Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDilepton azimuthal correlations in $t bar t$ production
70
0
0.0
(
0
)
Added by
Juan Antonio Aguilar-Saavedra
Publication date
2018
fields
and research's language is
English
Authors
J.A. Aguilar-Saavedra
Ask ChatGPT about the research
No Arabic abstract
The dilepton azimuthal correlation, namely the difference $phi$ between the azimuthal angles of the positive and negative charged lepton in the laboratory frame, provides a stringent test of the spin correlation in $t bar t$ production at the Large Hadron Collider. We introduce a parameterisation of the differential cross section $dsigma / dphi$ in terms of a Fourier series and show that the third-order expansion provides a sufficiently accurate approximation. This expansion can be considered as a `bridge between theory and data, making it very simple to cast predictions in the Standard Model (SM) and beyond, and to report measurements, without the need to provide the numbers for the whole binned distribution. We show its application by giving predictions for the coefficients in the presence of (i) an anomalous top chromomagnetic dipole moment; (ii) an anomalous $tbW$ interaction. The methods presented greatly facilitate the study of this angular distribution, which is of special interest given the $3.2(3.7)sigma$ deviation from the SM next-to-leading order prediction found by the ATLAS Collaboration in Run 2 data.
rate research
Read More
We discuss lepton charge asymmetries in $t bar t$ and $t bar t gamma$ production at the LHC, which can be measured in the semileptonic decay channel $t bar t to W^+ b , W^- bar b to ell^+ u b , q bar q bar b$ (or the charge conjugate). Considering several variants of a new physics scenario with a light colour octet, it is seen that for $t bar t$ these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For $t bar t gamma$ the new leptonic asymmetries, as well as the $t bar t$ charge asymmetry, will reach their full potential with the high luminosity LHC upgrade. These asymmetries can pinpoint deviations at the $3sigma-4sigma$ level for new physics scenarios where the charge asymmetries already measured in $t bar t$ production agree within $1sigma$.
Many extensions of the Standard Model contain (pseudo)scalar bosons with masses in the TeV range. At hadron colliders, such particles would predominantly be produced in gluon fusion and would decay into top quark pair final sates, a signal that interferes with the large QCD background $gg to tbar t$. This phenomenon is of interest for searches for by the LHC experiments. Here, we consider the signal and background interference in this process and study it in various benchmark scenarios, including models with extra singlet (pseudo)scalar resonances, two-Higgs doublet models, and the minimal supersymmetric extension of the SM with parameters chosen to obtain the measured light Higgs mass (the hMSSM). We allow for the possible exchanges of beyond the SM vector-like particles as well as scalar quarks. We calculate the possible interference effects including realistic estimates of the attainable detection efficiency and mass resolution. Studies of our benchmark scenarios indicate that searches with an LHC detector could permit the observation of the $tbar t$ final states or constrain significantly large regions of the parameter spaces of the benchmark scenarios.
We present results of a computation of NLO QCD corrections to the production of an off-shell top--antitop pair in association with an off-shell $text{W}^+$ boson in proton--proton collisions. As the calculation is based on the full matrix elements for the process $text{p}text{p}to {text{e}}^+ u_{text{e}},mu^-bar{ u}_mu,tau^+ u_tau,{text{b}},bar{text{b}}$, all off-shell, spin-correlation, and interference effects are included. The NLO QCD corrections are about $20%$ for the integrated cross-section. Using a dynamical scale, the corrections to most distributions are at the same level, while some distributions show much larger $K$-factors in suppressed regions of phase space. We have performed a second calculation based on a double-pole approximation. While the corresponding results agree with the full calculation within few per cent for integrated cross-sections, the discrepancy can reach $10%$ and more in regions of phase space that are not dominated by top--antitop production. As a consequence, on-shell calculations should only be trusted to this level of accuracy.
We investigate a charge asymmetry in $t bar t gamma$ production at the LHC that provides complementary information to the measured asymmetries in $t bar t$ production. We estimate the experimental uncertainty in its measurement at the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce the asymmetry excess in $t bar t$ at the Tevatron and the SM-like asymmetry at the LHC, the measurement in $t bar t gamma$ at the LHC could exhibit significant deviations with respect to the SM prediction.
The Wtb vertex can be probed on future colliders in the processes of single top production (LHC, pp mode, NLC, $gamma e$ mode) and of top pair production (NLC, e^+ e^- mode). We analyse observables sensitive to anomalous Wtb couplings in the top pair production process of e^+ e^- collisions. In particular, forward-backward and spin-spin asymmetries of the top decay products and the asymmetry of the lepton energy spectum are considered. Possible bounds on anomalous couplings obtained are competitive to those expected from the upgraded Tevatron and LHC. The validity of the infinitely small width approximation for the three-body top decay is also studied in detail.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
