Pure Leptonic Decays Research Articles

Non-universality of leptons as a source of new physics from tree level interactions of pseudoscalar mesons

This article is based on the study of pure leptonic decays of charged pseudoscalar mesons taking non-universality into account. We calculate the branching ratios of the processes π±,K±,D±,Ds±,B±. For the search for new physics (NP), we examine the discrepancies between theoretical and experimental results. The discrepancies are possibly due to massive neutrinos, processed massless in the Standard Model (SM), and universal coupling of leptons. We focus on the non-universality of leptons in order to find the bounds on Non-Standard Interaction (NSI) parameters ɛ. We use charge current like NSI and conclude that these decays could provide strong constraints on the NSI parameter.

Lepton collider probes for Majorana neutrino effective interactions

The extension of the standard model with new high-scale weakly coupled physics involving right-handed neutrinos in an effective field theory framework (SMNEFT) allows for a systematic study of heavy neutrinos phenomenology in current and future experiments. We exploit the outstanding angular resolution in future lepton colliders to study the sensitivity of forward–backward asymmetries to discover the possible single production of heavy Majorana neutrinos via e^{+}e^{-} rightarrow N nu , followed by a purely leptonic decay N rightarrow mu ^{-} mu ^{+} nu or a semi-leptonic decay N rightarrow mu ^{-} text {j} text {j} , for masses m_N > 50 GeV. In this regime, we consider the N production and decays to be dominated by scalar and vectorial four-fermion d=6 single N_R operators. This is an alternative analysis to searches using displaced vertices and fat jets, in a higher mass regime, where the N is short-lived but can be found by the angular distribution of its decay products. We find that a forward–backward asymmetry between the final muons in the pure leptonic decay mode provides a sensitivity up to 12sigma for m_N=100 GeV, for effective couplings alpha =0.2 and new physics scale Lambda =1 TeV. In the case of the semi-leptonic decay, we can compare the final muon and higher p_T jet flight directions, again finding up to 12sigma sensitivity to the effective signals.

Prospects of CKM elements |V_{cs}| and decay constant f_{D_{s}^+} in D_s^+rightarrow mu ^+nu _mu decay at STCF

We report a feasibility study of pure leptonic decay D_s^+rightarrow mu ^+nu _mu by using a fast simulation software package at STCF. With an expected luminosity of 1~mathrm {ab}^{-1} collected at STCF at a center-of-mass energy of 4.009 GeV, the statistical sensitivity of the branching fraction is determined to be 0.3%. Combining this result with the c rightarrow s quark mixing matrix element |V_{cs}| determined from the current global Standard Model fit, the statistical sensitivity of D_s^+ decay constant, f_{D_s^+}, is estimated to be 0.2%. Alternatively, combining the current results of f_{D_s^+} calculated by lattice QCD, the statistical sensitivity of |V_{cs}| is determined to be 0.2%, which helps probe possible new physics beyond Standard Model. The unprecedented precision to be achieved at STCF will provide a precise calibration of QCD and rigorous test of Standard Model.

Sensitivity analysis for the anomalous $$W^+W^-\gamma $$ couplings at the LHeC and the FCC-he

We study the anomalous $W^+W^-\gamma$ couplings in performing the production of the W-pair through the process $e^- p\,\rightarrow\,e^-\gamma^*\gamma^* p\,\rightarrow\,e^-W^+W^-p$ at the Large Hadron electron Collider (LHeC) and the Future Circular Collider-hadron electron (FCC-he). We examine the pure hadronic, the semi-leptonic and the pure leptonic decay channels of the produced W-pair. We assume the center-of-mass energies of $\sqrt{s}=1.30$ and $1.98$ TeV and the integrated luminosities of 10-100 fb$^{-1}$ for the LHeC and the center-of-mass energies of $\sqrt{s}=3.46$ and $5.29$ TeV and the integrated luminosities of 100-2000 fb$^{-1}$ for the FCC-he. The best limits at 95$\%$ confidence level obtained for the anomalous couplings $\Delta\kappa_{\gamma}$ and $\lambda_{\gamma}$ are $\Delta\kappa_{\gamma}=[-0.00208; 0.00206]$ and $\lambda_{\gamma}=[-0.00174; 0.00834]$. By comparing these limits with the experimental limits, we present the potentials of the process and future $ep$ colliders.

