arXiv subjects

Junegone Chay

Publications and source records attributed to Junegone Chay.

At least 37 records · Page 2Linked to original sources

arXiv2007

Probing electroweak physics using B -> XM decays in the endpoint region

Using soft-collinear effective theory we describe at leading order in 1/m_b all the semi-inclusive hadronic B -> XM decays near the endpoint, where an energetic light meson M recoils against an inclusive jet X. We also include the decays involving eta, eta' mesons that receive additional contributions from gluonic operators. The predicted branching ratios and CP asymmetries depend on fewer hadronic parameters than the corresponding two-body B decays. This makes semi-inclusive hadronic B -> XM decays a powerful probe of the potential nonperturbative nature of charming penguins as well as a useful probe of new physics effects in electroweak flavor changing transitions. A comparison with B -> KX data from BaBar points to an enhanced charming penguin, albeit with large experimental errors.

hep-ph↗

arXiv2006

Deep inelastic scattering near the endpoint in soft-collinear effective theory

We apply the soft-collinear effective theory (SCET) to deep inelastic scattering near the endpoint region. The forward scattering amplitude, and the structure functions are shown to factorize as a convolution of the Wilson coefficients, the jet functions, the parton distribution functions. The behavior of the parton distribution functions near the endpoint region is considered. It turns out that it evolves with the Altarelli-Parisi kernel even in the endpoint region, and the parton distribution function can be factorized further into a collinear part and the soft Wilson line. The factorized form for the structure functions is obtained by the two-step matching, and the radiative corrections or the evolution for each factorized part can be computed in perturbation theory. We present the radiative corrections of each factorized part to leading order in alpha_s, including the zero-bin subtraction for the collinear part.

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arXiv2006

Semi-inclusive hadronic B decays in the endpoint region

We consider in the soft-collinear effective theory semi-inclusive hadronic B decays, B-> XM, in which an energetic light meson M near the endpoint recoils against an inclusive jet X. We focus on a subset of decays where the spectator quark from the B meson ends up in the jet. The branching ratios and direct CP asymmetries are computed to next-to-leading order accuracy in alpha_s and to leading order in 1/m_b. The contribution of charming penguins is extensively discussed, and a method to extract it in semi-inclusive decays is suggested. Subleading 1/m_b corrections and SU(3) breaking effects are discussed.

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arXiv2005

SCET sum rules for heavy-to-light form factors

We consider a sum rule for heavy-to-light form factors in soft-collinear effective theory (SCET). Using the correlation function given by the time-ordered product of a heavy-to-light current and its hermitian conjugate, the heavy-to-light soft form factor zeta_P can be related to the leading-order B meson shape function. Using the scaling behavior of the heavy-to-light form factor in Lambda_QCD/m_b, we put a constraint on the behavior of the $B$ meson shape function near the endpoint. We employ the sum rule to estimate the size of zeta_P with the model for the shape function and find that it ranges from 0.01 to 0.07.

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arXiv2005

Quark mass effects in the soft-collinear effective theory and B -> X_s + photon in the endpoint region

We consider the effects of a light quark mass in the soft-collinear effective theory (SCET) and we apply them to B -> X_s gamma in the endpoint region. We find that the reparameterization invariance can be extended by including the collinear quark mass in the SCET Lagrangian. This symmetry constrains the theory with the quark mass terms, and we present explicit results at one loop. It also relates the Wilson coefficients of some mass operators to those of the leading operators, which are useful in organizing the subleading effects due to the quark mass in B -> X_s gamma. We present strange quark mass corrections to B -> X_s gamma in the endpoint region as an application. The forward scattering amplitude from the mass corrections is factorized, and it can be expressed as a convolution of the m_s^2/p_X^2-suppressed jet function and the leading-order shape function of the B meson. This contribution should be added to the existing subleading contributions from the B meson shape functions to obtain complete subleading corrections.

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arXiv2004

Soft Wilson lines in soft-collinear effective theory

The effects of the soft gluon emission in hard scattering processes at the phase boundary are resummed in the soft-collinear effective theory (SCET). In SCET, the soft gluon emission is decoupled from the energetic collinear part, and is obtained by the vacuum expectation value of the soft Wilson-line operator. The form of the soft Wilson lines is universal in deep inelastic scattering, in the Drell-Yan process, in the jet production from e+e- collisions, and in the gamma* gamma* -> pi0 process, but its analytic structure is slightly different in each process. The anomalous dimensions of the soft Wilson-line operators for these processes are computed along the light-like path at leading order in SCET and to first order in alpha_s, and the renormalization group behavior of the soft Wilson lines is discussed.

