Search

Urgent theoretical progress is needed in order to provide an estimate in the Standard Model of the recent measurement by LHCb of direct CP violation in charm-meson two-body decays. Rescattering effects must be taken into account for a meaningful theoretical description of the amplitudes involved in such category of observables, as signaled by the presence of large strong phases. We discuss the computation of the latter effects based on a two-channel coupled dispersion relation, which exploits isospin-zero phase shifts and inelasticity parameterizations of data coming from the rescattering processes ππ→ππ, πK→πK, and ππ→KK¯. The determination of the subtraction constants of the dispersive integrals relies on the leading contributions to the transition amplitudes from the 1∕NC counting, where NC is the number of QCD colors. Furthermore, we use the measured values of the branching ratios to help in selecting the non-perturbative inputs in the isospin limit, from which we predict values for the CP asymmetries. We find that the predicted level of CP violation is much below the experimental value. [ABSTRACT FROM AUTHOR]

In recent years, it has been reported that rare charm decays have immense potential to probe physics beyond the standard model (SM). The Glashow–Iliopoulos–Maiani mechanism effectively suppresses the flavor changing neutral currents decays involving c → u transitions which makes them sensitive to new physics (NP) effects. In this work, we study D meson decays undergoing c → u l + l − transitions in nonuniversal Z ′ model. We determine the NP coupling from D 0 − D 0 ̄ mixing and D → μ + μ − process. We then estimate the upper limits of branching fractions and forward–backward asymmetries for the decays D → π μ + μ − , D s → K μ + μ − and D → ρ μ + μ − . The upper limits of the branching fractions obtained in the Z ′ model show a significant enhancement from their SM results. [ABSTRACT FROM AUTHOR]

In recent times, there have been several observations suggesting deviations from lepton universality in semileptonic decays of B mesons. These deviations have been noticed both in the neutral-current transitions (b → s l l) and charged-current transitions (b → c l ν ̄ l ). Motivated by these intriguing findings, we investigate the semileptonic decays involving the quark-level transitions of b → c l ν ̄ l . To explore the presence of new physics, we adopt a model-independent approach and analyze the processes Λ b → Λ c τ ν ̄ τ , B c + → η c τ + ν τ and B → D ∗ ∗ τ ν ̄ τ , where D ∗ ∗ = D 0 ∗ , D 1 ∗ , D 1 , D 2 ∗ represent the four lightest excited charm mesons. Considering a comprehensive effective Hamiltonian, we perform a global fit using various sets of new coefficients and incorporate measurements of R D , R D ∗ , R J ∕ ψ , P τ D ∗ , as well as the upper limit on the branching ratio of B c + → τ + ν τ . Subsequently, we examine the impact of constrained new couplings on the branching ratios, forward–backward asymmetry parameters, lepton nonuniversality (LNU) ratios, as well as lepton and hadron polarization asymmetries in these decay modes. [ABSTRACT FROM AUTHOR]

