Further evidence for neutrino oscillations from LSND: the νμ → νe decay-in-flight channel

A search for ν_μ → ν_e oscillations has been conducted at the Los Alamos Meson Physics Facility (LAMPF) using ν_μ from π⁺ decay in flight. An excess in the number of beam-related events from the ν_e C → e⁻ X inclusive reaction is observed. The excess is too large to be explained by normal ν_e contamination in the beam at a confidence level greater than 99%. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 ± 1.3 ± 0.5) × 10⁻³ is consistent with the previously reported oscillation evidence from LSND.     

Atmospheric neutrinos in the Soudan-2 and MACRO experiments

The results of Soudan-2 and MACRO experiments are summarized. Both experiments observe atmospheric neutrino anomalies in agreement with ν_μ → ν_τ oscillations with maximum mixing. The ν_μ → ν_s oscillations are disfavoured by the MACRO experiment at 98% C.L.     

Status of the CHORUS neutrino oscillation experiment

The CHORUS experiment is designed to search for ν_μ → ν_τ oscillation with a hybrid detector system containing 800 kg nuclear emulsions as target and vertex detector. Run I (320 000 recorded ν_μCC in 1994/5) and more than half of the run II (460 000 ν_μCC in 1996/7) data taking have been successfully completed. Approximately 80 000 events have been analyzed so far, searching for and τ⁻ → h⁻ (nπ⁰) ν_τ decays. No candidate has been found, leading to a limit sin² 2θ_μτ ≤ 4.5 10⁻³ for large Δm².     

KARMEN: Neutrino oscillation limits and new results with the upgrade

The neutrino experiment KARMEN is situated at the beam stop neutrino source ISIS which provides ν_μ's, ν_e's and from the π⁺−μ⁺-decay at rest. The oscillation channels ν_{μ → νe} and are investigated with a 56 t liquid scintillation calorimeter. No evidence for oscillations could be found with KARMEN, resulting in 90% CL exclusion limits of sin²(2Θ) < 8.5 · 10⁻³ ( ) and sin²(2Θ) < 4.0 · 10⁻² (ν_μ → ν_e) for Δm² > 100 eV². In 1996, the experiment has been upgraded by an additional veto counting system with a total coverage of 300 m². The new system allows the identification of cosmic muons in the vicinity of the detector. Vetoing these muons suppresses energetic neutrons from deep inelastic scattering of muons as well as from μ-capture by a factor of 40. Up to 1996, these neutrons represented the main background for oscillation search. The experimental sensitivity for will be significantly enhanced towards sin²(2Θ) 1.0 · 10⁻³ after a further measuring period of 2–3 years.     

Extracting (α/π) Σa,μνGμνGμν from gauge theories on a lattice

The quantity G = (α/π) Σ_a,μνG_μν^aG_μν^a is extracted from Monte Carlo data for SU(2) lattice gauge theory We find G = 0.015 ± 0.002 GeV⁴.     

Future atmospheric neutrino data from Super-Kamiokande

Expected sensitivity of future atmospheric neutrino data from Super-Kamiokande on neutrino oscillation physics is discussed. We expect that the accuracy of the sin ²θ₂₃ measurement will be improved with (exposure time) . By analyzing high energy fully contained events, it could be possible to statistically demonstrate the existence of charged current ν_τ interactions at the 3 standard deviation level with a few more years of data. Subdominant ν_μ → ν_e oscillations could be observed if θ₁₃ is near the present limit. However, significantly more data will be required to observe a 3 standard deviation effect.     

Update on the search for μ→ e oscillations by the 2 experiment

The neutrino experiment sets the most stringent exclusion limits for _μ→ _e oscillations. Analyzing the data set recorded from Feb.1997 up to March 2000 with the upgraded experimental configuration, the search of _e appearance via the p( _e, e⁺)n reaction yields no hints for neutrino oscillations. Applying a likelihood method to the measured event sample of 11 events (background expectation 12.3 events), we deduce an upper limit of sin² (2Θ) < 1.3 · 10⁻³ for large Δm² > 100 eV² and Δm² < 0.049 eV² for sin² (2Θ)=1.     

Observation of χb production in the exclusive reaction ′→γγχb→γγ→γγ(eeorμμ−)

We report on the observation of 1 ³P_J (χ_b) production in the reaction ′→γχ_b→γγ→γγ(e⁺e⁻ or μ⁺μ⁻). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV.     

