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H. S. Song

Publications and source records attributed to H. S. Song.

At least 37 records · Page 2Linked to original sources
arXiv2001

Probing large extra dimensions with spin configuration of top quark pair production at the JLC

We explore signatures of large extra dimensions with a polarized electron/positrn beam at the Joint Linear Collider (JLC). We point out that spin informations can be useful to study indirect signals for large extra dimensions due to spin-2 nature of Kaluza-Klein gravitons. The spin configurations of the top quark pair production at $e^+ e^-$ and $γγ$ collisions provide an unique testing ground to search for effects of the large extra dimensions. Especially we show the forward-backward asymmetry is a good probe at $e^+ e^- \to t \bar{t}$ process and we can define a new asymmetry observable effective for $γγ\to t \bar{t}$ process.

hep-ph↗
arXiv2001

Role of degenerate atomic levels in the entanglement and the decoherence

We studied the dispersive dissipation of denegerate-level atom interacting with a single linearly-polarized mode field. It is found that the degeneracy of the atomic level affects the dissipation bahavior of the system as well as the subsystems. The degeneracy of the atomic level augment the periods of entanglement and increase the degree of the maxima statistical mixture states.

quant-ph↗
arXiv2001

Muon anomalous magnetic moment and the stabilized Randall-Sundrum scenario

We study the effects of extra dimension on the muon anomalous magnetic moment in the stabilized Randall-Sundrum scenario. The effects of the Kaluza-Klein states heavier than the cut-off scale expected to be of order $Λ_π$ are neglected. Contribution from the spin-2 Kaluza-Klein states dominates over that from the spin-0 radion. The recent BNL E821 results impose a strict constraint on the parameter space of the model: $Λ_π\approx 0.4 - 2.1$ TeV with $k/ M_{\rm Pl} =0.01 - 0.1$. Small $k/M_{\rm Pl}$ is preferred if $Λ_π$ is TeV scale.

hep-ph↗
arXiv2001

Radion effects on the production of an intermediate-mass scalar and Z at LEP II

We have studied the $e^+ e^- \to Z ϕ_i \to Z jj$ process, where $ϕ_i$ is the Higgs and/or radion bosons. The implications of the radion effects on the preliminary ALEPH data are also discussed. The case of the lighter radion than Higgs boson is disfavored by the ALEPH analyses of the $b$ tagged four-jet data, since the radion predominantly decays into two gluon jets due to the QCD trace anomaly. If the radion is highly degenerate in mass with the Higgs, the cross section can be increased more than at one sigma level, with natural scale of the vacuum expectation value of the radion.

hep-ph↗
arXiv2000

Neutralino-Nucleus Elastic Cross Section in the Minimal Supersymmetric Standard Model with Explicit CP Violation

We study the elastic scattering of the lightest neutralino with a nucleus in the framework of the minimal supersymmetric standard model (MSSM) with explicit flavor preserving CP violation, including the one-loop CP-violating neutral Higgs-boson mixing effects induced dominantly by the CP phases in the top and bottom (s)quark sectors. We construct the most general form of the effective Lagrangian for the neutralino-nucleus scattering in the limit of vanishing momentum transfers and then we perform a comprehensive analysis of the effects of the complex CP phases on the mass spectra of the lightest neutralino, neutral Higgs bosons and top squarks, and on the the spin-dependent and spin-independent neutralino-nucleus scattering cross section for three neucleus targets F, Si and Ge. The CP phases can reduce or enhance the neutralino-nucleus cross sections significantly, depending on the values of the real parameters in the MSSM.

hep-ph↗
arXiv2000

Leading Isgur-Wise form factor of $Λ_b\toΛ_{c1}$ transition using QCD sum rules

The leading Isgur-Wise form factor $ξ(y)$ parametrizing the semileptonic transitions $Λ_b\toΛ^{1/2}_{c1}\ell\barν$ and $Λ_b\toΛ^{3/2}_{c1}\ell\barν$ is calculated by using the QCD sum rules in the framework of heavy quark effective theory, where $Λ^{1/2}_{c1}$ and $Λ^{3/2}_{c1}$ is the orbitally excited charmed baryon doublet with $J^P=(1^-/2,3^-/2)$. The interpolating currents with transverse covariant derivative are adopted for $Λ^{1/2}_{c1}$ and $Λ^{3/2}_{c1}$ in the analysis. The slope parameter $ρ^2$ in linear approximation of the Isgur-Wise function is obtained to be $ρ^2=2.01$, and the interception to be $ξ(1)=0.29$. The decay branching ratios are estimated.

hep-ph↗
arXiv2000

Probing Z' gauge boson with the spin configuration of top quark pair production at future $e^- e^+$ linear colliders

