Biomedical subjects

K-F Chen

Publications and source records attributed to K-F Chen.

At least 19 recordsLinked to original sources

PubMed2006

Observation of new states decaying into Lambda(c)(+)Kappa(-)pi(+) and Lambda(c)(+)Kappa(0)/(s)pi(-).

We report the first observation of two charmed strange baryons that decay into Lambda(c)(+)Kappa(-)pi(+). The broader of the two states is measured to have a mass of 2978.5+/-2.1+/-2.0 MeV/c2 and a width of 43.5+/-7.5+/-7.0 MeV/c2. The mass and width of the narrow state are measured to be 3076.7+/-0.9+/-0.5 MeV/c;{2} and 6.2+/-1.2+/-0.8 MeV/c2, respectively. We also perform a search for the isospin partner states that decay into Lambda(c)(+)Kappa(0)/(s)pi(-) and observe a significant signal at the mass of 3082.8+/-1.8+/-1.5 MeV/c2. The data used for this analysis were accumulated at or near the Upsilon(4S) resonance, using the Belle detector at the e+ e- asymmetric-energy collider KEKB. The integrated luminosity of the data sample used is 461.5 fb(-1).

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PubMed2006

Observation of a near-threshold D(0)D[over](0)pi(0) enhancement in B-->D(0)D[over](0)pi(0)Kappa decay.

We report the first observation of a near-threshold enhancement in the D(0)D[over](0)pi(0) system from B-->D(0)D[over](0)pi(0)Kappa decays using a 414 fb(-1) data sample collected at the Upsilon(4S) resonance. The enhancement peaks at a mass M=3875.2+/-0.7(+0.3)/(-1.6) +/-0.8 MeV/c2 and the branching fraction for events in the peak is B(B-->D(0)D[over](0)pi(0)Kappa)=(1.22+/-0.31(+0.23)/(-0.30))x10(-4). The data were collected with the Belle detector at the KEKB energy-asymmetric e+ e- collider.

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PubMed2006

Evidence for large direct CP violation in B+/- --> rho(770)0K+/- from analysis of three-body charmless B+/- --> K+/-pi+/-pi+/- decays.

We report results on a Dalitz analysis of three-body charmless B+/- --> K+/-pi+/-pi+/- decay including searches for direct CP violation. We report the first observation of the decay B+/- --> f2(1270)K+/- with a statistical significance above 6sigma. We also observe first evidence for large direct CP violation in the B+/- --> rho(770)0K+/- channel. The results are obtained with a data sample that contains 386 10(6) BB pairs collected at the Y(4s) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider.

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PubMed2006

Observation of b-->dgamma and determination of /Vtd/Vts/.

We report the observation of the flavor-changing neutral current process b-->dgamma using a sample of 386 x 106 B meson pairs accumulated by the Belle detector at the KEKB e+e- collider. We measure branching fractions for the exclusive modes B--->rho-gamma, B0rho0gamma, and B0omegagamma. Assuming that these three modes are related by isospin, we find B(B-->(rho,gamma)gamma)=[Formula: See Text] with a significance of 5.1sigma. This result is used to determine the ratio of Cabibbo-Kobayashi-Maskawa matrix elements /Vtd/Vts/ to be [Formula: See Text].

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PubMed2005

Measurements of B decays to two kaons.

We report measurements of B meson decays to two kaons using 253 fb(-1) of data collected with the Belle detector at the KEKB energy-asymmetric e+ e- collider. We find evidence for signals in B+ --> K0 K+ and B0 --> K0 K0 with significances of 3.0sigma and 3.5sigma, respectively. (Charge-conjugate modes are included.) The corresponding branching fractions are measured to be [symbol: see text](B+ --> K0 K+) = (1.0 +/- 0.4 +/- 0.1) x 10(-6) and [symbol: see text](B0 --> K0 K0) = (0.8 +/- 0.3 +/- 0.1) x 10(-6). These decay modes are examples of hadronic bd transitions. No signal is observed in the decay B0 --> K+ K-, and we set an upper limit of 3.7 x 10(-7) at 90% confidence level.

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PubMed2005

Measurement of the wrong-sign decays D0 --> K+ pi- pi0 and D0 --> K+ pi- pi+ pi-, and search for CP violation.

Using 281 fb-1 of data from the Belle experiment recorded at or near the (4S) resonance, we have measured the rates of the "wrong-sign" decays D0 --> K+ pi- pi0 and D0 --> K+ pi- pi+ pi- relative to those of the Cabibbo-favored decays D0 --> K- pi+ pi0 and D0 --> K- pi+ pi+ pi-. These wrong-sign decays proceed via a doubly Cabibbo-suppressed amplitude or via D0-D0 mixing; the latter has not yet been observed. We obtain R(WS)(K pi pi0) = [0.229 +/- 0.015(stat)(+0.013)(-0.009)(syst)]% and R(WS)(K3pi) = [0.320 +/- 0.018(stat)(+0.018)(0.013)(syst)]%. The CP asymmetries are measured to be -0.006 +/- 0.053 and -0.018 +/- 0.044 for the K+ pi- pi0 and K+ pi- pi+ pi- final states, respectively.

