arXiv subjects

Qazi Maaz Us Salam

Publications and source records attributed to Qazi Maaz Us Salam.

9 recordsLinked to original sources

arXiv2026

A Phenomenological Study of Semileptonic $B^+$ and $B_s^0$ Decays into Axial-Vector Mesons $\big(D_1(2420),\, D_1^\prime(2430),\, D_{s1}(2460),\, \text{and } D_{s1}^\prime(2536)\big)$ within the Standard Model

We study semileptonic $B$ meson decays $B^+ \to D_1^{(\prime)}\ell^+ν_\ell$ and $B_s^0 \to D_{s1}^{-(\prime)}\ell^+ν_\ell$, where $\ell=μ,τ$. The final state axial vector mesons are treated as mixtures of the heavy quark basis states with light degree of freedom angular momenta $j_\ell=1/2$ and $j_\ell=3/2$, parametrized by the mixing angle $θ_{D_1}$. Using form factors obtained in the covariant light front quark model, we analyze the dependence of various observables on $θ_{D_1}$ such as polarized and unpolarized branching ratios, the lepton forward-backward asymmetry, the longitudinal polarization fraction, and the lepton flavor universality ratios. In addition, we also discuss correlations among different observables. We study these observables in the experimentally motivated mixing angle regions as well as over a wider range of $θ_{D_1}$. Our results show that branching ratios and other observables are sensitive to the axial-vector mixing structure. These predictions provide useful Standard Model benchmarks for future measurements of semileptonic $B_{(s)}$ decays into orbitally excited mesons and may help to clarify the long standing $1/2$ vs. $3/2$ puzzle through semileptonic $B$ decays.

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arXiv2026

Testing Minimal $U(2)^3$ Right-Handed Flavor Breaking in a Singlet-Scalar Vector-Like Quark Portal

We study a portal of a $Z_2$-odd singlet scalar and a vector like down quark, in which a right handed flavor breaking spurion extends the portal coupling from $b_R$ to $d_R$ and $s_R$. This single coupling vector links the $b\to s$, $b\to d$, and $s\to d$ transitions. We compute the one loop dipole and $ΔF=2$ Wilson coefficients, and show that a real scalar generates no $ΔF=2$ amplitude at one loop. Using a seven observable profile likelihood of $B$ meson mixing, $ε_K$, and radiative decays, with the CKM, lattice, and short distance inputs treated as nuisance parameters, we compare a generic spurion, minimal $U(2)^3$ with a free size of the light quark couplings, and a CKM-aligned ansatz. We have found that the present data cannot yet test the flavor structure: the Standard Model is compatible with the data, with a pseudo experiment $p$-value of $0.20$, and no direction of the light quark couplings can be excluded at 95% CL. For $M_D\simeq m_{\mathcal{S}}=1$ TeV and $|λ_b|=1$, the relative light quark coupling $ε_R$ is bounded at 95% CL by $0.227$ for a generic spurion and by $0.211$ for minimal $U(2)^3$. More precise measurements of the $B_s$ mixing phase at the LHC and of $\sin2β$ at LHCb and Belle-II, together with improved lattice and CKM inputs, can make the minimality of the flavor structure testable if a deviation from the Standard Model is observed.

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arXiv2026

The effects of polarization on the observables in the decay $Ξ_{cc}^{++} \rightarrow Ξ_{c}^{+} \bar{\ell}ν_{\ell}$

We investigate the effects of polarization on several physical observables in the semileptonic decay $Ξ_{cc}^{++} \rightarrow Ξ_c^{+} \bar{\ell}ν_{\ell}$. We analyze the polarization effects of the particles involved in the decay, namely $Ξ_{cc}^{++}$, $Ξ_c^{+}$, and the charged muon $\ell$. Using the form factors obtained from QCD sum rules, we compute the $q^{2}$-dependent observables including the differential branching ratio, forward-backward asymmetry, and polarization asymmetries for both longitudinal and transverse polarization states. We also define and examine several polarization ratios and discuss correlations among different observables. In addition, we evaluate the lepton flavor universality ratio defined as $\mathcal{R}_{Ξ_c^+}(μ/e) \equiv \mathcal{D}(Ξ_{cc}^{++}\to Ξ_c^+μ^+ν_μ)/\mathcal{D}(Ξ_{cc}^{++}\to Ξ_c^+e^+ν_e)$ and analyze its behavior over the available dynamical range. Our results show that these observables are quite sensitive to polarization effects, and can provide suitable probes for testing Standard Model predictions.