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arXiv2004

Gauge-invariant Lagrangian of the soft-collinear effective theory and its application to soft-collinear currents

We construct the soft-collinear effective Lagrangian which is manifestly gauge invariant order by order. Field redefinitions of collinear gauge fields and a proper decomposition of quark fields are necessary to make the Lagrangian gauge invariant. We can obtain the effective Lagrangian order by order in SCET_I and SCET_II by adopting appropriate power counting methods. Various types of current operators can be investigated using this formalism, and we choose the soft-collinear current as a specific example to present explicit radiative corrections. The hard-collinear, collinear, and ultrasoft modes in SCET_I and the collinear and soft modes in SCET_II reproduce the infrared divergences of the full theory and the matching can be performed. We show our results explicitly using two types of regularization schemes. The first scheme is the dimensional regularization both for the ultraviolet and the infrared divergences with on-shell particles, and the second scheme is regulating the infrared divergence with the off-shellness of external particles. We discuss other types of operators in terms of the two-step matching.

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arXiv2003

Factorization of B decays into two light mesons in soft-collinear effective theory

We show that the amplitudes for B decays into two light mesons at leading order in soft-collinear effective theory are factorized to all orders in alpha_s. We construct gauge-invariant four-quark operators by employing the effective theories SCET_I for sqrt{m_b Λ} <μ<m_b, and SCET_II for μ<sqrt{m_b Λ} with Lambda ~0.5 GeV. These operators do not allow gluon exchanges between different sectors of the current and the matrix elements are reduced to the products of current matrix elements. The spectator interactions are also factorized at leading order in SCET and to all orders in alpha_s.

hep-ph↗

arXiv2003

Nonleptonic B decays into two light mesons in soft-collinear effective theory

We consider nonleptonic B decays into two light mesons at leading order in soft-collinear effective theory, and show that the decay amplitudes are factorized to all orders in alpha_s. The operators for nonleptonic B decays in the full theory are first matched to the operators in SCET_I, which is the effective theory appropriate for sqrt{m_b Lambda} pi,pi in soft-collinear effective theory.

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arXiv2003

Rare radiative exclusive B decays in soft-collinear effective theory

We consider rare radiative B decays such as B -> K^* gamma or B -> rho gamma in soft-collinear effective theory, and show that the decay amplitudes are factorized to all orders in alpha_s and at leading order in Lambda/m_b.By employing two-step matching, we classify the operators for radiative B decays in powers of a small parameter lambda(~ \sqrt{Lambda/m_b}) and obtain the relevant operators to order lambda in SCET_I. These operators are constructed with or without spectator quarks including the four-quark operators contributing to annihilation and W-exchange channels. And we employ SCET_II where the small parameter becomes of order Lambda/m_b, and evolve the operators in order to compute the decay amplitudes for rare radiative decays in soft-collinear effective theory. We show explictly that the contributions from the annihilation channels and the W-exchange channels vanish at leading order in SCET. We present the factorized result for the decay amplitudes in rare radiative B decays at leading order in SCET, and at next-to-leading order in alpha_s.

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arXiv2002

Consequences of symmetries in renormalizing collinear effective theory

We consider effects of symmetries on renormalization properties of the collinear effective theory. We investigate which types of operators are possible in the effective theory satisfying gauge invariance, reparameterization invariance and residual energy invariance. Each symmetry puts a constraint on the possible structure of the theory, and there can appear only specific combinations of operators in the effective Lagrangian satisfying all the symmetry requirements. And the final effective Lagrangian is not renormalized to all orders in alpha_s as long as no other nonlocal operators are induced at higher order. We explicitly prove this at one loop by renormalizing one-gluon vertices and discuss their features.

hep-ph↗

arXiv2002

Symmetries in collinear effective theory

We consider various symmetries present in the collinear effective theory and their implications. There are collinear, soft and ultrasoft gauge symmetries and we discuss transformation properties of a collinear quark and gauge fields under these gauge transformations. If we require the gauge invariance order by order, the gauge fields have definite transformation properties. We also probe reparameterization invariance and residual energy invariance in the collinear effective theory and discuss their physical consequences.

