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Y. Y. Keum

Publications and source records attributed to Y. Y. Keum.

15 recordsLinked to original sources
arXiv2010

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super $B$ factory, an asymmetric-energy $e^+e^-$ collider with a design luminosity of $8 \times 10^{35}$ cm$^{-2}$s$^{-1}$, which is around 50 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented.

hep-ex↗
arXiv2005

Theory of Neutrinos: A White Paper

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled ``The Neutrino Matrix'' accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

hep-ph↗
arXiv2004

Theory of Neutrinos

After a brief overview of the present knowledge of neutrino masses and mixing, we summarize what can be learned about physics beyond the standard model from the various proposed neutrino experiments. We also comment on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe as well as what can be learned from some experiments outside the domain of neutrinos.

hep-ph↗
arXiv2004

Working Group Report: Neutrino and Astroparticle Physics

This is the report of neutrino and astroparticle physics working group at WHEPP-8. We present the discussions carried out during the workshop on selected topics in the above fields and also indicate progress made subsequently. The neutrino physics subgroup studied the possibilites of constraining neutrino masses, mixing and CPT violation in lepton sector from future experiments. Neutrino mass models in the context of abelian horizontal symmetries, warped extra dimensions and in presence of triplet Higgs were studied. Effect of threshold corrections on radiative magnification of mixing angles was investigated. The astroparticle physics subgroup focused on how various particle physics inputs affect the CMBR fluctuation spectrum, and on brane cosmology. This report also contains an introduction on how to use the publicly available code CMBFAST to calculate the CMBR fluctuations.

hep-ph↗
arXiv2004

Physics at Super B Factory

This report presents the results of studies that investigate the physics reach at a Super B factory, an asymmetric-energy e^+e^- collider with a design luminosity of 5 x 10^35 cm^-2s^-1, which is around 40 times as large as the peak luminosity achieved by the KEKB collider. The studies focus on flavor physics and CP violation measurements that could be carried out in the LHC era. The physics motivation, key observables, measurement methods and expected precisions are presented. The sensitivity studies are a part of the activities associated with the preparation of a Letter of Intent for SuperKEKB, which has been submitted recently.

hep-ex↗
arXiv2002

Possible Large Direct CP Violations in Charmless B-Decays

We discuss the perturbative QCD approach for the exclusive two body B-meson decays to light mesons. We briefly review its ingredients and some important theoretical issues on factorization approach. We show numerical results which are compatible with present experimantal data for the charmless B-meson decays. Specailly we predict the possibility of large direct CP violation effects in $B^0 \to π^{+}π^{-}$ $(23\pm7 %)$ and $B^0\to K^{+}π^{-}$ $(-17\pm5%)$. In the last section we investigate two methods to determine the weak phases $ϕ_2$ and $ϕ_3$ from $B \to ππ,Kπ$ processes. We obtain bounds on $ϕ_2$ and $ϕ_3$ from present experimental measurements.

hep-ph↗
arXiv1995

A Model for the decay of the $D_s^{+}$ meson into three pions,

We propose a phenomenological two component model describing the decay amplitude of the process $D_s^{+} \ra 3 π$, whose rate has been found surprisingly large. The first component is a constant background $F_{NR}$, and the second one is a Breit-Wigner type amplitude associated to a quasi two body $f_0(980)$ $π^{+}$ state. We show that it is possible to reproduce the observed rate for $D_s^{+} \ra π^{+}π^{+}π^{-}$ as well as the two other measured branching ratios for the non resonant part and the resonant $f_0π^{+}$ one, with a common parameter $F_{NR}$. Predictions are given for the $D_s^{+} \ra π^{0}π^{0}π^{+}$ rates, as well as for the various $π^{+}$ and $π^{-}$, or $π^{0}$ and $π^{+}$ energy distributions for the two possible final states.

hep-ph↗
arXiv1995

SU(2) HEAVY FLAVOUR SYMMETRY FOR B -> K(K^*) HADRONIC FORM FACTORS

We show that the factorization assumption in colour-suppressed $B$ meson decays is not ruled out by experimental data on $B \ra K(K^*) + J/Ψ(Ψ^{'})$. The problem previously pointed out might be due to an inadequate choice of hadronic form factors. Within the Isgur-Wise SU(2) heavy flavour symmetry framework, we search for possible $q^2$-dependences of form factors that satisfy both the large longitudinal polarization $ρ_L$ observed in $B \ra K^* + J/Ψ$ and the relatively small ratio of rates $R_{J/Ψ} = Γ(B \ra K^* + J/Ψ)/Γ(B \ra K + J/Ψ)$. We find out that the puzzle could be essentially understood if the $A_1(q^2)$ form factor is frankly decreasing (instead of being almost constant or increasing as commonly assumed). Of course, the possibility of understanding experimental data is not necessarily a proof of factorization.

hep-ph↗
arXiv1995

Factorization and SU(2) Heavy Flavor Symmetry for B-Meson Decays Producing Charmonium

