arXiv subjects

S. Uehara

Publications and source records attributed to S. Uehara.

24 records · Page 2Linked to original sources

arXiv2008

High-statistics measurement of neutral-pion pair production in two-photon collisions

We present a high-statistics measurement of differential cross sections and the total cross section for the process gamma gamma -> pi^0 pi^0 in the kinematic range 0.6 GeV <= W <= 4.0 GeV and |cos theta*| <= 0.8, where W and theta* are the energy and pion scattering angle, respectively, in the gamma gamma center-of-mass system. Differential cross sections are fitted to obtain information on S, D_0, D_2, G_0 and G_2 waves. The G waves are important above W ~= 1.6 GeV. General behavior of partial waves is studied by fitting differential cross sections in a simple parameterization where amplitudes contain resonant contributions and smooth background. The D_2 wave is dominated by the f_2(1270) meson whose parameters are consistent with the with the current world averages. The D_0 wave contains a f_2(1270) component, whose fraction is fitted. For the S wave, the f_0(980) parameters are found to be consistent with the values determined from our recent pi^+ pi^- data. In addition to the f_0(980), the S wave prefers to have another resonance-like contribution whose parameters are obtained.

hep-ex↗

arXiv2008

Amplitude Analysis of High Statistics Results on $γγ\toπ^+π^-$ and the Two Photon Width of Isoscalar States

We perform an Amplitude Analysis of the world published data on $γγ\toπ^+π^-$ and $π^0π^0$. These are dominated in statistics by the recently published results from Belle on the charged pion channel. Nevertheless, having only limited angular information, a range of solutions remain possible. We present two solutions with $Γ(f_0(980)\toγγ) = 0.42$ and 0.10 keV, and $Γ(f_2(1270)\toγγ) = 3.14 \pm 0.20$ and $3.82 \pm 0.30$ keV, respectively: the former being the solution favoured by $χ^2$, the latter at the edge of acceptability. Models of the structure of the $f_0(980)$ predict two photon widths to be between 0.2 and 0.6 keV, depending on its composition as mainly ${\bar K}K$, ${\bar s}s$ or ${\bar{qq}}qq$. Presently available data cannot yet distinguish unambiguously between these predictions. However, we show how forthcoming results on $γγ\toπ^0π^0$ can not only discriminate between, but also refine, these classes of partial wave solutions.

hep-ph↗

arXiv2007

Study of charmonia in four-meson final states produced in two-photon collisions

We report measurements of charmonia produced in two-photon collisions and decaying to four-meson final states, where the meson is either a charged pion or a charged kaon. The analysis is based on a 395fb^{-1} data sample accumulated with the Belle detector at the KEKB electron-positron collider. We observe signals for the three C-even charmonia eta_c(1S), chi_{c0}(1P) and chi_{c2}(1P) in the pi^+pi^-pi^+pi^-, K^+K^-pi^+pi^- and K^+K^-K^+K^- decay modes. No clear signals for eta_c(2S) production are found in these decay modes. We have also studied resonant structures in charmonium decays to two-body intermediate meson resonances. We report the products of the two-photon decay width and the branching fractions, Gamma_{gamma gamma}B, for each of the charmonium decay modes.

hep-ex↗

arXiv2007

Search for Invisible Decay of the $Υ(1S)$

We report results of a search for the invisible decay of the Upsilon(1S) via the Upsilon(3S)->pi+pi-Upsilon(1S) transition using a data sample of 2.9 fb^{-1} at the Upsilon(3S) resonance. The data were collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signal is found, and an upper limit for the branching fraction at the 90% confidence level is determined to be B(Upsilon(1S)->invisible) < 2.5x10^{-3}.

hep-ex↗

arXiv2006

Observation of a chi'_(c2) candidate in gamma gamma --> D Dbar production at Belle

We report on a search for new resonant states in the process gamma gamma --> D Dbar. A candidate C-even charmonium state is observed in the vicinity of 3.93 GeV/c^2. The production rate and the angular distribution in the gamma gamma center-of-mass frame suggest that this state is the previously unobserved chi'_(c2), the 2^3P_2 charmonium state.

hep-ex↗

arXiv1997

A Search for Very High Energy Neutrinos from Active Galactic Nuclei

We report the results of a search for neutrino-induced particle cascades using a deep ocean water Cherenkov detector. The effective mass of the detector, a string of seven 40 cm diameter photomultipliers at 5.2 m spacing, is found through simulation analysis to be surprisingly large: greater than 1 megaton of water at incident neutrino energies of 1 PeV. We find no evidence for neutrino-induced cascades in 18.6 hours of observation. Although the limit implied by this observation is the strongest yet for predictions of active galatic nuclei (AGN) neutrinos at energies above 100 TeV, perhaps the more intriguing result is that the power of these techniques can be exploited to test these AGN models in a relatively short time.

astro-ph↗