arXiv subjects

T. Luo

Publications and source records attributed to T. Luo.

At least 91 records · Page 5Linked to original sources

arXiv2018

Measurement of Time-dependent $CP$ Asymmetries in $B^{0}\to K_S^0 ηγ$ Decays

We report a measurement of time-dependent $CP$ violation parameters in ${B^0 \to K_S^0 ηγ}$ decays. The study is based on a data sample, containing ${772 \times 10^6 B\bar{B}}$ pairs, that was collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We obtain the $CP$ violation parameters of ${{\cal S} = -1.32 \pm 0.77 {\rm (stat.)} \pm 0.36{\rm (syst.)}}$ and ${{\cal A} = -0.48 \pm 0.41 {\rm (stat.)} \pm 0.07{\rm (syst.)}}$ for the invariant mass of the $K_S^0 η$ system up to 2.1 GeV/$c^2$.

hep-ex↗

arXiv2018

Observation of $Υ(4S)\to η' Υ(1S)$

We report the first observation of the hadronic transition $Υ(4S)\toη'Υ(1S)$, using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We reconstruct the $η'$ meson through its decays to $ρ^0γ$ and to $π^+π^-η$, with $η\toγγ$. We measure: ${\cal B}(Υ(4S)\toη'Υ(1S))=(3.43\pm 0.88 {\rm(stat.)} \pm 0.21 {\rm(syst.)})\times10^{-5}$, with a significance of 5.7$σ$.

hep-ex↗

arXiv2018

Production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation near $\sqrt{s} = 10.52$~GeV

We measure the inclusive production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation using a 800 fb$^{-1}$ data sample taken near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for $S=-1$ hyperons follow an exponential function with a single slope parameter except for the $Σ(1385)^+$ resonance. Suppression for $Σ(1385)^+$ and $Ξ(1530)^0$ hyperons is observed. Among the production cross sections of charmed baryons, a factor of three difference for $Λ_c^+$ states over $Σ_c$ states is observed. This observation suggests a diquark structure for these baryons.

hep-ex↗

arXiv2018

Inclusive study of bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near $Υ(5S)$

We study bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near the $Υ(5S)$, at a center of mass energy of $\sqrt{s}=10.866\,$GeV. The results are based on the $121.4\,$fb$^{-1}$ data sample collected by the Belle experiment at the asymmetric energy KEKB collider. Only the $η$ meson is reconstructed and the missing-mass spectrum of $η$ candidates is investigated. We observe the $e^+e^-\toηΥ_J(1D)$ process and find evidence for the $e^+e^-\toηΥ(2S)$ process, while no significant signals of $Υ(1S)$, $h_b(1P)$, nor $h_b(2P)$ are found. Cross sections for the studied processes are reported.

hep-ex↗

arXiv2018

Search for $CP$ violation in the $D^{+}\toπ^{+}π^{0}$ decay at Belle

We search for $CP$ violation in the charged charm meson decay $D^{+}\toπ^{+}π^{0}$, based on a data sample corresponding to an integrated luminosity of $\rm 921~fb^{-1}$ collected by the Belle experiment at the KEKB $e^{+}e^{-}$ asymmetric-energy collider. The measured $CP$ violating asymmetry is $[+2.31\pm1.24({\rm stat})\pm0.23({\rm syst})]\%$, which is consistent with the standard model prediction and has a significantly improved precision compared to previous results.

hep-ex↗

arXiv2018

Observation of Excited $Ω_c$ Charmed Baryons in $e^+e^-$ Collisions

Using the entire Belle data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ collisions, we present the results of a study of excited $Ω_c$ charmed baryons in the decay mode $Ξ_c^+K^-$. We show confirmation of four of the five narrow states reported by the LHCb Collaboration: the $Ω_c(3000)$ , $Ω_c(3050)$, $Ω_c(3066)$, and $Ω_c(3090)$.

