arXiv subjects

W. W. Jacobs

Publications and source records attributed to W. W. Jacobs.

At least 37 records · Page 2Linked to original sources

arXiv2024

Search for Two-Body $B$ Meson Decays to $Λ^{0}$ and $Ω^{(*)0}_{c}$

We report the results of the first search for Standard Model and baryon-number-violating two-body decays of the neutral $B$ mesons to $Λ^{0}$ and $Ω^{(*)0}_c$ using 711~${\rm fb^{-1}}$ of data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe no evidence of signal from any such decays and set 95\% confidence-level upper limits on the products of $B^0$ and $\bar{B}^0$ branching fractions for these two-body decays with $\mathcal{B}(Ω_{c}^{0} \to π^+ Ω^-)$ in the range between 9.5~$\times 10^{-8}$ and 31.2~$\times 10^{-8}$.

hep-ex↗

arXiv2024

Search for charged-lepton flavor violation in $Υ(2S) \to \ell^\mpτ^\pm$ ($\ell=e,μ$) decays at Belle

We report a search for the charged-lepton flavor violation in $Υ(2S) \to \ell^\mpτ^\pm$ ($\ell=e,μ$) decays using a $25~\fbi$ $Υ(2S)$ sample collected by the Belle detector at the KEKB $e^{+}$$e^-$ asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ($\mathcal{B}$) at 90\% confidence level. We obtain the most stringent upper limits: $\mathcal{B}(\Ytomutau) < 0.23 \times 10^{-6}$ and $\mathcal{B}(\Ytoetau) < 1.12 \times 10^{-6}$.

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arXiv2024

Observation of the electromagnetic field effect via charge-dependent directed flow in heavy-ion collisions at the Relativistic Heavy Ion Collider

The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion collisions enables the exploration of the fundamental properties of matter under extreme conditions. Non-central collisions can produce strong magnetic fields on the order of $10^{18}$ Gauss, which offers a probe into the electrical conductivity of the QGP. In particular, quarks and anti-quarks carry opposite charges and receive contrary electromagnetic forces that alter their momenta. This phenomenon can be manifested in the collective motion of final-state particles, specifically in the rapidity-odd directed flow, denoted as $v_1(\mathsf{y})$. Here we present the charge-dependent measurements of $dv_1/d\mathsf{y}$ near midrapidities for $π^{\pm}$, $K^{\pm}$, and $p(\bar{p})$ in Au+Au and isobar ($_{44}^{96}$Ru+$_{44}^{96}$Ru and $_{40}^{96}$Zr+$_{40}^{96}$Zr) collisions at $\sqrt{s_{\rm NN}}=$ 200 GeV, and in Au+Au collisions at 27 GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The combined dependence of the $v_1$ signal on collision system, particle species, and collision centrality can be qualitatively and semi-quantitatively understood as several effects on constituent quarks. While the results in central events can be explained by the $u$ and $d$ quarks transported from initial-state nuclei, those in peripheral events reveal the impacts of the electromagnetic field on the QGP. Our data put valuable constraints on the electrical conductivity of the QGP in theoretical calculations.

nucl-ex↗

arXiv2024

Search for a dark leptophilic scalar produced in association with $τ^+τ^-$ pair in $e^+e^-$ annihilation at center-of-mass energies near 10.58 GeV

A dark leptophilic scalar $(ϕ_L)$ is a hypothetical particle that couples only to leptons rather than quarks. We report on a search for $ϕ_L$ in the $e^+e^- \to τ^+ τ^- ϕ_L, ~ϕ_L \to \ell^+ \ell^- ~(\ell = e, μ)$ process using 626~\invfb of data collected by the Belle experiment near the \Y4S resonance. We validate the backgrounds with multiple control regions in data, using a novel multiclass multivariate event classifier. In absence of a signal, we quote upper limits at the 90\% confidence level on the coupling between $ϕ_L$ and leptons. Our bounds, obtained in a blinded approach, are 19\% more constraining than the previous limits, averaged over the mass range $0.04 \leq m_{ϕ_L} \leq 6.5~\gev$. We exclude the parameter space below 4~\gev favored by measurement of the anomalous magnetic moment of the muon.

