http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Resumming Relativistic Corrections to Γ[J/ψ→e+e-]
Chaehyun Yu,Jungil Lee,Hee Sok Chung 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.2
We calculate the relativistic corrections to the color-singlet contributions to the leptonic decay width of the spin-triplet $S$-wave heavy quarkonium resummed to all orders in $v$. The formula is obtained by using the threshold-expansion method and is consistent with that based on the exact spin-projection operator. The color-singlet nonrelativistic quantum chromodynamics (NRQCD) matrix elements for the $J/\psi$ and $\psi(2S)$ mesons are determined by comparing the resummed formula with the measured leptonic decay widths of the two charmonia. A significant enhancement of the numerical values for the NRQCD matrix elements may result in a large increase in the theoretical predictions for the color-singlet contributions to the $S$-wave charmonium production cross-sections.
Resummation of Relativistic Corrections to ηc → γγ
Chaehyun Yu,Jungil Lee,Hee Sok Chung 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.1
By using the threshold-expansion approach, we compute the relativistic corrections to the two-photon decay width of a spin-singlet $S$-wave heavy quarkonium. The corrections are resummed to all orders in the heavy-quark velocity $v$ in the quarkonium-rest frame, where we keep all the contributions of the color-singlet $Q\bar{Q}$ potential. Our result agrees with a previous derivation based on the exact spin-projector approach. We also discuss the phenomenological implications of the resummed formula. By using the threshold-expansion approach, we compute the relativistic corrections to the two-photon decay width of a spin-singlet $S$-wave heavy quarkonium. The corrections are resummed to all orders in the heavy-quark velocity $v$ in the quarkonium-rest frame, where we keep all the contributions of the color-singlet $Q\bar{Q}$ potential. Our result agrees with a previous derivation based on the exact spin-projector approach. We also discuss the phenomenological implications of the resummed formula.
Time-independent perturbation theory with Lagrange multipliers
Yu Chaehyun,Jung Dong-Won,Kim U-Rae,Lee Jungil 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.12
We derive the formulas for the energy and wavefunction of the time-independent Schrödinger equation with perturbation in a compact form. Unlike the conventional approaches based on Rayleigh–Schrödinger or Brillouin–Wigner perturbation theories, we employ a recently developed approach of matrix-valued Lagrange multipliers that regularizes an eigenproblem. The Lagrange-multiplier regularization makes the characteristic matrix for an eigenproblem invertible. After applying the constraint equation to recover the original equation, we find the solutions of the energy and wavefunction consistent with the conventional approaches. This formalism does not rely on an iterative way and the order-by-order corrections are easily obtained by taking the Taylor expansion. The Lagrange-multiplier regularization formalism for perturbation theory presented in this paper is completely new and can be extended to the degenerate perturbation theory in a straightforward manner. We expect that this new formalism is also pedagogically useful to give insights on the perturbation theory in quantum mechanics.
QCD Radiative Corrections to J/ψ Leptonic Decay by Using the Scalar-Integral Reduction Method
Jungil Lee,Chaehyun Yu 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
We study the scalar-integral reduction method, which uses the integration-by-parts method, in calculating s corrections to heavy-quarkonium amplitudes. We apply this method to leptonic decay of the spin-triplet S-wave heavy quarkonium as an illustrative example. All possible scalar integrals are reduced into a single master integral in the J=A ! `+`¡ decay at this order. One drawback of this method is that one cannot avoid a mixture of ultraviolet (UV) and infrared (IR) poles during the reduction. We show a way to classify the origin of divergences in loop integrals in the scalar-integral reduction method. We expect this method to be useful in constructing a fast algebraic algorithm for QCD radiative corrections to quarkonium processes.
One-Loop Master Integral for Order-v2n Relativistic Corrections Γ[J/ψ→e+e-]
Jungil Lee,Chaehyun Yu,Hyeon-Kyun Noh 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.2
We show that one-loop scalar integrals contributing to the order-$v^{2n}$ relativistic corrections to the QCD vertex corrections to the spin-triplet $S$-wave heavy-quark-antiquark pair annihilation into a virtual photon can be expressed in terms of a single master integral. With an algebraic reduction combined with the tensor-integral reduction method, we first simplify the scalar integrals as linear combinations of two-point functions. The two-point functions are reduced into a single master integral by using the recurrence relations derived from integration by parts. Order-$v^2$ formulas are explicitly derived, and a strategy to calculate the higher-order relativistic corrections at order $\alpha_s$ is also given. The result may be very useful in calculating the order-$v^{2n}$ relativistic corrections to the leptonic decay width of the spin-triplet $S$-wave heavy quarkonium at order $\alpha_s$.
Probing a new strongly interacting sector via composite diboson resonances
Ko, P.,Yu, Chaehyun,Yuan, Tzu-Chiang American Physical Society 2017 Physical Review D Vol.95 No.11
<P>Diphoton resonance was a crucial discovery mode for the 125 GeV Standard Model Higgs boson at the Large Hadron Collider (LHC). This mode or the more general diboson modes may also play an important role in probing for new physics beyond the Standard Model. In this paper, we consider the possibility that a diphoton resonance is due to a composite scalar or pseudoscalar boson, whose constituents are either new hyperquarks Q or scalar hyperquarks (Q) over tilde confined by a new hypercolor force at a confinement scale Lambda(h). Assuming the mass m(Q) (or m((Q) over tilde))>> Lambda(h), a diphoton resonance could be interpreted as either a Q (Q) over bar (S-1(0)) state eta(Q) with J(PC) = 0(-+) or a (Q) over tilde(Q) over tilde (+) (S-1(0)) state eta((Q) over tilde) with J(PC) = 0(++) For the Q (Q) over bar scenario, there will be a spintriplet partner psi(Q) which is slightly heavier than eta(Q) due to the hyperfine interactions mediated by hypercolor gluon exchange; while for the (Q) over bar(Q) over bar (+) scenario, the spin-triplet partner chi(Q) over tilde arises from higher radial excitation with nonzero orbital angular momentum. We consider productions and decays of eta(Q),eta(Q) over tilde,psi(Q),and psi((Q) over tilde) at the LHC using the nonrelativistic QCD factorization approach. We discuss how to test these scenarios by using the Drell-Yan process and the forward dijet azimuthal angular distributions to determine the JPC quantum number of the diphoton resonance. Constraints on the parameter space can be obtained by interpreting some of the small diphoton 'excesses' reported by the LHC as the composite scalar or pseudoscalar of the model. Another important test of the model is the presence of a nearby hypercolor-singlet but color-octet state like the S-1(0) state eta(8)(Q) or eta(8)((Q) over tilde), which can also be constrained by dijet or monojet plus monophoton data. Both possibilities of a large or small width of the resonance can be accommodated, depending on whether the hyper-glueball states are kinematically allowed in the final state or not.</P>