Analysis of the anomalous quartic WWWW couplings at the LHeC and the FCC-he

The quartic gauge boson couplings that identify the strengths of the gauge boson self-interactions are exactly determined by the non-Abelian gauge nature of the Standard Model. The examination of these couplings at $ep$ collisions with high center-of-mass energy and high integrated luminosity provides an important opportunity to test the validity of the Standard Model and the existence of new physics beyond the Standard Model. The quartic gauge boson couplings can contribute directly to multi-boson production at colliders. Therefore, we examine the potential of the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron to study non-standard $WWWW$ couplings in a model independent way by means of the effective Lagrangian approach. We present an investigation on measuring $W^{+}W^{-}$ production in pure leptonic and semileptonic decay channels. In addition, we calculate the sensitivity limits at $95\%$ Confidence Level on the anomalous $\frac{f_{M0}}{\Lambda^{4}}$, $\frac{f_{M1}}{\Lambda^{4}}$, $\frac{f_{M7}}{\Lambda^{4}}$, $\frac{f_{S0}}{\Lambda^{4}}$, $\frac{f_{S1}}{\Lambda^{4}}$, $\frac{f_{T0}}{\Lambda^{4}}$, $\frac{f_{T1}}{\Lambda^{4}}$ and $\frac{f_{T2}}{\Lambda^{4}}$ couplings obtained by dimension-8 operators through the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ for the Large Hadron Electron Collider and the Future Circular Hadron Electron Collider's different center-of-mass energies and integrated luminosities. Our results show that with the process $ep \rightarrow \nu_{e}W^{+}W^{-} j$ at the Large Hadron Electron Collider and the Future Circular Collider-hadron electron the sensitivity estimated on the anomalous $WWWW$ couplings can be importantly strengthened.

Investigation on effects of new physics in transitions * *Supported in part by the National Natural Science Foundation of China (11975195, 11705159); the Natural Science Foundation of Shandong province (ZR2019JQ004, ZR2018JL001) and the Project of Shandong Province Higher Educational Science and Technology Program (2019KJJ007)

Anomalies in decays induced by ( ) transitions may imply lepton flavor universality violations, which raises questions on such phenomena in the D decays induced by transitions. Current measurements of the pure leptonic and semi-leptonic D decays agree with the standard model (SM) predictions, and such agreements can be used to constrain the new physics (NP) contributions. In this work, we extend SM by assuming general effective Hamiltonians describing the transitions including the full set of the four-fermion operators. With the latest experimental data, we perform a least fit of the Wilson coefficient corresponding to each operator. The results indicate that the Wilson coefficients of tensor and scalar operators in the muon sector are in the order of while others are in the order of . The lepton flavor universality could be violated by interactions with the scalar operators. We also determine that the pure leptonic decays are significantly sensitive to scalar operators. The effects of NP on the semi-leptonic decays with electron final state are negligible; however, for the decays with the muon final state, the effects of scalar and tensor operators will appear in the forward-backward asymmetries and the muon helicity asymmetries of decays. The future measurements of these decays in the BESIII and Belle II experiments will facilitate the evaluation of NP effects.

