M. Dubinin

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.

CompHEP is a package for automatic calculations of elementary particle decay and collision properties in the lowest order of perturbation theory (the tree approximation). The main idea prescribed into the CompHEP is to make available passing on from the Lagrangian to the final distributions effectively with a high level of automation.

This work summarizes the studies for the Higgs boson searches in CMS at the LHC collider. The main discovery channels are presented and the potential is given for the discovery of the SM Higgs boson and the Higgs bosons of the MSSM. The phenomenology, detector, trigger and reconstruction issues are briefly discussed.

There are many possibilities for new physics beyond the Standard Model that feature non-standard Higgs sectors. These may introduce new sources of CP violation, and there may be mixing between multiple Higgs bosons or other new scalar bosons. Alternatively, the Higgs may be a composite state, or there may even be no Higgs at all. These non-standard Higgs scenarios have important implications for collider physics as well as for cosmology, and understanding their phenomenology is essential for a full comprehension of electroweak symmetry breaking. This report discusses the most relevant theories which go beyond the Standard Model and its minimal, CP-conserving supersymmetric extension: two-Higgs-doublet models and minimal supersymmetric models with CP violation, supersymmetric models with an extra singlet, models with extra gauge groups or Higgs triplets, Little Higgs models, models in extra dimensions, and models with technicolour or other new strong dynamics. For each of these scenarios, this report presents an introduction to the phenomenology, followed by contributions on more detailed theoretical aspects and studies of possible experimental signatures at the LHC and other colliders.

Deviations from the standard Higgs sector generated by some new (nonstandard) physics at an energy scale $\mathrm{\ensuremath{\Lambda}}$ could be described by effective $\mathrm{SU}{(3)}_{c}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ 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 ($\ensuremath{\gamma}\ensuremath{\gamma}$, $ZZ$, $WW$, $b\overline{b}$, $\ensuremath{\tau}\overline{\ensuremath{\tau}}$) caused by effective operators is carried out beyond the $\text{production}\ifmmode\times\else\texttimes\fi{}\text{decay}$ 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.

A non-minimal approximation for effective masses of light and heavy neutrinos in the framework of a type-I seesaw mechanism with three generations of sterile Majorana neutrinos which recover the symmetry between quarks and leptons is considered. The main results are: (a) the next-order corrections to the effective mass matrix of heavy neutrinos due to terms O({\theta}MD) are obtained, which modify the commonly used representation for the effective mass (MD is a Dirac neutrino mass when the electroweak symmetry is spontaneously broken); and (b) the general form of the mixing matrix is found in non-minimal approximation parametrized by a complex 3x3 matrix satisfying a nontrivial constraint. Numerical analysis within the {\nu}MSM framework demonstrates the very small effect of new contributions of direct collider observables as opposed to their possible significance for cosmological models.

We discuss the SM Higgs discovery potential of LHC in the reaction pp→H+jet→γγ+jet when the jet is observed at sufficiently high Et to be reliably identified. We conclude that this channel gives promising discovery possibilities for the Higgs boson mass range 100–140 GeV, during LHC operation at a low luminosity. With 30 fb−1 of accumulated data and for MH=120 GeV about 100 signal events could be observed with the number of background events larger by a factor of 2 only, showing a signal significance S/B∼7. We use the difference of distributions in the partonic subprocess energy ŝ for the signal and background for a better separation of the signal.

We consider the two-Higgs-doublet model with explicit CP-violation, where the effective Higgs potential is not CP-invariant at the tree level. The three neutral Higgs bosons of the model are the mixtures of CP-even and CP-odd bosons which exist in the CP-conserving limit of the theory. The mass spectrum and tree-level couplings of the neutral Higgs bosons to gauge bosons and fermions are significantly dependent on the parameters of the Higgs boson mixing matrix. We calculate the Higgs-gauge boson, Higgs-fermion, triple and quartic Higgs self-interactions in the MSSM with explicit CP-violation in the Higgs sector and CP-violating Yukawa interactions of the third generation scalar quarks. In some regions of the MSSM parameter space substantial changes of the self-interaction vertices take place, leading to significant suppression or enhancement of the multiple Higgs boson production cross sections.