hep-ex↗

arXiv2017

Search for $B^{-}\toμ^{-}\barν_μ$ Decays at the Belle Experiment

We report the result of a search for the decay $B^{-}\toμ^{-}\barν_μ$. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic $B$-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of ${\cal B}(B^{-}\toμ^{-}\barν_μ) =(6.46 \pm 2.22 \pm 1.60 )\times10^{-7}$ or a frequentist 90% confidence level interval on the $B^{-}\toμ^{-}\barν_μ$ branching fraction of $[2.9, 10.7]\times 10^{-7}$. This result is obtained from a $711\ \text{fb}^{-1}$ data sample that contains $772 \times 10^6$ $B\bar{B}$ pairs, collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.

hep-ex↗

arXiv2017

Measurement of branching fraction and direct $CP$ asymmetry in charmless $B^+ \to K^+K^- π^+$ decays at Belle

We report a study of the charmless hadronic decay of the charged $B$ meson to the three-body final state $K^+ K^- π^+$. The results are based on a data sample that contains $772\times10^6$ $B \bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The measured inclusive branching fraction and the direct $CP$ asymmetry are $(5.38\pm0.40\pm0.35)\times 10^{-6}$ and $-0.170\pm0.073\pm0.017$, respectively, where the first uncertainties are statistical and the second are systematic. The $K^{+}K^{-}$ invariant mass distribution of the signal candidates shows an excess in the region below $1.5$ GeV/$c^2$, which is consistent with the previous studies from BaBar and LHCb. In addition, strong evidence of a large direct $CP$ asymmetry is found in the $K^{+}K^{-}$ low-invariant-mass region.

hep-ex↗

arXiv2017

Study of $K^0_S$ pair production in single-tag two-photon collisions

We report a measurement of the cross section for $K^0_S$ pair production in single-tag two-photon collisions, $γ^* γ\to K^0_S K^0_S$, for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon. The measurement covers the kinematic range 1.0 GeV < W < 2.6 GeV and $|\cos θ^*| < 1.0$ for the total energy and kaon scattering angle, respectively, in the $γ^* γ$ center-of-mass system. These results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For the first time, the transition form factor of the $f_2'(1525)$ meson is measured separately for the helicity-0, -1, and -2 components and also compared with theoretical calculations. Finally, the partial decay widths of the $χ_{c0}$ and $χ_{c2}$ mesons are measured as a function of $Q^2$.

hep-ex↗

arXiv2017

Measurement of the Decays $\boldsymbol{B\toη\ellν_\ell}$ and $\boldsymbol{B\toη^\prime\ellν_\ell}$ in Fully Reconstructed Events at Belle

We report branching fraction measurements of the decays $B^+\toη\ell^+ν_\ell$ and $B^+\toη^\prime\ell^+ν_\ell$ based on 711~fb$^{-1}$ of data collected near the $Υ(4S)$ resonance with the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. This data sample contains 772 million $B\bar B$~events. One of the two $B$~mesons is fully reconstructed in a hadronic decay mode. Among the remaining ("signal-$B$") daughters, we search for the $η$~meson in two decay channels, $η\toγγ$ and $η\toπ^+π^-π^0$, and reconstruct the $η^{\prime}$~meson in $η^\prime\toηπ^+π^-$ with subsequent decay of the $η$ into $γγ$. Combining the two $η$ modes and using an extended maximum likelihood, the $B^+\toη\ell^+ν_\ell$ branching fraction is measured to be $(4.2\pm 1.1 (\rm stat.)\pm 0.3 (\rm syst.))\times 10^{-5}$. For $B^+\toη^\prime\ell^+ν_\ell$, we observe no significant signal and set an upper limit of $0.72\times 10^{-4}$ at 90\% confidence level.

hep-ex↗

arXiv2017

Search for $Λ_c^+\toϕp π^0$ and branching fraction measurement of $Λ_c^+\to K^-π^+ p π^0$

