arXiv subjects

Hai-Yang Cheng

Publications and source records attributed to Hai-Yang Cheng.

At least 73 records · Page 4Linked to original sources

arXiv2013

Branching Fractions and Direct CP Violation in Charmless Three-body Decays of B Mesons

Charmless three-body decays of B mesons is studied using a simple model based on the framework of the factorization approach. Hadronic three-body decays receive both resonant and nonresonant contributions. Dominant nonresonant contributions to tree-dominated three-body decays arise from the $b\to u$ tree transition which can be evaluated using heavy meson chiral perturbation theory valid in the soft meson limit. For penguin-dominated decays, nonresonant signals come mainly from the penguin amplitude governed by the matrix elements of scalar densities $ $. We use the measurements of $\bar B^0\to K_SK_SK_S$ to constrain the nonresonant component of $ $. The intermediate vector meson contributions to three-body decays are identified through the vector current, while the scalar meson resonances are mainly associated with the scalar density. While the calculated direct CP violation in $B^-\to K^+K^-K^-$ and $B^-\to π^+π^-π^-$ decays agrees well with experiment in both magnitude and sign, the predicted CP asymmetries in $B^-\to π^- K^+K^-$ and $B^-\to K^-π^+π^-$ are wrong in signs when confronted with experiment. It has been conjectured recently that a possible resolution to this CP puzzle may rely on final-state rescattering of $π^+π^-$ and $K^+K^-$. Assuming a large strong phase associated with the matrix element $ $ arising from some sort of power corrections, we fit it to the data of $K^-π^+π^-$ and find a correct sign for $π^- K^+K^-$.

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arXiv2013

Mixing angle of $K_1$ axial vector mesons

Analyses of various experimental measurements all indicate that the mixing angle $θ_{K_1}$ of $K_1(1270)$ and $K_1(1400)$ is in the vicinity of $33^\circ$ or $57^\circ$. However, whether $θ_{K_1}$ is greater or less than $45^\circ$ is still quite controversial. For example, there were two very recent studies of the strong decays of $K_1$ mesons. One group claimed that $θ_{K_1}\approx 60^\circ$, while the other group obtained $θ_{K_1}=(33.6\pm4.3)^\circ$. Since the determination of the mixing angles $α_{^3\!P_1}$ and $α_{^1\!P_1}$ with the former (latter) being the mixing angle of $f_1(1285)$ ($h_1(1170)$) and $f_1(1420)$ ($h_1(1380)$) in the flavor basis through mass relations depend on $θ_{K_1}$, we show that $θ_{K_1}\approx 57^\circ$ is ruled out as it leads to a too large deviation from ideal mixing in the $^1\!P_1$ sector, inconsistent with the lattice calculation of $α_{^1\!P_1}$ and the observation of strong decays of $h_1(1170)$ and $h_1(1380)$. We find that for $θ_{K_1}\approx (28-30)^\circ$, the corresponding $α_{^3\!P_1}$ and $α_{^1\!P_1}$ agree well with all lattice and phenomenological analyses. This again reinforces the statement that $θ_{K_1}\sim 33^\circ$ is much more favored than $57^\circ$.

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arXiv2013

Revisiting charmless hadronic B decays to scalar mesons

Hadronic charmless B decays to scalar mesons are studied within the framework of QCD factorization (QCDF). Considering two different scenarios for scalar mesons above 1 GeV, we find that the data favor the scenario in which the scalars $a_0(1450)$ and $K_0^*(1430)$ are the lowest lying $q\bar q$ bound states. This in turn implies a preferred four-quark nature for light scalars below 1 GeV. Assuming $K_0^*(1430)$ being a lowest lying $q\bar s$ state, we show that the data of $B\to K_0^*(1430)η^{(')}$ and $B\to K_0^*(1430)(ρ,ω,ϕ)$ can be accommodated in QCDF without introducing power corrections induced from penguin annihilation, while the predicted $B^-\to \ov K_0^{*0}(1430)π^-$ and $\ov B^0\to K_0^{*-}(1430)π^+$ are too small compared to experiment. In principle, the data of $K_0^*(1430)π$ modes can be explained if penguin-annihilation induced power corrections are taken into account. However, this will destroy the agreement between theory and experiment for $B\to K_0^*(1430)(η^{(')},ρ,ω,ϕ)$. Contrary to the pseudoscalar meson sector where $B\to Kη'$ has the largest rate in 2-body decays of the $B$ meson, we show that $Br(B\to K_0^*η')<\B(B\to K_0^*η)$. The decay $\ov B^0\to a_0(980)^+K^-$ is found to have a rate much smaller than that of $\ov B^0\to a_0(980)^+π^-$ in QCDF, while it is the other way around in pQCD. Experimental measurements of these two modes will help discriminate between these two different approaches. Assuming 2-quark bound states for $f_0(980)$ and $f_0(500)$, the observed large rates of $f_0(980)K$ and $f_0(980)K^*$ modes can be explained in QCDF with the $f_0(980)\!-\!f_0(500)$ mixing angle $θ$ in the vicinity of $20^\circ$.