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arXiv2024

Search for Baryon-Number-Violating Processes in $B^-$ Decays to the $\barΞ_{c}^{0} \barΛ_{c}^{-}$ Final State

We report the results of the first search for $B^-$ decays to the $\barΞ_{c}^{0} \barΛ_{c}^{-}$ final state using 711~${\rm fb^{-1}}$ of data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The results are interpreted in terms of both direct baryon-number-violating $B^-$ decay and $Ξ_{c}^{0}-\barΞ_{c}^{0}$ oscillations which follow the Standard Model decay $B^- \to Ξ_{c}^{0} \barΛ_{c}^{-}$. We observe no evidence for baryon number violation and set the 95\% confidence-level upper limits on the ratio of baryon-number-violating and Standard Model branching fractions ${\mathcal{B}(B^- \rightarrow \barΞ_{c}^{0} \barΛ_{c}^{-})}/{\mathcal{B}(B^- \rightarrow Ξ_{c}^{0} \barΛ_{c}^{-})}$ to be $< 2.7\%$ and on the $Ξ_{c}^{0} - \barΞ_{c}^{0}$ oscillation angular frequency $ω$ to be $< 0.76\ \mathrm{ps}^{-1}$ (equivalent to $τ_{\rm mix} > 1.3$~ps).

hep-ex↗

arXiv2024

Measurements of the branching fraction, polarization, and $CP$ asymmetry for the decay $B^0\rightarrow ωω$

We present a measurement of $B^{0} \rightarrow ωω$, a charmless decay into two vector mesons, using 772 $\times 10^6$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB $e^+e^-$ collider. The decay is observed with a significance of 7.9 standard deviations. We measure a branching fraction $\mathcal{B} = (1.53 \pm 0.29 \pm 0.17) \times 10^{-6}$, a fraction of longitudinal polarization $f_L = 0.87 \pm 0.13 \pm 0.13$, and a time-integrated $CP$ asymmetry $A_{CP}$ = $-0.44 \pm 0.43 \pm 0.11$, where the first uncertainties listed are statistical and the second are systematic. This is the first observation of $B^{0} \rightarrow ωω$, and the first measurements of $f_L$ and $A_{CP}$ for this decay.

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arXiv2023

Search for the semileptonic decays $Ξ_c^0 \to Ξ^0\ell^+\ell^-$ at Belle

Using the full data sample of 980 $\mathrm{fb}^{-1}$ collected with the Belle detector at the KEKB asymmetric energy electron-positron collider, we report the results of the first search for the rare semileptonic decays $Ξ_c^0 \to Ξ^0\ell^+\ell^-$ ($\ell=e$ or $μ)$. No significant signals are observed in the $Ξ^0\ell^+\ell^-$ invariant-mass distributions. Taking the decay $Ξ_c^0 \to Ξ^- π^+$ as the normalization mode, we report 90\% credibility upper limits on the branching fraction ratios ${\cal{B}} (Ξ_c^0 \to Ξ^0 e^+ e^-) / {\cal{B}}(Ξ_c^0\to Ξ^-π^+) < 6.7 \times 10^{-3}$ and ${\cal{B}} (Ξ_c^0 \to Ξ^0 μ^+ μ^-) / {\cal{B}}(Ξ_c^0\to Ξ^-π^+) < 4.3 \times 10^{-3}$ based on the phase-space assumption for signal decays. The 90\% credibility upper limits on the absolute branching fractions of ${\cal{B}} (Ξ_c^0 \to Ξ^0 e^+ e^-)$ and ${\cal{B}} (Ξ_c^0 \to Ξ^0 μ^+ μ^-)$ are found to be $9.9 \times 10^{-5}$ and $6.5 \times 10^{-5}$, respectively.

hep-ex↗

arXiv2023

Search for a heavy neutrino in $τ$ decays at Belle

We report on a search for a heavy neutrino in the decays $τ^- \to π^- ν_h$, $ν_h \to π^\pm \ell-+$, $\ell = e, μ$. The results are obtained using the full data sample collected with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. We observe no significant signal and set 90% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional SM left-handed neutrinos in the mass range 0.2-1.6 GeV/c$^2$.

