Search for new light gauge bosons in Higgs boson decays to four-lepton final states in pp collisions at root s=8 TeV with the ATLAS detector at the LHC
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Search for a new heavy gauge-boson resonance decaying into a lepton and missing transverse momentum in 36 fb$^{-1}$ of pp collisions at $\sqrt{s} = 13$ TeV with the ATLAS experiment
The results of a search for new heavy W ' bosons decaying to an electron or muon and a neutrino using proton–proton collision data at a centre-of-mass energy of √s = 13 TeV are presented. The dataset was collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 36.1 fb –1 . As no excess of events above the Standard Model prediction is observed, the results are used to set upper limits on the W ' boson cross-section times branching ratio to an electron or muon and a neutrino as a function of the W ' mass. Here, assuming a W ' boson with the same couplings as the Standard Model W boson, W ' masses below 5.1 TeV are excluded at the 95% confidence level.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for Anomalous Trilinear Couplings of Electroweak Gauge Bosons Using Angular Variables at $\sqrt{s}$ = 13 TeV at CMS
A study of techniques for improving limits placed on anomalous trilinear couplings of electroweak gauge bosons is presented. Electroweak gauge bosons couple to one another as well as to fermions. Deviations of these couplings from their standard model values would be a sign of new physics. Parameters that affect the couplings of the gauge bosons to each other also affect their helicity, which in turn may be measured from their decay products. Angles between the decay planes of the gauge bosons, as well as between their decay products, are measured. The analysis uses $35.9\,\text{fb}^{-1}$ of proton-proton collision data from the LHC taken with the CMS detector. Building on a prior analysis that measured the fiducial cross section of $pp \to WW/WZ \to \ell\nu jj$, we show that angular variables can improve limits on anomalous couplings even further.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Portal matter models of kinetic mixing with two light dark gauge bosons
The kinetic mixing (KM) portal mandates the existence of at least one new gauge boson, the dark photon (DP) based on the group 𝑈(1) 𝐷 , which mixes with the Standard Model (SM) photon via loops of other new heavy particles carrying both SM and dark charges called portal matter (PM). Arguments exist based on the renormalization group equations running of the 𝑈(1) 𝐷 gauge coupling suggesting that at higher scales 𝑈(1) 𝐷 becomes part of a more complex non-Abelian group, a simple example being just the SM-like 𝐺 𝐷 =𝑆𝑈(2)𝐼 ×𝑈(1) 𝑌 𝐼 . In our past analyses, it was always assumed that 𝐺 𝐷 broke in a SM-like manner directly to the DP’s 𝑈(1) 𝐷 which then subsequently broke at low energies ≲1 GeV. However, this need not be the case, and 𝐺 𝐷 can instead break to 𝑈(1) 𝑇 3𝐼 ×𝑈(1) 𝑌 𝐼 , with 𝑇 3𝐼 being the diagonal generator of 𝑆𝑈(2) 𝐼 , now producing two light gauge bosons which obtain masses at the ≲1 GeV scale. In this paper, we explore the phenomenology of a very simple realization of this kind of alternative setup employing non-Abelian KM and having a minimal, leptonlike PM sector, demonstrating its distinctive nature in comparison to the previously examined symmetry breaking path. The effects of interference between these gauge bosons on thermal dark matter annihilation, the production of new heavy gauge, and Higgs and PM states at colliders, as well as the corresponding signatures for the light dark gauge bosons are examined. Collider signatures of this setup are found to be particularly challenging.
extensions of Higgs sector↗
Identification of Family Non-universal Gauge Bosons in High-energy Electron-positron Collisions
We examine effects on measurable observables in e{sup +}e{sup -} collisions resulting from the existence of additional neutral gauge bosons originating in extensions of the standard model. In particular, we consider family non-universal neutral gauge bosons occurring in the minimal supersymmetric standard model and in the Sp(6){sub L} x U(1){sub Y} model, as well as other theoretically motivated popular neutral gauge bosons. We show how the proper employment of the generation-dependent couplings of the extra gauge boson, and the appropriate adjustment of the beam polarization, not only improved the identification of the models but also enhanced the discovery potential of the family non-universal extra gauge bosons.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Gauge boson signals at the cosmological collider
We study the production of massive gauge bosons during inflation from the axion-type coupling to the inflaton and the corresponding oscillatory features in the primordial non-Gaussianity. In a window in which both the gauge boson mass and the chemical potential are large, the signal is potentially reachable by near-future large scale structure probes. This scenario covers a new region in oscillation frequency which is not populated by previously known cosmological collider models. We also demonstrate how to properly include the exponential factor and discuss the subtleties in obtaining power dependence of the gauge boson mass in the signal estimate.