The extension of the Standard Model lepton sector by three right-handed Majorana neutrinos [heavy neutral leptons (HNLs)] with masses up to GeV scale is considered. While the lightest heavy neutral lepton is the dark matter particle with mass of the order of 5 keV, the remaining two HNLs ensure standard (active) neutrino mass generation by means of the seesaw type I mechanism. Two heavy sterile neutrinos with quasidegenerate masses up to 5 GeV can induce the deviation of lepton universality violation parameter in the decays of ${\ensuremath{\pi}}^{+}$ and ${K}^{+}$ mesons from the Standard Model value. Contours are obtained for the permissible values of this parameter within the framework of two mixing scenarios, taking into account the lifetime boundary for heavy neutral lepton from big bang nucleosynthesis in the Universe. When calculating the HNL decay width in the framework of the model with six Majorana neutrinos, three active and three heavy, both two-particle and three-particle lepton decays, essential for masses below the mass of the pion, were taken into account. When calculating the decay widths, the limiting case known as the ``Dirac limit'' is not used. The results based on the explicit form of mixing matrices for three HNL generations and the diagram technique for Majorana neutrinos, which explicitly take into account the interference terms for diagrams with identical mass states, can lead to some differences in lifetime from the results using the Dirac limit and the displacement of the corresponding experimental exclusion contours of the ``mass-mixing'' type. For the second mixing scenario, a mass region of $460\text{ }\text{ }\mathrm{MeV}<M<485\text{ }\text{ }\mathrm{MeV}$ has been found that allows violation of lepton universality in charged kaon decays at the level observed in the experiment.

Abstract A decline in routine vaccinations, attributed to vaccine hesitancy, undermines preventative healthcare, impacting health and exacerbating vaccine disparities. University-public health partnerships can improve vaccination services. This study describes and evaluates a university-public health use case employing social determinants of health (SDoH)-based strategies to address vaccination disparities. Guided by the Translational Science Benefits Logic Model, the partnership offered no-cost preventative vaccines at community-based organization (CBO) sites, collected CBO clientele’s vaccination interest, hesitancy, and demographic data, and conducted descriptive analyses. One hundred seven vaccination events were held, administering 3,021 vaccines. This partnership enhanced health outcomes by addressing disparities through co-located vaccination and SDoH services.

Single top quark cross section evaluations for the complete sets of tree-level diagrams in the $e^+ e^-$, $e^- e^-$, $\gamma e$ and $\gamma \gamma$ modes of the next linear collider with unpolarized and polarized beams are performed within the Standard Model and beyond. From comparison of all possibilities we conclude that the process $\gamma_+ e^-_L \to e^- t \bar b$ is extremely favoured due to large cross section, no $t \bar t$ background, high degrees of beam polarization, and exceptional sensitivities to $V_{tb}$ and anomalous $Wtb$ couplings. Similar reasons favour the process $e^- e^- \to e^- \nu_e \bar t b$ for probing top quark properties despite a considerably lower cross section. Less favourable are processes like $e^+ e^-, \gamma \gamma \to e^- \nu_e t \bar b$. Three processes were chosen to probe their sensitivity to anomalous $Wtb$ couplings, with best bounds found for $\gamma_+ e^-_L \to e^- t \bar b$ and $e^+_R e^-_R \to e^- \nu_e t \bar b$.

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 analyze 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 spectrum 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.

We consider the effective two-Higgs-doublet potential with complex parameters, when the CP invariance is broken both explicitly and spontaneously. Diagonal mass term in the local minimum of the potential is constructed for the physical basis of Higgs fields, keeping explicitly the limiting case of CP-conservation if the parameters are taken real. For special case of the two-doublet Higgs sector of the minimal supersymmetric model, when CP invariance is violated by the Higgs bosons interaction with scalar quarks of the third generation, we calculate by means of the effective pothential method the Higgs boson masses and evaluate the two-fermion Higgs boson decay widths and the widths of rare one-loop mediated decays H -> \gamma \gamma, H -> gg.

Cross sections for Higgs boson associated production in γe collisions are calculated for the γe→WHν and γe→ZHe processes. Calculations were performed with the help of the CompHEP computer system. Event signatures, event separation and background conditions are discussed.

Despite the fact that experimentally with a high degree of statistical significance only a single Standard Model-like Higgs boson is discovered at the LHC, extended Higgs sectors with multiple scalar fields not excluded by combined fits of the data are more preferable theoretically for internally consistent realistic models of particle physics. We analyze the inflationary scenarios which could be induced by the two-Higgs-doublet potential of the Minimal Supersymmetric Standard Model (MSSM) where five scalar fields have non-minimal couplings to gravity. Observables following from such MSSM-inspired multifield inflation are calculated and a number of consistent inflationary scenarios are constructed. Cosmological evolution with different initial conditions for the multifield system leads to consequences fully compatible with observational data on the spectral index and the tensor-to-scalar ratio. It is demonstrated that the strong coupling approximation is precise enough to describe such inflationary scenarios.

