arXiv subjects
Publications and source records attributed to Bhubanjyoti Bhattacharya.
Model-independent description of nonleptonic decays of charmed mesons is a challenging task due to large nonperturbative effects of strong interactions on the transition amplitudes. We discuss the equivalence of two different flavor-$SU(3)$-based descriptions of Cabibbo-favored non-leptonic decays of charmed mesons to two-pseudoscalars final states including the $η$ and $η^\prime$ mesons.
We offer a new solution to an old puzzle in the penguin-dominated $B\toπK$ decays. The puzzle is the inconsistency among the measurements of the branching ratios and CP asymmetries of the four $B\toπK$ decays: $B^+ \to π^+ K^0$, $B^+\to π^0 K^+$, $B_d^0\toπ^- K^+$, $B_d^0\toπ^0 K^0$. We solve the $B\toπK$ puzzle by considering the effect of an axion-like particle (ALP) that mixes with the $π^0$ and has mass close to the $π^0$ mass. We show that the ALP can also explain the anomalies in the electron and muon anomalous magnetic moments.
At present, the measurements of $R_{D^{(*)}}$ and $R_{J/ψ}$ hint at new physics (NP) in $b \to c τ^- {\barν}$ decays. The angular distribution of ${\bar B} \to D^* (\to D π) \, τ^{-} {\barν}_τ$ would be useful for getting information about the NP, but it cannot be measured. The reason is that the three-momentum ${\vec p}_τ$ cannot be determined precisely since the decay products of the $τ^-$ include an undetected $ν_τ$. In this paper, we construct a measurable angular distribution by considering the additional decay $τ^- \to π^- ν_τ$. The full process is ${\bar B} \to D^* (\to D π') \, τ^{-} (\to π^- ν_τ) {\barν}_τ$, which includes three final-state particles whose three-momenta can be measured: $D$, $π'$, $π^-$. The magnitudes and relative phases of all the NP parameters can be extracted from a fit to this angular distribution. One can measure CP-violating angular asymmmetries. If one integrates over some of the five kinematic parameters parametrizing the angular distribution, one obtains (i) familiar observables such as the $q^2$ distribution and the $D^*$ polarization, and (ii) new observables associated with the $π^-$ emitted in the $τ$ decay: the forward-backward asymmetry of the $π^-$ and the CP-violating triple-product asymmetry.
In order to explain the observed anomalies in the measurements of $R_{D^{(*)}}$ and $R_{J/ψ}$, a variety of new-physics (NP) models that contribute to $b\to cτ^-{\barν}$ have been proposed. In this paper, we show how CP-violating observables can be used to distinguish these NP models. Because ${\vec p}_τ$ cannot be measured (the decay products of the $τ$ include the undetected $ν_τ$), obtaining the angular distribution of ${\bar B}^0\to D^{*+}τ^{-}{\barν}_τ$ is problematic. Instead, we focus here on ${\bar B}^0\to D^{*+}(\to D^0 π^+)μ^- {\barν}_μ$. This process may also receive contributions from the same NP, and LHCb intends to measure the CP-violating angular asymmetries in this decay. There are two classes of NP models that contribute to $b\to cμ^-{\barν}_μ$. These involve (i) a $W'$ (two types) or (ii) a leptoquark (LQ) (six types). The most popular NP models predict no CP-violating effects, so the measurement of nonzero CP-violating symmetries would rule them out. Furthermore these measurements allow one to distinguish the $W'$ and LQ models, and to differentiate among several LQ models.
The weak phase $γ$ is extracted from three-body charmless decays of $B$ mesons following a method proposed by Bhattacharya, Imbeault \& London. The result is obtained by combining the BABAR amplitude analyses for the processes $B^0 \rightarrow K^+ π^0 π^-$, $B^0 \rightarrow K_S^0 π^+ π^-$, $B^0 \rightarrow K_S^0 K_S^0 K_S^0$, $B^0 \rightarrow K^+ K_S^0 K^-$ and $B^+ \rightarrow K^+ π^+ π^-$, under the assumption of $α_{\rm{SU(3)}}$ flavour symmetry. Six possible solutions are found. One solution is compatible with the Standard Model while the others are not. It is also found that, when averaged over the entire Dalitz plane, the effect of $α_{\rm{SU(3)}}$ breaking on the analysis is only at the percent level.
To date, the weak-phase $γ$ has been measured using two-body $B$-meson decays such as $B\to D K$ and $B\to Dπ$, whose amplitudes contain only tree-level diagrams. But $γ$ can also be extracted from three-body charmless hadronic $B$ decays. Since the amplitudes for such decays contain both tree- and loop-level diagrams, $γ$ obtained in this way is sensitive to new physics that can enter into these loops. The comparison of the values of $γ$ extracted using tree-level and loop-level methods is therefore an excellent test for new physics. In this talk, we will show how U-spin and flavor-SU(3) symmetries can be used to develop methods for extracting $γ$ from $B\to Kππ$ and $B\to KK{\bar K}$ decays. We describe a successful implementation of the flavor-SU(3) symmetry method applied to BaBar data.