Probing the anomalous electromagnetic dipole moments of the top quark in γp collision at the LHC, the HL-LHC and the HE-LHC

The determination of the electromagnetic dipole moments of the top quark is one of the most important goals of the top quark physics program in the collider experiments. For this reason, the top quark pair production to investigate the sensitivity on the electric and magnetic dipole moments of the top quark via the process pp→pγp→ptt¯X at the Large Hadron Collider (LHC), the High-Luminosity Large Hadron Collider (HL-LHC) and High-Energy Large Hadron Collider (HE-LHC) is discussed. We apply pure leptonic and semileptonic decays for top quark pair production in the final state. Moreover, we consider systematic uncertainties of 0,3% and 5%. The best limits obtained from the process pp→pγp→ptt¯X on the anomalous aA and aV couplings are |aA|=0.0200 and aV=[−0.9959;0.0003]. Thus, our results indicate that the process pp→pγp→ptt¯X is a very good perspective to probe the electric and magnetic dipole moments of the top quark at the HL-LHC and the HE-LHC.

Search for the electromagnetic moments of the τ lepton in photon–photon collisions at the LHeC and the FCC-he

We examine the potential of the process at the Large Hadron Electron Collider (LHeC) and the Future Circular Collider-hadron electron (FCC-he) in order to examine non-standard coupling in a model-independent way by means of an effective Lagrangian approach. We perform pure leptonic and semileptonic decays for production in the final state. Furthermore, we use L = 10, 50, 100, 300, 500, 1000 fb−1 with , and we consider systematic uncertainties of δsys = 0, 5, 10%. The best sensitivity bounds obtained from the process on the anomalous couplings are and , respectively. Therefore, our results show that the process at the LHeC and FCC-he shows very good prospects for probing the anomalous magnetic and electric dipole moments of the τ lepton at the mode of the future ep collider.

Sterile neutrino and leptonic decays of the pseudoscalar mesons

We consider a scenario with only one sterile neutrino $ N $, negligible mixing with the active neutrinos $ \nu_{L} $, where its interactions with ordinary particles could be described in a model independent approach based on an effective theory. Under such a framwork, we consider the contributions of the sterile neutrino $N$ to the pure leptonic decays $ M \rightarrow l\nu $ and $ \nu \overline{\nu} $, and the radiative leptonic decays $ M \rightarrow l\nu\gamma $ with $M$ denoting the pseudoscalar mesons $ B $, $ D $ and $ K$. We find that it can produce significant effects on some of these rare decay processes.

Study of Rare Mesonic Decays Involving Di-Neutrinos in Their Final State

We have studied phenomenological implication of R-parity violating (Rp) Minimal Supersymmetric Model (MSSM) via analyses of pure leptonic (M→νν¯) and semileptonic decays of pseudoscalar mesons (M→Xνν¯). These analyses involve comparison between theoretical predictions made by Rp MSSM and the Standard Model (SM) with the experimental results like branching fractions (Br) of the said process. We have found, in general, that Rp contribution dominates over the SM contribution, i.e., by a factor of 10 for the pure leptonic decays of KL,S and by 102 and 104 in case of Bs and Bd, respectively. Furthermore, the limits obtained on Rp Yukawa couplings (λαkβ′λαkγ′⁎) by using Br (M→Xνν¯) are used to calculate Br (M→νν¯). This demonstrates the role of Rp MSSM as a viable model for the study of new physics contribution in rare decays at places like Super B factories, KOTO (J-PARC) and NA62 at CERN.

Looking for new physics via semi-leptonic and leptonic rare decays of D and Ds**Supported by National Natural Science Foundation of China (11675082, 11375128, 11405046) and Special Grant of the Xuzhou University of Technology (XKY2016211)

It is well recognized that looking for new physics at lower energy colliders is a path which is complementary to high energy machines such as the LHC. Using the large volume of data collected by BESIII, we may have a unique opportunity to tackle this. In this paper we calculate the branching ratios of the semi-leptonic processes and , and the leptonic processes D0→e−e+ and D0→e−μ+, in the frameworks of the U(1)′ model, 2HDM and unparticle model. It is found that both the U(1)′ model and 2HDM may influence the semi-leptonic decay rates, but only the U(1)′ model offers substantial contributions to the pure leptonic decays, and the resultant branching ratio of D0→e−μ+ can be as large as 10−7∼10−8. This might be observed at the future super τ-charm factory.

