Search

Flavour physics is one of the essential elements of the Standard Model (SM). Experimental studies of weak decays of B and D mesons at B factories have, together with the discovery of the Higgs boson at LHC, provided the final confirmation of the validity of the SM. The present generation of precision flavour physics experiments is looking for departures from the SM. We discuss studies of anomalies in b hadron decays, and studies of rare decays, which are a very promising method for searching for new physics. This article is part of the theme issue 'The particle-gravity frontier'. [ABSTRACT FROM AUTHOR]

Relativistic corrections to the pair production of mesons and baryons consisting of heavy quarks and in the Higgs boson decay are calculated. Relativistic amplitudes and decay rates are constructed within perturbative Standart Model and relativistic quark model. The numerical values of the relativistic effects turn out to be significant and must be taken into account in order to achieve good calculation accuracy. [ABSTRACT FROM AUTHOR]

It was demonstrated in a series of papers employing unitarized chiral perturbation theory that the phenomenology of the scalar open-charm state, the D 0 ∗ (2300) , can be understood as the interplay of two poles, corresponding to two scalar-isospin doublet states with different SU(3) flavor content. Within this formalism the lightest open charm positive parity states emerge as being dynamically generated from the scattering of the Goldstone-boson octet off D mesons, a picture that at the same time solves various problems that the experimental observations posed. However, in recent lattice studies of D π scattering at different pion masses only one pole was reported in the D 0 ∗ channel, while it was not possible to extract reliable parameters of a second pole from the lattice data. In this paper we demonstrate how this seeming contradiction can be understood and that imposing SU(3) constraints on the fitting amplitudes allows one to extract information on the second pole from the lattice data with minimal bias. The results may also be regarded as a showcase how approximate symmetries can be imposed in the K-matrix formalism to reduce the number of parameters. [ABSTRACT FROM AUTHOR]

The associated production of prompt J/ψ and Υ mesons in pp collisions at a centre-of-mass energy of s = 13 TeV is studied using LHCb data, corresponding to an integrated luminosity of 4 fb−1. The measurement is performed for J/ψ (Υ) mesons with a transverse momentum pT< 10 (30) GeV/c in the rapidity range 2.0 < y < 4.5. In this kinematic range, the cross-section of the associated production of prompt J/ψ and Υ(1S) mesons is measured to be 133 ± 22 ± 7 ± 3 pb, with a significance of 7.9 σ, and that of prompt J/ψ and Υ(2S) mesons to be 76 ± 21 ± 4 ± 7 pb, with a significance of 4.9 σ. The first uncertainty is statistical, the second systematic, and the third due to uncertainties on the used branching fractions. This is the first observation of the associated production of J/ψ and Υ(1S) in proton-proton collisions. Differential cross-sections are measured as functions of variables that are sensitive to kinematic correlations between the J/ψ and Υ(1S) mesons. The effective cross-sections of the associated production of prompt J/ψ and Υ mesons are obtained and found to be compatible with measurements using other particle productions. [ABSTRACT FROM AUTHOR]

The CKM angle γ is determined from CP-violating observables measured in B± → D[K∓π±π±π∓]h±, (h = K, π) decays, where the measurements are performed in bins of the decay phase-space of the D meson. Using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to a total integrated luminosity of 9 fb−1, γ is determined to be γ = 54.8 + 6.0 − 5.8 + 0.6 − 0.6 + 6.7 − 4.3 ∘ , where the first uncertainty is statistical, the second systematic and the third from the external inputs on the coherence factors and strong phases of the D-meson decays. [ABSTRACT FROM AUTHOR]

The production of inclusive, prompt and non-prompt J/ψ was studied for the first time at midrapidity (−1.37 < ycms< 0.43) in p-Pb collisions at s NN = 8.16 TeV with the ALICE detector at the LHC. The inclusive J/ψ mesons were reconstructed in the dielectron decay channel in the transverse momentum (pT) interval 0 < pT< 14 GeV/c and the prompt and non-prompt contributions were separated on a statistical basis for pT> 2 GeV/c. The study of the J/ψ mesons in the dielectron channel used for the first time in ALICE online single-electron triggers from the Transition Radiation Detector, providing a data sample corresponding to an integrated luminosity of 689 ± 13 μb−1. The proton-proton reference cross section for inclusive J/ψ was obtained based on interpolations of measured data at different centre-of-mass energies and a universal function describing the pT-differential J/ψ production cross sections. The pT-differential nuclear modification factors RpPb of inclusive, prompt, and non-prompt J/ψ are consistent with unity and described by theoretical models implementing only nuclear shadowing. [ABSTRACT FROM AUTHOR]

