Search for the exotic Θ+ resonance in the NOMAD experiment

12 pages, 16 figures.-- PACS nrs.: 13.15.+g; 13.60.Le; 13.87.Fh; 14.40.Ev.-- ISI Article Identifier: 000243973100007.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ex/0612063.-- et al.

Kalman filter tracking and vertexing in a silicon detector for neutrino physics

Abstract This article describes the application of Kalman filter techniques for the tracking and vertexing of particles inside the NOMAD-STAR detector, a silicon vertex detector installed in NOMAD, one of the neutrino oscillation experiments at the CERN-SPS. The use of the Kalman filter simplifies computationally the tracking and vertex procedure for NOMAD-STAR. The alignment of NOMAD-STAR is shown as an example of the application of the Kalman filter for tracking purposes. The accuracy of the method is such that one obtains alignment residuals between 9 and 12 μm . Furthermore, a preliminary measure of the impact parameter (with an RMS ∼36 μm ) illustrates the vertexing capabilities of thi…

A more sensitive search for νμ→ντ oscillations in NOMAD

With additional data and improved algorithms, we have enhanced the sensitivity of our appearance search for $\numunutau$ oscillations in the NOMAD detector in the CERN-SPS wide-band neutrino beam. The search uses kinematic criteria to identify $\nutau$ charged current interactions followed by decay of the $\tau^-$ to one of several decay modes. Our ``blind'' analyses of deep-inelastic scattering data taken in 1996 and 1997, combined with consistent reanalyses of previously reported 1995 data, yield no oscillation signal. For the two-family oscillation scenario, we present the contour outlining a 90\% C.L. confidence region in the $\sin^22\theta_{\mu \tau} - \Delta m^2$ plane. At large $\Del…

Search for eV (pseudo)scalar penetrating particles in the SPS neutrino beam

We carried out a model-independent search for light scalar or pseudoscalar particles $a$'s (an example of which is the axion) that couple to two photons by using a photon-regeneration method at high energies allowing a substantial increase in the sensitivity to $eV$ masses.\ The experimental set-up is based on elements of the CERN West Area Neutrino Facility (WANF) beam line and theNOMAD neutrino detector.\ The new particles, if they exist, could be produced through the Primakoff effect in interactions of high energy photons, generated by the 450 $GeV$ protons in the CERN SPS neutrino target, with virtual photons from the WANF horn magnetic field.\ The particles would penetrate the downstre…

Search for νμ→νe oscillations in the NOMAD experiment

We present the results of a search for vμ → v e oscillations in the NOMAD experiment at CERN. The experiment looked for the appearance of ve in a predominantly vμ wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Δm2 < 0.4 eV 2 for maximal mixing and sin2(2θ) < 1.4 × 10-3 for large Δm2. This result excludes the LSND allowed region of oscillation parameters with Δm2 ≳ 10 eV2. © 2003 Elsevier B.V. All rights reserved.

A Search for Single Photon Events in Neutrino Interactions

We present a search for neutrino induced events containing a single, exclusive photon using data from the NOMAD experiment at the CERN SPS where the average energy of the neutrino flux is ≃25 GeV. The search is motivated by an excess of electron-like events in the 200-475 MeV energy region as reported by the MiniBooNE experiment. In NOMAD, photons are identified via their conversion to e + e - in an active target embedded in a magnetic field. The background to the single photon signal is dominated by the asymmetric decay of neutral pions produced either in a coherent neutrino-nucleus interaction, or in a neutrino-nucleon neutral current deep inelastic scattering, or in an interaction occurr…

Production properties of $K*(892)\pm$ vector mesons and their spin alignment as measured in the NOMAD experiment

First measurements of K*(892) mesons production properties and their spin alignment in nu_mu charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD experiment is performed in different kinematic regions. For K*+ and K*- mesons produced in nu_mu CC interactions and decaying into K0 pi+/- we have found the following yields per event: (2.6 +/- 0.2 (stat.) +/- 0.2 (syst.))% and (1.6 +/- 0.1 (stat.) +/- 0.1 (syst.))% respectively, while for the K*+ and K*- mesons produced in nu NC interactions the corresponding yields per event are: (2.5 +/- 0.3 (stat.) +/- 0.3 (syst.))% and (1.0 +/- 0.3 (stat.) +/- 0.2 (syst.))%. The results o…

Performance of long modules of silicon microstrip detectors

This note describes the performance of modules assembled with up to twelve silicon microstrip detectors. These modules were built for the instrumented Silicon Target (STAR) that has been installed in the NOMAD spectrometer. Laboratory and test beam results are compared with model predictions. For a module of nine detectors, test beam results indicate a signal--to--noise ratio of 19, a hit finding efficiency of 99.8\% and a spatial resolution of 6.0 $\mu$m. Laboratory measurements indicate that modules of twelve detectors exhibit a signal--to--noise ratio of the order of 16.

