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تسجيل مستخدم جديدA Storm in a T Cup
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We revisit the process of transversification and agglomeration of particle momenta that are often performed in analyses at hadron colliders, and show that many of the existing mass-measurement variables proposed for hadron colliders are far more closely related to each other than is widely appreciated, and indeed can all be viewed as a common mass bound specialized for a variety of purposes.
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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 inter
feres 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.
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 H
adron 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.
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 s
everal 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 $1sigma$.
New scalars from an extended Higgs sector could have weak scale masses and still have escaped detection. In a Type I Two Higgs Doublet Model, for instance, even the charged Higgs can be lighter than the top quark. Because electroweak production of th
ese scalars is modest, the greatest opportunity for their detection might come from rare top decays. For mass hierarchies of the type $m_t>m_{H^pm}>m_{A^0,,H^0}$, the natural signal can arise from top quark pair production, followed by the decay chain $t rightarrow b,H^+$, $H^+ rightarrow W^{+(*)} phi^0$, $phi^0rightarrow boverline{b},,tau^+tau^-$, where $phi^0=A^0,,H^0$. These final states largely overlap with those of the Standard Model $t,bar{t},H^0_{_text{SM}}$ process, and therefore can potentially contaminate $t,bar{t},H^0_{_text{SM}}$ searches. We demonstrate that existing $t,bar{t},H^0_{_text{SM}}$ analyses can already probe light extended Higgs sectors, and we derive new constraints from their results. Furthermore, we note that existing excesses in $t,bar{t},H^0_{_text{SM}}$ searches can be naturally explained by the contamination of rare top decays to new light Higgses. We discuss how to distinguish this signal from the Standard Model process.
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