The rare $b\to sν\barν$ decays are sensitive to contributions of new physics (NP) and helpful to resolve the puzzle of multiple $B$ flavor anomalies. In this work, we propose to study the $b\to sν\barν$ transition at a future lepton collider operating at the $Z$ pole through the $B_s \to ϕν\barν$ decay. Using the $B_s\toϕ$ decay form factors from lattice simulations, we first update the SM prediction of BR($B_s \to ϕν\barν)_{\mathrm{SM}}=(9.93\pm 0.72)\times 10^{-6}$ and the corresponding $ϕ$ longitudinal polarization fraction $F_{L,{\mathrm{SM}}}=0.53\pm 0.04$. Our analysis uses the full CEPC simulation samples with a net statistic of $\mathcal{O}(10^9)$ $Z$ decays. Precise $ϕ$ and $B_s$ reconstructions are used to suppress backgrounds. The results show that BR($B_s \to ϕν\barν)$ can be measured with a statistical uncertainty of $\mathcal{O}(\%)$ and an $S/B$ ratio of $\mathcal{O}(1)$ at the CEPC. The quality measures for the event reconstruction are also derived. By combining the measurement of BR($B_s \to ϕν\barν)$ and $F_L$, the constraints on the effective theory couplings at low energy are given.
Accurately measuring the properties of the Higgs boson is one of the core physics objectives of the Circular Electron Positron Collider (CEPC). As a Higgs factory, the CEPC is expected to operate at a centre-of-mass energy of $240\,GeV$, deliver an integrated luminosity of $5.6\,ab^{-1}$, and produce one million Higgs bosons according to the CEPC Conceptual Design Report (CDR). Combining measurements of the $\ell^+\ell^-H$, $ν\barν H$, and $q\bar{q}H$ channels, we conclude that the signal strength of $H\to b\bar{b}/c\bar{c}/gg$ can be measured with a relative accuracy (statistic uncertainty on…
In the Circular Electron Positron Collider (CEPC), a measurement of the Higgs CP mixing through $e^{+} e^{-} \rightarrow Z H \rightarrow l^{+} l^{-}(e^{+} e^{-} /μ^{+} μ^{-}) H(\rightarrow b \bar{b} / c \bar{c} / g g)$ process is presented, with $5.6\ \mbox{ab}^{-1}$ $e^{+} e^{-}$ collision data at the center-of-mass energy of $240\ \mathrm{GeV}$. In this study, the CP-violating parameter $\tilde{c}_{Z γ}$ is constrained between the region of $ -0.30$ and $0.27$ and $\tilde{c}_{Z Z}$ between $-0.06$ and $0.06$ at $68\%$ confidence level. This study demonstrates the great potential of probing H…
The existence of dark matter has been established in astrophysics. However, there is no candidate for DM in the Stand Model (SM). In SM, the Higgs boson can only decay invisibly via $H\rightarrow ZZ^\ast \rightarrow ν\barνν\barν$ or DM, so any evidence of invisible Higgs decay that exceeds BR (H$\rightarrow$inv.) will immediately point to a phenomenon that is beyond the standard model (BSM). In this paper, we report on the upper limit of BR (H$\rightarrow$invisible) estimated for three channels, including two leptonic channels and one hadronic channel, under the assumption predicted by SM. Wit…
We study the production of heavy sterile neutrino $N$, $e^+ e^- \to N ν({\bar ν})$, at the Circular Electron Positron Collider(CEPC) and its $ljj$ signal in its decay to three charged fermions. We study background events for this process which are mainly events coming from W pair production. We study the production of a single heavy sterile neutrino and the sensitivity of CEPC to the mixing of sterile neutrino with active neutrinos. We study the production of two degenerate heavy sterile neutrinos in a low energy see-saw model by taking into account the constraints on mixings of sterile neutri…
The current knowledge on the $D^{\ast}$ mesons are still inadequate. Encouraged by the positive development prospects of high-luminosity and high-precision experiments, the Cabibbo-favored nonleptonic $D^{\ast}$ ${\to}$ $\bar{K}π^{+}$, $\bar{K}^{\ast}π^{+}$, $\bar{K}ρ^{+}$ weak decays are studied with the naive factorization approach. It is found that branching ratios of these processes can reach up to ${\cal O}(10^{-10})$ or more, and can be accessible at STCF, CEPC, FCC-ee and LHCb@HL-LHC experiments in the future. It might even be possible to search for the $D^{{\ast}0}$ ${\to}$ $K^{{\ast}-…
We study the four-body semileptonic baryonic decay of $B^-\to Λ\bar pν\bar ν$ in the standard model. We find that the decay branching ratio is $(7.9\pm 1.9)\times 10^{-7}$. Similar to the rare decays of $B^-\to K^{(*)-}ν\bar ν$, this baryonic decay of $B^-\to Λ\bar pν\bar ν$ is also sensitive to new physics and accessible to the future $B$ factories.