We revisit calculations of invisible widths of heavy mesons in the standard model, which serve as benchmarks for the studies of production of light, long-lived neutral particles in heavy meson decays. We challenge the common assumption that in the standard model these widths are dominated by meson decays into a two-neutrino final state and prove that they are dominated by decays into four-neutrino final states. We show that current estimates of the invisible widths of heavy mesons in the standard model underestimate the effect by orders of magnitude. We examine currently available experimental data on invisible widths and place constraints on the properties of dark photons. We also comment on the invisible widths of the kaons.
We examine the charged lepton flavor violating process $gg \rightarrow μ^\pm τ^\mp$ at the $\sqrt{s} = 13$ TeV LHC. Operators generating this process can be induced by new physics (NP) at dimension 8. Despite the power suppression associated with dimension 8 operators, we show that the LHC's large gluon luminosity makes it possible to probe this channel. For an integrated luminosity of 100 fb$^{-1}$ at the LHC, we predict a constraint on the NP scale $Λ\gtrsim 3$ TeV. In addition, we point out that such operators can be induced through top quark loops in models that generate dimension 6 operators of the form $\overline{t} t \, μτ$. We find that the NP scale of these dimension 6 operators can be constrained to be $Λ\gtrsim 3.4-4.1$ TeV with 100 fb$^{-1}$ of data.
The recent measurement of $R_{K^*}$ is yet another hint of new physics (NP), and supports the idea that it is present in $b\to sμ^+μ^-$ decays. We perform a combined model-independent and model-dependent analysis in order to deduce properties of this NP. Like others, we find that the NP must obey one of two scenarios: (I) $C_9^{μμ}({\rm NP}) < 0$ or (II) $C_9^{μμ}({\rm NP}) = - C_{10}^{μμ}({\rm NP}) < 0$. A third scenario, (III) $C_9^{μμ}({\rm NP}) = - C_{9}^{\prime μμ}({\rm NP})$, is rejected largely because it predicts $R_K = 1$, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a $Z'$ boson. We show that scenario (II) can arise in LQ or $Z'$ models, but scenario (I) is only possible with a $Z'$. Fits to $Z'$ models must take into account the additional constraints from $B^0_s$-${\bar B}^0_s$ mixing and neutrino trident production. Although the LQs must be heavy, O(TeV), we find that the $Z'$ can be light, e.g., $M_{Z'} = 10$ GeV or 200 MeV.
We study implications of a recent observation of non-leptonic $B^+_c\to D^0 K^+$ decay and a bound on $B^+_c\to D^0 π^+$ transition on CP-violating asymmetries in $B_c$ decays. In the U-spin symmetry limit, we derive a relation between the CP-asymmetries in the $B^+_c\to D^0 K^+$ and $B^+_c\to D^0 π^+$ channels and the corresponding branching ratios. We also derive several relations between non-leptonic $B_c$ decays into the final states with $D$ mesons in the flavor $SU(3)_F$ limit. We point out that a combined study of $SU(3)_F$ amplitudes in these decays can be used to constrain the angle $γ$ of the Cabibbo-Kobayashi-Maskawa (CKM) matrix.
At present, there are several measurements of $B$ decays that exhibit discrepancies with the predictions of the SM, and suggest the presence of new physics (NP) in $b \to s μ^+ μ^-$ transitions. Many NP models have been proposed as explanations. These involve the tree-level exchange of a leptoquark (LQ) or a flavor-changing $Z'$ boson. In this paper we examine whether it is possible to distinguish the various models via CP-violating effects in $B \to K^{(*)} μ^+ μ^-$. Using fits to the data, we find the following results. Of all possible LQ models, only three can explain the data, and these are all equivalent as far as $b \to s μ^+ μ^-$ processes are concerned. In this single LQ model, the weak phase of the coupling can be large, leading to some sizeable CP asymmetries in $B \to K^{(*)} μ^+ μ^-$. There is a spectrum of $Z'$ models; the key parameter is $g_L^{μμ}$, which describes the strength of the $Z'$ coupling to $μ^+μ^-$. If $g_L^{μμ}$ is small (large), the constraints from $B^0_s$-${\bar B}^0_s$ mixing are stringent (weak), leading to a small (large) value of the NP weak phase, and corresponding small (large) CP asymmetries. We therefore find that the measurement of CP-violating asymmetries in $B \to K^{(*)} μ^+ μ^-$ can indeed distinguish among NP $b \to s μ^+ μ^-$ models
$R_K$ and $R_{D^{(*)}}$ are two $B$-decay measurements that presently exhibit discrepancies with the SM. Recently, using an effective field theory approach, it was demonstrated that a new-physics model can simultaneously explain both the $R_K$ and $R_{D^{(*)}}$ puzzles. There are two UV completions that can give rise to the effective Lagrangian: (i) $VB$: a vector boson that transforms as an $SU(2)_L$ triplet, as in the SM, (ii) $U_1$: an $SU(2)_L$-singlet vector leptoquark. In this paper, we examine these models individually. A key point is that $VB$ contributes to $B^0_s$-${\bar B}^0_s$ mixing and $τ\to 3μ$, while $U_1$ does not. We show that, when constraints from these processes are taken into account, the $VB$ model is just barely viable. It predicts ${\cal B} (τ^-\toμ^-μ^+μ^-) \simeq 2.1 \times 10^{-8}$. This is measurable at Belle II and LHCb, and therefore constitutes a smoking-gun signal of $VB$. For $U_1$, there are several observables that may point to this model. Perhaps the most interesting is the lepton-flavor-violating decay $Υ(3S) \to μτ$, which has previously been overlooked in the literature. $U_1$ predicts ${\cal B}(Υ(3S) \to μτ)|_{\rm max} = 8.0 \times 10^{-7}$. Thus, if a large value of ${\cal B}(Υ(3S) \to μτ)$ is observed -- and this should be measurable at Belle II -- the $U_1$ model would be indicated.
