Results from the NOMAD experiment

The NOMAD experiment has sought ν_μ ? ν_τ oscillations by looking for the emergence of τ^? in events from the CERN SPS neutrino beam. With some improvements in the techniques of analysis in relation to the results published previously and with the inclusion of data from the 1998 run, no evidence for the oscillations has been found, which results in an updated limit on the oscillation probability [P(ν_μ → ν_τ) < 0.5 × 10^?3 at a 90% C.L.]. The corresponding limit on the oscillation mixing angle is given by sin²2θ_μτ < 1.0 × 10^?3 for large Δm ². By using a 1% contamination of ν_e in the neutrino beam, we can also rule out ν _e ? ν_τ oscillations and constrain the probability of the relevant transition as P(ν _e → ν_τ) < 3 × 10^?2 at a 90% C.L. (sin²2θ _eτ < 6 × 10^?2 at large Δm ²).     

Fast proton decay

We consider proton decay in the testable flipped SU(5)×UX₍₁₎$\mathit{SU}(5)\times U{(1)}_X$ models with TeV-scale vector-like particles which can be realized in free fermionic string constructions and F-theory model building. We significantly improve upon the determination of light threshold effects from prior studies, and perform a fresh calculation of the second loop for the process p→e⁺π⁰$p\to e^{+}{\pi }^0$ from the heavy gauge boson exchange. The cumulative result is comparatively fast proton decay, with a majority of the most plausible parameter space within reach of the future Hyper-Kamiokande and DUSEL experiments. Because the TeV-scale vector-like particles can be produced at the LHC, we predict a strong correlation between the most exciting particle physics experiments of the coming decade.     

Results from the forward G0 experiment

The G0 experiment is dedicated to the determination of the strange quark contribution to the electric and magnetic nucleon form factors for a large range of momentum transfers between 0.1 to 1(GeV/c)² . This information is provided by the asymmetries of cross-sections measured with longitudinally polarized electrons in elastic electron-proton scattering and quasi-elastic electron-deuteron scattering. A set of measurements at two different Q² will allow the complete separation of the electric and magnetic weak, as well as axial nucleon form factors. This report summarizes the physics case, gives details about the dedicated set-up used, and shows the results of the combination of the strange quark contribution in the electric and magnetic form factors of the protons. The experiment was performed at the Jefferson Laboratory, during years 2003 and 2004, and will be completed after backward-angle measurements in 2006, 2007.     

Results from the T2K experiment

The T2K (Tokai-to-Kamioka) experiment is a long baseline neutrino oscillation experiment designed to probe the θ ₁₃ neutrino mixing parameter by looking for the appearance of ν _e in an almost pure ν _μ beam. The concurrent measurement of the ν _μ disappearance allows refined measurements of the atmospheric Δm ² and θ ₂₃ mixing parameters.     

Supersymmetry and proton decay

Using supergraph techniques it is shown that all one-loop contributions to the proton decay amplitude, which are suppressed by only one power of the unification mass and are not of fourth order in Higgs couplings, vanish in a general supersymmetric grand unification setting. Corrections to this statement due to soft supersymmetry breaking are analysed.     

Results from the mainz neutrino mass experiment

The presently lowest limit for the mass of the electron neutrino is m _ν<2.2 eV/c ² 95% C.L.) derived from measurements at Mainz up to 1999. The data taken in 2000 are not fully analyzed yet, but limits of possible distortions as reported by the Troitsk group can be given.     

Results from STAR experiment at RHIC

We present some of the important experimental results from nucleus-nucleus collision studies carried out by the STAR experiment at Relativistic Heavy Ion Collider (RHIC). The results suggests that central Au+Au collisions at RHIC has produced a dense and rapidly thermalizing matter with initial energy densities above the critical values predicted by lattice QCD for establishment of a quark-gluon plasma (QGP).     

Results from the MUNU experiment on neutrino-electron scattering

The MUNU experiment studies electron antineutrino-electron elastic scattering. The detector is a time projection chamber surrounded by an anti-Compton detector. The distance between the reactor (serving as the neutrino source) and the detector is 18 m. Here, data are presented corresponding to 66.6-d live time reactor on and 16.7-d reactor off. The electron recoil spectrum obtained by using a visual scanning procedure is presented. The upper limit on the neutrino magnetic moment ν_π<1.0×10^?10π_B is derived.     

