P. G. Mercadante

It has recently been pointed out that viable sparticle mass spectra can be generated in Yukawa unified SO(10) supersymmetric grand unified models consistent with radiative breaking of electroweak symmetry. Model solutions are obtained only if $\tan\beta \sim 50$, $\mu <0$ and positive $D$-term contributions to scalar masses from SO(10) gauge symmetry breaking are used. In this paper, we attempt to systematize the parameter space regions where solutions are obtained. We go on to calculate the relic density of neutralinos as a function of parameter space. No regions of the parameter space explored were actually cosmologically excluded, and very reasonable relic densities were found in much of parameter space. Direct neutralino detection rates could exceed 1 event/kg/day for a $^{73}$Ge detector, for low values of GUT scale gaugino mass $m_{1/2}$. We also calculate the branching fraction for $b\to s \gamma$ decays, and find that it is beyond the 95% CL experimental limits in much, but not all, of the parameter space regions explored. However, recent claims have been made that NLO effects can reverse the signs of certain amplitudes in the $b\to s\gamma$ calculation, leading to agreement between theory and experiment in Yukawa unified SUSY models. For the Fermilab Tevatron collider, significant regions of parameter space can be explored via $b\bar{b}A$ and $b\bar{b}H$ searches. There also exist some limited regions of parameter space where a trilepton signal can be seen at TeV33. Finally, there exist significant regions of parameter space where direct detection of bottom squark pair production can be made, especially for large negative values of the GUT parameter $A_0$.

The inert 2-Higgs Doublet Model (i2HDM) is a well-motivated minimal consistent Dark Matter (DM) model, but it is rather challenging to test at the Large Hadron Collider (LHC) in the parameter space allowed by relic density and DM direct detection constraints. This is especially true when considering the latest XENON 1T data on direct DM searches which we use here to present the best current combined limit on the i2HDM parameter space. In this analysis, we present prospects to advance the exploitation of DM mono-jet signatures from the i2HDM at the LHC, by emphasising that a shape analysis of the missing transverse momentum distribution allows one to sizably improve the LHC discovery potential. As a key element of our analysis, we explore the validity of using an effective vertex, $ggH$, for the coupling of the Higgs boson to gluons using a full one-loop computation. We have found sizeable differences between the two approaches, especially in the high missing transverse momentum region, and incorporated the respective K-factors to obtain the correct kinematical distributions. As a result, we delineate a realistic search strategy and present the improved current and projected LHC sensitivity to the i2HDM parameter space.

The branching fraction for the decays of gluinos to third generation quarks is expected to be enhanced in classes of supersymmetric models where either third generation squarks are lighter than other squarks, or in mixed-higgsino dark matter models constructed so as to be in concordance with the measured density of cold dark matter. In such scenarios, gluino production events at the CERN Large Hadron Collider should be rich in top and bottom quark jets. Requiring b jets in addition to E miss should, therefore, enhance the supersymmetry signal relative to Standard Model backgrounds from V + jet, VV and QCD backgrounds (V=W,Z). We quantify the increase in the supersymmetry reach of the LHC from b-tagging in a variety of well-motivated models of supersymmetry. We also explore “top tagging” at the LHC. We find that while the efficiency for this turns out to be too low to give an increase in reach beyond that obtained via b-tagging, top tagging can indeed provide a confirmatory signal if gluinos are not too heavy. We also examine c jet tagging but find that it is not useful at the LHC. Finally, we explore the prospects for detecting the direct production of third generation squarks in models with an inverted squark mass hierarchy. This is signaled by b jets + E miss events being harder than in the Standard Model, but softer than those from the production of gluinos and heavier squarks. We find that while these events can be readily separated from the SM background (for third generation squark masses ∼300–500 GeV), the contamination from the much heavier gluinos and squarks remains formidable if these are also accessible.