This document contains a summary of the LHCb workshop on multi-body decays of D and B mesons, held at CBPF, Rio de Janeiro, in July 2015. The workshop was focused on issues related to amplitude analysis of three- and four-body hadronic decays. In addition to selected LHCb results, contributions from guest theorists are included.
According to the Particle Data Group, the measurements of ${\cal B}(W^+ \to τ^+ ν_τ)$ and ${\cal B}(W^+ \to \ell^+ ν_\ell)$ ($\ell = e,μ$) disagree with one another at the $2.3σ$ level. In this paper, we search for a new-physics (NP) explanation of this $W \to τν$ puzzle. We consider two NP scenarios: (i) the $W$ mixes with a $W'$ boson that couples preferentially to the third generation, (ii) $τ_{L,R}$ and $ν_{τL}$ mix with isospin-triplet leptons. Unfortunately, once other experimental constraints are taken into account, neither scenario can explain the above experimental result. Our conclusion is that the $W \to τν$ puzzle is almost certainly just a statistical fluctuation.
In this paper we consider CP-violating new-physics contributions to the decay $t \to b \bar b c$. We examine the prospects for detecting such new physics at the LHC, which requires studying the process $gg \to t (\to b \bar b c) \bar t (\to \bar b \ell \bar ν)$. We find two observables that can be used to reveal the presence of CP-violating new physics in $t \to b \bar b c$. They are (i) the partial-rate asymmetry and (ii) the triple-product correlations involving the momenta of various particles associated with the interaction. A Monte Carlo analysis is performed to determine how well these observables can be used to detect the presence of new physics, and to measure its parameters. We find that there is little difficulty in extracting the value of the relevant new-physics parameter from the partial-rate asymmetry. For the triple-product correlations, we test multiple strategies that can be used for the extraction of the corresponding combination of new-physics parameters.
It is an intriguing possibility that dark matter (DM) could have flavor quantum numbers like the quarks. We propose and investigate a class of UV-complete models of this kind, in which the dark matter is in a scalar triplet of an SU(3) flavor symmetry, and interacts with quarks via a colored flavor-singlet fermionic mediator. Such mediators could be discovered at the LHC if their masses are $\sim 1$ TeV. We constrain the DM-mediator couplings using relic abundance, direct detection, and flavor-changing neutral-current considerations. We find that, for reasonable values of its couplings, scalar flavored DM can contribute significantly to the real and imaginary parts of the $B_s$-$\bar B_s$ mixing amplitude. We further assess the potential for such models to explain the galactic center GeV gamma-ray excess.
Understanding the charged current quasielestic (CCQE) neutrino-nucleus interaction is important for precision studies of neutrino oscillations. The theoretical description of the interaction depends on the combination of a nuclear model with the knowledge of form factors. While the former has received considerable attention, the latter, in particular the axial form factor, is implemented using the historical dipole model. Instead, we use a model-independent approach, presented in a previous study, to analyze the muon antineutrino CCQE mineral oil data published by the MiniBooNE collaboration. We combine the cross section for scattering of antineutrinos off protons in carbon and hydrogen, using the same axial form factor for both. The extracted value of the axial mass parameter $m_A = 0.84^{+0.12}_{-0.04} \pm {0.11} \, {\rm GeV}$ is in very good agreement with the model-independent value extracted from MiniBooNE's neutrino data. Going beyond a one-parameter description of the axial form factor, we extract values of the axial form factor in the range of $Q^2=0.1...1.0$ GeV$^2$, finding a very good agreement with the analogous extraction from the neutrino data. We discuss the implications of these results.
Some years ago, a method was proposed for measuring the CP-violating phase gamma using pairs of two-body decays that are related by U-spin reflection (d <-> s). In this paper we adapt this method to charmless B -> PPP decays. Time-dependent Dalitz-plot analyses of these three-body decays are required for the measurement of the mixing-induced CP asymmetries. However, isobar analyses of the decay amplitudes are not necessary. A potential advantage of using three-body decays is that the effects of U-spin breaking may be reduced by averaging over the Dalitz plot. This can be tested independently using the measurements of direct CP asymmetries and branching ratios in three-body charged B decays.