arXiv subjects
Publications and source records attributed to C. S. Kim.
We study the distribution function of the b-quark for inclusive semileptonic B decays in the framework of the parton model. We compare the functional behavior of the fragmentation inspired function and the Gaussian ACCMM function, and discuss their validity. Using the HQET parameters, we can critically test these models.
The T-odd top-quark chromoelectric dipole moment, $d_t$, is probed through top-quark-pair production via gluon fusion at the CERN LHC with the possibility of having polarized proton beams in account. At 1-$σ$ level, the typical CP-odd lepton energy and tensor correlations enable us to measure $Re(d_t)$ and $Im(d_t)$ up to the order of 10$^{-18}$ ($g_scm$) in the unpolarized case and the initial CP-odd gluon spin correlation allows us to probe $Im(d_t)$ up to the order of 10$^{-20}$ ($g_scm$) for $\sqrt{s}=14$ TeV and the integrated luminosity $L_{pp}=10 fb^{-1}$.
At the first PPPP workshop, I gave a review talk on physics of B and CP-phases. In my talk, I explained DRG method and our extension to extract CP angles $α$ and $γ$ from measurements of the decay rates of $B_{d,s}^0 \to ππ, πK, K K$. There are several advantages to this extension: discrete ambiguities are removed, fewer assumptions are necessary, and the method works even if all strong phases vanish. I also talked on several other topics.
We study the potential impacts of a new type of particle collider -- an $eμ$ collider -- on the search for new physics beyond the Standard Model. As our first attempt for exploring its physics potential, we demonstrate that the the $eμ$ collision experiment can be highly efficient in searching for lepton-number-violating Flavor Changing Neutral Current phenomena.
There is a widespread belief that the general two-Higgs-doublet model (G2HDM) behaves unnaturally with respect to evolution of the flavor-changing neutral Yukawa coupling parameters (FCNYCP's) -- i.e., that the latter, although being suppressed at low energies of probes, in general increase by a large factor as the energy of probes increases. We investigate this, by evolving Yukawa parameters by one-loop renormalization group equations (RGE's) and neglecting contributions of the first quark generation. For patterns of FCNYCP suppression at low energies suggested by the existing quark mass hierarchies, FCNYCP's remain remarkably stable (suppressed) up to energies very close to the Landau pole. This indicates that G2HDM preserves FCNYCP suppression, for reasonably chosen patterns of that suppression at low energies.
We propose a new method for precise determination of |V_{td} / V_{ub}| from the ratios of branching ratios BR(B -> ρν\bar ν) / BR(B ->ρl ν) and BR(B -> πν\bar ν) / BR(B -> πl ν). These ratios depend only on the ratio of the Cabibbo-Kobayashi-Maskawa (CKM) elements |V_{td} / V_{ub}|$ with little theoretical uncertainty, when very small isospin breaking effects are neglected. As is well known, |V_{td} / V_{ub}| equals to (\sin γ) / (\sin β) for the CKM version of CP-violation within the Standard Model. We also give in detail analytical and numerical results on the differential decay width dΓ(B -> K^* ν\bar ν) / dq^2 and the ratio of the differential rates dBR(B -> ρν\bar ν)/dq^2 / dBR(B -> K^* ν\bar ν)/dq^2 as well as BR(B -> ρν\bar ν) / BR(B -> K^* ν\bar ν) and BR(B -> πν\bar ν) / BR(B -> K ν\bar ν).
In order to determine the ratio of CKM matrix elements |V_{ub}/V_{cb}| (and |V_{ub}|), we propose a new model-independent method based on the heavy quark effective theory, which is theoretically described by the phase space factor and the well-known perturbative QCD correction only. In the forthcoming asymmetric B-experiments with microvertex detectors, BABAR and BELLE, the total separation of b --> u semileptonic decays from the dominant b --> c semileptonic decays would be experimentally viable. We explore the possible experimental option: the measurement of inclusive hadronic invariant mass distributions. We also clarify the relevant experimental backgrounds.
