We review recent results from the BABAR and Belle experiments on rare electroweak B-meson decays, with emphasis on those occurring through flavor changing neutral current interactions of the type b -> s l l. The recent results include measurements of the isospin asymmetry and lepton forward-backward asymmetry in B -> K* l+ l- decays from BABAR, a search for B -> pi l+ l- from Belle, and searches for B \to K(*) nu anti-nu from BABAR. We also briefly review the status of B0 -> l+ l- and B+ -> l+ nu searches.
We review recent measurements of leptonic $D_s$-meson decays performed by Belle and BaBar collaborations. Described measurements enable experimental extraction of the $D_s$-meson decay constant which can be compared with lattice QCD calculations.
We will present a review of the most interesting results on rare B decays from the B Factories, based on the data collected by the BaBar and Belle detectors at asymmetric $e^+ e^-$ colliders at the center of mass energy of the $Υ(4S)$ resonance.
Virtual fermionic N_f = 1 and N_f = 2 contributions to Bhabha scattering are combined with realistic real corrections at next-to-next-to-leading order in QED. The virtual corrections are determined by the package bha_nnlo_hf, and real corrections with the Monte Carlo generators Bhagen-1Ph, Helac-Phegas and Ekhara. Numerical results are discussed at the energies of and with realistic cuts used at the Phi factory DAFNE, at the B factories PEP-II and KEK, and at the charm/tau factory BEPC II. We compare these complete calculations with the approximate ones realized in the generator BabaYaga@NLO u…
We summarize recent results by the BABAR and Belle Collaborations on the search for CP violation and new physics beyond the Standard Model in several rare B meson decays. The measurements exploit the final BABAR and Belle Upsilon(4S) datasets, which consist of approximately 470 and 772 million BBbar pairs, respectively.
We have performed a search for the rare leptonic decays \Bp \to \ellp \nul ($l=e,μ$), using data collected at the \FourS resonance by the \babar\ detector at the \pep2 storage ring. In a sample of 468 million \BB pairs we find no evidence for a signal and set an upper limit on the branching fractions $\BR(\bmunu) < 1.0\times10^{-6}$ and $\BR(\benu) < 1.9\times10^{-6}$ at the 90% confidence level, using a Bayesian approach.
A review of the experimental status of purely leptonic ${B^0_{[s]}\to\ell^+\ell^-}$ decays is given and the new analysis of ${B^0_{[s]}\toμ^+μ^-}$ observables with the LHCb experiment is presented. The new results are the most precise single experiment measurements of the quantities to date and are consistent with the Standard Model. However, they also match the recent anomalies found in $b\to s\ell\ell$ transitions excellently.
In this talk, a wide range of recently published results on rare B decays from BABAR and Belle are covered. The decays of B->XsGamma, B->K(*)l+l-, and lepton-number violation in B decays are measured for new physics searches.
Leptonic and semileptonic decays in the charm sector have been well studied in recent years. With the largest data sample near $D\bar D$ threshold, precision measurements of leptonic and semileptonic decays of charm meson and baryon are perfromed at BESIII. Test for letpon flavor universality is also performed. Sensitivity for rare leptonic and semileptonic charm decays is significantly improved taking advantage of the huge statistics in LHCb and the $B$ factories.
Rare lepton decays of the B(s), D and K mesons are sensitive probes of New Physics. In particular, the search for the decays $B^0_(s) -> μ^+ μ^-$ provides information on the presence of new (pseudo-)scalar particles. LHCb is well suited for these analyses due to its large acceptance and trigger efficiency, as well as its excellent invariant mass resolution and lepton identification capabilities. The status of these analyses with $\sim1$ fb$^{-1}$ of pp collisions collected by LHCb in 2011 at $\sqrt{s}=7$ TeV is reviewed.
We present a review of the searches for very rare decays to muonic final states performed at LHCb using 1.0 fb-1 of pp collisions at 7 TeV centre of mass energy. Flavour changing neutral current processes, such as B->mumu and B->mumumumu are highly suppressed in the Standard Model (SM). Such decays therefore allow contributions from new processes or new heavy particles to significantly modify the expected SM rates. Charged lepton flavour violating processes, such as the neutrino-less tau->mumumu decay, have vanishingly small decay rates in the SM, but can be significantly enhanced in extended …
Non-leptonic two-body weak decays of baryons are an important tool to probe the combined charge-conjugation--parity symmetry (CP) violation. We explain why the decays of strange baryons provide complementary information to the decays of kaons. A model-independent parameterization of the non-leptonic decays of the $Λ$- and $Ξ$-baryons is reviewed, and the amplitudes are updated according to the latest experimental input. We demonstrate the potential of performing precision tests in strange baryon decays at the next generation electron-positron $J/ψ$ factories with luminosity of $10^{35}$ cm$^{-…
Semi-leptonic D decays continue to play an important role in the field of flavor physics. During this presentation, recent measurements from pseudo-scalar to pseudo-scalar modes, pseudo-scalar to vector modes, and rare modes will be discussed. These results are important for many purposes, such as validating the machinery of lattice QCD, extracting CKM matrix elements, and searching for new physics and new interactions.
