Vector Boson Research Articles

Search for nonresonant Higgs boson pair production in final state with two bottom quarks and two tau leptons in proton-proton collisions at [formula omitted

A search for the nonresonant production of Higgs boson pairs (HH ) via gluon-gluon and vector boson fusion processes in final states with two bottom quarks and two tau leptons is presented. The search uses data from proton-proton collisions at a center-of-mass energy of s=13TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 138fb−1. Events in which at least one tau lepton decays hadronically are considered and multiple machine learning techniques are used to identify and extract the signal. The data are found to be consistent, within uncertainties, with the standard model (SM) predictions. Upper limits on the HH production cross section are set to constrain the parameter space for anomalous Higgs boson couplings. The observed (expected) upper limit at 95% confidence level corresponds to 3.3 (5.2) times the SM prediction for the inclusive HH cross section and to 124 (154) times the SM prediction for the vector boson fusion HH cross section. At 95% confidence level, the Higgs field self-coupling is constrained to be within −1.7 and 8.7 times the SM expectation, and the coupling of two Higgs bosons to two vector bosons is constrained to be within −0.4 and 2.6 times the SM expectation.

Operator solution of the light-front Thirring-Wess model

We present an operator solution of the Thirring-Wess model, formulated and quantized in terms of light-front (LF) variables. The model describes a system of massless fermions interacting with massive vector bosons in two space-time dimensions. An important ingredient of the solution is a consistent quantization of the two-dimensional massless LF fermion field. The field equations are solved exactly on an operator level and the quantum LF Hamiltonian is derived in terms of independent field variables. The axial anomaly and the interacting correlation functions are computed nonperturbatively from the operator solution. An analogous operator solution in the conventional field theory is briefly described for comparison. While in the LF case the ``empty'' Fock vacuum is the lowest-energy eigenstate of the full Hamiltonian, the corresponding Hamiltonian in the conventional theory has to be diagonalized in order to find the true physical ground state, which is a dynamical state with a complicated structure. A comment concerning a recently discussed equivalence between the LF and conventional form of field theory concludes the paper.

Vector Boson Fusion topology and simplified models for dark matter searches at colliders

In this paper, we study the possible searches at colliders using Vector Boson Fusion topology in the context of Simplified Models signatures. We examine the possible physics reach of these searches with regard to monojet-type searches, and determine how these two signatures are complementary. We determine the generic characteristics for dark matter signatures in the LHC if the underlying physics imply Vector Boson Fusion type of production.

Lepton flavor specific extended Higgs model

In extended Higgs models, a discrete symmetry is needed in the quark sector to avoid tree-level flavor-changing neutral currents. However, this is not necessary the case in the lepton sector. We consider a model in which one Higgs couples to quarks and three others couple to the electron, muon and tau, respectively. This four-doublet model is presented with the full scalar potential and the gauge and Yukawa couplings. The constraints from boundedness, perturbativity and oblique parameters are incorporated as well as constraints from meson-antimeson mixing, radiative B-decays and the diphoton Higgs decay rate. We also consider bounds from searches for heavy neutral and charged scalars at the LHC. Since the Standard Model Higgs couplings match predictions very well, we focus on the alignment limit of the model. It is shown that for a wide range of parameters, the lightest additional scalar, pseudoscalar and charged scalar can have substantial decays into electrons and muons (in contrast to the usual leptonic decays into taus). An interesting signature in the neutral sector would be the production, through vector boson fusion, of a pair of scalars, each of which decays into an electron or muon pair.

NNLO QCD predictions for Z-boson production in association with a charm jet within the LHCb fiducial region

We compute next-to-next-to-leading order (NNLO) QCD corrections to neutral vector boson production in association with a charm jet at the LHC. This process is studied in the forward kinematics at sqrt{s}=13 TeV, which may provide valuable constraints on the intrinsic charm component of the proton. A comparison is performed between fixed order and NLO predictions matched to a parton shower showing mutual compatibility within the respective uncertainties. NNLO corrections typically lead to a reduction of theoretical uncertainties by a factor of two and the perturbative convergence is further improved through the introduction of a theory-inspired constraint on the transverse momentum of the vector boson plus jet system. A comparison between these predictions with data will require an alignment of a flavour-tagging procedure in theory and experiment that is infrared and collinear safe.

