Narrow Results

We briefly review some recent Cold Dark Matter (CDM) models. Our main focus are charge symmetric models of WIMPs which are not the standard SUSY LSP's (Lightest Supersymmetric Partners). We indicate which experiments are most sensitive to certain aspects of the models. In particular, we discuss the manifestations of the new models in neutrino telescopes and other setups. We also discuss some direct detection experiments and comment on measuring the direction of recoil ions — which is correlated with the direction of the incoming WIMP. This could yield daily variations providing along with the annual modulation signatures for CDM.

Some theories of particle physics are so compelling that it is worth doing a comprehensive and systematic set of experimental searches to see if they are realized in nature. Supersymmetry is one such theory. This review focuses on the motivation for a broad set of cosmology-inspired search strategies at the Tevatron and on their implementation and results at the Collider Detector at Fermilab (CDF) with the first few fb^-1 of integrated luminosity of data.

Compressed mass spectra are generally more difficult to identify than spectra with large splittings. In particular, gluino pair production with four high energy top or bottom quarks leaves a striking signature in a detector. However, if any of the mass splittings are compressed, the power of traditional techniques may deteriorate. Searches for direct stop/sbottom pair production can be recast as searches for gluinos in order to extend the sensitivitity. As a demonstration, we show that for $\tilde{g}\to t{\tilde{t}}_1$ and $m_{{\tilde{t}}_1}~m_{{\tilde{\chi }}_1^0}$, limits on the stop mass at 8 TeV can be extended by least 300 GeV for a 1.1 TeV gluino using a $pp\to {\tilde{t}}_1{\tilde{t}}_1$ search. At 13 TeV, the effective cross-section for the gluino mediated process is twice the direct stop pair production cross-section, suggesting that direct stop searches could be sensitive to discover new physics earlier than expected.

We have calculated the high spin parton splitting amplitudes postulating the Yangian symmetry of the scattering amplitudes for tensor gluons. The resulting splitting amplitudes coincide with the earlier calculations, which were based on the BCFW recursion relations. The resulting formula unifies all known splitting probabilities found earlier in gauge field theories. It describes splitting probabilities for integer and half-integer spin particles. We also checked that the splitting probabilities fulfil the generalised Kounnas–Ross ${𝒩}$ = 1 supersymmetry relations hinting to the fact that the underlying theory can be formulated in an explicit supersymmetric manner.

I present a unified approach to calculating the next-to-next-to-leading order (NNLO) soft and virtual QCD corrections to cross-sections for electroweak, Higgs, QCD, and SUSY processes. I derive master formulas that can be used for any of these processes in hadron–hadron and lepton–hadron collisions. The formulas are based on a unified threshold resummation formalism and can be applied to both total and differential cross-sections for processes with either simple or complex color flows and for various factorization schemes and kinematics. As a test of the formalism, I rederive known NNLO results for Drell–Yan and Higgs production, deep inelastic scattering, and W⁺γ production, and I obtain expressions for several two-loop anomalous dimensions and other quantities needed in next-to-next-to-leading-logarithm (NNLL) resummations. I also present new results for the production of supersymmetric charged Higgs bosons; massive electroweak vector bosons; photons; heavy quarks in lepton–hadron and hadron–hadron collisions and in flavor-changing neutral current processes; jets; and squarks and gluinos. The NNLO soft and virtual corrections are often dominant, especially near threshold, and they reduce the scale dependence of the cross-section. Thus, a unified approach to these corrections is important in the search for new physics at present and future colliders.

The CDMS collaboration has completed its first WIMP search run at the Soudan Underground Laboratory. This run consisted of operating 4 Ge and 2 Si ZIP detectors for 52.6 live days and yields a post-analysis WIMP exposure of 19.4 kg-d for recoil energies between 10-100 keV. Analysis of this data sets the world's lowest exclusion limits on the coherent WIMP-nucleon scalar cross-section for all WIMP masses above 15 GeV/c².

We present the results of a search for new particles with long lifetime that decay to a Z⁰ boson. A long-lived parent of the Z⁰ is predicted by several models in addition to being an experimentally clean channel. We vertex dimuons with invariant mass near the Z⁰ peak and study the decay length distribution. No evidence of a long-lived component is found, and cross-section limits are presented on a fourth generation quark model.

The Collider Detector at Fermilab Collaboration has analyzed events with two photons in the central detector. The cross section is measured and compared to theoretical models. The diphoton mass spectrum is searched for anomalous narrow peaks and a search for gauge–mediated SUSY is performed with events with two photons and missing E_t.

A brief review of searches for physics beyond the Standard Model using single- and multi-photon events with missing energy at LEP is given here. These include searches for supersymmetry, large extra dimensions, and anomalous neutrino production. Recent results from all four LEP experiments are presented, including improved limits on the new scale of gravity for models with large extra dimensions and the most precise direct measurement of the number of light neutrino species. Status and prospects of the LEP combined searches are also discussed.