With anomalies found in cosmic ray observations and unsolved questions of the Standard Model of particle physics like the discrepancy in the muon's anomalous magnetic moment, the idea of an U(1) extension of the Standard Model arose. This extension allows for the interaction of Dark Matter by exchange of a photon-like massive force carrier $A'$ not included in the Standard Model. We discuss the possibility to constrain the dark photon parameter space by using data taken from rare kaon decays. Therefore we analyze the decay $K\rightarrow μνA'$ as a signal process and calculate the expected Stan…
The branching fractions of radiative leptonic $τ$ decays $(τ\to l ν\barν γ$, $l=e,μ)$ were recently measured by the Babar collaboration with a relative error of about 3%. The measurement of the branching ratio $\mathcal{B} (τ\to e \barν νγ)$, for a minimum photon energy of 10 MeV in the $τ$ rest frame, differs from our recent SM prediction by 3.5 standard deviations, whereas our result agrees with Babar's value for $\mathcal{B} (τ\to μ\barν νγ)$. Our predictions also agree with the measurement of $\mathcal{B} (μ\to e \barν νγ)$ by the MEG collaboration. We also report on a recent proposal to t…
We propose a new method to probe the magnetic and electric dipole moments of the $τ$ lepton using precise measurements of the differential rates of radiative leptonic $τ$ decays at high-luminosity $B$ factories. Possible deviations of these moments from the Standard Model values are analyzed in an effective Lagrangian approach, thus providing model-independent results. Analytic expressions for the relevant non-standard contributions to the differential decay rates are presented. Earlier proposals to probe the $τ$ dipole moments are examined. A detailed feasibility study of our method is perfor…
The rare decays $B_{s,d}^0 \to μ^+μ^-$ are important probes for new physics beyond the Standard Model. These decays are subjects of studies at the LHC. The ATLAS and CMS collaborations have analyzed the proton-proton collisions data at 7 TeV centre-of-mass energy collected in the year 2011. They have established upper limits on the branching fractions of the two decays. This paper presents a report.
The NA62 experiment at CERN aims to use rare kaon decays to search for new phenomena beyond the Standard Model. During the current short term phase (data taking completed in years 2007-8), the ratio $R_K = Γ(K^+ \rightarrow e ν_e (γ)) / Γ(K^+ \rightarrow μν_μ (γ))$ of leptonic decay rates is studied, which tests the structure of weak interactions and lepton flavour universality. In this paper, the $R_K$ analysis is summarized, and the preliminary result is discussed, based on 59963 $K^+ \rightarrow e ν_e $ candidates collected in 2007.
Studying flavor changing neutral current transitions provides important information that helps searches for physics beyond the standard model. In this paper we report on recent measurements of these transitions using data collected by the CDF and D0 experiments at the Tevatron $p\bar{p}$ collider, including world-leading limits on the branching fraction of the decay $B^0_{(s)} \to μ^+ μ^-$, a forward-backward asymmetry measurement in $B^0 \to K^{*0} μ^+ μ^-$ and $B^+ \to K^+ μ^+ μ^-$ decays which is consistent and competitive with best $B$-factories results, and the first observation of the de…
Flavour-changing neutral-current processes, such as $b\to s \ell^+\ell^-$, are forbidden at tree level in the Standard Model and hence might receive comparatively large corrections from new particles. This document highlights recent measurements from LHCb on $b\to s \ell^+\ell^-$ and purely-leptonic decays, including tests of lepton flavour universality and searches for lepton flavour violation.
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.