The branching fractions of the rare weak $B\to πl^+l^-(ν\barν)$ and $B\toρl^+l^-(ν\barν)$ decays are calculated in the framework of the relativistic quark model based on the quasipotential approach. The form factors parametrizing weak decay matrix elements are explicitly determined in the whole kinematical $q^2$ range without additional assumptions and extrapolations. Relativistic effects are systematically taken into account including recoil effects in meson wave functions and contributions of the intermediate negative-energy states. New experimental data on the differential distributions in …
The rare pion decays $π^+{\rightarrow}μ^+ν_μν\barν$ and $π^+{\rightarrow}e^+ν_{e}ν\barν$ are allowed in the Standard Model but highly suppressed. These decays were searched for using data from the PIENU experiment. A first result for $Γ(π^+{\rightarrow}μ^+ν_μν\barν)/Γ(π^+{\rightarrow}μ^+ν_μ)<8.6{\times}10^{-6}$, and an improved measurement $Γ(π^+{\rightarrow}{e}^+ν_{e}ν\barν)/Γ(π^+{\rightarrow}μ^+ν_μ)<1.6{\times}10^{-7}$ were obtained.
We compute the contribution of the decays $K_L \rightarrow π^0 Q \bar Q$ and $K^+ \rightarrow π^+ Q \bar Q$, where $Q$ is a dark fermion of the dark sector, to the measured widths for the rare decays $K^+\rightarrow π^+ ν\bar ν$ and $K_L\rightarrow π^0 ν\bar ν$. The recent experimental limit for $Γ(K^+ \rightarrow π^+ ν\bar ν)$ from NA62 sets a new and very strict bound on the dark-sector parameters. A branching ratio for $K_L \rightarrow π^0 Q \bar Q$ within the reach of the KOTO sensitivity is possible. The Grossman-Nir bound is weakened by the asymmetric effect of the different kinematic cu…
We investigate the implications of the model with a SU(2)-singlet up-type quark, heavy enough not to be produced at the LHC, namely, the contribution of the new quark to the branching ratios of the K to πν\barν, B to πν\barν and B to K ν\barν decays. We show that the deviation from the Standard Model can be up to 10% in the case of a 5 TeV quark. Precise measurements of these branching ratios at the future experiments will allow to observe the contributions of the new quark or to impose stronger constraints on its mass.
FCNC processes offer important tools to test the Standard Model (SM), and to search for possible new physics. In this work, we investigate the $s\to dν\barν$ rare hyperon decays in SM and beyond. We find that in SM the branching ratios for these rare hyperon decays range from $10^{-14}$ to $10^{-11}$. When all the errors in the form factors are included, we find that the final branching fractions for most decay modes have an uncertainty of about $5\%$ to $10\%$. After taking into account the contribution from new physics, the generalized SUSY extension of SM and the minimal 331 model, the deca…
We review the present status of rare B decays, focusing on inclusive decay modes and their role in our search for new physics. We also briefly discuss direct CP violation in rare B decays and the rare kaon decays $K^+\to π^+ν\barν$ and $K_L \to π^0 ν\barν$, which offer complementary opportunities for precision flavour physics.
