Standard Model Branching Ratio Research Articles

Non-universality Relationships for Charged Higgs Boson Yukawa Couplings in the Two Higgs Doublet Model Type III

In the context of the two Higgs doublet model type III with flavor-changing neutral currents at the tree level, I obtain non-universality relationships of charged Higgs boson Yukawa coupling constants by calculating the widths of the pure leptonic decays of the tau lepton τ→eν¯eντ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au \\rightarrow e \\bar{\ u }_e \ u _\ au$$\\end{document} and τ→μν¯μντ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au \\rightarrow \\mu \\bar{\ u }_\\mu \ u _\ au$$\\end{document}. To this end, I first calculate these total widths by including the effects of the exchanges of the Higgs boson H-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H^-$$\\end{document} and the gauge boson W-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$W^-$$\\end{document}, with the purpose to obtain the flavor-violating contribution ΔlH-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _l^{H^-}$$\\end{document} and then to calculate the fraction ΔμH-/ΔeH-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta _\\mu ^{H^-}/\\Delta _e^{H^-}$$\\end{document}. By writing this fraction in terms of the experimental and electroweak standard model branching ratios of these decays and assuming that flavors of neutrino and antineutrino in the final state are defined but unknown, I obtain fractions of charged Higgs boson Yukawa coupling constants that differ from one. These fractions establish non-universality relationships associated with the scalar interaction in contrast to the universality relationships associated with the electroweak interaction.

Dark photon effect on the rare kaon decay

We present an analysis of the effect of a dark photon on the rare kaon decay . All relevant couplings of the dark photon to the standard model particles are derived explicitly in terms of the dark photon mass and the mixing parameter. We find that the dark photon yields no more than a few percent correction to the standard model branching ratio in the region of interest.

Measurement of the very rare K+\u2192 {pi}^{+}nu overline{nu} decay

The NA62 experiment reports the branching ratio measurement mathrm{BR}left({K}^{+}to {pi}^{+}nu overline{nu}right)=left({10.6}_{-3.4}^{+4.0}left|{}_{mathrm{stat}}right.pm {0.9}_{mathrm{syst}}right)times {10}^{-11} at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016–2018. This provides evidence for the very rare K+→ {pi}^{+}nu overline{nu} decay, observed with a significance of 3.4σ. The experiment achieves a single event sensitivity of (0.839 ± 0.054) × 10−11, corresponding to 10.0 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. This measurement is also used to set limits on BR(K+→ π+X), where X is a scalar or pseudo-scalar particle. Details are given of the analysis of the 2018 data sample, which corresponds to about 80% of the total data sample.

An investigation of the very rare {K}^{+}to {pi}^{+}nu overline{nu} decay

The NA62 experiment reports an investigation of the {K}^{+}to {pi}^{+}nu overline{nu} mode from a sample of K+ decays collected in 2017 at the CERN SPS. The experiment has achieved a single event sensitivity of (0.389 ± 0.024) × 10−10, corresponding to 2.2 events assuming the Standard Model branching ratio of (8.4 ± 1.0) × 10−11. Two signal candidates are observed with an expected background of 1.5 events. Combined with the result of a similar analysis conducted by NA62 on a smaller data set recorded in 2016, the collaboration now reports an upper limit of 1.78 × 10−10 for the {K}^{+}to {pi}^{+}nu overline{nu} branching ratio at 90% CL. This, together with the corresponding 68% CL measurement of ( {0.48}_{-0.48}^{+0.72} ) × 10−10, are currently the most precise results worldwide, and are able to constrain some New Physics models that predict large enhancements still allowed by previous measurements.

Inspection of new physics in Bs→K+K− decay mode

We scrutinize the penguin dominated $ B_s \to K^+ K^-$ decay mode involving $b \to s$ quark level transition in family non-universal $Z^ \prime$ and vector-like down quark model. There is discrepancy in the standard model branching ratio value of this mode with the experimental results reported by Belle, CDF and LHCb Collaborations. Additionally, the measured values of CP-violating asymmetries $ C_{K^+K^-}$ and $ S_{K^+K^-}$ deviate from the SM results. We constrain the new parameter space by using the existing experimental limits on leptonic $ B_s\to \ell \ell$ ($\ell = e, \mu, \tau$) processes. We then check the effects of new physics on the branching ratio and CP violating parameters of the $ B_s \to K^+ K^-$ process.