The first observation of the B s 0 → D∗+D∗− decay and the measurement of its branching ratio relative to the B0→ D∗+D∗− decay are presented. The data sample used corresponds to an integrated luminosity of 9 fb−1 of proton-proton collisions recorded by the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV between 2011 and 2018. The decay is observed with more than 10 standard deviations and the time-integrated ratio of branching fractions is determined to be B B s 0 → D ∗ + D ∗ − B B 0 → D ∗ + D ∗ − = 0.269 ± 0.032 ± 0.011 ± 0.008 , where the first uncertainty is statistical, the second systematic and the third due to the uncertainty of the fragmentation fraction ratio fs/fd. The B s 0 → D*+D*− branching fraction is calculated to be B B s 0 → D ∗ + D ∗ − = 2.15 ± 0.26 ± 0.09 ± 0.06 ± 0.16 × 10 − 4 , where the fourth uncertainty is due to the B0→ D*+D*− branching fraction. These results are calculated using the average B s 0 meson lifetime in simulation. Correction factors are reported for scenarios where either a purely heavy or a purely light B s 0 eigenstate is considered. [ABSTRACT FROM AUTHOR]

Using a symmetry-preserving regularisation of a vector × vector contact interaction (SCI), we complete a systematic treatment of twelve semileptonic transitions with vector meson final states: D → ρ , D (s) → K ∗ , D s → ϕ , B → ρ , B s → K ∗ , B (s) → D (s) ∗ , B c → B (s) ∗ , J / ψ , D ∗ ; and thereby finalise a unified analysis of semileptonic decays of heavy + heavy and heavy + light pseudoscalar mesons to both pseudoscalar and vector meson final states. The analysis is marked by algebraic simplicity, few parameters, and the ability to consistently describe systems from Nambu-Goldstone modes to heavy + heavy mesons. Regarding the behaviour of the transition form factors, the SCI results compare well wherever sound experimental or independent theory analyses are available; hence, the SCI branching fraction predictions should be a reasonable guide. Considering the ratios R (D (s) (∗)) , R (J / ψ) , R (η c) , whose values are key tests of lepton universality in weak interactions, the SCI values agree with Standard Model predictions. The B (s) → D (s) ∗ transitions are used to predict the precursor functions that evolve into the universal Isgur–Wise function in the heavy-quark limit, with results that conform with those from other sources where such are available. The study also exposes effects on the transition form factors that flow from interference between emergent hadron mass from the strong interaction and Higgs boson couplings via current-quark masses, including flavour symmetry violation. [ABSTRACT FROM AUTHOR]

We present a likelihood analysis of the general two Higgs doublet model, using the most important currently measured flavour observables, in view of the anomalies in charged current tree-level and neutral current one-loop rare decays of B mesons in b → cl ν ¯ and b → sμ+μ− transitions, respectively. We corroborate that the model explains the latter and it is able to simultaneously fit the experimental values of the R(D) charged current ratio at 1σ, but it can not accommodate the D* charmed meson observables R(D*) and FL(D*). We find that the fitted values for the angular observables in b → sμ+μ− transitions exhibit better agreement with the general two Higgs double model in comparison to the SM. We also make predictions for future collider observables BR(t → ch), BR(h → bs), BR(h → τμ), BR(Bs → τ+τ−), BR(B+ → K+τ+τ−) and the flavour violating decays of the τ lepton, BR(τ → 3μ) and BR(τ → μγ). The model predicts values of BR(t → ch), BR(Bs → τ+τ−) and BR(B+ → K+τ+τ−) that are out of reach of future experiments, but its predictions for BR(h → bs) and BR(h → τμ) are within the future sensitivity of the HL-LHC or the ILC. We also find that the predictions for the τ → 3μ and τ → μγ decays are well within the projected limits of the Belle II experiment. Finally, using the latest measurement of the Fermilab Muon g − 2 Collaboration, we performed a simultaneous fit to ∆aμ constrained by the charged anomalies, finding solutions at the 1σ level. Once the neutral anomalies are included, however, a simultaneous explanation is unfeasible. [ABSTRACT FROM AUTHOR]

