrix element. The formfactor fitted to dependence: FF(OM) = FF(1)*(1-CONST*(OM-1)).
VCB is the KCM matrix element.
VCB is the KCM matrix element.
We have studied (p̄, p) reactions on 12 C , 63 Cu, and 209 Bi to search for possible nuclear states formed ny antiprotons and nuclei. The experiments used the 180 MeV antiproton beam from LEAR, and the high-resolution magnetic spectrometer, SPES II, to detect the outgoing protons. No evidence of antiproton-nucleus states was found. The gross features of the proton spectra are reasonably well described by intranuclear cascade model calculations, which consider proton emission following antiproton annihilations in the target nucleus.
Parameters resulting from the best fits to the proton spectra with the expression D2(SIG)/D(OMEGA)/D(E) = CONST*SQRT(E)*EXP(-E/SLOPE).
In four-jet events from e + e − →Z 0 →multihadrons one can separate the three principal contributions from the triple-gluon vertex, double gluon-bremsstrahlung and the secondary quark-antiquark production, using the shape of the two-dimensional angular distributions in the generalized Nachtmann-Reiter angle θ NR ∗ and the opening angle of the secondary jets. Thus one can identify directly the contribution from the triple-gluon vertex without comparison with a specific non-QCD model. Applying this new method to events taken with the DELPHI-detector we get for the ratio of the colour factor N c to the fermionic Casimir operator C F : N c C F = 2.55 ± 0.55 ( stat. ) ± 0.4 ( fragm. + models ) ± 0.2 ( error in bias ) in agreement with the value 2.25 expected in QCD from N c =3 and C F = 4 3 .
NC, CF, and TR are the color factors for SU(3) group.
The study of the J ψ transverse momentum distribution in oxygen-uranium reactions at 200 GeV/nucleon shows that 〈 P T 〉 and 〈 P T 2 〉 increase with the transverse energy of the reaction. Muon pairs in the mass continuum do not exhibit the same behaviour. The comparison of the J ψ production rates in central and peripheral collisions shows a significant diminution for low P T central events.
Two parametrization of the D(SIG)/D(PT) are used: first is : PT*exp(-SLOPE*PT**CONST(C=PT)) and second is : PT*exp(-2*MT/CONST(C=MT)).
D(SIG)/D(PT) is parameterized as PT*exp(-SLOPE*PT**CONST).
D(SIG)/D(PT) is parameterized as PT*exp(-SLOPE*PT**CONST).
None
NC, CF, and TF are the color factors for SU(N) group. For SU(3) they are equal to: NC = 3, CF = 4/3, and TF = 1/2.
This letter reports the results of the measurement of single photon production in the reaction e + e − → γ + invisible particles at centre-of-mass energies s =130 and 136 GeV and an integrated luminosity of 5.83 pb −1 , collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process e + e − → ν ν γ , and the number of neutrino families has been determined to be N ν = 3.1 ± 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model.
SIG with C=HPC and C=FEMC correpond to the events in the barrel and forwardregion, respectively.
Forum