B physics in the next millennium

During the last years several Dark Sector Models have been proposed in order to address striking and puzzling astrophysical observations which fail standard interpretations. In the minimal case a new vector particle, the so called dark photon or U-boson, is introduced, with small coupling with Standard Model particles. Also, the existence of a dark Higgs boson h’ is postulated, in analogy with the Standard Model, to give mass to the U-boson through the Spontaneous Symmetry Breaking mechanism. The discovery of such a Dark Force Mediator would belong to a new field of Physics Beyond the Standard Model. The KLOE experiment, working on the DAΦNE e+e− collider in Frascati, searched for the existence of the U-boson in a quite complete way, investigating several different processes and final states. Tight limits on the model parameters have been set at 90%CL. Further improvements are expected in terms of sensitivity and discovery potential with the new KLOE-2 detector working on the improved DAΦNE e+e− collider, which has collected more than 5 fb−1.

The tiny neutrino masses and the associated large lepton mixings provide an interesting puzzle and a likely window to the physics beyond the standard model. This is certainly true if neutrinos are Majorana particles, since then, unlike in the Dirac case, the standard model is not a complete theory. The Majorana case leads to lepton number violation manifested through neutrinoless-double-beta decay and same-sign dileptons potentially accessible to colliders such as the LHC. This is covered at length. I discuss in these lectures possible theories of neutrino mass whose predictions are dictated by their structure only and this points strongly to grand unification. I cover in detail both SU(5) and SO(10) grand unified theories, and study the predictions of their minimal versions. The main message I wish to bring across is a serious hope of probing the origin of neutrino mass in near future, through the combined effort of high-energy collider and low-energy lepton number and lepton flavor violation experiments.

Although there have been a number of very fine experiments probing the nature of CP violation, even after 25 years we don't know whether we understand the basic theory involved. We do not know if CP violation is a profound clue to physics beyond the Standard Model and to the origin of the baryon asymmetry, or a trivial accident involving (for example) diagonalizing a mass matrix of quarks or Higgs scalars or neutralinos or squarks. The Standard Model can give a satisfactory description of CP violation in kaon decays to pions without any other contribution, if the phase angle in the CKM matrix is fairly large. The Standard model description of e and e I depends on some poorly known parameters. Some of those, such as m,, will be better known soon. Unfortunately, the hadronic matrix elements that enter are not well known, and may not be for a long time. Better measurements of e and e I will provide valuable input to eventually understanding the origin of CP violation, but unless the hadronic matrix elements can be calculated, measurements of e and e ~ can never give us real confidence that we understand CP violation. In particular, they may never be able to tell us whether a second source of CP violation, about the same size as the Standard Model one, is present. Most people do not expect the Standard Model to be the sole source of CP violation, for very general reasons. Although the Standard Model describes the world accessible to experiment so far, it leaves unanswered many questions and it is conceptually unsatisfactory. Everyone believes that new physics will appear to help explain why the weak scale is where it is, why there are families, and so on. Every form of new physics that has been thought of so far involves new sets of particles whose interactions will normally have phase factors. That all the new phase angles which enter the more complete theory should be zero would seem to be a miraculous coincidence. These particles could come in the Higgs sector, and/or be supersymmetric partners, and/or leptoquarks, and/or new gauge bosons, or new quarks, or other objects. It cannot be emphasized enough that if the Standard Model were the only origin of CP violation it would be a remarkable fact that would require explanation. Indeed, if the view of a number of people that the excess baryon number of the universe is generated at the weak scale is correct, either new sources of CP violation must exist that are larger than the CP violation in K decay, or that source must have a rapid growth with energy. Given this situation, it is extremely important to find new ways to get information about the source of CP violation. Even if very accurate experiments

During the last years several Dark Sector Models have been proposed in order to address striking astrophysical observations which fail standard interpretations. In the minimal case a new vector particle, the so called dark photon or U-boson, is introduced, with small coupling with Standard Model particles. Also, the existence of a dark Higgs boson h’ is postulated, in analogy with the Standard Model, to give mass to the U-boson through the Spontaneous Symmetry Breaking mechanism. The experiment KLOE, working on the DAΦNE e+e- collider in Frascati, searched for the existence of the U-boson in a quite complete way, investigating several different processes and final states. Tight limits on the model parameters have been set at 90%CL. Further improvements are expected in terms of sensitivity and discovery potential with the new KLOE-2 detector working on the improved DAFNE e+e- collider.

