arXiv subjects

Aritra Biswas

Publications and source records attributed to Aritra Biswas.

At least 19 recordsLinked to original sources

arXiv2026

Precision Study of Semileptonic and Non-Leptonic $B_c$ Decays to $η_c$ and P Wave Charmonia

We analyse semileptonic and non-leptonic decays of the $B_c$ meson into P wave charmonium states. The analytic expressions for the transition form factors are taken from NRQCD, while their normalisations and shapes are constrained directly using experimental data, without introducing any additional model-dependent inputs. Using radiative decay data of $χ_{c0}$, $χ_{c1}$, and $h_c$, we extract the derivatives of their radial wave functions at the origin and update the $B_c \to (χ_{c0}, χ_{c1}, h_c)$ form factors. We present predictions for the semileptonic branching fractions, the lepton flavour universality ratios $R(χ_{c0})=0.185(3)$, $R(χ_{c1})=0.147(26)$, and $R(h_c)=0.068(2)$, as well as selected non-leptonic $B_c$ decays and P-wave charmonium production in $e^+e^-$ annihilation and $Z$-boson decays.

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arXiv2026

Light-cone sum rules with $B$-meson distribution amplitudes for the $B\to p$ form factors in $B$-mesogenesis models

New decay modes of $B$-meson into a baryon and invisible dark antibaryon $Ψ$ are among the most distinctive signatures of the $B$-mesogenesis scenario. We concentrate on the proton mode and consider two versions of the underlying interaction of $Ψ$ with quarks, the so-called models $(d)$ and $(b)$. To estimate the width of the $B^+\to p Ψ$ decay, we obtain the $B^+\to p$ transition form factors, applying QCD light-cone sum rules (LCSRs) with $B$-meson distribution amplitudes with an accuracy up to twist-5, while interpolating the proton with a current. This method is independent of the previously applied one, which was based on the nucleon distribution amplitudes. We estimate the partial width of the $B^+\to p Ψ$ decay as a function of the dark antibaryon mass. Furthermore, we use the ratio of this width to the inclusive $B\to X_N Ψ$ width, the latter predicted earlier using the heavy quark expansion method. This ratio, which is independent of the effective coupling, when combined with the minimal inclusive branching fraction of $O(10^{-4})$, necessary for the feasibility of $B$-mesogenesis, yields lower limits on the $B^+\to p Ψ$ branching fraction. We confront these limits with the most recent upper bounds obtained from BaBar and Belle/Belle II searches for the decays of $B^+$-meson into a proton and missing energy. The comparison indicates that experimental upper bounds on the branching fraction of $B\to p Ψ$ at the level of $10^{-8}-10^{-7}$ are needed for a decisive probe of this invisible mode of $B$ decays.

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arXiv2025

Impact on $L$-observables of a new combined analysis of $B_{d,s}\to K^{(*)}$ form factors

We explore the impact of a combined analysis of $B_{d,s}\to K^{(*)}$ form factors on a set of $L$-observables. The $L$-observables are constructed from ratios of branching fractions in $B_{s}\to VV,PP,PV$ versus $B_d \to VV,PP,PV$ decays with $P=K^0,\bar{K}^0$ and $V=K^{*0},\bar{K}^{*0}$, thereby partially reducing their hadronic uncertainties. We show the change of the Standard Model predictions of the $L$-observables under different determinations of the ratio of the relevant form factors (with correlations) including lattice QCD data and a novel light-cone sum rule analysis. In addition, we provide precise results for all $B_{d,s} \to K^{(*)}$ form factors in machine-readable files. We find that the inclusion of our up-to-date results, as well as the use or omission of lattice QCD data for the form factors, has a significant impact on the $L$-observables. We also discuss how the New Physics interpretation is affected by the updated form factors and present revised predictions for the mechanism identified in our analysis of $B \to VP$ decays, now employing more suitable new experimental observables defined in this paper.