We investigate the weak leptonic and semileptonic decay widths of pseudoscalar light and heavy mesons in a Dirac formalism. We take relativistic-independent quark model of the form V q (r) = 1 2 (1 + γ 0) (a 2 r + V 0) , where a > 0. This is computed using the binding quark eigenfunction and taking the assumptions of a significant relationship between the quark and antiquark momenta inside the decaying meson in the rest frame. To calculate the decay constant (f M) , decay width and branching fractions of pseudoscalar mesons, we employ the model parameters that we used earlier. The experimental findings and various similar models are in good agreement with our predictions such as " f B C > f B S > f B , f D S > f D , f D > f B and f B > f π ". Finally, we calculate the form factors and branching fractions for the semileptonic D (D 0) decays " D + → K S 0 e + ν e ,  D + → K L 0 e + ν e ,  D + → π 0 e + ν e ,  D 0 → K − e + ν e and D 0 → π − e + ν e " and find reasonable agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The most precise measurement of decay-time-dependent CP violation in the decays of B 0 → J / ψ K S 0 and B 0 → ψ (2 S) K S 0 was reported by LHCb collaboration with the values of S J / ψ K S 0 = 0. 8 3 ± 0. 0 8 ± 0. 0 1 , C J / ψ K S 0 = 0. 1 2 ± 0. 0 7 ± 0. 0 2 and S ψ (2 S) K S 0 = 0. 8 4 ± 0. 1 0 ± 0. 0 1 , C ψ (2 S) K S 0 = − 0. 0 5 ± 0. 1 0 ± 0. 0 1. In this study, the parameters of CP violation in these decay modes have been calculated under the factorization approach. In these decays, CP violation in the interference of mixing and decay has has arisen from decay-time-dependent asymmetry. This type of CP violation has been characterized by Im λ f ≠ 0. We have estimated the parameters of S J / ψ K S 0 = 0. 8 8 ± 0. 0 0 and C J / ψ K S 0 = 0. 1 1 ± 0. 0 1 for the B 0 → J / ψ K S 0 decay and S ψ (2 S) K S 0 = 0. 8 9 ± 0. 0 1 and C ψ (2 S) K S 0 = − 0. 0 4 ± 0. 0 2 correspond to the B 0 → ψ (2 S) K S 0 decay which are compatible with the experimental values approved by the LHCb collaboration. In the following, we have obtained the value of sin 2 β. Finally, we have calculated the total amplitude and obtained comparable results with the experimental values for the branching ratios of both decays. [ABSTRACT FROM AUTHOR]

This paper covers the recent experimental development on spin alignment measurements of K ∗ 0 and ϕ vector mesons in heavy-ion and p p collisions at RHIC and LHC energies. Measurements in e + e − collisions at LEP energies are also discussed. Spin alignment of vector mesons is studied by measuring the second diagonal element ρ 0 0 of spin density matrix. The spin density matrix element ρ 0 0 is obtained by measuring the angular distribution of vector meson decay daughter with respect to the quantization axis in vector meson rest frame. Measured ρ 0 0 values for vector mesons are found to be larger than 1 / 3 at high momentum in e + e − collisions at LEP energies, suggesting the preferential production of vector meson with helicity zero state from the fragmentation process. The ρ 0 0 values are found to be smaller than 1 / 3 ( ρ 0 0 = 1 / 3 implies no spin alignment) for K ∗ 0 and ϕ vector mesons at low transverse momentum in Pb–Pb collisions at s NN = 2. 7 6  TeV. These observations are qualitatively consistent with the expectation from models which attribute the spin alignment effect due to polarization of quarks in the presence of large initial angular momentum in noncentral heavy-ion collisions and its subsequent hadronization by the process of recombination. No significant spin alignment effect is observed for K S 0 (spin = 0) in mid-central Pb–Pb collisions and for vector mesons in p p collisions. However, the preliminary results of ρ 0 0 for ϕ mesons are larger than 1 / 3 at intermediate p T in Au–Au collisions at RHIC energies and can be attributed to the presence of ϕ meson field. Although there is evidence of spin alignment effect of vector mesons in heavy-ion collisions but the measured effect is surprisingly larger in context of hyperon polarization. Therefore, these results will trigger further theoretical study. [ABSTRACT FROM AUTHOR]

In the system of a pair of quantum-entangled neutral kaons from meson decays, when one kaon collapses into the K S state, the other will collapse instantaneously into the K L state, due to entanglement and nonlocality. However, if the alternative hypothesis is correct and there is a time window during which one kaon is unaware that the other has decayed, some quantum mechanically prohibited K S K S decays may occur. We calculate the branching ratios of K S K S in vector meson decays under locality hypothesis and compare them with experimental results. We show that the branching ratio of J / ψ → K S K S under locality assumption is already excluded by the BESIII experimental upper limit. Additional experimental results are proposed to perform this test in the future. [ABSTRACT FROM AUTHOR]