We discuss the process $${{\ell }^{ + }}{{\ell }^{ - }} \to N{{W}^{ \pm }}{{\ell }^{ \mp }}$$ , where N is a heavy Majorana neutrino and $$\ell = e,\mu $$ . Large cross sections are expected for these processes at high center-of-mass energies, which can be reached at future lepton–lepton colliders. The Monte Carlo simulation of the studied processes is produced within the framework of the seesaw type-I model, where the Majorana neutrinos (or heavy neutral leptons, HNL), are introduced in the standard leptonic sector. Recently the possibility to search for the direct HNL production was studied in the $${{\ell }^{ + }}{{\ell }^{ - }} \to N{{\nu }_{\ell }}$$ process with the subsequent decay $$N \to {{W}^{ \pm }}{{\ell }^{ \mp }}$$ . In this paper we investigate an alternative process $${{\ell }^{ + }}{{\ell }^{ - }} \to N{{W}^{ \pm }}{{\ell }^{ \mp }} \to {{W}^{ \pm }}{{W}^{ \pm }}{\kern 1pt} {{\ell }^{ \mp }}{\kern 1pt} {{\ell }^{ \mp }}$$ with the lepton number violation by two units. The similar processes appear in collisions with the same-sign beams, $${{e}^{ - }}{{e}^{ - }} \to N{{W}^{ - }}{\kern 1pt} {{e}^{ - }} \to {{W}^{ - }}{\kern 1pt} {{W}^{ - }}{\kern 1pt} {{e}^{ + }}{\kern 1pt} {{e}^{ - }}$$ or $${{\mu }^{ + }}{{\mu }^{ + }}$$ $$ \to $$ $$N{{W}^{ + }}{\kern 1pt} {{\mu }^{ + }} \to {{W}^{ + }}{\kern 1pt} {{W}^{ + }}{\kern 1pt} {{\mu }^{ + }}{\kern 1pt} {{\mu }^{ - }}$$ . The cross sections of the processes under consideration are enhanced by the soft photon exchange in the t -channel. We calculate the cross sections for the signals and potential Standard Model backgrounds for the $${{e}^{ + }}{{e}^{ - }}$$ beam collisions at the 1 TeV center-of-mass energy and the $${{\mu }^{ + }}{{\mu }^{ - }}$$ collisions at 3 and 10 TeV. Due to the diagrams with soft t -channel photons and respective interference the promptly emitted leptons are produced in the direction close to the corresponding beam. These leptons will be lost in the beam pipe or badly measured by forward detectors. However, the signal events can be well separated from backgrounds using the rest of the event containing the $$WW\ell $$ particles. Finally, the expected upper limits on the mixing parameters $${{\left| {{{V}_{{\ell N}}}} \right|}^{2}}$$ as a function of M ( N ) are calculated.

This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.

In the framework of the effective field theory approach to heavy supersymmetry radiative corrections in the Higgs sector of the minimal supersymmetric standard model (MSSM) for the effective potential decomposition up to the dimension-six operators are calculated. Symbolic expressions for the threshold corrections induced by $F$- and $D$-soft supersymmetry breaking terms are derived, and the Higgs boson mass spectrum respecting the condition ${m}_{h}=125\text{ }\text{ }\mathrm{GeV}$ for the lightest $CP$-even scalar is evaluated.

Inflationary scenarios motivated by the minimal supersymmetric standard model (MSSM) where five scalar fields are non-minimally coupled to gravity are considered. The potential of the model and the function of non-minimal coupling are polynomials of two Higgs doublet convolutions. We show that the use of the strong coupling approximation allows to obtain inflationary parameters in the case when a combination of the four scalar fields plays a role of inflaton. Numerical calculations show that the cosmological evolution leads to inflationary scenarios fully compatible with observational data for different values of the MSSM mixing angle [Formula: see text].

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.

We present the results of a complete tree level calculation for the process e+e−→ννbb at the energies of LEP200 and Next Linear Colliders. Automatic generation of the squared matrix element was carried out by GRACE and CompHEP systems. We study in detail the behavior of the cross-section as a function of CMS energy and Higgs boson mass. Particularly we point out the possibility of Higgs boson detection at LEP200 energies under the resonance threshold (√s<mH+mz). We compare the complete tree level result with the effective 2→2 process approximation for Higgs production. The approximation is satisfactory at LEP200 energies, but at higher energies a rather large discrepancy is observed.

