Narrow Results

Hadronic form factors for the rare weak transitions Λ_b → Λ^(*) are calculated using a nonrelativistic quark model. The form factors are extracted in two ways. An analytic extraction using single-component wave functions (SCA) with the quark current being reduced to its nonrelativistic Pauli form is employed in the first method. In the second method, the form factors are extracted numerically using the full quark model wave function (MCN) with the full relativistic form of the quark current. Although there are differences between the two sets of form factors, both sets satisfy the relationships expected from the heavy quark effective theory (HQET). Differential decay rates, branching ratios (BRs) and forward–backward asymmetries (FBAs) are calculated for the dileptonic decays Λ_b → Λ^(*) ℓ⁺ ℓ^-, for transitions to both ground state and excited daughter baryons. Inclusion of the long distance contributions from charmonium resonances significantly enhances the decay rates. In the MCN model the Λ(1600) mode is the dominant mode in the μ channel when charmonium resonances are considered; the Λ(1520) mode is also found to have a comparable BR to that of the ground state in the μ channel.

Almost two decades after its discovery at Fermilab's Tevatron collider experiments, the top quark is still under the spotlight due to its connections to some of the most interesting puzzles in the Standard Model. The Tevatron has been shut down two years ago, yet some interesting results are coming out of the CDF and D0 collaborations. The LHC collider at CERN produced two orders of magnitude more top quarks than Tevatron's, thus giving birth to a new era for top quark physics. While the LHC is also down at the time of this writing, many top quark physics results are being extracted out of the 7 TeV and 8 TeV proton proton collisions by the ATLAS and CMS collaborations, and many more are expected to appear before the LHC will be turned on again sometime in 2015. These proceedings cover a selection of recent results produced by the Tevatron and LHC experiments.

NA62 is a fixed target experiment at CERN with the main goal of measuring the Branching Ratio of the decay $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ at 10% precision level. It also searches for exotic particles such as invisible vector bosons or axion-like particles. First preliminary results of a subset of 2016 data sample are shown.

The one-loop contributions to the flavor-changing neutral current decays of the top quark into a light quark and a gauge boson or Higgs boson, namely, $t\to qV,qh$, with q being u or c, and V being $\gamma$, g, or Z, are analyzed in this study within the framework of the minimal R-symmetric supersymmetric standard model. The charginos in this model have been separated into two sets, i.e. $\chi$-chargino and $\rho$-chargino. The numerical results reveal that gluino or $\rho$-chargino predominantly dictate the predictions for BR ($t\to qV,qh$), while the impact of neutralino or $\chi$-chargino contributions is insignificant. By incorporating the constraints imposed by the squark mixing parameters from $\bar{B}\to X_s\gamma$ and $B_{d,s}^0\to {\mu }^{+}{\mu }^{-}$, the theoretical predictions for BR($t\to qg$) can be significantly augmented to approximately $\mathcal{𝒪}(10^{-5}-10^{-6})$. On the other hand, the values of BR($t\to q\gamma ,qZ,qh$) are predicted to be at least four orders of magnitude below the current experimental limits.

We calculate bounds for the branching ratio of the $B_s^0\to \tau e$ decay, for the first time, in the context of flavor changing neutral currents mediated by a $Z^{\prime }$ gauge boson, which can arise from five extended models. In this sense, by using experimental measurements on the $B\to X_s\gamma$ decay and the $B_s^0\to {\mu }^{+}{\mu }^{-}$ process, we look for constraints of the $Z^{\prime }bs$ coupling, where the more restrictive bound is offered by the last one. On the other hand, by employing the experimental restriction on the $\tau \to eeē$ decay, the strength of the $Z^{\prime }\tau e$ coupling is estimated. Our analysis is based on the more recent experimental results on searches for the $Z^{\prime }$ gauge boson in ATLAS and CMS detectors. In addition, we revisited the $B_s^0\to \tau \mu ,\mu e$ meson decays by using different approaches not previously reported. The strengths of the $Z^{\prime }\tau \mu$ and $Z^{\prime }\mu e$ couplings were estimated by employing experimental restrictions on the $\tau \to \mu \mu \bar{\mu }$ decay and the $\mu -e$ conversion rate, respectively. Thus, we predict the following upper bounds: $B_s^0\to \tau e\sim 10^{-6}$, $B_s^0\to \tau \mu \sim 10^{-6}$ and $B_s^0\to \mu e\sim 10^{-11}$.