The anomalous results of recent measurements on various $b\to sμ^+μ^-$ processes could be initial evidence of physics beyond the standard model (SM). Assuming this to be the case, we entertain the possibility that the underlying new physics also affects the rare nonleptonic decays of the $\bar B_s^0$ meson. We consider in particular new physics arising from the interactions of a heavy $Z'$ boson and investigate their influence on the decay modes $\bar B_s^0\to(η,η',ϕ)ω$, which receive sizable QCD- and electroweak-penguin contributions. These decays are not yet observed, and their rates are est…
Deep-learning jet flavor tagging for precision hadronic Higgs measurements at future $e^+e^-$ Higgs factories
Shanghai Jiao Tong University（上海交通大学）；Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）
[Review for "Chinese Science Bulletin" and CEPC+SPPC Proposal] Rare decays in flavor physics often suffer from Helicity suppress and Loop suppress. Helicity flip is a direct consequence of chiral $U(3)$ symmetry breaking and electroweak symmetry breaking. The identical feature is also shared by the mass generation of SM fermions. In this review, we use MSSM as an example to illustrate an explicit connection between bottom Yukawa coupling and rare decay process of $b\to sγ$. We take a symmetry approach to study the common symmetry breaking in supersymmetric correction to bottom quark mass gener…
We review the current status of flavor-changing neutral currents in the charm sector. We focus on the standard-model predictions and identify the main sources of theoretical uncertainties in both charm mixing and rare charm decays. The potential of these observables for constraining short-distance physics in the standard model and its extensions is compromised by the presence of large nonperturbative effects. We examine the possible discovery windows in which short-distance physics can be tested and study the effects of various extensions of the standard model. The current experimental situati…
The present data on a number of observables in $b\to sμ^+μ^-$ processes manifest some tensions with the standard model (SM). Assuming that these anomalies have a new physics origin, we consider the possibility that a $Z'$ boson is responsible for them. We further assume that its interactions with quarks also affect rare nonleptonic decays of the $\bar B_s^0$ meson which are purely isospin-violating and tend to be dominated by electroweak-penguin contributions, namely $\bar B_s^0\to(η,η',ϕ)(π^0,ρ^0)$. Most of these decays are not yet observed, and their rates are expected to be relatively small…
Rare inclusive $B$ decays such as $\bar{B}\to X_{s(d)} \ell^+\ell^-$ are interesting probes for physics beyond the Standard Model. Due to the complementarity to their exclusive counterparts, they might shed light on the anomalies currently seen in exclusive $b \to s$ transitions. Distinguishing new-physics effects from the Standard Model requires precise predictions and necessitates the control of long distance effects. In the present work we revisit and improve the description of various long distance effects in inclusive decays such as charmonium and light-quark resonances, nonfactorisable p…
Exclusive rare Higgs decays into lepton pair plus one light hadron, such as $h\to ρ^0(ω)\ell\bar{\ell}$, $h\to π^0\ell\bar{\ell}$, $h\to π^+ (K^+)\ell^-\barν_\ell$, and $h\to ρ^+(K^{*+})\ell^-\barν_\ell$, have been explored in the standard model. Decay amplitudes are dominantly from the Higgs couplings to gauge bosons and to charged leptons, and their branching ratios are predicted in the range of $10^{-8}\sim 10^{-5}$. We have also analyzed the differential dilepton invariant mass and angular distributions of $h\to ρ^0 \ell^+\ell^-$ decays. It will be challenging to search for these rare proc…
We study the $D-\bar D$ mixing and rare D decays in the Littlest Higgs model. As the new weak singlet quark with the electric charge of 2/3 is introduced to cancel the quadratic divergence induced by the top-quark, the standard unitary $3\times 3$ Cabibbo-Kobayashi-Maskawa matrix is extended to a non-unitary $4\times 3$ matrix in the quark charged currents and Z-mediated flavor changing neutral currents are generated at tree level. In this model, we show that the $D-\bar D$ mixing parameter can be as large as the current experimental value and the decay branching ratio (BR) of $D\to X_u \ga$ i…
We study the rare decay process of $Z$ boson into photon, accompanied by a CP-even or CP-odd scalar. We present the analytical delineation of the processes through the model-independent parametrizations of the new physics couplings and, finally, consider the Next-to-Minimal Supersymmetric Standard Model to mark out the parameter space where the branching fraction can have the maximum value. As a part of the necessary phenomenological and experimental cross-checks, we aim to fit the anomalous magnetic moment of the muon and $W$ boson mass anomaly through the supersymmetric contributions. We als…
We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, $Ξ_c^+\toΣ^+\,(\to pπ^0)\ell^+\ell^-$, $Ξ_c^0\toΛ^0\,(\to p π^-)\ell^+\ell^-$ and $Ω_c^0\toΞ^0\,(\to Λ^{0} π^0)\ell^+\ell^-$. Such self-analyzing decay chains allow for seven additional observables compared to three-body decays such as $Λ_c \to p \ell^+ \ell^-$, with different sensitivities to the $|Δc|=|Δu|=1$ weak couplings. Opportunities to test the standard model in $c \to u$ transitions with standard model null tests and ot…
The decay width of the rare decay Z \to ν\barνγγis strictly constrained from the LEP data. Tensor unparticles provide a tree-level contribution to this rare decay. We have calculated the tensor unparticle contribution to the rare decay Z\to ν\barνγγ. The current experimental limit have been used to constrain unparticle couplings ν\barνZ {U}^{μν} and γγ{U}^{μν}.
