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P. Ko

Publications and source records attributed to P. Ko.

144 records · Page 8Linked to original sources
arXiv2001

Gluino-squark contributions to CP violations in the kaon system

Recently it was shown, within the mass insertion approximation (MIA), that the gluino mediated flavor changing neutral current (FCNC) interactions can saturate both epsilon_K and Re(epsilon'/epsilon_K) even for the real Cabibbo-Kobayashi-Maskawa (CKM) matrix through a single CP violating parameter (delta^d_12)_LL. In this work, we extend our previous analysis to the nonvanishing KM phase, and to the effective SUSY model where the MIA is no longer a good approximation. In our model, epsilon_K and B0 - B0 bar mixing can receive significant SUSY contributions. Therefore the usual constraints on rho and eta in the Wolfenstein parametrization of the CKM matrix can be relaxed except for the |V_ub/V_cb| from the semileptonic b -> u transition. This affects K -> pi nu nu bar and K_L -> mu+ mu- indirectly, even if they are not directly induced by gluino-mediated FCNC, while K_L -> pi0 e+ e- is influenced both directly and indirectly. Differences between our model and other SUSY models enhancing Re(epsilon'/epsilon_K) are discussed in detail.

hep-ph↗
arXiv2001

Muon Anomalous $g -2$ and Gauged $L_μ- L_τ$ Models

In this paper we study $Z'$ contribution to $g -2$ of the muon anomalous magnetic dipole moment in gauged $U(1)_{L_μ- L_τ}$ models. Here $L_i$ are the lepton numbers. We find that there are three classes of models which can produce a large value of $g-2$ to account for possible discrepancy between the experimental data and the Standard Model prediction. The three classes are: a) Models with an exact $U(1)_{L_μ- L_τ}$. In these models, $Z'$ is massless. The new gauge interaction coupling $e a/\cosθ_W$ is constrained to be $ 0.8\times 10^{-3} < |a| < 2.24\times 10^{-3}$. b) Models with broken $U(1)_{L_μ- L_τ}$ and the breaking scale is not related to electroweak symmetry breaking scale. The $Z'$ gauge boson is massive. The allowed range of the coupling and the $Z'$ mass are constrained, but $Z'$ mass can be large; And c) The $U(1)_{L_μ-L_τ}$ is broken and the breaking scale is related to the electroweak scale. In this case the $Z'$ mass is constrained to be $\sim 1.2$ GeV. We find that there are interesting experimental signatures in $μ^+μ^-\to μ^+μ^-, τ^+τ^-$ in these models.

hep-ph↗
arXiv2001

Radion Phenomenology in the Randall Sundrum Scenario

Phenomenology of a radion ($ϕ$) in the Randall-Sundrum scenario is discussed. The radion couples to the trace of energy momentum tensor of the standard model with a strength suppressed only by a new scale ($Λ_ϕ$) which is an order of the electroweak scale. In particular, the effective coupling of a radion to two gluons is enhanced due to the trace anomaly of QCD. Therefore, its production cross section at hadron colliders could be enhanced, and the dominant decay mode of a relatively light radion is $ϕ\to g g$, unlike the SM Higgs boson case. We also present constraints on the mass $m_ϕ$ and the new scale $Λ_ϕ$ from the Higgs search limit at LEP, perturbative unitarity bound and the stability of the radion/Higgs potential under radiative corrections.

hep-ph↗
arXiv2000

Fully supersymmetric CP violations in the kaon system

We show that, on the contrary to the usual claims, fully supersymmetric CP violations in the kaon system are possible through the gluino mediated flavor changing interactions. Both $ε_K$ and ${\rm Re} (ε' / ε_K)$ can be accommodated for relatively large $\tanβ$ without any fine tunings or contradictions to the FCNC and EDM constraints.

hep-ph↗
arXiv2000

Fully supersymmetric CP violations in the kaon system

We show that, on the contrary to the usual claims, fully supersymmetric CP violations in the kaon system are possible through the gluino mediated flavor changing interactions. Both $ε_K$ and ${\rm Re} (ε' / ε_K)$ can be accommodated for relatively large $\tanβ$ without any fine tunings or contradictions to the FCNC and EDM constraints.

