In $Λ_b^0 \to Λ_c^+ (\to Λ^0 π^+) τ^- \barν_τ$ decay, the solid angle of the final-state particle $τ^-$ cannot be determined precisely since the decay products of the $τ^-$ include an undetected $ν_τ$. Therefore, the angular distribution of this decay cannot be measured. In this work, we construct a {\it measurable} angular distribution by considering the subsequent decay $τ^- \to π^- ν_τ$. The full cascade decay is $Λ_b^0 \to Λ_c^+ (\to Λ^0 π^+)τ^- (\to π^- ν_τ)\barν_τ$. The three-momenta of the final-state particles $Λ^0$, $π^+$, and $π^-$ can be measured. Considering all Lorentz structures of the new physics (NP) effective operators and an unpolarized initial $Λ_b$ state, the five-fold differential angular distribution can be expressed in terms of ten angular observables ${\cal K}_i (q^2, E_π)$. By integrating over some of the five kinematic parameters, we define a number of observables, such as the $Λ_c$ spin polarization $P_{Λ_c}(q^2)$ and the forward-backward asymmetry of $π^-$ meson $A_{FB}(q^2)$, both of which can be represented by the angular observables $\widehat{\cal K}_i (q^2)$. We provide numerical results for the entire set of the angular observables $\widehat{\cal K}_i (q^2)$ and $\widehat{\cal K}_i$ both within the Standard Model and in some NP scenarios, which are a variety of best-fit solutions in seven different NP hypotheses. We find that the NP which can resolve the anomalies in $\bar{B} \to D^{(*)} τ^- \barν_τ$ decays has obvious effects on the angular observables $\widehat{\cal K}_i (q^2)$, except $\widehat{\cal K}_{1ss} (q^2)$ and $\widehat{\cal K}_{1cc} (q^2)$.
We present a systematic study of the proton spin structure in terms of measurable parton distributions. For a transversely-polarizedproton, we derive a polarization sum rule from the leading generalized parton distributions appearing in hard exclusive processes. For a longitudinally-polarized proton, we obtain a helicity decomposition from well-known quark and gluon helicity distributions and orbital angular-momentum contributions. The latter is shown to be related to measurable subleading generalized parton distributions and quantum-phase space Wigner distributions.
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^{-} (…
We show that the recent claim that the expression 1/2 \int x dx [ H_q (x,0,0) + E_q(x,0,0)], involving the generalized parton distributions H and E, measures the transverse angular momentum of quarks in a transversely polarized nucleon, is incorrect.
Radiative corrections to the three-body region of the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons: The initial-baryon rest frame case
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.
The associated production of a Higgs boson and a top-quark pair, $t{\bar t} H$, in proton-proton collisions is addressed in this paper for a center of mass energy of 13TeV at the LHC. Dileptonic final states of $t{\bar t}H$ events with two oppositely charged leptons and four jets from the decays $t\rightarrow bW^+ \rightarrow b \ell^+ν_\ell$, $\bar{t}\rightarrow \bar{b}W^- \rightarrow \bar{b} \ell^-\barν_\ell$ and $h\rightarrow b\bar{b}$, are used. Signal events, generated with MadGraph5_aMC@NLO, are fully reconstructed by applying a kinematic fit. New angular distributions of the decay produc…
In principle, this paper suggests powerful laser technology as a promising instrument that can be experimentally useful to control the lifetime and branching ratio for an unstable particle decay. In a recent paper [arXiv:2101.00224], we calculated theoretically the $W^{-}$-boson leptonic decay $(W^{-}\rightarrow \ell^{-} \barν_{\ell})$ in the presence of a circularly polarized laser and we showed that the laser significantly contributed to the diminution of the leptonic decay rate. In this paper, as a continuation of the previous one, we mainly deal with the theoretical calculation of the $W^{…
Radiative corrections to the three-body region of the Dalitz plot of baryon semileptonic decays with angular correlation between polarized emitted baryons and charged leptons
We calculate the angular distribution spectra between beauty ($B$) and anti-beauty ($\bar B$) mesons in proton-proton collisions in the leading order approximation of the parton Reggeization approach consistently merged with the next-to-leading order corrections from the emission of additional hard gluon. To describe b-quark hadronization we use the universal scale-depended parton-to-meson fragmentation functions extracted from the world $e^+e^-$ annihilation data. We have obtained good agreement between our predictions and data from the CMS Collaboration at the energy $\sqrt{S}=7$ TeV for $B …
Using the helicity formalism, we calculate the combined angular distribution function of the two gamma photons ($γ_1$ and $γ_2$) and the electron ($e^-$) in the triple cascade process $\bar{p}p\rightarrow{}^3D_3\rightarrow{}^3P_2+γ_1\rightarrow(ψ+γ_2) +γ_1 \rightarrow (e^- + e^+) +γ_2 +γ_1$, when $\bar{p}$ and $p$ are arbitrarily polarized. We also derive six different partially integrated angular distribution functions which give the angular distributions of one or two particles in the final state. Our results show that by measuring the two-particle angular distribution of $γ_1$ and $γ_2$ and…
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）
Angular distribution of the final particles in the decay $Λ_c^+\to K^- \, Δ(1232)^{++} \to K^- \, p \, π^+$ of the polarized charmed baryon is discussed. Asymmetries are proposed which allow for determination of the components of the $Λ_c^+$ polarization vector. The precession angle of the polarization in the process of baryon channeling in a bent crystal is directly related to these asymmetries. The decay rate and asymmetry parameter for the $Λ_c^+\to K^- \, Δ(1232)^{++}$ decay are calculated in the pole model and compared with experiment.