Non-perturbative parameters to the order ${\cal O}({1 \over m_Q})$ in HQET expansion, $\bar{ Λ}$, $λ_1$ and $λ_2$, as well as the masses, $m_b$ and $m_c$, are estimated phenomenologically from $B$ and $D$ meson system spectroscopy. We found relatively large value of $m_b$ and quite small value of $\bar{ Λ}$ compared to previous estimates.
Dighe, Gronau and Rosner have shown that, by assuming SU(3) flavor symmetry and first-order SU(3) breaking, it is possible to extract the CP angles αand γfrom measurements of the decay rates of B_d^0(t) --> π^+π^-, B_d^0 --> π^- K^+ and B^+ --> π^+ K^0, along with their charge-conjugate processes. We extend their analysis to include the SU(3)-related decays B_s^0 --> π^+ K^-, B_s^0(t) --> K^+ K^- and B_s^0 --> K^0 {\bar K^0}. There are several advantages to this extension: discrete ambiguities are removed, fewer assumptions are necessary, and the method works even if all strong phases vanish. In addition, we show that γcan be obtained cleanly, with no penguin contamination, by using the two decays B_s^0(t) --> K^+ K^- and B_s^0 --> K^0 {\bar K^0}.
We propose a new method to extract |Vtd/Vts| from the ratio of the decay distributions dR/ds = dB(B->Xdl+l-)/ds/dB(B->Xsl+l-)/ds. This ratio depends only on the KM ratio |Vtd/Vts| with 15% theoretical uncertainties, if dilepton invariant mass-squared s is away from the peaks of the possible resonance states, J/psi, psiprime, and etc. We also give a detailed analytical and numerical analysis on dB(B-Xql+l-)/ds (q=d,s) and dR/ds.
Based on experimental mass hierarchy, a set of flavor-democratic (FD) quark mass matrices at low energies is discussed. The model predicts CP violation parameters $J_{CP}=(0.3 \pm 0.2) 10^{-4}$ and ${ε'/ε} = (0.6 \pm 0.5) 10^{-3}$. However, this simple FD model also predicts a physical top quark mass not much higher than 100 GeV. As a next step, we assume that the Standard Model (SM) breaks down around some high energy $Λ$, and is replaced by a new FD flavor gauge theory (FGT). This possibility can be investigated by studying renormalization group equations for the Yukawa couplings of the SM with two Higgs doublets for various $m_t$ and VEV ratios $v_U/v_D$. With appropriate flavor-democratic boundary conditions at $Λ_{FGT}$, bounds on masses of top quark and tau-neutrino are derived, which are compatible with experimental bounds.
We derive one-loop renormalization group equations (RGE's) for Yukawa coupling parameters of quarks and for the vacuum expectation values of the Higgs doublets in a general framework of the Standard Model with two Higgs doublets (2HDM ``type III''). In the model, the neutral-Higgs-mediated flavor-changing neutral currents are allowed but are assumed to be reasonably suppressed at low energies. The popular ``type II'' and ``type I'' models are just special cases of this framework. We also present a numerical example for the RGE flow of Yukawa coupling parameters and masses of quarks. Detailed investigation, through RGE's, of connection between the low energy and the high energy structure of these 2HDM's would give us some additional insights into the viability of such frameworks, i.e., it would tell us for which choices of phenomenologically acceptable values of low energy parameters such frameworks can be regarded as reasonably natural (without excessive changes in the parameter structure as energy of probes increases over a wide range). Furthermore, such analyses could provide us with possible signals of new physics at high energies.