During the last years several Dark Sector Models have been proposed in order to address striking astrophysical observations which failed standard interpretations. In the minimal case a new vector particle, the so called dark photon, or A′ or U boson, is introduced, with small coupling with Standard Model particles. Also, the existence of a dark Higgs boson h′ is postulated, in analogy with the Standard Model, to give mass to the U boson through the Spontaneous Symmetry Breaking mechanism. The KLOE experiment working at DAΦNE, an e+e− collider operating in Frascati (near Rome), searched for the existence of the U boson investigating three different processes and six different final states: (1) in Dalitz decays of the ϕ meson ϕ → ηU, with U → e+e− and η → π+π−π0 and π0π0π0, (2) in e+e− → Uh′ events, with U decaying into lepton and pion pairs, (3) in the dark Higgsstrahlung process, e+e− → Uh′, U → μ+μ−, h′ invisible. Limits on the model parameters have been set at 90 % CL for U boson masses below 1 GeV. Further improvements are expected in terms of sensitivity and discovery potential with the new KLOE-2 detector.

We revisit constraints on the value of the electric charge of the neutron and the neutrinos as well as on the electric-charge proton–electron difference ep+ee. We consider phenomenological constraints based on laboratory study of the electrical neutrality of would-be neutral subatomic, atomic, and molecular species under assumption of the conservation of the electric charge in the β decay that relates the values of ep+ee,en,eν. Some of constraints published previously utilized an additional assumption eν=0, which we do not. We dismiss a cosmological constraint at the level of 10-35e utilized by Particle Data Group (PDG) in their Review of particle properties Workman et al. (Particle Data Group) (Prog Theor Exp Phys 2022:083C01, 2022) as a controversial one which makes the laboratory constraints on eν dominant. The phenomenological constraints from the available data of laboratory experiments are obtained as ep+ee=(0.2±2.6)×10-21e, en=(-0.4±1.1)×10-21e, and eν=(0.6±3.2)×10-21e. The ones on ep+ee and en are at the same level as the related constraints of PDG but somewhat different because of releasing the value of eν. Our eν constraint is several orders of magnitude weaker than the controversial cosmological result dominated in the PDG constraint, but several orders of magnitude stronger than the other individual eν constraints considered by PDG. We also consider consistency of the phenomenological constraints and the Standard Model (SM). The SM ignores the mass term of the neutrinos and cannot describe the neutrino oscillations which makes it not a complete theory but a part of it. We demonstrate that the condition of the cancellation of the triangle anomalies within the complete theory does not disagree with the phenomenological constraints since different extensions of the SM may produce different additional contributions to the anomalies. A choice of the extension fixes the way how those contributions are organized. In particular, we consider a minimal extension of the SM, where leptons (ν,e) are treated the same ways as quarks, which sets ep+ee=0 and allows for numerical strengthening the constraint on en and eν, which is en=-eν=(-0.4±1.0)×10-21e.Graphical Phenomenological constraint on the value of the electric charge of the neutrino

