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.

The contributions of the vector leptoquarks of Pati–Salam type to the branching ratios of $K_L^0,B^0,B_s\to l{l}^{\prime }$ decays are calculated with account of the fermion mixing in the leptoquark currents of the general type. Using the general parametrizations of the mixing matrices the lower vector leptoquark mass limit $m_V$$>$ 86 TeV is found from the current experimental data on these decays. The branching ratios of the decays $B^0,B_s\to l{l}^{\prime }$ predicted at $m_V$ = 86 TeV are calculated. These branching ratios for the decays $B^0,B_s\to {\mu }^{+}{\mu }^{-},e\mu$ are close to the experimental data whereas those for the decays $B^0\to e^{+}{e}^{-},e\tau ,\mu \tau$ and $B_s\to e^{+}{e}^{-}$ are by order of 2–4 less than their current experimental limits. For the decays $B_s\to e\tau ,\mu \tau$ these branching ratios are of orders $10^{-10}$ and $10^{-9}$, respectively. The predicted branching ratios will be useful in the current and future experimental searches for these decays.

Low counting experiments (search for double $\beta$ decay and dark matter particles, measurements of neutrino fluxes from different sources, search for hypothetical nuclear and subnuclear processes, low background $\alpha$, $\beta$, $\gamma$ spectrometry) require extremely low background of a detector. Scintillators are widely used to search for rare events both as conventional scintillation detectors and as cryogenic scintillating bolometers. Radioactive contamination of a scintillation material plays a key role to reach low level of background. Origin and nature of radioactive contamination of scintillators, experimental methods and results are reviewed. A programme to develop radiopure crystal scintillators for low counting experiments is discussed briefly.

We review the effective Lagrangian of the Higgs penguin in the Standard Model and its minimal supersymmetric extension (MSSM). As a master application of the Higgs penguin, we discuss in some detail the B-meson decays into a lepton–antilepton pair. Furthermore, we explain how this can probe the Higgs sector of the MSSM provided that some of these decays are seen at Tevatron Run II and B-factories. Finally, we present a complete list of observables where the Higgs penguin could be strongly involved.

The form factors of the rare ${\mathrm{\Lambda }}_b\to n{l}^{+}{l}^{-}$ decays are calculated in the framework of the relativistic quark–diquark picture of baryons with the consistent account of the relativistic effects. Their momentum transfer squared dependence is determined explicitly in the whole accessible kinematical range. The decay branching fractions, forward–backward asymmetries and the fractions of longitudinally polarized dileptons are determined. The branching fraction of the rare ${\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-}$ decay are found to be $\mathrm{\text{Br}}({\mathrm{\Lambda }}_b\to n{\mu }^{+}{\mu }^{-})=(3.75\pm 0.38)\times 10^{-8}$ and thus could be measured at the LHC. Prediction for the branching fraction of the rare radiative ${\mathrm{\Lambda }}_b\to n\gamma$ decay is also given.

New physics search is a part of 30 years of BES physics program, which started during BESII days. The richness of physics features in the τ-charm energy region enabled many published results. At BESIII, the clean environments, high luminosity and excellent detector performance provide ideal opportunities for searches for new physics beyond standard model. Though most obtained upper limits are still above than the SM predictions, they may help to discriminate the different new physics models or to constrain the parameters in the different physics models. With the accumulation of large data sets and possible increase of luminosity and cms energy, as well as an ever-improving understanding of the detector performance, BESIII will have great potential in NP searches in the coming years.

We study the CP-violating asymmetry , which arises, in η → π⁺π^-e⁺e^-, from the angular correlation of the e⁺e^- and π⁺ π^- planes due to the interference between the magnetic and electric decay amplitudes. With the phenomenologically determined magnetic amplitude and branching ratio as input, the asymmetry, induced by the electric bremsstrahlung amplitude through the CP-violating decay η → π⁺π^-, and by an unconventional tensor type operator, has been estimated respectively. The upper bound of from the former is about 10^-3, and the asymmetry from the latter might be up to O(10^-2). One can therefore expect that this CP asymmetry would be an interesting CP-violating observable for the future precise measurements in the η factories.