Jet-veto resummation at N3LLp + NNLO in boson production processes

Vetoing energetic jet activity is a crucial tool for suppressing backgrounds and enabling new physics searches at the LHC, but the introduction of a veto scale can introduce large logarithms that may need to be resummed. We present an implementation of jet-veto resummation for color-singlet processes at the level of N3LLp matched to fixed-order NNLO predictions. Our public code MCFM allows for predictions of a single boson, such as Z/γ*, W± or H, or with a pair of vector bosons, such as W+W−, W±Z or ZZ. The implementation relies on recent calculations of the soft and beam functions in the presence of a jet veto over all rapidities, with jets defined using a sequential recombination algorithm with jet radius R. However one of the ingredients that is required to reach full N3LL accuracy is only known approximately, hence N3LLp. We describe in detail our formalism and compare with previous public codes that operate at the level of NNLL. Our higher-order predictions improve significantly upon NNLL calculations by reducing theoretical uncertainties. We demonstrate this by comparing our predictions with ATLAS and CMS results.

Constraining lepton flavor violating Higgs couplings at the HL-LHC in the vector boson fusion channel

We explore the parameter space of lepton flavor violating (LFV) neutral Higgs Yukawa couplings with the muon and tau leptons that can be probed at the high-luminosity Large Hadron Collider (HL-LHC) via the vector boson fusion (VBF) Higgs production process. Our projected sensitivities for the Standard Model Higgs ($h$) LFV branching ratio $\text{Br}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})$ in the $pp\ensuremath{\rightarrow}hjj\ensuremath{\rightarrow}(h\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau})jj$ channel at the HL-LHC are contrasted with the current and future low-energy constraints from the anomalous magnetic moment and electric dipole moment of the muon, as well as with other LFV observables, such as $\ensuremath{\tau}\ensuremath{\rightarrow}3\ensuremath{\mu}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$. We also study the LFV prospects of a generic beyond the Standard Model neutral Higgs boson ($H$) with a mass in the range of ${m}_{H}\ensuremath{\in}[20,800]\text{ }\text{ }\mathrm{GeV}$ and give the projected model-independent upper limits on the VBF production cross section of $Hjj$ times the branching ratio of $H\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\tau}$ at the HL-LHC. We interpret these results in the context of a two-Higgs doublet model as a case study.

Modified general relativity and dark matter

Modified General Relativity (MGR) is the natural extension of General Relativity (GR). MGR explicitly uses the smooth regular line element vector field [Formula: see text], which exists in all Lorentzian spacetimes, to construct a connection-independent symmetric tensor that represents the energy–momentum of the gravitational field. It solves the problem of the nonlocalization of gravitational energy–momentum in GR, preserves the ontology of the Einstein equation, and maintains the equivalence principle. The line element field provides MGR with the extra freedom required to describe dark energy and dark matter. An extended Schwarzschild solution for the matter-free Einstein equation of MGR is developed, from which the Tully–Fisher relation is derived, and the gravitational energy density is calculated. The mass of the invisible matter halo of galaxy NGC 3198 calculated with MGR is identical to the result obtained from GR using a dark matter profile. Although dark matter in MGR is described geometrically, it has an equivalent representation as a particle with the property of a vector boson or a pair of fermions; the geometry of spacetime and the quantum nature of matter are linked together by the unit line element covectors that belong to both the Lorentzian metric and the spin-1 Klein–Gordon wave equation. The three classic tests of GR provide a comparison of the theories in the solar system and several parts of the cosmos. MGR provides the flexibility to describe inflation after the Big Bang and galactic anisotropies.

Revealing the origin of neutrino masses through the Type II Seesaw mechanism at high-energy muon colliders

The future muon collider can play as an ideal machine to search for new physics at high energies. In this work, we study the search potential of the heavy Higgs triplet in the Type II Seesaw mechanism at muon colliders with high collision energy and high luminosity. The latest neutrino oscillation data are taken into account for realizing the leptonic decay modes of the charged Higgs bosons (H±±, H±) in the Type II Seesaw. We show the impact of neutrino mass and mixing parameters on the purely leptonic decays. The pair production of doubly charged Higgs H++H−− is through direct μ+μ− annihilation and vector boson fusion (VBF) processes at muon collider. The associated production H±±H∓ can only be induced by VBF processes. We simulate both the purely leptonic and bosonic signal channels of charged Higgs bosons in Type II Seesaw, together with the Standard Model backgrounds. We show the required luminosity for the discovery of the charged Higgses and the reachable limits on the leptonic decay branching fractions.

