arXiv subjects

Sechul Oh

Publications and source records attributed to Sechul Oh.

51 records · Page 3Linked to original sources

arXiv2001

Determination of the CP violating weak phase $γ$ from the Decays $B \to D π$

We propose a new method to extract the CP violating weak phase $γ$ (the phase of $V_{ub}^*$) in the CKM paradigm of the Standard Model, using $B^- \rightarrow D^0 π^- \rightarrow f π^-$ and $B^- \rightarrow \bar D^0 π^- \rightarrow f π^-$ decays, where $f$ are final states such as $K^+ π^-$, $K^+ ρ^-$, $K ππ$, {\it etc.} We also study the experimental feasibility of our new method. With possibility of new phases in the CKM matrix, we re-examine some of the previously proposed methods to determine $γ$, and find that it would be in principle possible to identify $γ$ and a new phase angle $θ$ separately.

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arXiv2001

Determination of the CP Phase $γ$ with Possibility of New Physics

We propose a new method to extract the CP violating weak phase $γ$ in the CKM paradigm of the Standard Model, using $B^- \to D^0 π^- \to f π^-$ and $B^- \to \bar D^0 π^- \to f π^-$ decays, where $f$ are final states such as $K^+ π^-$, $K^+ ρ^-$, $K ππ$, {\it etc.} We also study the experimental feasibility of our new method. With possibility of new phases in the CKM matrix, we re-examine some of the previously proposed methods to determine $γ$, and find that it would be in principle possible to identify $γ$ and a new phase angle $θ$ separately.

hep-ph↗

arXiv2001

Charmless Hadronic Decays of B Mesons to a Pseudoscalar and a Tensor Meson

We study two-body charmless hadronic decays of $B$ mesons to a pseudoscalar meson ($P$) and a tensor meson ($T$) in the frameworks of both flavor SU(3) symmetry and generalized factorization. Certain ways to test validity of the generalized factorization are proposed, based on the flavor SU(3) analysis. We present a set of relations between a flavor SU(3) amplitude and a corresponding amplitude in the generalized factorization which bridge both approaches in $B \to PT$ decays. The branching ratios and CP asymmetries are calculated using the \emph{full} effective Hamiltonian including all the \emph{penguin} operators and the form factors obtained in the non-relativistic quark model of Isgur, Scora, Grinstein and Wise. We identify the decay modes in which the branching ratios and CP asymmetries are expected to be relatively large.

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arXiv2001

Charmless hadronic B decays and the recent CLEO data

In the light of recent experimental data from the CLEO Collaboration we study, the decays of B mesons to a pair of pseudoscalar (P) mesons, and a vector (V) meson and a pseudoscalar meson, in the framework of factorization. In order to obtain the best fit for the recent CLEO data, we critically examine the values of several input parameters to which the predictions are sensitive. These input parameters are the form factors, the strange quark mass, $ξ\equiv 1/ N_c$ (N_c is the effective number of color), the CKM matrix elements and in particular, the weak phase $γ$. It is possible to give a satisfactory account of the recent experimental results in $B \to PP$ and VP decays, with constrained values of a \emph{single} $ξ$. We identify the decay modes in which CP asymmetries are expected to be large.

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arXiv2000

A combined study of $b \to s γ$ and the muon anomalous magnetic moment in gauge-mediated supersymmetry breaking models

We study both the branching ratio for $b \to s γ$ decay and the muon anomalous magnetic moment, $a_μ \equiv (g-2)_μ /2$, in the minimal supersymmetric standard model with gauge-mediated supersymmetry breaking. Combining new experimental data on $a_μ$ and the branching ratio for $b \to s γ$, useful limits on the parameter space of these models are derived. In particular, we explicitly show that, with the presently available experimental data, constraints from the decay $b \to s γ$ are more stringent than those from $a_μ$ in broad region of the parameter space. We include the supersymmetric one-loop correction to the mass of $b$ quark, $m_b$, and find that in order to have a correct value of $m_b$, the region of large tan$β$ and $μ<0$ (in our convention) is not allowed in these models (if there are no further assumptions like $b - τ$ Yukawa coupling unification). The region of large tan$β$ and $μ>0$ is also strongly constrained. We present bounds on supersymmetric particle masses as a function of $\tan β$.

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arXiv1999

Constraints from the muon anomalous magnetic moment and $b \to s γ$ on gauge-mediated supersymmetry-breaking models

We present a combined study of the muon anomalous magnetic moment, $a_μ \equiv (g-2)_μ /2$, and $b \to s γ$ decay in the minimal supersymmetric standard model with gauge-mediated supersymmetry-breaking. Combining new experimental data on $a_μ$ and the branching ratio for $b \to s γ$, useful limits on the parameter space of these models are derived. Bounds on supersymmetric particle masses as a function of $\tan β$ are also presented.

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arXiv1999

Flavor SU(3) Symmetry and Factorization in B Decays to Two Charmless Vector Mesons

We first present a model-independent analysis using flavor SU(3) symmetry with SU(3) breaking effects in $B$ decays to two charmless vector mesons ($VV$) in the final state. In order to bridge the flavor SU(3) symmetry approach and the factorization approach in $B \to VV$ decays, we explicitly show how to translate each SU(3) amplitude into a corresponding amplitude in factorization. Various decay modes, including $B \to K^* ϕ$ which is so far the only $B \to VV$ mode having some experimental evidence, are discussed in both the SU(3) symmetry and factorization approaches. Within the generalized factorization approximation, the flavor SU(3) amplitudes and SU(3) breaking effects are numerically estimated as a function of the parameter $ξ\equiv 1/ N_c$ ($N_c$ the effective number of color).