Testing lepton flavour universality with (semi)-leptonic varvec{D_{(s)}} decays

Data in B-meson decays indicate violations of lepton flavour universality, thereby raising the question about such phenomena in the charm sector. We perform a model-independent analysis of NP contributions in (semi)-leptonic decays of D_{(s)} mesons which originate from c rightarrow d bar{{ell }} nu _l and c rightarrow s bar{{ell }} nu _{ell } charged-current interactions. Starting from the most general low-energy effective Hamiltonian containing four-fermion operators and the corresponding short-distance coefficients, we explore the impact of new (pseudo)-scalar, vector and tensor operators and constrain their effects through the interplay with current data. We pay special attention to the elements |V_{cd}| and |V_{cs}| of the Cabibbo–Kobayashi–Maskawa matrix and extract them from the D_{(s)} decays in the presence of possible NP decay contributions, comparing them with determinations utilizing unitarity. We find a picture in agreement with the Standard Model within the current uncertainties. Using the results from our analysis, we make also predictions for leptonic D_{(s)}^+ rightarrow e^+ nu _e modes which could be hugely enhanced with respect to their tiny Standard Model branching ratios. It will be interesting to apply our strategy at the future high-precision frontier.

Search for Higgs boson pair production in the gamma gamma WW^* channel using pp collision data recorded at sqrt{s}=13 TeV with the ATLAS detector

Searches for non-resonant and resonant Higgs boson pair production are performed in the gamma gamma WW^* channel with the final state of gamma gamma ell nu jj using 36.1 hbox {fb}^{-1} of proton–proton collision data recorded at a centre-of-mass energy of sqrt{s}=13 TeV by the ATLAS detector at the Large Hadron Collider. No significant deviation from the Standard Model prediction is observed. A 95% confidence-level observed upper limit of 7.7 pb is set on the cross section for non-resonant production, while the expected limit is 5.4 pb. A search for a narrow-width resonance X decaying to a pair of Standard Model Higgs bosons HH is performed with the same set of data, and the observed upper limits on sigma (pprightarrow X)times B(Xrightarrow HH) range between 40.0 and 6.1 pb for masses of the resonance between 260 and 500 GeV, while the expected limits range between 17.6 and 4.4 pb. When deriving the limits above, the Standard Model branching ratios of the H{rightarrow }{gamma gamma } and H{rightarrow }WW^* are assumed.

Search for new light gauge bosons in Higgs boson decays to four-lepton final states inppcollisions ats=8 TeVwith the ATLAS detector at the LHC

This paper presents a search for Higgs bosons decaying to four leptons, either electrons or muons, via one or two light exotic gauge bosons $Z_d$, $H\to Z Z_d \to 4\ell$ or $H\to Z_d Z_d \to 4\ell$. The search was performed using $pp$ collision data corresponding to an integrated luminosity of about 20 fb$^{-1}$ at the center-of-mass energy of $\sqrt{s}=8 $TeV recorded with the ATLAS detector at the Large Hadron Collider. The observed data are well described by the Standard Model prediction. Upper bounds on the branching ratio of $H\to Z Z_d \to 4\ell$ and on the kinetic mixing parameter between the $Z_d$ and the Standard Model hypercharge gauge boson are set in the range $(1$--$9)\times10^{-5}$ and $(4$--$17)\times10^{-2}$ respectively, at 95% confidence level assuming the Standard Model branching ratio of $H\to Z Z^* \to 4\ell$, for $Z_d$ masses between 15 and 55 GeV. Upper bounds on the effective mass mixing parameter between the $Z$ and the $Z_d$ are also set using the branching ratio limits in the $H \to ZZ_d\to 4\ell$ search, and are in the range $(1.5$--$8.7)\times 10^{-4}$ for $15<m_{Z_d} < 35$ GeV. Upper bounds on the branching ratio of $H\rightarrow Z_dZ_d \to 4\ell$ and on Higgs portal coupling parameter, controlling the strength of the coupling of the Higgs boson to dark vector bosons, are set in the range $(2$--$3)\times10^{-5}$ and $(1$--$10)\times 10^{-4}$ respectively, at 95% confidence level assuming the Standard Model Higgs boson production cross sections, for $Z_d$ masses between 15 and 60 GeV.