Non-standard neutrino interactions in the Zee–Babu model

We investigate non-standard neutrino interactions (NSIs) in the Zee–Babu model. The size of NSIs predicted by this model is obtained from a full scan over the parameter space, taking into account constraints from low-energy experiments such as searches for lepton flavor violation (LFV) and the requirement to obtain a viable neutrino mass matrix. The dependence on the scale of new physics as well as on the type of the neutrino mass hierarchy is discussed. We find that NSIs at the source of a future neutrino factory may be at an observable level in the ν_e→ν_τ and/or ν_μ→ν_τ channels. In particular, if the doubly charged scalar of the model has a mass in reach of the LHC and if the neutrino mass hierarchy is inverted, a highly predictive scenario is obtained with observable signals at the LHC, in upcoming neutrino oscillation experiments, in LFV processes, and for NSIs at a neutrino factory.     

Transition dipole moment measurements for the ν2 band of NH3 with molecular beam laser Stark spectroscopy

Rabi oscillations were observed in the ASR(110), ΔM = 0 and ASQ(222), ΔM = 0 transitions of the ν₂ band of ¹⁴NH₃ in a molecular beam crossed by a CO₂ laser beam. The frequency (in terms of the laser field amplitude) of the oscillations was used to determine the transition dipole moment of the ν₂ band, yielding μ_s←a = 0.261 ± 0.006 D. The hyperfine structure due to the electric quadrupole interaction of the nitrogen nucleus was clearly resolved.     

ATLAS discovery potential for a heavy charged Higgs boson

The sensitivity of the ATLAS detector to the discovery of a heavy charged Higgs boson is presented. Assuming a heavy SUSY spectrum, the most promising channels above the top quark mass are H^± → tb and H^± → τ^±ν_τ which provide coverage in the low and high tanβ regions up to ∼ 600 GeV. The achievable precisions on the charged Higgs mass and tanβ determination are also discussed. The H^± → W^± h⁰ channel, though restricted to a small MSSM parameter space, shows a viable signal in NMSSM where the parameter space is less constrained. The observation of the channel H⁻ → τ⁻_L ν_τ + c.c. may constitute a distinctive evidence for models with singlet neutrinos in large extra dimensions.     

Soft photon problem in leptonic B-decays

We point out at the peculiarity of B→μν_μ decay, namely the enhancement of the soft photon events which originate from the structure dependent part of the B→μν_μγ amplitude. This may be a dominant source of systematic uncertainty and compromise the projected experimental uncertainty on Γ(B→μν_μ). We show that the effect of these soft photons can be controlled if the experimental cut on identification of soft photons is lowered and especially if the better resolution in identifying the momentum of muon emerging from B→μν_μ is made. A lattice QCD computation of the relevant form factors would be highly helpful for a better numerical control over the structure dependent soft photon emission.     

Line Intensities in the ν1, ν3, and 2ν2 Bands of H2Se

Using a high-resolution Fourier transform spectrum of hydrogen selenide in natural abundance, about 600 intensities of lines belonging to the ν₁, ν₃, and 2ν₂ bands of H₂⁸⁰Se were measured. A least-squares fit of these intensities was performed, allowing determination of the vibrational transition moments of these bands and their rotational corrections. Finally, the first derivatives of the dipole moment with respect to the normal coordinates q₁ and q₃ were found to be ∂μ_χ/∂q₁ = (−0.5938 ± 0.010) × 10⁻¹ and ∂μ_z/∂q₃ = (0.5683 ± 0.010) × 10⁻¹ Debye, respectively.     

Direct measurement of the pseudoscalar decay constant

The absolute branching fraction for the decay D⁺→μ⁺ν has been directly measured based on a data sample of about 33 pb⁻¹ collected around with the BES-II detector at the BEPC collider. A total of 5321±149±160 D⁻ mesons are reconstructed in nine hadronic decay modes. In the system recoiling against these singly tagged D⁻ mesons, 2.67±1.74 purely leptonic decay events of D⁺→μ⁺ν_μ are observed. Those yield the branching fraction of , and a corresponding value of the pseudoscalar decay constant .     

Short baseline projects

In a search for ν_μ → ν_e oscillations, the LSND experiment has observed an excess of events which are consistent with an oscillation signal. The KARMEN experiment, which is the only ongoing experiment which can test the LSND hypothesis, does not observe an excess, but also does not cover the full LSND allowed region. In this report, the results of these two experiments are discussed, together with the expectations of the MiniBooNE experiment which has been approved to run at FNAL in 2001. MiniBooNE's goal is to definitely verify or disprove the LSND oscillation hypothesis. Finally, the implications of the experimental techniques developed for current short baseline experiments for a future short baseline program, assuming the verification of the LSND signal, is also discussed.     