We investigate rare production of the pair of S- and P-wave B c -meson in the Higgs boson decay in the perturbative Standard Model and relativistic quark model. Relativistic amplitudes and decay widths are constructed with the account of the relative motion of heavy quarks forming B c mesons. When constructing the Higgs boson decay amplitudes, the method of projection operators on the S- and P-wave states of quarks is used. Relativistic corrections are expressed in terms of special relativistic parameters and are calculated numerically in the quark model. The dependence of the decay widths of the Higgs boson on various sources of relativistic corrections is investigated. [ABSTRACT FROM AUTHOR]

A symmetry-preserving regularisation of a vector × vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving π , K, D (s) , B (s , c) initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu–Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured B s , c branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on B (s) → D (s) transitions yield a prediction for the Isgur–Wise function in fair agreement with contemporary data. [ABSTRACT FROM AUTHOR]

Many models of dark matter predict long-lived particles (LLPs) that can give rise to striking signatures at the LHC. Existing searches for displaced vertices are however tailored towards heavy LLPs. In this work we show that this bias severely affects their sensitivity to LLPs with masses at the GeV scale. To illustrate this point we consider two dark sector models with light LLPs that decay hadronically: a strongly-interacting dark sector with long-lived exotic mesons, and a Higgsed dark sector with a long-lived dark Higgs boson. We study the sensitivity of an existing ATLAS search for displaced vertices and missing energy in these two models and find that current track and vertex cuts result in very low efficiency for light LLPs. To close this gap in the current search programme we suggest two possible modifications of the vertex reconstruction and the analysis cuts. We calculate projected exclusion limits for these modifications and show that they greatly enhance the sensitivity to LLPs with low mass or short decay lengths. [ABSTRACT FROM AUTHOR]

Experimental measurements collected by the BABAR, Belle, and LHCb experiments on different observables associated with the semileptonic transition , indicate the existence of disagreement respect with the Standard Model predictions. We analyze the charged scalar boson contributions to these charged-current B meson anomalies within the framework of two Higgs doublet model (2HDM) with the most general Yukawa couplings to quarks and leptons from the third generation, involving left-handed and right-handed (sterile) neutrinos. We perform a phenomenological study of the Yukawa couplings parameter space that accommodates these anomalies. We consider the most recent data from HFLAV world-average and Belle combination, and the upper limits and 10%. In addition, we include in our study the prospect measurements on R(D(*)) that the Belle II experiment could achieve and explore, for the first time, the future implications for the corresponding charged scalar Yukawa couplings. This analysis updates the existing literature and includes new important observables. Our results show that current experimental data and Belle II projection favor the interpretation of a charged scalar boson interacting with right-handed neutrinos. Furthermore, as a side analysis regarding the charged scalar boson interpretation, we revisit the relation between R(D*) and by investigating whether the claim that pseudoscalar new physics interpretations of R(D*) are implausible due to the Bc lifetime is still valid, to the light of the recent data and Belle II prospects on R(D*). Lastly, we reexamine addressing the R(D(*)) anomalies in the context of the 2HDM of type II. We show that with the current Belle combined data is possible to obtain an available parameter space on the plane for a simultaneous explanation of the anomalies, in consistency with and bounds from inclusive radiative B decays. Moreover, projections at the Belle II experiment suggest that the 2HDM of type II would be no longer disfavored. [ABSTRACT FROM AUTHOR]

Decays of the 125 GeV Higgs boson into a Z boson and a ρ0(770) or ϕ(1020) meson are searched for using proton-proton collision data collected by the CMS experiment at the LHC at s = 13 TeV. The analysed data set corresponds to an integrated luminosity of 137 fb−1. Events are selected in which the Z boson decays into a pair of electrons or a pair of muons, and the ρ and ϕ mesons decay into pairs of pions and kaons, respectively. No significant excess above the background model is observed. As different polarization states are possible for the decay products of the Z boson and ρ or ϕ mesons, affecting the signal acceptance, scenarios in which the decays are longitudinally or transversely polarized are considered. Upper limits at the 95% confidence level on the Higgs boson branching fractions into Zρ and Zϕ are determined to be 1.04–1.31% and 0.31–0.40%, respectively, where the ranges reflect the considered polarization scenarios; these values are 740–940 and 730–950 times larger than the respective standard model expectations. These results constitute the first experimental limits on the two decay channels. [ABSTRACT FROM AUTHOR]

