379 research outputs found
Search for tetraquark states in final states at Belle
No full textA search for double-heavy tetraquark state candidates decaying to and is presented for the first time using the data samples of 102 million and 158 million events, and the data samples at = 10.52~GeV, 10.58~GeV, and 10.867~GeV corresponding to integrated luminosities of 89.5~fb, 711.0~fb, and 121.4~fb, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the and are studied to search for possible resonances. No significant signals are observed, and the 90% confidence level upper limits on the product branching fractions [] in inclusive decays and the product values of Born cross section and branching fraction [] in collisions at = 10.52~GeV, 10.58~GeV, and 10.867~GeV under different assumptions of masses and widths are obtained
Search for Z′ →μ+μ- in the Lμ-Lτ gauge-symmetric model at Belle
No full textWe search for a new gauge boson Z′ that couples only to heavy leptons and their corresponding neutrinos in the process e+e-→Z′(→μ+μ-)μ+μ-, using a 643 fb-1 data sample collected by the Belle experiment at or near the Υ(1S,2S,3S,4S,5S) resonances at the KEKB collider. While previous searches for Z′ performed a data-based estimation of the initial state radiation effect, our search for the Z′ is the first to include effects due to initial state radiation in the signal simulated samples that were used in estimating the detection efficiency. No signal is observed in the Z′ mass range of 0.212-10 GeV/c2, and we set an upper limit on the coupling strength, g′, constraining the possible Z′ contribution to the anomalous magnetic dipole moment of the muon
Search for an invisible in a final state with two muons and missing energy at Belle II
No full textThe extension of the standard model predicts the existence of a lepton-flavor-universality-violating boson that couples only to the heavier lepton families. We search for such a through its invisible decay in the process . We use a sample of electron-positron collisions at a center-of-mass energy of 10.58GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7fb. We find no excess over the expected standard-model background. We set 90-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from at low masses to 1 at masses of 8
Search for in the gauge-symmetric model at Belle
No full textWe search for a new gauge boson that couples only to heavy leptons and their corresponding neutrinos in the process , using a 643 fb data sample collected by the Belle experiment at or near the resonances at the KEKB collider. For the first time, effects due to initial state radiation are used in estimating the detection efficiency. No signal is observed in the mass range of and we set an upper limit on the coupling strengh, , constraining as a possible contributor to the anomalous magnetic dipole moment of muon
Search for tetraquark states Xcc s- s- in Ds+ Ds+ (Ds∗+ Ds∗+) final states at Belle
No full textA search for double-heavy tetraquark state candidates Xccs ̄s ̄ decaying to Ds+Ds+ and Ds∗+Ds∗+ is presented for the first time using the data samples of 102×106 Υ(1S) and 158×106 Υ(2S) events, and the data samples at s=10.52, 10.58, and 10.867 GeV corresponding to integrated luminosities of 89.5, 711.0, and 121.4 fb-1, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the Ds+Ds+ and Ds∗+Ds∗+ are studied to search for possible resonances. No significant signals are observed, and the 90% confidence level upper limits on the product branching fractions [B(Υ(1S,2S)→Xccs ̄s ̄+anything)×B(Xccs ̄s ̄→Ds+Ds+(Ds∗+Ds∗+))] in Υ(1S,2S) inclusive decays and the product values of Born cross section and branching fraction [σ(e+e-→Xccs ̄s ̄+anything)×B(Xccs ̄s ̄→Ds+Ds+(Ds∗+Ds∗+))] in e+e- collisions at s=10.52, 10.58, and 10.867 GeV under different assumptions of Xccs ̄s ̄ masses and widths are obtained
Search for an invisibly decaying boson at Belle II in plus missing energy final states