Precision measurement of scaled momentum, charge multiplicity, and thrust in νμN and interactions

By focusing on the notion of electronic document, we differentiate two evolutions which are useful to distinct titles: on the one hand are the documents, which have value of reference. Its administrator will take care to preserve its integrity and its context of production which is strongly significant. On the other hand are resources, evolutionary elements by nature, which the user must be able to appropriate and who must thus be placed at the disposal so that the production is erased, to focus on a logic of exploitation and service.

A study of strange particle production in nu(mu) charged current interactions in the NOMAD experiment

A study of strange particle production in $\nu_\mu$ charged current interactions has been performed using the data from the NOMAD experiment. Yields of neutral strange particles ($K^0_s, \Lambda, \bar{\Lambda}$) have been measured. Mean multiplicities are reported as a function of the event kinematic variables $E_\nu$, $W^2$ and $Q^2$ as well as of the variables describing particle behaviour within a hadronic jet: $x_F$, $z$ and $p_T^2$. Decays of resonances and heavy hyperons with identified $K^0_s$ and $\Lambda$ in the final state have been analyzed. Clear signals corresponding to $\rm {K^\star}^\pm$ $\rm {\Sigma^\star}^\pm$, $\rm \Xi^-$ and $\rm \Sigma^0$ have been observed. A study of s…

Search for heavy neutrinos mixing with tau neutrinos

We report on a search for heavy neutrinos ($\nus$) produced in the decay $D_s\to \tau \nus$ at the SPS proton target followed by the decay $\nudecay$ in the NOMAD detector. Both decays are expected to occur if $\nus$ is a component of $\nu_{\tau}$.\ From the analysis of the data collected during the 1996-1998 runs with $4.1\times10^{19}$ protons on target, a single candidate event consistent with background expectations was found. This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the $\nus$ mass range from 10 to 190 $\rm MeV$. Windows between the SN1987a and Big Bang Nucleosynthesis lower limits and our result are still open for f…

Updated Results from the $\nu_{\tau}$ Appearance Search in NOMAD

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 cor…

Inclusive production of ρ0(770), f0(980) and f2(1270) mesons in νμ charged current interactions

The inclusive production of the meson resonances $\rho^{0}(770)$, $f_0(980)$ and $f_2(1270)$ in neutrino-nucleus charged current interactions has been studied with the NOMAD detector exposed to the wide band neutrino beam generated by 450 GeV protons at the CERN SPS. For the first time the $f_{0}(980)$ meson is observed in neutrino interactions. The statistical significance of its observation is 6 standard deviations. The presence of $f_{2}(1270)$ in neutrino interactions is reliably established. The average multiplicity of these three resonances is measured as a function of several kinematic variables. The experimental results are compared to the multiplicities obtained from a simulation b…

Limit on νe→ντ oscillations from the NOMAD experiment

Abstract In the context of a two-flavour approximation we reinterpret the published NOMAD limit on ν μ → ν τ oscillations in terms of ν e → ν τ oscillations. At 90% C.L. we obtain sin 2 2θ eτ 5.2×10 −2 for large Δm 2 , while for sin 2 2 θ eτ =1 the confidence region includes Δm 2 2 / c 4 .

New results on a search for a 33.9 MeV/c2 neutral particle from π+ decay in the NOMAD experiment

We report on a direct search in NOMAD for a new 33.9 MeV/c^2 neutral particle (X) produced in pion decay in flight, pi-->mu_X followed by the decay X -->nu e^+e^-. Both decays are postulated to occur to explain the time anomaly observed by the KARMEN experiment. From the analysis of the data collected during the 1996?1998 runs with 4.1×10^19 protons on target, a single candidate event consistent with background expectations was found. The search is sensitive to a pion branching ratio BR(pi-->muX >3.7×10^-15, significantly smaller than previous experimental limits.