We study the constraints on the vertices $W^+W^- Z\gamma$, $W^+W^-\gamma\gamma$, and $ZZ\gamma\gamma$ that can be obtained from triple-gauge-boson production at the next generation of linear $e^+e^-$ colliders operating in the $\gamma\gamma$ mode. We analyze the processes $\gamma\gamma \to W^+W^-V$ ($V=Z$, or $\gamma$) and show that these reactions increase the potential of $e^+e^-$ machines to search for anomalous four-gauge-boson interactions.

We analyze the potentiality of hadron colliders to search for large extra dimensions via the production of photon pairs. The virtual exchange of Kaluza-Klein gravitons can significantly enhance this process provided the quantum gravity scale ${(M}_{S})$ is in the TeV range. We studied in detail the subprocesses $q\overline{q}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$ and $g\stackrel{\ensuremath{\rightarrow}}{g}\ensuremath{\gamma}\ensuremath{\gamma}$ taking into account the complete standard model and graviton contributions as well as the unitarity constraints. We show that the Fermilab Tevatron run II will be able to probe ${M}_{S}$ up to 1.5--1.9 TeV at $2\ensuremath{\sigma}$ level, while the CERN LHC can extend this search to 5.3--6.7 TeV, depending on the number of extra dimensions.

Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation matter scalars, and sub-TeV third generation scalars) can ameliorate problems arising from flavor changing neutral currents, $CP$ violating phases and electric dipole moments, while at the same time satisfying conditions on naturalness. It has recently been shown that such an IMH can be generated radiatively, making use of infra-red fixed point properties of renormalization group equations given Yukawa coupling unification and suitable $GUT$ scale boundary conditions on soft SUSY breaking masses. In these models, explicit spectra cannot be obtained due to problems implementing radiative electroweak symmetry breaking (REWSB). We show that use of SO(10) $D$-term contributions to scalar masses can allow REWSB to occur, while maintaining much of the desired IMH. A somewhat improved IMH is obtained if splittings are applied only to Higgs scalar masses.

A promising way to reconcile naturalness with a decoupling solution to the SUSY flavor and $\mathrm{CP}$ problems is suggested by models with a radiatively driven inverted mass hierarchy (RIMH). The RIMH models arise naturally within the context of SUSY $\mathrm{SO}(10)$ grand unified theories. In their original form, RIMH models suffer from two problems: (1) obtaining the radiative breakdown of electroweak symmetry; and (2) generating the correct masses for third generation fermions. The first problem can be solved by the introduction of $\mathrm{SO}(10)D$-term contributions to scalar masses. We show that correct fermion masses can indeed be obtained, but at the cost of limiting the magnitude of the hierarchy that can be generated. We go on to compute predictions for the neutralino relic density as well as for the rate for the decay $\stackrel{\ensuremath{\rightarrow}}{b}s\ensuremath{\gamma},$ and show that these yield significant constraints on model parameter space. We show that only a tiny corner of model parameter space is accessible to Fermilab Tevatron searches, assuming an integrated luminosity of 25 ${\mathrm{fb}}^{\ensuremath{-}1}.$ We also quantify the reach of the CERN LHC collider for this class of models, and find values of ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}\ensuremath{\sim}1600$ GeV to be accessible assuming just 10 ${\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity. In an appendix, we list the two loop renormalization group equations for the MSSM plus right handed neutrino model that we have used in our analysis.

Assuming that supersymmetry is realized with parameters in the hyperbolic branch/focus point region of the minimal supergravity model, we show that by searching for $\mathrm{\text{multijet}}+{E}_{T}^{\mathrm{miss}}$ events with tagged $b$ jets the reach of experiments at the LHC may be extended by as much as 20% from current projections. The reason for this is that gluino decays to third generation quarks are enhanced because the lightest neutralino has substantial Higgsino components. Although we were motivated to perform this analysis because the hyperbolic branch/focus point region is compatible with the recent determination of the relic density of cold dark matter, our considerations may well have a wider applicability since decays of gluinos to third generation quarks are favored in a wide variety of models.