Rare $|Δc|=|Δu|=1$ transitions into dineutrinos are strongly GIM-suppressed and constitute excellent null tests of the standard model. While branching ratios of $D \to P \,ν\bar ν$, $D \to P^+ P^- \, ν\bar ν$, $P=π, K$, baryonic $Λ_c^+ \to p \,ν\bar ν$, and $Ξ_c^+ \to Σ^+ \, ν\bar ν$ and inclusive $D \to X ν\bar ν$ decays are experimentally unconstrained, signals of new physics can be just around the corner. We provide model-independent upper limits on branching ratios reaching few $\times 10^{-5}$ in the most general case of arbitrary lepton flavor structure, $\sim 10^{-5}$ for scenarios with…
Rare $\vert Δc \vert=\vert Δu \vert=1$ processes uniquely probe flavor in the Standard Model and beyond from the up-type quark sector. Opportunities to search for BSM physics in charm arise from the severe GIM suppression which kills SM contributions to leptonic axial-vector contributions and suppresses CP violation. Semileptonic decays of charmed hadrons offer a variety of clean null test observables, featuring new physics effects which are even enhanced by resonance contributions. In particular, angular observables in three- and self-analyzing four-body baryon decays, such as $Λ_c\to p \ell^…
A resonance $Y(4630)$ at the invariant mass spectrum of $Λ_c \barΛ_c$ observed by the Belle Collaboration triggers a hot discussion about its inner structure. Since it preferably decays into two charmed baryons $Λ_c\barΛ_c$, it is tempted to conjecture it as a tetraquark. Because the dominant decay portal $Y(4630)\to Λ_c \barΛ_c$ is close to the energy threshold, the final state interactions may be significant and result in other baryonic and/or mesonic final states whose branching fractions are sizable to be measured in the future experiments. In this work we calculate the branching ratios of…
The rare $B\to K^{*}ν\barν$ decay when $K^{*}$ meson is longitudinally or transversely polarized is analysed in the context of the fourth generation model. A significant enhancement to the missing energy spectrum over the SM is recorded.
We give a status report on inclusive rare B decays, highlighting recent developments and open problems. We focus on the decay modes $B \to X_{s,d} γ$, $ B \to X_s \ell^+\ell^-$ and $B \to X_s ν\bar ν$ and on their role in the search for new physics. Most of the inclusive rare B decays are important modes of flavour physics due to the small hadronic uncertainties. They can be regarded as laboratories to search for new physics. We collect the experimental data already available from CLEO and the $B$ factories BABAR and BELLE. We review the NLL and NNLL QCD calculations of the inclusive decay rat…
The rare decay b -> s s bar{d} is studied in the supersymmetric standard model by considering the contribution from the chargino box diagrams. We find that this contribution amounts to 10^{-9} in the branching ratio.
In this paper we consider CP-violating new-physics contributions to the decay $t \to b \bar b c$. We examine the prospects for detecting such new physics at the LHC, which requires studying the process $gg \to t (\to b \bar b c) \bar t (\to \bar b \ell \bar ν)$. We find two observables that can be used to reveal the presence of CP-violating new physics in $t \to b \bar b c$. They are (i) the partial-rate asymmetry and (ii) the triple-product correlations involving the momenta of various particles associated with the interaction. A Monte Carlo analysis is performed to determine how well these o…
We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized $Λ_c \to p \ell^+ \ell^-$, $\ell=e, μ$ decays, and study the new physics sensitivities. We find that the longitudinal dilepton polarization fraction $F_L$ is sensitive to electromagnetic dipole couplings $C_{7}^{(\prime)}$, and to the right-handed 4-fermion vector coupling $C_{9}^\prime$. The forward-backward asymmetry, $A_{\rm FB}$, due to the GIM-suppression a standard model null test already, probes the left-handed axialvector 4-fermion coupling $C_{10}$; its CP-asy…
Using the most general, model-independent form of effective Hamiltonian, the exclusive, rare $B \rar K^\ast ν\bar ν$ decay is analyzed. The sensitivity of the branching ratios and missing mass-squared spectrum to the new Wilson coefficients is discussed.
We explore the impact of topflavour model to $B-\bar{B}$ mixings and rare decays of $B$ mesons. By the flavour-changing neutral current interactions of this model, the $B-\bar{B}$ mixing amplitudes are substantially affected while it is hard to investigate the effects on rare decays. Violation of the unitarity of the CKM matrix is also discussed. We find that the bound on $|V_{td}|$ can be stronger in this model by combining the experimental bound of the $B-\bar{B}$ mixing and the bound from violated unitarity.
