Iskanje po katalogu digitalne knjižnice

Opis: We 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.
Ključne besede: Extensions of gauge sector, leptonic, semileptonic & radiative decays
Objavljeno v DKUM: 25.09.2023; Ogledov: 455; Prenosov: 39
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Opis: We report an observation of the $B^{\pm } \to J/\psi \eta K^{\pm }$ and $B^0 \to J/\psi \eta K^0_S$ decays using $772\times 10^{6}B\overline {B}$ pairs collected at the $\Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain the branching fractions ${\mathcal B}(B^{\pm }\rightarrow J/\psi \eta K^{\pm })=(1.27\pm 0.11(\hbox {stat.})\pm 0.11(\hbox {syst.}))\times 10^{-4}$ and ${\mathcal B}(B^0\to J/\psi \eta K^0_S)=(5.22 \pm 0.78 (\hbox {stat.}) \pm 0.49 (\hbox {syst.}))\times 10^{-5}$. We search for a new narrow charmonium(-like) state $X$ in the $ J/\psi \eta$ mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, ${\mathcal B}(B^\pm \to XK^\pm){\mathcal B}(X \to J/\psi \eta)$, at $3872\,\hbox {MeV}\,c^{-2}$ where a $C$-odd partner of $X(3872)$ may exist, at $\psi (4040)$ and $\psi (4160)$ assuming their known mass and width, and over a range from 3.8 to $4.8\,\hbox {GeV}\,c^{-2}$. The obtained upper limits at 90% confidence level for $X^{C\hbox {-}{\rm odd}}(3872)$, $\psi (4040)$, and $\psi (4160)$ are $3.8\times 10^{-6}$, $15.5\times 10^{-6}$, and $7.4\times 10^{-6}$, respectively.
Ključne besede: C07, C21, particle properties, lepton collider experiments, experimental particle physics
Objavljeno v DKUM: 21.07.2017; Ogledov: 1540; Prenosov: 245
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Opis: We report a measurement of the amplitude ratio $r_S$ of $B^0 \to D^0K^{\ast 0}$ and $B^0 \to \bar {D^0}K^{\ast 0}$ decays with a Dalitz analysis of $D\to K_S^0\pi ^+\pi ^-$ decays, for the first time using a model-independent method. We set an upper limit $r_S < 0.87$ at the 68% confidence level, using the full data sample of $711\,{\rm fb}^{-1}$ corresponding to $772\times 10^6$ $B\bar {B}$ pairs collected at the $\Upsilon (4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. This result is obtained from observables $x_- = +0.4 ^{+1.0 +0.0}_{-0.6 -0.1} \pm 0.0$, $y_- = -0.6 ^{+0.8 +0.1}_{-1.0 -0.0} \pm 0.1$, $x_+ = +0.1 ^{+0.7 +0.0}_{-0.4 -0.1} \pm 0.1$, and $y_+ = +0.3 ^{+0.5 +0.0}_{-0.8 -0.1} \pm 0.1$, where $x_\pm = r_S \cos (\delta _S \pm \phi _3)$, $y_\pm = r_S \sin (\delta _S \pm \phi _3)$, and $\phi _3\ (\delta _S)$ is the weak (strong) phase difference between $B^0 \to D^0K^{\ast 0}$ and $B^0 \to \bar {D^0}K^{\ast 0}$.
Ključne besede: CO2, CO3, Cabibbo-Kobayashi-Maskawa quark-mixing matrix, CP violation, experimental particle physics
Objavljeno v DKUM: 21.07.2017; Ogledov: 1788; Prenosov: 310
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Opis: We report a search for B decays to selected final states with the ηc meson: B± → K±ηcπ+π−, B± → K±ηcω, B± → K±ηcη and B± → K±ηcπ0. The analysis is based on 772 × 10^6 B¯B pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0.6–5.3)×10^−4. We also search for molecular-state candidates in the D^0 ¯D^∗0 − ¯D^0D^∗0, D^0 ¯D^0 + ¯D^0D^0 and D^∗0¯D^∗0 + ¯D^∗0D^∗0 combinations, neutral partners of the Z(3900)± and Z(4020)±, and a poorly understood state X(3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0.6–6.9)×10^−5.
Ključne besede: exotics, quarkonium, e+-e- experiments, B physics, particle and resonance production
Objavljeno v DKUM: 27.06.2017; Ogledov: 1376; Prenosov: 538
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Ključne besede: experimental particle physics, elementary particles, B mesons, B factories
Objavljeno v DKUM: 26.06.2017; Ogledov: 1493; Prenosov: 678
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