Quenched random mass disorder in the large N theory of vector bosons

We study the critical bosonic O(N) vector model with quenched random mass disorder in the large N limit. Due to the replicated action which is sometimes not bounded from below, we avoid the replica trick and adopt a traditional approach to directly compute the disorder averaged physical observables. At N=\infty, we can exactly solve the disordered model. The resulting low energy behavior can be described by two scale invariant theories, one of which has an intrinsic scale. At finite N, we find that the previously proposed attractive disordered fixed point at d=2 continues to exist at d=2+\epsilon spatial dimensions. We also studied the system in the 3<d<4 spatial dimensions where the disorder is relevant at the Gaussian fixed point. However, no physical attractive fixed point is found right below four spatial dimensions. Nevertheless, the stable fixed point at 2+\epsilon dimensions can still survive at d=3 where the system has experimental realizations. Some critical exponents are predicted in order to be checked by future numerics and experiments.

Flavor changing interactions confronted with meson mixing and hadron colliders

We have witnessed some flavor anomalies appearing in the past years, and explanations based on extended gauge sectors are among the most popular solutions. These beyond the Standard Model (SM) theories often assume flavor-changing interactions mediated by new vector bosons. Still, at the same time, they could yield deviations from the SM in the ${K}^{0}\ensuremath{-}{\overline{K}}^{0}$, ${D}^{0}\ensuremath{-}{\overline{D}}^{0}$, ${B}_{d}^{0}\ensuremath{-}\overline{B}{{\text{ }}^{0}}_{d}$, and ${B}_{s}^{0}\ensuremath{-}\overline{B}{{\text{ }}^{0}}_{s}$ meson systems. Using up-to-date data on the mass difference of these meson systems, we derive lower mass bounds on vector mediators for two different parametrizations of the quark mixing matrices. Focusing on a well-motivated model based on the fundamental representation of the weak SU(3) gauge group, we put our findings into perspective with current and future hadron colliders to conclude that meson mass systems can give rise to bounds much more stringent than those from high-energy colliders and that recent new physics interpretations of the $b\ensuremath{\rightarrow}s$ and $R({D}^{*})$ anomalies are disfavored.

Z 0 boson associated b-jet production in high-energy nuclear collisions* *Supported by the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008), the Science and Technology Program of Guangzhou (2019050001), and the NSFC of China (11935007, 12035007, 12247127). S. Wang is supported by China Postdoctoral Science Foundation (2021M701279)

The production of vector boson tagged heavy quark jets potentially provides new tools to probe the jet quenching effect. In this paper, we present the first theoretical study on the angular correlations (), transverse momentum imbalance (), and nuclear modification factor () of boson tagged b-jets in heavy-ion collisions, which was performed using a Monte Carlo transport model. We find that the medium modification of the for + b-jet has a weaker dependence on than that for + jet, and the modification patterns are sensitive to the initial jet distribution. Additionally, with the high purity of the quark jet in + (b-) jet production, we calculate the momentum imbalance and the nuclear modification factor of + b-jet in Pb+Pb collisions. We observe a smaller and larger of + b-jet in Pb+Pb collisions relative to those of + jet, which may be an indication of the mass effect of jet quenching and can be tested in future measurements.

Z boson mixing and the mass of the W boson

We explore the possibility of explaining the $W$ boson mass with an extra gauge boson mixing with the $Z$ boson at tree level. Extra boson mixing with the $Z$ boson will change the expression of the $Z$ boson mass, thus altering the $W$ boson mass. We explore two models in this work. We find that in the Derivative Portal Dark Matter model, there are parameters space which can give the observed $W$ boson mass, as well as the observed Dark Matter relic density. These parameters space can also fulfill the constraints from the electroweak oblique parameters and Dark Matter indirect detection. In the U(1) extension model, the kinetic mixing between extra boson and $B$ boson can also give the observed $W$ boson mass. However, to fulfill electroweak oblique parameters fit the kinetic mixing in the U(1) model can only contribute about $27~\mathrm{MeV}$ extra mass to the Standard Model $W$ boson mass. Both models indicate the extra vector boson with the best fit mass around $120~\mathrm{GeV}$.