We examine signals for sparticle production at the Fermilab Tevatron within the framework of gauge-mediated supersymmetry breaking models for four different model lines, each of which leads to qualitatively different signatures. We identify cuts to enhance the signal above standard model backgrounds, and use ISAJET to evaluate the supersymmetry reach of experiments at the Fermilab Main Injector and at the proposed TeV33. For the model lines that we have examined, we find that the reach is at least as large, and frequently larger, than in the minimal supergravity framework. For two of these model lines, we find that the ability to identify b-quarks and $\ensuremath{\tau}$-leptons with high efficiency and purity is essential for the detection of the signal.

We examine signals for sparticle production at the CERN Large Hadron Collider (LHC) within the framework of gauge mediated supersymmetry breaking models with a low SUSY breaking scale for four different model lines, each of which leads to qualitatively different signatures. We first examine the reach of the LHC via the canonical ${E}_{T}$ and multilepton channels that have been advocated within the MSUGRA framework. Next, we examine special features of each of these model lines that could serve to further enhance the SUSY signal over standard model backgrounds. We use ISAJET to evaluate the SUSY reach of experiments at the LHC. We find that the SUSY reach, measured in terms of ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}},$ is at least as large, and sometimes larger, than in the MSUGRA framework. In the best case of the co-NLSP scenario, the reach extends to ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}&gt;~3$ TeV, assuming 10 ${\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity.

We study the production of composite scalar leptoquarks in eγ colliders, and we show that an e+e− machine operating in its eγ mode is the best way to look for these particles in e+e− collisions, due to the hadronic content of the photon.

We analyze the low energy features of a supersymmetric standard model where the anomaly-induced contributions to the soft parameters are dominant in a scenario with bilinear R-parity violation. This class of models leads to mixings between the standard model particles and supersymmetric ones which change the low energy phenomenology and searches for supersymmetry. In addition, R-parity violation interactions give rise to small neutrino masses which we show to be consistent with the present observations.

We present an analysis of the discovery reach for supersymmetric particles at the upgraded Tevatron collider, assuming that SUSY breaking results in universal soft breaking parameters at the grand unification scale, and that the lightest supersymmetric particle is stable and neutral. We first present a review of the literature, including the issues of unification, renormalization group evolution of the supersymmetry breaking parameters and the effect of radiative corrections on the effective low energy couplings and masses of the theory. We consider the experimental bounds coming from direct searches and those arising indirectly from precision data, cosmology and the requirement of vacuum stability. The issues of flavor and CP-violation are also addressed. The main subject of this study is to update sparticle production cross sections, make improved estimates of backgrounds, delineate the discovery reach in the supergravity framework, and examine how this might vary when assumptions about universality of soft breaking parameters are relaxed. With 30 fb$^{-1}$ luminosity and one detector, charginos and neutralinos, as well as third generation squarks, can be seen if their masses are not larger than 200-250 GeV, while first and second generation squarks and gluinos can be discovered if their masses do not significantly exceed 400 GeV. We conclude that there are important and exciting physics opportunities at the Tevatron collider, which will be significantly enhanced by continued Tevatron operation beyond the first phase of Run II.

Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first and second generation matter scalars, and sub-TeV third generation and Higgs scalars) have been proposed to ameliorate phenomenological problems arising from flavor changing neutral currents and $\mathrm{CP}$ violating processes, while satisfying conditions of naturalness. Models with an IMH already in place at the grand unified theory (GUT) scale have been shown to be constrained in that, for many model parameter choices, the top squark squared mass is driven to negative values. We delineate regions of parameter space where viable models with a GUT scale IMH can be generated. We find that larger values of GUT scale first and second generation scalar masses act to suppress third generation scalars, leading to acceptable solutions if GUT scale gaugino masses are large enough. We show examples of viable models and comment on their characteristic features. For example, in these models the gluino mass is bounded from below, and effectively decouples, whilst third generation scalars remain at sub-TeV levels. While possibly fulfilling criteria of naturalness, these models present challenges for detection at future $\mathrm{pp}$ and ${e}^{+}{e}^{\ensuremath{-}}$ collider experiments.

