arXiv subjects

C. Q. Geng

Publications and source records attributed to C. Q. Geng.

At least 91 records · Page 5Linked to original sources

arXiv2005

Study of $B\to Λ\barΛK$ and $B\to Λ\barΛπ$

We study three-body charmless baryonic B decays of $B \to Λ\barΛP$ with $P=π$ and $K$ in the standard model. We find that the branching ratios of the $K$ modes are about one order of magnitude larger than those of the corresponding $π$ modes unlike the cases of $B\to p\bar p P$. Explicitly, we obtain that $Br(B^-\to Λ\bar ΛK^-)=(2.8\pm 0.2)\times 10^{-6}$ and $Br(\bar B^0 \toΛ\bar Λ\bar K^0)=(2.5\pm 0.3)\times 10^{-6}$. The former agrees well with the BELLE experimental measurement of $(2.91^{+0.90}_{-0.70}\pm 0.38)\times 10^{-6}$, while the latter should be seen at the ongoing B factories soon.

hep-ph↗

arXiv2005

Some Tests on CPT Invariance

We first briefly review tests on CPT invariance based on the consequences of the CPT theorem and then present some possible CPT tests due to exotic models in which some of the CPT conditions are lost, such as those without hermiticity.

hep-ph↗

arXiv2005

Radiative Baryonic $B$ Decays

We study the structure-dependent contributions to the radiative baryonic $B$ decays of $B \to {\bf B}{\bf \bar B'}γ$ in the standard model. We show that the decay branching ratios of $Br(B \to {\bf B}{\bf \bar B'}γ)$ are $O(10^{-7})$, which are larger than the estimated values of $O(10^{-9})$ induced from inner bremsstrahlung effects of the corresponding two-body modes. In particular, we find that $Br(B^- \to Λ\bar p γ)$ is around $1 \times 10^{-6}$, which is close to the pole model estimation but smaller than the experimental measurement from BELLE.

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arXiv2004

T violation in $B\to K ϕϕ$ decays

We present the general form of the decay width angular distributions with T-odd terms in $B\to K ϕϕ$ decays. We concentrate on the T violating effects by considering various possible T-odd momentum correlations. In a generic class of CP violating new physics interactions, we illustrate that the T violating effect could be more than 10%.

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arXiv2004

Axial-vector Form Factors for $K_{\ell 2γ}$ and $π_{\ell 2γ}$ at $O(p^6)$ in Chiral Perturbation Theory

We present two-loop calculations on the axial-vector form factors $F_A$ of semileptonic radiative kaon and pion decays in chiral perturbation theory. The relevant dimension-6 terms of the lagrangian are evaluated from the resonance contribution and the results of the irreducible two-loop graphs of the sunset topology are given in detail. We also explicitly show that the divergent parts in $F_A$ are cancelled exactly as required.

hep-ph↗

arXiv2003

T-violating triple product asymmetries in Lambda_b --> Lambda pi pi decay

We study Lambda_b --> Lambda pi pi. The branching fraction is predicted to be about 4.38 x 10^{-6}%. Within the standard model, we compute T-odd triple product asymmetries to be about 1.4, 4.3, 6.5 and 7.2% respectively due to s_{Lambda_b}(s_Lambda) . (p_Lambda x p_pi) and p_Lambda (p_pi) . (s_Lambda x s_{Lambda_b}).

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arXiv2003

Tau Radiative Decays in the Light Front Quark Model

We study the decays of $τ^- \to ν_τ P^-γ(P=π^-, K^-)$ in the light front quark model. We calculate the form factors and use them to evaluate the decay widths. We find that, in the standard model, the decay widths are $1.62\times 10^{-2} (3.86\times10^{-3}) Γ_{τ^- \to ν_τ π^-}$ and $1.91\times 10^{-3} (5.38\times 10^{-4}) Γ_{τ^- \to ν_τ K^-}$ with the cuts of $E_γ=50 (400)$ MeV and $t_{0}=800 (1200)$ MeV for $τ^- \to ν_τ π^- γ$ and $τ^- \to ν_τ K^- γ$, respectively. We also show that with including the radiative decay widths, the experimental rate for $τ^-\to ν_τP^-$ can be explained.

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arXiv2003

Triple product correlations in B --> anti-Lambda p pi

Triple product correlations (TPC's) involving strange quark spin are elucidated in b --> u u(bar) s process within the standard model. They arise when light quark masses are nonzero. As the momenta and spins of constituent quarks are related to that of the parent hadron, the quark masses are, however small, important and relevant in TPC studies. At this level the TPC's of interest are of the form s_s.[p_u X p_u(bar)] and s_s.[p_s X p_u]. As an application, we look at T-violating effects in B --> anti-Lambda p pi through the TPC s_Λ.[p_ΛX p_p] for which triple product asymmetry is found to be 5.7%-7.6% in the vanishing limit of the strong phase.

hep-ph↗

arXiv2003

Study of $B_{s}\to (η,η',ϕ)\ell\bar{\ell}$ Decays

We study the rare decays of $B_{s} \to M_s\ell \bar{\ell}$ ($M_s=η, η',ϕ$ and $\ell=ν,e,μ,τ$) in the standard model. With the hadronic form factors evaluated in the light front and constituent quark models, we estimate the decay branching ratios, respectively. We also discuss the longitudinal lepton polarization and forward-backward asymmetries.