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arXiv2026

Search for New Physics through the Observables of Semileptonic $B_{c}^+\to D^{\ast+}\ell^{+}\ell^{-}$ Decay

Motivated by the current flavor anomalies and the comparatively less explored nature of the $b\to d$ sector, we present a model-independent study of the rare semileptonic $B_c^{+}\to D^{\ast+}\ell^{+}\ell^{-}$ ($\ell=μ,τ$) decay, to investigate its sensitivity to New Physics effects. The analysis incorporates penguin-box contributions, long-distance resonance effects, and the sizable weak-annihilation amplitudes. Using the $B_c\to D^\ast$ transition form factors calculated in the covariant confined quark model and the weak-annihilation form factors obtained within the Bethe--Salpeter approach, we analyze the differential branching fraction, forward-backward asymmetry, longitudinal helicity fraction, and a comprehensive set of normalized angular observables in several one- and two-dimensional New Physics scenarios and compare our results with the Standard Model predictions. Notably, the branching fraction, forward-backward asymmetry, and the normalized angular coefficients such as, $\langle I_{2c}\rangle$, $\langle I_{3}\rangle$, $\langle I_{5}\rangle$, and $\langle I_{6s} \rangle$, show clear sensitivity to New Physics effects. Our results indicate that the decay $B_c^{+}\to D^{\ast+}\ell^{+}\ell^{-}$ serves as a complementary probe of the flavor structure of New Physics and can therefore be investigated in future measurements at LHCb and other high-luminosity flavor experiments.

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arXiv2026

Real and Complex Singlet-Scalar Benchmarks with a Vector-Like Down Quark for $B\to X_sγ$ and $B_s-\bar B_s$ Mixing

We study a simple extension of the Standard Model with a vector-like down-type quark $D$ and a neutral singlet scalar ${\cal S}=S_R,Φ$. The scalar is considered in two forms, a real field $S_R=S_R^\dagger$ and a complex field $Φ\neqΦ^\dagger$. The interaction $-λ_i{\cal S}\bar D_L d_{Ri}+{\rm h.c.}$ generates the radiative transitions $b\to sγ$ and $b\to sg$ at one loop. Since ${\cal S}$ has no electric charge or color, the gauge boson is emitted from the internal $D$ line, giving $C_{7γ}^{\rm NP}/C_{8G}^{\rm NP}=Q_D=-1/3$ at the matching scale for $ΔB=1$ dipole transitions. For $M_D=m_{\cal S}=1~{\rm TeV}$ and $|λ_s^\astλ_b|=1$, the low scale contribution is $|C_{7γ}^{\rm NP,eff}(μ_b)|\simeq 1.1\times10^{-3}$, This is about $0.4\%$ of the Standard Model value $|C_{7γ}^{\rm SM,eff}(μ_b)|\simeq 0.30$. We also discuss $B_s-\bar B_s$ mixing. In the real-scalar case, the direct and crossed box diagrams cancel in the exact minimal limit. In the complex-scalar case, the direct box contribution remains and gives a bound on the flavor $|λ_s^\astλ_b|$ at the level of a few tenths for TeV-scale masses. Thus, in these minimal benchmarks, $B\to X_sγ$ is radiatively safe, while $B_s-\bar B_s$ mixing gives the stronger constraint in the complex-scalar $Φ$ benchmark.

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arXiv2026

Weak Annihilation Contribution to Angular Observables in $B_{c}^+\to D^{\ast+}\ell^{+}\ell^{-}$ Decays

We analyze the rare semileptonic decays $B_{c}^+ \to D^{\ast+}(\to P_1 P_2)\ell^{+}\ell^{-}$, with $P_1 P_2 = D^+ π^0$ or $D^0 π^+$, and $\ell=μ, τ$. We focus on the impact of weak annihilation contributions alongside penguin, box, and long-distance effects. Using the effective Hamiltonian for $b \to d \ell^+ \ell^-$ transitions and $B_c \to D^{*}$ form factors from covariant confined quark model inputs, we compute the differential branching ratios, forward-backward asymmetry, longitudinal helicity fraction of the $D^{\ast}$, and various normalized angular coefficients. The results of the observables show that weak annihilation effects are sizable, particularly at low $q^2$, significantly modifying several observables and shifting zero-crossings. Resonance effects dominate at high $q^2$, restricting reliable analysis windows. We conclude that the inclusion of weak annihilation is essential for precise Standard Model predictions and for isolating possible New Physics effects in $B_c^+ \to D^{*+} \ell^+ \ell^-$ decays.

