arXiv subjects

K. T. Chao

Publications and source records attributed to K. T. Chao.

14 recordsLinked to original sources

arXiv2023

STCF Conceptual Design Report: Volume 1 -- Physics & Detector

The Super $τ$-Charm facility (STCF) is an electron-positron collider proposed by the Chinese particle physics community. It is designed to operate in a center-of-mass energy range from 2 to 7 GeV with a peak luminosity of $0.5\times 10^{35}{\rm cm}^{-2}{\rm s}^{-1}$ or higher. The STCF will produce a data sample about a factor of 100 larger than that by the present $τ$-Charm factory -- the BEPCII, providing a unique platform for exploring the asymmetry of matter-antimatter (charge-parity violation), in-depth studies of the internal structure of hadrons and the nature of non-perturbative strong interactions, as well as searching for exotic hadrons and physics beyond the Standard Model. The STCF project in China is under development with an extensive R\&D program. This document presents the physics opportunities at the STCF, describes conceptual designs of the STCF detector system, and discusses future plans for detector R\&D and physics case studies.

hep-ex↗

arXiv2016

$Υ(nS)$ and $χ_b(nP)$ production at hadron colliders in nonrelativistic QCD

$Υ(nS)$ and $χ_b(nP)$ (n=1,2,3) production at the LHC is studied at next-to-leading order in $α_s$ in nonrelativistic QCD. Feeddown contributions from higher $χ_b$ and $Υ$ states are all considered for lower $Υ$ cross sections and polarizations. The long distance matrix elements (LDMEs) are extracted from the yield data, and then used to make predictions for the $Υ(nS)$ polarizations, which are found to be consistent with the measured polarization data within errors. In particular, the $Υ(3S)$ polarization puzzle can be understood by a large feeddown contribution from $χ_b(3P)$ states. Our results may provide a good description for both cross sections and polarizations of prompt $Υ(nS)$ and $χ_b(nP)$ production at the LHC.

hep-ph↗

arXiv2015

Yields and polarizations of prompt $\jpsi$ and $\psits$ production in hadronic collisions

We give predictions of $\jpsi$ and $\psits$ yields and polarizations in prompt production at hadron colliders based on non-relativistic QCD factorization formula. We calculate short-distance coefficients of all important color-octet intermediate channels as well as color-singlet channels up to $\mathcal{O}(α_S^4)$, i.e. next-to-leading order in $α_S$. For prompt $\jpsi$ production, we also take into account feeddown contributions from $χ_{cJ}$(J=0,1,2) and $\psits$ decays. Color-singlet long-distance matrix elements (LDMEs) are estimated by using potential model, and color-octet LDMEs are extracted by fitting the Tevatron yield data only. The predictions are satisfactory for both yields and polarizations of prompt $\jpsi$ and prompt $\psits$ production at the Tevatron and the LHC. In particular, we find our predictions for polarizations of prompt $\jpsi$ production have only a little difference from our previous predictions for polarizations of direct $\jpsi$ production.

hep-ph↗

arXiv2008

Physics at BES-III

This physics book provides detailed discussions on important topics in $τ$-charm physics that will be explored during the next few years at \bes3 . Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and \DzDzb-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed.

hep-ex↗

arXiv2007

On Two-Body Decays of A Scalar Glueball

We study two body decays of a scalar glueball. We show that in QCD a spin-0 pure glueball (a state only with gluons) cannot decay into a pair of light quarks if chiral symmetry holds exactly, i.e., the decay amplitude is chirally suppressed. However, this chiral suppression does not materialize itself at the hadron level such as in decays into $π^+π^-$ and $K^+K^-$, because in perturbative QCD the glueball couples to two (but not one) light quark pairs that hadronize to two mesons. Using QCD factorization based on an effective Lagrangian, we show that the difference of hadronization into $ππ$ and $KK$ already leads to a large difference between ${\rm Br} (π^+π^-)$ and ${\rm Br}(K^+K^-)$, even the decay amplitude is not chirally suppressed. Moreover, the small ratio of $R={\rm Br}(ππ)/{\rm Br}(K\bar K)$ of $f_0(1710)$ measured in experiment does not imply $f_0(1710)$ to be a pure glueball. With our results it is helpful to understand the partonic contents if ${\rm Br}(ππ)$ or ${\rm Br}(K\bar K)$ is measured reliably.

