Measurement of the Ratio of Branching Fractions B(B_{c}^{+}→J/ψτ^{+}ν_{τ})/B(B_{c}^{+}→J/ψμ^{+}ν_{μ})

Measurement of the Ratios of Branching Fractions R(D^{*}) and R(D^{0})

The ratios of branching fractions R(D^{*})≡B(B[over ¯]→D^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]→D^{*}μ^{-}ν[over ¯]_{μ}) and R(D^{0})≡B(B^{-}→D^{0}τ^{-}ν[over ¯]_{τ})/B(B^{-}→D^{0}μ^{-}ν[over ¯]_{μ}) are measured, assuming isospin symmetry, using a sample of proton-proton collision data corresponding to 3.0  fb^{-1} of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode τ^{-}→μ^{-}ν_{τ}ν[over ¯]_{μ}. The measured values are R(D^{*})=0.281±0.018±0.024 and R(D^{0})=0.441±0.060±0.066, where the first uncertainty is statistical and the second is systematic. The correlation between these measurements is ρ=-0.43. The results are consistent with the current average of these quantities and are at a combined 1.9 standard deviations from the predictions based on lepton flavor universality in the standard model.

The role of multi-parton interactions in doubly-heavy hadron production

Beauty and charm quarks are ideal probes of pertubative Quantum Chromodymanics in proton–proton collisions, owing to their large masses. In this paper the role of multi-parton interactions in the production of doubly-heavy hadrons is studied using simulation samples generated with Pythia, a Monte Carlo event generator. Comparisons are made to the stand-alone generators BcVegPy and GenXicc. New methods of speeding up Pythia simulations for events containing heavy quarks are described, enabling the production of large samples with multiple heavy-quark pairs. We show that significantly higher production rates of doubly-heavy hadrons are predicted in models that allow heavy quarks originating from different parton–parton interactions (within the same hadron–hadron collision) to combine to form such hadrons. Quantitative predictions are sensitive to the modelling of colour reconnections. We suggest a set of experimental measurements capable of differentiating these additional contributions.

Anomalies in the heavy sector

Heavy flavour physics is well described by the Standard Model with the exception of some measurements which could be signalling new physics. We briefly review status and prospects of R(K) and R(D(*)) anomalies and also address the issue of the long standing tension in the |Vcb| and |Vub| exclusive /inclusive determinations.

B Discrepancies Hold Their Ground

This write-up aims at a comprehensive discussion of the status of the so-called B-anomalies, as well as their interpretation from an effective-theory point of view. The focus is on presenting facts and physics arguments using the bare minimum of equations and pointing instead to the relevant literature in each specific case.

R(J/ψ) and B_{c}^{-}→J/ψℓ^{-}ν[over ¯]_{l} Lepton Flavor Universality Violating Observables from Lattice QCD

We use our lattice QCD computation of the B_{c}→J/ψ form factors to determine the differential decay rate for the semitauonic decay channel and construct the ratio of branching fractions R(J/ψ)=B(B_{c}^{-}→J/ψτ^{-}ν[over ¯]_{τ})/B(B_{c}^{-}→J/ψμ^{-}ν[over ¯]_{μ}). We find R(J/ψ)=0.2582(38) and give an error budget. We also extend the relevant angular observables, which were recently suggested for the study of lepton flavor universality violating effects in B→D^{*}ℓν, to B_{c}→J/ψℓν and make predictions for their values under different new physics scenarios.

Pharmacological Modulators of Tau Aggregation and Spreading

Tauopathies are neurodegenerative disorders characterized by the deposition of aggregates composed of abnormal tau protein in the brain. Additionally, misfolded forms of tau can propagate from cell to cell and throughout the brain. This process is thought to lead to the templated misfolding of the native forms of tau, and thereby, to the formation of newer toxic aggregates, thereby propagating the disease. Therefore, modulation of the processes that lead to tau aggregation and spreading is of utmost importance in the fight against tauopathies. In recent years, several molecules have been developed for the modulation of tau aggregation and spreading. In this review, we discuss the processes of tau aggregation and spreading and highlight selected chemicals developed for the modulation of these processes, their usefulness, and putative mechanisms of action. Ultimately, a stronger understanding of the molecular mechanisms involved, and the properties of the substances developed to modulate them, will lead to the development of safer and better strategies for the treatment of tauopathies.