In the minimal supersymmetric standard model (MSSM) the one-loop finite-temperature corrections from the squark-Higgs bosons sector are calculated, the effective two-Higgs-doublet potential is reconstructed and possibilities of the electroweak phase transition in full MSSM ($m_{H^\pm}$, ${\tt tg}\beta$, $A_{t,b}$, $\mu$, $m_Q$, $m_U$, $m_D$) parameter space are studied. At large values of $A_{t,b}$ and $\mu$ of around 1 TeV, favored indirectly by LEP2 and Tevatron data, the threshold finite-temperature corrections from triangle and box diagrams with intermediate third generation squarks are very substantial. The four types of bifurcation sets are defined for the two-Higgs-doublet potential. High sensitivity of the low-temperature evolution to the effective two-doublet and the MSSM squark sector parameters is observed, but rather extensive regions of the full MSSM parameter space allow the first-order electroweak phase transition respecting the phenomenological constraints at zero temperature. As a rule, these regions of the MSSM parameter space are in line with the case of a light stop quark.

At present time when a new generation of TeV colliders are beginning to operate one needs to calculate cross-sections for a great number of various reactions. Such calculations are united in the framework of the collider physical program, providing definite predictions how to detect the signatures of the new physics and separate them from the background. The CompHEP package was created for calculation of decay and high energy collision processes of elementary particles in the lowest order (tree) approximation. The main idea put into the CompHEP was to make available passing from the lagrangian to the final distributions effectively with the high level of automatization what is extremely needed in collider physics.

CompHEP, as a partonic event generator, and PYTHIA, as a generator of final states of detectable objects, are interfaced. Thus, integrated tool is proposed for simulation of (almost) arbitrary collision processes at the level of detectable particles. Exact (multiparticle) matrix elements, convolution with structure functions, decays, partons hadronization and (optionally) parton shower evolution are basic stages of calculations. The PEVLIB library of event generators for LHC processes is described.

This report summarises the results of the four-fermion working group of the LEP2-MC workshop, held at CERN from 1999 to 2000. Recent developments in the calculation of four-fermion processes in electron-positron collisions at LEP-2 centre-of-mass energies are presented, concentrating on predictions for four main reactions: W-pair production, visible photons in four-fermion events, single-W production and Z-pair production. Based on a comparison of results derived within different approaches, theoretical uncertainties on these predictions are established.

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.

Ten three-body processes in e + e − collisions for heavy particle productions such as Higgs, t-quark, W ± and Z 0 are calculated by two independent computer codes for automatic calculation of Feynman amplitude. The results are in excellent agreement within statistical error of numerical integration (about 0.5%). This demonstrates that these systems are quite powerful for theoretical study for future e + e − , e ± γ and γγ colliders. Numerical values of cross sections are summarized in tables and a figure.

Abstract We consider the possibility to detect the Higgs boson signal in the process e + e − → Zb b at LEP200 energies. The calculations are performed in the tree approximation for complete set of diagrams, including not only the signal ( e + e − → HZ → Zb b ) and the main background ( e + e − → ZZ → Zb b ) contributions, but also additional background (for instance, Z emission from the b-quark line) and interference terms. We calculate the Higgs signal in the total cross section and b b invariant mass distribution.

A review of various systems for automated calculation of tree-level and loop Feynman diagrams, Monte Carlo integration over multidimensional phase space, and event generation for modern and future colliders (LHC and ILC) is presented. The CompHEP system possibilities are considered in greater detail.

Представлен хиггсовский сектор неминимальной суперсимметричной стандартной модели с нарушением CP-инвариантности в суперпотенциале и в секторе мягкого нарушения суперсимметрии

Review of Monte Carlo event generators for signals of new particles at LEP2. The areas covered include SUSY, HIGGS and Leptoquarks.

Possible realistic scenarios are investigated in the minimal supersymmetric standard model (MSSM) Higgs sector extended by dimension-six effective operators. The CP-odd Higgs boson with low mass around 30–90 GeV could be consistently introduced in the regime of large threshold corrections to the effective MSSM two-doublet Higgs potential.