ATLAS is one of the four experiments at the Large Hadron Collider (LHC) at CERN. This experiment has been designed to study a large range of physics topics, including searches for previously unobserved phenomena such as the Higgs Boson and super-symmetry. The physics analysis package HiggsToFourLeptonsEV for the Standard Model (SM) Higgs to four leptons channel with ATLAS is presented. The physics goal is to investigate with the ATLAS detector, the SM Higgs boson discovery potential through its observation in the four-lepton (electron and muon) final state. HiggsToFourLeptonsEV is based on the official ATLAS software ATHENA and the EventView (EV) analysis framework. EventView is a highly flexible and modular analysis framework in ATHENA and it is one of several analysis schemes for ATLAS physics user analysis. At the core of the EventView is the representative “view” of an event, which defines the contents of event data suitable for event-level physics analysis. The HiggsToFourLeptonsEV package, presented in this paper, prepares the data for the given analysis context on the Analysis Object Data (AOD) files, the event-level physics analysis is performed and finally the output information is written as an Ntuple which can be read in stand-alone ROOT. This paper describes the HiggsToFourLeptonsEV package and its structure as a collection of EVTools and EVModules. It also presents some illustrative results from the SM Higgs baseline analysis, like the SM Higgs into four-lepton mass reconstruction for a nominal Higgs mass of 130 GeV. The lepton reconstruction performance as well as the SM Higgs to four leptons analysis performance is studied in detail, in particular the dependence on kinematics, lepton reconstruction algorithms, isolation cuts and Higgs masses. Finally the paper discusses plans to adapt the code in order to produce Derived Physics Data (DPD) in POOL format which can be read in ROOT or ATHENA, thus following the ATLAS analysis model recommendations.

The properties of matter at the atomic level are expressed in terms of a few fundamental constants, while, going down to the level subnuclear constituents, the present theoretical description requires the introduction of a large number of independent parameters. The main goal of elementary particle physics is to arrive at a complete theory which describes all subnuclear phenomena in terms of a unified interaction with the least number of fundamental constants. We discuss the lines of research in this field, which are mainly based on the implementation of higher symmetries. Grand Unified Theories unify the couplings of the fundamental interactions and, with the implement of family symmetry, some of the parameters of the basic fermions become related. Supersymmetry is an essential ingredient of the present theories and the introduction of hidden space-time dimensions appears to be a common feature. The gravitational interaction plays an important role in the unifying picture, linking low-energy parameters with the physics at the Plank scale.KeywordsCharged LeptonVector BosonGrand Unify TheoryFundamental ConstantFamily SymmetryThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Despite the great success of the Standard Model, many key questions in particle physics, astrophysics, and cosmology are unanswered. In particular, more than 95% of the universe consists of unknown dark matter and dark energy. Today, a major goal of particle physics is to look for evidence of new physics beyond the Standard Model. Collider searches for new physics are well suited to the direct production of new high-mass particles, whereas low-energy precision experiments search for traces that new particles leave in known processes. Direct and indirect evidence of new physics are highly complementary. High-precision experiments with extremely slow, cold and ultra-cold neutrons address some of the unanswered questions, for instance, on the nature of the fundamental forces and underlying symmetries, the origin, evolution, and fate of the universe, or on the nature of the gravitational force at very small distances. For example, the limit on the electric dipole moment of the neutron constrains the CP violating phases, the lifetime of the neutron determines the relative helium abundance in the universe, and neutrons bouncing over a mirror probe dark matter and dark energy. New facilities and technological developments now give window for significant improvement in precision by one to two orders of magnitude. In this paper, we will give an overview of current and planned facilities and experiments, as well as an overview of some of the applications of neutrons to astrophysics, cosmology, and physics beyond the Standard Model.

A possible goal of fundamental physics is to reduce all natural phenomena to a set of basic laws and theories which, at least in principle, can quantitatively reproduce and predict experimental observations. At the microscopic level all the phenomenology of matter and radiation, including molecular, atomic, nuclear, and subnuclear physics, can be understood in terms of three classes of fundamental interactions: strong, electromagnetic, and weak interactions. For all material bodies on the Earth and in all geological, astrophysical, and cosmological phenomena, a fourth interaction, the gravitational force, plays a dominant role, but this remains negligible in atomic and nuclear physics. In atoms, the electrons are bound to nuclei by electromagnetic forces, and the properties of electron clouds explain the complex phenomenology of atoms and molecules. Light is a particular vibration of electric and magnetic fields (an electromagnetic wave). Strong interactions bind the protons and neutrons together in nuclei, being so strongly attractive at short distances that they prevail over the electric repulsion due to the like charges of protons. Protons and neutrons, in turn, are composites of three quarks held together by strong interactions occur between quarks and gluons (hence these particles are called “hadrons” from the Greek word for “strong”). The weak interactions are responsible for the beta radioactivity that makes some nuclei unstable, as well as the nuclear reactions that produce the enormous energy radiated by the stars, and in particular by our Sun. The weak interactions also cause the disintegration of the neutron, the charged pions, and the lightest hadronic particles with strangeness, charm, and beauty (which are “flavour” quantum numbers), as well as the decay of the top quark and the heavy charged leptons (the muon μ− and the tau τ−). In addition, all observed neutrino interactions are due to these weak forces.

