We included a discussion on detection of presence of light right handed neutrinos and experimental prospects of the new experimental determination of FL, also more references are added. Final version to appear in JHEP. 39 pages and 9 figures
We apply the formalism of amplitude symmetries to the angular distribution of the decays $B \to D^* \ell ν$ for $\ell=e,μ,τ$. We show that the angular observables used to describe the distribution of this class of decays are not independent in absence of New Physics contributing to tensor operators. We derive sets of relations among the angular coefficients of the decay distribution for the massless and massive lepton cases which can be used to probe in a very general way the consistency among the angular observables and the underlying New Physics at work. We use these relations to access the longitudinal polarisation fraction of the $D^*$ using different angular coefficients from the ones used by Belle experiment. This in the near future can provide an alternative strategy to measure $F_L^{D^*}$ in $B \to D^* τν$ and to understand the relatively high value measured by the Belle experiment. Using the same symmetries, we identify three observables which may exhibit a tension if the experimental value of $F_L^{D^*}$ remains high. We discuss how these relations can be exploited for binned measurements. We also propose a new observable that could test for specific scenarios of New Physics generated by light right-handed neutrinos. Finally we study the prospects of testing these relations based on the projected experimental sensitivity of new experiments.
We propose a one-loop radiative Majorana-type neutrino-mass matrix without any kind of additional symmetries by introducing two leptoquark-like bosons only. In this scenario, we show that the anomaly appearing in the process $b\to s\ell\bar\ell$ can be explained without any conflicts against various constraints such as lepton-flavor violations, flavor-changing neutral currents, oblique parameters $ΔS,\ ΔT$, and the Drell-Yan process. We make the predictions for the flavor-violating lepton-pair production ($eμ$, $eτ$, and $μτ$) at the LHC, as well as the cross sections for pair production of th…
A sensitivity study of the unbinned angular analysis of the $B\to D^*(Dπ)\ell ν_\ell$ decay is presented. In the analysis, it is shown that the Wilson coefficient of the right-handed vector current, $C_{V_R}$, can be measured to precision of 2-4$\%$ using either the full set of normalised angular observables or the forward-backward asymmetry $A_{FB}$ of the charged lepton in 10 $w$ bins. Such angular measurements are independent of the $V_{cb}$ puzzle.
We investigate the rare electroweak penguin transition $b \to s \ell^+ \ell^-$ though angular analyses in baryonic $b$-decays. Instead of performing likelihood fits, that might suffer from ambiguity issues, we employ the moments technique, which is a simple counting experiment. The method is known to be robust under low statistics conditions and avoids the ambiguity problem by construction. We provide the full set of 32 orthonormal moments for $Λ^0_b\to p h^-\ell^+\ell^-$, where $h\in\{π,K\}$, for a polarized $Λ^0_b$ and the dihadron system $[ph]$ being in a spin-1/2 state.
At the present time, there are hints of new physics (NP) in several observables involving $b \to c \ell^- {\barν}_\ell$ decays. In this talk, I describe measurable angular distributions for ${\bar B} \to D^* μ^- {\barν}_μ$ and ${\bar B} \to D^* τ^- (\to π^- ν_τ) {\barν}_τ$ decays, including the most general NP contributions. These angular distributions contain enough information to pin down the Lorentz structure of the NP, which will help to identify it. They also have the ability to reveal the presence of non-SMEFT (non-decoupling) NP.
