Polarized observables to probe Z' at the e+e- linear collider

We study the sensitivity to the Z' couplings of the processes $e^+e^-\to l^+l^-,\bar{b}b$ and $\bar{c}c$ at the linear collider with $\sqrt{s}=500 GeV$ with initial beam polarization, for typical extended model examples. To this aim, we use suitable integrated, polarized, observables directly related to the helicity cross sections that carry information on the individual Z' chiral couplings to fermions. We discuss the derivation of separate, model-independent limits on the couplings in the case of no observed indirect Z' signal within the expected experimental accuracy. In the hypothesis that such signals were, indeed, observed we assess the expected accuracy on the numerical determination of such couplings and the consequent range of Z' masses where the individual models can be distinguished from each other as the source of the effect.Comment: 14 pages, 4 figures, LaTe

Contact interaction probes at the Linear Collider with polarized electron and positron beams

For contact-interaction searches at the Linear Collider, we discuss the advantages of polarizing both the electron and the positron beams as compared with polarizing only the electron beam. In particular, for the processes e^+e^-\to \mu^+\mu^-, \tau^+\tau^-, b\bar{b} and c\bar{c} at a future e^+e^- collider with \sqrt{s}=0.5 TeV we derive model-independent bounds on the four-fermion contact interaction parameters from studies of the helicity cross sections.Comment: 1+15 pages, LaTeX2e, including 7 figure

Updated constraints on Z′ and W′ bosons decaying into bosonic and leptonic final states using the run 2 ATLAS data

The full ATLAS run 2 dataset with a time-integrated luminosity of 139  fb−1 in the diboson and dilepton channels is used to probe benchmark models with extended gauge sectors: the E6-motivated grand unification models, the left-right symmetric model, and the sequential standard model [extended gauge model (EGM)]. These all predict neutral Z′ vector bosons, decaying into lepton pairs ℓℓ or into electroweak gauge boson pairs WW, where one W in turn decays semileptonically. The 95% C.L. exclusion limits on the Z′ resonance production cross section times the branching ratio to electroweak gauge boson pairs and to lepton pairs in the mass range of ∼1 to 6 TeV are converted to constraints on the Z−Z′ mixing parameter and the heavy resonance mass. We present exclusion regions on the parameter space of the Z′ which are significantly extended compared to those obtained from the previous analyses performed with LHC data collected at 7 and 8 TeV in run 1 as well as at 13 TeV in run 2 at a time-integrated luminosity of 36.1  fb−1 and are the most stringent bounds to date. Also presented, from a similar analysis of electrically charged W′ bosons arising in the EGM, which can decay through W′→WZ and W′→ℓν, are limits on the W−W′ mixing parameter and the charged W′ vector boson mass.publishedVersio

Model-independent limits on four-fermion contact interactions at LC with polarization

Fermion compositeness, and other types of new physics that can be described by the exchange of very massive particles, can manifest themselves as the result of an effective four-fermion contact interaction. In the case of the processes $e^+e^-\to \mu^+\mu^-,\tau^+\tau^-,\bar{b}b$ and $\bar{c}c$ at future $e^+e^-$ colliders with $\sqrt{s}=0.5-1$ TeV, we examine the sensitivity to four-fermion contact interactions of two new integrated observables, $\sigma_+$ and $\sigma_-$, conveniently defined for such kind of analysis. We find that, if longitudinal polarization of the electron beam were available, these observables would offer the opportunity to separate the helicity cross sections and, in this way, to derive model-independent bounds on the relevant parameters.Comment: 13 pages, LaTe

Optimal observables for new-physics search at LEP2

New observables \sigma_\pm for the process e^+e^-\to\mu^+\mu^- allow one to get more direct information on additional Z' boson effects than what is obtained from the canonical ones, \sigma and A_{FB}. Their deviations from the Standard Model predictions have very specific energy dependences, which are precisely determined by SM parameters. At energies varying from TRISTAN to LEP2, one can uniquely predict the signs of \Delta\sigma_{\pm} induced by a Z' as well as the locations of their extrema and zeros. This unambiguous energy correlation could be quite useful in distinguishing effects due to Z' exchange from those caused by other new physics sources. Furthermore, there are two energy points, \sqrt{s_{+}}\simeq 78 GeV and \sqrt{s_{-}}\simeq 113 GeV, where the SM quantities \sigma_\pm^{SM} as well as the deviations \Delta\sigma_{\pm} attain their minimum values or vanish. These points could be very favourable for a search for new physics beyond the SM and beyond Z' effects.Comment: LaTeX2e + 7 eps figures. References added, version to appear in Phys. Lett.