We performed an analysis on the detection of a long-lived slepton at a linear collider with $\sqrt{s}=500 \mathrm{GeV}.$ In gauge-mediated symmetry breaking models a long-lived NLSP is predicted for a large value of the supersymmetry breaking scale $\sqrt{F}.$ Furthermore in a large portion of the parameter space this particle is a stau. Such heavy charged particles will leave a track in the tracking volume and hit the muonic detector. In order to disentangle this signal from the muon background, we explore the kinematics and particle identification tools: a time-of-flight device, $dE/dX,$ and Cherenkov devices. We show that a linear collider will be able to detect long-lived staus with masses up to the kinematical limit of the machine. We also present our estimation of the sensitivity to the stau lifetime.

We evaluate the supersymmetry reach of the Large Hadron Collider within the gauge-mediated low energy supersymmetry breaking framework, assuming that a neutralino is the second lightest sparticle and that it decays promptly into a gravitino which escapes detection. We find that the maximum reach is obtained via a search for inclusive γγ+E/T events coming dominantly from chargino and neutralino production. Assuming an integrated luminosity of 10 fb−1, we find that LHC experiments will be able to probe values of the model parameter Λ≲400 TeV, corresponding to mg̃≤2.8 TeV. A measure of the model parameter Λ may be possible from the photon pT spectrum.

The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Depending on the supersymmetry breaking scale, these decays can occur promptly or on a scale comparable to or larger than the size of a detector. A systematic analysis based on a classification in terms of the identity of the NLSP and its decay length is presented. The various scenarios are discussed in terms of signatures and possible event selection criteria. The Run II and beyond discovery and exclusion reaches, including the effects of background, are detailed for the most compelling cases. In addition to standard event selection criteria based on missing energy and photons, leptons, jets, taus, tagged b-jets, or reconstructed Z-bosons, more exotic signals of metastable NLSPs such as displaced photons, large negative impact parameter tracks, kink tracks, both opposite and same-sign highly ionizing tracks, time of flight measurements, charge-changing tracks, charge-exchange tracks, and same-sign di-top events are investigated. The interesting possibility of observing a Higgs boson signal in events that are efficiently ''tagged'' by the unique signatures of low-scale supersymmetry breaking is also considered.

We perform a detailed analysis of the potentiality of the CERN Large Hadron Collider to study the single production of leptoquarks via $p\stackrel{\ensuremath{\rightarrow}}{p}{e}^{\ifmmode\pm\else\textpm\fi{}}\stackrel{\ensuremath{\rightarrow}}{q}$ leptoquark $\ensuremath{\rightarrow}{e}^{\ifmmode\pm\else\textpm\fi{}}q,$ with ${e}^{\ifmmode\pm\else\textpm\fi{}}$ generated by the splitting of photons radiated by the protons. Working with the most general $\mathrm{SU}{(2)}_{L}\ensuremath{\bigotimes}\mathrm{U}{(1)}_{Y}$ invariant effective Lagrangian for scalar and vector leptoquarks, we analyze in detail the leptoquark signals and backgrounds that lead to a final state containing an ${e}^{\ifmmode\pm\else\textpm\fi{}}$ and a hard jet with approximately balanced transverse momenta. Our results indicate that the LHC will be able to discover leptoquarks with masses up to 2--3 TeV, depending on their type, for Yukawa couplings of the order of the electromagnetic one.

We analyze the potential of the CERN Large Hadron Collider on the reach of the focus point (FP) region in the mSUGRA parameter space.This region, consistent with WMAP results, is characterized by multi-TeV masses for the superpartners of quarks and leptons and relatively light charginos and neutralinos.Moreover, since the LSP has a substantial higgsino component, it is expected that the gluino decays predominantly to third generation quarks, producing a final state with multiple hard b jets.Analyzing events with E T + n jets + tagged b-jets, we show that the LHC reach can improve as much as 20% from current projections.Although we performed the analysis specifically for the FP region, the b-tagging should be important to enhance the SUSY signal in a variety of models where a relatively light gluino decays mostly to third generation quarks.