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arXiv2025

Subatomic Heroes

Sharing the amazing achievements of the (particle) physics world with the general public is at the heart of the mission of the Subatomic Heroes, based at the University of Siegen, Germany. Originally this started out as an endeavor of theoretical particle physics, now we are steadily spreading out to cover and include more branches of physics and science. Our activities range from merging art with public physics lectures via marvelous artistic performances at the local theater, over dedicated events for high-school students, to our Subatomic Heroes channel on Instagram and TikTok where you may also find out when and where our famous "hadronic ice-cream" will be served next! So follow us on https://www.instagram.com/subatomic_heroes and https://www.tiktok.com/@subatomic_heroes.

physics.ed-ph↗

arXiv2025

Penguin decays of B mesons

We propose a set of optimized observables using penguin mediated $\bar{B}_d$ and $\bar{B}_s$ decays to $K^{(*)}\bar{K}^{(*)}$ and $K^*ϕ$ final states that exhibhit a reduced sensitivity to power corrections than the corresponding branching ratios. Using these observables, branching ratios for the related vector-vector and pseudoscalar-pseudoscalar modes and branching ratios for modes involving other relevant pseudoscalar-vector final states ($Kϕ$, $K^*\bar{K})$, we attempt to resolve the emergent combined pattern by assuming new physics contributions to the weak effective operators at the scale of the mass of the $b$ quark that are already present in the Standard Model. We find that the simplest scenario that can offer a simultaneous explanation is the two-operator scenario $Q_{4s,d}-Q_{6s,d}$. We briefly discuss how future experimental measurements may alter this picture and try to motivate such measurements for specific modes from our analysis.

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arXiv2025

Analyzing the semileptonic and nonleptonic $B_c \to J/ψ, η_c$ decays

This study focuses on the decay of the $B_c$ meson to S-wave charmonia. Starting with lattice inputs on $B_c\to J/ψ$ form factors, we have obtained the $B_c\toη_c$ form factors using heavy quark spin symmetry (HQSS) relations between the associated form factors after parametrizing and extracting the possible symmetry breaking corrections. Using the $q^2$ shapes of these form factors, we have computed the branching fractions $\mathcal{B}(B_c^-\to η_c\ell^-\barν)$ (with $\ell =τ, μ(e)$) and the decay rate distributions and have predicted the Standard model estimate for the observable $R(η_c)=Γ(B_c^-\to η_cτ^-\barν)/Γ(B_c^-\to η_cμ^-\barν) =0.310 \pm 0.042$. In addition, we have estimated the radial wave functions $ψ_{B_c}^R(0)$, $ψ_{J/ψ}^R(0)$ and $ψ_{η_c}^R(0)$ at small quark-antiquark distances from the available information on the form factors from lattice, the lattice inputs on the decay constants $f_{J/ψ}$, $f_{η_c}$, $f_{B_c}$ and experimental data on radiative and rare decays of the $J/ψ$ and $η_c$ mesons. To do so, we choose the theory framework of non-relativistic QCD (NRQCD) effective theory. Using our results, we have predicted the branching fractions of a few non-leptonic decays of $B_c \to J/ψ$ or $η_c$ and other light mesons. We have also updated the numerical estimates of the cross sections $σ(e^+e^- \to J/ψη_c, η_cγ)$ and predicted the branching fractions of $Z$ boson decays to either $J/ψ$ or $η_c$ final states or both.

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arXiv2024

Optimised observables and new physics prospects in the penguin-mediated decays $B_{d(s)}\to K^{(*)0}ϕ$