We study the $B\to K^{(\ast )}\nu \bar{\nu }$ decays within the Standard Model (SM) by using the relevant transition form factors obtained from the covariant confined quark model (CCQM) developed by us. The $B\to K$ and $B\to K^{\ast }$ transition form factors are calculated in the full kinematic $q^2$ range. The branching fractions are then calculated. It is shown that our results are in an agreement with those obtained in other theoretical approaches. Currently, the BaBar and Belle collaborations provide us by the upper limits at 90% confidence limit. The obtained bounds are roughly an order of magnitude larger than the SM predictions. This should stimulate experimental collaborations to set up experiments that allow one to obtain more accurate branching values, which is quite achievable on the updated LHCb and Belle machines. If the discrepancies between theory and experiment are confirmed, this will open up opportunities for constructing models with new particles and interactions leading to an extension of the SM.

LHCb is a dedicated detector for b physics at the LHC (Large Hadron Collider). In this paper we present a concise review of the detector design and performance together with the main physics goals and their relevance for a precise test of the Standard Model and search of New Physics beyond it.

We study rare decays and in the framework of nonstandard neutrino interactions (NSIs). We calculate branching ratios of these decays. We explore the possibility for second generation of quarks in NSIs just like leptonic contribution in and . We study the dependence of on . We show that there exists a possibility for , also from this reaction and other two reactions, and . Three other processes, and are investigated with s quark in the loop for NSIs instead of d quark. Constraints on and are provided. We point out that constraints for both u and c quark are equal and similarly for d and s quarks the constraints are equal .

This review discusses the present experimental and theoretical status of rare flavor-changing neutral current b-quark decays at the beginning of 2018. It includes a discussion of the experimental situation and details of the currently observed anomalies in measurements of flavor observables, including lepton flavor universality. Progress on the theory side within and beyond the Standard Model theory is also discussed, together with potential New Physics interpretations of the present measurements.

Possible manifestations of new physics in rare (exotic) decays of orthopositronium (o - Ps) are briefly reviewed. It is pointed out that models with infinite additional dimension(s) of Randall–Sundrum type predict disappearance of orthopositronium into additional dimension(s). The experimental signature of this effect is the invisible decay of orthopositronium. We point out that this process may occur at a rate within two or three orders of magnitude of the present experimental upper limit. We also propose a model with a light weakly interacting boson leading to o - Ps → invisible decays at the experimentally interesting rate. We discuss this in details and stress that the existence of invisible decay of orthopositronium in vacuum could explain the o - Ps decay rate puzzle. Thus, our result enhances the existing motivation and justifies efforts for a more sensitive search for o - Ps → invisible decay in a near future experiment.

We summarize the theoretical virtues of the rare decays and emphasize the unique role of in probing the nature of physics beyond the Standard Model, in particular concerning possible new sources of CP violation and flavor-symmetry breaking. A brief summary of the prospects for the measurement of the rate is also given.

The LHC (Large Hadron Collider) will be a top-quark factory. With 80 million pairs of top quarks and an additional 34 million single tops produced annually at the designed high luminosity, the properties of this particle will be studied to a great accuracy. The fact that the top quark is the heaviest elementary particle in the Standard Model with a mass right at the electroweak scale makes it tempting to contemplate its role in electroweak symmetry breaking, as well as its potential as a window to unknown new physics at the TeV scale. We summarize the expectations for top-quark physics at the LHC, and outline new physics scenarios in which the top quark is crucially involved.

We present a review of heavy flavor physics results from the CDF and DØ Collaborations operating at the Fermilab Tevatron Collider. A summary of results from Run 1 is included, but we concentrate on legacy results of charm and b physics from Run 2, including results up to Summer 2014.

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 .