No full textUsing data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a in the process and of a lepton-flavor-violating in . We do not find any excess of events and set 90 credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an theory, into upper limits on the coupling constant at the level of for GeV/
Study of e+e- → D (1 S,2 S)η and e+e- → D (1S)η′ at s =10.866 GeV with the Belle detector
No full textWe report the first observation of the processes e+e-→D(1S,2S)η at s=10.866 GeV, with significance exceeding 10σ for both processes. The measured Born cross sections are σ(e+e-→D(2S)η)=2.07±0.21±0.19 pb, and σ(e+e-→D(1S)η)=0.42±0.08±0.04 pb. We also set the upper limit on the cross section of the process e+e-→D(1S)η′ to be σ(e+e-→D(1S)η′)<0.037 pb at 90% C.L. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider in the energy range from 10.63 to 11.02 GeV
Measurement of the branching fractions for Cabibbo-suppressed decays D+→K+K−π+π0 and D(s)+→K+π−π+π0 at Belle
No full textWe present measurements of the branching fractions for the singly Cabibbo-suppressed decays D+→K+K−π+π0 and D+s→K+π−π+π0, and the doubly Cabibbo-suppressed decay D+→K+π−π+π0, based on 980 fb−1 of data recorded by the Belle experiment at the KEKB e+e− collider. We measure these modes relative to the Cabibbo-favored modes D+→K−π+π+π0 and D+s→K+K−π+π0. Our results for the ratios of branching fractions are B(D+→K+K−π+π0)/B(D+→K−π+π+π0)=(11.32±0.13±0.26)%, B(D+→K+π−π+π0)/B(D+→K−π+π+π0)=(1.68±0.11±0.03)%, and B(D+s→K+π−π+π0)/B(D+s→K+K−π+π0)=(17.13±0.62±0.51)%, where the uncertainties are statistical and systematic, respectively. The second value corresponds to (5.83±0.42)×tan4θC, where θC is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for B(D+→K−π+π+π0) and B(D+s→K+K−π+π0) yields B(D+→K+K−π+π0)=(7.08±0.08±0.16±0.20)×10^−3, B(D+→K+π−π+π0)=(1.05±0.07±0.02±0.03)×10^−3, and B(D+s→K+π−π+π0)=(9.44±0.34±0.28±0.32)×10^−3, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction
Search for rare decays , , , and
No full text7 pages, 2 figuresInternational audienceWe present a study of rare decay modes , , and , where denotes the neutral mesons or , using a data sample of events produced at the resonance. The data were collected by the Belle detector operating at the asymmetric-energy KEKB collider. We observe no evidence for these decays, so we provide upper limits at the 90 confidence level on the branching fractions of , , and decay modes. Along with rare decay modes, we report improved measurements of the color-suppressed decay branching fractions = (26.6 1.2 2.1) and = (5.6 0.5 0.2) . The first and second uncertainties are statistical and systematic, respectively
Observation of charmed strange meson pair production in Y(2S) decays and in e+e− annihilation at sqrt(s)=10.52 GeV
No full textWe observe the process Y(2S)→D(*)+s D−sJ and continuum production e+e-→D(*)+s D-sJ at sqrt(s)=10.52 GeV (and their charge conjugates) using the data samples collected by the Belle detector at KEKB, where D-sJ is Ds1(2536)− or D*s2(2573)−. Both D-sJ states are identified through their decay into KD(*). We measure the products of branching fractions B(Y(2S)→D(*)+s D−sJ)B(D-sJ→KD(*)) and the Born cross sections σBorn(e+e-→D(*)+s D-sJ)B(D-sJ→KD(*)), and then compare the ratios R1=B(Y(2S)→D(*)+s D−sJ)/B(Y(2S)→μ+μ−) for Y(2S) decays and R1=σBorn(e+e-→D(*)+s D-sJ)/σBorn(e+e-→μ+μ−) for continuum production. We obtain R1/R2=9.7±2.3±1.1, 6.8±2.1±0.8, 10.2±3.3±2.5, and 3.4±2.1±0.8 for the D+s Ds1(2536)−, D*+s Ds1(2536)−, D+s D*s2(2573)−, and D*+s D*s2(2573)− final states in the D-sJ→K−D(*)0 modes, respectively. The measured R1/R2 values indicate that the strong decay dominates in Y(2S)→D(*)+s D−sJ processes. We also measure the ratios of branching fractions B(Ds1(2536)−→K0SD*(2010)−)/B(Ds1(2536)−→K-D*(2007)0)=0.48±0.07±0.02 and B(D*s2(2573)−→K0SD-)/B(D*s2(2573)−→K-D0)=0.49±0.10±0.02, which are consistent with isospin symmetry. The second ratio is the first measurement of this quantity. Here, the first uncertainties are statistical and the second are systematic
- …