We explore the effects of extra neutral gauge boson involved in the supersymmetric E6 model on the spin configuration of the top quark pair produced at the polarized e- e+ collider. Generic mixing terms are considered including kinetic mixing terms as well as mass mixing. In the off-diagonal spin basis of the standard model, we show that the cross sections for the suppressed spin configurations can be enhanced with the effects of the Z' boson through the modification of the spin configuration of produced top quark pair enough to be measured in the Linear Colliders, which provides the way to observe the effects of Z' boson and discriminate the pattern of gauge group decomposition. It is pointed out that the kinetic mixing may dilute the effects of mass mixing terms, and we have to perform the combined analysis.

hep-ph↗
arXiv2000

Excited Heavy Baryon Masses from the 1/N_c Expansion of HQET

The mass spectra of the L=1 orbitally excited heavy baryons with light quarks in both the spin-flavor symmetric and the mixed representations are studied by the $1/N_c$ expansion method in the framework of the heavy quark effective theory. The mixing effect between the baryons in the two representations is also considered. The general pattern of the spectrum is predicted which will be verified by the experiments in the near future.

hep-ph↗
arXiv2000

Measuring MSSM CP-violating Phases through Spin Correlated Supersymmetric Tri-lepton Signatures at the Tevatron

We provide a detailed analysis of the supersymmetric tri-lepton signals for sparticle searches at the Tevatron in the minimal supersymmetric standard model with general CP-violating phases but without flavor mixing among sfermions of different generation. The stringent experimental constraints on the CP-violating phases from the electron and neutron electric dipole moments are included in the analysis for two exemplary scenarios of the SUSY parameters; one with decoupled first two generation sfermions and the other with non-decoupled sfermions. In both scenarios, the production cross section and the branching fractions of the leptonic chargino and neutralino decays are sensitive to CP-violating phases. The production-decay spin correlations lead to several non-trivial CP-even observables such as the lepton invariant mass distribution and the lepton angular distribution, and several interesting T-odd (CP-odd) momentum triple products. The possibility of measuring the CP-violating phases directly through those T-odd observables is investigated in detail.

hep-ph↗
arXiv2000

$1/m_Q$ and $1/N_c$ Expansions for Excited Heavy Baryons with Light Quarks in the Spin-Flavor Symmetric Representation

The mass spectrum of the L=1 orbitally excited heavy baryons with light quarks in the spin-flavor symmetric representation is studied by the $1/N_c$ expansion method in the framework of the heavy quark effective theory. The mixing effect from the baryons in the mixed representation is considered. The general pattern of the spectrum is predicted which will be verified by the experiments in the near future. The $1/m_Q$ and SU(3) corrections are also considered. Mass relations for the baryons $Λ_{c1}^{(*)}$, $Σ_{c1}^{(*)}$, $Ξ_{c1}^{(')(*)}$, and $Ω_{c1}^{(*)}$ are derived.

hep-ph↗
arXiv2000

Reconstructing the Chargino System at $e^+e^-$ Linear Colliders

In most supersymmetric theories charginos, $\tildeχ^\pm_{1,2}$, belong to the class of the lightest supersymmetric particles. The chargino system can be reconstructed completely in $e^+e^-$ collider experiments: $e^+e^-\to\tildeχ_i^+ \tildeχ_j^- [i,j=1,2]$. By measuring the total cross sections and the asymmetries with polarized beams, the chargino masses and the gaugino-higgsino mixing angles of these states can be determined accurately. If only the lightest charginos $\tildeχ_1^\pm$ are kinematically accessible in a first phase of the machine, transverse beam polarization or the measurement of chargino polarization in the final state is needed to determine the mixing angles. From these observables the fundamental SUSY parameters can be derived: the SU(2) gaugino mass $M_2$, the modulus and the cosine of the CP-violating phase of the higgsino mass parameter $μ$, and $\tanβ= v_2/v_1$, the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. The remaining two-fold ambiguity of the phase can be resolved by measuring the normal polarization of the charginos. Sum rules of the cross sections can be exploited to investigate the closure of the two-chargino system.

hep-ph↗
arXiv2000

QCD sum rule analysis of excited $Λ_c$ mass parameter

The mass parameter of orbitally excited $Λ_c$ baryons is calculated by using QCD sum rule in the framework of heavy quark effective theory. Two kinds of interpolating current for the excited heavy baryons are introduced. It is obtained that $\barΛ=1.08^{+0.095}_{-0.104}$ GeV for the non-derivative current and $\barΛ=1.06^{+0.090}_{-0.107}$ GeV for the current with derivative. These results are consistent with experimental data.