Rare decays of hyperons involving di-neutrinos in the final state $\mathrm{\Lambda }\to n\bar{\nu }\nu$, ${\mathrm{\Sigma }}^{+}\to p\bar{\nu }\nu$, ${\mathrm{\Xi }}^0\to \mathrm{\Lambda }\bar{\nu }\nu$, ${\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^0\bar{\nu }\nu$, ${\mathrm{\Xi }}^{-}\to {\mathrm{\Sigma }}^{-}\bar{\nu }\nu$, ${\mathrm{\Omega }}^{-}\to {\mathrm{\Xi }}^{-}\bar{\nu }\nu$ in the Standard Model and beyond are studied. It is claimed that the branching ratios (Brs) calculated in this work are larger than the previously calculated values. For the search of NP the nonstandard neutrino interactions (NSI) are explored and constrains on NSI free parameters ${𝜖}_{\tau \tau }^{uL}$ are found. Stringent bounds on ${𝜖}_{\tau \tau }^{uL}$ of $O(10^{-2})$ are obtained. It is shown that Brs could be closed to BES-III, if the constraints are $O(0.3)$. We predict that these reactions with the current value of parameter of $O(1)$ will be in sensitivity of BES-III. To check the validity of our approach we also calculate Brs of these reactions by using 331 model and finding them consistent with previously available values of the same model.

In this work, we present a Mathematica package Peng4BSM@LO which calculates the contributions to the Wilson Coefficients of certain effective operators originating from the one-loop penguin Feynman diagrams. Both vector and scalar external legs are considered. The key feature of our package is the ability to find the corresponding expressions in almost any New Physics model which extends the SM and has no flavor changing neutral current (FCNC) transitions at the tree level.

We investigate the nonstandard neutrino interactions (NSI) in the rare decays of $B_c^{+}$ mesons involving neutrinos in the final state. It is suggested that the interference between Standard Model and nonstandard interaction can provide sizeable contribution. We calculate the limits on NSI free parameters (${𝜖}_{\tau \tau }^{uL}$, ${𝜖}_{\tau \tau }^{dL}$) and compare them with experimental data.

Processes τ→lγ, τ→lll with l = e, μ and μ(τ) →e (μ) γ are evaluated in the framework of a model based on the extended symmetry gauge SU(3)_c ⊗SU(3)_L ⊗U(1)_Y with a leptonic sector consisting of five triplets. Lepton flavor violating processes are allowed at tree level in this model through the new Z′ gauge boson. We obtained bounds for the mixing angles in the leptonic sector of the model, considering the experimental measurements of the processes from the BELLE and the BABAR collaborations.

We study rare decays , and in NSIs. We calculate the NSIs branching ratios of these decays. There is a strong dependence of these on new physics parameter. They provide stringent constraints on , and (α, β = e, μ).

The rare semileptonic $B\to K{\mu }^{+}{\mu }^{-}$ and $B\to \varphi {\mu }^{+}{\mu }^{-}$ decay modes mediated by the $b\to s{\mu }^{+}{\mu }^{-}$ transition are studied in this paper. We analyze observables such as the differential branching ratio, lepton polarization asymmetry and forward–backward asymmetry within the standard model in the low $q^2$ region. We then perform an analysis of the same modes within the 331 or $S{U}_C(3)\times S{U}_L(3)\times U_X(1)$ model in which a new heavy $Z^{\prime }$ boson contributes. The effects of the $Z^{\prime }$-mediated flavor-changing neutral current (FCNC) transitions on these modes are investigated by varying the mass $M_{Z^{\prime }}$ and the model parameter $\beta$. The new $Z^{\prime }$ couplings are constrained by flavor observables of $B_s-{\bar{B}}_s$ mixing and branching ratio of $B_s\to {\mu }^{+}{\mu }^{-}$. We find that for some values of these couplings, the observables are quite sensitive to $Z^{\prime }$ effects and deviations from Standard Model can be large.

We study the rare semileptonic $B\to \pi {\mu }^{+}{\mu }^{-}$ and $B\to \rho {\mu }^{+}{\mu }^{-}$ decay modes mediated by the quark level $b\to d{\mu }^{+}{\mu }^{-}$ transition in this paper. We analyze observables such as the differential branching ratio, lepton polarization asymmetry and forward–backward asymmetry within the standard model in the large hadronic recoil region. We then analyze these observables within the 331 or $S{U}_C(3)\times S{U}_L(3)\times U_X(1)$ model in which a new heavy $Z^{\prime }$ boson contributes. The effects of the $Z^{\prime }$-mediated flavor changing neutral current (FCNC) transitions on these modes are examined by varying the mass $M_{Z^{\prime }}$ and the model parameter $\beta$. The new $Z^{\prime }$ couplings are constrained by flavor observables of $B_d-{\bar{B}}_d$ mixing. For the obtained parameter space, we observe $Z^{\prime }$ sensitivities of our observables of interest and deviations from standard model can range from moderate to large depending on the $\beta$ value.