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arXiv2012

Connected-Sea Partons

According to the path-integral formalism of the hadronic tensor, the nucleon sea contains two distinct components called connected sea (CS) and disconnected sea (DS). We discuss how the CS and DS are accessed in the lattice QCD calculation of the moments of the parton distributions. We show that the CS and DS components for $\bar u(x) + \bar d(x)$ can be extracted by using recent data on the strangeness parton distribution, the CT10 global fit, and the lattice result of the ratio of the strange to $u(d)$ moments in the disconnected insertion. The extracted CS and DS for $\bar u(x) + \bar d(x)$ have distinct Bjorken $x$ dependence in qualitative agreement with expectation. The analysis also shows that the momentum fraction of the $\bar u(x) + \bar d(x)$ is about equally divided between CS and DS at $Q^2 = 2.5 {\rm GeV}^2$. Implications on future global analysis for parton distributions are presented.

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arXiv2012

Top Decays with Flavor Changing Neutral Higgs Interactions at the LHC

We investigate the prospects for discovering a top quark decaying into one light Higgs boson along with a charm quark in top quark pair production at the CERN Large Hadron Collider (LHC). A general two Higgs doublet model is adopted to study the signature of flavor changing neutral Higgs decay $t \to cϕ^0$, %or $\bar{t} \to \bar{c}ϕ^0$ where $ϕ^0$ could be CP-even ($H^0$) or CP-odd ($A^0$). The dominant physics background is evaluated with realistic acceptance cuts as well as tagging and mistagging efficiencies. For a reasonably large top-charm-Higgs coupling ($λ_{tc}/λ_{t} \agt 0.09$), the abundance of signal events and the %that our acceptance cuts reduction in physics background allow us to establish a $5σ$ signal for $M_ϕ\sim 125$ GeV at the LHC with a center of mass energy ($\sqrt{s}$) of 8 TeV and an integrated luminosity of 20 fb$^{-1}$. The discovery potential will be greatly enhanced with the full energy of $\sqrt{s} = 14$ TeV.

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arXiv2012

Recent Neutrino Data and a Realistic Tribimaximal-like Neutrino Mixing Matrix

In light of the recent neutrino experimental results from Daya Bay and RENO Collaborations, we construct a realistic tribimaximal-like Pontecorvo-Maki-Nakagawa-Sakata (PMNS) leptonic mixing matrix. Motivated by the Qin-Ma (QM) parametrization for the quark mixing matrix in which the CP-odd phase is approximately maximal, we propose a simple ansatz for the charged lepton mixing matrix, namely, it has the QM-like parametrization, and assume the tribimaximal mixing (TBM) pattern for the neutrino mixing matrix. The deviation of the leptonic mixing matrix from the TBM one is then systematically studied. While the deviation of the solar and atmospheric neutrino mixing angles from the corresponding TBM values, i.e. $\sin^2θ_{12}=1/3$ and $\sin^2θ_{23}=1/2$, is fairly small, we find a nonvanishing reactor mixing angle given by $\sinθ_{13}\approx λ/\sqrt{2}$ ($λ\approx 0.22$ being the Cabibbo angle). Specifically, we obtain $θ_{13}\simeq 9.2^{\circ}$ and $δ_{CP} \simeq δ_{\rm QM} \simeq {\cal O}(90^{\circ})$. Furthermore, we show that the leptonic \CP violation characterized by the Jarlskog invariant is $|J^{\ell}_{CP}|\simeq λ/6$, which could be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