We study penguin-mediated $\bar{B}_{d(s)}\to\bar{K}^{*0}(K^{*0})ϕ$ transitions, proposing a new optimised observable $L_{K^*ϕ}$ from the ratio of the corresponding branching ratios of these decays, with limited hadronic uncertainties and enhanced New Physics sensitivity. It deviates by $1.48σ$ between its experimental value and SM determination within QCD factorisation. This can be accommodated together with significant deviations found in the $K^{(*)}\bar{K}^{(*)}$ modes in our earlier works if New Physics affects either the QCD penguin operator $Q_4$ or the chromomagnetic dipole operator $Q_{8g}$ for both $b\to d$ and $b\to s$ transitions. The allowed range for the Wilson coefficients $C_{4s,8gs}$ is narrower than $C_{4d,8gd}$ since the $b\to s$ transition channel $\bar{B}_d\to\bar{K}^{*0}ϕ$ is in better agreement with the SM. However, if we add the measured $\bar{B}_{d}\to \bar{K}^{0}ϕ$ branching ratio, simultaneous explanation of all experimental data for $K^{(*)}\bar{K}^{(*)}$ and $K^*(\bar{K}^{(*)})ϕ$ channels in terms of New Physics in $C_{4d,s}$ or $C_{8gd,s}$ only, is not possible. They can be explained more easily if we assume New Physics in both $f=d,s$ sectors. The addition of the branching ratios of the charged modes $B^-\to K^{(*)-}ϕ$ to the above mix of observables results in a reduction of the parameter space for the $(C_{4f},C_{6f})$ scenario, while discarding the $(C_{6f},C_{8gf})$ scenario completely. This is because of the discrepancy of more than 1 $σ$ between the experimental measurements of the branching ratios of the $\bar{B}_{d}(B^-)\to\bar{K}^0(K^-)ϕ$ transitions. This provides a strong incentive for the LHCb/Belle II experiments to measure the branching ratios of $\bar{B}_{d}\to\bar{K}^{(*)0}ϕ$, $\bar{B}_s\to K^{*0}ϕ$ and particularly $B^-\to K^-ϕ$ to confirm or dismiss the conclusions hinted at by present data.

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arXiv2024

To (b)e or not to (b)e: No electrons at LHCb

We discuss the impact of the recent LHCb update on the two lepton-flavour universality ratios $R_K$ and $R_{K^*}$, and the CMS update of $B({B_s \to μ^+μ^-})$ regarding the possibility of New Physics in $b\to s\ell^+\ell^-$ decays. We perform global fits of the New Physics Wilson coefficients defined in the model-independent approach of the Weak Effective Theory at the $b$-quark mass. We discuss three different frameworks for this analysis: i) an update limited to the experimental data using the same theoretical framework as in earlier works, ii) a full update concerning both the experimental inputs and the theoretical framework, iii) an analysis without the LHCb results on electron modes. The comparison between these sets of results allows us to identify the differences stemming from the various components of the analysis: new experimental results, new inputs for the hadronic form factors, the role played by LHCb data on electron modes. As expected, the significance of all New Physics hypotheses gets reduced after the LHCb announcements on $R_{K^{(\ast)}}$ while the hypothesis of a lepton-flavour-universal contribution to the Wilson coefficient of the semileptonic $O_{9\ell}$ operators (possibly with a very small lepton-flavour-universality violating component) is reinforced. We also discuss the possibility of a long-distance charm-loop contribution through a mode-by-mode analysis and we find that the preferred values for the $\mathcal{C}_{9μ}$ Wilson coefficient are consistent throughout the different $b\to sμ^+μ^-$ modes and that there is no significant evidence of non-constant $q^2$ dependencies, which would indicate the presence of a long-distance charm-loop contribution beyond those already included.

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arXiv2023

A new puzzle in non-leptonic B decays

We propose a set of new optimized observables using penguin mediated $\bar{B}_d$ and $\bar{B}_s$ decays: ${\bar B}_{d,s} \to K^{*0} \bar{K}^{*0}$, ${\bar B}_{d,s} \to K^{0} \bar{K}^{0}$, ${\bar B}_{d,s} \to K^{0} \bar{K}^{*0}$ and ${\bar B}_{d,s} \to \bar{K}^{0} {K^{*0}}$ together with their CP conjugate partners. These observables are substantially cleaner than the corresponding branching ratios, which are plagued by large end point divergences. We find that the dominant contribution to the uncertainties of these observables stem from the corresponding form factors. The Standard Model estimates for these observables corresponding to the $K^{*0}\bar{K}^{*0}$ and $K^0\bar{K}^0$ final states are in tension with their respective experimental numbers at the $\sim2.5 σ$ level. The pattern of deviations w.r.t these observables as well as the individual branching ratios suggest that a possible explanation might be new physics both in $b\to s$ and $b\to d$ transitions. We find that, taken one at a time, only the Wilson coefficients $C_{4d,s}^{NP}$ and $C_{8gd,s}^{NP}$ can potentially satisfy all the current experimental data on the branching ratios as well as the optimized observables. Furthermore, such observables involving mixed (pseudoscalar-vector) states like $K^{*0}\bar{K}^0$ etc show distinctive patterns sensitive to these different new physics explanations.