79 ASTRONOMY AND ASTROPHYSICS↗
A search for a new gauge boson A'
In the Standard Model, gauge bosons mediate the strong, weak, and electromagnetic forces. New forces could have escaped detection only if their mediators are either heavier than order(TeV) or weakly coupled to charged matter. New vector bosons with small coupling {alpha}' arise naturally from a small kinetic mixing with the photon and have received considerable attention as an explanation of various dark matter related anomalies. Such particles can be produced in electron-nucleus fixed-target scattering and then decay to e + e -+ pairs. New light vector bosons and their associated forces are a common feature of Standard Model extensions, but existing constraints are remarkably sparse. The APEX experiment will search for a new vector boson A' with coupling α'/α fs > 6 × 10 -8 to electrons in the mass range 65MeV < mass A' < 550MeV. The experiment will study e + e - production off an electron beam incident on a high-Z target in Hall A at Jefferson Lab. The e - and e + will be detected in the High Resolution Spectrometers (HRSs). The invariant mass spectrum of the e + e - pairs will be scanned for a narrow resonance corresponding to the mass of the A'. A test run for the APEX experiment was held in the summer of 2010. Using the test run data, an A' search was performed in the mass range 175-250 MeV. The search found no evidence for an A' → e + e - reaction, and set an upper limit of {alpha}'/{alpha}{sub fs} ~ 10 -6 .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Infrared weak corrections to strongly interacting gauge boson scattering
We evaluate the impact of electroweak corrections of infrared origin on strongly interacting longitudinal gauge boson scattering, calculating all-order resummed expressions at the double log level. As a working example, we consider the standard model with a heavy Higgs. At energies typical of forthcoming experiments (LHC, International Linear Collider, Compact Linear Collider), the corrections are in the 10%-40% range, with the relative sign depending on the initial state considered and on whether or not additional gauge boson emission is included. We conclude that the effect of radiative electroweak corrections should be included in the analysis of longitudinal gauge boson scattering.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Family gauge bosons with an inverted mass hierarchy
A model that gives family gauge bosons with an inverted mass hierarchy is proposed, stimulated by Sumino's cancellation mechanism for the QED radiative correction to the charged lepton masses. The Sumino mechanism cannot straightforwardly be applied to SUSY models because of the non-renormalization theorem. In this talk, an alternative model which is applicable to a SUSY model is proposed. It is essential that family gauge boson masses m(A{sub i}{sup j}) in this model is given by an inverted mass hierarchy m(A{sub i}{sup i}){proportional_to}1/{radical}(m{sub ei}), in contrast to m(A{sub i}{sup i}){proportional_to}{radical}(m{sub ei}) in the original Sumino model. Phenomenological meaning of the model is also investigated. In particular, we notice a deviation from the e-{mu} universality in the tau decays.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for the Higgs Boson and for Anomalous Quartic Gauge Boson Couplings in the WW Channel with Dielectron Events with the D0 Experiment at the Tevatron; Recherche du boson de Higgs et de couplages de jauge quartiques anormaux dans le canal WW en électrons dans l'expérience D0 au Tevatron
Le paysage de la physique des particules a subi des changements majeurs entre le début de cette thèse, en septembre 2010, et sa n en juin 2013. On peut notamment qualier l'année 2012 de date-clé dans l'histoire de la physique des particules. En 2012, une nouvelle particule a été découverte au LHC [1, 2], dont la majeure partie de la communauté s'accorde aujourd'hui à dire qu'il s'agit très probablement du boson de Higgs. Cet événement est intervenu peu après une sorte de passage de relais entre le Tevatron, arrêté le 30 septembre 2011, et le LHC, dont les toutes premières collisions sont intervenues le 23 novembre 2009.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Chiral and deconfinement phase transitions in QED{sub 3} with finite gauge boson mass
