Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFrugal $U(1)_X$ models with non-minimal flavor violation for $b to s ell ell$ anomalies and neutrino mixing
63
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We analyze the class of models with an extra $U(1)_X$ gauge symmetry that can account for the $b to s ell ell$ anomalies by modifying the Wilson coefficients $C_{9e}$ and $C_{9mu}$ from their standard model values. At the same time, these models generate appropriate quark mixing, and give rise to neutrino mixing via the Type-I seesaw mechanism. Apart from the gauge boson $Z$, these frugal models only have three right-handed neutrinos for the seesaw mechanism, an additional $SU(2)_L$ scalar doublet for quark mixing, and a SM-singlet scalar that breaks the $U(1)_X$ symmetry. This set-up identifies a class of leptonic symmetries, and necessitates non-zero but equal charges for the first two quark generations. If the quark mixing beyond the standard model were CKM-like, all these symmetries would be ruled out by the latest flavor constraints on Wilson coefficients and collider constraints on $Z$ parameters. However, we identify a single-parameter source of non-minimal flavor violation that allows a wider class of $U(1)_X$ symmetries to be compatible with all data. We show that the viable leptonic symmetries have to be of the form $L_e pm 3 L_mu - L_tau$ or $L_e - 3 L_mu + L_tau$, and determine the $(M_{Z^prime}, g_{Z^prime})$ parameter space that may be probed by the high-luminosity data at the LHC.
rate research
Read More
One of the fundamental predictions of the Standard Model is Lepton Flavour Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. Recent LHCb measurements present a pattern of deviations from this prediction in rare B-meson decays. While not yet statistically significant (currently $2.2-2.6 sigma$), these measurements show an imbalance in the ratio of B-meson decays to a pair of muons in association with a Kaon and decays to a pair of electrons in association with a Kaon. If the measured deviations are indeed present in nature, new physics may mediate interactions involving a pair of same flavour leptons, a $b$- and an $s$-quark. We present the prospect for a search of new physics in this type of interactions at the LHC, in a process that involves an $s$-quark, and a final state with two leptons and a $b$-jet. The proposed search can improve the sensitivity to new physics in these processes by a factor of four compared to current searches with in the total dataset expected at the LHC.
Ratios of branching fractions of semileptonic B decays, $(B to H mu mu)$ over $(B to H ee)$ with $H=K, K^*,X_s, K_0(1430), phi, ldots$ are sensitive probes of lepton universality. In the Standard Model, the underlying flavor changing neutral current process $brightarrow s ell ell$ is lepton flavor universal. However models with new flavor violating physics above the weak scale can give substantial non-universal contributions. The leading contributions from such new physics can be parametrized by effective dimension six operators involving left- or right-handed quarks. We show that in the double ratios $R_{X_s}/R_K$, $R_{K^*}/R_K$ and $R_phi/R_K$ the dependence on new physics coupling to left-handed quarks cancels out. Thus a measurement of any of these double ratios is a clean probe of flavor nonuniversal physics coupling to right-handed quarks. We also point out that the observables $R_{X_s}$, $R_{K^*}$, $R_{K_0(1430)}$ and $R_phi$ depend on the same combination of Wilson coefficients and therefore satisfy simple consistency relations.
Recently the LHCb collaboration has confirmed the evidence for lepton flavour nonuniversality at the $3.1sigma$ level via an updated measurement of $R_K$. In this work we analyse this evidence within a model-independent approach. We make projections for future measurements which indicate that LHCb will be in the position to discover lepton nonuniversality with the Run 3 data in a single observable. We analyse other ratios based on our analysis of the present measurements of the ratios $R_{K^{(*)}}$ and analyse if they are able to differentiate between various new physics options within the effective field theory at present or in the near future. We also compare the present deviations in the ratios with NP indications in the angular observables of exclusive $b to s ellell$ transitions. Finally, we update our global analysis considering all $b to s ellell$ observables altogether, including a 20-parameter fit in connection of a Wilks test.
Considering the recent experimental results on exclusive semileptonic $B$ meson decays showing sizable departure from their Standard Model prediction of lepton flavor universality and keeping ongoing and proposed non-standard Higgs searches in mind, we explore the charged current flavor observables ($mathcal{R}_{D^{(*)}}$, $mathcal{R}_{J/psi}$), among other $bto cell u$ transitions, in the presence of a relevant scalar current effective new physics operator. We use $B_c$ lifetime and predicted bounds on the branching fraction of $B_c to tau u$ decay as constraints. We show the allowed parameter space in terms of the real and imaginary parts of the corresponding Wilson coefficients for such interactions. Under the light of obtained results, we study the prospect of two benchmark models, rendering the Wilson coefficients real (Georgi-Machacek (GM)) and complex (Leptoquark (LQ)) respectively. We show that constraints from $bto cell u$ on GM parameters are consistent with other flavor constraints on the model, if we drop the Babar~results. Including those disfavors the model by more than $3sigma$. On the other hand, one benchmark LQ scenario, which gives rise to a single scalar current effective interaction, is still allowed within $68%$ confidence level, albeit with a shrunk parameter space.
A measurement of the ratio of branching fractions of the decays $B^+to K^+mu^+mu^-$ and $B^+to K^+e^+e^-$ is presented. The proton-proton collision data used correspond to an integrated luminosity of $5.0,$fb$^{-1}$ recorded with the LHCb experiment at centre-of-mass energies of $7$, $8$ and $13,$TeV. For the dilepton mass-squared range $1.1 < q^2 < 6.0,$GeV$^2!/c^4$ the ratio of branching fractions is measured to be $R_K = {0.846,^{+,0.060}_{-,0.054},^{+,0.016}_{-,0.014}}$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $R_K$ to date and is compatible with the Standard Model at the level of 2.5 standard deviations.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