We calculate bounds for the branching ratio of the B s 0 → τ e decay, for the first time, in the context of flavor changing neutral currents mediated by a Z ′ gauge boson, which can arise from five extended models. In this sense, by using experimental measurements on the B → X s γ decay and the B s 0 → μ + μ − process, we look for constraints of the Z ′ b s coupling, where the more restrictive bound is offered by the last one. On the other hand, by employing the experimental restriction on the τ → e e ē decay, the strength of the Z ′ τ e coupling is estimated. Our analysis is based on the more recent experimental results on searches for the Z ′ gauge boson in ATLAS and CMS detectors. In addition, we revisited the B s 0 → τ μ , μ e meson decays by using different approaches not previously reported. The strengths of the Z ′ τ μ and Z ′ μ e couplings were estimated by employing experimental restrictions on the τ → μ μ μ ̄ decay and the μ − e conversion rate, respectively. Thus, we predict the following upper bounds: B s 0 → τ e ∼ 1 0 − 6 , B s 0 → τ μ ∼ 1 0 − 6 and B s 0 → μ e ∼ 1 0 − 1 1 . [ABSTRACT FROM AUTHOR]

The masses of the strange mesons (K , K ∗ and ϕ) are investigated in the presence of strong magnetic fields. The changes in the masses of these mesons arise from the mixing of the pseudoscalar and vector mesons in the presence of a magnetic field. For the charged mesons, these mass modifications are in addition to the contributions from the lowest Landau energy levels to their masses. The decay widths, ϕ → K K ̄ and K ∗ → K π , in the presence of the magnetic field are studied using a field theoretic model of composite hadrons with constituent quarks/antiquarks. The model uses the free Dirac Hamiltonian in terms of the constituent quark fields as the light quark–antiquark pair creation term and explicit constructions for the meson states in terms of the constituent quarks and antiquarks to study the decay processes. The pseudoscalar–vector (PV) meson mixing leads to a drop (rise) in the mass of the pseudoscalar (longitudinal component of the vector) meson. It is observed that the mass modifications for the hidden strange mesons, arising from ϕ − η ′ mixing, are quite prominent, whereas the neutral open strange mesons have only marginal changes in their masses due to mixing. The mass modifications of the charged open strange mesons are due to interplay between the Landau-level contributions and the PV mixing, and, the latter effect is observed to dominate at large values of the magnetic field. The vector meson decay widths (ϕ → K K ̄ and K ∗ → K π) involving the charged mesons are observed to be quite different from the widths involving neutral mesons, due to the additional contribution for the charged mesons from the Landau levels. [ABSTRACT FROM AUTHOR]

We study the resonances ϕ (1 0 2 0) and ϕ (1 6 8 0) contributions for the three-body decays B + → D s + K K ̄ in the perturbative QCD approach. The branching ratios for B + → D s + ϕ (1 0 2 0) → D s + K + K − and B + → D s + ϕ (1 0 2 0) → D s + K 0 K ̄ 0 are predicted to be (1. 5 3 ± 0. 2 3) × 1 0 − 7 and (1. 0 2 − 0. 1 3 + 0. 1 9) × 1 0 − 7 , respectively. The decay B + → D s + ϕ (1 6 8 0) with ϕ (1 6 8 0) decays into K + K − or K 0 K ̄ 0 , has the branching fraction (6. 9 4 − 2. 0 2 + 1. 8 3) × 1 0 − 9 , which is about 5 % of the result for B + → D s + ϕ (1 0 2 0) → D s + K + K − . [ABSTRACT FROM AUTHOR]

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the B s 0 meson decay into the two light vectors K ∗ 0 K ̄ ∗ 0 by calculating the helicity amplitude in the framework of quantum chromodynamics (QCD) factorization approach. We find the BR of B s 0 → K ∗ 0 K ̄ ∗ 0 = (1. 1 3 ± 0. 1 8) × 1 0 − 5 which is in full agreement with the recent theoretical predictions and experimental measurements. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are 𝒜 C P dir = 0. 0 0 3 5 3 ± 0. 0 0 1 5 4 , (𝒜 C P mix ) = − 0. 0 0 6 8 6 ± 0. 0 3 1 1 9 , and (𝒜 C P Δ Γ) = 0. 9 9 9 9 7 ± 0. 0 0 0 2 1 , respectively. [ABSTRACT FROM AUTHOR]