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PubMed2005

Measurements of the branching fraction and polarization in B+ --> rho+ K*0 decays.

We present the results of a study of the charmless vector-vector decay B+ --> rho+ K*0, based on 253 fb(-1) of data collected with the Belle detector at the KEKB asymmetric-energy e+ e- collider. We obtain the branching fraction B(B+ --> rho+ K*0) = [8.9 +/- 1.7(stat) +/- 1.2(syst)] x 10(-6). We also perform a helicity analysis of the rho and K* vector mesons, and obtain the longitudinal polarization fraction f(L)(B+ --> rho+ K*0) = 0.43 +/- 0.11(stat)(-0.02)(+0.05) (syst).

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PubMed2005

Improved evidence for direct CP violation in B0-->pi+pi- decays and model-independent constraints on phi2.

We present a new measurement of the time-dependent CP-violating parameters in B(0)--> pi(+)pi(-) decays with 275 x 10(6) BB pairs collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider operating at the Gamma(4S) resonance. We find 666 +/- 43 B(0) --> pi(+)pi(-) events and measure the CP-violating parameters: S(pipi) = -0.67 +/- 0.16(stat) +/- 0.06(syst) and A(pipi) = +0.56 +/- 0.12(stat) +/- 0.06(syst). We find evidence for large direct CP violation with a significance greater than 4 standard deviations for any S(pipi) value. Using isospin relations, we obtain 95.4% confidence intervals for the Cabibbo-Kobayashi-Maskawa quark-mixing matrix angle phi(2) of 0 degree < phiv(2) < 19 degrees and 71 degrees < phi(2) < 180 degrees.

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PubMed2005

Studies of CP violation in B-->J/PsiK* decays.

CP violation in B-->J/PsiK* decays is studied using an angular analysis in a data sample of 253 fb(-1) recorded with the Belle detector at the KEKB e(+)e(-) collider. The flavor separated measurements of the decay amplitudes indicate no evidence for direct CP violation. T-odd CP violation is studied using the asymmetries in triple product correlations, and the results are consistent with the standard model null predictions. The time-dependent angular analysis gives the following values of CP-violating parameters: sin(2phi(1) = 0.24 +/- 0.31 +/- 0.05 and cos(2phi(1)=0.56 +/- 0.79 +/- 0.11.

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PubMed2005

Observation of B+ --> plambdagamma.

We report the first observation of the radiative hyperonic B decay B+ --> plambdagamma, using a 140 fb(-1) data sample recorded on upsilom(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e- collider. The measured branching fraction is [symbol: see text](B+ --> plambdagamma) = (2.16(+0.58)(-0.53) +/- 0.20) x 10(-6). We examine its M(plambda) distribution and observe a peak near threshold. This feature is expected by the short-distance b --> sgamma transition. A search for B+ --> pepsilon0gamma yields no significant signal, and we set a 90% confidence-level upper limit on the branching fraction of [symbol: see textB+ --> pepsilon0gamma <4.6 x 10(-6).

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PubMed2005

Measurement of time-dependent CP-violating asymmetries in B0 --> K(s)0K(s)0K(s)0 decay.

We present a measurement of CP-violation parameters in the B0 --> K(s)0K(s)0K(s)0 decay based on a sample of 275 x 10(6) BB pairs collected at the upsilon(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. One neutral B meson is fully reconstructed in the decay B0 --> K(s)0K(s)0K(s)0, and the flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetry in the distributions of the proper-time interval between the two B decays: S = +1.26 +/- 0.68(stat) +/- 0.20(syst) and [symbol: see text] = +0.54 +/- 0.34(stat) +/- 0.09(syst).

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PubMed2005

Evidence for B0 --> D+ D- and observation of B- --> D0D- and B- -->D0D*- decays.

We report evidence for B(0) --> D(0)D(-) and the first observation of the decay modes B(-) --> D(0)D(-) and B(-) --> D(0)D(*-) based on a sample of 152 x 10(6) BB events collected by the Belle detector at KEKB. The branching fractions for B(0) --> D(+) D(-), B--->D(0)D(-), and B--> D(0)D(*-) are found to be (1.91 +/- 0.51 +/- 0.30) x10(-4), (4.83 +/- 0.78 +/- 0.58) x 10(-4), and (4.57 +/- 0.71 +/- 0.56) x 10(-4), respectively. Charge asymmetries in the B---> D(0)D(-) and B(-) --> D(0)D(*-) channels are consistent with zero.

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PubMed2005

Measurement of the time-dependent CP-violating asymmetry in B(0)-->K(0)(S)pi(0)gamma decays.