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arXiv2012

SU(3) symmetry breaking and CP violation in D -> PP decays

Evidence of CP violation in the charm sector has been observed recently by the LHCb and CDF Collaborations. Adopting the topological diagram approach, we study flavor SU(3) symmetry breaking effects in the weak decay tree amplitudes of singly Cabibbo-suppressed $D\to PP$ decays. The symmetry breaking in the color-allowed and color-suppressed amplitudes is estimated with the help of the factorization ansatz, while that in the $W$-exchange amplitude is done by fitting to related branching fraction data. We find that the $W$-exchange amplitudes stay in the second quadrant relative to the color-allowed tree amplitude, albeit there are two possibilities for one type of $W$-exchange amplitude. The weak decay penguin amplitudes, on the other hand, are evaluated within the framework of QCD factorization. Using the input of topological tree amplitudes extracted from the Cabibbo-favored decay modes and the perturbative results for QCD penguin amplitudes, we make predictions for the branching fractions and CP asymmetries of singly Cabibbo-suppressed modes. The predictions of branching fractions are generally improved from those in the SU(3) limit. We conclude that the direct CP asymmetry difference between $D^0 \to K^+ K^-$ and $D^0 \to π^+ π^-$ is about $-(0.139\pm 0.004)%$ and $-(0.151\pm 0.004)%$ for the two solutions of $W$-exchange amplitudes, respectively. We also find that the CP asymmetry of $D^0\to K^0\ov K^0$ dominated by the interference between $W$-exchange amplitudes ranges from $-0.62\times 10^{-3}$ to $-1.82\times 10^{-3}$. We study phenomenological implications of two new physics scenarios for explaining the observed CP asymmetry in the charm sector, one with large penguin amplitudes and the other with a large chromomagnetic dipole operator. We find that the two scenarios can be discriminated by the measurements of CP asymmetries of a set of decay modes.

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arXiv2012

Direct CP Violation in D -> hh Decays

Evidence of CP violation in the charm sector has been observed recently by the LHCb and CDF Collaborations. The issue of whether it can be accommodated within the standard model (SM) is examined in this talk. We conclude that the CP asymmetry difference $Δa_{CP}^{\rm dir}$ between $D^0 \to K^+ K^-$ and $D^0 \to π^+ π^-$ is of order $-(0.14\sim 0.15)%$. If the improved theoretical estimate of $Δa_{CP}^{\rm dir}$ in the SM remains to be a few per mille and the experimental measurement continues to be large with more statistics in the future, it will be clear evidence of physics beyond the SM in the charm sector.

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arXiv2012

Revisiting Scalar and Pseudoscalar Couplings with Nucleons

Certain dark matter interactions with nuclei are mediated possibly by a scalar or pseudoscalar Higgs boson. The estimation of the corresponding cross sections requires a correct evaluation of the couplings between the scalar or pseudoscalar Higgs boson and the nucleons. Progress has been made in two aspects relevant to this study in the past few years. First, recent lattice calculations show that the strange-quark sigma term $σ_s$ and the strange-quark content in the nucleon are much smaller than what are expected previously. Second, lattice and model analyses imply sizable SU(3) breaking effects in the determination on the axial-vector coupling constant $g_A^8$ that in turn affect the extraction of the isosinglet coupling $g_A^0$ and the strange quark spin component $Δs$ from polarized deep inelastic scattering experiments. Based on these new developments, we re-evaluate the relevant nucleon matrix elements and compute the scalar and pseudoscalar couplings of the proton and neutron. We also find that the strange quark contribution in both types of couplings is smaller than previously thought.

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arXiv2012

Direct CP violation in two-body hadronic charmed meson decays

Motivated by the recent observation of CP violation in the charm sector by LHCb, we study direct CP asymmetries in the standard model (SM) for the singly Cabibbo-suppressed two-body hadronic decays of charmed mesons using the topological-diagram approach. In this approach, the magnitude and the phase of topological weak annihilation amplitudes which arise mainly from final-state rescattering can be extracted from the data. Consequently, direct CP asymmetry $a_{dir}^{\rm (tree)}$ at tree level can be reliably estimated. In general, it lies in the range $10^{-4}<a_{dir}^{\rm (tree)}<10^{-3}$. Short-distance QCD penguins and penguin annihilation are calculated using QCD factorization. Their effects are generally small, especially for $D\to VP$ modes. Since weak penguin annihilation receives long-distance contributions from the color-allowed tree amplitude followed by final-state rescattering, it is expected to give the dominant contribution to the direct CP violation in the decays $D^0\to K^+K^-$ and $D^0\to π^+π^-$ in which $a_{dir}^{\rm (tree)}$ is absent. The maximal $Δa_{CP}^{\rm dir}$, the direct CP asymmetry difference between the above-mentioned two modes, allowed in the SM is around -0.25%, more than $2σ$ away from the current world average of $-(0.645\pm 0.180)%$.