Experimental Review on Lepton Universality and Lepton Flavour Violation tests in B decays

Tests of lepton flavour universality in B decays offer an excellent opportunity to test the Standard Model, and show hints of new physics in analyses performed by the LHCb, Belle and BaBar experiments. Several theoretical models proposed to explain possible violation of lepton flavour universality claim a connection with lepton flavour violation in B decays. These proceedings review the experimental status of the tests of lepton flavour universality and the searches of lepton flavour violation in B decays.

Mono-τ Signatures at the LHC Constrain Explanations of B-decay Anomalies

We investigate the crossing-symmetry relation between b→cτ^{-}ν[over ¯] decay and bc[over ¯]→τ^{-}ν[over ¯] scattering to derive direct correlations of new physics in semitauonic B-meson decays and the mono-tau signature at the LHC (pp→τ_{h}X+MET). Using an exhaustive set of effective operators and heavy mediators we find that the current ATLAS and CMS data constrain scenarios addressing anomalies in B decays. Pure tensor solutions, completed by leptoquark, and right-handed solutions, completed by W_{R}^{'} or leptoquark, are challenged by our analysis. Furthermore, the sensitivity that will be achieved in the high-luminosity phase of the LHC will probe all the possible scenarios that explain the anomalies. Finally, we note that the LHC is also competitive in the b→u transitions and bounds in some cases are currently better than those from B decays.

Observation of the Decay D^{0}→K^{-}π^{+}e^{+}e^{-}

We report the observation of the rare charm decay D^{0}→K^{-}π^{+}e^{+}e^{-}, based on 468  fb^{-1} of e^{+}e^{-} annihilation data collected at or close to the center-of-mass energy of the ϒ(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675<m(e^{+}e^{-})<0.875  GeV/c^{2} of the electron-positron pair to be B(D^{0}→K^{-}π^{+}e^{+}e^{-})=(4.0±0.5±0.2±0.1)×10^{-6}, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D^{0}→K^{-}π^{+}π^{+}π^{-} used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D^{0}→K^{-}π^{+}μ^{+}μ^{-} branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m(e^{+}e^{-}), where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B(D^{0}→K^{-}π^{+}e^{+}e^{-})<3.1×10^{-6}.

Importance of Loop Effects in Explaining the Accumulated Evidence for New Physics in B Decays with a Vector Leptoquark

In recent years experiments revealed intriguing hints for new physics (NP) in B decays involving b→cτν and b→sℓ^{+}ℓ^{-} transitions at the 4σ and 5σ level, respectively. In addition, there are slight disagreements in b→uτν and b→dμ^{+}μ^{-} observables. While not significant on their own, they point in the same direction. Furthermore, V_{us} extracted from τ decays shows a slight tension (≈2.5σ) with its value determined from Cabibbo-Kobayashi-Maskawa unitarity, and an analysis of BELLE data found an excess in B_{d}→τ^{+}τ^{-}. Concerning NP explanations, the vector leptoquark SU(2) singlet is of special interest since it is the only single particle extension of the standard model which can (in principle) address all the anomalies described above. For this purpose, large couplings to τ leptons are necessary and loop effects, which we calculate herein, become important. Including them in our phenomenological analysis, we find that neither the tension in V_{us} nor the excess in B_{d}→τ^{+}τ^{-} can be fully explained without violating bounds from K→πνν[over ¯]. However, one can account for b→cτν and b→uτν data finding intriguing correlations with B_{q}→τ^{+}τ^{-} and K→πνν[over ¯]. Furthermore, the explanation of b→cτν predicts a positive shift in C_{7} and a negative one in C_{9}, being nicely in agreement with the global fit to b→sℓ^{+}ℓ^{-} data. Finally, we point out that one can fully account for b→cτν and b→sℓ^{+}ℓ^{-} without violating bounds from τ→ϕμ, ϒ→τμ, or b→sτμ processes.

Feynman Rules, Ward Identities and Loop Corrections in Very Special Relativity Standard Model

In this paper, we want to study one loop corrections in Very Special Relativity Standard Model(VSRSM). In order to satisfy the Ward identities and the S i m ( 2 ) symmetry of the model, we have to specify the Feynman rules, including the infrared regulator. To do this, we adapt the Mandelstam–Leibbrandt (ML) prescription to incorporate external momentum-dependent null vectors. As an example, we use the new S i m ( 2 ) invariant dimensional regularization to compute one loop corrections to the effective action in the subsector of the VSRSM that describe the interaction of photons with charged leptons. New stringent bounds for the masses of ν e and ν μ are obtained.