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arXiv1998

Alpha_s and Gauge Coupling Unification in Flipped SU(5) Models with Gauge-Mediated Supersymmetry Breaking

We examine gauge coupling unification and prediction for $α_s (M_Z)$ in minimal flipped SU(5) with gauge-mediated supersymmetry breaking. We include threshold corrections at weak scale, messenger scale and unification scale, and explicitly show that in this model there can be either \emph{one-step} or \emph{two-step} gauge coupling unification, depending on unification-scale threshold corrections. The experimental value of $α_s (M_Z)$ constrains heavy particle masses in one-step unification. In the case of two-step unification, we examine the prediction for $α_s (M_Z)$ with two-loop, light, messenger and heavy threshold corrections, and find it to be compatible with the updated experimental data.

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arXiv1998

A Critical Study of B Decays to Light Pseudoscalar

Motivated by the large branching ratios observed for the process $B\toη^{\prime}K$, we examine critically all the ingredients that go into estimates of B decays into two light pseudoscalars. Within factorization approximation, we examine several assumptions on the input parameters that could have a strong bearing on the predictions. Among these are (i) the QCD scale $μ$ (ii) value of the form factors (iii) value of the light quark masses, and in particular $m_s$ (iv) the value $ξ=1/N_c$, (v) charm content of $η^{\prime}$. It is possible to account for all the data without invoking new physics, though future experiments will provide tighter constraints on the parameter space. We fin that CP violating asymmetries are in the observable range for some modes.

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arXiv1997

Branching Ratios and CP Asymmetries of B Decays to a Vector and a Pseudoscalar Meson

We consider two body decays of B meson into a light vector (V) and a pseudoscalar (P) meson. The constraint obtained from the $B\to P P$ modes on the parameter space of the input parameters is imposed also on $B\to V P$ modes. In particular we constrain $ξ\equiv (1/N_c)$ for those modes from recently measured $B\to ωK, ϕK$ and are able to get a satisfactory pictures for all modes where data exists. Modes that should be seen shortly and those with possibly large CP asymmetries are identified.

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arXiv1997

Constraints from $b \to s γ$ on gauge-mediated supersymmetry breaking models

We consider the branching ratio of $b \to sγ$ in gauge mediated supersymmetry breaking theories. Useful bounds on the parameter space of these models are derived from the experimental bounds on $b \to sγ$. Constraints on masses of NLSP are presented as a function of $tanβ$ and $M/Λ$ for $μ<0$ and $μ>0$.

hep-ph↗

arXiv1996

SUSY GUTs contributions and model independent extractions of CP phases

We consider the origin of new phases in supersymmetric grand unification model, and show how significant new contributions arise from the gluino mediated diagram. We then present a more general model independent analysis of various modes of B-decays suggested previously for measurement of the CKM phases and point out what they really measure. It is in principle possible to separate out all the phases.

hep-ph↗

arXiv1996

On Measuring CP Violating Phase $γ$ Using Neutral $B$ Decays

We propose two independent methods to determine the CKM phase $γ$ and the tree and penguin amplitudes using neutral $B$ decays, assuming that the phase $β$ is known. Based on flavor SU(3) symmetry and SU(3) breaking effect, one method uses the decay processes $B^0(t) \rightarrow π^0 K_S$, $B^0 \rightarrow ηK^0 \; (K_S \rightarrow ππ)$ and their charge-conjugate processes, and the other uses the processes $B^0(t) \rightarrow π^0 K_S$, $B^0 \rightarrow π^0 π^0$ and their charge-conjugate processes. From SU(3) breaking consideration, the latter method would be more useful.

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arXiv1996

Remarks on a Technique of Measuring CP phase $α$

We present a method to measure the CKM phase $α$ and the tree and penguin (strong and electroweak) amplitudes in $B \rightarrow ππ$ decays, based on isospin consideration and the weak assumption that all tree amplitudes have a common strong phase and all penguin amplitudes have a different common phase. The method needs only the time-independent measurements of the relevant decay rates in $B \rightarrow ππ$. We also propose a method to experimentally examine the validity of the assumption that all penguin amplitudes have the same strong phases, and to extract detailed informations about the hadronic matrix elements.

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arXiv1995

A Study of Some Methods for Measuring CKM CP Violating Phases

We study the influence of penguin (especially, electroweak penguin) effects on some methods of measuring the angles $α$, $β$, and $γ$ in the CKM unitarity triangle. We use next-to-leading order effective Hamiltonian, and present numerical estimates based on the factorization approximation. We find that some techniques suggested in the literature, especially for $α$ determination, are not workable in light of the electroweak penguin effects. Nevertheless, there are methods that would work for each angle determination. For angle $β$ we consider $B \rightarrow D^{+} D^{-}$ mode and estimate the penguin contamination. For angle $γ$ we consider a method based on SU(3) symmetry and carefully consider SU(3) breaking effects. We point out regions in the parameter space where this method could be used reliably.

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