Рассматривается общий случай температурной эволюции двухдублетного потенциала Хиггса минимальной суперсимметричной стандартной модели, когда вакуумные конденсаты хиггсовских дублетов произвольно перемещаются по поверхности равновесия (или поверхности экстремумов), проходя через области бифуркаций. В рамках теории катастроф двухдублетный потенциал Хиггса минимальной суперсимметричной стандартной модели представляется cпециальным случаем потенциала градиентной системы. Получены нелинейные преобразования вакуумных конденсатов указанной модели, приводящие двухдублетный потенциал к канонической форме, а также функции-катастрофы типа $A_3$ и $A_5$, соответствующие электрослабому фазовому переходу первого рода в данной модели.

Results are reported from a search for the effects of contact interactions using events with a high-mass, oppositely charged muon pair. The events are collected in proton-proton collisions at √s=7  TeV using the Compact Muon Solenoid detector at the Large Hadron Collider. The data sample corresponds to an integrated luminosity of 5.3  fb^(-1). The observed dimuon mass spectrum is consistent with that expected from the standard model. The data are interpreted in the context of a quark- and muon-compositeness model with a left-handed isoscalar current and an energy scale parameter Λ. The 95% confidence level lower limit on Λ is 9.5 TeV under the assumption of destructive interference between the standard model and contact-interaction amplitudes. For constructive interference, the limit is 13.1 TeV. These limits are comparable to the most stringent ones reported to date.

We discuss the process $\ell^+\ell^- \to N W^{\pm} \ell^{\mp}$, where $N$ is a heavy Majorana neutrino and $\ell = e, \mu$. Large cross sections are expected for these processes at high center-of-mass energies, which can be reached at future lepton-lepton colliders. The Monte Carlo simulation of the studied processes is produced within the framework of the seesaw type-I model, where the Majorana neutrinos (or heavy neutral leptons, HNL), are introduced in the standard leptonic sector. Recently the possibility to search for the direct HNL production was studied in the $\ell^+\ell^- \to N \nu_{\ell}$ process with the subsequent decay $N \to W^{\pm} \ell^{\mp}$. In this paper we investigate an alternative process $\ell^+\ell^- \to N W^{\pm} \ell^{\mp} \to W^{\pm}W^{\pm}\,\ell^{\mp}\,\ell^{\mp}$ with the lepton number violation by two units. The similar processes appear in collisions with the same-sign beams, $e^-e^- \to N W^-\,e^- \to W^-\,W^-\,e^+\,e^-$ or $\mu^+\mu^+ \to N W^+\,\mu^+ \to W^+\,W^+\,\mu^+\,\mu^-$. The cross sections of the processes under consideration are enhanced by the soft photon exchange in the $t$-channel. We calculate the cross sections for the signals and potential Standard Model backgrounds for the $e^+e^-$ beam collisions at the 1 TeV center-of-mass energy and the $\mu^+\mu^-$ collisions at 3 TeV and 10 TeV. Due to the diagrams with soft $t$-channel photons and respective interference the promptly emitted leptons are produced in the direction close to the corresponding beam. These leptons will be lost in the beam pipe or badly measured by forward detectors. However, the signal events can be well separated from backgrounds using the rest of the event containing the $WW\ell$ particles. Finally, the expected upper limits on the mixing parameters $|V_{\ell N}|^2$ as a function of M($N$) are calculated.

We consider the possibility of Higgs boson detection at LEP II under the resonance threshold [Formula: see text] in the framework of complete tree level approach to the calculation of the [Formula: see text] amplitude, simulating b quark fragmentation to hadrons and taking into account typical detector properties. At the energy below the 2m Z threshold [Formula: see text] Higgs boson production under the m H + m Z threshold is almost background free.

We examine the prospects for measuring the $H Z \gamma$ coupling of a Standard Model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear \ee collider, assuming an integrated luminosity of 1 ab$^{-1}$ and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with $\nu_e \bar{\nu_e}$ via the $W W$ fusion reaction $e^+e^- \to \nu_e \bar{\nu_e} H$, followed by the rare decay into a $Z$ boson and a photon, $H \to Z \gamma$. Accounting for all main background contributions, different selection procedures are discussed. Uncertainties on the \hZg branching fraction of approximately 48% (27%, 44%) can be achieved in unpolarised \ee collisions for $M_H$ = 120 (140, 160) GeV. With appropriate initial state polarisations $\Delta$BF(\hZg)/BF(\hZg), or the precisions on the \hZg partial width, can be improved to 29% (17%, 27%) and provide valuable information on the $HZ\gamma$ coupling. We regard our results as a convincing confirmation of the great potential of a linear collider to access and reliably measure important parameters of the Higgs boson despite initially overwhelming background with final state signature similar to the signal events.