hep-ph↗

arXiv2023

Extractions of $|V_{ub}|/|V_{cb}|$ from a combined study of the exclusive $b\to u(c) \ellν_{\ell}$ decays

We have extracted the ratio $|V_{ub}|/|V_{cb}|$ from a combined study of the available inputs on $\bar{B}\to (π,ρ,ω)\ell^- \barν_{\ell}$ and $\bar{B}(\bar{B}_s)\to (D^{(\ast)}, D_s^{(\ast)})\ell^- \barν_{\ell}$ ($\ell = μ$ or $e$) decays. We have done our analysis with and without the inclusion of the available experimental results on the branching fraction $\mathcal{BR}(\bar{B}_s\to K^+μ^-\barν_μ)$ or the ratio of the rates $Γ(\bar{B}_s\to K^+ \ell^-\barν_{\ell})/ Γ(\bar{B}_s \to D_s^+ \ell^- \barν_{\ell})$. We have used all the available experimental data on the branching fractions in different $q^2$-bins, the available theory inputs on the form factors from lattice and the light cone sum rule (LCSR) approach; analysed the data in different possible scenarios and presented the results. From a combined analysis of all the $b\to c\ell^- \barν_{\ell}$ exclusive decays, we have obtained $|V_{cb}|=(40.5 \pm 0.6)\times 10^{-3}$ and from all the $b\to u\ell^- \barν_{\ell}$ modes, we obtain $|V_{ub}|=(3.46\pm 0.12)\times 10^{-3}$ which changes to $|V_{ub}|=(3.51 \pm 0.13)\times 10^{-3}$ after dropping $\mathcal{BR}(\bar{B}_s\to K^+μ^-\barν_μ)$. We hence report the values of the ratio $|V_{ub}|/|V_{cb}| = 0.085 \pm 0.003$ and $0.087 \pm 0.003$ with and without the input from $\bar{B}_s\to K^+μ^-\barν_μ$ modes, respectively. We have also predicted the ratio $Γ(\bar{B}_s\to K^+ \ell^-\barν_{\ell})/ Γ(\bar{B}_s \to D_s^+ \ell^- \barν_{\ell})$ using the fit results. In addition, we provide the predictions of $\mathcal{BR}(\bar{B}_s\to K^+μ^-\barν_μ)$ and $\mathcal{BR}(\bar{B}\to (ρ,ω)\ell^- \barν_{\ell})$ in the Standard Model (SM) in small $q^2$-bins.

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arXiv2023

Study of the $b \to d \ell\ell$ transitions in the Standard Model and test of New Physics sensitivities

After incorporating all the available experimental data and the most up-to-date Lattice and light cone sum rule (LCSR) inputs on the form factors, we analyze the exclusive $b\to u\ellν_{\ell}$ and $b\to d\ell \ell$ decays simultaneously. We have extracted the shape of all the associated form factors using which we provide predictions in the standard model for the branching ratios, direct CP asymmetries and isospin asymmetry for $B\toπ\ell \ell$ and various angular observables for $B\toρ\ell \ell$ transitions. Also, we have tested the sensitivities of these observables towards physics beyond the standard model (BSM).For the $B\toρ\ell \ell$ decays, we have defined tagged and untagged observables and predicted them in the SM and BSM. In the context of BSM, we have found some compelling information. The respective predictions in a few benchmark scenarios are given, which can be tested in the experiments at the LHCb and the Belle.