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…
The distributions of the bottom quark in the process $e^+ e^- \to t \, \bar{t} \to b \, W^+ \, \bar{t}$ are considered at the $e^+ e^-$ energy corresponding to the first construction stage of the Compact Linear Collider. The cross sections of $e^+ e^- \to b \ldots$, as functions of the $b$-quark energy and angle with respect to the direction of the electron beam, are derived and calculated. The effects of physics beyond the Standard Model are included via the modified $γt \bar{t}$ and $Z t \bar{t}$ couplings which naturally appear in effective field theories. In addition to the cross sections,…
One can determine antiquark polarizations in proton using the information from deep inelastic scattering, $β$ decays of baryons, orbital angular momenta of quarks, as well as their integrated magnetic distributions. The last quantities were determined previously by us performing a fit to magnetic moments of baryon octet. However, because of the SU(3) symmetry our results depend on two parameters. The quantity $Γ_{V}$, measured recently in a COMPASS experiment, gives the relation between these parameters. We can fix the last unknown parameter using the ratio of up and down quark magnetic moment…
Excluding Local Hidden Variables in $Λ\barΛ$ Production: The Incompatibility with Angular-Momentum Conservation and CPT Invariance
Institute of Physics, Henan Academy of Sciences（河南省科学院物理研究所）；School of Sciences, Xi’an Technological University（西安工业大学理学院）；School of Physics, Henan Normal University（河南师范大学物理学院）
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…
The nonleptonic two-body $B^{\ast}$ ${\to}$ $\bar{D}D$ weak decays are studied phenomenologically with the perturbative QCD factorization approach. It is found that the $B_{s}^{{\ast}0}$ ${\to}$ $D_{s}^{-}D_{s}^{+}$, $B_{d}^{{\ast}0}$ ${\to}$ $D_{d}^{-}D_{s}^{+}$, and $B_{u}^{{\ast}+}$ ${\to}$ $\bar{D}_{u}^{0}D_{s}^{+}$ decays have branching ratios ${\gtrsim}$ $10^{-9}$, and might be promisingly measurable at the running LHC and forthcoming SuperKEKB experiments in the future.
We show that, when boosted to the infinite momentum frame, the quark and gluon orbital angular momentum operators defined in the nucleon spin sum rule of X. S. Chen et al. are the same as those derived from generalized transverse momentum distributions. This completes the connection between the infinite momentum limit of each term in that sum rule and experimentally measurable observables. We also show that these orbital angular momentum operators can be defined locally, and discuss the strategies of calculating them in lattice QCD.