Using the light cone QCD Sum Rules Method, we study the rare B -> nu barnu gamma decay and and find that the branching ratios are, B(B_s -> nu barnu gamma) = 7.5 10^{-8}, B(B_d -> nu -> nu gamma) = 4.2 10^{-9}. A comparision of our results, on branching ratio, with constituent quark and pole dominance model predictions are presented.
We compute the branching fraction of the decays $B \to K ν\barν$ and $B \to K^* ν\barν$ in the Standard Model. We also comment on the experimental difficulties and procedures to detect such modes at B factories.
Using the most general, model independent effective Hamiltonian, the rare B_s ->γν\barν decay with polarized photon is studied. The sensitivity of the branching ratio and photon polarization to the new Wilson coefficients are investigated. It is shown that these physical observables are sensitive to the vector and tensor type interactions, which would be useful in search of new physics.
The rare k+--->pi+ ν\barν decay is investigated in the context of type II two-Higgs-doublet model (2HDM). By using the existing experimental data of the branching ratio, restrictions on the free parameters of the model m_H, and tanβare obtained: tanβbelong to the range 0.7- o.8, and m_H belong to the range 500- 700 GeV.
The rare decay B^+ \to D_s^+ \bar K^{*0} can occur only via annihilation diagrams in the Standard Model. We calculate the branching ratio in perturbative QCD approach based on k_T factorization theorem. We found that the branching ratio of this decay is about of order 10^{-8}, which may be sensitive to new physics.
We study the rare decays of $B_c^+\to D_{q}^{(*)+}l\bar{l}$ ($q=d,s$ and $l=ν_l,e,μ,τ)$ in the standard model. The form factors are evaluated in the light front and constituent quark models, respectively. We find that the decay branching ratios calculated in the two models for $B_c^+\to D^+_q l\bar{l}$ agree well with each other, whereas those for $B_c^+\to D_q^{*+}l\bar{l}$ are different.
Rare decays $Λ_b \to Λγ$ and $Λ_b \to Λl^{+} l^{-}$ (l= e, $μ$) are examined. We use QCD sum rules to calculate the hadronic matrix elements governing the decays. The $Λ$ polarization in the decays is analyzed and it is shown that the polarization parameter in $Λ_b \to Λγ$ does not depends on the values of hadronic form factors. And the energy spectrum of $Λ$ in $Λ_b \to Λl^{+} l^{-}$ is given.
Exclusive $B_c^\ast \rightarrow D_{s}~ν\barν$ decay is studied in the framework of the three--point QCD sum rules approach. The two gluon condensate contributions to the correlation function are calculated and the form factors of this transition are found. The decay width and total branching ratio for this decay is also calculated.
We study the exclusive rare decay B -> K l(bar) l. We calculate the relevant form factors within a relativistic constituent quark model, for the first time without employing the impulse approximation. The calculated form factors are used to evaluate differential decay rates and polarization observables. We present results on the q2-dependence of a set of observables with and without long-distance contributions. A similar analysis is done for the exclusive rare decays B_c -> D (D*) l(bar) l with special emphasis on the cascade decay B_c -> D* (-> D pi) l(bar) l. We derive a four-fold angular de…
In this paper, I study the branching ratio of the rare radiative decay $B_s \to ν\barν γ$ in the framework of the Fourth-Generation Standard Model and the Two-Higgs-Doublet Model. It is shown that this quantity is a very effective tool for establishing new physics beyond the Standard Model. It is observed that there is a region in the parameter space in both extensions of the Standard Model for which the branching ratio show considerable departure from the Standard Model.
We present an independent calculation of ${\cal{O}}(α_s)$ matrix elements of the QCD penguin operators for the decays $\bar{B}\to X_{s(d)}γ$. The Mellin-Barnes representation technique is applied for the systematic numerical evaluation of involved two-loop diagrams. The numerical effect of the calculated contributions is confirmed to be of order of 1%. We also present an updated numerical analysis for $\bar{B}\to X_{s(d)}γ$ decay rates.
In the framework of the topcolor-assisted technicolor ($TC2$) model and the littlest Higgs model with $T$-parity ($LHT$ model), we consider the rare B decays $B\to Mν\barν$ with $M=π,K,ρ,$ or $K^{\ast}$. We find that the contributions of the $TC2$ model to the branching ratios of these decay processes are larger than those for the $LHT$ model. The experimental upper limits for some branching ratios can give severe constraints on the free parameters of the $TC2$ model.