Study of the process ee→ππγ in c.m. energy range 600–970 MeV at CMD-2

The cross section of the process e⁺e⁻→π⁰π⁰γ has been measured in the c.m. energy range 600–970 MeV with the CMD-2 detector. The following branching ratios have been determined:

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and

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. Evidence for the ρ⁰→f₀(600)γ decay has been obtained:

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. From a search for the process e⁺e⁻→ηπ⁰γ the following upper limit has been obtained: at 90% CL.     

Analysis of high resolution fourier transform and diode laser spectra of the ν9 band of ethane

Fourier transform measurements with an apodized apparatus function up to 0.002 cm⁻¹ are reported for the ν₉ band (ρ_u) of ethane in the 12-μm region, together with an integrated band strength obtained from intensity measurements on selected Q-branch lines recorded using a diode laser spectrometer. Since the ν₉ band falls in an atmospheric window, these data may be useful in studies of the ethane concentration in the atmosphere of Jupiter and other outer planets. Torsional splittings in the ν₉ level caused by a higher-order Coriolis interaction with the close lying 3ν₄ state (a_1u) have been analyzed in a global least squares fit of 2206 Fourier transform lines and 58 diode splittings to a molecular Hamiltonian containing 20 parameters, with a standard deviation of 0.35 × 10⁻³ cm⁻¹. Rotational levels of one component of the torsionally split 3ν₄ state cross interacting rotational levels of the ν₉ state for K = 17, and the spectrum is followed to K = 19 on the ^pP subband side to permit inclusion of ν₉ levels beyond this crossing. No transitions to 3ν₄ levels were observed. The theoretical treatment presented here makes use of standard symmetric top formalism and of the G₃₆^† double-group formalism for ethane.     

Oxalyl halides : Analysis of the 3480 Å absorption system of oxalyl chloridefluoride

Oxalyl chloridefluoride (COCl)(COF) exhibits moderately strong discrete absorption in the 3050–3540Å region. The band spectrum has been analyzed as an allowed electronic transition of the planar trans molecule. The most active vibrations are the carbonyl stretching modes ν₁′ and ν₂′ and the in-plane bending mode ν₉. Various other fundamental frequencies in the combining electronic states have been identified. The 0₀⁰ band is at 28 724.5 cm⁻¹; partial rotational analysis confirms that this band is type C. The appearance of “line” structure in the wings of the band is discussed and an explanation offered. The vibrational and rotational analyses confirm that the transition is under the C_s point group, as expected for a singlet-singlet n → π^* type of excitation.     

Line Positions and Intensities of the ν1+ ν2+ 3ν3, ν2+ 4ν3, and 3ν1+ 2ν2Bands of Ozone

Using a Fourier transform spectrometer, we have recorded the spectra of ozone in the region of 4600 cm⁻¹, with a resolution of 0.008 cm⁻¹. The strongest absorption in this region is due to the ν₁+ ν₂+ 3ν₃band which is in Coriolis interaction with the ν₂+ 4ν₃band. We have been able to assign more than 1700 transitions for these two bands. To correctly reproduce the calculation of energy levels, it has been necessary to introduce the (320) state which strongly perturbs the (113) and (014) states through Coriolis- and Fermi-type resonances. Seventy transitions of the 3ν₁+ 2ν₂band have also been observed. The final fit on 926 energy levels withJ_max= 50 andK_max= 16 gives RMS = 3.1 × 10⁻³cm⁻¹and provides a satisfactory agreement of calculated and observed upper levels for most of the transitions. The following values for band centers are derived: ν₀(ν₁+ ν₂+ 3ν₃) = 4658.950 cm⁻¹, ν₀(3ν₁+ 2ν₂) = 4643.821 cm⁻¹, and ν₀(ν₂+ 4ν₃) = 4632.888 cm⁻¹. Line intensities have been measured and fitted, leading to the determination of transition moment parameters for the two bands ν₁+ ν₂+ 3ν₃and ν₂+ 4ν₃. Using these parameters we have obtained the following estimations for the integrated band intensities,S_V(ν₁+ ν₂+ 3ν₃) = 8.84 × 10⁻²²,S_V(ν₂+ 4ν₃) = 1.70 × 10⁻²², andS_V(3ν₁+ 2ν₂) = 0.49 × 10⁻²²cm⁻¹/molecule cm⁻²at 296 K, which correspond to a cutoff of 10⁻²⁶cm⁻¹/molecule cm⁻².     

Limits on the neutrino magnetic moment from solar neutrino experiments

If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μ_νe ≤ (2.2 − 2.3) × 10⁻¹⁰μ_B, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the ν_e,χe⁻ scattering is decreased.