hep-ph↗

arXiv2002

Collinear effective theory at subleading order and its application to heavy-light currents

We consider a collinear effective theory of highly energetic quarks with energy E, interacting with collinear and soft gluons by integrating out collinear degrees of freedom to subleading order. The collinear effective theory offers a systematic expansion in power series of a small parameter lambda ~ p_{\perp}/E, where p_{\perp} is the transverse momentum of a collinear particle. We construct the effective Lagrangian to first order in $λ$, and discuss its features including additional symmetries such as collinear gauge invariance and reparameterization invariance. Heavy-light currents can be matched from the full theory onto the operators in the collinear effective theory at one loop and to order lambda. We obtain heavy-light current operators in the effective theory, calculate their Wilson coefficients at this order, and the renormalization group equations for the Wilson coefficients are solved. As an application, we calculate the form factors for decays of B mesons to light energetic mesons to order lambda and at leading-logarithmic order in alpha_s.

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arXiv2001

QCD-improved factorization in nonleptonic B decays

I consider nonleptonic decays of B mesons into two light mesons using the light-cone wave functions for the mesons. In the heavy quark limit, nonfactorizable contributions are calculable from first principles in some decay modes. I review the idea of the QCD-improved factorization method and discuss the implications in phenomenology.

hep-ph↗

arXiv2000

Analysis of the QCD-improved factorization in B -> J/ψK

We consider the exclusive decay $B\to J/ψK$ using the QCD-improved factorization method in the heavy quark limit. It is shown that the decay amplitude is factorizable in this limit and nonfactorizable contributions are calculable from first principles in perturbation theory. Also the spectator contributions at order $α_s$ are finite and suppressed in the heavy quark limit. We present the result at next-to-leading order in strong interaction, and leading order in $1/m_b$ in the heavy quark limit.

hep-ph↗

arXiv2000

B to D(*) pi- beyond naive factorization in the heavy quark limit

Nonleptonic decays B to D pi- or B to D* pi- are dominated by factorizable contributions. In the heavy quark limit, nonfactorizable contribution arises from strong radiative correction and power corrections in 1/m_b. I calculate the decay rates for B to D(*) pi- at next-to-leading order in strong interaction, including nonfactorizable corrections. The result is expressed in terms of a convolution of the hard scattering amplitude and the pion wave function. The decay amplitudes in this method are independent of the gauge, the renormalization scale, and the renormalization scheme. The effects of the nonfactorizable contribution are discussed and numerical estimates are presented.

hep-ph↗

arXiv1999

Phenomenology of V_ub from Ratios of Inclusive B Decay Rates

We explore the theoretical feasibility of extracting V_ub from two ratios built from B meson inclusive partial decays, R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d). We discuss contributions to these quantities from perturbative and nonperturbative physics, and show that they can be computed with overall uncertainties at the level of 10%.

hep-ph↗

arXiv1998

Bounds of the mass of Z' and the neutral mixing angles in general SU(2)_L x SU(2)_R x U(1) models

We consider phenomenological constraints on the mass $M_{Z^{\prime}}$ and the two mixing angles $θ_R$ and $ξ$ of the neutral sector in a very general class of $SU(2)_L \times SU(2)_R \times U(1)$ models using electroweak data. We do not make any specific assumptions such as left-right symmetry or the Higgs structure. The analysis of the neutral sector has the advantage that it has relatively fewer parameters compared to the charged sector since the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements in the right-handed sector do not enter into the analysis, hence the number of various possibilities from a big parameter space is reduced. We utilize theoretical considerations on the masses of the gauge particles and the mixing angles. We combine the precision electroweak data from LEP I and the low-energy neutral-current experimental data to constrain the parameters introduced in the model. It turns out that $M_{Z^{\prime}}> 400$ GeV, $-0.0028 <ξ<0.0065$ with little constraint on $θ_R$. In the left-right symmetric theory, $M_{Z^{\prime}}$ should be larger than 900 GeV. With these constraints, we compare the values for $σ(e^+ e^- \to μ^+ μ^-)$, $σ(e^+ e^- \to b\bar{b})$ and $A_{FB}^{\ell}$ at LEP II with experimental values.

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