hep-ex↗

arXiv2023

Search for $CP$ violation in $D^{+}_{(s)}\rightarrow K^{+}K^{0}_{S}h^{+}h^{-}$ $(h=K,π)$ decays and observation of the Cabibbo-suppressed decay $D^{+}_{s}\rightarrow K^{+}K^{-}K^{0}_{S}π^{+}$

We search for $CP$ violation by measuring a $T$-odd asymmetry in the Cabibbo-suppressed $D^{+}\rightarrow K^{+}K^{0}_{S}π^{+}π^{-} $ decay, and in the Cabibbo-favored $D^{+}_{s}\rightarrow K^{+}K^{0}_{S}π^{+}π^{-}$ and $D^{+}\rightarrow K^{+}K^{-}K^{0}_{S}π^{+}$ decays. We use 980 ${\rm fb}^{-1}$ of data collected by the Belle detector running at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The $C\!P$-violating $T$-odd parameter ${a}^{T\text{-}\rm{odd}}_{CP}$ is measured to be ${a}^{T\text{-}\rm{odd}}_{CP}(D^{+}\rightarrow K^{+}K^{0}_{S}π^{+}π^{-})=(0.34\pm0.87\pm0.32)\%,$ ${a}^{T\text{-}\rm{odd}}_{CP}(D^{+}_{s}\rightarrow K^{+}K^{0}_{S}π^{+}π^{-})=(-0.46\pm0.63\pm0.38)\%,$ and ${a}^{T\text{-}\rm{odd}}_{CP}(D^{+}\rightarrow K^{+}K^{-}K^{0}_{S}π^{+})=(-3.34\pm2.66\pm0.35)\%,$ where the first uncertainty is statistical and the second is systematic. We also report the first observation of the Cabibbo-suppressed decay $D^{+}_{s}\rightarrow K^{+}K^{-}K^{0}_{S}π^{+}$. The branching fraction is measured relative to that of the analogous Cabibbo-favored decay : $B(D^{+}_{s}\rightarrow K^{+}K^{-}K^{0}_{S}π^{+}) / B(D^{+}_{s}\rightarrow K^{+}K^{0}_{S}π^{+}π^{-}) = (1.36\pm 0.15\pm 0.04)\%$.

hep-ex↗

arXiv2023

Measurement of Angular Coefficients of $\bar{B} \to D^* \ell \barν_\ell$: Implications for $|V_{cb}|$ and Tests of Lepton Flavor Universality

We measure the complete set of angular coefficients $J_i$ for exclusive $\bar{B} \to D^* \ell \barν_\ell$ decays ($\ell = e, μ$). Our analysis uses the full $711\,\mathrm{fb}^{-1}$ Belle data set with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the $B \to D^*$ transition and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{\rm cb}|$. Using recent lattice QCD calculations for the hadronic form factors, we find $|V_{\rm cb}| = (41.0 \pm 0.7) \times 10^3 $ using the BGL parameterization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter $w$, and investigate the differences of the electron and muon angular distributions. We find no deviation from Standard Model expectations.

hep-ex↗

arXiv2023

Search for $B{}^0_s \rightarrow \ell^{\mp} τ^{\pm}$ with the Semi-leptonic Tagging Method at Belle

We present a search for the lepton-flavor-violating decays $B{}^0_s \rightarrow \ell^{\mp}τ^{\pm}$, where $\ell = e, μ$, using the full data sample of $121~\mathrm{fb}^{-1}$ collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We use $B{}^0_s \overline{B}{}^0_s$ events in which one $B{}^0_s$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for $B{}^0_s \rightarrow \ell^{\mp}τ^{\pm}$ decays and set upper limits on their branching fractions at $90\%$ confidence level as $\mathcal{B}(B{}^0_s \rightarrow e^{\mp}τ^{\pm}) < 14 \times 10^{-4}$ and $\mathcal{B}(B{}^0_s \rightarrow μ^{\mp}τ^{\pm}) < 7.3 \times 10^{-4}$. Our result represents the first upper limit on the $B{}^0_s \rightarrow e^{\mp}τ^{\pm}$ decay rate.

