We present a new measurement of the Cabibbo-Kobayashi-Maskawa matrix element |Vcb| from B0→D*−ℓ+νℓ decays, reconstructed with the full Belle data set of 711 fb−1 integrated luminosity. Two form ...factor parametrizations, originally conceived by the Caprini-Lellouch-Neubert (CLN) and the Boyd, Grinstein and Lebed (BGL) groups, are used to extract the product F(1)ηEW|Vcb| and the decay form factors, where F(1) is the normalization factor and ηEW is a small electroweak correction. In the CLN parametrization we find F(1)ηEW|Vcb|=(35.06±0.15±0.56)×10−3, ρ2=1.106±0.031±0.007, R1(1)=1.229±0.028±0.009, R2(1)=0.852±0.021±0.006. For the BGL parametrization we obtain F(1)ηEW|Vcb|=(34.93±0.23±0.59)×10−3, which is consistent with the world average when correcting for F(1)ηEW. The branching fraction of B0→D*−ℓ+νℓ is measured to be B(B0→D*−ℓ+νℓ)=(4.90±0.02±0.16)%. We also present a new test of lepton flavor universality violation in semileptonic B decays, B(B0→D*−e+ν)B(B0→D*−μ+ν)=1.01±0.01±0.03. The errors quoted correspond to the statistical and systematic uncertainties, respectively. This is the most precise measurement of F(1)ηEW|Vcb| and form factors to date and the first experimental study of the BGL form factor parametrization in an experimental measurement.
Global decay chain vertex fitting at Belle II Krohn, J.-F.; Tenchini, F.; Urquijo, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2020, Letnik:
976, Številka:
C
Journal Article
Recenzirano
Odprti dostop
In this paper we report the implementation of a global vertex fitting algorithm within the Belle II analysis software environment, which was originally developed for BaBar (Hulsbergen, 2005). We ...explore the impact of global vertex fitting algorithms for flavour physics analyses with the Belle II detector at the SuperKEKB e+e− collider, such as in the reconstruction of final states with neutral particles, and in fits with geometrical constraints from SuperKEKB’s nano-beam interaction region. The algorithm is compared to the standard vertex fitting algorithm employed by the Belle experiment. We have developed the fitting framework to utilise the EIGEN library for linear algebra operations, reducing the computation time for vertex fitting operations by an order of magnitude over previous methods. This has a significant impact on physics analysis computing efficiency, where vertex fitting over large combinations of final state particles is one of the most CPU intensive operations at Belle II.
This paper describes the implementation and performance of CsI(Tl) pulse shape discrimination for the Belle II electromagnetic calorimeter, representing the first application of CsI(Tl) pulse shape ...discrimination for particle identification at an electron–positron collider. The pulse shape characterization algorithms applied by the Belle II calorimeter are described. Control samples of γ, μ+, π±, K± and p∕p̄ are used to demonstrate the significant insight into the secondary particle composition of calorimeter clusters that is provided by CsI(Tl) pulse shape discrimination. Comparisons with simulation are presented and provide further validation for newly developed CsI(Tl) scintillation response simulation techniques, which when incorporated with GEANT4 simulations allow the particle dependent scintillation response of CsI(Tl) to be modelled. Comparisons between data and simulation also demonstrate that pulse shape discrimination can be a new tool to identify sources of improvement in the simulation of hadronic interactions in materials. The KL0 efficiency and photon-as-hadron fake-rate of a multivariate classifier that is trained to use pulse shape discrimination is presented and comparisons are made to a shower-shape based approach. CsI(Tl) pulse shape discrimination is shown to reduce the photon-as-hadron fake-rate by over a factor of 3 at photon energies of 0.2 GeV and over a factor 10 at photon energies of 1 GeV.
The Full Event Interpretation Keck, T.; Abudinén, F.; Bernlochner, Florian U. ...
Computing and software for big science,
12/2019, Letnik:
3, Številka:
1
Journal Article
Odprti dostop
The full event interpretation is presented: a new exclusive tagging algorithm used by the high-energy physics experiment Belle II. The experimental setup of Belle II allows the precise measurement of ...otherwise inaccessible
B
meson decay modes. The Full Event Interpretation algorithm enables many of these measurements. The algorithm relies on machine learning to automatically identify plausible
B
meson decay chains based on the data recorded by the detector. Compared to similar algorithms employed by previous experiments, the Full Event Interpretation provides a greater efficiency, yielding a larger effective sample size usable in the measurement.
The acquisition of clandestine human sources - or agents - inside Russia and China likely remains the key priority for Western HUMINT agencies, and yet their ability to do this safely is quickly ...waning. This paper considers the utility of cyberspace for espionage recruitment in these two hard target states, and assesses its value as a potential solution to emerging surveillance threats. With the aid of history, this paper proposes that hard target espionage is fundamentally afflicted by a tradecraft paradox, one that will severely curtail the utility of cyberspace to agent recruitment.
