arXiv subjects

M. H. Ahn

Publications and source records attributed to M. H. Ahn.

4 recordsLinked to original sources

arXiv2006

Measurement of Neutrino Oscillation by the K2K Experiment

We present measurements of nu_mu disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1^{+9.2}_{-8.6} events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muon-like events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3sigma). In a two flavor oscillation scenario, the allowed Delta m^2 region at sin^2(2theta) is between 1.9 and 3.5 x 10^{-3} eV^2 at the 90% C.L. with a best-fit value of 2.8 x 10^{-3} eV^2.

hep-ex↗

arXiv2004

Search for Electron Neutrino Appearance in a 250 km Long-baseline Experiment

We present a search for electron neutrino appearance from accelerator produced muon neutrinos in the K2K long baseline neutrino experiment. One candidate event is found in the data corresponding to an exposure of 4.8*10^19 protons on target. The expected background in the absence of neutrino oscillations is estimated to be 2.4+-0.6 events and is dominated by mis-identification of events from neutral current pi^0 production. We exclude the ν_μto ν_e oscillations at 90% C.L. for the effective mixing angle in 2-flavor approximation of sin^2(2theta_μ_e) (~= 1/2 sin^2 2 th_13) > 0.15 at Delta m^2_μ_e = 2.8*10^{-3} eV^2, the best fit value of the ν_μdisappearance analysis in K2K. The most stringent limit of sin^2(2theta_μ_e) < 0.09 is obtained at Delta m^2_μ_e = 6*10^{-3} eV^2.

hep-ex↗

arXiv2003

Observation of the Narrow State $X(3872)\to J/ψπ^{+}π^{-}$ in $\bar{p}p$ Collisions at $\sqrt{s}=1.96 \TeV$

We report the observation of a narrow state decaying into $J/ψπ^+π^-$ and produced in $220 pb^{-1}$ of $\bar{p} p $ collisions at $\sqrt{s}=1.96 TeV$ in the CDF II experiment. We observe $ 730 \pm 90 $ decays. The mass is measured to be $3871.3 \pm 0.7 (stat) \pm 0.4 (syst) MeV/c2$, with an observed width consistent with the detector resolution. This is in agreement with the recent observation by the Belle Collaboration of the X(3872) meson.

hep-ex↗

arXiv2002

Indications of Neutrino Oscillation in a 250 km Long-baseline Experiment

The K2K experiment observes indications of neutrino oscillation: a reduction of $ν_μ$ flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of $80.1^{+6.2}_{-5.4}$. Twenty-nine one ring $μ$-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.

hep-ex↗