A $B_4C$-silicon target for the detection of neutrino interactions

This note describes the construction of a target for neutrino interactions composed of passive boron carbide plates interleaved with silicon microstrip detectors. The target contains four layers of passive material with a total mass of 45 kg and 600 single--sided silicon microstrip detectors with a total surface of 1.14 m$^2$ distributed over five layers. It is installed in the NOMAD spectrometer at the CERN SPS neutrino beam. During the 1997 run about 8000 \nm\ charged current interactions were estimated to have occurred in the target. For these events it will be possible to perform a precise measurement of both vertex and kinematical variables. This will provide invaluable experience towa…

Measurement of the polarization in νμ charged current interactions in the NOMAD experiment

The Λ polarization in νμ charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed Λ 's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. We observe negative polarization along the W -boson direction which is enhanced in the target fragmentation region: Px(xF 0)=−0.09±0.06(stat)±0.03(sys) . These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the Λ production plane) has been observed for the first time in…

Performance of the NOMAD-STAR detector

The NOMAD-STAR detector is a silicon vertex installed in the NOMAD spectrometer at the CERN SPS neutrino beam. It consists of four layers of a passive boron carbide target with a total mass of 45 kg and five layers of 600 single sided silicon microstrip detectors covering a total area of 1.14m^2. About 11,500 nu_mu charged current interactions were reconstructed in the fiducial volume of NOMAD-STAR from the neutrino run in 1998. The potential use of silicon detectors for nu_mu (nu_e) nu_tau oscillations depends on the observation of the tau candidates by the experimental signature of a large impact parameter, in the case of the one prong decay of the tau, or a double vertex, in the case of …

A study of quasi-elastic muon neutrino and antineutrino scattering in the NOMAD experiment

We have studied the muon neutrino and antineutrino quasi-elastic (QEL) scattering reactions ($\nu_\mu n\to \mu^- p$ and $\bar{\nu}_\mu p\to \mu^+ n$) using a set of experimental data collected by the NOMAD collaboration. We have performed measurements of the cross-section of these processes on a nuclear target (mainly Carbon) normalizing it to the total $\nu_\mu$ ($\bar{\nu}_\mu$) charged current cross-section. The results for the flux averaged QEL cross-sections in the (anti)neutrino energy interval 3-100 GeV are $\sigma^{qel}_{\nu_\mu} = (0.92 \pm 0.02 (stat) \pm 0.06 (syst))\times 10^{-38} \cm^2$ and $\sigma{qel}_{\bar{\nu}_\mu} = (0.81 \pm 0.05 (stat) \pm 0.08 (syst))\times 10^{-38} \cm…

Results of prototype studies for a spaghetti calorimeter

In the framework of the LAA project, prototypes for a new type of calorimeter, intended for the detection of both electromagnetic (e.m.) and hadronic showers, muons and missing energy (e.g. neutrinos) at high-luminosity multi-TeV pp colliders, were tested. The detector consists of scintillating plastic fibres embedded in a lead matrix at a volume ratio 1:4, such as to achieve compensation. The optimization of the construction of the detector modules is described, as well as the performance concerning e.m. shower and muon detection and e/π separation. We used electron, pion and muon beams in the energy range 10–150 GeV for this purpose. For the energy resolution of electrons we found 13%/trE…

Study of D*+ production in nu_mu charged current interactions in the NOMAD experiment

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.

Neutrino production of opposite sign dimuons in the NOMAD experiment

The NOMAD Collaboration presents a study of opposite sign dimuon events in the framework of Leading Order QCD. A total of 2714 neutrino- and 115 antineutrino-induced opposite sign dimuon events with $E_{\mu 1}, E_{\mu 2} > 4.5$ GeV, $15 1\;(\mbox{GeV}/\mbox{c})^{2}$ are observed %in the data from the 1995 and 1996 runs. in the Front-Calorimeter of NOMAD during the 1995 and 1996 runs. The analysis yields a value for the charm quark mass of $m_{c} = 1.3^{+0.3\;+0.3}_{-0.3\;-0.3}\;\mbox{GeV}/\m box{c}^{2}$ and for the average semileptonic branching ratio of $B_{c} = 0.095^{+0.007\;+0.014}_{-0.007\;-0.013}$. The ratio of the strange to non-strange sea in the nucleon is measured to be $\kappa = …