Precision boson-jet azimuthal decorrelation at hadron colliders

The azimuthal angular decorrelation of a vector boson and jet is sensitive to QCD radiation, and can be used to probe the quark-gluon plasma in heavy-ion collisions. By using a recoil-free jet definition, the sensitivity to contamination from soft radiation on the measurement is reduced, and the complication of non-global logarithms is eliminated from our theoretical calculation. Specifically we will consider the {p}_T^n recombination scheme, as well as the n → ∞ limit, known as the winner-take-all scheme. These jet definitions also significantly simplify the calculation for a track-based measurement, which is preferred due to its superior angular resolution. We present a detailed discussion of the factorization in Soft-Collinear Effective Theory, revealing why the transverse momentum {overrightarrow{q}}_T is more complicated than the azimuthal angle. We show that potential glauber contributions do not spoil our factorization formalism, at least up to and including order {alpha}_s^3 . The resummation is carried out using the renormalization group, and all necessary ingredients are collected or calculated. We conclude with a detailed phenomenological study, finding an enhanced matching correction for high jet pT due to the electroweak collinear enhancement of a boson emission off di-jets. We also compare with the Pythia event generator, finding that our observable is very robust to hadronization and the underlying event.

Threshold enhanced cross sections for colorless productions

We study the threshold effect for neutral and charged Drell-Yan productions, associated production of Higgs boson with a massive vector boson and Higgs production in bottom quark annihilation at LHC to the third order in QCD. Using the third order soft-virtual results for these processes and exploiting the universality of the threshold logarithms, we extract the process-dependent coefficients for these processes and resum large threshold logarithms to next-to-next-to-next-to leading logarithmic (N$^3$LL) accuracy. By matching our results to the recently available N$^3$LO results, we provide the most precise theoretical predictions for these processes. We present numerical results for invariant mass distribution and total production cross-sections. We find the conventional scale uncertainties of about $0.4\%$ at N$^3$LO level in the fixed order results get reduced to as small as less than $0.1\%$ at N$^3$LO+N$^3$LL level in the high invariant mass region.

Anomalous Higgs boson couplings in weak boson fusion production at NNLO in QCD

The production of Higgs bosons in weak boson fusion has the second largest cross section among Higgs-production processes at the LHC. As such, this process plays an important role in detailed studies of Higgs interactions with vector bosons. In this paper we extend the available description of Higgs boson production in weak boson fusion by considering anomalous $HVV$ interactions and NNLO QCD radiative corrections at the same time. We find that, while leading order QCD predictions are too uncertain to allow for detailed studies of the anomalous couplings, NLO QCD results are sufficiently precise, most of the time. The NNLO QCD corrections alter the NLO QCD predictions only marginally, but their availability enhances the credibility of conclusions based on NLO QCD computations.

Search for Higgs boson pair production in the bb¯μ+μ− final state at the LHC

The Higgs boson pair production via gluon-gluon fusion and vector boson fusion in the $b\bar{b}\mu^+\mu^-$ final state at the LHC is studied to probe the Higgs self-coupling $\kappa_\lambda$ and the four-boson HHVV coupling $\kappa_{\rm{2V}}$ for the first time. A cut-based analysis and a machine learning analysis using boosted decision trees are performed with categorizations and optimizations depending on the variations of these couplings. The expected sensitivities are extracted with different integrated luminosities assumed up to the full HL-LHC runs. The expected upper limit at 95\% confidence level on the HH production is calculated as 47 (28) times the Standard Model cross-section using the cut-based method (boosted decision trees) for the gluon-gluon fusion production, and 928 for the vector boson fusion production, assuming an integrated luminosity of 3000 fb$^{-1}$. The expected constraints on the couplings at 95\% confidence level are calculated to be $-13.8< \kappa_{\lambda}< 19.1$ ($-10.0< \kappa_{\lambda}< 15.5$) and $-3.4< \kappa_{\rm{2V}}< 5.5$ using the cut-based method (boosted decision trees), respectively, assuming an integrated luminosity of 3000 fb$^{-1}$.

