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2.
CompHEP 4.4—automatic computations from Lagrangians to events Boos, E.; Bunichev, V.; Dubinin, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2004, Volume:
534, Issue:
1
Journal Article
Peer reviewed
Open access
We present a new version of the CompHEP program (version 4.4). We describe shortly new issues implemented in this version, namely, simplification of quark flavor combinatorics for the evaluation of ...hadronic processes, Les Houches Accord-based CompHEP-PYTHIA interface, processing the color configurations of events, implementation of MSSM, symbolical and numerical batch modes, etc. We discuss how the CompHEP program is used for preparing event generators for various physical processes. We mention a few concrete physics examples for CompHEP-based generators prepared for the LHC and Tevatron.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Deviations from the standard Higgs sector generated by some new (nonstandard) physics at an energy scale Lambda could be described by effective SU (3)c x SU (2)L x U(1) invariant nonrenormalizable ...Lagrangian terms of dimension six. The set of dimension-six operators involving the Higgs field is chosen in such a way that the form of the gauge boson kinetic terms remains untouched, preserving all high-precision electroweak constraints. A systematic study of effects in various Higgs boson production channels ( gamma gamma , ZZ, WW, bb, tautau) caused by effective operators is carried out beyond the production x decay approximation (or infinitely small width approximation). Statistical methods are used to establish the consistency of the standard Higgs sector with the available LHC data. A global fit in the two-parametric anomalous coupling space indicating possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings is performed, using post-Moriond 2012 data and more precise LC2013 data. We find that the standard Higgs sector is consistent with the current CMS and ATLAS experimental results both in the infinitely small width approximation and the calculation with complete gauge-invariant sets of diagrams. However, a visible difference between the exclusion contours is found for some combinations of production and decay channels, although it is minor for the global fits for all possible channels. Updates of the signal strength and the signal strength error reported at LC2013 result in significant improvements of the allowed regions in the anomalous coupling space, which are also recalculated at complete tree level.
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Using the optical theorem from the conditions of perturbative unitarity, we have established the upper bounds on the ratios of the Wilson coefficients to the square of the new physics scale for ...anomalous operators contributing to the processes of single t-quark production in hadron collisions. The limitations are found in an analytical form and are given numerically in the form of characteristic regions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We present prospects for the search for signals of light dark matter production mediated by a leptophilic scalar
and dark photon
in experiments at the Super Charm-Tau Factory (SCTF). Based on an ...analysis of the associative formation of scalar and vector mediators and
leptons in the final state at the energies of the future collider, the possibility of searching for manifestations of dark matter in the nonexcluded region of the parameter space is found.
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The Effective Field Theory (EFT) approach is widely used in the search for possible deviations from the predictions of the Standard Model. Such an approximation of possible BSM physics is valid up to ...a certain levels of energy scale and accuracy. In this article, we investigate potential limitation of the EFT approach related to unitarity to describe possible contributions of flavor-changing neutral currents (FCNC) involving the top quark. The numerical and analytical calculations of the FCNC processes used in the EFT approach demonstrate the constant asymptotic behavior of the total cross section with increasing energy. It is shown that the EFT approach for studying the possible contribution of FCNC does not violate the restrictions following from perturbative unitarity, the asymptotic behavior of the cross section does not exceed the Froissart bound, and the approach itself can be used to set the corresponding experimental limits for FCNC couplings or Wilson coefficients at present and future colliders.
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Modeling of the pair and single top quark production are discussed in the context of searches for the anomalous
couplings. For the simulation of the anomalous
couplings in the top quark production ...and/or decay, the Subsidiary Fields method allows to generate a minimal number of event samples to cover all possible values of the couplings. In the paper the Subsidiary Fields method is applied to simulate the full
process with
final state including the subsequent top quark and
boson decays. Correctness of the differential cross sections for arbitrary values of the
couplings is demonstrated for the case of the simultaneous presence of the left- and right-handed vector operators in the Wtb vertex.
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Numerical simulations of processes of three and four top quark hadroproduction are carried out in the SMEFT model framework. The simulated data are used to derive theoretical constraints on Wilson ...coefficients of relevant SMEFT operators of dimension six. Obtained limits for both cases are discussed and compared in terms of processes sensitivity to possible BSM contribution. Results show that operators
and
are better constrained by the process of triple top production, whereas for operator
more accurate limits are obtained from the production of four top quarks. The last considered operator
is relatively loosely constrained by both processes.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Deviations from the standard Higgs sector generated by some new physics at an energy scale Λ could be described by an effective SU(3)c×SU(2)L×U(1) invariant non-renormalizable Lagrangian terms of ...dimension six. A systematic study of various Higgs boson production × decay channels (γγ, ZZ, WW, bb¯, ττ¯) at the International Linear Collider (ILC) in the SM extension by effective operators is carried out. Statistical methods are used to establish a degree of consistency for the standard Higgs sector with the forthcoming data, using the expected ILC accuracies of the Higgs boson production channels. Global fits in the two-parametric anomalous coupling space indicating possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The new method for studying polarized parton distribution functions via the Drell-Yan process with tau production is proposed. The hadronic decay of tau to single charged pi-meson and neutrino is ...utilised for determination of the polarization state of the tau-lepton. The key feature of our approach is that we do not sum over the polarizations states of tau, but preserve this information through energies ofpions produced in corresponding decays. The new method in addition to existing ones should improve the accuracy of measurements of polarized structure functions of hadrons. In the current work, the feasibility of such an approach is assessed through numerical simulations.
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