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arXiv2023

Constraining New Physics with Possible Dark Matter Signatures from a Global CKM Fit

We constrain the parameters of a representative new physics model with possible dark matter (DM) signature from a global CKM fit analysis. The model has neutral quark current interactions mediated by a scalar, impacting the semileptonic and purely leptonic meson decays at one-loop. We take this opportunity to update the fit results for the Wolfenstein parameters and the CKM elements with and without a contribution from the new model using several other updated inputs. Alongside, we have analyzed and included in the CKM fit the $B\to D^*\ellν_{\ell}$ decay. The newly available inputs on the relevant form factors from lattice are included, and the possibility of new physics effects in $B\to D^*\ellν_{\ell}$ is considered. We obtain tight constraints on the relevant new physics parameters. We have studied the possible implications of this constraint on DM phenomenology. Apart from DM, the bounds are also applicable in other relevant phenomenological studies.

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arXiv2023

A new puzzle in non-leptonic B decays

We build a set of new observables using closely related non-leptonic penguin-mediated $B_d$ and $B_s$ decays: ${\bar B}_{d,s}\to K^{*0}\bar{K}^{*0}$, ${\bar B}_{d,s}\to K^{0}\bar{K}^{0}$, ${\bar B}_{d,s}\to K^{0}\bar{K}^{*0}$ and ${\bar B}_{d,s}\to\bar{K}^{0}{K^{*0}}$ together with their CP conjugate partners. These optimised observables are designed to reduce hadronic uncertainties, mainly coming from form factors and power-suppressed infrared divergences, and thus maximize their sensitivity to New Physics (NP). The deviations observed with respect to the SM in the ratios of branching ratios of ${\bar B}_{d,s}\to K^{*0}\bar{K}^{*0}$ ($2.6σ$) and ${\bar B}_{d,s}\to K^{0}\bar{K}^{0}$ ($2.4σ$) can be explained by simple NP scenarios involving the Wilson coefficients ${\cal C}_4$ and ${\cal C}_6$ (QCD penguin operators) and the coefficient ${\cal C}_{8g}$ (chromomagnetic operator). The optimised observables for ${\bar B}_{d,s}\to K^{0}\bar{K}^{*0}$ and ${\bar B}_{d,s}\to\bar{K}^{0}{K^{*0}}$ show distinctive patterns of deviations with respect to their SM predictions under these NP scenarios. The pattern of deviations of individual branching ratios, though affected by significant hadronic uncertainties, suggests that NP is needed both in $b\to d$ and $b\to s$ transitions. We provide the regions for the Wilson coefficients consistent with both optimised observables and individual branching ratios. The NP scenarios considered to explain the deviations of ${\bar B}_{d,s}\to K^{*0}\bar{K}^{*0}$ and ${\bar B}_{d,s}\to K^{0}\bar{K}^{0}$ can yield deviations up to an order of magnitude among the observables that we introduced for ${\bar B}_{d,s} \to K^{0} \bar{K}^{*0}$ and ${\bar B}_{d,s}\to\bar{K}^{0} {K^{*0}}$. Probing these new observables experimentally may confirm the consistency of the deviations already observed and provide a highly valuable hint of NP in the non-leptonic sector.

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arXiv2021

A closer look at observables from exclusive semileptonic $B\to(π,ρ)\ellν_{\ell}$ decays

This article analyses the available inputs in $\btopilnu$ and $\btorholnu$ decays which include the measured values of differential rate in different $q^2$-bins (lepton invariant mass spectrum), lattice, and the newly available inputs on the relevant form-factors from the light-cone sum rules (LCSR) approach. We define different fit scenarios, and in each of these scenarios, we predict a few observables in the standard model (SM). For example, $R(M) =\frac{\mathcal{B}(B \to M\ell_iν_{\ell_i})}{\mathcal{B}(B\to M\ell_jν_{\ell_j})} $, $R^{\ell_i}_{\ell_j}(M) =\frac{\mathcal{B}(B\to \ell_iν_{\ell_i})}{\mathcal{B}(B \to M\ell_jν_{\ell_j})}$ with M = $π$ or $ρ$ and $\ell_{i,j} = e, μ$ or $τ$. We also discuss the new physics (NP) sensitivities of all these observables and obtain bounds on a few NP Wilson coefficients in $b\to u τν_τ$ decays using the available data. We have noted that the data at present allows sizeable NP contributions in this mode. Also, we have predicted a few angular observables relevant to these decay modes.