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arXiv2011

An extension of tribimaximal lepton mixing

Harrison, Perkins and Scott have proposed simple charged lepton and neutrino mass matrices that lead to the tribimaximal mixing $U_{\rm TBM}$. We consider in this work an extension of the mass matrices so that the leptonic mixing matrix becomes $U_{\rm PMNS}=V_L^{\ell\dagger}U_{\rm TBM}W$, where $V_L^\ell$ is a unitary matrix needed to diagonalize the charged lepton mass matrix and $W$ measures the deviation of the neutrino mixing matrix from the bimaximal form. Hence, corrections to $U_{\rm TBM}$ arise from both charged lepton and neutrino sectors. Following our previous work to assume a Qin-Ma-like parametrization $V_{\rm QM}$ for the charged lepton mixing matrix $V_L^\ell$ in which the {\it CP}-odd phase is approximately maximal, we study the phenomenological implications in two different scenarios: $V_L^\ell=V_{\rm QM}^\dagger$ and $V_L^\ell=V_{\rm QM}$. We find that the latter is more preferable, though both scenarios are consistent with the data within $3σ$ ranges. The predicted reactor neutrino mixing angle $θ_{13}$ in both scenarios is consistent with the recent T2K and MINOS data. The leptonic {\it CP} violation characterized by the Jarlskog invariant $J_{\rm CP}$ is generally of order $10^{-2}$.

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arXiv2011

Revisiting Axial-Vector Meson Mixing

Various phenomenological studies indicate that the mixing angle $θ_{K_1}$ of $K_{1A}$ and $K_{1B}$, the strange partners of the axial-vector mesons $a_1(1260)$ and $b_1(1235)$, respectively, lies in the vicinity of $35^\circ$ or $55^\circ$, but whether this angle is larger or smaller than $45^\circ$ still remains controversial. When the $f_1(1285)$-$f_1(1420)$ mixing angle $θ_{^3P_1}$ and the $h_1(1170)$-$h_1(1380)$ mixing angle $θ_{^1P_1}$ are determined from the mass relations, they depend on the masses of $K_{1A}$ and $K_{1B}$, which in turn depend on the mixing angle $θ_{K_1}$. We show that the approximate decoupling of the light $q\bar q$ state from the heavier $s \bar s$ state, which is empirically valid for vector, tensor and $3^{--}$ mesons, when applied to isoscalar axial-vector mesons, will enable us to discriminate different solutions of $θ_{^3P_1}$ and $θ_{^1P_1}$ and pick up $θ_{K_1}\sim 35^\circ$. Indeed, for $θ_{K_1}\sim 55^\circ$, the predicted $θ_{^1P_1}$ disagrees sharply with the recent lattice calculation and the implied large $s\bar s$ content of $h_1(1170)$ and $q\bar q$ component of $h_1(1380)$ cannot explain the observation of their strong decays. We conclude that $θ_{K_1}$ is smaller than $45^\circ$.

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arXiv2011

Some Results on Vector and Tensor Meson Mixing in a Generalized QCD-like Theory

We present results for the mixing of quark flavor eigenstates to form low-lying vector and tensor meson mass eigenstates in a generalized QCD-like theory with $\ell$ massless or light, degenerate quarks and one quark of substantial mass, $m_Q$. We show that as $m_Q/Λ$ gets large, where $Λ$ is the confinement scale, the angle governing this mixing approaches $\arctan(1/\sqrt{\ell})$. We give a generalization of the Gell-Mann Okubo mass relation for this theory. A comparison of the $\ell=2$ results with data on $ω$-$ϕ$ and $f_2(1275)$-$f_2'(1525)$ mixing is included.

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arXiv2011

Wolfenstein Parametrization at Higher Order: Seeming Discrepancies and Their Resolution

In different Wolfenstein parametrizations derived from different exact parametrizations of the Cabibbo-Kobayashi-Maskawa matrix, we explicitly study seeming discrepancies between the matrix elements at the higher order of the expansion parameter $λ$. A systematic way of resolving the seeming discrepancies is proposed. We find that most of the discrepancies can be naturally resolved by a proper redefinition of the numerically small (of order $λ$) parameters. Our approach is further applied to the cases for the Wolfenstein-{\it like} parametrizations, such as the Qin-Ma parametrization.