We show that the factorization assumption in color-suppressed $B$ meson decays is not ruled out by experimental data on $B \ra K(K^*) + J/Ψ(Ψ^{'})$. The problem previously pointed out might be due to an inadequate choice of hadronic form factors. Within the Isgur-Wise SU(2) heavy flavor symmetry framework, we search for possible $q^2$ dependence of form factors that are capable of explaining simultaneously the large longitudinal polarization $ρ_L$ observed in $B \ra K^* + J/Ψ$ and the relatively small ratio of rates $R_{J/Ψ} = Γ(B \ra K^* + J/Ψ)/Γ(B \ra K + J/Ψ)$. We find out that the puzzle could be essentially understood if the $A_1(q^2)$ form factor is frankly decreasing, instead of being almost constant or increasing as commonly assumed. Of course, the possibility of understanding experimental data is not necessarily a proof of factorization.

hep-ph↗
arXiv1994

On the determination of the relative sign of $a_1$ and $a_2$ from polarization measurements in $B^- \rightarrow ρ^- {D^*}^o$ decay

We point out that polarization measurements such as the longitudinal fraction and the transverse left-right asymmetry in the Bauer-Stech-Wirbel (BSW) class III processes involving two final vector mesons, $B^- \ra ρ^- {D^*}^o$ taken as an example, are useful in determining the relative sign as well as the relative magnitudes of the coefficients $a_1$ and $a_2$.

hep-ph↗
arXiv1994

Testing factorization in colour-suppressed beauty decays with the B -> η_c + K(K^*) modes

The large discrepancy recently observed between $B \ra J/Ψ+ K (K^*)$ data and commonly used hadronic form factor models might be due to a breakdown of the factorization assumption. By showing that the $B \ra η_c + K (K^*)$ rates can be calculated without relying on any form factor model, we propose a test of the factorization hypothesis. This test is free of possible uncertainties caused by final state interactions and $W$-exchange graph contributions. If factorization holds, the measurable ratio $Γ(B \ra η_c + K^*)/Γ(B \ra η_c + K )$ is predicted to be in the range from 0.18 to 0.95 when the CLEO II data on $B \ra J/Ψ+ K (K^*)$ are used.

hep-ph↗
arXiv1994

Implications of factorization for the determination of hadronic form factors in $D_s^+ \ra ϕ$ transition

Using factorization we determine the allowed domains of the ratios of form factors, $x = A_2(0)/A_1(0)$ and $y = V(0)/A_1(0)$, from the experimentally measured ratio $R_h \equiv Γ(D_s^+ \ra ϕρ^+)/Γ(D_s^+ \ra ϕπ^+)$ assuming three different scenarios for the $q^2$-dependence of the form factors. We find that the allowed domains overlap with those obtained by using the experimentally measured ratio $R_{s\ell} = Γ(D^+_s \ra ϕ\ell^+ ν_{\ell})/Γ(D^+_s \ra ϕπ^+)$ provided that the phenomenological parameter $a_1$ is $1.23$. Such a comparison presents a genuine test of factorization. We calculate the longitudinal polarization fraction, $Γ_L/Γ\equiv Γ(D_s^+ \ra ϕ_L ρ^+_L)/Γ(D_s^+ \ra ϕρ^+)$, in the three scenarios for the $q^2$-dependence of the form factors and emphasize the importance of measuring $Γ_L/Γ$. Finally we discuss the $q^2$-distribution of the semileptonic decay and find that it is rather insensitive to the scenarios for the $q^2$-dependence of the form factors, and unless very accurate data can be obtained it is unlikely to discriminate between the different scenarios. Useful information on the value of $x$ might be obtained by the magnitude of the $q^2$-distribution near $q^2 = 0$. However the most precise information on $x$ and $y$ would come from the knowledge of the longitudinal and left-right transverse polarizations of the final vector mesons in hadronic and/or semileptonic decays.

hep-ph↗
arXiv1994

On the Determination of $a_1$ and $a_2$ from Hadronic Two Body $B$ Decays

{}From Class I decays : $B^o \ra π^+ ( ρ^+ ) + D^- ( {D^*}^- )$, we determine $a_1$, and from Class III decays : $B^+ \ra π^+ ( ρ^+ ) + \ol{D}^o ( {\ol{D}^*}^o )$, we determine an allowed domain in the $( a_1, a_2 )$ plane. We find that within one standard deviation errors, the allowed band of $a_1$ from Class I decays is at least three standard deviations removed from the allowed domain $( a_1, a_2 )$ from Class III decays.If we expand the experimental errors to two standard deviations we do find a small intersection between the $a_1$ band and the allowed $( a_1, a_2 )$ domain. The results usually quoted in the literature lie in this intersection. We suggest : (1) an independent measurement of the branching ratio for the Class III decay, $B^+ \ra ρ^+ \ol{D}^o $, (2) a high-statistics measurement of the branching ratio of the Class I decay, $B \ra \ol{D} ( \ol{D}^* ) + D_s ( D_s^* )$ in both charged states, and (3) a measurement of the longitudinal polarization fraction in the Class III decay $B^+ \ra ρ^+ {\ol{D}^*}^o $ to shed more light on the questions involved .

hep-ph↗
arXiv1993

Possible huge enhancement in the radiative decay of the weal W boson into the charmed $D_{s} $ meson

We point out that the rare decay mode $W^{\pm} \rightarrow γ+ D^{\pm}_{s} $ could be spectacularly enhanced, with a branching ratio around $10^{-6} $ which is three order of magnitude larger than previous predictions. Its observation will determine the W boson mass with great accuracy, providing additional high precision tests of the standard model, as well as reveal eventual deviation from the trilinear non-abelian gauge coupling.

hep-ph↗