We derive the virial theorem of the relativistic two-body system for the study of the B-meson physics. It is also shown that the solution of the variational equation always satisfies the virial theorem. From the virial theorem we also obtained $μ_π^2 \equiv -λ_1 \equiv < p^2> = 0.40\sim 0.58$ GeV$^2$, which is consistent with the result of the QCD sum rule calculations of Ball $et$ $al.$
The T-odd top-quark chromoelectric dipole moment (tCEDM) is probed through top-quark-pair production via gluon fusion at the CERN Large Hadron Collider (LHC) by considering the possibility of having polarized protons. The complete analytic expressions for the tree-level helicity amplitudes of gg-> ttbar is also presented. For the derived analytic results we determine the 1-sigma statistical sensitivities to the tCEDM form factor for (i) typical CP-odd observables composed of lepton and anti-lepton momenta from t and tbar semileptonic decays for unpolarized protons, and (ii) a CP-odd event asymmetry for polarized protons by using the so-called Berger-Qiu (BQ) parametrization of polarized gluon distribution functions. We find that at the CERN LHC, the CP-odd energy and angular correlations can put a limit of 10^{-18} to 10^{-17} g_scm on the real and imaginary parts of the tCEDM, while the simple CP-odd event asymmetry with polarized protons could put a very strong limit of 10^{-20} g_scm on the imaginary part of the tCEDM.
We propose a new method to extract the value of |Vtd/Vts| from the ratio of the decay distributions dBr/ds[B->Xd l^+ l^-}] and dBr/ds[B Xs l^+ l^-].
We provide a detailed, model-independent, study for CP violation effects due to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment (WDM) in the top-quark pair production via $e^+e^-$ and two-photon annihilation at a next $e^+e^-$ linear collider (NLC). There are two methods in detecting CP violation effects in these processes. One method makes use of measurements of various spin correlations in the final decay products of the produced top-quark pair, while the other is to measure various CP-odd polarization asymmetry effects of the initial states. In the $e^+e^-$ case only the first method can be used, and in the $γγ$ case both methods can be employed. We provide a complete classification of angular correlations of the $t$ and $\bar{t}$ decay products under CP and CP\tilde{T} which greatly faciliate CP tests in the $e^+e^-$ mode. Concentrating on the second method with the Compton back-scattered high-energetic laser light off the electron or positron beam in the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial polarization configurations and apply them to investigating CP-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the 1-σsensitivities to the top-quark EDM and WDM in the $e^+e^-$ mode and the two-photon mode. Some model expectation values of the T-odd parameters are compared with the results.
Recent CDF data of the inclusive jet cross section shows threshold-like structured deviation, around transverse momentum $E_T(j)\approx 200 \sim 350$ GeV. If this data is real, not just some statistical fluctuation, is it possible to interpret the anomaly in terms of virtual SUSY effects? The purpose of this note is to address this question. However, we find that virtual SUSY loop interference effects [near the threshold] are too small to explain the CDF data. Our main conclusion seems to be on the right track if we assume that the recent global analysis of improved parton distributions by Lai et al. is correct. PACS number(s): 14.65.Ha, 12.38.Bx, 12.60.Jv, 13.85.-t
I first introduce the importance of measuring V_ub precisely. Then, from a theoretician's point of view, I review (a) past history, (b) present trials, and (c) possible future alternatives on measuring |V_ub| and/or |V_ub/V_cb|. As of my main topic, I introduce a model-independent method, which predicts Γ(B -> X_u l ν) / Γ(B -> X_c l ν) \equiv (γ_u / γ_c) \times | V_{ub} / V_{cb}|^2 \simeq (1.83 \pm 0.28) \times |V_ub / V_cb|^2 and |V_ub/V_cb| \equiv (γ_c / γ_u)^{1/2} \times [{\cal{B}}(B -> X_u l ν)/{\cal{B}}(B -> X_c l ν)]^{1/2} \simeq (0.74 \pm 0.06) \times [{\cal{B}}(B -> X_u l ν)/ {\cal{B}}(B -> X_c l ν)]^{1/2}, based on the heavy quark effective theory. I also explore the possible experimental options to separate B -> X_u l νfrom the dominant B -> X_c l ν: the measurement of inclusive hadronic invariant mass distributions, and the `D - π' (and `K - π') separation conditions. I also clarify the relevant experimental backgrounds.