We perform an analysis of angular distributions in semileptonic decays of charmed baryons $B_1^{(\prime)}\to B_2^{(\prime)}(\to B_3^{(\prime)}B_4^{(\prime)})\ell^+ν_{\ell}$, where the $B_1=(Λ_c^+,Ξ_c^{(0,+)})$ are the SU(3)-antitriplet baryons and $B_1'=Ω_c^-$ is an SU(3) sextet. We will firstly derive analytic expressions for angular distributions using helicity amplitude technique. Based on the lattice QCD results for $Λ_c^+\toΛ$ and $Ξ_c^0\toΞ^-$ form factors and model calculation of the $Ω_c^0\toΩ^-$ transition, we predict branching fractions: $\mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} e^{…
The orbital angular momentum ($L_q$) of the proton is studied by employing the extended constituent quark model. Contributions from different flavors, namely, up, down, strange, and charm quarks in the proton are investigated. Probabilities of the intrinsic $q\bar{q}$ pairs are calculated using a $^{3}P_{0}$ transition operator to fit the sea flavor asymmetry $I_a=\bar{d}-\bar{u}=0.118\pm0.012$ of the proton. Our numerical results lead to $L_q=0.158 \pm 0.014$, in agreement with $4/3I_a=0.157 \pm 0.016$, and consistent with findings based on various other approaches.
We study the $d^2 Γ_d /(dωd\cosθ_d) $, $dΓ_d /d\cosθ_d$ and $ dΓ_d /dE_d $ distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the $τ-$decay in $b\to c τ\, (μ\bar ν_μν_τ,πν_τ,ρν_τ) \barν_τ$ reactions. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the $H_b\to H_cτ\barν_τ$ parent decay and, from a dynamical point of view, they are richer than the commonly used one, $d^2 Γ_d /(dωdE_d) $, since the latter only depends on the tau longitudinal polarization. We pay attention to the…
The $\bar{B}_{q}^{\ast}$ ${\to}$ $DP$, $DV$ weak decays are studied with the perturbative QCD approach, where $q$ $=$ $u$, $d$ and $s$; $P$ and $V$ denote the ground $SU(3)$ pseudoscalar and vector meson nonet. It is found that the branching ratios for the color-allowed $\bar{B}_{q}^{\ast}$ ${\to}$ $D_{q}ρ^{-}$ decays can reach up to $10^{-9}$ or more, and should be promisingly measurable at the running LHC and forthcoming SuperKEKB experiments in the near future.
Suppose a heavy neutral Higgs or scalar boson $H$ is discovered at the LHC, it is important to investigate its couplings to the standard model particles as much as possible. Here in this work we attempt to probe the CP-even and CP-odd couplings of the heavy Higgs boson to a pair of top quarks, through the decay $H \to t\bar t \to b W^+ \bar b W^-$. We use the helicity-amplitude method to write down the most general form for the angular distributions of the final-state $b$ quarks and $W$ bosons. We figure out that there are 6 types of angular observables and, under CP$\widetilde{\rm T}$ conserv…
In $B_c^- \to J/ψ(\to μ^+ μ^-)τ^-\barν_τ$ decay, the three-momentum $\boldsymbol{p}_{τ^-}$ cannot be determined accurately due to the decay products of $τ^-$ inevitably include an undetected $ν_τ$. As a consequence, the angular distribution of this decay cannot be measured. In this work, we construct a {\it measurable} angular distribution by considering the subsequent decay $τ^- \to π^- ν_τ$. The full cascade decay is $B_c^- \to J/ψ(\to μ^+ μ^-)τ^- (\to π^- ν_τ)\barν_τ$, in which the three-momenta $\boldsymbol{p}_{μ^+}$, $\boldsymbol{p}_{μ^-}$, and $\boldsymbol{p}_{π^-}$ can be measured. The …
We examine the validity of the generalized factorization method and calculate the angular correlations in the charmful three-body baryonic decays of $\bar B^0\to Λ\bar p D^{(*)+}$. With the timelike baryonic form factors newly extracted from the measured baryonic $B$ decays, we obtain ${\cal B}(\bar B^0\to Λ\bar p D^+,Λ\bar p D^{*+})=(1.85\pm 0.30,2.75\pm 0.24)\times 10^{-5}$ to agree with the recent data from the BELLE Collaboration, which demonstrates that the theoretical approach based on the factorization still works well. For the angular distribution asymmetries, we find ${\cal A}_θ(\bar …
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…
Analysis of the measured value of the integrated \bar{d}-\bar{u} asymmetry (Ifas = 0.147+-0.027) in the nucleon show it to arise from nucleon fluctuations into baryon plus pion. Requiring angular momentum conservation in these fluctuations shows the associated orbital angular momentum is equal to the value of the flavor asymmetry.