Using existing experimental information from K, B and D decays as well as electroweak precision tests and oblique parameters, we provide constraints and correlations on the parameters of the 4X4 mixing matrix for the Standard Model with four generations (SM4). We emphasize that some correlations amongst the parameters have important repercussions for key observables. We work with a particular representation of this matrix which is highly suited for extracting information from B-decays. Implications of the resulting constraints for time dependent and semileptonic CP asymmetries for $D^0$, $B^0$…
Semileptonic decays of $B$ mesons that proceed via $b\rightarrow u$ and $b\rightarrow c$ transitions, as well as rare leptonic $B$ decays, are fertile grounds for probing new physics beyond the Standard Model. The Belle II experiment presents as an excellent opportunity to study such decays, and since beginning operation in 2019, Belle II has already recorded half of the data collected by its predecessor and reached an instantaneous luminosity greater than $4\times 10^{34}$ cm$^{-2}$s$^{-1}$. Belle II expects to explore flavour physics with $B$ and charmed mesons with unprecedented precision, …
In the last decade the CDF experiment at the Tevatron clearly demonstrated that it is possible to study extensively heavy flavour physics in hadron collisions and achieve remarkable results, competitive and complementary to $B$-factories. In this paper we report on the indirect searches for physics beyond the standard model via measurements of rare $b$-hadron decays. The final limits, based on the analysis of the full CDF data set, on the branching fraction of the $B^0_{(s)}$ decay into a pair of muons are presented and discussed. Moreover we review the latest measurements, with 6.8 fb$^{-1}$ …
The decay $B^0_s\toμ^+μ^-$ is a key probe for the search of physics beyond the Standard Model. While the current measurements of the corresponding branching ratio agree with the Standard Model within the uncertainties, significant New-Physics effects may still be hiding in $B^0_s\toμ^+μ^-$. In order to reveal them, the observable $\mathcal{A}^{μμ}_{ΔΓ_s}$, which is provided by the decay width difference $ΔΓ_s$ of the $B^0_s$-meson system, plays a central role. We point out that a measurement of a CP-violating observable ${\cal S}_{\rm μμ}$, which is induced through interference between $B^0_s$…
I review the current status of measurements involving semi-tauonic $B$ meson decay at the $B$-factories. I briefly discuss the experimental methods and highlight the importance of background contributions especially from poorly understood $D^{**}$ in this study. Perhaps this can also shed some light on the discrepancy in the BaBar measurement of ratio of semi-tauonic and semi-leptonic ($e$/$μ$) modes of $B$ decay from the Standard Model (SM) at 3.2$σ$. I will also discuss one of the New Physics (NP) models that could be experimentally sensitive in being distinguished from the Standard Model (S…
The available data on $|ΔB| = |ΔS| = 1$ decays are in good agreement with the Standard Model when permitting subleading power corrections of about 15% at large hadronic recoil. Constraining new-physics effects in $\mathcal{C}_7$, $\mathcal{C}_9$, $\mathcal{C}_{10}$, the data still demand the same size of power corrections as in the Standard Model. In the presence of chirality-flipped operators, all but one of the power corrections reduce substantially. The Bayes factors are in favor of the Standard Model. Using new lattice inputs for $B\to K^*$ form factors, the evidence of models with chirali…
Decays of the kind $B^0_{s,d}\to\ell^+\ell^-$ belong to the most favourable processes for probing the flavour structure of the Standard Model, with outstanding sensitivity to new (pseudo)-scalar contributions. While the branching ratio of $B^0_s\toμ^+μ^-$ has already been measured at the LHC in the ballpark of the Standard Model expectation, there is still significant room for New-Physics effects. We discuss how these may be revealed in the future super-high precision era of $B$-decay studies by utilising new theoretically clean observables, including CP-violating asymmetries. Another promisin…
Rare B hadron decays provide an excellent test bench for the Standard Model and can probe new physics models. We review the experimental progress of the searches for rare leptonic B decays ($b\rightarrow \ell^+ \ell^-$ and $b\rightarrow s \ell^+ \ell^-$) at LHC and Tevatron experiments.
We present a summary of recent WW, WZ, and ZZ measurements carried out in $\sqrt{s} = 1.96$ TeV at the Tevatron. The observation of rare ZZ events and the precise measurement of the WW cross section in fully leptonic decay modes are described. Results in semi-leptonic decay modes where one boson decays to two quarks are also presented. The measurements described are all in good agreement with the Standard Model and are relevant to searches for the Higgs boson at the Tevatron.
Several deviations from the Standard Model predictions have been recently observed in the decays mediated by $b \rightarrow s l^+ l^-$ transitions. These could be pointing towards new vector-current contributions or could be explained by underestimated charm-loop effects. New results from an LHCb Run 1 $B^+\rightarrow K^+ μ^+ μ^- $ analysis that includes the decays via intermediate charm- resonances are discussed. Also, new results from the fully leptonic rare modes searches are presented. This includes the latest Run 1 and Run 2 $B^0_{(s)} \rightarrow μ^+ μ^-$ analysis from LHCb where the $B^…
Rare B decays allow to investigate fundamental interactions regarding their flavor, chiral, Dirac and CP properties. In anticipation of the large data samples of exclusive B decays into muons from the forthcoming LHC experiments, in particular LHCb, as well as possible super flavor factories, we review the theoretical status and outline future opportunities to explore the borders of the Standard Model and beyond.
Rare kaon decays are excellent probes of light, new weakly-coupled particles. If such particles $X$ couple preferentially to muons, they can be produced in $K\to μνX$ decays. In this letter we evaluate the future sensitivity for this process at NA62 assuming $X$ decays either invisibly or to di-muons. Our main physics target is the parameter space that resolves the $(g-2)_μ$ anomaly, where $X$ is a gauged $L_μ-L_τ$ vector or a muon-philic scalar. The same parameter space can also accommodate dark matter freeze out or reduce the tension between cosmological and local measurements of $H_0$ if th…