The B ¯ → K ¯ πℓℓ $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and B ¯ s → K ¯ Kℓℓ $$ {\overline{B}}_s\ \to \overline{K}K\ell \ell $$ distributions at low hadronic recoil

The rare multi-body decays $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ are both important as backgrounds to precision analyses in the benchmark modes $$ \overline{B}\to {\overline{K}}^{*}\ell \ell $$ and $$ {\overline{B}}_s\to \phi \ell \ell $$ as well as sensitive probes of flavor physics in and beyond the standard model. We work out non-resonant contributions to $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ amplitudes, where l = e,μ, at low hadronic recoil in a model-independent way. Using the operator product expansion in 1/m b , we present expressions for the full angular distribution. The latter allows to probe new combinations of |ΔB| = |ΔS| = 1 couplings and gives access to strong phases between non-resonant and resonant contributions. Exact endpoint relations between transversity amplitudes based on Lorentz invariance are obtained. Several phenomenological distri- butions including those from the angular projections to the S-, P-, D-waves are given. Standard model branching ratios for non-resonant $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ decays are found to be in the few 10−8 region, but drop significantly if cuts around the K * or ϕ mass are employed. Nevertheless, the non-resonant contributions to $$ \overline{B}\to \overline{K}\pi \ell \ell $$ provide the dominant background in the $$ \overline{B}\to {\overline{K}}^{*}\ell \ell $$ signal region with respect to the low mass scalars. In $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ , the narrowness of the ϕ allows for more efficient background control. We briefly discuss lepton-flavor non-universal effects, also in view of the recent data on R K .

Probing new physics with $B^0_s\to\mu^+\mu^-$: Status and perspectives

The rare decay [Formula: see text] plays a key role for the testing of the Standard Model. It is pointed out that the sizable decay width difference ΔΓsof the Bs-meson system affects this channel in a subtle way. As a consequence, its calculated Standard Model branching ratio has to be upscaled by about 10%. Moreover, the sizable ΔΓsmakes a new observable through the effective [Formula: see text] lifetime accessible, which probes New Physics in a way complementary to the branching ratio and adds an exciting new topic to the agenda for the high-luminosity upgrade of the LHC. Further probes of New Physics are offered by a CP-violating rate asymmetry. Correlations between these observables and the [Formula: see text] branching ratio are illustrated for specific models of New Physics.

Constraining New Physics with D meson decays

Latest Lattice results on D form factors evaluation from first principles show that the Standard Model (SM) branching ratios prediction for the leptonic Ds→ℓνℓ decays and the semileptonic SM branching ratios of the D0 and D+ meson decays are in good agreement with the world average experimental measurements. It is possible to disprove New Physics hypothesis or find bounds over several models beyond the SM. Using the observed leptonic and semileptonic branching ratios for the D meson decays, we performed a combined analysis to constrain non-standard interactions which mediate the cs¯→lν¯ transition. This is done either by a model-independent way through the corresponding Wilson coefficients or in a model-dependent way by finding the respective bounds over the relevant parameters for some models beyond the Standard Model. In particular, we obtain bounds for the Two Higgs Doublet Model Type-II and Type III, the Left–Right model, the Minimal Supersymmetric Standard Model with explicit R-parity violation and Leptoquarks. Finally, we estimate the transverse polarization of the lepton in the D0 decay and we found it can be as high as PT=0.23.