Based on the experimental observation that there is a coexisting region between the antiferromagnetic (AF) and d-wave superconducting (dSC) phases, the influences of gauge boson mass m{sub a} on chiral symmetry restoration and deconfinement phase transitions in QED{sub 3} are investigated simultaneously within a unified framework, i.e., Dyson–Schwinger equations. The results show that the chiral symmetry restoration phase transition in the presence of the gauge boson mass m{sub a} is a typical second-order phase transition; the chiral symmetry restoration and deconfinement phase transitions are coincident; the critical number of fermion flavors N{sup c}{sub f} decreases as the gauge boson mass m{sub a} increases, which implies that there exists a boundary that separates the N{sup c}{sub f}–m{sub a} plane into chiral symmetry breaking/confinement region for (N{sup c}{sub f}, m{sub a}) below the boundary and chiral symmetry restoration/deconfinement region for (N{sup c}{sub f}, m{sub a}) above it.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Gravitational wave probes of massive gauge bosons at the cosmological collider
We extend the reach of the "cosmological collider" for massive gauge boson production during inflation from the CMB scales to the interferometer scales. Considering a Chern-Simons coupling between the gauge bosons and the pseudoscalar inflaton, one of the transverse gauge modes is efficiently produced and its inverse decay leaves an imprint in the primordial scalar and tensor perturbations. We study the correlation functions of these perturbations and derive the updated constraints on the parameter space from CMB observables. We then extrapolate the tensor power spectrum to smaller scales consistently taking into account the impact of the gauge field on inflationary dynamics. Our results show that the presence of massive gauge fields during inflation can be detected from characteristic gravitational wave signals encompassing the whole range of current and planned interferometers.
79 ASTRONOMY AND ASTROPHYSICS↗
Perturbativity constraints on U(1) B-L and left-right models and implications for heavy gauge boson searches
We derive perturbativity constraints on beyond standard model scenarios with extra gauge groups, such as SU(2) or U(1), whose generators contribute to the electric charge, and show that there are both upper and lower limits on the additional gauge couplings, from the requirement that the couplings remain perturbative up to the grand unification theory (GUT) scale. This leads to stringent constraints on the masses of the corresponding gauge bosons and their collider phenomenology. We specifically focus on the models based on SU(2) L × U(1) I 3R × U(1) B-L and the left-right symmetric models based on SU(2) L × SU(2) R × U(1) B-L , and discuss the implications of the perturbativity constraints for new gauge boson searches at current and future colliders. In particular, we find that the stringent flavor constraints in the scalar sector of left-right model set a lower bound on the right-handed scale v R ≳ 10 TeV, if all the gauge and quartic couplings are to remain perturbative up to the GUT scale. This precludes the prospects of finding the Z R boson in the left-right model at the LHC, even in the high-luminosity phase, and leaves only a narrow window for the W R boson. A much broader allowed parameter space, with the right-handed scale v R up to ≃ 87 TeV, could be probed at the future 100 TeV collider.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Radiative corrections to longitudinal and transverse gauge boson and Higgs production
Radiative corrections to gauge boson and Higgs production computed recently using soft-collinear effective theory require the one-loop high-scale matching coefficients in the standard model. We give explicit expressions for the matching coefficients for the effective field theory operators for qq{yields}VV and qq{yields}{phi}{sup {dagger}{phi}}for a general gauge theory with an arbitrary number of gauge groups. The group theory factors are given explicitly for the standard model, including both QCD and electroweak corrections.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Anomalous photon-gauge boson coupling contribution to the exclusive vector boson pair production from two photon exchange in pp collisions at 13 TeV
