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I. Nakano

Publications and source records attributed to I. Nakano.

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Toward CP-even Neutrino Beam

The best method of measuring CP violating effect in neutrino oscillation experiments is to construct and use a neutrino beam made of an ideal mixture of $\barν_e$ and $ν_e$ of monochromatic lines. The conceptual design of such a beam is described, together with how to measure the CP-odd quantity. We propose to exploit an accelerated unstable hydrogen-like heavy ion in a storage ring, whose decay has both electron capture and bound beta decay with a comparable fraction.

hep-ex

Macro-coherent two photon and radiative neutrino pair emission

We discuss a possibility of detecting a coherent photon pair emission and related radiative neutrino pair emission from excited atoms. It is shown that atoms of lambda- and ladder-type three level system placed in a pencil-like cylinder give a back to back emission of two photons of equal energy $Δ/2$, sharply peaked with a width $\propto $ 1/(target size) and well collimated along the cylinder axis. This process has a measurable rate $\propto$ (target number density) $^2 \times$ target volume, while a broader spectral feature of one-photon distribution separated by (mass sum of a neutrino pair)$^2/(2Δ)$ from the two photon peak may arise from radiative neutrino pair emission, with a much smaller rate.

hep-ph

Les Houches Physics at TeV Colliders 2005, Standard Model and Higgs working group: Summary report

This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics.

hep-ph

Search for Anomalous Couplings in Top Decay at Hadron Colliders

We present a quantitative study on sensitivities to the top-decay anomalous couplings, taking into account realistic experimental conditions expected at Tevatron and LHC. A double angular distribution of W and charged lepton in the top decay is analyzed, using ttbar events in the lepton+jets channel. In order to improve sensitivities to the anomalous couplings, we apply two techniques: (1) We use a likelihood fitting method for full kinematical reconstruction of each top event. (2) We develop a new effective spin reconstruction method for leptonically-decayed top quarks; this method does not require spin information of the antitop side. For simplicity, we neglect couplings of right-handed bottom quark as well as CP violating couplings. The 95% C.L. estimated bound on a ratio of anomalous couplings reads -0.81 < f_2/f_1 < -0.70, -0.12<f_2/f_1<0.14 using 1000 reconstructed top events at Tevatron, while -0.74<f_2/f_1<-0.72, -0.01<f_2/f_1<0.01 is expected with 100k reconstructed top events at LHC, where only statistical errors are taken into account. A two-fold ambiguity in the allowed range remains when the number of events exceeds a few hundred.

hep-ex

New Method of Enhancing Lepton Number Nonconservation

The lepton number nonconserving (LENNON) conversion of type $ e^- \to e^+$ in heavy atoms, when irradiated by intense laser beam, is considered to determine the Majorana nature and precise values of neutrino masses. When the photon energy is fine tuned, the LENNON process is greatly enhanced by both the resonance effect and a large occupancy of photons. The signal of this process would be a positron of definite energy, and a further nuclear $γ$-ray in a favorable case of transition to an excited nuclear level. By constructing a united target-detector system, it is possible to explore $O[1meV]$ range of the neutrino mass parameter with a good positron energy resolution.

hep-ph

Near Muon Range Detector for the K2K Experiment -Construction and Performance-

A muon range detector (MRD) has been constructed as a near detector for the KEK-to-Kamioka long-baseline neutrino experiment (K2K). It monitors the neutrino beam properties at the near site by measuring the energy, angle and production point of muons produced by charged-current neutrino interaction. The detector has been working stably since the start of the K2K experiment.

hep-ex

Bound on the tau neutrino magnetic moment from the TRISTAN experiments

We set limits on the magnetic moment and charge radius of the tau neutrino by examining an extra contribution to the electroweak process $e^+ e^- \to ν\barνγ$ using VENUS, TOPAZ and AMY results. We find that $κ(ν_τ) < 9.1\times{10}^{-6}$ (i.e. $μ(ν_τ) < 9.1\times{10}^{-6}μ_B, μ_B = e/2m_e$) and $ < 3.1\times{10}^{-31}$cm$^2$ with Poisson statistics by combining their results. Whereas, similar to this method, with the Unified Approach we find that $κ(ν_τ) < 8.0\times{10}^{-6}$ and $ < 2.7\times{10}^{-31}$cm$^2$.

hep-ph