Higgs boson induced reheating and ultraviolet frozen-in dark matter

A reheating phase in the early universe is an essential part of all inflationary models during which not only the Standard Model (SM) quanta are produced but it can also shed light on the production of dark matter. In this work, we explore a class of reheating models where the reheating is induced by a cubic interaction of the inflaton ϕ to the SM Higgs boson h of the form ghϕMPlϕ|h|2 adopting the α-attractor T-model of inflation. Assuming inflaton as a background field such interaction implies a ϕ-dependent mass term of the Higgs boson and a non-trivial phase-space suppression of the reheating efficiency. As a consequence, the reheating is prolonged and the maximal temperature of the SM thermal bath is reduced. In particular, due to oscillations of the inflaton field the ϕ-dependent Higgs boson mass results in periodic transitions between phases of broken and unbroken electroweak gauge symmetry. The consequences of these rapid phase transitions have been studied in detail. A purely gravitational reheating mechanism in the presence of the inflaton background, i.e., for ghϕ = 0, has also been investigated. It turned out that even though it may account for the total production of SM radiation in the absence of ghϕ, its contribution to the reheating is subdominant for the range of ghϕ considered in this work. Approximate analytical solutions of Boltzmann equations for energy densities of the inflaton and SM radiation have been obtained. As a dark matter candidate a massive Abelian vector boson, Xμ, has been considered. Various production mechanisms of Xμ have been discussed including (i) purely gravitational production from the inflaton background, (ii) gravitational freeze-in from the SM quanta, (iii) inflaton decay through a dim-5 effective operator, and (iv) Higgs portal freeze-in and Higgs decay through a dim-6 effective operator. Parameters that properly describe the observed relic abundance have been determined.

Exploring dark Z_d-boson in future large hadron-electron collider

The interaction between the dark U(1)_d sector with the visible Standard Model (SM) sector takes place through the kinetic mixing between the dark photon U(1)_d field Z_d^mu and the SM U(1)_Y gauge field B_mu . After the electroweak and U(1)_d symmetry breaking, the dark photon Z_d^mu acquires a mass and mixes with the SM neutral vector boson Z_mu . This mixing leads to parity-violating coupling between the Z_d^mu and SM. The coupling between the dark photon and SM can be explored in low energy phenomenology as well as in collider experiments. The Lorentz structure of dark photon interaction with SM fermions is explored in the proposed high energy future Large Hadron-electron collider, which would provide efficient energy and a clean environment using cross-section and asymmetries associated with polarisation observable of the dark photon in leptons decay. A chi ^2-analysis is performed to compare the strength of various variables for both the charge- and neutral-current processes. Based on this analysis, 90% confidence level (C.L.) contours in the varepsilon -m_{Z_d} and varepsilon -g_V plane are obtained to put limits on the Z_d^mu mass up to 100 GeV, coupling strength varepsilon and on the Lorentz structure of dark photon coupling with the SM fermions (g_V) at sqrt{s} approx 1.3 TeV.

Two-loop QCD corrections to the V → qoverline{q}g helicity amplitudes with axial-vector couplings

We compute the two-loop corrections to the helicity amplitudes for the coupling of a massive vector boson to a massless quark-antiquark pair and a gluon, accounting for vector and axial-vector couplings of the vector boson and distinguishing isospin non-singlet and singlet contributions. A new four-dimensional basis for the decomposition of the amplitudes into 12 invariant tensor structures is introduced. The associated form factors are then computed up to two loops in QCD using dimensional regularization. After performing renormalization and infrared subtraction, the finite parts of the renormalized non-singlet vector and axial-vector form factors are shown agree with each other, and to reproduce the previously known two-loop amplitudes. The singlet axial-vector amplitude receives a contribution from the axial anomaly from two loops onwards. This amplitude is computed for massless and massive internal quarks. Our results provide the last missing two-loop amplitudes entering the NNLO QCD corrections of vector-boson-plus-jet production at hadron colliders.