The measurements of the top quark flavor changing neutral current interactions are one of the most important goals of the top quark physics program in the present and the future collider experiments. These measurements provide direct information on nonstandard interactions of the top quark. Within the framework of new physics beyond the Standard Model, these interactions can be defined by an effective Lagrangian. In this study, we have investigated the potential of the future $\mu p$ colliders on the top quark flavor changing neutral current interactions through the subprocesses $\gamma q\to t\to Wb$, where $q=u,c$. These subprocesses have been produced through the main reaction $\mu p\to \mu \gamma p\to \mu WbX$ at the LHC-$\mu p$, the FCC-$\mu p$ and the SPPC-$\mu p$. For the main reaction, the total cross-sections have been calculated as a function of the anomalous $tq\gamma$ couplings. In addition, sensitivities on $\mathrm{\text{BR}}(t\to q\gamma )$ at 95% Confidence Level have been calculated. We obtain that the best constraints on $\mathrm{\text{BR}}(t\to q\gamma )$ are at the order of $10^{-7}$ which is four orders of magnitude better than the LHC’s experimental results.

We report on a search for the flavor-changing neutral current decays D⁰ → e⁺e^- and D⁰ → μ⁺μ^-, and the lepton-flavor violating decay D⁰ → e^±μ^∓. The measurement is based on 122 fb^-1 of data collected by the BABAR detector at the PEP-II asymmetric e⁺e^- collider. No evidence is found for any of the decays. The upper limits on the branching fractions, at the 90% confidence level, are 1.2 × 10^-6 for D⁰ → e⁺e^-, 1.3 × 10^-6 for D⁰ → μ⁺μ^-, and 8.1 × 10^-7 for D⁰ → e^±μ^∓.

Branching ratios, lepton forward–backward asymmetries, and lepton polarization asymmetries for the flavor-changing neutral current (FCNC) dileptonic decays of the ${\Lambda }_b$ baryon to the ground state and a number of excited state $\Lambda$ baryons are calculated using form factors extracted using wave functions from a constituent quark model. The SM branching ratios for the transition to the ground state calculated using these quark model form factors are consistent with the recent measurement reported by the LHCb collaboration. It is shown that the lepton polarization asymmetries are largely insensitive to the transition form factors and, therefore, may also be insensitive to the effects of QCD in the nonperturbative regime. These observables could therefore provide somewhat model independent ways of extracting various combinations of the Wilson coefficients.

We study the rare mesonic decays and for the search of new physics (NP) in the form of nonstandard neutrino interactions (NSIs). We calculate branching ratios (BRs) of these decays in the framework of NSIs. We try to explore the possibility for second and third generations of quarks in NSIs, exactly on the same footing as for leptonic case we have and . We show that there exist a possibility for and also from these reactions. Three other processes and are investigated with s and b quarks in the loop for NSIs instead of d quark only. Constraints on and (where q = s, b and l, l′ ≠ τ) are provided. We point out that constraints for u, c and t quarks are equal and similarly for d, s and b quarks the constraints are equal .

The current experimental status of the searches for the very rare decays and is discussed. These channels are highly sensitive to various extensions of the Standard Model, especially in the scalar and pseudoscalar sector. The recent, most sensitive measurements from the CDF, ATLAS, CMS and LHCb collaborations are discussed and the combined upper exclusion limit on the branching fractions determined by the LHC experiments is shown to be 4.2×10^-9 for and 0.8×10^-9 for . The implications of these tight bounds on a selected set of New Physics models is sketched.

In this work, we overhaul previous studies of Flavor Changing Neutral Current processes in the context of the Reduced Minimal 3-3-1 (RM331) model. We sift the individual contributions from the CP-even scalars and the Z′ gauge boson using two different parametrizations schemes and compare our results with current measurements. In particular, studying the meson system we find the most stringent bounds in the literature on this model, namely and .

We consider flavor-changing decays of neutral Higgs bosons in the context of CP-conserving BGL model — a variant of 2HDM Type 3 model suggested by Branco, Grimus and Lavoura — in which tree-level FCNC couplings are suppressed by elements of known fermion mixing matrices. The relevant regions of parameter space compatible with experimental restrictions on the SM Higgs properties are studied. We also include current bounds on $h\to \mu \tau$ into consideration. In addition, different FCNC decay modes are analyzed for heavier Higgs states $(H/A)$ and conservative estimates for $\mathrm{\text{Br}}(A/H\to \mu \tau )$ are provided. We updated previous studies and found that it cannot be more than 30% for heavy Higgses with masses around 350 GeV.

We study rare decays , and in NSIs. We calculate the NSIs branching ratios of these decays. There is a strong dependence of these on new physics parameter. We include second and third generation of quarks in the loop for these decays. We show that these provide stringent constraints on , where Q = u, c, t, and , where q = d, s, b. It is also pointed out that for α, β = e, μ.