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C. Verzegnassi

Publications and source records attributed to C. Verzegnassi.

65 records · Page 4Linked to original sources

Anomalous $Z'$ effects in the WW channel at $LC 2000$

We consider the virtual signals of a $Z'$ of very general type in the process $e^+e^-\to W^+W^-$ at a future linear $e^+e^-$ collider of 2000 GeV c.m. energy ($LC2000$). We show that possible deviations from the SM predictions in this channel are related to similar deviations in the purely leptonic one in a way that is only characteristic of this $Z'$ model, and not in general of possible competitor models with anomalous gauge couplings.

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Hadrophilic Z':a bridge from LEP1, SLC and CDF to LEP2 anomalies

In order to explain possible departures from the Standard Model predictions for $b\bar b$ and $c\bar c$ production at $Z$ peak, we propose the existence of a $Z'$ vector boson with enhanced couplings to quarks. We first show that this proposal is perfectly consistent with the full set of LEP1/SLC results. In particular, $Z-Z'$ mixing effects naturally explain the fact that $Γ_b$ and $Γ_c$ deviate from the SM in opposite directions. We then show that there is a predicted range for enhanced $Z'q\bar q$ couplings which explains, for a precise and interesting range of $Z'$ masses, the excess of dijet events seen at CDF. A $Z'$ with such couplings and mass would produce clean observable effects in $b\bar b$ and in total hadronic production at LEP2.

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Triple Gauge Boson Couplings

We present the results obtained by the "Triple Gauge Couplings" working group during the LEP2 Workshop (1994-1995). The report concentrates on the measurement of $WWγ$ and $WWZ$ couplings in $e^-e^+\to W^-W^+$ or, more generally, four-fermion production at LEP2. In addition the detection of new interactions in the bosonic sector via other production channels is discussed.

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Z' Reservation at LEP2

We consider the possibility that one extra $Z\equiv Z'$ exists with arbitrary mass and fermion couplings that do not violate (charged) lepton universality. We show that, in such a situation, a functional relationship is generated between the \underline{deviations} from the SM values of three leptonic observables of two-fermion production at future $e^+e^-$ colliders that is completely independent of the values of the $Z'$ mass and couplings. This selects a certain region in the 3-d space of the deviations that is \underline{characteristic} of the model ($Z'$ "reservation"). As a specific and relevant example, we show the picture that would emerge at LEP2 under realistic experimental conditions.

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Universal and Non Universal New Physics Effects in a General Four-fermion Process: a Z-peak Subtracted Approach

We calculate, using a Z-peak subtracted representation of four-fermion processes previously illustrated for the case of electron-positron annihilation into charged lepton-antilepton, the corresponding expressions of the new physics contributions for the case of final quark-antiquark states, allowing the possibility of both universal and non universal effects. We show that, in each case, the main result obtained for the final lepton channel can be generalized, so that every experimentally measurable quantity can be expressed in terms of input parameters \underline{measured} on Z resonance, of $α(0)$ and of a small number of subtracted one loop expressions. Some examples of models are considered for several c.m. energy values, showing that remarkable simplifications are often introduced by our approach. In particular, for the case of a dimension-six lagrangian with anomalous gauge couplings, the same reduced number of parameters that would affect the observables of final leptonic states are essentially retained when one moves to final hadronic states. This leads to great simplifications in the elaboration of constraints and, as a gratifying byproduct, to the possibility of making the signal from these models clearly distinguishable from those from other (both universal and non universal) competitors.

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Anomalous $Z'$ effects in the WW channel at NLC

We consider the virtual signals of a $Z'$ of very general type in the process $e^+e^-\to W^+W^-$ at a future linear collider (NLC). We show that possible deviations from the SM predictions in this channel are related to similar deviations in the purely leptonic one in a way that is only characteristic of this $Z'$ model, and not in general of possible competitor models with anomalous gauge couplings.

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Residual heavy quark and boson interactions: the role of the $Zb\bar b$ vertex

We establish the most general parametrization of the new physics tested by present precision measurements and possibly responsible for any deviation of the $Z\to b \bar b $ amplitude from its Standard Model result, under the assumption that it is CP symmetric and is induced by degrees of freedom which are too heavy to be ~directly produced at the future Colliders. This is achieved by writing the complete list of the $SU(3)_c\times SU(2) \times U(1) $ gauge invariant and CP symmetric $dim=6$ operators, involving only quarks of the third family and/or bosons. The quark ~containing operators are divided into two classes, according to whether they involve the $t_R$ field or not. Each class contains 14 quark operators. We then proceed to derive the constraints from present precision measurements, on the first class of the 14 $t_R$ involving operators. We show that the $Zb \bar b$ vertex plays a fundamental role to discriminate not only between these operators, but also between this whole scheme and an alternative one like \eg\@ an MSSM description with light chargino and neutral Higgs.

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A Probe of New Resonant Structures with Four Fermion Processes at a 1 TeV $e^+e^-$ Collider

Oblique contributions from vector particles that are strongly coupled to the known gauge bosons are calculated for the case of various observables at a 1 TeV $e^+e^-$ collider. Constraints provided by LEP 1 results are taken into account in a model-independent way through a dispersion relation technique. Depending on the assumed theoretical properties, mass limits of several TeV should be observable.

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Information and Discrimination from b Quark Production on Z Resonance

We introduce and define operatively in a model independent way a new ``heavy" b-vertexparameter, $η_b$, that can be derived from the measurement of a special polarization asymmetry for production of b-quarks on Z resonance. We show that the combination of the measurement of $η_b$ with that of a second and previously defined ``heavy" b-vertex parameter $δ_{bV}$ can discriminate a number of models of New Physics that remain associated to different ``trajectories" in the plane of the variations of the two parameters. This is shown in particular for some popular SUSY and technicolor-type models. In general, this discrimination is possible if a measurement of \underline{both} parameters is performed.

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Four Fermion Processes at Future $e^+e^-$ Colliders as a Probe of New Resonant Structures

Possible oblique effects from vector particles that are strongly coupled to the known gauge bosons are calculated for the case of final hadronic states produced at future $e^+e^-$ colliders, using a formalism that was recently proposed and that exploits the information and the constraints provided by LEP 1 results. Combining the hadronic channels with the previously analysed leptonic ones we derive improved limits for the masses of the resonances that,in technicolour-like cases, would range from one to two TeV for a 500 GeV linear collider, depending on the assumed theoretical constraints.

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One Loop Corrections To The Lightest Higgs Mass In The Minimal $η$ Model

We have evaluated the one loop correction to the bound on the lightest Higgs mass valid in the minimal, $ E_{6}$ based, supersymmetric $ η$ model. Under the assumption that the theory remains perturbative up to the $10^{16}$ GeV scale, we derive a conservative bound that decreases with the top mass for $M_t \leq 2 M_W$ and varies from $ \sim 160$ GeV to $\sim 145$ GeV when $90 \leq M_t \leq 200$ GeV.

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