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arXiv2025

Chirality structure of vector like new physics operators in charged current transitions

We investigate the cascade decay $B^{*0}_{s} \rightarrow D_s^-(\rightarrow τ^-\,\barν_τ)\,\ell^{+}\,ν_\ell$ induced by flavor changing charged currents in the context of the Standard Model and in vector-like couplings beyond the Standard Model. We employ the helicity amplitude formalism for analysis and highlight the role of new vector-like couplings in charged current interactions. We find, in particular, that while new left handed chiral-vector like interactions contribute to the branching ratio, they do not affect the forward-backward asymmetry, or the angular observables. On the other hand, the right handed chiral vector-like coupling in the case of this decay contributes to the branching ratio, forward-backward asymmetry and the angular observables. We confirm that this difference in behavior between the left and right handed NP couplings is a general feature of charged current processes with a vector meson going to a pseudoscalar at the tree level in effective weak theory by cross checking with the cascade decays $B^{*+}_c \rightarrow P(\rightarrow P'\,μ^+\,ν_μ)\,\ell^{+}\,ν_\ell$ where $P$ is $B_s^0$ ($D^0$) and $P'$ is $D_s^{*-}$ ($K^-$).

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arXiv2025

Investigating New Physics through the Observables of Semileptonic $B_{s}\to K^{\ast}(\to K π)μ^{+}μ^{-}$ Decay

The rare four-fold decay $B_s \to K^*(\to Kπ)μ^+μ^- $, governed by the flavor-changing neutral current transition $b \to dμ^+μ^-$, provides a sensitive probe for testing the Standard Model (SM) and investigating signatures of new physics (NP). This work presents a comprehensive model-independent analysis of the decay using the framework of the weak effective field theory. We compute a set of key physical observables, including the differential branching ratio, forward-backward asymmetry, longitudinal polarization fraction, and several normalized angular coefficients $\langle I_i\rangle$, as a function of the dilepton invariant mass squared $q^2$. The impact of NP is explored via both one-dimensional (1D) and two-dimensional (2D) scenarios involving NP Wilson coefficients $C_7^{\text{NP}}$, $C_9^{(\prime)\text{NP}}$, and $C_{10}^{(\prime)\text{NP}}$. Our findings reveal notable deviations from the SM predictions across multiple observables. Furthermore, we analyze the correlations between different observables and their 2D contour plots which would be useful to further constrain the parametric space of possible NP contributions. This study reinforces the potential of $B_s \to K^* μ^+ μ^-$ decay as a complementary channel in the search for physics beyond the SM.

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arXiv2025

Exploring New Physics in transition $b\to s\,\ell^+\ell^-$ through different $B_c\to D_s^{(\ast)} \,\ell^+\ell^-$ observables

Inspired by the discrepancies observed in the $b\to s\ell^+\ell^-$ neutral current decays, we study the decay channel $B_c\to D_s^{(\ast)} \,\ell^+\ell^-$ ($\ell=μ,τ$), which is based on the same flavor changing neutral current (FCNC) transition at the quark level. The current study shows that this decay channel can provide a useful probe for physics beyond the standard model. We use the helicity formalism while employing the effective theory approach where we include the effects of vector and axial vector `new' physics (NP) operators. In this study, we have computed the branching ratio $\mathcal{B}_r$, the $D^\ast$ helicity fraction $f_L$, the lepton forward-backward asymmetry $\mathcal{A}_{FB}$, and the lepton flavor universality ratio (LFU) $R^{τμ}_{D_s^*}$. In addition, as a complementary check on the LFU, we also calculate the various other LFU observables, $R_{i}^{τμ}$ where $i=A_{FB}$, $f_L$. We assume that the NP universal coupling is present for both muons and tauons, while the non-universal coupling is only present for muons. Regarding these couplings, we employ the latest global fit to the $b\to s\ell^+\ell^-$ data, which is recently computed in arXiv:2304.07330. We give predictions of some of the mentioned observables within the SM and the various NP scenarios. We have found that not only are the considered observables sensitive to NP but are also helpful in distinguishing among the different NP scenarios. These results can be tested at the LHCb, HL-LHC, and FCC-ee, and therefore, a precise measurements of these observables not only deepens our understanding of the $b\to s\ell^+\ell^-$ process but also provides a window of opportunity to possibly study various NP scenarios.

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