New physics signatures at a Linear Collider: model-independent analysis from `conventional' polarized observables

We discuss four-fermion contact-interaction searches in the processes e^+e^-\to\mu^+\mu^-, c{\bar c} and b{\bar b} at a future e^+e^- Linear Collider with c.m. energy \sqrt{s}=0.5 TeV and with both beams longitudinally polarized. Our analysis is based on the measurements of familiar polarized observables such as the total cross section and the forward-backward/left-right asymmetries, and accounts for the general set of contact interaction couplings as independent, non-zero, parameters thus avoiding simplifying, model-dependent, assumptions. We derive the corresponding model-independent constraints on the above-mentioned coupling constants, and evaluate the corresponding reach at the Linear Collider, emphasizing the role of beam polarization. We compare the results with a model-dependent procedure where only one coupling is varied at a time.Comment: 13 pages, including 3 figure

Surface waves in mesh synthetic photonic lattices

Eigenmodes and dispersion curves in different configurations of synthetic photonic lattices are studied numerically. Eigenmodes localized on borders between areas with different optical potential are found. Stability of these eigenmodes against potential disturbances of different type is studied

Role of beam polarization in the determination of WWγWW\gamma and WWZWWZ couplings from e+e−→W+W−e^+e^-\to W^+W^-

We evaluate the constraints on anomalous trilinear gauge-boson couplings that can be obtained from the study of electron-positron annihilation into $W$ pairs at a facility with either the electron beam longitudinally polarized or both electron and positron beams transversely polarized. The energy ranges considered in the analysis are the ones relevant to the next-linear collider and to LEP~200. We discuss the possibilities of a model independent analysis of the general $CP$ conserving anomalous effective Lagrangian, as well as its restriction to some specific models with reduced number of independent couplings. The combination of observables with initial and final state polarizations allows to separately constrain the different couplings and to improve the corresponding numerical bounds.Comment: 24 pages, LaTeX, 9 figures (available on request from the authors

Discriminating Z' from anomalous trilinear gauge coupling signatures in e+e- \to W+W- at ILC with polarized beams

New heavy neutral gauge bosons Z' are predicted by many models of physics beyond the Standard Model. It is quite possible that Z's are heavy enough to lie beyond the discovery reach of the CERN Large Hadron Collider LHC, in which case only indirect signatures of Z' exchanges may emerge at future colliders, through deviations of the measured cross sections from the Standard Model predictions. We discuss in this context the foreseeable sensitivity to Z's of W^\pm-pair production cross sections at the e^+e^- International Linear Collider (ILC), especially as regards the potential of distinguishing observable effects of the Z' from analogous ones due to competitor models with anomalous trilinear gauge couplings (AGC) that can lead to the same or similar new physics experimental signatures at the ILC. The sensitivity of the ILC for probing the Z-Z' mixing and its capability to distinguish these two new physics scenarios is substantially enhanced when the polarization of the initial beams and the produced W^\pm bosons are considered. A model independent analysis of the Z' effects in the process e^+e^- \to W^+W^- allows to differentiate the full class of vector Z' models from those with anomalous trilinear gauge couplings, with one notable exception: the sequential SM (SSM)-like models can in this process not be distinguished from anomalous gauge couplings. Results of model dependent analysis of a specific Z' are expressed in terms of discovery and identification reaches on the Z-Z' mixing angle and the Z' mass.Comment: 33 pages; v2: version to appear in EPJ

Model-independent Z' searches at modern colliders

The model-independent constraints on the Abelian Z' couplings from the LEP data are applied to estimate the Z' production in experiments at hadron colliders. The Z' contribution to the Drell-Yan process at modern hadron colliders is analyzed. The results are compared with model-dependent predictions and present experimental data from the Tevatron and the LHC. The lower bounds on the Z' mass are derived and the Z' discovery limit in the LHC experiments is found.С помощью модельно-независимых ограничений на константы связи абелевого Z'-бозона получены оценки процессов рождения Z' в экспериментах на адронных коллайдерах. Изучен вклад Z'-бозона в процесс Дрелла-Яна. Проведено сравнение полученных результатов с модельно-зависимыми предсказаниями и экспериментальными данными ускорителей Tevatron и LHC. Получена нижняя граница значения массы Z'-бозона, а также предельные значения массы, при которых Z' будет обнаружен в эксперименте LHC.За допомогою модельно-незалежних обмежень констант зв’язку абелевого Z'-бозона отримано оцінки процесів народження Z'-бозона в експериментах на гадронних колайдерах. Досліджено внесок Z' в процес Дрелла-Яна. Виконано порівняння отриманих результатів з модельно-залежними результатами та експериментальними даними прискорювачів Tevatron та LHC. Отримана нижня границя маси Z'-бозона, а також граничні значення маси, при яких Z'-бозон буде знайдено в експериментах LHC