Consistent and phenomenologically successful scenarios of the Minimal Supersymmetric Standard Model (MSSM) include the Higgs potential which is positively defined at large fields and has two minima, one of them is true and stable vacuum in which we live. However, the effective terms of the MSSM potential which appear at a loop level can spoil the vacuum stability leading to a metastable or unstable vacuum configurations. Such a situation is analysed and the general necessary conditions of vacuum stability in the MSSM parameter space are imposed. For a majority of the MSSM “benchmark scenarios” which are used for reconstruction of production channels at the LHC, the effective potential is found to be always stable, except light stop and τ-phobic scenarios.

The CompHEP package was developed for calculations of decay and high energy collision processes with, correspondingly, up to 5 and 4 final particles in the lowest order (tree) approximation. The main idea put into CompHEP was to make available passing from the Lagrangian to final distributions efficiently with high level automation what is extremely needed in collider physics. The present talk describes a general structure of the CompHEP facilities and reports some physical results obtained with its help. The main purpose of the talk is to attract the attention of high energy physicists to this user-friendly package which is completely aimed at making easier their routine and tedious calculations in the TeV region.

We present the results of complete tree level calculation for W boson production processes e^- p -> e^- mu^+ nu_mu X and e^- p -> e^- mu^- nu_mubar X introducing anomalous WWgamma and WWZ couplings. Detailed results for the distributions of final state particles are obtained. In the region of small momentum transferred we calculate the contribution of hadronlike photon component in the structure function approach.

We present a new version of the CompHEP program package, version 4.5. We describe new options and techniques implemented in the version: interfaces to ROOT and HERWIG, parallel calculations, generation of the XML-based header in event files (HepML), full implementation of the Les Houches agreements (LHA I, SUSY LHA, LHA PDF, Les Houches Event format), cascade matching for intermediate scalar resonances, etc.

The processes involving single top quark production have an electroweak nature with unique properties. They are very interesting from both theoretical and experimental points of view. The article contains a brief overview of possible “New Physics” manifestations in the single top quark production processes.

The CP-even and CP-odd scalar states of the two-Higgs-doublet model (THDM) and the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM), with properties which could lead to the 750 GeV excess in the γγ invariant mass distribution, are studied.It is shown that THDM and MSSM are viable in explaining the observed excess without additional assumptions only when the alignment and decoupling limits break down.If the origin of the excess is not in a Higgs sector, regions of the MSSM parameter space are separated where the lightest CP-even Higgs boson is identical to the Standard Model scalar.

Higgs sector of the Next-to-Minimal Sypersymmetric Model with CP violation in superpotential and in in the soft supersymmetry breaking sector is considered. One-loop corrections to effective potential parameters were calculated and incorporated to the evaluation of neutral Higgs bosons masses.

The report summarizes the results of the activities of the Working Group on Event Generators for WW Physics at CERN during 1995.

We consider the K^0 - \bar K^0 and B^0 - \bar B^0 mixings in the MSSM with the two-Higgs-doublet scalar sector featuring explicit CP violation, and the Yukawa sector of type II. In the case of strong mixing between CP-odd and CP-even states the existence of light charged Higgs is allowed in the model. The mass splitting Δm_{LS} and the amount of indirect CP violation εare calculated. In the limit of effective low-energy approximation the nonstandard effects are shown to be negligibly small in Δm_{LS} and εfor the K^0-mesons, being almost independent on the charged Higgs boson mass. However, for the B_d^0 - \bar B_d^0 and B_s^0 - \bar B_s^0 systems the effects of nonstandard physics are shown to be larger, limiting the MSSM parameter space.

New developments of the CompHEP package and its applications to the top quark and the Higgs boson physics at the LHC collider are reviewed. These developments were motivated mainly by the needs of experimental searches of DO (Tevatron) and CMS (LHC) collaborations where identification of the top quark and the Higgs boson in the framework of the Standard Model (SM) or possible extensions of the SM played an important role. New useful features of the CompHEP Graphics User Interface (GUI) are described.

We present a new version of the CompHEP program package, version 4.5.We describe new options and techniques implemented in the version: interfaces to ROOT and HERWIG, parallel calculations, generation of the XML-based header in event files (HepML), full implementation of the Les Houches agreements (LHA I, SUSY LHA, LHA PDF, Les Houches Event format), cascade matching for intermediate scalar resonances, etc.