hep-ph↗

arXiv2003

Forward-backward Asymmetry in $K^+\toπ^+ \ell^+\ell^-$

We study the forward-backward asymmetries in the decays of $K^+\toπ^+\ell^+ \ell^-$ ($\ell=e$ and $μ$) in the presence of scalar or tensor terms. We find that with the scalar (tensor) type interaction the asymmetry can be up to ${\cal O}(10^{-3})$ (${\cal O}(10^{-1}))$ and arbitrary large for the electron and muon modes, respectively, without conflict with the experimental data. We also discuss the cases in the minimal supersymmetric standard model where the scalar terms can be induced. In particular we show that the asymmetry in $K^+\toπ^+μ^+μ^-$ can be as large as ${\cal O}(10^{-3})$ in the large $\tanβ$ limit, which can be tested in future experiments such as CKM at Fermilab.

hep-ph↗

arXiv2002

T violation in $Λ_b\toΛ\ell^+\ell^-$ decays

We examine the T-odd transverse lepton and $Λ$ polarizations in the baryonic decays of $Λ_b\toΛl^+l^- (l=e ,μ)$ to study the T violating effects. We show that the lepton polarizations are suppressed but the $Λ$ ones can be as large as 50% in CP violating theories beyond the standard model such as the SUSY models, which can be tested in various future hadron colliders.

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arXiv2002

Probing New Physics in $B\to K^{(*)} \ell^+\ell^-$ decays

We study the exclusive decays of $B\to K^{(*)}\ell^+ \ell^-$ by the results in the perturbative QCD with the heavy quark effective theory and lattice calculations. We obtain the form factors for the $B\to K^{(*)}$ transitions in the whole allowed region. Our predictions on the branching ratios of $B\to K \ell^{+} \ell^{-}$, $B\to K^{*} e^{+}e^{-}$, and $B\to K^{*} μ^{+} μ^{-}$ are $0.53\pm 0.05 ^{+0.10}_{-0.07}$, $1.68\pm 0.17^{+0.14}_{-0.09}$, and $1.34\pm 0.13 ^{+0.11}_{-0.06}\times 10^{-6}$, where the errors are from the quark mixing elements and hadronic effects, respectively. We also find that our definitions of the T-odd observable and the up-down asymmetry of the $K$ meson in $B\to K^*\ell^+ \ell^-\to Kπ\ell^+ \ell^-$ can be used to probe new physics.

hep-ph↗

arXiv2002

Long distance contributions in $B\toK^\ell^+\ell^-$ decays with polarized $K^$

We use momentum correlations as physical observables in $B\to K^{*}l^{+}l^{-}$ decays with $K^{*}$ polarized to study the long distance contributions. We show that these observables are sensitive to the scenarios of the long distance parametrizations. We find that the T-odd observable is directly related to the nonfactorizable effect in the standard model.

hep-ph↗

arXiv2002

Lepton pair decays of the $K_L$ meson in the light-front model

We analyze $K_L$ lepton pair decays of $K_L \to l^+ł^-γ$ and $K_L \to l^+l^-l'^+l'^-$ $(l, l'=e, μ)$ within the framework of the light-front QCD approach (LFQA). With the $K_L \to γ^* γ^*$ form factors evaluated in a model with the LFQA, we calculate the decay branching ratios and find out that our results are all consistent with the experimental data. In addition, we study $K_L \to l^+l^-$ decays. We point out that our prediction on $K_L\to e^+e^-$ is about 20% smaller than that in the ChPT. We also discuss whether one could extract the short-distance physics from $K_L\to μ^+μ^-$.

hep-ph↗

arXiv2002

CP Violation in the Decay $η\toπ^+π^-γ$

We study the CP violating effects in the decay of $η\toπ^+π^-γ$. We show that to have CP violation in the decay, one has to consider both linear and circular photon polarizations. In the standard model, the polarizations are vanishingly small. However, model-independently, i.e. using only experimental constraint imposed by the limit on $Br(η\toπ^+π^-)$ it can be up to $O(10%)$. We also explore various possible operators and we find that the tensor type operator, possibly arising from a nonzero CP violating electric dipole moment of the strange quark, can induce a sizable linear photon polarization.

hep-ph↗

arXiv2002

Analysis of $B\to K^* \ell^+ \ell^-$ decays at large recoil

We study the exclusive decays of $B\to K^{*}\ell^+ \ell^-$ within the framework of the perturbative QCD (PQCD). We obtain the form factors for the $B\to K^{*}$ transition in the large recoil region, where the PQCD for heavy $B$ meson decays is reliable. We find that our results for the form factors at $q^2=0$ are consistent with those from most of the other QCD models in the literature. Via the decay chain of $B\to K^* (Kπ) \ell^+ \ell^-$, we obtain many physical observables related to the different helicity combinations of $B\to K^* \ell^+ \ell^-$. In particular, we point out that the T violating effect suppressed in the standard model can be up to $O(10%)$ in some CP violating models with new physics.

hep-ph↗

arXiv2002

T violation in $B\to K^* \ell^+ \ell^-$ from SUSY

We propose to use T-odd momentum correlations as physical observables to study T violation in $B\to K^{*}l^{+}l^{-} (l=e,μ)$ decays. We show that these observables are zero in the standard model but sizable at the level of 10% in the supersymmetric model. These large T violating effects are measurable at the B-factories in KEK and SLAC and future hadron colliders. We also point out that the T violating effects are insensitive to nonperturbative QCD contributions.

hep-ph↗

arXiv2002

Study of Rare $B_c^+\to D_{d,s}^{(*) +}l\bar{l}$ Decays

We study the rare decays of $B_c^+\to D_{q}^{(*)+}l\bar{l}$ ($q=d,s$ and $l=ν_l,e,μ,τ)$ in the standard model. The form factors are evaluated in the light front and constituent quark models, respectively. We find that the decay branching ratios calculated in the two models for $B_c^+\to D^+_q l\bar{l}$ agree well with each other, whereas those for $B_c^+\to D_q^{*+}l\bar{l}$ are different.

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