Decay constants and distribution amplitudes of B meson in the relativistic potential model

In this work we study the decay constants of $B$ and $B_s$ mesons based on the wave function obtained in the relativistic potential model. Our results are in good agreement with experimental data which enables us to apply this method to the investigation of $B$-meson distribution amplitudes. A very compact form of the distribution amplitude is obtained. We also investigate the one-loop QCD corrections to the pure leptonic decays of $B$ mesons. We find that, after subtracting the infrared divergence in the one-loop corrections using the factorization method, the QCD one-loop corrections to the hard amplitude of leptonic decay will be zero.

Leptonic Decays of Heavy Vector and Pseudoscalar Mesons**Supported by the National Natural Science Foundation of China under Grant Nos. 11375021, 11575017, the New Century Excellent Talents in University (NCET) under Grant No. NCET-13-0030, the Major State Basic Research Development Program of China under Grant No. 2015CB856701, and the Fundamental Research Funds for the Central Universities

Pure leptonic decays of and are investigated. The hadronic contributions such as are also explored. We then obtain the updated branching fractions of the pseudoscalar mesons to lepton pairs are modified by a factor of few percentages. Specifically, the is reduced by a factor 13%.

Probing triple-W production and anomalous WWWW coupling at the CERN LHC and future O 100 $$ \mathcal{O}(100) $$ TeV proton-proton collider

Triple gauge boson production at the LHC can be used to test the robustness of the Standard Model and provide useful information for VBF di-boson scattering measurement. Especially, any derivations from SM prediction will indicate possible new physics. In this paper we present a detailed Monte Carlo study on measuring WWW production in pure leptonic and semileptonic decays, and probing anomalous quartic gauge WWWW couplings at the CERN LHC and future hadron collider, with parton shower and detector simulation effects taken into account. Apart from cut-based method, multivariate boosted decision tree method has been exploited for possible improvement. For the leptonic decay channel, our results show that at the sqrt{s}=8(14)[100] TeV pp collider with integrated luminosity of 20(100)[3000] fb-1, one can reach a significance of 0.4(1.2)[10]sigma to observe the SM WWW production. For the semileptonic decay channel, one can have 0.5(2)[14]sigma to observe the SM WWW production. We also give constraints on relevant Dim-8 anomalous WWWW coupling parameters.

CERN LHC sensitivity on measuringW±Zγproduction and anomalousWWZγcoupling

In this paper we present for the first time a detailed Monte Carlo study of measuring ${W}^{\ifmmode\pm\else\textpm\fi{}}Z\ensuremath{\gamma}$ production with pure leptonic decays and probing anomalous quartic gauge-boson $WWZ\ensuremath{\gamma}$ couplings at the $\sqrt{s}=14\text{ }\text{ }\mathrm{TeV}$ LHC, with parton shower and detector simulation effects taken into account. We find that with an integrated luminosity of $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ and proper selection cuts, the Standard Model ${W}^{\ifmmode\pm\else\textpm\fi{}}Z\ensuremath{\gamma}$ signal significance can be improved to as much as $3\ensuremath{\sigma}$. After reviewing previous parametrizations on anomalous $WWZ\ensuremath{\gamma}$ couplings [see e.g. ${a}_{n}/{\ensuremath{\Lambda}}^{2}$ or ${k}_{2}^{m}/{\ensuremath{\Lambda}}^{2}$ as shown in Belanger et al. Eur. Phys. J. C 13, 283 (2000)], we propose a more general parametrization scheme with four free inputs leading only to genuine $WWZ\ensuremath{\gamma}$ aQGC couplings. Finally, our numerical results show that one can reaches constraints at 95% confidence level of $\ensuremath{-}5.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}l{k}_{2}^{m}/{\ensuremath{\Lambda}}^{2}l5.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}$ and $\ensuremath{-}2.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}l{a}_{n}/{\ensuremath{\Lambda}}^{2}l2.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\text{ }\text{ }{\mathrm{GeV}}^{\ensuremath{-}2}$, which are more stringent than LEP's results by three orders of magnitude.