Because of their Yukawa interactions, third generation squarks may be substantially lighter than those of the first two generations. Assuming that ${b}_{1}\ensuremath{\rightarrow}b{Z}_{1}$ and ${Z}_{1}$ escapes experimental detection, we show that experiments at the Main Injector upgrade (integrated luminosity of $2{\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$) of the Fermilab Tevatron should be sensitive to $b$-squark masses up to 210 GeV for ${m}_{{Z}_{1}}&lt;~120\mathrm{GeV}.$ For integrated luminosities of $10{\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$ $(25{\mathrm{fb}}^{\mathrm{\ensuremath{-}}1})$ the bottom squark mass reach increases by 20 GeV (35 GeV). If the channel ${b}_{1}\ensuremath{\rightarrow}b{Z}_{2}$ is also accessible, the reach becomes model dependent and may be degraded relative to the case where only the decay to ${Z}_{1}$ is allowed. In models with gaugino mass unification and \ensuremath{\mu} much larger than gaugino masses, we argue that this degradation is unlikely to be larger than 30--40 GeV.

We analyze the potential of the next generation of ${e}^{+}{e}^{\ensuremath{-}}$ linear colliders to search for large extra dimensions via the production of fermion pairs in association with Kaluza-Klein gravitons $(G),$ i.e., ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}f\overline{f}G.$ This process leads to a final state exhibiting a significant amount of missing energy in addition to acoplanar lepton or jet pairs. We study in detail this reaction using the full tree level contributions due to the graviton emission and the standard model backgrounds. After choosing the cuts to enhance the signal, we show that a linear collider with a center-of-mass energy of 500 GeV will be able to probe quantum gravity scales from 0.96 (0.86) up to 4.1 (3.3) TeV at a 2 $(5)\ensuremath{\sigma}$ level, depending on the number of extra dimensions.

We show that a supersymmetric standard model exhibiting anomaly mediated supersymmetry breaking can generate naturally the observed neutrino mass spectrum as well mixings when we include bilinear $R$-parity violation interactions. In this model, one of the neutrinos gets its mass due to the tree-level mixing with the neutralinos induced by the $R$-parity violating interactions while the other two neutrinos acquire their masses due to radiative corrections. One interesting feature of this scenario is that the lightest supersymmetric particle is unstable and its decay can be observed at high energy colliders, providing a falsifiable test of the model.

We study the production of three gauge bosons at the next generation of linear $e^+e^-$ colliders operating in the $\gamma\gamma$ mode. The processes $\gamma\gamma \rightarrow W^+W^-V$ ($V=Z^0$, or $\gamma$) can provide direct information about the quartic gauge-boson couplings. We analyze the total cross section as well as several dynamical distributions of the final state particles including the effect of kinematical cuts. We find out that a linear $e^+e^-$ machine operating in the $\gamma\gamma$ mode will produce 5--10 times more three-gauge-boson states compared to the standard $e^+e^-$ mode at high energies.

It is generally accepted that the LHC is the accelerator facility at which weak scale supersymmetry will either be discovered or definitely excluded.I give a brief introduction to weak scale supersymmetry presenting the general argument that limit the supersymmetrical spectrum to be below TeV energies.We will see that the LHC is able to search for supersymmetry in several of its realization far above the expected spectrum masses.However, in the last section we will see some well motivated scenarios where supersymmetric sparticles might be very heavy, thus beyond the LHC reach.Such scenarios deserve a more detailed study to push the LHC reach.