We study phenomenological constraints on the simple 3-3-1 model with flavor-violating Yukawa couplings. Both Higgs triplets couple to leptons and quarks, which generates flavor-violating signals in both lepton and quark sectors. We have shown that this model allows for a large Higgs lepton flavor-violating rate decay h → μ τ and also may reach perfect agreement with other experimental constraints such as τ → μ γ and (g - 2) μ . The contributions of flavor-changing neutral current couplings, Higgs–quark–quark couplings, mixing to the mesons are investigated. Br (h → q q ′) can be enhanced acknowledging the measurements of meson mixing. The branching ratio for t → q h can reach up to 10 - 3 , but it could be as low as 10 - 8 . [ABSTRACT FROM AUTHOR]

We investigate supersymmetric models with left-right symmetry based on the group S U (4) c × S U (2) L × S U (2) R (4-2-2) with negative sign of bilinear Higgs potential parameter μ in the context of the latest experimental results. In the backdrop of experimental results from the Large Hadron Collider, we investigate the possibility of Yukawa unification in 4-2-2 and find out the same is still not ruled out. Furthermore, this scenario also provides a satisfactory dark matter candidate. The current experimental bounds on sparticle masses, mass bounds on Higgs particle, updated phenomenological constraints from the rare decays of B meson and the anomalous magnetic moment of muon with the requirement of a Yukawa unified theory having 10% or better third family Yukawa unification are utilized to bound the parametric space of these models. [ABSTRACT FROM AUTHOR]

I discuss how to access dense baryonic matter of compact stars by combining hidden local symmetry (HLS) of light-quark vector mesons with spontaneously broken scale invariance of a (pseudo) Nambu-Goldstone boson, dilaton, in a description that parallels the approach to dilatonic Higgs. Some of the surprising observations are that the bulk of proton mass is not Nambu-Goldstonian, parity doubling emerges at high density and the EoS of baryonic matter can be soft enough for heavy-ion processes at low density and stiff enough at high density for solar mass neutron stars. [ABSTRACT FROM AUTHOR]

Weak radiative B-meson decays are known to provide strong bounds on the charged Higgs boson mass in the Two-Higgs-Doublet Model. In the so-called Model-II, the 95% C.L. lower bound on MH± is now in the 570–800 GeV range, depending quite sensitively on the method applied for its determination. Here, we present and discuss the updated bounds. [ABSTRACT FROM AUTHOR]

In this work we investigate the observability of inert doublet model scalars at the LHC operating at the center of mass energy of 14TeV. The signal production process is pp → AH± → ZHW±H leading to two different final states of ℓ+ℓ-H jj H and ℓ+ℓ-Hℓ ± νH based on the hadronic and leptonic decay channels of theWboson. All the relevant background processes are considered and an event selection is designed to distinguish the signal from the large Standard Model background. We found that signals of the selected search channels are well observable at the LHC with an integrated luminosity of 300 fb-1. [ABSTRACT FROM AUTHOR]

Ever since the discovery of the electron more than 100 years ago, scientists have asked the questions -'what is our universe made of?' and 'why is the universe the way it is?' Not long before, it was found that these two questions are related to each other. The interactions of particles in the universe determines its evolution, its very form, and existence. In this article, we will trace the discovery of some of these particles, learn about their interactions, and try to understand their properties such as electric charge and mass. [ABSTRACT FROM AUTHOR]

In this work, we study the radiative leptonic decays of and mesons in the Standard Model (SM) and two-Higgs-doublet-model (2HDM) Type II. The results are obtained using the factorization procedure, and the contribution of the order is included. The numerical results are calculated using the wave function obtained in relativistic potential model. As a result, the decay mode is found to be sensitive to the effect of the charged Higgs boson. Using the constraint on the free parameters of 2HDM given in previous works, we find the contribution of the charged Higgs boson in the decay mode can be as large as about 13%. [ABSTRACT FROM AUTHOR]

In two-Higgs-doublet models with exact symmetry, putting at the alignment limit, the following limits on the heavy scalar masses are obtained from the conditions of unitarity and stability of the scalar potential: , , and . The constraints from and neutral meson mass differences, when superimposed on the unitarity constraints, put a tighter lower limit on depending on . It has also been shown that larger values of can be allowed by introducing soft breaking term in the potential at the expense of a correlation between and the soft breaking parameter. [ABSTRACT FROM AUTHOR]