hep-ph↗
arXiv2000

Phenomenology of the radion in Randall-Sundrum scenario at colliders

Phenomenology of a radion ($ϕ$) that stabilizes the modulus in the Randall-Sundrum scenario is considered. The radion couples to the trace of energy momentum tensor of the standard model (SM) with a strength suppressed only by a new scale ($Λ_ϕ$) of an order of the electroweak scale. In particular, the effective coupling of a radion to two gluons are enhanced due to the trace anomaly of QCD. Therefore, its production cross section at hadron colliders could be enhanced, and the dominant decay mode of a relatively light radion is $ϕ$ -> g g, unlike the SM Higgs boson case. We also present constraints on the mass $m_ϕ$ and the new scale $Λ_ϕ$ from the Higgs search limit at LEP and perturbative unitarity bound.

hep-ph↗
arXiv1999

Effects of $A_t$ and $μ$ phases on B and K physics in the effective supersymmetric models

In the minimal supersymmetric standard model (MSSM), the $μ-$parameter and the trilinear coupling $A_t$ may be generically complex and can affect various observables at B factories. Working in the effective SUSY models and imposing the edm constraints from Chang-Keung-Pilaftsis (CKP) mechanism, we find that (i) there is no new large phase shift in the $B^0 - \bar{B^0}$ mixing from the A_t and $μ$ phases, (ii) CP violating dilepton asymmetry is smaller than 0.1%, (iii) the direct CP violation in $B\to X_s γ$ can be as large as $\sim \pm 16 %$, (iv) the ${\rm Br} (B\to X_s l^+ l^-)$ can be enhanced by upto $\sim 85 %$ compared to the standard model (SM) prediction, and its correlation with ${\rm Br} (B \to X_s γ)$ is distinctly different from the minimal supergravity scenario. Also, we find $1 \leq ε_K / ε_K^{SM} \leq 1.4$, and $ε_K$ cannot be saturated by the A_t and $μ$ phases alone : namely, $|ε_K^{\rm SUSY}| \leq O(10^{-5})$ if the phases of $μ$ and A_t are the sole origin of CP violation.

hep-ph↗
arXiv1999

Possible New Physics Signals in b -> s gamma and b -> s l^+ l^-

We consider possible new physics contributions to b\to s l^+ l^- assuming the new physics modifies (chromo)magnetic and electric form factors in b\to s γ^* and b\to s g with the same chirality structure as in the standard model. Parametrizing the new physics effects on b\to s γ^* and b\to s g in terms of four real parameters, one finds that there are enough region of parameter space in which the measured branching ratio for B \to X_s γcan be accomodated, and the predicted CP violation effect could be as large as \sim 30%. Moreover, the branching ratio and the forward-backward asymmetry of a lepton in B \to X_s l^+ l^- and the tau polarization asymmetry in B \to X_s τ^+ τ^- can be deviated from the SM predictions by a factor of \sim 2, which can be accessible at B factories. We also discuss these observables in a specific class of supersymmetric models with gluino-mediated flavor changing neutral current (FCNC).

hep-ph↗
arXiv1998

Contribution of $b\to s gg$ through the QCD anomaly in exclusive decays $B \to (η',η) (K, K^{*})$

The charm content in $η'$ is estimated using the QCD U(1) axial anomaly applied to $b\to s g g \to η' s$. We find $f_{η'}^{(c)} \approx - 3.1$ MeV for $m_c = 1.3$ GeV. Our estimate agrees with other independent methods by Feldmann and Kroll, and Araki, Musakhanov and Toki. The resulting branching ratios for $B \to η' K$ in the generalized factorization model are marginally consistent with the CLEO data, although they are lower than the data by $\sim 2$.

hep-ph↗
arXiv1998

Polarized J/psi production at CLEO

Polarizations of the prompt $J/ψ$'s produced in the $e^+e^-$ annihilation at CLEO energy ($\sqrt{s} = 10.58$ GeV) are considered in the framework of NRQCD factorization formalism. We find that the $J/ψ$ polarization has strong dependence on the production mechanism. At CLEO energy, the most dominant $J/ψ$ production mechanism in the most phase space is the color-singlet mechanism, $e^+e^- \to J/ψ+gg$, for which $J/ψ$'s are highly longitudinally polarized. On the other hand, the dominant $J/ψ$ production mechanism at the upper end point of $J/ψ$ energy distribution is the color-octet process, $e^+e^- \to (c\bar{c})^{(8)} +g$, for which $J/ψ$'s are almost unpolarized. Thus, the measurement of the polarization of the end point $J/ψ$'s can give another test of color-octet mechanism, and constraint on the NRQCD matrix elements.

hep-ph↗
arXiv1998

Contribution of $b \to sgg$ through the QCD anomaly in exclusive decays $B^{\pm}\to (η^{\prime},η)(K^{\pm}, K^{*\pm})$ and $B^{0}\to (η^{\prime},η)(K^{0},K^{*0})$