Angular and invariant-mass observables in the four-body Higgs decay $h\to\ell\barν_\ell\bar{\ell}^\primeν_{\ell^\prime}$
Zhengzhou University（郑州大学）；Chongqing University of Posts & Telecommunications（重庆邮电大学）；Chongqing University（重庆大学）；Chongqing University of Science and Technology（重庆科技大学）
The flavor changing rare decay $B\to K^{*}(\to Kπ)\ell^+\ell^-$ is one of the most studied modes due to its sensitivity to physics beyond the standard model and several discrepancies have come to light among the plethora of observables that are measured. In this paper we revisit the analogous baryonic decay mode $Λ_{b}\rightarrow Λ(\to pπ) \ell^{+}\ell^{-}$ and we present a complete set of ten angular observables that can be measured using this decay mode. Our calculations are done retaining the finite lepton mass so that the signal of lepton non-universality observed in $B\to K^{*} \ell^+\ell…
Rare $b \to s\ell^+\ell^-$ flavour-changing-neutral-current processes provide important tests of the Standard Model of particle physics. Angular observables in exclusive $b \to s\ell^+\ell^-$ processes can be particularly powerful as they allow hadronic uncertainties to be controlled. Amongst the exclusive processes that have been studied by experiments, the decay $Λ_b\to Λ\ell^+\ell^-$ is unique in that the $Λ_b$ baryon can be produced polarised. In this paper, we derive an expression for the angular distribution of the $Λ_b\to Λ\ell^+\ell^-$ decay for the case where the $Λ_b$ baryon is produ…
We present the fully general, model independent study of a few rare semileptonic $B$ decays that get dominant contributions from $W$-annihilation and $W$-exchange diagrams, in particular $B^0 \to \bar{D}^0 \ell^+\ell^-$, where $\ell = e,μ$. We consider the most general Lagrangian for the decay, and define three angular asymmetries in the Gottfried-Jackson frame, which are sensitive to new physics. We show how these angular asymmetries can be easily extracted from the distribution of events in the Dalitz plot for $B \to D \ell^+ \ell^-$ decays. Especially a non-zero forward-backward asymmetry w…
We generalise the Jacob-Wick helicity formalism, which applies to sequential decays, to effective field theories of rare decays of the type $B \to K_{J_K}(\to K π) \bar{\ell}_1 \ell_2$. This is achieved by reinterpreting local interaction vertices $\bar b Γ'_{μ_1 ..μ_n} s \bar \ell Γ^{μ_1 ..μ_n} \ell$ as a coherent sum of $1 \to 2$ processes mediated by particles whose spin ranges between zero and $n$. We illustrate the framework by deriving the full angular distributions for $B \to K\bar{\ell}_1 \ell_2$ and $B \to K^*(\to K π) \bar{\ell}_1 \ell_2$ for the complete dimension-six effective Hami…
This paper describes the angular distribution of $Λ_b^0\to Λ(\to pK^-)\ell^+\ell^-$ decays. A full expression is given for the case of multiple interfering spin-states with spin $\leq \tfrac{5}{2}$. This distribution is relevant for future measurements of $Λ_b^0\to pK^-\ell^+\ell^-$ decays, where different states cannot easily be separated based on their mass alone. New observables arise when considering spin-$\tfrac{5}{2}$ states as well as interference between states. An exploration of their behaviour for a variety of beyond the Standard Model scenarios shows that some of these observables e…
We provide a determination of the complete angular distribution for the four body rare decay $Λ_b \to Λ(\to N π) \ell^+\ell^-$, with unpolarized $Λ_b$ baryons and massive leptons, in the operator basis approach which includes the scalar, pseudo-scalar, vector, axial-vector and tensor operators. Especially, the contributions of tensor operators have been calculated for the first time in this work. Since the lepton mass is retained in our calculations, the lepton flavour universality and the decay mode $Λ_b \to Λ(\to N π) τ^+τ^-$ can be investigated in detail. For comparison with the experiment,…