hep-ph↗

arXiv2006

Next-to-Leading Order QCD Correction to $\bm{e^+ e^- \to J/ψ+ η_c}$ at $\sqrt {s}=10.6$GeV}

One of the most challenging open problems in heavy quarkonium physics is the double charm production in $e^+e^-$ annihilation at B factories. The measured cross section of $e^+ e^- \to J/ψ+ η_c$ is much larger than leading order (LO) theoretical predictions. With the nonrelativistic QCD factorization formalism, we calculate the next-to-leading order (NLO) QCD correction to this process. Taking all one-loop self-energy, triangle, box, and pentagon diagrams into account, and factoring the Coulomb-singular term into the $c\bar c$ bound state wave function, we get an ultraviolet and infrared finite correction to the cross section of $e^+e^-\to J/ψ+ η_c$ at $\sqrt{s} =10.6$ GeV. We find that the NLO QCD correction can substantially enhance the cross section with a K factor (the ratio of NLO to LO) of about 1.8-2.1; hence it greatly reduces the large discrepancy between theory and experiment. With $m_c=1.4{\rm GeV}$ and $μ=2m_c$, the NLO cross section is estimated to be 18.9 fb, which reaches to the lower bound of experiment.

hep-ph↗

arXiv2003

Understanding the $e^+e^-\to D^{()+}D^{()-}$ processes observed by Belle

We calculate the production cross sections for $D^{*+}D^{*-}$, $D^+D^{*-}$ and $D^+D^-$ in $e^+e^-$ annihilation through one virtual photon in the framework of perturbative QCD with constituent quarks. The calculated cross sections for $D^{*+}D^{*-}$ and $D^+D^{*-}$ production are roughly in agreement with the recent Belle data. The helicity decomposition for $D^{*}$ meson production is also calculated. The fraction of the $D^{*\pm}_LD^{*\mp}_T$ final state in $e^+e^-\to D^{*+}D^{*-}$ process is found to be 65%. The fraction of $DD^*_T$ production is 100% and $DD^*_L$ is forbidden in $e^+e^-$ annihilation through one virtual photon. We further consider $e^+e^-$ annihilation through two virtual photons, and then find the fraction of $DD^{*}_T$ in $e^+e^-\to DD^{*}$ process to be about 91%.

hep-ph↗

arXiv2002

Polarized J/psi production in deep inelastic scattering at HERA

We perform a calculation on the polarization of J/psi production in deep inelastic scattering in the HERA energy range. For the inclusive production distributions, we find that the color-singlet contributions are consistent with the experimental data in the major region of z (z>0.4). Only in low z regions, there are some hints of the need of the color-octet contributions to describe the experimental data. For the polarization of J/psi in DIS processes, we find the parameter alpha changes with Q^2. Especially, at higher Q^2, difference on alpha between color-singlet and color-octet contributions become more distinctive. In the two regions of lower and larger z, the polarization parameter alpha have different features. These properties can provide important information on the polarization mechanism for J/psi production.

hep-ph↗

arXiv2000

Color-singlet direct J/ψand ψ' production at Tevatron in the k_t factorization approach

Direct $J/ψ$ and $ψ'$ production rates at Tevatron are calculated in the $k_t$-factorization approach within the color-singlet model. In this approach, the production rates are enhanced by a factor of 20 compared to the naive collinear parton model. However, the theoretical predictions are still below the experimental data by at least one order of magnitude. This means that to explain charmonium productions at Tevatron, we still need to call for the contributions from color-octet channels or other production mechanisms.

hep-ph↗

arXiv1995

Gluonic and leptonic decays of heavy quarkonia and the determination of $α_s(m_c)$ and $α_s(m_b)$

QCD running coupling constant $α_s(m_c)$ and $α_s(m_b)$ are determined from heavy quarkonia $c\overline{c}$ and $b\overline{b}$ decays. The decay rates of $V\rightarrow 3g$ and $V\rightarrow e^+ e^-$ for $V=J/ψ$ and $Υ$ are estimated by taking into account both relativistic and QCD radiative corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism, and the decay rates are estimated by using the meson wavefunctions which are obtained with a QCD-inspired inter-quark potential. For the $V\rightarrow 3g$ decay we find the relativistic correction to be very large and to severely suppress the decay rate. Using the experimental values of ratio $R_g\equiv \frac {Γ(V\longrightarrow 3g)}% {Γ(V\longrightarrow e^{+}e^{-})}\approx 10,~32 $ for $V=J/ψ, ~Υ$ respectively, and the calculated widths , we find $α_{s}(m_c)=0.29\pm 0.02 $ and $α_s(m_b)=0.20\pm 0.02$. These values for the QCD running coupling constant are substantially enhanced, as compared with the ones obtained without relativistic corrections, and are consistent with the QCD scale parameter $Λ_{\overline {MS}}^{(4)}% \approx 200MeV$. We also find that these results are mainly due to kinematic corrections and not sensitive to the dynamical models.

