分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： We report a measurement of differential cross section of π0 pair production in single-tag two-photon collisions. These results are obtained with 759fb−1 of the data collected with the Belle detector at the KEKB asymmetric energy e+e−collider. The cross section is measured for Q2 up to 30 GeV2, where Q2 is the negative of the invariant mass squared of the tagged virtual photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and |cosθ∗| < 1.0 for the total energy and pion scattering angle, respectively. The transition form factor of the f0(980) and that of the f2(1270)with the helicity-0,-1, and -2 components separately are measured for the first time and are compared with theoretical calculations.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report the first observation of the decay Λ+c→pK+π− using a 980 fb−1 data sample collected by the Belle detector at the KEKB asymmetric-energy e+e− collider. This is the first doubly Cabibbo-suppressed decay of a charmed baryon to be observed. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be B(Λ+c→pK+π−)/B(Λ+c→pK−π+)=(2.35±0.27±0.21)×10−3, where the uncertainties are statistical and systematic, respectively.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report a measurement of the B0→ψ(2S)π0 branching fraction based on the full Υ(4S) data set of 772×106 BB¯ pairs collected by the Belle detector at the KEKB asymmetric-energy e+e− collider. We obtain B(B0→ψ(2S)π0)=(1.17±0.17(stat)±0.08(syst))×10−5. The result has a significance of 7.2 standard deviations and is the first observation of the decay B0→ψ(2S)π0.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We review the results on the XYZ states from the Belle experiment, including the measurement of inclusive hadronic cross sections and exclusive cross sections in e+e- annihilation and the Z_b states in the bottomonium energy region; and the study of the Y states and the Z_c states in charmonium energy region.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We search for the rare radiative decay D0→γγ using a data sample with an integrated luminosity of 832fb−1recorded by the Belle detector at the KEKB e+e− asymmetric-energy collider. We find no statistically significant signal and set an upper limit on the branching fraction of B(D0→γγ)<8.5×10−7 at 90% confidence level. This is the most restrictive limit on the decay channel to date.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report inclusive and exclusive measurements for χc1 and χc2 production in B decays. We measure B(B→χc1X)= (3.03±0.05(stat)±0.24(syst))×10−3 and B(B→χc2X)= (0.70±0.06(stat)±0.10(syst))×10−3. For the first time, χc2 production in exclusive B decays in the modes B0→χc2π−K+ and B+→χc2π+π−K+ has been observed, along with first evidence for the B+→χc2π+K0S decay mode. For χc1 production, we report the first observation in the B+→χc1π+π−K+, B0→χc1π+π−K0S and B0→χc1π0π−K+ decay modes. Using these decay modes, we observe a difference in the production mechanism of χc2 in comparison to χc1 in B decays. In addition, we report searches for X(3872) and χc1(2P) in the B+→(χc1π+π−)K+ decay mode. The reported results use 772×106 BB¯¯¯¯ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We measure the decay B0s→K0K¯¯¯¯¯0 using data collected at the Υ(5S) resonance with the Belle detector at the KEKB e+e− collider. The data sample used corresponds to an integrated luminosity of 121.4 fb−1. We measure a branching fraction B(B0s→K0K¯¯¯¯¯0)=[19.6+5.8−5.1(stat.)±1.0(sys.)±2.0(NB0sB¯¯¯¯0s)]×10−6 with a significance of 5.1 standard deviations. This measurement constitutes the first observation of this decay.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| using the decay B→Dℓνℓ (ℓ=e,μ) based on 711 fb−1 of e+e−→Υ(4S) data recorded by the Belle detector and containing 772×106 BB¯ pairs. One B meson in the event is fully reconstructed in a hadronic decay mode while the other, on the signal side, is partially reconstructed from a charged lepton and either a D+ or D0 meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay B→Dℓνℓ is found to be B(B0→D−ℓ+νℓ)=(2.31±0.03(stat)±0.11(syst))%. Analyzing the differential decay rate as a function of the hadronic recoil with the parameterization of Caprini, Lelouch and Neubert and using the form-factor prediction G(1)=1.0541±0.0083 calculated by FNAL/MILC, we obtain ηEW|Vcb|=(40.12±1.34)×10−3, where ηEW is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parameterization of Boyd, Grinstein and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find ηEW|Vcb|=(41.10±1.14)×10−3.