At the LHC, dileptonic events may turn up new physics interacting with quarks and leptons. The poster child for this scenario is a resonant $Z'$, much anticipated in $\ell^+ \ell^-$ invariant mass spectra. However, angular spectra of dileptons may play an equal or stronger role in discovering a non-resonant species. This paper avails of their LHC measurements to corner the couplings and masses of leptoquarks (LQs), that can mediate $q \bar{q} \rightarrow \ell^+ \ell^-$ in the $t$-channel and dramatically alter Standard Model angular spectra. Also derived are constraints from alterations to $m_…
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 $C_{9μ}$ 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 ident…
我们考虑轻子质量矩阵的剩余对称性的两个新的方案。首先，我们假设带电轻子质量矩阵具有Z2 × Z2对称性G_ell，轻中微子质量矩阵具有Z2对称性G_nu。通过这种设置，轻子混合矩阵的一列元素的模被固定到重新排序。在这种情况下，可以互换G_ell和G_nu的角色，从而约束混合矩阵的行而不是列。其次，我们假设一个剩余对称群G_ell \cong Zm（m>2）是由一个具有双退化特征值的矩阵生成的。然后，用G_nu \cong Z 2 x Z 2，轻子混合矩阵的一行元素的模得到固定。使用小群组的库，我们已经执行了对可能在这两个场景中的每一个中嵌入G_ell和G_nu的群组的搜索。我们只发现了两种现象学上可行的可能性，其中一种约束混合矩阵的一列，另一种约束混合矩阵的一行。
In this article, we perform a sensitivity study of an unbinned angular analysis of the $B\to D^*\ell ν_\ell$ decay, including the contributions from the right-handed current. We show that the angular observable can constrain very strongly the right-handed current without the intervention of the yet unsolved $V_{cb}$ puzzle.
In a bottom-up approach we investigate lepton-flavour violating processes $τ\to 3 \ell$ that are mediated by New Physics encoded in effective-theory operators of dimension six. While the opportunity to scrutinize the underlying operator structure has been investigated before, we explore the benefits of utilising the polarization direction of the initial $τ$ lepton and the angular distribution of the decay. Given the rarity of these events (if observed at all), we focus on integrated observables rather than spectra, such as partial rates and asymmetries. In an effort to estimate the number of e…
We consider the time-dependent analysis of $B_d\to K_S\ell\ell$ taking into account the time-evolution of the $B_d$ meson and its mixing into $\bar{B}_d$. We discuss the angular conventions required to define the angular observables in a transparent way with respect to CP conjugation. The inclusion of time evolution allows us to identify six new observables, out of which three could be accessed from a time-dependent tagged analysis. We also show that these observables could be obtained by time-integrated measurements in a hadronic environment if flavour tagging is available. We provide simple …
We re-examine higgsino pair production in association with a hard QCD jet at the LHC. We focus on \ell^+\ell^- +MET +jet events from the production and subsequent decay, \tchi_2^0\to\tchi_1^0\ell^+\ell^-, of the heavier neutral higgsino. The novel feature of our analysis is that we propose angular cuts to reduce the irreducible background from Z(-> τ\barτ)+jet events more efficiently than the m_{ττ}^2<0 cut that has been used by the ATLAS and CMS collaborations. Additional cuts, needed to reduce backgrounds from t\bar{t}, WWj and W/Z+\ell\bar{\ell} production, are also delineated. We evaluate …
Lepton polarization dependent angular observables and the polarization asymmetries in the four-fold $Λ_b \rightarrow Λ(\rightarrow N π) \ell^+\ell^-$ decay
National University of Sciences and Technology (NUST)（国立科学技术大学）；National Centre for Physics（国家物理中心）；Quaid-i-Azam University（奎德-e-阿扎姆大学）
Investigation of the difference in the angular distributions of $Z\to \ell^{+}\ell^{-}$ events produced in quark-antiquark, quark-gluon and gluon-gluon collisions
University of Rochester（罗切斯特大学）；Seoul National University（首尔大学）