We present the first measurements of absolute branching fractions of Ξc0 decays into Ξ−π+, ΛK−π+, and pK−K−π+ final states. The measurements are made using a dataset comprising (772±11)×106 BB¯ pairs ...collected at the ϒ(4S) resonance with the Belle detector at the KEKB e+e− collider. We first measure the absolute branching fraction for B−→Λ¯c−Ξc0 using a missing-mass technique; the result is B(B−→Λ¯c−Ξc0)=(9.51±2.10±0.88)×10−4. We subsequently measure the product branching fractions B(B−→Λ¯c−Ξc0)B(Ξc0→Ξ−π+), B(B−→Λ¯c−Ξc0)B(Ξc0→ΛK−π+), and B(B−→Λ¯c−Ξc0)B(Ξc0→pK−K−π+) with improved precision. Dividing these product branching fractions by the result for B−→Λ¯c−Ξc0 yields the following branching fractions: B(Ξc0→Ξ−π+)=(1.80±0.50±0.14)%, B(Ξc0→ΛK−π+)=(1.17±0.37±0.09)%, and B(Ξc0→pK−K−π+)=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξc0→Ξ−π+) can be combined with Ξc0 branching fractions measured relative to Ξc0→Ξ−π+ to yield other absolute Ξc0 branching fractions.
We report the result for a search for the leptonic decay of B+→μ+νμ using the full Belle dataset of 711 fb−1 of integrated luminosity at the ϒ(4S) resonance. In the Standard Model leptonic B-meson ...decays are helicity and Cabibbo-Kobayashi-Maskawa suppressed. To maximize sensitivity an inclusive tagging approach is used to reconstruct the second B meson produced in the collision. The directional information from this second B meson is used to boost the observed μ into the signal B-meson rest frame, in which the μ has a monochromatic momentum spectrum. Though its momentum is smeared by the experimental resolution, this technique improves the analysis sensitivity considerably. Analyzing the μ momentum spectrum in this frame we find B(B+→μ+νμ)=(5.3±2.0±0.9)×10−7 with a one-sided significance of 2.8 standard deviations over the background-only hypothesis. This translates to a frequentist upper limit of B(B+→μ+νμ)<8.6×10−7 at 90% confidence level. The experimental spectrum is then used to search for a massive sterile neutrino, B+→μ+N, but no evidence is observed for a sterile neutrino with a mass in a range of 0–1.5 GeV. The determined B+→μ+νμ branching fraction limit is further used to constrain the mass and coupling space of the type II and type III two-Higgs-doublet models.
We present the first measurements of the absolute branching fractions of Ξc+ decays into Ξ−π+π+ and pK−π+ final states. Our analysis is based on a data set of (772±11)×106 BB¯ pairs collected at the ...ϒ(4S) resonance with the Belle detector at the KEKB e+e− collider. We measure the absolute branching fraction of B¯0→Λ¯c−Ξc+ with the Ξc+ recoiling against Λ¯c− in B¯0 decays resulting in B(B¯0→Λ¯c−Ξc+)=1.16±0.42(stat.)±0.15(syst.)×10−3. We then measure the product branching fractions B(B¯0→Λ¯c−Ξc+)B(Ξc+→Ξ−π+π+) and B(B¯0→Λ¯c−Ξc+)B(Ξc+→pK−π+). Dividing these product branching fractions by B¯0→Λ¯c−Ξc+ yields B(Ξc+→Ξ−π+π+)=2.86±1.21(stat.)±0.38(syst.)% and B(Ξc+→pK−π+)=0.45±0.21(stat.)±0.07(syst.)%. Our result for B(Ξc+→Ξ−π+π+) can be combined with Ξc+ branching fractions measured relative to Ξc+→Ξ−π+π+ to set the absolute scale for many Ξc+ branching fractions.
Study of γγ→γψ(2S) at Belle Wang, X. L.; Aihara, H.; Asner, D. M. ...
Physical review. D,
06/2022, Letnik:
105, Številka:
11
Journal Article
Recenzirano
Odprti dostop
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, the two-photon process γγ → γψ(2S) is ...studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of γψ(2S): one at MR1 = 3922.4 ± 6.5 ± 2.0 MeV/c2 with a width of ΓR1 = 22 ± 17 ± 4 MeV, and another at MR2 = 4014.3 ± 4.0 ± 1.5 MeV/c2 with a width of ΓR2 = 4 ± 11 ± 6 MeV; the signals are parametrized with the incoherent sum of two Breit- Wigner functions. The first structure is consistent with the X(3915) or the χc2(3930), and the local statistical significance is determined to be 3.1σ with the systematic uncertainties included. The second matches none of the known charmonium or charmonium like states, and its global significance is determined to be 2.8σ including the look-elsewhere effect. The production rates are Γγγ B(R1 → γψ(2S)) = 9.8 ± 3.6 ± 1.2 eV assuming (JPC, |λ|) = (0++, 0) or 2.0 ± 0.7 ± 0.2 eV with (2++, 2) for the first structure and Γγγ B(R2 → γψ(2S)) = 6.2 ± 2.2 ± 0.8 eV with (0++, 0) or 1.2 ± 0.4 ± 0.2 eV with (2++, 2) for the second one. Furthermore, the first errors are statistical and the second systematic, and λ is the helicity.
Using a data sample of 921.9 fb-1 collected with the Belle detector, we study the process of $e^+e^- → D^+_s D_{s1}(2536)^-+c.c.$ via initial-state radiation. We report the first observation of a ...vector charmoniumlike state decaying to $D^+_s D_{s1}(2536)^-+c.c.$ with a significance of $5.9σ$, including systematic uncertainties. The measured mass and width are $(4625.9^{+6.2}_{-6.0}$(stat)$±0.4$(syst)) MeV/$c_2$ and ($49.8^{+13.9}_{-11.5}$(stat)$±4.0$(syst)) MeV, respectively. The product of the $e^+e^- → D^+_s D_{s1}(2536)^-+c.c.$ cross section and the branching fraction of $D_{s1}(2536)^- → \bar{D}^{*0}K^-$ is measured from the $D_s \bar{D}_{s1}(2536)$ threshold to $5.59$ GeV.
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