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 …
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…
The differential decay rates of the processes $J/ψ\to p\bar{p}π^{0}$ and $J/ψ\to p\bar{p}η$ close to the $p\bar{p}$ threshold are calculated with the help of the $N\bar{N}$ optical potential. The same calculations are made for the decays of $ψ(2S)$. We use the potential which has been suggested to fit the cross sections of $N\bar{N}$ scattering together with $N\bar{N}$ and six pion production in $e^{+}e^{-}$ annihilation close to the $p\bar{p}$ threshold. The $p\bar{p}$ invariant mass spectra is in agreement with the available experimental data. The anisotropy of the angular distributions, whi…
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…
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）
It is proposed to search for $C\!P$ violation through the two-fold angular distributions in the four-body decays of bottom and charmed hadrons. The two polar angles in the two-fold angular distributions are correlated, to which the interferences of intermediate resonances are one important origin. These interferences will leave tracks in the two-fold angular distributions, with which the $C\!P$ violation can be studied. Special attention is paid to the case when all the intermediate resonances are different, which is unique to four-body decays. It is suggested to look for $C\!P$ violation in f…
The $\bar{B}\to D^{*+} l^-\barν_{l}$ branching fraction ratio $R(D^{*})$ has shown intriguing discrepancies between the Standard Model prediction and measurements performed at BaBar, Belle and LHCb experiments, a possible sign of beyond the Standard Model physics. Theoretical studies prove how observables related to the $\bar{B}\to D^{*+} l^-\barν_{l}$ differential decay distribution can be used to further constrain New Physics contributions, but their experimental measurements is lacking to date. This article presents the attainable precision on the measurement of $\bar{B}\to D^{*+} l^-\barν_…
We introduce a set of observables representing angular distribution asymmetries, which can be viewed as a generalization of the forward-backward asymmetry of angular distributions, and can be used as an effective tool to search for $C\!P$ violation in three-body decays of bottom and charmed baryons. We propose to search for such $C\!P$ asymmetries (1) in decays with $Λ^0$, $Σ^\pm$, or $Λ_c^+$ involved, such as $Λ_b\to Λ^0 D$ and $Λ_b\toΛ^0ρ(770)^0$; and (2) in three-body decays of bottom baryons with opposite parity intermediate resonances involved. Typical examples include $Ξ_b^-\to p K^- K^-…
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 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…
The standard-model Higgs boson couples to quarks through a parity-even scalar $Hq{\bar q}$ coupling. We show that the rare Higgs decay $H\to VZ$, where $V$ is a vector quarkonium state such as $J/ψ$ ($c{\bar c}$) or $Υ(1S)$ ($b{\bar b}$), can be used to search for the presence of a parity-odd pseudoscalar $Hq{\bar q}$ coupling. Since both $V$ and $Z$ can decay to a pair of charged leptons, this presents an experimentally-clean channel that can be observed at the high-luminosity LHC or a future hadron collider. The P-even and P-odd $Hq{\bar q}$ couplings can be measured by analyzing the angular…
Masjuan, Arriola, and Broniowski [Phys. Rev. D85, 094006 (2012)] claim that the slope of the light-quark radial trajectories is 1.35 +- 0.04 GeV^2, disagreeing with the Crystal Barrel value 1.143 +- 0.013 GeV^2. There are defects in their choice of data. When these defects are revised, results come back close to the Crystal Barrel average for the slope. A revised average value is given here.
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…
With full data set that corresponds to an integrated luminosity of 9.4 fb$^{-1}$, CDF has updated the top quark forward-backward asymmetry (FBA) as functions of rapidity difference $|Δy|$ and $t\bar t$ invariant mass $M_{t\bar t}$. Beside the sustained inconsistency between experiments and standard model (SM) predictions at large $|Δy|$ and $M_{t\bar t}$, an unexpected large first Legendre moment with $a_1= 0.39\pm 0.108 $ is found. In order to solve the large top FBA, we study the contributions of color triplet scalar and color octet vector boson. We find that the top FBA at $|Δy| >1$ and $M_…
An optimal-observable analysis of the angular and energy distributions of the leptons and bottom quarks in the process e+e- --> tt-bar --> l^{+-}/b(b-bar)... has been performed in order to measure the most general top-quark couplings to gauge bosons at polarized linear colliders. The optimal beam polarization for determination of each coupling has been found. A very sensitive test of CP violation in tt-bar production and decay has been proposed.