We study the light output, light collection efficiency and signal timing of a variety of organic scintillators that are being considered for the upgrade of the hadronic calorimeter of the CMS detector. The experimental data are collected at the H2 test-beam area at CERN, using a 150 GeV muon beam. In particular, we investigate the usage of over-doped and green-emitting plastic scintillators, two solutions that have not been extensively considered. We present a study of the energy distribution in plastic-scintillator tiles, the hit efficiency as a function of the hit position, and a study of the signal timing for blue and green scintillators.

The possibility of the presence of a light pseudoscalar with the mass of 28 GeV in the MSSM Higgs sector extended by dimension-six operators is analyzed. The perturbative unitarity and vacuum stability constraints are discussed. Tree-level production cross sections of a light pseudoscalar in the process gg → µµbb − , and cross sections of a light pseudoscalar production in the topquark decay are evaluated for suitable benchmark points.

The process of single W-boson production at the energies of Next Linear Colliders is considered. We discuss in details the contributions from s and t channel diagrams, technical aspects of the complete tree level calculation with a finite W width, and the quark mass effects.

In this report we review the prospects for Higgs physics at LEP2. The theoretical aspects and the phenomenology of Higgs particles are discussed within the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM). The experimental search techniques are described and the discovery limits for Higgs bosons in the LEP2 energy range are summarized. In addition, opportunities of detecting Higgs particles in non-minimal extensions of the SM and the MSSM are investigated.

The activities of the QCD working group concentrated on improving the understanding and Monte Carlo simulation of multi-jet final states due to hard QCD processes at LEP, i.e. quark-antiquark plus multi-gluon and/or secondary quark production, with particular emphasis on four-jet final states and b-quark mass effects. Specific topics covered are: relevant developments in the main event generators PYTHIA, HERWIG and ARIADNE; the new multi-jet generator APACIC++; description and tuning of inclusive (all-flavour) jet rates; quark mass effects in the three- and four-jet rates; mass, higher-order and hadronization effects in four-jet angular and shape distributions; b-quark fragmentation and gluon splitting into b-quarks.

Deviations from the standard Higgs sector generated by some new physics at an energy scale $Λ$ could be described by an effective $SU(3)_c \times SU(2)_L \times U(1)$ invariant non-renormalizable Lagrangian terms of dimension six. A systematic study of various Higgs boson production channels ($γγ$, $ZZ$, $WW$, $b \bar b$, $τ\bar τ$) 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 to possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.

Higgs boson discovery at the LHC with the mass mH = 125.09± 0.24 GeV [1] results in an important consequences for the minimal supersymmetric standard model (MSSM) two-doublet Higgs sector. The Higgs sector includes five physical states in the CP-conserving limit: two CP-even neutral Higgs bosons h and H, two charged scalars H± and one CP-odd neutral Higgs boson A [2]. Large radiative corrections from the third generation quarks and quark superpartners play an important role in the generation of the effective two-doublet Higgs potential at the scale below MSUSY. If in the absence of any corrections the tree mass of the lightest state mh can not exceed the Z 0-boson mass [3] and the observables (masses and couplings) can be defined by means of the two parameters, the mixing angle tan β = v2/v1 and the charged scalar mass mH± 2, then the primary calculation [4] of radiative corrections to the effective potential changes significantly this simple picture. Multidimensional MSSM parameter space even in the simplified variant is described besides the two-dimensional set tan β, mH± by the three additional parameters: μ (Higgs superfield mass parameter), At = Ab (degenerate trilinear Higgs boson third generation squarks mixing parameters) 3, MSUSY (the quark superpartners mass scale). Radiative corrections which ’bring up’ the lightest Higgs bosonmass from the tree limit mZ to the observable avegage value 125.09GeV are defined by the terms of the order of μ/MSUSY, At,b/MSUSY, see explicit formulas in [5, 6], also [7]. In the framework of parametric scenarios it is natural to simplify as much as one can the parametrization of the Higgs sector in the five-dimensional parameter space mH± , tan β, μ, At = Ab, MSUSY separating most essential variables which demonstrate the strongest influence on the masses and couplings of scalar particles4. Such parametrizations [8, 9] are based on the observation that the leading and the subleading