After summarizing the current theoretical status of the four-body decay B --> K^*(--> K pi) mu^+ mu^-, we apply the formalism of spin-symmetries to the full angular distribution, including the S-wave part involving a broad scalar resonance K0^*. While we recover in the P-wave sector the known relation between the angular observables Pi('), we find in the S-wave sector two new relations connecting the coefficients of the S-wave angular distribution and reducing the number of independent S-wave observables from six to four. Included in the experimental data analysis, these relations can help to …
Using the helicity amplitude technique, we derive differential decay widths and angular distributions for the decay cascade $D\to K_{1}(1270,1400)\ell^+ν_{\ell}\to (Kππ)\ell^+ν_{\ell} (\ell=e,μ)$, in which the electron and muon mass is explicitly included. Using a set of phenomenological results for $D\to K_1$ form factors, we calculate partial decay widths and branching fractions for $D^0\to K_1^-\ell^+ν_{\ell}$ and $D^+\to K_1^0\ell^+ν_{\ell}$, but find that results for ${\cal B}(D\to K_1(1270)e^+ν_{e})$ are larger than recent BESIII measurements by about a factor 1.5. We further demonstrate…
Exclusive semileptonic decays based on $b\to s$ transitions have been attracting a lot of attention as some angular observables deviate significantly from the Standard Model (SM) predictions in specific $q^2$ bins. B meson decays induced by other Flavor Changing Neutral Current (FCNC), $b\to d$, can also offer a probe to new physics with an additional sensitivity to the weak phase in Cabibbo-Kobayashi-Masakawa (CKM) matrix. We provide predictions for angular observables for $b\to d$ semileptonic transitions, namely $\bar{B}_s\to K^{\ast}\ell^+\ell^-$, $\bar{B}^0\toρ^0 \ell^+\ell^-$, and their …
As an update to our previous calculation for spin $J\leq2$, we present the angular moments for exclusive $\overline{B} \to X_J \ell_1 \ell_2$, where $\ell_1$ is a charged massless lepton and $\ell_2$ is a charged or neutral massless lepton, and $X_J$ is a mesonic system with spin $J\leq4$. The expected applications include higher resonances in the $[Kπ]$ system in $\overline{B}^0 \to K^- π^+ μ^- μ^+$ at LHCb in Run~II, and in the $[ππ]$ system for $ \overline{B} \to ππ\ell^- \barν_\ell$ at Belle~II. For the $J\leq2$ case, we also provide a set of consistency relations among the measured moment…
(A)symmetries of weak decays at and near the kinematic endpoint
在零反冲运动学终点，物理动量是平行的，这导致衰变分布的对称性。我们通过扩展螺旋度形式主义来实现对$A \to (B_1 B_2) C$型衰变的观察，以包括非物理的类时极化。计算了一般六维$B \to V \ell \ell$衰变哈密顿量的螺旋度振幅的对称性。我们获得了角观测量的\emph{exact}预测，例如，对纵向极化矢量介子的分数$F_L = 1/3$进行了计算，可用于指导实验分析。我们通过矢量介子的三个动量展开来研究端点附近。新的物理学可以在端点附近的可观测量的斜率中寻找。目前的实验数据$B \to K^* \ell \ell$衰变被发现与我们的预测在不确定性。对于其他半轻子$B$和$D$衰变，包括$B \to V \ell^+ \ell^-$、$V=K^*,ϕ, ρ$和$B \to V \ell ν$，$V=ρ,D^*$的应用是直接的。对于$B \to V p \bar p, V Λ\bar Λ, ..$和$B \to V ππ, V πK, .. $类型的强子模，只要它们不被$V$和强子对之间相当大的末态相互作用所压倒，端点关系就适用。
Motivated by the fact that naturalness arguments strongly suggest that the SUSY-preserving higgsino mass parameter mu cannot be too far above the weak scale, we re-examine higgsino pair production in association with a hard QCD jet at the HL-LHC. We focus on \ell^+\ell^-+\eslt+j events from the production and subsequent decay, \tchi_2^0\to\tchi_1^0\ell^+\ell^-, of the heavier neutral higgsino. The novel feature of our analysis is that we suggest angular cuts to reduce the important background from Z(\to ττ)+j events more efficiently than the m_{ττ}^2<0 cut that has been used by the ATLAS and C…
Hints of lepton flavor universality violation observed in various flavor ratios such as $R_D$, $R_{D^*}$, $R_{J/ψ}$, $P_τ^{D^*}$ and $F_L^{D^*}$ in $B\to D^{(*)}\,\ell \, ν$ and $B_c\to J/ψ\, \ell\, ν$ charge current decays have opened new avenues to search for indirect evidences of beyond the standard model physics. Motivated by these anomalies, we perform a detailed angular analysis of $B_s\to D_s^*(\to D_sγ,\,D_sπ)\, \ell\, ν$ decays that proceed via similar $b \to c\, \ell\, ν$ quark level transition. We use the most general effective Hamiltonian for $b\to \,c\, lν$ process and give predic…