Prediction of neutrino fluxes in the NOMAD experiment

The method developed for the calculation of the flux and composition of the West Area Neutrino Beam used by NOMAD in its search for neutrino oscillations is described. The calculation is based on particle production rates computed using a recent version of FLUKA and modified to take into account the cross sections measured by the SPY and NA20 experiments. These particles are propagated through the beam line taking into account the material and magnetic fields they traverse. The neutrinos produced through their decays are tracked to the NOMAD detector. The fluxes of the four neutrino flavours at NOMAD are predicted with an uncertainty of about 8% for nu(mu) and nu(e), 10% for antinu(mu), and…

Search for a new gauge boson in $\pi^{0}$ decays

A search was made for a new light gauge boson $X$ which might be produced in $\pi^{0}\to\gamma + X$ decay from neutral pions generated by 450-GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of $X \to\pi^{0}$ conversion in the external Coulomb field of a nucleus. With $1.45\times10^{18}$ protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1$\pm$2.8 background events from standard neutrino processes. A new 90% C.L. upper limit on the branching ratio…

Advances in Technology for High-Energy Subnuclear Physics. Contribution of the LAA Project.

Bose-Einstein correlations in charged current muon-neutrino interactions in the NOMAD experiment at CERN

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 lambda = 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 lambda_KP = 0.29+/-0.06(stat)+0.01-0.04(sys). Different paramet…

A precision measurement of charm dimuon production in neutrino interactions from the NOMAD experiment

We present our new measurement of the cross-section for charm dimuon production in neutrino iron interactions based upon the full statistics collected by the NOMAD experiment. After background subtraction we observe 15 344 charm dimuon events, providing the largest sample currently available. The analysis exploits the large inclusive charged current sample - about 9 x 10(6) events after all analysis cuts - and the high resolution NOMAD detector to constrain the total systematic uncertainty on the ratio of charm dimuon to inclusive Charged Current (CC) cross-sections to similar to 2%. We also perform a fit to the NOMAD data to extract the charm production parameters and the strange quark sea…

A precise measurement of the muon neutrino nucleon inclusive charged current cross section off an isoscalar target in the energy range 2.5

Abstract We present a measurement of the muon neutrino–nucleon inclusive charged current cross section, off an isoscalar target, in the neutrino energy range 2.5 ⩽ E ν ⩽ 40 GeV . The significance of this measurement is its precision, ±4% in 2.5 ⩽ E ν ⩽ 10 GeV , and ±2.6% in 10 ⩽ E ν ⩽ 40 GeV regions, where significant uncertainties in previous experiments still exist, and its importance to the current and proposed long baseline neutrino oscillation experiments.

A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment

Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (K0s, Lambda, Lambda-bar) have been measured. Decays of resonances and heavy hyperons with an identified K0s or Lambda in the final state have been analyzed. Clear signals corresponding to K* and Sigma(1385) have been observed. First results on the measurements of the Lambda polarization in neutral current interactions have been obtained.

A measurement of coherent neutral pion production in neutrino neutral current interactions in the NOMAD experiment

We present a study of exclusive neutral pion production in neutrino-nucleus Neutral Current interactions using data from the NOMAD experiment at the CERN SPS. The data correspond to $1.44 \times 10^6$ muon-neutrino Charged Current interactions in the energy range $2.5 \leq E_{\nu} \leq 300$ GeV. Neutrino events with only one visible $\pi^0$ in the final state are expected to result from two Neutral Current processes: coherent $\pi^0$ production, {\boldmath $\nu + {\cal A} \to \nu + {\cal A} + \pi^0$} and single $\pi^0$ production in neutrino-nucleon scattering. The signature of coherent $\pi^0$ production is an emergent $\pi^0$ almost collinear with the incident neutrino while $\pi^0$'s pro…

Electron-pion discrimination with a scintillating fiber calorimeter

Abstract We report on an experimental study of a variety of techniques for discriminating between (isolated) electrons and pions in a lead and scintillating fiber calorimeter without longitudinal segmentation. Using information from the lateral shower development, from a pre-shower detector, from the time structure of the signals, or from a combination of these we measure pion rejection factors of up to several thousand while maintaining electron efficiencies of 95% or higher.