서지주요정보
$b\bar{b}$ events in the $e^+e^-$ collision at Z resonance = Z 공명에서의 $e^+e^-$ 충돌에 의한 $b\bar{b}$ 사건들
서명 / 저자 $b\bar{b}$ events in the $e^+e^-$ collision at Z resonance = Z 공명에서의 $e^+e^-$ 충돌에 의한 $b\bar{b}$ 사건들 / Yeong-Gyun Kim.
저자명 Kim, Yeong-Gyun ; 김영균
발행사항 [대전 : 한국과학기술원, 1997].
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8007535

소장위치/청구기호

학술문화관(문화관) 보존서고

DPH 97005

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초록정보

We study the some topics on the $b\bar{b}$ events in the $e^+e^-$ collision at Z resonance. According to the Standard Model, b quarks are produced almost completely longitudinally polarized at $\sqrt{s}\simeqM_Z$. Unfortunately, a measurement of $P_b$ is not as much straightforward. This is mainly due to hadronization and fragmentation properties b quarks that largely dilute and obscure b polarization effects in the observed final states. We suggest a strategy for detecting b polarization effects in the $e^+e^-$ collision on Z resonance. We select dilepton events in the $Z → b\bar{b}$ events, in which both b hadrons decay semileptonically. Then we catalog these events into the 'like-sign' events in which leptons have same charge and the 'unlike-sign' events in which leptons have different charge. Clearly the existence of the 'like-sign' events is a signal of b-$\bar{B}$ mixing. In the 'like-sign' events, one of the b hadrons must be a $B_s$ or $B_d$ meson. However this is not the case in the 'unlike-sign' events. So the fractions of $∧_b$ would be different for each types of events. Then we have two types of inclusive leptonic samples with different $∧_b$ fractions. With these dileptonic events, the several polarization-dependent variables are calculated. Using this method, the b polarization effects may be detected without large uncertainties of b fragmentation and $∧_b$ decay model. The inclusive semi-leptonic decays of b mesons are attracting a lot of attention as testing ground for hadronic models and as a source for the weak parameters $V_ub$ and $V_cb$. In general there are two kinds of models which predict the lepton energy spectrum of inclusive decays of b meson. In the ACCMM model, the free quark decay picture is improved by taking into account the Fermi motion of the spectator in the b-meson. The second approach uses the parton model at an infinite momentum frame(IMF). It pictures the mesonic decay as the decay of the partons. The probability of finding a b-quark in a b-meson carrying a fraction x of the mesons momentum in the IMF is given by the distribution function f(x). We study both of the model by comparing their own distribution functions. The distribution function of the ACCMM model is obtained in the infinite momentum frame to show the results consistently. We show that the definitions of b-quark mass which is consistent with the result of HQET are equivalent between both models. So the specific choice adopted in ACCMM model for the weight function φ(p) corresponds to a particular form of the distribution function f(x) in the parton model. Also we compare the behaviors of the distribution functions and obtain the heavy quark effective theory parameters in terms of each model parameters.

서지기타정보

서지기타정보
청구기호 {DPH 97005
형태사항 iv, 71 p. : 삽도 ; 26 cm
언어 영어
일반주기 저자명의 한글표기 : 김영균
지도교수의 영문표기 : Jae-Kwan Kim
지도교수의 한글표기 : 김재관
학위논문 학위논문(박사) - 한국과학기술원 : 물리학과,
서지주기 Reference : p. 57-61
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