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We present a measurement of the branching fraction and the longitudinal polarization fraction of B0→ρ+ρ− decays, as well as the time-dependent CP violating parameters in decays into longitudinally polarized ρ+ρ− pairs with Belle's final data set of 772×106 BB¯ pairs, at the Υ(4S) resonance, collected at the asymmetric-energy e+e− collider KEKB. We obtain B(B0→ρ+ρ−)=(28.3±1.5(stat)±1.5(syst))×10−6, fL=0.988±0.012(stat)±0.023(syst), ACP=0.00±0.10(stat)±0.06(syst), SCP=−0.13±0.15(stat)±0.05(syst). We perform an isospin analysis to constrain the CKM angle ϕ2 and obtain two solutions with ϕ2=(93.7±10.6)∘, being most compatible with other Standard-Model based fits to the data.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report an improved measurement of D0-D0bar mixing and a search for CP violation in D0 decays to CP-even final states K+K- and pi+pi-. The measurement is based on the final Belle data sample of 976/fb. The results are y_CP=(1.11 +- 0.22 +- 0.09)% and A_Gamma=(-0.03 +- 0.20 +- 0.07)%, where the first uncertainty is statistical and the second is systematic.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report the first observation of the decays B0→pΛ¯D(∗)−. The data sample of 711 fb−1 used in this analysis corresponds to 772 million BB¯ pairs, collected at the Υ(4S) resonance by the Belle detector at the KEKB asymmetric-energy e+e− collider. We observe 19.8σ and 10.8σ excesses of events for the two decay modes and measure the branching fractions of B0→pΛ¯D− and B0→pΛ¯D∗− to be (25.1±2.6±3.5)×10−6 and (33.6±6.3±4.4)×10−6, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon (pΛ¯) system is observed, consistent with that observed in similar B decays.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report a measurement of the amplitude ratio rS of B0→D0K∗0 and B0→D0¯K∗0 decays with a Dalitz analysis of D→K0Sπ+π− decays, for the first time using a model-independent method. We set an upper limit rS<0.87 at the 68\% confidence level, using the full data sample of 772×106 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB e+e− collider. This result is obtained from observables x−=+0.4+1.0+0.0−0.6−0.1±0.0, y−=−0.6+0.8+0.1−1.0−0.0±0.1, x+=+0.1+0.7+0.0−0.4−0.1±0.1 and y+=+0.3+0.5+0.0−0.8−0.1±0.1, where x±=rScos(δS±ϕ3), y±=rSsin(δS±ϕ3) and ϕ3 (δS) is the weak (strong) phase difference between B0→D0K∗0 and B0→D0¯K∗0.
分类： 物理学 >> 核物理学 提交时间： 2016-09-12
摘要： We report the first double differential cross sections of two charged pions and kaons (e+e−→hhX) in electron-positron annihilation as a function of the fractional energies of the two hadrons for any charge and hadron combination. The dependence of these di-hadron cross sections on the topology (same, opposite-hemisphere or anywhere) is also studied with the help of the event shape variable thrust and its axis. The ratios of these di-hadron cross sections for different charges and hadron combinations directly shed light on the contributing fragmentation functions. For example, we find that the ratio of same-sign pion pairs over opposite-sign pion pairs drops toward higher fractional energies where disfavored fragmentation is expected to be suppressed. These di-hadron results are obtained from a 655fb−1 data sample collected near the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. Extending the previously published single-pion and single-kaon cross sections, single-proton (e+e−→pX) cross sections are extracted from a 159fb−1 data sub-sample.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We report a measurement of the differential cross section of π0 pair production in single-tag two-photon collisions, γ∗γ→π0π0, in e+e− scattering. The cross section is measured for Q2 up to 30 GeV2, where Q2 is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and |cosθ∗| < 1.0 for the total energy and pion scattering angle, respectively, in the γ∗γ center-of-mass system. The results are based on a data sample of 759 fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− collider. The transition form factor of the f0(980) and that of the f2(1270) with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： Using data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider, we measure the energy dependence of the e+e−→hb(nP)π+π− (n=1,2) cross sections from thresholds up to 11.02GeV. We find clear Υ(10860) and Υ(11020) peaks with little or no continuum contribution. We study the resonant substructure of the Υ(11020)→hb(nP)π+π− transitions and find evidence that they proceed entirely via the intermediate isovector states Zb(10610) and Zb(10650). The relative fraction of these states is loosely constrained by the current data: the hypothesis that only Zb(10610) is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only Zb(10650) is produced is not excluded at a significant level.