We present a new measurement of CP-violation parameters in B(0)-->K(0)(S)pi(0)gamma decay based on a sample of 275 x 10(6) BB pairs collected at the Gamma(4S) resonance with the Belle detector at the KEKB energy-asymmetric e(+)e(-) collider. One of the B mesons is fully reconstructed in the B(0)-->K(0)(S)pi(0)gamma decay. The flavor of the accompanying B meson is identified from its decay products. CP-violation parameters are obtained from the asymmetry in the distribution of the proper time intervals between the two B decays. We obtain SK(0)(S)(pi(0)gamma) = -0.58(+0.46)(-0.38)(stat) +/- 0.11(syst) and AK(0)(S)(pi(0)gamma) = +0.03 +/- 0.34(stat) +/- 0.11(syst), for the K(0)(S)pi(0) invariant mass covering the full range up to 1.8 GeV/c2. We also measure the CP-violation parameters for the case B(0)-->K(*0)(-->K(0)(S)pi(0))gamma and obtain S(K(*0)gamma) = -0.79(+0.63)(-0.50)(stat) +/- 0.10(syst) for A(K(*0)gamma) fixed at 0.

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PubMed2005

Observation of the D1(2420)-->Dpi + pi- decays.

We report on the first observation of D0/1(2420)-->D0pi- pi+ and D+/1(2420-->D+ pi- pi+ decays (where the contribution from the dominant known D1-->D*pi decay mode is excluded) in the B- -->D0/1pi-) and (-)B0-->D+/1pi- decays, respectively. The observation is based on 15.2 x 10(7) B(-)B events collected with the Belle detector at the KEKB collider. We also set 90% confidence level upper limits for the branching fractions of the four following decays: B- -->D0/1pi-, D01-->D(*0)pi- pi+, (-)B0-->D+/1pi-, D+/1-->D(*+) pi- pi+, B- -->D(*0)2(2460)pi-, D(*0)2 -->D(*0) pi- pi+, (-)B0-->D(*+)2(2460)pi-, D(*+)2-->D(*+)pi- pi+.

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PubMed2005

Measurement of polarization and triple-product correlations in B-->phiK* decays.

We present measurements of decay amplitudes and triple-product correlations in B-->phiK* decays based on 253 fb(-1) of data recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) storage ring. The decay amplitudes for the three different helicity states are determined from the angular distributions of final-state particles. The longitudinal polarization amplitudes are found to be 0.45 +/- 0.05 +/- 0.02 for B0-->phiK(*0) and 0.52 +/- 0.08 +/- 0.03 for B+ -->phiK(*+) decays. CP- and T-odd CP-violating triple-product asymmetries are measured to be consistent with zero.

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PubMed2005

Observation of B0-->pi0pi0.

We report the observation of the decay B0-->pi(0)pi(0), using a 253 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. The measured branching fraction is B(B0-->pi(0)pi(0))=(2.3(+0.4+0.2)(-0.5-0.3))x10(-6), with a significance of 5.8 standard deviations including systematic uncertainties. We also make a measurement of the direct CP violating asymmetry in this mode.

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PubMed2005

Study of B0-->rho+/- pi-/+ time-dependent CP violation at Belle.

We present a time-dependent analysis of CP violation in B0-->rho(+/-)pi(-/+) decays based on a 140 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at KEKB. We obtain the charge asymmetry A(rhopi)(CP)=-0.16+/-0.10(stat)+/-0.02(syst). An unbinned maximum-likelihood fit to the Deltat distributions yields C(rhopi)=0.25+/-0.17(stat)+0.02-0.06(syst), DeltaC(rhopi)=0.38+/-0.18(stat)+0.02-0.04(syst), S(rhopi)=-0.28+/-0.23(stat)+0.10-0.08(syst), and DeltaS(rhopi)=-0.30+/-0.24(stat)+/-0.09(syst). The direct CP violation parameters for B-->rho(+)pi(-) and B-->rho(-)pi(+) decays are A(+-)(rhopi)=-0.02+/-0.16(stat)+0.05-0.02(syst) and A(-+)(rhopi)=-0.53+/-0.29(stat)+0.09-0.04(syst).

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PubMed2005

Study of the suppressed decays B- -->[K+pi-](D)K- and B- -->[K+pi-]Dpi-.

We report a study of the suppressed decays B--->[K(+)pi(-)](D)K- and B--->[K(+)pi(-)](D)pi(-), where [K(+)pi(-)](D) indicates that the K+pi(-) pair originates from a neutral D meson. These decay modes are sensitive to the unitarity triangle angle varphi(3). We use a data sample containing 275 x 10(6) BB pairs recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric e(+)e(-) storage ring. The signal for B--->[K(+)pi(-)](D)K- is not statistically significant, and we set a limit r(B)<0.27 at 90% confidence level, where r(B) is the magnitude of the ratio of amplitudes |A(B--->D 0K-)/A(B--->D0K-)|. We observe a signal with 6.4sigma statistical significance in the related mode, B--->[K(+)pi(-)](D)pi(-).

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