arXiv subjects

Tahira Yasmeen

Publications and source records attributed to Tahira Yasmeen.

3 recordsLinked to original sources

arXiv2025

Addressing the $R_{τ/{μ,e}}\left(D^{(*)}\right)$ puzzle through New Physics four-fermion operators and their impact on $Λ_{b}\rightarrowΛ_{c}τ\barν_τ$ decay

The Lepton Flavor Universality ratio $R_{τ/{μ,e}}\left(D^{(*)}\right)$ poses a challenge to the Standard Model (SM), as B-factory experiments, BaBar, Belle, and the LHCb show $3.31σ$ deviations from their theoretical predictions. Utilizing the latest HFLAV averages and incorporating the branching ratio constraints $60\%$, $30\%$ and $10\%$ from the lifetime of the $B_c$ meson, we determine the values of the Wilson coefficients (WCs) for different New Physics (NP) four-fermion operator with specific Lorentz structures. Our analysis finds that the WC scenario $\left(C_{S_{L}},C_{S_{R}}\right)$ is the most probable, the maximum pull from the SM, and strongly influenced by branching ratio constraints. Furthermore, we identify three degenerate solutions involving $C_{V_{L}}$, $C_{V_{L}}^{\prime}$, $C_{V_{L}}^{\prime\prime}$, and $C_{S_{R}}^{\prime\prime}$ as the second most probable NP scenarios. We then studied the influence of these NP operators on various physical observables in $Λ_{b}\rightarrowΛ_{c}τ\barν_τ$ decay by using the Lattice QCD form factors. Our results highlighted $C_{S_{L}}^{\prime\prime}$, $C_{S_{R}}$, $C_{T}$, $\left(C_{S_{L}},C_{S_{R}}\right)$, $\left(C_{S_{R}},C_{T}\right)$, and the three degenerate scenarios involving $\left(C_{S_{L}},C_{T}\right)$, $\left(C_{S_{L}}^{\prime},C_{T}^{\prime}\right)$ and $\left(C_{S_{L}}^{\prime\prime},C_{T}^{\prime\prime}\right)$ as strong indicators of NP. The correlation of different physical observables shows a direct correlation between $dΓ/dq^{2}$ and $P_{L}^τ$ for WC $\left(C_{S_{L}},C_{S_{R}}\right)$; and between $A_{FB}$ and $P_{L}^{Λ_{c}}$ for three degenerate WCs involving $\left(C_{S_{L}},C_{T}\right)$. We hope that the measurements of these observables in ongoing and future experiments will help us scrutinize these constraints on the various NP couplings.

hep-ph↗

arXiv2024

Probing New Physics in light of recent developments in $b \rightarrow c \ell ν$ transitions

The experimental studies of the observables associated with the $b \rightarrow c$ transitions in the semileptonic $B-$ meson decays at BaBar, Belle and LHCb have shown some deviations from the Standard Model (SM) predictions, consequently, providing a handy tool to probe the possible new physics (NP). In this context, we have first revisited the impact of recent measurements of $R({D^{(*)}})$ and $R(Λ_c)$ on the parametric space of the NP scenarios. In addition, we have included the $R(J/ψ)$ data in the analysis and found that their influence on the best-fit points and the parametric space is mild. Using the recent HFLAV data, after validating the well established sum rule of $R(Λ_c)$, we derived the similar sum rule for $R(J/ψ)$. Furthermore, according to the updated data, we have modified the correlation among the different observables, giving us their interesting interdependence. Finally, to discriminate the various NP scenarios, we have plotted the different angular observables and their ratios for $B \to D^* τν_τ$ against the transfer momentum square $\left(q^2\right)$, using the $1σ$ and $2σ$ parametric space of considered NP scenarios. By implementing the collider bounds on NP Wilson coefficients, we find that, in the parametric space of some NP WCs is significantly restrained. To see the clear influence of NP on the amplitude of the angular observables, we have also calculated their numerical values in different $q^2$ bins and shown them through the bar plots. We hope their precise measurements will help to discriminate various NP scenarios.

hep-ph↗

arXiv2024

Analysis of $b\rightarrow cτ\barν_τ$ anomalies using weak effective Hamiltonian with complex couplings

Recently, the experimental measurements of the branching ratios and different polarization asymmetries for the processes occurring through flavor-changing-charged current $b\rightarrow cτ\overlineν_τ$ transitions by BABAR, Belle, and LHCb show some sparkling differences with the corresponding SM predictions. Assuming the left handed neutrinos, we add the dimension-six vector, (pseudo-)scalar, and tensor operators with complex WCs to the SM WEH. Together with 60%, 30% and 10% constraints coming from the branching ratio of $B_{c}\toτ\barν_τ$, we analyze the parametric space of these new physics WCs accommodating the current anomalies in the purview of the most recent HFLAV data of $R_{τ/{μ,e}}\left(D\right)$, $R_{τ/{μ,e}}\left(D^*\right)$ and Belle data of $F_{L}\left(D^*\right)$ and $P_τ\left(D^*\right)$. Furthermore, we derive the sum rules which correlate these observables with $R_{τ/{μ,e}}\left(D\right)$ and $R_{τ/{μ,e}}\left(D^*\right)$. Using the best-fit points of the new complex WCs along with the latest measurements of $R_{τ/{μ,e}}\left(D^{(*)}\right)$, we predict the numerical values of the observable $R_{τ/\ell}\left(Λ_c\right)$, $R_{τ/μ}\left(J/ψ\right)$ and $R_{τ/\ell}\left(X_c\right)$ from the sum rules. Apart from finding the correlation matrix among the observables under consideration, we plot them graphically which is useful to discriminate different NP scenarios. Finally, we study the impact of these NP couplings on various angular and the CP triple product asymmetries, that could be measured in some ongoing and future experiments. The precise measurements of these observables are important to check the SM and extract the possible NP.

hep-ph↗