We calculate B ̄ s 0 → ϕ translation form factors V , A 0 , A 1 , A 2 based on QCD sum rule and study the nonleptonic two-body decay of B ̄ s 0 → J / ψ ϕ with the form factors obtained. We calculate the time-integrated branching ratio of B ̄ s 0 → J / ψ ϕ decay. The results for both the total branching ratio and the cases for the final vectors in longitudinal and transverse polarizations are consistent with experimental data. [ABSTRACT FROM AUTHOR]

In this paper the decays of B c + → D s ∗ + D ̄ ∗ 0 , B c + → D s ∗ + D ∗ 0 , B c + → D ∗ + D ̄ ∗ 0 and B c + → D ∗ + D ∗ 0 have been investigated. The available experimental results for these decays are (in units of 1 0 − 5 ): (f c / f u) ℬ B c + → D s ∗ + D ̄ ∗ 0 = 2. 8 8 ± 0. 3 9 , (f c / f u) ℬ B c + → D s ∗ + D ∗ 0 = 6. 3 0 ± 0. 8 3 , (f c / f u) ℬ B c + → D ∗ + D ̄ ∗ 0 = 1 2. 9 0 ± 0. 9 0 , (f c / f u) ℬ B c + → D ∗ + D ∗ 0 = − 1. 5 6 ± 0. 2 9. By applying the theoretical value of the f c / f u that span the range of [ 0. 2 4 – 1. 2 0 ] % , the results for QCDF approach are about 1 0 2 times smaller than experimental one. Therefore, it is decided to calculate the theoretical branching ratio by applying the final state interaction (FSI) through the t (crossed and uncrossed) channels. The FSI effects are very sensitive to the changes in the phenomenological parameter η. This parameter appears in the FSI form factors that increase strong interaction share. In most calculation changing two units in this parameter, makes the final result multiply in the branching ratio, therefore the decision to use FSI is not unexpected. In this study there are thirteen intermediate states for B c + → D s ∗ + D ̄ ∗ 0 decay, fifteen intermediate states for B c + → D ∗ + D ̄ ∗ 0 decay and four intermediate states for B c + → D s ∗ + D ∗ 0 and B c + → D ∗ + D ∗ 0 decays, in which the contribution of each one is calculated and summed in the final amplitude. Considering f c / f u = 1. 2 4 % and fixing η between four and five acceptable results have been obtained. [ABSTRACT FROM AUTHOR]

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the B s 0 meson decays to D + D − by calculating the amplitude and the decay width of the process including the chiral loop and gluon condensate to first-order. We find the BR of B s 0 → D s + D s − = (1. 8 ± 0. 4) × 1 0 − 3 which is in agreement with other experimental measurements and theoretical predictions. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are A CP dir = 0. 0 0 3 4 8 ± 0. 0 0 0 1 2 , (A CP mix ) = − 0. 0 4 3 9 5 ± 0. 0 0 1 2 9 and (A Δ Γ) = − 0. 9 9 9 0 3 ± 0. 0 0 1 2 2 , respectively. [ABSTRACT FROM AUTHOR]

Recently, some small hints of lepton flavor violating (LFV) decays have been probed in different colliders and accelerators. Although these processes are forbidden in the Standard Model (SM), observation of LFV decays are considered as good probes to test theory beyond the SM. In this paper, we study some LFV decays, e.g. three-body decay channels of μ lepton like μ → 3 e , μ → e ν ν ̄ and two-body decays of B meson and τ lepton like B s , d → μ ± e ∓ and τ → e ϕ in Z ′ model. We calculate the branching ratio of the above decays considering the effect of both Z and Z ′ -mediated flavor-changing neutral-current (FCNC). [ABSTRACT FROM AUTHOR]