CPsuperH2.3: An updated tool for phenomenology in the MSSM with explicit CP violation

We describe the Fortran code CPsuperH2.3, which incorporates the following updates compared with its predecessor CPsuperH2.0. It implements improved calculations of the Higgs-boson masses and mixing including stau contributions and finite threshold effects on the tau-lepton Yukawa coupling. It incorporates the LEP limits on the processes e+e−→HiZ,HiHj and the CMS limits on Hi→τ̄τ obtained from 4.6 fb−1 of data at a center-of-mass energy of 7 TeV. It also includes the decay mode Hi→Zγ and the Schiff-moment contributions to the electric dipole moments of Mercury and Radium 225, with several calculational options for the case of Mercury. These additions make CPsuperH2.3 a suitable tool for analyzing possible CP-violating effects in the MSSM in the era of the LHC and a new generation of EDM experiments.11The program may be obtained from http://www.hep.man.ac.uk/u/jslee/CPsuperH.html, or by contacting the first author at jslee@jnu.ac.kr. Program summaryProgram title: CPsuperH2.3Catalogue identifier: ADSR_v3_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADSR_v3_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 24058No. of bytes in distributed program, including test data, etc.: 158721Distribution format: tar.gzProgramming language: Fortran77.Computer: PC running under Linux and computers in Unix environment.Operating system: Linux.RAM: 32 MBClassification: 11.1.Does the new version supersede the previous version?: YesCatalogue identifier of previous version: ADSR_v2_0Journal reference of previous version: Comput. Phys. Comm. 180(2009)312Nature of problem:The calculations of mass spectrum, decay widths and branching ratios of the neutral and charged Higgs bosons in the Minimal Supersymmetric Standard Model with explicit CP violation have been improved. The program is based on renormalization-group-improved diagrammatic calculations that include dominant higher-order logarithmic and threshold corrections, b-quark and τ-lepton Yukawa-coupling resummation effects and improved treatment of Higgs-boson pole-mass shifts. The couplings of the Higgs bosons to the Standard Model gauge bosons and fermions, to their supersymmetric partners and all the trilinear and quartic Higgs-boson self-couplings are also calculated. Also included are a full treatment of the 4×4 (2×2) neutral (charged) Higgs propagator matrix together with the center-of-mass dependent Higgs-boson couplings to gluons and photons, and an integrated treatment of several B-meson observables. The new implementations include the EDMs of Thallium, neutron, Mercury, Deuteron, Radium, and muon, as well as the anomalous magnetic moment of muon, (gμ−2), the top-quark decays, improved calculations of the Higgs-boson masses and mixing including stau contributions, the LEP limits, and the CMS limits on Hi→ττ̄. It also implements the decay mode Hi→Zγ and includes the corresponding Standard Model branching ratios of the three neutral Higgs bosons in the array GAMBRN(IM,IWB = 2,IH).Solution method:One-dimensional numerical integration for several Higgs-decay modes and EDMs, iterative treatment of the threshold corrections and Higgs-boson pole masses, and the numerical diagonalization of the neutralino mass matrix.Reasons for new version:Mainly to provide the full calculations of the EDMs of Thallium, neutron, Mercury, Deuteron, Radium, and muon as well as (gμ−2), improved calculations of the Higgs-boson masses and mixing including stau contributions, the LEP limits, the CMS limits on Hi→ττ̄, the top-quark decays, Hi→Zγ decay, and the corresponding Standard Model branching ratios of the three neutral Higgs bosons.Summary of revisions:Full calculations of the EDMs of Thallium, neutron, Mercury, Deuteron, Radium, and muon as well as (gμ−2). Improved treatment of Higgs-boson masses and mixing including stau contributions. The LEP limits. The CMS limits on Hi→ττ̄. The top-quark decays. The Hi→Zγ decay. The corresponding Standard Model branching ratios of the three neutral Higgs bosons.Running time:Less than 1.0 s.

LEPTON FLAVOR CONSERVING Z BOSON DECAYS AND SCALAR UNPARTICLE

We predict the contribution of scalar unparticle to the branching ratios of the lepton flavor conserving Z → l+l- decays and we study the discrepancy between the experimental and the QED corrected standard model branching ratios. We observe that these decays are sensitive to the unparticle scaling dimension du for its small values, especially for heavy lepton flavor output.