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arXiv2021

New physics in $b\to s \ell\ell$ decays with complex Wilson coefficients

We perform a data-driven analysis of new physics (NP) effects in exclusive $b \to s \ell^+\ell^-$ decays in a model-independent effective theory approach with dimension six operators considering scalar, pseudo-scalar, vector and axial-vector operators with the corresponding Wilson coefficients (WC) taken to be complex. The analysis has been done with the most recent data while comparing the outcome with that from the relatively old data-set. We find that a left-handed quark current with vector muon coupling is the only one-operator $(\mathcal{O}_9)$ scenario that can explain the data in both the cases with real and complex WC with a large non-zero imaginary contribution. We simultaneously apply model selection tools like cross-validation and information-theoretic approach like Akaike Information Criterion (AIC) to find out the operator or sets of operators that can best explain the available data in this channel. The $\mathcal{O}_9$ with complex WC is the only one-operator scenario which survives the test. However, there are a few two and three-operator scenarios (with real or complex WCs) which survive the test, and the operator $\mathcal{O}_9$ is common among them.

hep-ph↗

arXiv2021

A closer look at the extraction of $|V_{ub}|$ from $B\toπlν$

To extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $|V_{ub}|$, we have re-analyzed all the available inputs (data and theory) on the $B\toπlν$ decays including the newly available inputs on the form-factors from light cone sum rule (LCSR) approach. We have reproduced and compared the results with the procedure taken up by the Heavy Flavor Averaging Group (HFLAV), while commenting on the effect of outliers on the fits. After removing the outliers and creating a comparable group of data-sets, we mention a few scenarios in the extraction of $|V_{ub}|$. In all those scenarios, the extracted values of $|V_{ub}|$ are higher than that obtained by HFLAV. Our best results for $|V_{ub}|^{exc.}$ are $(3.88 \pm 0.13)\times 10^{-3}$ and $(3.87 \pm 0.13)\times 10^{-3}$ in frequentist and Bayesian approaches, respectively, which are consistent with that extracted from inclusive decays $|V_{ub}|^{inc}$ within $1~σ$ confidence interval.

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arXiv2020

Exhaustive Model Selection in $b \to s \ell \ell$ Decays: Pitting Cross-Validation against AIC$_c$

In the light of recent data, we study the new physics effects in the exclusive $b \to s \ell^+\ell^-$ decays from a model independent perspective. Different combinations of the dimension six effective operators along with their respective Wilson coefficients are chosen for the analysis. To find out the operator or sets of operators that can best explain the available data in this channel, we simultaneously apply popular model selection tools like cross-validation and the information theoretic approach like Akaike Information Criterion (AIC). There are one, two, and three-operator scenarios which survive the test and a left-handed quark current with vector muon coupling is common among them. This is also the only surviving one-operator scenario. Best-fit values and correlations of the new Wilson coefficients are supplied for all the selected scenarios. We find that the angular observables play the dominant role in the model selection procedure. We also note that while a left-handed quark current with axial-vector muon coupling is the only one-operator scenario able to explain the ratios $R_{K^{(*)}}$ ($R_{K^*}$ for $q^2\in [ 0.045, 1.1] {\rm GeV}^2$ in particular), there are also a couple of two operator scenarios that can simultaneously explain the measured $R_{K^{(*)}}$.

hep-ph↗

arXiv2020

Collider signature of $U_1$ Leptoquark and constraints from $b\to c$ observables

One of the most popular models that is known to be able to solve the lepton flavour universality violating charged ($b\to c$) and neutral current ($b\to s$) anomalies is the Leptoquark Model. In this work we examine the {\it multijet} + $\mET$ collider signature of a vector leptoquark ($U_1$) which has the potential to mediate both the charged and neutral current processes at tree level. From our collider analysis we derive the exclusion limits on mass for the $U_1$ leptoquark at 95\% C.L. at the current and future experiment of the Large Hadron Collider. We also calculate the effect of such a leptoquark in $b\to c$ observables.

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