The apparent unification of gauge couplings around 10¹⁶ GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model (SM). In this contribution a new analysis, using the latest experimental data, is performed. The strong coupling α_s emerges as the key factor for evaluating the results of the fits, as the experimental and theoretical uncertainties in its measurements are substantially higher than for the electromagnetic and weak couplings. The present analysis pays special attention to numerical and statistical details. The results, combined with the current limits on the supersymmetric particle masses, favor a value for the SUSY scale ≲ 150 GeV and for α_s = 0.118 - 0.119.

We studied single Higgs boson production in γγ collisions proceeding via the hadronic content of the photon. For SM Higgs masses of current theoretical interest, the resolved photon contributions are non-negligible in precision cross section measurements. We found that production of the heavier Higgs bosons H⁰ and A⁰ of the MSSM can probe regions of the SUSY parameter space that will complement other measurements. Finally, we showed that associated tH^± production in γγ collisions can be used to make an accurate determination of tan β for low and high tan β by precision measurements of the γγ → H^±t + X cross section.

We discuss the ATLAS physics programme for the first year of LHC operation. The layout of the initial (staged) detector will be described, as well as the impact of staging on the physics reach. The main data samples and strategies which will be used to calibrate, align and understand the detector response will be presented. Finally, the physics channels which will be addressed in the first months of operation will be discussed. These include a low-mass Higgs boson, for which a striking signal might be observed after only a few months of data taking. The impact of a realistic non-optimal detector performance, as expected at the beginning, will be illustrated in some cases.

Various aspects of the Higgs boson phenomenology of the Minimal Supersymmetric Standard Model (MSSM) are reviewed. Emphasis is put on the effects of higher-order corrections. The masses and couplings are discussed in the MSSM with real and complex parameters. Higher-order corrections to Higgs boson production channels at a prospective e⁺e^- linear collider are investigated. Corrections to Higgs boson decays to SM fermions and their phenomenological implications for hadron and lepton colliders are explored.

Three-body cluster-model calculations are performed for the new types of big-bang nucleosynthesis (BBN) reactions that are calalyzed by a supersymmetric (SUSY) particle stau, a scalar partner of the tau lepton. If a stau has a lifetime ≳ 10³s, it would capture a light element previously synthesized in standard BBN and form a Coulombic bound state. The bound state, an exotic atom, is expected to induce various reactions, such as (αX^-) + d → ⁶Li + X^-, in which a negatively charged stau (denoted as X^-) works as a catalyzer. Recent literature papers have claimed that some of these stau-catalyzed reactions have significantly large cross sections so that inclusion of the reactions into the BBN network calculation can change drastically abundances of some elements, giving not only a solution to the ⁶Li-⁷Li problem (calculated underproduction of ⁶Li by ~ 1000 times and overproduction of ⁷Li+⁷Be by ~ 3 times) but also a constraint on the lifetime and the primordial abundance of the elementary particle stau. However, most of these literature calculations of the reaction cross sections were made assuming too naive models or approximations that are unsuitable for those complicated low-energy nuclear reactions. We use a few-body calculational method developed by the authors, and provides precise cross sections and rates of the stau-catalyzed BBN reactions for the use in the BBN network calculation.

The latest status of LHC and the performances of ATLAS and CMS detectors are summarized in the first part. Physics potential to solve the origin of the ElectroWeak Symmetry Breaking is summarized in the 2nd part, focusing especially on two major scenarios, (1) the light Higgs boson plus SUSY and (2) the Strong Coupling Gauge Theory. Both ATLAS and CMS detectors have the excellent potential to discover them, and we can perform crucial test on the ElectroWeak Symmetry Breaking.

We study the production of a light top-squark pair in association with the lightest Higgs boson $({\tilde{t}}_1{\tilde{t}}_1^{\ast }{h}_1)$, as predicted by the Next-to-Minimal Supersymmetric Standard Model (NMSSM) in proton–proton collisions at center-of-mass energies of 13 TeV and 33 TeV. We scan randomly about 10 million points of the NMSSM parameter space, allowing all possible decays of the lightest top-squark and lightest Higgs boson, with no further assumptions, except for known physical constraints such as perturbative bounds, dark matter relic density consistent with recent Planck experiment measurements, Higgs mass bounds on the next to lightest Higgs boson, $h_2$, assuming it is consistent with LHC measurements for the Standard Model Higgs boson, LEP bounds for the chargino mass and $Z$ invisible width, experimental bounds on $B$ meson rare decays and some LHC experimental bounds on SUSY particle spectra different to the particles involved in our analysis. We find that for low mass top-squark, the dominating decay mode is ${\tilde{t}}_1\to b{\tilde{\chi }}_1^{\pm }$ with ${\tilde{\chi }}_1^{\pm }\to W^{\pm }{\tilde{\chi }}_1^0$. We use three benchmark points with the highest cross-sections, which naturally fall within the compressed spectra of the top-squark, and make a phenomenological analysis to determine the optimal event selection that maximizes the signal significance over backgrounds. We focus on the leptonic decays of both $W$’s and the decay of the lightest Higgs boson into $b$-quarks $(h_1\to b\bar{b})$. Our results show that the high luminosity LHC will have limitations to observe the studied SUSY scenario and only a proton collider with a collision energy above 33 TeV will be able to observe this signal with more than three standard deviations over background, albeit for stop masses below 300 GeV.