We study the differential decay rate for the rare decay $Λ_b\to Λ(1520)(\to NK)\ell^+\ell^-$ where $\ell$ is a light lepton, as this decay mode can provide new and complementary constraints on the Wilson coefficients in $b\to s\ell^+\ell^-$ transitions compared to other modes. We provide a determination of the complete angular distribution, assuming unpolarised $Λ_b$ baryons and neglecting the lepton mass. The resulting angular observables are expressed in terms of helicity amplitudes involving hadronic form factors within the Standard Model and New physics models with chirality-flipped operat…
We study mixing of the Dirac neutrinos in the residual symmetries approach. The key difference from the Majorana case is that the Dirac mass matrix may have larger symmetries: $G_ν=\mathbf{Z}_{n}$ with $n\geq3$. The symmetry group relations have been generalized to the case of Dirac neutrinos. Using them we have found all new relations between mixing parameters and corresponding symmetry assignments which are in agreement with the present data. The viable relations exist only for the charged lepton residual symmetry $G_{\ell} = \mathbf{Z}_{2}$. The relations involve elements of the rows of the…
We study the differential decay rate for the rare $Λ_b \to Λ(\to N π)\ell^+\ell^-$ transition, including a determination of the complete angular distribution, assuming unpolarized $Λ_b$ baryons. On the basis of a properly chosen parametrization of the various helicity amplitudes, we provide expressions for the angular observables within the Standard Model and a subset of new physics models with chirality-flipped operators. Hadronic effects at low recoil are estimated by combining information from lattice QCD with (improved) form-factor relations in Heavy Quark Effective Theory. Our estimates f…
We present the differential rates for exclusive $\Bbar\to X \ell_1 \ell_2$, where $\ell_1$ is a charged massless lepton and $\ell_2$ is a charged or neutral massless lepton, and $X$ is a mesonic system up to spin 2. The cases of interest are semileptonic (SL) $\Bbar\to \xcu\ellm \barnuell$ decays, and $\Bbar \to X_s \ellm \ellp$ where the the di-lepton can be $c \bar{c}$ resonances or non-resonant electroweak penguins (EWP). We consider helicity amplitudes having non-zero relative phases that can be potential new sources for CP-violation. Our motivations for these additional phases include a c…
Angular observables and branching ratio for $B_s\to ϕ\ell^+ \ell^-$ decay
The Institute of Nuclear Physics, Agency of the Republic of Kazakhstan for Atomic Energy（哈萨克斯坦原子能机构核物理研究所）；Joint Institute for Nuclear Research（俄罗斯杜布纳联合核研究所）
In this work, we study the flavor-changing neutral-current process $B_{c}\to{D}_{s}^{*}(\to{D}_{s}π)\ell^{+}\ell^{-}$ ($\ell$= $e$, $μ$, $τ$). The relevant weak transition form factors are obtained by using the covariant light-front quark model, in which, the main inputs, i.e., the meson wave functions of $B_{c}$ and $D_{s}^{*}$, are adopted as the numerical wave functions from the solution of the Schrödinger equation with the modified Godfrey-Isgur model. With the obtained form factors, we further investigate the relevant branching fractions and their ratios, and some angular observables, i.e…
We revisit the decay $Λ_b^0\to Λ_c^+ \ell^-\barν$ ($\ell = e,μ,τ$) with a subsequent two-body decay $Λ_c^+ \to Λ^0 π^+$ in the Standard Model and in generic New Physics models. The decay's joint four-differential angular distribution can be expressed in terms of ten angular observables, assuming negligible polarization of the initial $Λ_b$ state. We present compact analytical results for all angular observables, which enables us to discuss their possible New Physics reach. We find that the decay at hand probes more and complementary independent combinations of Wilson coefficients compared to i…