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We report a measurement of the branching fraction ratios R(D(*)) of Bbar -> D(*) tau- nubar_tau relative to Bbar -> D()* l- nubar_l (where l = e or mu) using the full Belle data sample of 772 x 10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured values are R(D)= 0.375 +- 0.064(stat.) +- 0.026(syst.) and R(D*) = 0.293 +- 0.038(stat.) +- 0.015(syst.). The analysis uses hadronic reconstruction of the tag-side B meson and purely leptonic tau decays. The results are consistent with earlier measurements and do not show a significant deviation from the standard model prediction.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： The process e+e−→γχcJ (J=1, 2) is studied via initial state radiation using 980 fb−1 of data at and around the Υ(nS) (n=1, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy e+e−collider. No significant signal is observed except from ψ(2S) decays. Upper limits on the cross sections between s√=3.80 and 5.56 GeV are determined at the 90% credibility level, which range from few pb to a few tens of pb. We also set upper limits on the decay rate of the vector charmonium [ψ(4040), ψ(4160), and ψ(4415)] and charmoniumlike [Y(4260), Y(4360), and Y(4660)] states to γχcJ.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We present an extraction of azimuthal correlations between two pairs of charged pions detected in opposite jets from electron-positron annihilation. These correlations may arise from the dependence of the di-pion fragmentation on the polarization of the parent quark in the process e+e−→qq¯. Due to the correlation of the quark polarizations, the cross-section of di-pion pair production, in which the pion pairs are detected in opposite jets in a dijet event, exhibits a modulation in the azimuthal angles of the planes containing the hadron pairs with respect to the production plane. The measurement of this modulation allows access to combinations of fragmentation functions that are sensitive to the quark's transverse polarization and helicity. Within our uncertainties we do not observe a significant signal from the previously unmeasured helicity dependent fragmentation function G⊥1. This measurement uses a dataset of 938~fb−1 collected by the Belle experiment at or near s√≈10.58 GeV.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0 decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S omega. The measurement is performed combining the final data samples collected at the Y(4S) resonance by the BaBar and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06 (syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results correspond to the first observation of CP violation in B0->D(*)CP h0 decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.
分类： 物理学 >> 核物理学 提交时间： 2016-09-09
摘要： We report a measurement of the amplitude ratio rS of B0→D0K∗0 and B0→D0¯K∗0 decays with a model-independent Dalitz plot analysis using D→K0Sπ+π− decays. Using the full data sample of 772×106 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at KEKB accelerator the upper limit is rS<0.87 at the 68 % confidence level. This result is the first measurement of rS with a model-independent Dalitz analysis, and is consistent with results from other analyses. The value of rS indicates the sensitivity of the decay to ϕ3 because the statistical uncertainty is proportional to 1/rS. The rS result is obtained from observables (x±, y±) x−y−x+y+,====+0.4+1.0+0.0−0.6−0.1±0.0−0.6+0.8+0.1−1.0−0.0±0.1+0.1+0.7+0.0−0.4−0.1±0.1+0.3+0.5+0.0−0.8−0.1±0.1 where x±=rScos(δS±ϕ3), y±=rSsin(δS±ϕ3) and ϕ3(δS) are the weak (strong) phase difference between B0→D0K∗0 and B0→D0¯K∗0. The first uncertainty is statistical, the second is the experimental systematic and the third is the systematic due to the uncertainties on ci and si parameters measured by CLEO.
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