We present the estimate of the branching ratio for the rare decay $\bar B^0\to D^*γ$. We use QCD factorization approach in order to compute the amplitude of the process. The calculation is carried out with the leading order accuracy. % Our consideration is based on the % factorization for the amplitude of the process which % has been derived with the leading order accuracy. The appearing non-perturbative matrix elements have been estimated using the large$-N_c$ limit and QCD sum rule approach. We obtained that $\mathcal{B}(\bar B^0\to D^*γ)\simeq 1.52\times 10^{-7}$. Such value of the branchin…
The rare kaon decay K^+ --> π^+ ν\barν is considered in the framework of the models based on the SU(3)_C X SU(3)_L X U(1)_N (3 - 3 - 1) gauge group. It is shown that a lower bound of the Z' mass in the 3 - 3 - 1 model with right-handed neutrinos at a value of 3 TeV is derived, while that in the minimal version -- 1.7 TeV.
We study the effect of the FCNC mediated $Z$ boson in the rare semileptonic baryonic decays $Λ_b \to Λl^+ l^-$. We consider the model where the standard model fermion sector is extended by an extra vector like down quark, as a consequence of which it allows CP violating Z mediated flavor changing neutral current at the tree level. We find that due to this non-universal $Zbs $ coupling, branching ratios of the rare semileptonic $Λ_b$ decays are enhanced reasonably from their corresponding standard model values and the zero point of the forward backward asymmetry for $Λ_b \to Λμ^+ μ^-$ is shifte…
Anomalous couplings of the $Z$ boson to top quarks are only marginally constrained by direct searches and are still sensitive to new particle dynamics at the TeV scale. Employing an effective field theory approach we consider the dimension-six operators which generate deviations from the standard-model vector and axial-vector interactions. We show that rare $B$ and $K$ meson decays together with electroweak precision observables provide strong constraints on these couplings. We also consider constraints from t-channel single-top production.
Taking into account the gluon correction contributions to the correlation function, the form factors relevant to the rare $B_c \rar X ν\barν$ decays are calculated in the framework of the three point QCD sum rules, where $X$ stands for axial vector particle, $AV(D_{s1})$, and vector particles, $V(D^*,D^*_s)$. The total decay width as well as the branching ratio of these decays are evaluated using the $q^2$ dependent expressions of the form factors. A comparison of our results with the predictions of the relativistic constituent quark model is presented.
In this paper, we study rare decays $B_c\rightarrow D^{(*)}_{s,d}l\bar{l}$ within the Standard Model. The penguin, box, annihilation, color-favored cascade and color-suppressed cascade contributions are included. Based on our calculation, the annihilation and color-favored cascade diagrams play important roles in the differential branching fractions, forward-backward asymmetries, longitudinal polarizations of the final vector mesons and leptonic longitudinal polarization asymmetries. More importantly, color-favored cascade decays largely enhance the resonance cascade contributions. To avoid th…
An analytical expression for the spin-averaged amplitude squared of the rare muon decay $μ^+ \to e^+e^-e^+ν_e\bar{ν_μ}$ is calculated. Monte Carlo phase space simulation using the analytical expression for the amplitude has been used to get various differential distributions of charged leptons. The approximate analytical expression for the total energy spectrum of charged leptons near the end point is presented. The dependence of branching ratio on cuts in total energy of charged leptons is studied taking into account an experimental energy resolution. It is shown that the measured branching r…
We point out new ways to search for charmless baryonic B decays: baryon pair production in association with $η^\prime$ is very likely as large as or even a bit larger than two body $Kπ/ππ$ modes. We extend our argument, in weaker form, to $B\to γ+ X_s$ and $\ellν+X$. Although calculations are not reliable, estimates give branching ratios of order $10^{-5}$--$10^{-6}$, where confidence is gained from recent experimental finding that $B \to D^{*} p \bar n$, $D^{*} p \bar p π$ are not far below $D^*π$ and $D^*ρ$ rates. Observation of charmless baryon modes would help clarify the dynamics of weak …
We review some recent theoretical results on rare kaon decays. Particular attention is devoted to find Standard Model tests. This is theoretically easy in $K\to πν\barν$, while a careful study of the long distance contributions is needed for $K_{L}\to π^{0}e% \bar{e}$, $K_{L}\to μ\barμ$ and $K\to ππγ$