hep-ex↗

arXiv2023

Observation of charmed strange meson pair production in $Υ(2S)$ decays and in $e^{+}e^{-}$ annihilation at $\sqrt{s} = 10.52~ \rm{GeV}$

We observe the process $Υ(2S)\to D_s^{(*)+} D_{sJ}^{-}$ and continuum production $e^+e^- \to 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 $D_{s1}(2536)^-$ or $D^{*}_{s2}(2573)^-$. Both $D_{sJ}^-$ states are identified through their decay into $\bar{K}\bar{D}^{(*)}$. We measure the products of branching fractions ${\cal B}(Υ(2S) \to D_{s}^{(*)+} D_{sJ}^-) {\cal B}(D_{sJ}^-\to \bar{K} \bar{D}^{(*)})$ and the Born cross sections $σ^{\rm Born}(e^+e^- \to D_{s}^{(*)+} D_{sJ}^-) {\cal B}(D_{sJ}^-\to \bar{K} \bar{D}^{(*)})$, and then compare the ratios $R_1 \equiv {\cal B}(Υ(2S)\to D_{s}^{(*)+} D_{sJ}^-)/{\cal B}(Υ(2S)\toμ^{+}μ^-)$ for $Υ(2S)$ decays and $R_2 \equiv σ^{\rm Born}(e^+e^-\to D_{s}^{(*)+}D_{sJ}^-)/σ^{\rm Born}(e^+e^-\to μ^{+}μ^-)$ for continuum production. We obtain $R_1/R_2 = 9.7\pm 2.3 \pm 1.1$, $6.8 \pm 2.1 \pm 0.8$, $10.2 \pm 3.3 \pm 2.5$, and $3.4 \pm 2.1 \pm 0.5$ for the $D_s^+ D_{s1}(2536)^-$, $D_s^{*+} D_{s1}(2536)^-$, $D_s^+ D_{s2}^{*}(2573)^{-}$, and $D_s^{*+} D_{s2}^{*}(2573)^{-}$ final states in the $D_{sJ}^-\to K^{-} \bar{D}^{(*)0}$ modes, respectively. Therefore, the strong decay is expected to dominate in the $Υ(2S)\to D_{s}^{(*)+}D_{sJ}^-$ processes. We also measure the ratios of branching fractions ${\cal B}(D_{s1}(2536)^-\to K_S^0 D^{*}(2010)^{-})/{\cal B}(D_{s1}(2536)^-\to K^{-} D^{*}(2007)^0) = 0.48 \pm 0.07 \pm 0.02$ and ${\cal B}(D_{s2}^{*}(2573)^- \to K_S^0 D^-)/{\cal B}(D_{s2}^{*}(2573)^- \to K^{-}D^0) = 0.49 \pm 0.10 \pm 0.02$, 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.

hep-ex↗

arXiv2023

Measurement of the $e^+e^- \to B_s^0 \bar{B}_s^0 X$ cross section in the energy range from $10.63$ to $11.02$ GeV using inclusive $D_s^{\pm}$ and $D^0$ production

We report the first measurement of the inclusive $e^+e^- \to b\bar{b} \to D_s^{\pm}X$ and $e^+e^- \to b\bar{b} \to D^0/\bar{D}^0X$ cross sections in the energy range from $10.63$ to $11.02$. Based on these results, we determine $σ(e^+ e^- \to B_s^0 \bar{B}_s^0 X)$ and $σ(e^+ e^- \to B\bar{B}X)$ in the same energy range. We measure the fraction of $B_s^0$ events at $Υ(10860)$ to be $f_{\rm s}=(22.0^{+2.0}_{-2.1})\%$. We determine also the ratio of the $B_s^0$ inclusive branching fractions $\mathcal{B}(B_s^0 \to D^0/\bar{D}^0X)/\mathcal{B}(B_s^0 \to D_s^{\pm} X)=0.416 \pm 0.018 \pm 0.092$. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.