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arXiv2011

Remarks on the Qin-Ma Parametrization of Quark Mixing Matrix

Recently, Qin and Ma (QM) have advocated a new Wolfenstein-like parametrization of the quark mixing matrix based on the triminimal expansion of the Cabibbo-Kobayashi-Maskawa (CKM) parametrization. The CP-odd phase in the QM parametrization is around $90^\circ$ just as that in the CKM parametrization. We point out that the QM parametrization can be readily obtained from the Wolfenstein parametrization after appropriate phase redefinition for quark fields and that the phase $δ$ in both QM and CKM parametrizations is related to the unitarity angles $α$, $β$ and $γ$, namely, $δ= β+γ$ or $π-α$. We show that both QM and Wolfenstein parametrizations can be deduced from the CKM and Chau-Keung-Maiani ones. By deriving the QM parametrization from the Fritzsch-Xing (FX) parametrization of the quark mixing matrix, we find that the phase of the FX form is in the vicinity of $-270^\circ$ and hence $\sinδ\approx 1$. We discuss the seeming discrepancy between the Wolfenstein and QM parametrizations at the high order of $λ\approx |V_{us}|$.

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arXiv2011

Remarks on Strong CP-Violating Lagrangians

Owing to a different treatment of the vacuum alignment, the strong CP-violating Lagrangian obtained by Di Vecchia, Veneziano and Witten (DVW) 3 decades ago do not look quite the same as the one originally derived by Baluni at the quark or hadron level. We show that they are consistent with each other and emphasize that, within the DVW approach, the $θG\tilde G$ term is not entirely removed away after the vacuum is rotated from the CP-odd state to the CP-even one; strong CP violation resides not only in the quark mass terms but also in the residual topological sector. While the latter relies on the Dashen's theorem, the latter is based on the minimization of a potential energy with respect to the phase of the quark condensate. Contrary to some claims, it is necessary to include the SU(3)-singlet $η_0$ tadpole contribution for strong CP-odd effects induced by the Baluni-type Lagrangian to ensure that strong CP violation vanishes in the zero axial anomaly limit.

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arXiv2011

Flavor SU(3) symmetry and QCD factorization in $B \to PP$ and $PV$ decays

Using flavor SU(3) symmetry, we perform a model-independent analysis of charmless $\bar B_{u,d} (\bar B_s) \to PP, ~PV$ decays. All the relevant topological diagrams, including the presumably subleading diagrams, such as the QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be important in understanding the data for penguin-dominated decay modes. In this work we make efforts to bridge the (model-independent but less quantitative) topological diagram or flavor SU(3) approach and the (quantitative but somewhat model-dependent) QCD factorization (QCDF) approach in these decays, by explicitly showing how to translate each flavor SU(3) amplitude into the corresponding terms in the QCDF framework. After estimating each flavor SU(3) amplitude numerically using QCDF, we discuss various physical consequences, including SU(3) breaking effects and some useful SU(3) relations among decay amplitudes of $\bar B_s \to PV$ and $\bar B_d \to PV$.

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arXiv2011

Quark-lepton complementarity and tribimaximal neutrino mixing from discrete symmetry

The quark-lepton complementarity (QLC) relations indicate a deep structure that interrelates quarks and leptons. We propose new scenarios, in a seesaw framework with discrete $A_4$ flavor symmetry, which can accommodate the QLC relations and the nonzero neutrino mixing angle $θ_{13}$ together with all the available neutrino experimental data, in a consistent way to generate the Cabibbo-Kobayashi-Maskawa (CKM) matrix for the quark mixing. Certain effective dimension-5 operators are introduced, which induce a deviation of the lepton mixing matrix from the tribimaximal mixing (TBM) pattern and lead the quark mixing matrix to the CKM one in form. We explicitly demonstrate three different possibilities of constructing the charged lepton mixing matrix and point out that the {\it phases} of whose elements play a crucial role to satisfy the QLC relations. We find that for the reactor mixing angle $θ_{13}$ its possible values can vary around the center value $\sin θ_{13} \simeq λ/\sqrt{2}$ ($λ\simeq 0.22$ being the Cabbibo angle) and have the lower bound $θ_{13} \gtrsim 3.5^{\circ}$. We also show that sizable leptonic CP violation characterized by the Jarlskog invariant $|J_{\rm CP}|\sim{\cal O}(10^{-2})$ is allowed, which is expected to be tested in the future experiments such as the upcoming long baseline neutrino oscillation ones.

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