The present study investigates the decay of B to heavy meson using the soft collinear effective theory. By assigning different loop momenta, the factorization has been tested and it is found to be valid to all orders in the perturbation theory. It is noted that theory contains one hard collinear and two soft modes depending upon virtuality of different momenta. In the next step, symmetry-conserving relations (in heavy quark limits) to the form factors have been studied. These relations are then used to parametrize the form factors to get symmetry-breaking corrections. These symmetry-breaking corrections can be calculated using perturbative (vertex corrections) as well as nonperturbative (hard spectator interactions) QCD. It is found that in the heavy quark limit, these symmetry contributions do not contribute to the form factors that appear in physical observables for the case of B → D (D ∗) l ν l decays which are contrary to the heavy-to-light meson decays. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The weak decay of into , and mesons, observed by LHCb collaboration for the first time, are calculated in the model which takes into account the 'factorizable' contributions and 'nonfactorizable' corrections. The decays of mesons into charmonia and light hadrons are expected to be well described by the factorization approximation. In the standard model, , decays occur through only the tree-level diagrams and so there are no CP violation in these channels. The decay is expected to proceed mainly via a transition because the decay has identical final state and similar event topology, where it is chosen as the relative branching fraction channel. The ratio of branching fractions is of particular interest since the CKM matrix element is suppressed by a factor , in which the occur through transition, but the dominant amplitude of the decay is a transition. The decay is examined by color-allowed, color-suppressed spectator and weak annihilation diagrams. The weak annihilation topology, in contrast to decays of other beauty hadrons, is not suppressed and can contribute significantly to the decay amplitude. Because of the , and branching fractions are calculated relative to the decay, this decay mode is estimated separately, the ratio between them are , and , respectively, that are compatible with the experimental data. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Experimental era of rare -decays started with the measurement of by CLEO in 1993, followed by the measurement of the inclusive decay 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 at about 1 part in 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 -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 -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. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the baryonic semileptonic decays in the vector leptoquark model with state. Using the parameters' space constrained through some well-measured decay modes, such as , mixing and decays, we show the effects of vector leptoquark state on the double lepton polarization asymmetries of decays, and find that the double lepton polarization asymmetries, except for , and , are sensitive to the contributions of vector leptoquark model. [ABSTRACT FROM AUTHOR]

The inclusion of elastic rescattering and annihilation of quark-antiquarks pairs in final state can explain the -dependency for cross-section ratio of and mesons in charge exchange reaction. The estimation for mixing angle with isoscalar states and hidden strangeness has been obtained. The consistent description of and meson outputs in , and decays was also considered. [ABSTRACT FROM AUTHOR]

In this paper, the width of the decay is calculated in the framework of the Nambu-Jona-Lasinio (NJL) model. The contributions of the intermediate vector and scalar mesons are taken into account. It is shown that the main contribution to the width of this decay is given by the subprocesses with the intermediate -boson and vector meson. The scalar channel with the intermediate meson gives an insignificant contribution. In Appendix A, it is shown that the contribution of the subprocess with the intermediate meson is negligible as well. The obtained results are in satisfactory agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In the extended Nambu-Jona-Lasinio model the decay widths and are studied in the quark one-loop approximation. Our estimations of the decay widths are in satisfactory agreement with experimental data. In the paper, the decay widths are also calculated. [ABSTRACT FROM AUTHOR]

In this paper, we survey the radial and orbital excitations of I = 0 and systems anticipated up to 2.0 GeV in the framework of the chiral quark model. The Schrödinger equation is solved by using Gaussian expansion method. And using the wave functions obtained, instead of the simple harmonic oscillator wave functions, we study systematically the two-body strong decay (limited to S + S modes) of the systems. By comparing with the experimental data, we try to identify the normal states and exotic states. [ABSTRACT FROM AUTHOR]