We have searched for the Cabibbo-suppressed decay $Λ_c^+\toϕpπ^0$ in $e^+e^-$ collisions using a data sample corresponding to an integrated luminosity of 915 $\rm fb^{-1}$. The data were collected by the Belle experiment at the KEKB $e^+e^-$ asymmetric-energy collider running at or near the $Υ(4S)$ and $Υ(5S)$ resonances. No significant signal is observed, and we set an upper limit on the branching fraction of $\mathcal{B}(Λ_c^+\to ϕpπ^0) <15.3\times10^{-5}$ at 90% confidence level. The contribution for nonresonant $Λ_c^+\to K^+K^- pπ^0$ decays is found to be consistent with zero and the corresponding upper limit on its branching fraction is set to be $\mathcal{B}(Λ_c^+\to K^+K^-pπ^0)_{\rm NR} <6.3\times10^{-5} $ at 90% confidence level. We also measure the branching fraction for the Cabibbo-favored decay $Λ_c^+\to K^-π^+pπ^0$; the result is $\mathcal{B}(Λ_c^+\to K^-π^+pπ^0)= (4.42\pm0.05\, (\rm stat.) \pm 0.12\, (\rm syst.) \pm 0.16\, (\mathcal{B}_{\rm Norm}))\%$, which is the most precise measurement to date. Finally, we have searched for an intermediate hidden-strangeness pentaquark decay $P^+_s\toϕp$. We see no evidence for this intermediate decay and set an upper limit on the product branching fraction of ${\cal B}(Λ_c^+\to P^+_s π^0)\times {\cal B}(P^+_s\toϕp) <8.3\times 10^{-5}$ at 90% confidence level.

hep-ex↗

arXiv2017

Angular analysis of the $e^+ e^- \to D^{() \pm} D^{ \mp}$ process near the open charm threshold using initial-state radiation

We report a new measurement of the exclusive $e^+ e^- \to D^{(*) \pm} D^{*\mp}$ cross sections as a function of the center-of-mass energy from the $D^{(*) \pm} D^{* \mp}$ threshold through $\sqrt{s}=6.0$ GeV with initial-state radiation. The analysis is based on a data sample collected with the Belle detector with an integrated luminosity of $951$ fb$^{-1}$. The accuracy of the cross section measurement is increased by a factor of two over the first Belle study. We perform the first angular analysis of the $e^+ e^- \to D^{* \pm} D^{* \mp}$ process and decompose this exclusive cross section into three components corresponding to the $D^*$ helicities.

hep-ex↗

arXiv2017

RF system for the MICE demonstration of ionization cooling

Muon accelerators offer an attractive option for a range of future particle physics experiments. They can enable high energy (TeV+) high energy lepton colliders whilst mitigating the difficulty of synchrotron losses, and can provide intense beams of neutrinos for fundamental physics experiments investigating the physics of flavor. The method of production of muon beams results in high beam emittance which must be reduced for efficient acceleration. Conventional emittance control schemes take too long, given the very short (2.2 microsecond) rest lifetime of the muon. Ionisation cooling offers a much faster approach to reducing particle emittance, and the international MICE collaboration aims to demonstrate this technique for the first time. This paper will present the MICE RF system and its role in the context of the overall experiment.

physics.acc-ph↗

arXiv2017

Study of $η$ and dipion transitions in $Υ(4S)$ decays to lower bottomonia

We study hadronic transitions between bottomonium states using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}e^{-}$ collider. We measure: ${\cal B}(Υ(4S)\toπ^+π^-Υ(1S))=(8.2\pm 0.5 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, ${\cal B}(Υ(4S)\toπ^+π^-Υ(2S))=(7.9\pm 1.0 {\rm(stat.)} \pm 0.4 {\rm(syst.)})\times10^{-5}$, and ${\cal B}(Υ(4S)\toηΥ(1S))=(1.70\pm 0.23 {\rm(stat.)} \pm 0.08 {\rm(syst.)})\times10^{-4}$. We measure the ratio of branching fractions ${\cal R} = {\cal B}(Υ(4S)\toηΥ(1S))/{\cal B}(Υ(4S)\toπ^+π^-Υ(1S)) = 2.07\pm 0.30 {\rm(stat.)} \pm 0.11 {\rm(syst.)}$. We search for the decay $Υ(1^3D_{1,2})\toηΥ(1S)$, but do not find significant evidence for such a transition. We also measure the initial state radiation production cross sections of the $Υ(2S,3S)$ resonances and we find values compatible with the expected ones. Finally, the analysis of the $Υ(4S)\toπ^+π^-Υ(1S)$ events shows indications for a resonant contribution due to the $f_0(980)$ meson.