Probing new physics in B→φπ decay

We analyze the rare decay mode B→φπ, which is a pure penguin induced process, receiving dominant contribution from the electroweak penguins. Thus the Standard Model branching ratio is expected to be very small, which makes it as a sensitive probe of new physics. Using QCD factorization approach, we find the branching ratio in the Standard Model as Br(B−→φπ−)≃5×10−9. Exploring some of the beyond Standard Model scenarios the branching ratio is found to be ∼O(10−8) in the minimal supersymmetric Standard Model (MSSM) with mass insertion approximation and in the extended technicolor model (TC2). The existence of an extra vector-like down quark (VLDQ) model predicts it to be ∼O(10−7). The recent BaBar result on B0→φπ0 might be a strong indication of new physics effect present in the penguin induced process B→φπ.

Erratum: Distinguishing a minimal supersymmetric standard model Higgs boson from the SM Higgs boson at a linear collider [Phys. Rev. D65, 055005 (2002)

The decoupling properties of the Higgs sector in the Minimal Supersymmetric Standard Model (MSSM) imply that a light CP-even Higgs boson discovered at the Tevatron or LHC may closely resemble the Standard Model (SM) Higgs boson. In this paper, we investigate how precision measurements of Higgs properties at a Linear Collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson. We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle alpha and tan beta-enhanced vertex corrections. The general expectation is that the Higgs couplings to W+W-, ZZ, c cbar and t tbar should quickly approach their SM values for increasing CP-odd Higgs mass mA, while the couplings to b bbar and tau+ tau- do so more slowly. Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit. For a wide range of MSSM parameters, the LC is sensitive to mA ~ 600 GeV almost independently of tan beta. For large values of tan beta and some specific choices of MSSM parameters [e.g., A_t mu < 0 and |A_t| ~ |mu| ~ O(M_S)], one of the CP-even Higgs bosons can be SM-like independent of the value of mA. In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.

Distinguishing a minimal supersymmetric standard model Higgs boson from the SM Higgs boson at a linear collider

The decoupling properties of the Higgs sector in the minimal supersymmetric standard model (MSSM) imply that a light CP-even Higgs boson discovered at the Fermilab Tevatron or CERN LHC may closely resemble the standard model (SM) Higgs boson. In this paper, we investigate how precision measurements of Higgs properties at a linear collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson. We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle \ensuremath{\alpha} and $\mathrm{tan}\ensuremath{\beta}$-enhanced vertex corrections. The general expectation is that the Higgs couplings to ${W}^{+}{W}^{\ensuremath{-}},$ ZZ, $c\overline{c},$ and $t\overline{t}$ should quickly approach their SM values for increasing CP-odd Higgs boson mass ${m}_{A},$ while the couplings to $b\overline{b}$ and ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ do so more slowly. Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit. For a wide range of MSSM parameters, the LC is sensitive to ${m}_{A}\ensuremath{\sim}600\mathrm{GeV}$ almost independently of $\mathrm{tan}\ensuremath{\beta}.$ For large values of $\mathrm{tan}\ensuremath{\beta}$ and some specific choices of MSSM parameters [e.g., ${A}_{t}\ensuremath{\mu}&lt;0$ and $|{A}_{t}|\ensuremath{\simeq}|\ensuremath{\mu}|\ensuremath{\simeq}\mathcal{O}{(M}_{S})$], one of the CP-even Higgs bosons can be SM-like independent of the value of ${m}_{A}.$ In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.

CKM - Charged Kaons at the Main Injector

The CKM experiment is a proposal to measure the branching ratio of the rare decay K + → π +ν ν at the Main Injector at Fermilab using a decay in flight technique. The goal is to observe ⋍ 100 events, for a Standard Model branching ratio of 1 × 10 −10 with a background of less than 10 events.

Charged kaons at the main injector (CKM)

The CKM collaboration is proposing to measure the branching ratio of the rare K decay K + → π +ν ▪ at the Main Injector at Fermilab. Our goal is to be able to observe ⋍ 100 events, for a Standard Model branching ratio of ⋍ 1 × 10 −10. This implies that we must be able to reduce the background to a few events at a reasonable cost.