A measurement of the ratio of the branching fractions of the B_s^0 meson to J/ψf_0(980) and to J/ψϕ(1020) is presented. The J/ψ, f_0(980), and ϕ(1020) are observed through their decays to μ^+μ^−, π^+π^−, and K^+K^−, respectively. The f_0 and the ϕ are identified by requiring |Mπ^+π^− − 974 MeV|<50 MeV| and |MK^+K^− − 1020 MeV|<10 MeV. The analysis is based on a data sample of pp collisions at a centre-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3 fb^(−1). The measured ratio is B(B_s^0→J/ψf_0)B(f_0→π^+π^−)/B(B_s^0→Jψϕ)B(ϕ→K^+K^−)=0.140±0.008(stat)±0.023(syst), where the first uncertainty is statistical and the second is systematic.

b, t ¯ t) at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) in the Standard Model extension by the effective operators is carried out. Statistical methods are used to establish a degree of consistency for the standard Higgs sector with the accumulated LHC and the forthcoming ILC data. Global fits in the two-parametric anomalous coupling space indicating to possible deviations from the standard Higgs-fermion and Higgs-gauge boson couplings are performed.

The observation of a new b baryon via its strong decay into Ξ_b^-π^+ (plus charge conjugates) is reported. The measurement uses a data sample of pp collisions at √s=7  TeV collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5.3  fb^(-1). The known Ξb- baryon is reconstructed via the decay chain Ξ_b^-→J/ψΞ^-→μ^+μ^-Λ^0π^-, with Λ^0→pπ^-. A peak is observed in the distribution of the difference between the mass of the Ξ^b^-π^+ system and the sum of the masses of the Ξ_b^- and π^+, with a significance exceeding 5 standard deviations. The mass difference of the peak is 14.84±0.74(stat)±0.28(syst)  MeV. The new state most likely corresponds to the J^P=3/2^+ companion of the Ξ_b.

Higgs sector of the Next-to-Minimal Sypersymmetric Model with CP violation in superpotential and in in the soft supersymmetry breaking sector is considered. One-loop corrections to effective potential parameters were calculated and incorporated to the evaluation of neutral Higgs bosons masses.

A search for supersymmetry in the context of general gauge-mediated breaking with the lightest neutralino as the next-to-lightest supersymmetric particle and the gravitino as the lightest is presented. The data sample corresponds to an integrated luminosity of 36  pb^(-1) recorded by the CMS experiment at the LHC. The search is performed by using events containing two or more isolated photons, at least one hadronic jet, and significant missing transverse energy. No excess of events at high missing transverse energy is observed. Upper limits on the signal cross section for general gauge-mediated supersymmetry between 0.3 and 1.1 pb at the 95% confidence level are determined for a range of squark, gluino, and neutralino masses, excluding supersymmetry parameter space that was inaccessible to previous experiments.

Various technical aspects of CompHEP version 4.5 applications to the Tevatron and the LHC physics analyses and unweighted event generation are reviewed.Using the channel pp → γγ + 2 jets (irreducible background to Higgs boson production by vector boson fusion at the LHC) as an example, we describe the fine tuning of the numerical interface in CompHEP, the efficiency of simplification of flavor combinatorics, the need for parallel processing and mention briefly other recent developments.

Results are presented from a search for the rare decays B_s^0→μ^+μ^- and B^0→μ^+μ^- in pp collisions at √s=7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20  fb^(-1), respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribution gives a branching fraction B(B_s^0→μ^+μ^-)=(3.0_(-0.9)^(+1.0))×10^(-9), where the uncertainty includes both statistical and systematic contributions. An excess of B_s^0→μ^+μ^- events with respect to background is observed with a significance of 4.3 standard deviations. For the decay B^0→μ^+μ^- an upper limit of B(B^0→μ^+μ^-)<1.1×10^(-9) at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.

In the framework of the two-Higgs-doublet model with temperature-dependent effective parameters λ 1,...7 (T ) we define the four bifurcation sets which appear as a consequence of the condition det∂ 2 U i j /∂ v i ∂ v j =0 for the stability matrix.Numerical investigations of the electroweak phase transition are performed for the full MSSM parameter space (m H ± , tgβ , A t,b , µ, m Q , m U , m D ) using the temperature-dependent effective parameters λ 1 -λ 5 (T ) calculated at the one-loop in the imaginary time formalism.Four types of transitions can take place in the MSSM background field space (v 1 , v 2 ).They are different in the direction, defined by a critical angle in the (v 1 , v 2 ) plane, and in the strength, which is estimated by means of Shaposhnikov criteria v c /T c >1. Extensive regions in the (A t,b , µ) plane correspond to the strongly first order phase transition.The case of light top quark superpartner is favored, giving an acceptable configurations of surfaces for extrema of the effective potential.