Probing W + W −γ production and anomalous quartic gauge boson couplings at the CERN LHC

Triple gauge boson associated production at the LHC serves as an interesting channel to test the robustness of the Standard Model. Any deviation from its SM prediction may indicate possible existence of relevant new physics, e.g., anomalous quartic gauge boson couplings. In this paper, a Monte-Carlo feasibility study of measuring WWA production with pure leptonic decays and probing anomalous quartic gauge-boson (e.g., WWAA) couplings, is presented in detail for the first time, with parton shower and detector simulation effects taken into account. Our results show that at the sqrt{s} = 14 TeV LHC with an integrated luminosity of 100 (30) fb-1, one can reach a significance of 9 (5) sigma to observe the SM WWA production, and can constrain at the 95% CL the anomalous WWAA coupling parameters, e.g., a_{0,c}^W/\Lambda^2 (see Ref.[15] for their definitions), at 10^{-5} GeV^{-2}, respectively.

Constraints from the decay [formula omitted] and LHC limits on Supersymmetry

The pure leptonic decay Bs0→μ+μ− is strongly suppressed in the Standard Model (SM), but can have large enhancements in Supersymmetry, especially at large values of β. New limits on this decay channel from recent LHC data have been used to claim that these limits restrict the SUSY parameter space even more than the direct searches. However, direct searches are hardly dependent on tanβ, while Br(Bs0→μ+μ−) is proportional to tan6β. The relic density constraint requires large tanβ in a large region of the parameter space, which can lead to large values of Bs0→μ+μ−. Nevertheless, the experimental upper limit on Br(Bs0→μ+μ−) is not constraining the parameter space of the CMSSM more than the direct searches and the present Higgs limits, if combined with the relic density. We also observe SUSY parameter regions with negative interferences, where the Bs0→μ+μ− value is up to a factor three below the SM expectation, even at large values of tanβ.

Uncertainty study of D−S(D−)→γlν̄(l = e, μ) decays determined by wave function

Wave function is important for determining decay constants fD−S and fD−. Using the 5 types of D meson wave functions in the heavy quark limit, we studied the uncertainties of radiative pure-leptonic decays of D−S(D−) mesons. The branching ratios are (1.025390−1.706812)×10−5 and (0.953498−1.576725)×10−6 for D−S and D− decays, respectively, which are sensitive to the type of wave function.

Bs,d → μ+μ− decays in a flavor changing Z′ model

We study the pure leptonic decays Bs,d → μ+μ− in a Flavor Changing Z′ Model. From the recent measurements of the branching ratios ß(Bs,d → μ+μ−), we have derived the bounds on the effective μ-μ-Z′ lepton coupling BLμμ. We find that, (i) if neglecting the contribution from the right-handed lepton coupling BRμμ, we obtain 1.32 < BLμμ < 3.32; (ii) if considering the contribution from the right-handed lepton coupling BRμμ and setting BLμμ = BRμμ, we obtain 0.99 < BLμμ < 2.19. Our results could be useful for researching Z′ effects.

Radiative and flavor-violating transitions of leptons from interactions with color-octet particles

It has recently been proposed that neutrino mass could originate from Yukawa interactions of leptons with new colored particles. This raises the interesting possibility of testing mass generation through copious production of those particles at hadron colliders. A realistic assessment of this, however, should take into account how large those interactions could be, based on available precision results. In this work we make a systematic analysis of the flavor structure in Yukawa couplings, provide a convenient parametrization, and investigate the rare radiative and pure leptonic decays of the muon and tau leptons. For general values of the parameters, the muon decays set stringent constraints on the couplings, and all rare tau decays are far below the current experimental sensitivity. However, there is room in parameter space in which the muon decays could be significantly suppressed by destructive interference between colored particles without generically reducing the couplings themselves. This is also the region of parameters that is relevant to collider physics. We show that for this part of parameter space some tau decays can reach or are close to the current level of precision.