We study the W and Z pair production from two-photon exchange in proton-proton collisions at the LHC in order to evaluate the contributions of anomalous photon-gauge boson couplings, that simulates new particles and couplings predicted in many Standard Model (SM) extensions. The experimental results of W{sup +} W{sup −} exclusive production (pp → pW{sup +}W{sup −} p) at 7 TeV from the CMS collaboration [1] updates the experimental limits on anomalous couplings obtained at the Large Electron-Positron Collider (LEP). This motivates our present analysis hopefully anticipating the expected results using the Precision Proton Spectrometer (PPS) to be installed as part of CMS. In this work, we consider the W{sup +}W{sup −} exclusive production to present the p{sub T} distribution of the lepton pair corresponding to the SM signal with p{sub T} (e, μ) > 10 GeV. Next, we consider the photon-gauge boson anomalous couplings by calculating, from the FPMC and MadGraph event generators, the process γγ → W{sup +}W{sup −} from a model with gauge boson quartic couplings, by considering a 1 TeV scale for new physical effects. We present our results for an integrated luminosity of 5 fb{sup −1} at center-of-mass energy of 7 TeV and for an integrated luminosity of 100 fb{sup −1} at 13 TeV. We present our preliminary results for Z pair exclusive production from two-photon exchange with anomalous couplings, where the ZZγγ quartic coupling is absent in the SM. We calculate the total cross section for the exclusive process and present the four lepton invariant mass distribution. Finally we present an outlook for the present analysis.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Signals of a New Gauge Boson from IceCube and Muon g-2
Gauging the muon lepton flavor minus the tau lepton flavor number, which is a global symmetry of the SM, introduces a new gauge boson Z' upon symmetry breaking. Interestingly, it offers an economical solution to the long-standing g_µ-2 anomaly, confirmed and strengthened by recent measurements at Fermilab. Here, we revisit the impact of such a Z' on the spectrum of high-energy astrophysical neutrinos, as measured by the IceCube experiment. This spectrum has been observed to exhibit a dip-like feature at sub-PeV energies, which could plausibly arise from the physics of the sources themselves, but could also be the consequence of high-energy neutrinos resonantly scattering with the cosmic neutrino background, mediated by a Z' with a mass on the order of m_Z’ ~ 10 MeV. In this study, we calculate the impact of such a Z' on the high-energy neutrino spectrum for a variety of model parameters and source distributions. For couplings that can resolve the g-2 anomaly, we find that this model could self-consistently produce a spectral feature that is consistent with IceCube's measurement, in particular if the neutrinos observed by IceCube predominantly originate from high-redshift sources. We also briefly discuss a possible scenario where Z' could act as a portal to a dark sector.
79 ASTRONOMY AND ASTROPHYSICS↗
Bounds on dark matter interactions with electroweak gauge bosons
We investigate scenarios in which dark matter interacts with the Standard Model primarily through electroweak gauge bosons. We employ an effective field theory framework wherein the Standard Model and the dark matter particle are the only light states in order to derive model-independent bounds. Bounds on such interactions are derived from dark matter production by weak boson fusion at the LHC, indirect detection searches for the products of dark matter annihilation and from the measured invisible width of the Z 0 . We find that limits on the UV scale, Λ , reach weak scale values for most operators and values of the dark matter mass, thus probing the most natural scenarios in the weakly interacting massive particle dark matter paradigm. Our bounds suggest that light dark matter ( m χ ≲ m Z / 2 or m χ ≲ 100 – 200 GeV , depending on the operator) cannot interact only with the electroweak gauge bosons of the Standard Model, but rather requires additional operator contributions or dark sector structure to avoid overclosing the Universe.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Search for a new $Z$' gauge boson in 4$μ$ events with the ATLAS experiment
This paper presents a search for a new Z' vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at $\sqrt{s}$ = 13 TeV, corresponding to an integrated luminosity of 139 fb -1 . The new gauge boson Z' is predicted by Lμ - Lτ models to address observed phenomena that cannot be explained by the Standard Model. The search examines the four-muon (4μ) final state, using a deep learning neural network classifier to separate the Z' signal from the Standard Model background events. The di-muon invariant masses in the 4μ events are used to extract the Z' resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z' production cross-section times the decay branching fraction of pp → Z'μμ → 4μ are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, g Z' , of the Z' boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