hep-ph↗

arXiv1995

The quark axial vector coupling and heavy meson decays

Form factors and decay widths for $D^{\ast}\rightarrow D γ$ and $D^{\ast}\rightarrow D π$ decays are estimated in a relativistic constituent quark model. Relativistic corrections due to light quarks are found to be substantial and to suppress the vector and axial vector form factors. The CLEO experimental value of $R^0_γ\equiv Γ(D^{\ast 0}\rightarrow D^{0} γ)/ Γ(D^{\ast 0}\rightarrow D^{0} π^{0})=0.572\pm 0.057\pm 0.081$ is used to determine the quark axial vector coupling $g_A$, which is found to be $0.6-0.8$ for $m_u=(350-200) MeV$ correspondingly, as compared with the chiral model result $g_{A}= 0.8-0.9$. The heavy meson-pion strong coupling $g$ is found to be $0.4-0.6$, much smaller than $g=1$ which is expected in the large $N_{C}$ and nonrelativistic limit, but consistent with some heavy hadron chiral theory and QCD sum rule results. The failure of nonrelativistic treatment for the light quark in the heavy meson decays is also emphasized.

hep-ph↗

arXiv1995

$ξ(2230)$ is likely to be a glueball

On the basis of the recent results of $ξ(2230)\rightarrow π^+π^-, p\bar p$ and $ξ(2230)\rightarrow K^+K^-,~K_SK_S$, measured by the BES Collaboration in $J/ψ$ radiative decays, combined with the PS185 experiment of $p\bar p\rightarrow ξ(2230)\rightarrow K\bar K$, we argue that because of its very narrow partial decay widths to $ππ$ and $K\bar K$ ( less than $1~MeV$ ), its large production rate in $J/ψ$ radiative decays, and its flavor- symmetric couplings to $ππ$ and $K\bar K$, the $ξ(2230)$ is very likely to be a $J^{PC}=(even)^{++}$ glueball.

hep-ph↗

arXiv1995

Hadronic matrix elements and radiative $B\to K^{*}γ$ decay

Within the standard model, we calculate the radiative $B\rightarrow K^{\star}γ$ decay rate based on a Bethe-Salpeter description for the meson wave functions and the hadronic matrix elements. With a reasonable choice of parameters the branching ratio BR($B \rightarrow K^{\star}γ$) is found to be $(3.8-4.6)\times 10^{-5}$, which is in agreement with the CLEO experimental data. We also find with $m_{b}=5.12 GeV$ the ratio $R\equiv {Γ(B\rightarrow K^{\star}γ)}/{Γ(b\rightarrow sγ)}=(10-12)\%$, which can be slightly larger if a smaller $m_{b}$ is chosen. In this approach, the light degrees of freedom in mesons are treated as light constituent quarks with relativistic kinematics, and the form factors in the decay amplitude are essentially determined by the relativistic kenematics and the overlap of wave functions of the initial and final state mesons. Due to the large recoil momentum of the $K^{\star}$ meson at the $B$ meson rest frame, the form factors are sensitive to the overlap integral of the meson wave functions, which are determined dynamically by a QCD-motivated inter-quark potential. Relativistic effects on the meson wave functions mainly due to the Breit-Fermi interactions are found to be significant in determining the decay rate.

hep-ph↗

arXiv1995

Possible effects of color screening and large string tension in heavy quarkonium spectrum

Possible effects of the color screened confinement potential are investigated. Color screened linear potential with a large string tension $T=(0.26-0.32)GeV^2$ is suggested by a study of the $c\bar c$ and $b\bar b$ spectra. The $ψ(4160)$ and $ψ(4415)$ are respectively assigned as the $ψ(4S)$-dominated and the $ψ(5S)$ $c\bar c$ states. Satisfactory results for the masses and leptonic widths (with QCD radiative corrections) of $c\bar c$ and $b\bar b$ states are obtained.

hep-ph↗