Neste trabalho são investigados dois aspectos relacionados à experiência da Universidade Federal do ABC (UFABC) e da Universidade de São Paulo (USP) durante a realização do evento CERN Masterclasses Hands on Particle Physics, que envolveu estudantes tanto de Ensino Médio quanto de cursos de Licenciatura em Física. O primeiro aspecto considerado para este estudo refere-se ao perfil motivacional dos participantes, quais suas expectativas e interesses no evento. O segundo busca identificar, relativamente aos conteúdos conceituais e técnicos tratados no evento, quais os principais ganhos e dificuldades percebidas pelos participantes. A partir destas informações, analisamos o papel do evento como instrumento de comunicação científica. Para isso, tomamos como referencial teórico o modelo contemporâneo de comunicação científica de Burns, O’Connor e Stocklmayer, o qual entende a comunicação científica como um conjunto de etapas visando levar a Literacia Científica. À luz dos resultados encontrados, foi possível constatar que as ações do evento estão produzindo em seus participantes processos conducentes tanto a uma Consciência quanto Compreensão Públicas da Ciência. Estes processos operam de forma estrutural no desenvolvimento de uma cultura científica, a qual constitui-se, ao mesmo tempo, em causa e conseqüência do processo que leva ao ideal de Literacia Científica. Desta perspectiva, eventuais ajustes no desenho e composição das atividades do evento podem ser melhor subsidiadas, assim como questões relativas às contribuições sócio-educativas e culturais proporcionadas por iniciativas dessa natureza.

We calculate top pair production and decay at the Tevatron pp collider, with the emission of an extra gluon, and study the corresponding W + 5 jet top signals including full spin correlations in the W → ℓv leptonic and W → jj hadronic decays. We study the feasibility of reconstructing W + 5 jet top events with a single b-tag, including realistic energy resolution. Our suggested basic procedure based on kinematic fitting achieves about 74% reconstruction efficiency, with 74% of the reconstructed events correctly classified (purity); this improves to 82% efficiency with 77% purity in double-b-tagged events. We suggest possible refinements, based on virtuality criteria, that give higher purity at the cost of lower reconstruction efficiency.

We analyze the potential of the next generation linear collider (LC) to study the long-lived τ superpartner in the context of GMSB models. Depending on the parameter space of these models, the τ̃ is the next lightest superparticle and may travel some visible distance before decaying to τ and gravitino. From the decay product of the τ, it is possible to measure its polarization, and consequently determine the stau mixing angle at the decay level.

The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Depending on the supersymmetry breaking scale, these decays can occur promptly or on a scale comparable to or larger than the size of a detector. A systematic analysis based on a classification in terms of the identity of the NLSP and its decay length is presented. The various scenarios are discussed in terms of signatures and possible event selection criteria. The Run II and beyond discovery and exclusion reaches, including the effects of background, are detailed for the most compelling cases. In addition to standard event selection criteria based on missing energy and photons, leptons, jets, taus, tagged b-jets, or reconstructed Z-bosons, more exotic signals of metastable NLSPs such as displaced photons, large negative impact parameter tracks, kink tracks, both opposite and same-sign highly ionizing tracks, time of flight measurements, charge-changing tracks, charge-exchange tracks, and same-sign di-top events are investigated. The interesting possibility of observing a Higgs boson signal in events that are efficiently "tagged" by the unique signatures of low-scale supersymmetry breaking is also considered.

We performed an analysis on the detection of a long lived stau at a linear collider with $\sqrt{s}=500$ GeV. In GMSB models a long lived NLSP is predicted for large value of the supersymmetry breaking scale F. Furthermore in a large portion of the parameter space this particle is a stau. Such heavy charged particles will leave a track in the tracking volume and hit the muon detector. In order to disentangle this signal from the muon background we explore kinematics and particle identification tools: time of flight device, dE/dX and Cerenkov devices.

We study the constraints on the anomalous coupling $g^Z_5$ that can be obtained from the analysis of the reaction $\gamma\gamma \rightarrow W^+ W^- Z$ at future linear $e^+e^-$ colliders. We find out that a $0.5$ ($1$) TeV $e^+e^-$ collider operating in the $\gamma\gamma$ mode can probe values of $g_5^Z$ of the order of $0.15$ ($4.5 \times 10^{-2}$) for an integrated luminosity of $10$ fb$^{-1}$. This shows that the ability to search for this anomalous interaction of the $\gamma\gamma$ mode is better than the one of the usual $e^+e^-$ mode, and it is similar to the ability of the $e\gamma$ mode.