The $B\to K^*μμ$ decay exhibits deviations with respect to Standard Model expectations and the measurement of the ratio $R_K$ hints at a violation of lepton-flavour universality in $B\to K\ell\ell$ transitions. Both effects can be understood in model-independent fits as a short-distance contribution to the Wilson coefficient $C_{9μ}$, with some room for similar contributions in other Wilson coefficients for $b\to sμμ$ transitions. We discuss how a full angular analysis of $B\to K^*ee$ and its comparison with $B\to K^*μμ$ could improve our understanding of these anomalies and help confirming th…
New physics searches via angular distributions of $ \bar{B} \to D^* (\to D π) τ(\to \ell ν_τ\barν_\ell) \barν_τ$ decays
Lawrence Technological University（劳伦斯理工大学）；University of Hawaii（夏威夷大学）；University of Mississippi（密西西比大学）；Université Paris-Saclay（巴黎萨克雷大学）；Nankai University（南开大学）
We derive the expressions for the full angular distributions of $\bar B\to D\ell\bar ν_\ell$ and $\bar B\to D^{\ast }\ell\bar ν_\ell$ decays and discuss the spectra on each angle separately. The coefficient functions, depending on helicity amplitudes, can then be combined in an ensemble of observables which can then be used to check for the presence of New Physics. We examine the sensitivity of each of these observables on the presence of non-Standard Model interaction terms at low energies. The expressions presented here are general and can be used for studying any other semileptonic pseudosc…
We present a theoretical analysis of the $D^-\to π^+π^- \ell\barν$ and $\bar D^0\to π^+π^0 \ell\barν$ decays. We construct a general angular distribution which can include arbitrary partial waves of $ππ$. Retaining the S-wave and P-wave contributions we study the branching ratios, forward--backward asymmetries and a few other observables. The P-wave contribution is dominated by $ρ^0$ resonance, and the S-wave contribution is analyzed using the unitarized chiral perturbation theory. The obtained branching fraction for $D\to ρ\ellν$, at the order $10^{-3}$, is consistent with the available exper…
We derive the four-fold angular distribution for the semileptonic decay $\bar{B}\to D_2^*(\to D π)\,\ell \barν$ where $D_2^*$(2460) is a tensor meson. We start with the most general beyond the Standard Model (SM) dimension-six effective Hamiltonian which comprises (axial)vector, (pseudo)scalar and tensor operators for both quark and lepton currents, and it also includes the right-handed neutrinos. The decay can be described by 16 transversity amplitudes and it provides a multitude of observables which can be extracted from data. We investigate the observables in the context of the SM and the n…
We analyse the $\overline B_s^0\to K^+l^-\bar ν$ and $\overline B_s^0\to K^{*+}(\to Kπ) \ell^-\bar ν$ decays that are valuable for extracting the CKM matrix element $|V_{ub}|$. We calculate the differential and integrated partial widths in units of $|V_{ub}|^2$ based on various calculations of hadronic form factors and in particular the latest Lattice QCD calculation of the $B_s\to K^*$ form factors. For the decay $\overline B_s^0 \to Kπ\ell\bar ν$, we formulate the general angular distributions with the inclusion of the various partial-wave $Kπ$ contributions. Using the results for the $Kπ$ s…
We analyze in detail the angular distributions in $\bar{B}\to D^*\ell \barν$ decays, with a focus on lepton-flavour non-universality. We investigate the minimal number of angular observables that fully describes current and upcoming datasets, and explore their sensitivity to physics beyond the Standard Model (BSM) in the most general weak effective theory. We apply our findings to the current datasets, extract the non-redundant set of angular observables from the data, and compare to precise SM predictions that include lepton-flavour universality violating mass effects. Our analysis shows that…
