We present the results of a search for nu_mu → nu_e oscillations in the NOMAD experiment at Cern. The experiment looked for the appearance of nu_e in a predominantly nu_mu wide-band neutrino beam at ...the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Delta m^2 < 0.4 eV^2 for maximal mixing and sin^2(2theta) < 1.4 X 10^-3 for large Delta m^2. This result excludes the LSND allowed region of oscillation parameters with Delta m^2 >~ 10 eV^2.
Results from the
ν
τ
appearance search in a neutrino beam using the full NOMAD data sample are reported. A new analysis unifies all the hadronic
τ decays, significantly improving the overall ...sensitivity of the experiment to oscillations. The “blind analysis” of all topologies yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90% CL allowed region in the sin
22
θ
μτ
–
Δm
2 plane which includes sin
22
θ
μτ
<3.3×10
−4 at large
Δm
2 and
Δm
2< 0.7 eV
2/
c
4 at sin
22
θ
μτ
=1. The corresponding contour in the
ν
e
→
ν
τ
oscillation hypothesis results in sin
22
θ
eτ
<1.5×10
−2 at large
Δm
2 and
Δm
2<5.9 eV
2/
c
4 at sin
22
θ
eτ
=1. We also derive limits on effective couplings of the
τ lepton to
ν
μ
or
ν
e
.
A search for exotic Θ+ baryon via Θ+→p+K0S decay mode in the NOMAD νμN data is reported. The special background generation procedure was developed. The proton identification criteria are tuned to ...maximize the sensitivity to the Θ+ signal as a function of xF which allows to study the Θ+ production mechanism. We do not observe any evidence for the Θ+ state in the NOMAD data. We provide an upper limit on Θ+ production rate at 90% CL as 2.13×10-3 per neutrino interaction.
Bose–Einstein correlations in one and two dimensions have been studied, with high statistics, in charged current muon–neutrino interaction events collected with the NOMAD detector at CERN. In one ...dimension the Bose–Einstein effect has been analyzed with the Goldhaber and the Kopylov–Podgoretskii phenomenological parametrizations. The Goldhaber parametrization gives the radius of the pion emission region
R
G=1.01±0.05(stat)
+0.09
−0.06(sys) fm and for the chaoticity parameter the value
λ=0.40±0.03(stat)
+0.01
−0.06(sys). Using the Kopylov–Podgoretskii parametrization yields
R
KP=2.07±0.04(stat)
+0.01
−0.14(sys) fm and
λ
KP=0.29±0.06(stat)
+0.01
−0.04(sys). Different parametrizations of the long-range correlations have been also studied. The two-dimensional shape of the source has been investigated in the longitudinal comoving frame. A significant difference between the transverse and the longitudinal dimensions is observed. The high statistics of the collected sample allowed the study of the Bose–Einstein correlations as a function of rapidity, charged particle multiplicity and hadronic energy. A weak dependence of both radius and chaoticity on multiplicity and hadronic energy is found.
Updated results from the appearance searches for $\numunutau$ and $\nuenutau$ oscillations in the full NOMAD data sample are reported. The increased data and the use of more refined kinematic schemes ...for the $\nutau$ CC selection allow a significant improvement of the overall sensitivity. The ``blind analysis" of both the deep-inelastic and the low multiplicity samples yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90\% C.L. region in the $\sin^22\theta_{\mu\tau} - \Delta m^2$ plane which includes $\sin^22\theta_{\mu\tau}\ \ 4.4\times10^{-4}$ at large $\Delta m^2$ and $\Delta m^2 0.8$ eV$^2$/$c^4$ at $\sin^22\theta_{\mu \tau}=1$. The corresponding contour in the $\nuenutau$ oscillation hypothesis results in $\sin^22\theta_{e\tau}\ \ 2.2\times10^{-2}$ at large $\Delta m^2$ and $\Delta m^2 6.5$ eV$^2$/$c^4$ at $\sin^22\theta_{e \tau}=1$
A search was made among $\nu_\mu$ charged current events collected in the NOMAD experiment for the reaction: $\nu_\mu + N \rightarrow \mu^- + D^{\star+} + hadrons \hookrightarrow D^0 + \pi^+ ...\hookrightarrow K^- + \pi^+ A $D^{\star+}$ sample composed of 47 events, with 90% purity, was extracted. The $D^{\star+}$ yield in $\nu_\mu$ charged current interactions was measured to be $T = (0.99 \pm 0.15(stat.) \pm 0.11(syst.))$%. The mean fraction of the hadronic jet energy taken by the $D^{\star+}$ is $0.67 \pm 0.02(stat) \pm 0.02(syst.)$. The distributions of the fragmentation variables $z$, ${P_{T}}^2$ and $x_F$ for $D^{\star+}$ are also presented.
Backward proton and $\pi^-$ production has been studied in \numucc interactions with carbon nuclei. Detailed analyses of the momentum distributions, of the production rates, and of the general ...features of events with a backward going particle, have been carried out in order to understand the mechanism producing these particles. The backward proton data have been compared with the predictions of the reinteraction and the short range correlation models.
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