hep-ph↗
arXiv1999

Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders

Top quark pair production at photon-photon colliders is studied in low scale quantum gravity scenario. From the dependence of the cross sections on the spin configuration of the top quark and anti-quark, we introduce a new observable, top spin asymmetry. It is shown that there exists a special top spin basis where with the polarized parent electron beams the top spin asymmetry vanishes in the standard model but retains substantial values with the large extra dimension effects. We also present lower bounds of the quantum gravity scale $M_S$ from total cross sections with various combinations of the laser, electron beam, and top quark pair polarizations. The measurements of the top spin state $(t_\uparrow\bar{t}_\downarrow)$ with unpolarized initial beams are shown to be most effective, enhancing by about 5% the $M_S$ bounds with respect to totally unpolarized case.

hep-ph↗
arXiv1999

Spontaneous Violation of the CP Symmetry in the Higgs Sector of the Next-to-Minimal Supersymmetric Model

The spontaneous violation of the CP symmetry in the next-to-minimal supersymmetric standard Model (NMSSM) is investigated. It is found that the spontaneous violation of the CP symmetry can occur in the Higgs sector of the NMSSM for a wide region of the parameter space of the model, at the 1-loop level where the radiative corrections due to the top quark and scalar-top quark loops are found to generate the scalar-pseudoscalar mixings between the two Higgs doublets of the NMSSM. In our model, we assume that the masses of the left-handed and the right-handed scalar-top quarks are not degenerate. And we investigate our model anaytically: We derive analytical formulae of the 1-loop mass matrix for the neutral Higgs bosons. We calculate the upper bound on the lightest neutral Higgs boson mass under the assumption. It is found to be about 140 GeV for our choice of parameter values in the presence of the spontaneous violation of the CP symmetry in the NMSSM. Thus, the possibility of the spontaneous violation of the CP symmetry is not completely ruled out in the Higgs sector of the NMSSM if the masses of the left-handed and the right-handed scalar-top quarks are not degenerate. Further, the phenomenology of the $K$-${\bar K}$ mixing within the context of our model is studied. The lower bound on CP violating phase in the $K$-${\bar K}$ mixing is found to increase if either $\tanβ$ decreases or $A_t$ increases.

hep-ph↗
arXiv1999

$Λ_b\toΣ_c^{(*)}πl{\barν}$ in the heavy quark, chiral, and large $N_c$ limits

The decay of $Λ_b\toΣ_c^{(*)}πl{\barν}$ processes are calculated in the framework of heavy baryon chiral perturbation theory with help of the $1/N_c$ expansion. The decay rate distributions over $v\cdot v^{\prime}$ where $v$ and $v^{\prime}$ are the 4-vector velocities of $Λ_b$ and $Σ_c^{(*)}$ respectively, and over the pion and lepton energies are given. The decay branching ratios amount to about $1.21(0.971)%$ for $Λ_b\toΣ_cπl{\barν}$ and $0.798(0.640)%$ for $Λ_b\toΣ_c^*πl{\barν}$ by using the baryonic Isgur-Wise function predicted by QCD sum rule (large $N_c$ QCD).

hep-ph↗
arXiv1999

Color-octet mechanism in $γ+ p \to J/ψ+ X$

Photoproduction of $J/ψ$ is considered including the color-octet contributions from the various partial wave states, $^{2S+1}L_J$ = $^1S_0$, $^3S_1$ and $^3P_J$. The production cross section depends on three new nonperturbative parameters defined in NRQCD, called the color-octet matrix elements. Using the color-octet matrix elements determined by fitting the $J/ψ$ production at the Tevatron, we find that the color-octet($c\bar{c}) _{8}({^1S_0}~{\rm and~}~{^3P_J})$ contributions to the $J/ψ$ photoproductions at the fixed target experiments and HERA are too large compared to the data on $σ(γ+ p \to J/ψ+X)$ in the forward direction, the $z$ distribution of $J/ψ$. The $P_T^2$ distribution of $J/ψ$ and the total inelastic $J/ψ$ production rate as a function of $\sqrt{s_ {γp}}$ are predicted including color-octet contributions. We also briefly digress on the $B \to J/ψ+ X$ and observe the similar situation. This may be an indication that the color-octet matrix elements determined from the $J/ψ$ production at the Tevatron, especially $<0 | {\cal O}_{8}^ψ ({^1S_0}) | 0>$ and $<0 | {\cal O}_{8}^ψ ({^3P_J}) | 0>$, might have been overestimated by an order of magnitude.

hep-ph↗
arXiv1999

Polarization Effects on the $e+e- \to W^+W^-$ process with Large Extra Dimensions

We study large extra dimension effects on the polarizations of the $W$ pair and electron beam at the $e^+ e^-\to W^+ W^-$ process. It is shown that the measurements of the cross section for transversely polarized $W$ pair with the right-handed electron beam remarkably enhance the possibilities to see the low scale quantum gravity effects. Higher Linear Collider bounds on the string scale in this model can be obtained by using the left-handed electron beam.

hep-ph↗