Narrow Results

Assuming that the corrections to relevant Wilson coefficients from new physics (NP) contain the possible CP phases, we analyze the constraints on the NP corrections from the updated experimental data on rare B decays from LHCb, BABAR, and BELLE, etc. systematically. Through global fit among the theoretical evaluations and corresponding experimental observations, we find that the possible CP phases of the corrections to relevant Wilson coefficients from NP affect the allowed parameter space obviously.

Rare B^± decays to three charged kaons are analysed. The weak decay amplitudes are derived in the QCD factorization approach. The strong final state interactions between pairs of kaons are described using the kaon scalar and vector form factors. The scalar form factors at low K⁺K^- effective mass distributions are constrained by chiral symmetry and are related to the coupled channel meson-meson amplitudes describing all the transitions between three channels consisting of two kaons, two pions and four pions. The vector form factors are fitted to the data on e⁺e^- collisions. The model results are compared with the Belle and BaBar data.

The rare decay plays a key role for the testing of the Standard Model. It is pointed out that the sizable decay width difference ΔΓ_s of the B_s-meson system affects this channel in a subtle way. As a consequence, its calculated Standard Model branching ratio has to be upscaled by about 10%. Moreover, the sizable ΔΓ_s makes a new observable through the effective lifetime accessible, which probes New Physics in a way complementary to the branching ratio and adds an exciting new topic to the agenda for the high-luminosity upgrade of the LHC. Further probes of New Physics are offered by a CP-violating rate asymmetry. Correlations between these observables and the branching ratio are illustrated for specific models of New Physics.

Experimental era of rare $B$-decays started with the measurement of $B\to K^{\ast }\gamma$ by CLEO in 1993, followed by the measurement of the inclusive decay $B\to X_s\gamma$ in 1995, which serves as the standard candle in this field. The frontier has moved in the meanwhile to the experiments at the LHC, in particular, LHCb, with the decay $B^0\to {\mu }^{+}{\mu }^{-}$ at about 1 part in 10${}^{10}$ being the smallest branching fraction measured so far. Experimental precision achieved in this area has put the standard model to unprecedented stringent tests and more are in the offing in the near future. I review some key measurements in radiative, semileptonic and leptonic rare $B$-decays, contrast them with their estimates in the SM, and focus on several mismatches reported recently. They are too numerous to be ignored, yet, standing alone, none of them is significant enough to warrant the breakdown of the SM. Rare $B$-decays find themselves at the crossroads, possibly pointing to new horizons, but quite likely requiring an improved theoretical description in the context of the SM. An independent precision experiment such as Belle II may help greatly in clearing some of the current experimental issues.

The charge given to me by the organisers of the memorial meeting for Prof. Abdus Salam’s 90th birthday is to recall my personal impressions of him and review an aspect of the standard model (SM) physics related to my work. Salam was, first and foremost, a brilliant theoretical physicist whose work is still very much en vogue, currently being tested precisely by the experiments at the Large Hadron Collider (LHC). Salam was, however, equally effective as a scientific advisor to many institutions, such as IAEA and CERN, but also to the government of Pakistan as the chief scientific strategist. He was also an untiring advocate of scientific research and higher education in developing countries, which took a concrete form in the International Centre for Theoretical Physics (ICTP) in Trieste. I discuss these aspects of his scientific life seen from my perspective in the first part. In the second part of my talk, which may appear as a disjoint piece to the first, I summarise some selected topics in rare B-decays — the current flavour physics frontier. Experiments carried out over several decades are largely in agreement with the SM, thanks also to dedicated theoretical effort in their interpretation. However, this field is undergoing an anomalous phase in a number of key measurements, in particular reported by LHCb, triggering a very lively debate and model building. These anomalies, which I review here, are too numerous to be ignored, but none is individually significant enough to announce a breakdown of the SM.

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.

We analyze the exclusive rare B → K^(*)ℓ⁺ℓ⁻, and B → K^*γ decays in the Applequist-Cheng-Dobrescu model, an extension of the Standard Model in presence of universal extra dimensions. In the case of a single universal extra dimension, we study the dependence of several observables on the compactification parameter 1/R, and discuss whether the hadronic uncertainty due to the form factors obscures or not such a dependence. We find that, using present data, it is possible in many cases to put a sensible lower bound to 1/R, the most stringent one coming from B → K^*γ.

We present a Monte Carlo simulation study of measuring the rare leptonic decay with the CMS experiment at the LHC. The study is based on a full detector simulation for signal and background events. We discuss the high-level trigger algorithm and the offline event selection.

We report branching fractions and CP asymmetries for three-body and semi-three-body decays observed at Belle. The results were obtained from a 414 fb^-1 data sample collected at the ϒ(4S) resonance, with the Belle detector at the KEKB asymmetric energy e⁺e^- collider. The first observation of B^± → ϕϕK^± and a study of related charmonium decays are presented. Additionally, we show the measurement of the semi-three-body decay B → ηK* and evidence for B → ηρ. We find no evidence for CP asymmetries in these modes.

The charge given to me by the organisers of the memorial meeting for Prof. Abdus Salam’s 90th birthday is to recall my personal impressions of him and review an aspect of the standard model (SM) physics related to my work. Salam was, first and foremost, a brilliant theoretical physicist whose work is still very much en vogue, currently being tested precisely by the experiments at the Large Hadron Collider (LHC). Salam was, however, equally effective as a scientific advisor to many institutions, such as IAEA and CERN, but also to the government of Pakistan as the chief scientific strategist. He was also an untiring advocate of scientific research and higher education in developing countries, which took a concrete form in the International Centre for Theoretical Physics (ICTP) in Trieste. I discuss these aspects of his scientific life seen from my perspective in the first part. In the second part of my talk, which may appear as a disjoint piece to the first, I summarise some selected topics in rare B-decays — the current flavour physics frontier. Experiments carried out over several decades are largely in agreement with the SM, thanks also to dedicated theoretical effort in their interpretation. However, this field is undergoing an anomalous phase in a number of key measurements, in particular reported by LHCb, triggering a very lively debate and model building. These anomalies, which I review here, are too numerous to be ignored, but none is individually significant enough to announce a breakdown of the SM.

Experimental era of rare B-decays started with the measurement of B → K^*γ by CLEO in 1993, followed by the measurement of the inclusive decay B → X_sγ in 1995, which serves as the standard candle in this field. The frontier has moved in the meanwhile to the experiments at the LHC, in particular, LHCb, with the decay B⁰ → μ⁺μ⁻ at about 1 part in 1010 being the smallest branching fraction measured so far. Experimental precision achieved in this area has put the standard model to unprecedented stringent tests and more are in the offing in the near future. I review some key measurements in radiative, semileptonic and leptonic rare B-decays, contrast them with their estimates in the SM, and focus on several mismatches reported recently. They are too numerous to be ignored, yet, standing alone, none of them is significant enough to warrant the breakdown of the SM. Rare B-decays find themselves at the crossroads, possibly pointing to new horizons, but quite likely requiring an improved theoretical description in the context of the SM. An independent precision experiment such as Belle II may help greatly in clearing some of the current experimental issues.

A set of key measurements of B decays which have the potential to uncover New Physics at the LHC is discussed. Together with the general purpose detectors ATLAS and CMS, the LHCb detector, which is devoted to B physics, can study these effects precisely. Due to the large cross section at 14 TeV, LHCb has access to 10¹² B meson decays per year. This allows significant measurements of even very rare B decays and, in particular, the precision study of the B system.