100 research outputs found
Polarized observables to probe Z' at the e+e- linear collider
We study the sensitivity to the Z' couplings of the processes and at the linear collider with
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 and at future
colliders with TeV, we examine the sensitivity to
four-fermion contact interactions of two new integrated observables,
and , 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 and couplings from
We evaluate the constraints on anomalous trilinear gauge-boson couplings that
can be obtained from the study of electron-positron annihilation into 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 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
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