We report a measurement of the D0 and D+ lifetimes using D0→K−π+ and D+→K−π+π+ decays reconstructed in e+e−→cc¯ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e+e− collider. The...
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We report a measurement of the D0 and D+ lifetimes using D0→K−π+ and D+→K−π+π+ decays reconstructed in e+e−→cc¯ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e+e− collider. The data, collected at center-of-mass energies at or near the ϒ(4S) resonance, correspond to an integrated luminosity of 72 fb−1. The results, τ(D0)=410.5±1.1(stat)±0.8(syst) fs and τ(D+)=1030.4±4.7(stat)±3.1(syst) fs, are the most precise to date and are consistent with previous determinations.
We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e−→γa, a→γγ in the mass range 0....
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We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e+e−→γa, a→γγ in the mass range 0.2data corresponding to an integrated luminosity of (445±3) pb−1. Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength gaγγ of ALPs to photons at the level of 10−3 GeV−1. The limits are the most restrictive to date for 0.2
Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searc...
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Theories beyond the standard model often predict the existence of an additional neutral boson, the Z′. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z′ in the process e+e−→μ+μ−Z′ and of a lepton-flavor-violating Z′ in e+e−→e±μ∓Z′. 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 Lμ−Lτ theory, into upper limits on the Z′ coupling constant at the level of 5×10−2−1 for MZ′≤6 GeV/c2.
We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-depe...
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We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B0→D(*)h0 with D→KS0π+π− decays, where h0∈{π0,η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×106BB¯ pairs recorded by the BABAR detector and (772±11)×106BB¯ pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B0→D(*)h0 decays. The quoted model uncertainties are due to the composition of the D0→KS0π+π− decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e+e−→cc¯ data sample. CP violation is observed in B0→D(*)h0 decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2−β=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.
We report the first observation of the processes e+e−→ϒ(1S,2S)η at s=10.866 GeV, with significance exceeding 10σ for both processes. The measured Born cross sections are σ(e+e−→ϒ(2S)η)=2.07±0.21±0.19 ...
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We report the first observation of the processes e+e−→ϒ(1S,2S)η at s=10.866 GeV, with significance exceeding 10σ for both processes. The measured Born cross sections are σ(e+e−→ϒ(2S)η)=2.07±0.21±0.19 pb, and σ(e+e−→ϒ(1S)η)=0.42±0.08±0.04 pb. We also set the upper limit on the cross section of the process e+e−→ϒ(1S)η′ to be σ(e+e−→ϒ(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.
We report measurements of sin2β and cos2β using a time-dependent Dalitz plot analysis of B0→D(*)h0 with D→KS0π+π− decays, where the light unflavored and neutral hadron h0 is a π0, η, or ω meson. The analysis ...
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We report measurements of sin2β and cos2β using a time-dependent Dalitz plot analysis of B0→D(*)h0 with D→KS0π+π− decays, where the light unflavored and neutral hadron h0 is a π0, η, or ω meson. The analysis uses a combination of the final data sets of the BaBar and Belle experiments containing 471×106 and 772×106 BB¯ pairs collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We measure sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle is β=(22.5±4.4(stat)±1.2(syst)±0.6(model))°. The last quoted uncertainties are due to the composition of the D0→KS0π+π− decay amplitude model, which is newly established by a Dalitz plot amplitude analysis of a high-statistics e+e−→cc¯ data sample as part of this analysis. We find the first evidence for cos2β>0 at the level of 3.7 standard deviations. The measurement excludes the trigonometric multifold solution π/2−β=(68.1±0.7)° at the level of 7.3 standard deviations and therefore resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The hypothesis of β=0° is ruled out at the level of 5.1 standard deviations, and thus CP violation is observed in B0→D(*)h0 decays. The measurement assumes no direct CP violation in B0→D(*)h0 decays.
The first search for double charged charmoniumlike state production in ϒ(1S) and ϒ(2S) decays and in e+e− annihilation at s=10.52, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the...
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The first search for double charged charmoniumlike state production in ϒ(1S) and ϒ(2S) decays and in e+e− annihilation at s=10.52, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals are observed in any of the studied modes, and the 90% credibility level upper limits on their product branching fractions in ϒ(1S) and ϒ(2S) decays [B(ϒ(1S,2S)→Zc+Zc(′)−)×B(Zc+→π++cc¯) (cc¯=J/ψ, χc1(1P), ψ(2S))] and the product of Born cross section and branching fraction for e+e−→Zc+Zc(′)− (σ(e+e−→Zc+Zc(′)−)×B(Zc+→π++cc¯)) at s=10.52, 10.58, and 10.867 GeV are determined. Here, Zc refers to the Zc(3900) and Zc(4200) observed in the πJ/ψ final state, the Zc1(4050) and Zc2(4250) in the πχc1(1P) final state, and the Zc(4050) and Zc(4430) in the πψ(2S) final state.
This paper presents a search for the rare flavor-changing neutral current process B0→K*0τ+τ− using data taken with the Belle detector at the KEKB asymmetric energy e+e− collider. The analysis is based on the entire...
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This paper presents a search for the rare flavor-changing neutral current process B0→K*0τ+τ− using data taken with the Belle detector at the KEKB asymmetric energy e+e− collider. The analysis is based on the entire ϒ(4S) resonance data sample of 711 fb−1, corresponding to 772×106BB¯ pairs. In our search we fully reconstruct the companion B meson produced in the process e+e−→ϒ(4S)→BB¯ from its hadronic decay modes, and look for the decay B0→K*0τ+τ− in the rest of the event. No evidence for a signal is found. We report an upper limit on the branching fraction B(B0→K*0τ+τ−)<3.1×10−3 at 90% confidence level. This is the first direct limit on B(B0→K*0τ+τ−).
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