We compute the decay rates for the exclusive decays $B^{\pm} \to (η^{\prime},η) (K^{\pm}, K^{*\pm})$ and $B^{0}\to (η^{\prime},η) (K^{0}, K^{*0})$ in a QCD-improved factorization framework by including the contribution from the process $b\to sgg \to s (η^{\prime}, η)$ through the QCD anomaly. This method provides an alternative estimate of the contribution $b \to s c\bar{c} \to s(η,η^\prime)$ to these decays as compared to the one using the intrinsic charm content of the $η^{\prime}$ and $η$ mesons determined through the decays $J/ψ\to (η,η^\prime ,η_c) γ$. The resulting branching ratios are compared with the CLEO data on $B^{\pm} \to η^{\prime} K^{\pm}$ and $B^{0} \to η^{\prime} K^{0}$ and predictions are made for the rest.

hep-ph↗
arXiv1998

Supersymmetric interpretation of high--$Q^2$ HERA events and other related issues

In the framework of the minimal supersymmetric standard model (MSSM) with $R-$parity violation, the high--$Q^2$ HERA events can be interpreted as the $s-$channel production of a single stop of $M_{\tilde{t}_1} \approx 200$ GeV, whose dominant decay modes are assumed to be the $R-$parity violating $e^+ + d $ and the $R-$parity conserving $χ^+ + b$. Assuming only one coupling $\bar{λ_{131}^{'}}$ is nonzero of order $\sim 0.04-0.12$, we find that (i) the high$-Q^2$ HERA events can be understood as an $s-$channel stop production with a subsequent decay into $e^+ + (single ~jet)$, and (ii) the ALEPH 4-jet events can be understood in the scenario suggested by Carena et al.. We briefly discuss other physics signals of this scenario at other places such as HERA, LEP200 and Tevatron. The best test for our scenario is to observe the stop decay into $χ^+ + b$ followed by $χ^+ \to \tilde{e}^+ + ν_e $ and $\tilde{e}^+ \to q + \bar{q}^{'}$ via the $R-$parity violating coupling.

hep-ph↗
arXiv1997

Color-octet mechanism and J/psi polarization at LEP

Polarized heavy quarkonium productions in $Z^0$ decays are considered. We find that polarizations of the produced quarkonia are independent of that of the parent Z^0 provided that one considers the energy distribution or the total production rate. Produced J/psi's via the color-octet and the color- singlet mechanisms are expected to be 19% and 29% longitudinally polarized, respectively. The energy dependence of eta_{1,8}(x)=\frac{dGamma_{1,8}^L}{dx} /\frac{dGamma_{1,8}}{d x} is very sensitive to the production mechanism, and therefore the measurement of η(x)_exp will be an independent probe of the color-octet mechanism.

hep-ph↗
arXiv1996

Color-octet heavy quarkonium productions in Z0 decays at LEP

We consider the energy and the polar angle distributions of J/ψ's produced via the color-singlet and the color-octet (^3S_1^{(8)}) mechanisms in Z^0 \to J/ψ+X at LEP. Since both distributions of the J/ψproduced via color-octet mechanism are significantly different from those via color-singlet mechanism, these observables can be used as tests of color-octet production mechanism for heavy quarkonia. We also discuss Z^0 \rightarrow Υ+ X and W \to J/ψ( or Υ) + X in brief.

hep-ph↗
arXiv1996

Color-octet mechanism in J/psi productions

I review recent developments in theoretical understandings of J/psi productions in various processes at Tevatron, B decay and J/psi photoproduction including the color-octet mechanism.

hep-ph↗
arXiv1995

Search for $η_{c}^{'}$ and $h_{c} (^{1}P_{1})$ states in the $e^+ e^-$ annihilations

Productions and decays of spin-singlet $S,P-$wave charmonium states, $η_{c}^{'}$ and $h_{c} (^{1}P_{1})$, in the $e^+ e^-$ annihilations are considered in the QCD multipole expansion with neglecting nonlocality in time coming from the color-octet intermediate states. Our approximation is opposite to the Kuang-Yan's model. The results are $B (ψ^{'} \rightarrow h_{c} + π^{0}) \approx 0.3 \%$, $B ( ψ^{'} \rightarrow η^{'} + γ) \approx 0.34 \%$, $Γ(η_{c}^{'} \rightarrow J/ψ+ γ) \approx 0.26$ keV and $Γ(h_{c} \rightarrow J/ψ+ π^{0}) \approx 2.5$ keV.

hep-ph↗