hep-ex↗

arXiv2017

Invariant-mass and fractional-energy dependence of inclusive production of di-hadrons in $e^+e^-$ annihilation at $\sqrt{s}=$ 10.58 GeV

The inclusive cross sections for di-hadrons of charged pions and kaons ($e^+e^- \rightarrow hhX$) in electron-positron annihilation are reported. They are obtained as a function of the total fractional energy and invariant mass for any di-hadron combination in the same hemisphere as defined by the thrust event-shape variable and its axis. Since same-hemisphere di-hadrons can be assumed to originate predominantly from the same initial parton, di-hadron fragmentation functions are probed. These di-hadron fragmentation functions are needed as an unpolarized baseline in order to quantitatively understand related spin-dependent measurements in other processes and to apply them to the extraction of quark transversity distribution functions in the nucleon. The di-hadron cross sections are obtained from a $655\,{\rm fb}^{-1}$ data sample collected at or near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.

hep-ex↗

arXiv2017

Observation of an alternative $χ_{c0}(2P)$ candidate in $e^+ e^- \rightarrow J/ψD \bar{D}$

We perform a full amplitude analysis of the process $e^+ e^- \rightarrow J/ψD \bar{D}$, where $D$ refers to either $D^0$ or $D^+$. A new charmoniumlike state $X^*(3860)$ that decays to $D \bar{D}$ is observed with a significance of $6.5σ$. Its mass is ($3862^{+26}_{-32}{}^{+40}_{-13}$) MeV/$c^2$ and width is ($201^{+154}_{-67}{}^{+88}_{-82}$) MeV. The $J^{PC}=0^{++}$ hypothesis is favored over the $2^{++}$ hypothesis at the level of $2.5σ$. The analysis is based on the 980 $\mathrm{fb}^{-1}$ data sample collected by the Belle detector at the asymmetric-energy $e^+ e^-$ collider KEKB.

hep-ex↗

arXiv2017

First measurement of $\boldsymbol{T}$-odd moments in $\boldsymbol{D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}}$ decays

We report the first measurement of the $T$-odd moments in the decay $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ from a data sample corresponding to an integrated luminosity of $966\,{\rm fb}^{-1}$ collected by the Belle experiment at the KEKB asymmetric-energy $e^+ e^-$ collider. From these moments we determine the $CP$-violation-sensitive asymmetry $a_{CP}^{T\text{-odd}} = \left[-0.28 \pm 1.38 ~(\rm{stat.}) ^{+0.23}_{-0.76} ~(\rm{syst.})\right] \times 10^{-3}$, which is consistent with no $CP$ violation. In addition, we perform $a_{CP}^{T\text{-odd}}$ measurements in different regions of the $D^{0} \rightarrow K_{S}^{0} π^{+} π^{-} π^{0}$ phase space; these are also consistent with no $CP$ violation.

hep-ex↗

arXiv2017

Search for the $0^{--}$ Glueball in $Υ(1S)$ and $Υ(2S)$ decays

We report the first search for the $J^{PC}=0^{--}$ glueball in $Υ(1S)$ and $Υ(2S)$ decays with data samples of $(102\pm2)$ million and $(158\pm4)$ million events, respectively, collected with the Belle detector. No significant signals are observed in any of the proposed production modes, and the 90\% credibility level upper limits on their branching fractions in $Υ(1S)$ and $Υ(2S)$ decays are obtained. The inclusive branching fractions of the $Υ(1S)$ and $Υ(2S)$ decays into final states with a $χ_{c1}$ are measured to be $\BR(Υ(1S)\to χ_{c1}+ anything) = (1.90\pm 0.43(stat.)\pm 0.14(syst.))\times 10^{-4}$ with an improved precision over prior measurements and $\BR(Υ(2S)\to χ_{c1}+ anything) = (2.24\pm 0.44(stat.)\pm 0.20(syst.))\times 10^{-4}$ for the first time.

hep-ex↗