Naturalness, Wilsonian renormalization, and “fundamental parameters” in quantum field theory

After the discovery of a new particle at the Large Hadron Collider (LHC), it is crucial to definitely verify or disprove whether this new 125 − 126 GeV resonance is the Higgs boson of the Standard Model (SM). Thus, its features, including its spin, have to be determined. In order to distinguish the two most likely spin hypotheses, spin-0 or spin-2, the phenomenology of light spin-2 resonances produced in different gluon-fusion and vectorboson-fusion processes at the LHC is studied. Starting from an effective model for the interaction of a spin-2 particle with SM gauge bosons, cross sections and differential distributions are calculated within the Monte Carlo program Vbfnlo. Whereas with specific model parameters, such a spin-2 resonance can mimic rates and transverse-momentum distributions of a SM Higgs boson in the main decay channels γγ, WW and ZZ, several distributions allow to separate spin-2 from spin-0, almost independently of model parameters. Since the SM Higgs boson ensures the unitarity of the S-matrix in vector-boson scattering, another topic of this thesis is to investigate if the capability of unitarizing vector-boson scattering is a unique feature of the spin-0 Higgs boson or if particles with a different spin, i.e. spin-1 or spin-2, are able to perform the same task. Furthermore, the characteristics of heavy spin-2 resonances in vector-boson-fusion processes are analyzed at NLO QCD accuracy in order to facilitate the spin determination of heavy particles that might be detected at the LHC.

Recent advances in both computers and algorithms now allow realistic calculations of Quantum Chromodynamics (QCD) interactions using the numerical technique of lattice QCD. The methods used in so-called ‘2+1 flavor’ lattice calculations have been verified both by post-dictions of quantities that were already experimentally well-known and by predictions that occurred before the relevant experimental determinations were sufficiently precise. This suggests that the sources of systematic error in lattice calculations are under control, and that lattice QCD can now be reliably used to calculate those weak matrix elements that cannot be measured experimentally but are necessary to interpret the results of many high-energy physics experiments. These same calculations also allow stringent tests of the Standard Model of particle physics, and may therefore lead to the discovery of new physics in the future.

Experiments using nuclei to probe new physics beyond the Standard Model, such as neutrinoless $\beta\beta$ decay searches testing whether neutrinos are their own antiparticle, and direct detection experiments aiming to identify the nature of dark matter, require accurate nuclear physics input for optimizing their discovery potential and for a correct interpretation of their results. This demands a detailed knowledge of the nuclear structure relevant for these processes. For instance, neutrinoless $\beta\beta$ decay nuclear matrix elements are very sensitive to the nuclear correlations in the initial and final nuclei, and the spin-dependent nuclear structure factors of dark matter scattering depend on the subtle distribution of the nuclear spin among all nucleons. In addition, nucleons are composite and strongly interacting, which implies that many-nucleon processes are necessary for a correct description of nuclei and their interactions. It is thus crucial that theoretical studies and experimental analyses consider $\beta$ decays and dark matter interactions with a coupling to two nucleons, called two-nucleon currents.

This talk reviews the discovery potential of a light Standard Model Higgs boson (mass ∼ 114–200 GeV) at ATLAS with emphasis on the vector boson fusion production, which allows a better background rejection. Once discovered, Higgs boson couplings are studied by measuring the rate of events in various production and decay channels. The accuracy of these studies is described and the impact on the discrimination between Standard Model and a Supersymmetric model is shown.