hep-ex↗

arXiv2023

Evidence for $B^0 \to p\barΣ^0π^-$ at Belle

We search for the $B^0\to p\barΣ^0π^-$ decay with $\barΣ^0 \to \barΛγ$, where the $γ$ is not measured, using a data sample corresponding to an integrated luminosity of 711 $\rm{fb^{-1}}$ which contains 772 $\times$ $10^{6}$ $B\bar{B}$ pairs, collected around the $Υ$(4S) resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We measure for the first time the $B^0\to p\barΣ^0π^-$ branching fraction to be $\mathcal{B}(B^0 \to p \barΣ^0 π^-) = (1.17^{+0.43}_{-0.40}(\text{stat})\pm 0.07(\text{syst})) \times 10^{-6}$ with a significance of $3.0σ$. We simultaneously measure the branching fraction for the related channel $B^{0}\to p\barΛπ^{-}$ with much improved precision.

hep-ex↗

arXiv2023

First Simultaneous Determination of Inclusive and Exclusive $\left|V_{ub}\right|$

The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$ using inclusive and exclusive decays is performed with the full Belle data set at the $Υ(4S)$ resonance, corresponding to an integrated luminosity of 711 fb${}^{-1}$. We analyze collision events in which one $B$ meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic $X_u$ system of the semileptonic $b \to u \ell \bar ν_\ell$ decay. We separate exclusive $B \to π\, \ell\, \bar ν_{\ell}$ decays from other inclusive $B \to X_u \, \ell\, \bar ν_{\ell}$ and backgrounds with a two-dimensional fit, that utilizes the number of charged pions in the $X_u$ system and the four-momentum transfer $q^2$ between the $B$ and $X_u$ system. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the $B \to π\, \ell\, \bar ν_{\ell}$ form factor, we determine $\left|V_{ub}^{\mathrm{excl.}} \right| = (3.78 \pm 0.23 \pm 0.16 \pm 0.14)\times 10^{-3}$ and $\left|V_{ub}^{\mathrm{incl.}} \right| = (3.88 \pm 0.20 \pm 0.31 \pm 0.09)\times 10^{-3}$, respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of $\left|V_{ub}^{\mathrm{excl.}} \right| / \left|V_{ub}^{\mathrm{incl.}} \right| = 0.97 \pm 0.12$ is compatible with unity.

hep-ex↗

arXiv2023

Search for the double-charmonium state with $η_c J/ψ$ at Belle

We measure the cross section of $e^+e^-\rightarrowη_c J/ψ$ at the $Υ(nS) (n=1$ -- $5)$ on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of $955~\rm fb^{-1}$. We also search for double charmonium production in $e^+e^-\rightarrowη_c J/ψ$ via initial state radiation near the $η_c J/ψ$ threshold. No evident signal of the double charmonium state is found, but evidence for the $e^+e^-\rightarrowη_c J/ψ$ process is found with a statistical significance greater than $3.3σ$ near the $η_c J/ψ$ threshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.

hep-ex↗

arXiv2023

First measurement of the Q^2 distribution of X(3915) single-tag two-photon production

We report the first measurement of the $Q^2$ distribution of $X(3915)$ produced by single-tag two-photon interactions. The decay mode used is $X(3915) \rightarrow J/ψω$. The covered $Q^2$ region is from 1.5 (GeV/$c$)$^2$ to 10.0 (GeV/$c$)$^2$. We observe $7.9\pm 3.1({\rm stat.})\pm 1.5({\rm syst.})$ events, where we expect $4.1\pm 0.7$ events based on the $Q^2=0$ result from the no-tag two-photon process, extrapolated to higher $Q^2$ region using the $c\bar{c}$ model of Schuler, Berends, and van Gulik. The shape of the distribution is also consistent with this model; we note that statistical uncertainties are large.

hep-ex↗

arXiv2023

Study of the muon decay-in-flight in the $τ^-\toμ^-\barν_μν_τ$ decay to measure the Michel parameter $ξ^\prime$

We present the first measurement of the Michel parameter $ξ^\prime$ in the $τ^-\toμ^-\barν_μν_τ$ decay using the full data sample of $988\,\text{fb}^{-1}$ collected by the Belle detector operating at the KEKB asymmetric energy $e^+ e^-$ collider. The method is based on the reconstruction of the $μ^- \to e^- \barν_eν_μ$ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain $ξ^\prime=0.22\pm0.94\pm0.42$ where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of $ξ^\prime=1$.

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