Chiral quarks and proton decay

In this paper we calculate the hadronic matrix elements of baryon decay operators using a chiral effective lagrangian with quarks, gluons and Goldstone boson fields. We study in detail the cases where the ΔB = 1 operators arise from supersymmetric SU(5) GUT as well as the minimal SU(5) GUT model. In each model the results depend on two parameters. In particular there is a range of values for the two parameters, where the dominant decay modes in the minimal SU(5) GUT are: p → ηe⁺ and n → π^? e⁺.     

KAMIOKA nucleon decay experiment

Summary Recent results of KAMIOKA nucleon decay experiment are presented. The great majority, ∼95%, of the contained events can be naturally explained as due to the atmospheric neutrinos,i.e. the rate and the momentum distribution of the pseudoelastic ν_μ and ν_e events and the multiplicity distribution. However, 5 multiple-ring events remain each defying this interpretation at 90% c.l. Stringent flux upper limits are obtained for magnetic monopole from the searches for Rubakov effect in the detector and in the Sun. KAMIOKANDE collaboration:K. Arisaka, T. Kajita, T. Kifune, M. Koshiba, K. Miyano, M. Nakahata, Y. Oyama, T. Suda, A. Suzuki, K. Takahashi, M. Takita andY. Totsuka: ICEPP and Department of Physics, University of Tokyo; Institute of Cosmic Ray Research, University of Tokyo; KEK, National Laboratory for High Energy Physics and Department of Physics, Niigata University. (As of January 1985,K. Arisaka moved to Department of Physics, Pennsilvania University.)     

Nuclear effects on proton decay

It is shown that the nuclear field affects the probability of creation of a meson inside a nucleus, and not only the survival probability when travelling through the nuclear medium. Decay into heavy (m_M ≳ 500 MeV) mesons can be strongly affected by the interaction with the nuclear medium.     

Results on hyperon production from the NA57 experiment

Recent results on hyperon production in Pb-Pb collisions from the NA57 experiment are reported. Strangeness enhancements and the transverse mass spectra properties at 158 GeV per nucleon are described.     

Baryon poles in proton decay amplitudes

The decay rate of the p→π⁰e⁺ mode is calculated in SU(5) grand unified theory using a pole model with proton and $\text{1}\text{2}{}^{\mathrm{?}}$ baryon poles. Baryon-to-vacuum amplitudes are calculated in the framework of the MIT bag model. It is found that the partial decay rate [～(5×10³¹ yr)^?)] is close to the partial decay rates calculated by different methods.     

Effective baryon-lepton coupling and the proton decay modes

We present a simple model for the phenomenology of baryon-number violating nucleon decays in which the basic process is taken to be a direct conversion of a baryon into a lepton or an antilepton. A large number of branching modes are found to be correlated, independently of any specific grand unification scheme.     

Proton pole contribution in proton decay

We show that nucleon pole terms contribute significantly to proton decay, increasing the branching ratio for e⁺π⁰ and $\text{ν}{}_{\mathrm{<mtext>R</mtext>}}\text{π}{}^{\mathrm{+}}$ modes. The total lifetime is decreased to the point where keeping the SU(5) value of the lifetime below the experimental upper bound forces us to the choice of QCD scale parameter and proton radius parameter which are near the edge of the allowed region.     

Prompt neutrino results from a proton beam dump experiment

A study of prompt neutrino events from 400 GeV protons on a beam-dump is presented. The ratio of electron- to muon-neutrino rates is 0.86±0.14, in agreement withe– universality. The anti-neutrino to neutrino flux ratio is . The absolute rates and distributions observed are shown to be in quantitative agreement with the known properties of charmedquark production in hadron collisions.Supported by the Bundesministerium für Forschung und Technologic, Bonn, FRG     

The calculation of the matrix element for proton decay

Matrix elements and proton decay probabilities are calculated in the SU(5) model of grand unification with the help of the matrix element of the proton transition into three quarks, found previously by the QCD sum rules. The results show that an increase of the existing experimental lower limit for the proton lifetime by a factor of 3–4 would rule out the standard SU(5) model.