The second period of datataking at the Large Hadron Collider (LHC) has provided a large dataset of proton–proton collisions that is unprecedented in terms of its centre-of-mass energy of 13 TeV and integrated luminosity of almost 140 fb${}^{-1}$. These data constitute a formidable laboratory for the search for new particles predicted by models of supersymmetry. The analysis activity is still ongoing, but a host of results on supersymmetry had already been released by the general purpose LHC experiments ATLAS and CMS. In this paper, we provide a map into this remarkable body of research, which spans a multitude of experimental signatures and phenomenological scenarios. In the absence of conclusive evidence for the production of supersymmetric particles we discuss the constraints obtained in the context of various models. We finish with a short outlook on the new opportunities for the next runs that will be provided by the upgrade of detectors and accelerator.

The results from the CMS search for supersymmetric particles based on Run-2 data recorded at a center-of-mass energy of 13TeV are summarized. Strong and weak production of SUSY scenarios are considered. Results presented include the searches for squarks and gluinos, direct production of charginos, neutralinos and sleptons. These searches involve final state objects comprising jets, missing transverse momentum, electrons or muons, taus or photons, as well as long-lived particles. The data in these searches are found to be consistent with Standard Model predictions and no significant excess is observed. Upper limits have been set on the masses of supersymmetric particles from a variety of search channels.

The persistent $3-4\sigma$ discrepancy between the experimental result from Brookhaven National Laboratory (BNL) for the anomalous magnetic moment of the muon, ${(g-2)}_{\mu }$, and its Standard Model (SM) prediction, was confirmed recently by the “MUON G-2” result from Fermilab. The combination of the two measurements yields a deviation of $4.2\sigma$ from the SM value. Here, we review an analysis of the parameter space of the electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), which can provide a suitable explanation of the anomaly while being in full agreement with other latest experimental data like the direct searches for EW particles at the LHC and dark matter (DM) relic density and direct detection constraints. Taking the lightest supersymmetric particle (LSP) (the lightest neutralino in our case) to be the DM candidate, we discuss the case of a mixed bino/wino LSP, which can account for the full DM relic density of the universe and that of wino and higgsino DM, where we take the relic density only as an upper bound. We observe that an upper limit of $\sim 600\mathrm{\text{GeV}}$ can be obtained for the LSP and next-to (N)LSP masses establishing clear search targets for the future HL-LHC EW searches, but in particular for future high-energy $e^{+}{e}^{-}$ colliders such as the ILC or CLIC.

In this paper, a study of four different machine learning (ML) algorithms is performed to determine the most suitable ML technique to disentangle a hypothetical supersymmetry (SUSY) signal from its corresponding Standard Model (SM) backgrounds and to establish their impact on signal significance. The study focuses on the production of SUSY top squark pairs (stops), in the mass range of $500<m_{{\tilde{t}}_1}<800$GeV, from proton–proton collisions with a center of mass energy of 13TeV and an integrated luminosity of $140{\mathrm{\text{fb}}}^{-1}$, emulating the data-taking conditions of the run II Large Hadron Collider (LHC) accelerator. In particular, the semileptonic channel is analyzed, corresponding to final states with a single isolated lepton (electron or muon), missing transverse energy, and four jets, with at least one tagged as $b$-jet. The challenging compressed spectra region is targeted, where the stop decays mainly into a $W$ boson, a $b$-jet, and a neutralino (${\tilde{t}}_1\to W+b+{\tilde{\chi }}_1^0$), with a mass gap between the stop and the neutralino of about 150GeV. The ML algorithms are chosen to cover different mathematical implementations and features in ML. We compare the performance of a logistic regression (LR), a Random Forest (RF), an eXtreme Gradient Boosting, XGboost (XG) and a Neural Network (NN) algorithm. Our results indicate that XG and NN classifiers provide the highest improvements (over 17%) in signal significance, when compared to a standard analysis method based on sequential requirements of different kinematic variables. The improvement in signal significance provided by the NN increases up to 31% for the highest stop mass considered in this study (800GeV). The RF algorithm presents a smaller improvement that decreases with stop mass. On the other hand, the LR algorithm shows the worst performance in signal significance which even does not compete with the results obtained by an optimized cut and count method.