Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userPatterns of New Physics in $bto sell^+ell^-$ transitions in the light of recent data
61
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In the Standard Model (SM), the rare transitions where a bottom quark decays into a strange quark and a pair of light leptons exhibit a potential sensitivity to physics beyond the SM. In addition, the SM embeds Lepton Flavour Universality (LFU), leading to almost identical probabilities for muon and electron modes. The LHCb collaboration discovered a set of deviations from the SM expectations in decays to muons and also in ratios assessing LFU. Other experiments (Belle, ATLAS, CMS) found consistent measurements, albeit with large error bars. We perform a global fit to all available $bto sell^+ell^-$ data ($ell=e,mu$) in a model-independent way allowing for different patterns of New Physics. For the first time, the NP hypothesis is preferred over the SM by $5,sigma$ in a general case when NP can enter SM-like operators and their chirally-flipped partners. LFU violation is favoured with respect to LFU at the 3-4$,sigma$ level. We discuss the impact of LFU-violating New Physics on the observable $P_5^prime$ from $B to K^*mu^+mu^-$ and we compare our estimate for long-distance charm contributions with an empirical model recently proposed by a group of LHCb experimentalists. Finally, we discuss NP models able to describe this consistent pattern of deviations.
rate research
Read More
Motivated by deviations with respect to Standard Model predictions in $bto sell^+ell^-$ decays, we evaluate the global significance of the new physics hypothesis in this system, including the look-elsewhere effect for the first time. We estimate the trial-factor with psuedo-experiments and find that it can be as large as seven. We calculate the global significance for the new physics hypothesis by considering the most general description of a non-standard $bto sell^+ell^-$ amplitude of short-distance origin. Theoretical uncertainties are treated in a highly conservative way by absorbing the corresponding effects into a redefinition of the Standard Model amplitude. Using the most recent measurements of LHCb, ATLAS and CMS, we obtain the global significance to be $3.9$ standard deviations.
Motivated by renewed evidence for new physics in $b to sellell$ transitions in the form of LHCbs new measurements of theoretically clean lepton-universality ratios and the purely leptonic $B_stomu^+mu^-$ decay, we quantify the combined level of discrepancy with the Standard Model and fit values of short-distance Wilson coefficients. A combination of the clean observables $R_K$, $R_{K^*}$, and $B_sto mumu$ alone results in a discrepancy with the Standard Model at $4.0sigma$, up from $3.5sigma$ in 2017. One-parameter scenarios with purely left-handed or with purely axial coupling to muons fit the data well and result in a $sim 5 sigma$ pull from the Standard Model. In a two-parameter fit of %$C_9$ and $C_{10}$, new-physics contributions with both vector and axial-vector couplings to muons the allowed region is much more restricted than in 2017, principally due to the much more precise result on $B_s to mu^+ mu^-$, which probes the axial coupling to muons.Including angular observables data restricts the allowed region further.A by-product of our analysis is an updated average of $text{BR}(B_s to mu^+ mu^-) = (2.8pm 0.3) times 10^{-9}$.
$B$ decays proceeding via $bto cell u$ transitions with $ell=e$ or $mu$ are tree-level processes in the Standard Model. They are used to measure the CKM element $V_{cb}$, as such forming an important ingredient in the determination of e.g. the unitarity triangle; hence the question to which extent they can be affected by new physics contributions is important, specifically given the long-standing tension between $V_{cb}$ determinations from inclusive and exclusive decays and the significant hints for lepton flavour universality violation in $bto ctau u$ and $bto sellell$ decays. We perform a comprehensive model-independent analysis of new physics in $bto cell u$, considering all combinations of scalar, vector and tensor interactions occuring in single-mediator scenarios. We include for the first time differential distributions of $Bto D^*ell u$ angular observables for this purpose. We show that these are valuable in constraining non-standard interactions. Specifically, the zero-recoil endpoint of the $Bto Dell u$ spectrum is extremely sensitive to scalar currents, while the maximum-recoil endpoint of the $Bto D^*ell u$ spectrum with transversely polarized $D^*$ is extremely sensitive to tensor currents. We also quantify the room for $e$-$mu$ universality violation in $bto cell u$ transitions, predicted by some models suggested to solve the $bto ctau u$ anomalies, from a global fit to $Bto Dell u$ and $Bto D^*ell u$ for the first time. Specific new physics models, corresponding to all possible tree-level mediators, are also discussed. As a side effect, we present $V_{cb}$ determinations from exclusive $B$ decays, both with frequentist and Bayesian statistics, leading to compatible results. The entire numerical analysis is based on open source code, allowing it to be easily adapted once new data or new form factors become available.
We perform model-independent statistical analyses of three scenarios accommodating New Physics (NP) in Delta F=2 flavour-changing neutral current amplitudes. In a scenario in which NP in B_d-B_d-bar and B_s-B_s-bar is uncorrelated, we find the parameter point representing the Standard-Model disfavoured by 2.4 standard deviations. However, recent LHCb data on B_s neutral-meson mixing forbid a good accommodation of the D0 data on the semileptonic CP asymmetry A_SL. We introduce a fourth scenario with NP in both M_12^d,s and Gamma_12^d,s, which can accommodate all data. We discuss the viability of this possibility and emphasise the importance of separate measurements of the CP asymmetries in semileptonic B_d and B_s decays. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using Rfit to handle theoretical uncertainties.
We present results of global fits of all relevant experimental data on rare $b to s$ decays. We observe significant tensions between the Standard Model predictions and the data. After critically reviewing the possible sources of theoretical uncertainties, we find that within the Standard Model, the tensions could be explained if there are unaccounted hadronic effects much larger than our estimates. Assuming hadronic uncertainties are estimated in a sufficiently conservative way, we discuss the implications of the experimental results on new physics, both model independently as well as in the context of the minimal supersymmetric standard model and models with flavour-changing $Z$ bosons. We discuss in detail the violation of lepton flavour universality as hinted by the current data and make predictions for additional lepton flavour universality tests that can be performed in the future. We find that the ratio of the forward-backward asymmetries in $B to K^* mu^+mu^-$ and $B to K^* e^+e^-$ at low dilepton invariant mass is a particularly sensitive probe of lepton flavour universality and allows to distinguish between different new physics scenarios that give the best description of the current data.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