Precise Predictions of Charmed-Bottom Hadrons from Lattice QCD

We report the ground state masses of hadrons containing at least one charm and one bottom quark using lattice quantum chromodynamics. These include mesons with spin (J) and parity (P), (J^{P}): 0^{-}, 1^{-}, 1^{+}, and 0^{+} and the spin 1/2 and 3/2 baryons. Among these hadrons, only the ground state of 0^{-} is known experimentally, and therefore our predictions provide important information for the experimental discovery of all other hadrons with these quark contents.

B Meson Anomalies in a Pati-Salam Model within the Randall-Sundrum Background

Lepton number as a fourth color is the intriguing theoretical idea of the famous Pati-Salam (PS) model. While in conventional PS models, the symmetry breaking scale and the mass of the resulting vector leptoquark are stringently constrained by K_{L}→μe and K→πμe, the scale can be lowered to a few TeV by adding vectorlike fermions. Furthermore, in this case, the intriguing hints for lepton flavor universality violation in b→sμ^{+}μ^{-} and b→cτν processes can be addressed. Such a setup is naturally achieved by implementing the PS gauge group in the five-dimensional Randall-Sundrum background. The PS symmetry is broken by boundary conditions on the fifth dimension, and the resulting massive vector leptoquark automatically has the same mass scale as the vectorlike fermions and all other resonances. We consider the phenomenology of this model in the context of the hints for lepton flavor universality violation in semileptonic B decays. Assuming flavor alignment in the down sector, we find that in b→sℓ^{+}ℓ^{-} transitions, the observed deviations from the standard model predictions [including R(K) and R(K^{*})] can be explained with natural values for the free parameters of the model. Even though we find sizable effects in R(D), R(D^{*}), and R(J/Ψ), one cannot account for the current central values in the constrained setup of our minimal model due to the stringent constraints from D-D[over ¯] mixing and τ→3μ.

Searching for New Physics with b→sτ^{+}τ^{-} Processes

In recent years, intriguing hints for the violation of lepton flavor universality (LFU) have been accumulated in semileptonic B decays, both in the charged-current transitions b→cℓ^{-}ν[over ¯]_{ℓ} (i.e., R_{D}, R_{D^{*}}, and R_{J/ψ}) and the neutral-current transitions b→sℓ^{+}ℓ^{-} (i.e., R_{K} and R_{K^{*}}). Hints for LFU violation in R_{D^{(*)}} and R_{J/ψ} point at large deviations from the standard model (SM) in processes involving tau leptons. Moreover, LHCb has reported deviations from the SM expectations in b→sμ^{+}μ^{-} processes as well as in the ratios R_{K} and R_{K^{*}}, which together point at new physics (NP) affecting muons with a high significance. These hints for NP suggest the possibility of huge LFU-violating effects in b→sτ^{+}τ^{-} transitions. In this Letter, we predict the branching ratios of B→Kτ^{+}τ^{-}, B→K^{*}τ^{+}τ^{-}, and B_{s}→ϕτ^{+}τ^{-}, taking into account NP effects in the Wilson coefficients C_{9(^{'})}^{ττ} and C_{10(^{'})}^{ττ}. Assuming a common NP explanation of R_{D}, R_{D^{(*)}}, and R_{J/ψ}, we show that a very large enhancement of b→sτ^{+}τ^{-} processes, of around 3 orders of magnitude compared to the SM, can be expected under fairly general assumptions. We find that the branching ratios of B_{s}→τ^{+}τ^{-}, B_{s}→ϕτ^{+}τ^{-}, and B→K^{(*)}τ^{+}τ^{-} under these assumptions are in the observable range for LHCb and Belle II.

Scalar leptoquarks: From GUT to B anomalies

Leptoquarks are often used to explain B meson anomalies. The minimalistic approach assumes only one light leptoquark explaining both puzzles. However, one scalar leptoquark cannot explain both anomalies. Two relatively light leptoquarks can be accommodated within SU(5) GUT and might nicely explain both anomalies not being in a conflict with any low-energy flavour constraints or LHC results.

Overview of recent LHCb results

A selection of the most recent and relevant measurements by the LHCb experiment is presented. It includes the determination of the CKM angle γ, obtained from a combination of a number of measurements of B meson decays, the measurement of the D0 - D0 mixing parameters and the results of several tests of the lepton-flavour universality of the electroweak couplings.