48 research outputs found
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 downstream shieldingand would be observed in the NOMAD neutrino detector through their re-conversion into real high energy photons byinteracting with the virtual photons from the magnetic field of the NOMAD dipole magnet.\ From the analysis of the data collected during the 1996 run with 1.08Ă1019 protons on target, 312 candidate events with energy between 5 and 140 GeV were found.\ This number is in general agreement with the expectation of 272±18 background events from standard neutrino processes.\ A 90 % CL upper limit on the aγγ-coupling gaγγ< 1.5Ă10â4 GeVâ1 for a masses up to 40 eV is obtained
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 content of the nucleon within the NLO QCD approximation. We obtain a value of m(c)(m(c)) = 1.159 +/- 0.075 GeV/c(2) for the running mass of the charm quark in the (MS) over bar scheme and a strange quark sea suppression factor of kappa(s) = 0.591 +/- 0.019 at Q(2) = 20 GeV2/c(2).We extend our grateful appreciations to the CERN SPS staff for the magnificent performance of the neutrino beam. The experiment was supported by the following agencies: ARC and DIISR of Australia, IN2P3 and CEA of France, BMBF of Germany, INFN of Italy, JINR and INR of Russia, FNSRS of Switzerland, DOE, NSF, Sloan, and Cottrell Foundations of USA, and VP Research Office of the University of South Carolina. This work was partially supported by the University of South Carolina, by the DOE grant DE-FG02-95ER40910, by the Russian Federal grant 02.740.11.5220 and MK-432.2013.2, and JINR grant 13-201-01.Peer reviewe
Radiative Corrections to Neutrino Deep Inelastic Scattering Revisited
Radiative corrections to neutrino deep inelastic scattering are revisited.
One-loop electroweak corrections are re-calculated within the automatic SANC
system. Terms with mass singularities are treated including higher order
leading logarithmic corrections. Scheme dependence of corrections due to weak
interactions is investigated. The results are implemented into the data
analysis of the NOMAD experiment. The present theoretical accuracy in
description of the process is discussed.Comment: 19 pages, two figures are added, discussion of theoretical
uncertainties is extende
NuTeV anomaly and nuclear parton distributions revisited
By studying the Paschos-Wolfenstein (PW) ratio of deep inelastic and scattering cross sections, we show that it should
be possible to explain the NuTeV anomaly with quite
conventional physics, by introducing mutually different nuclear modifications
for the valence- and valence- quark distributions of the protons in iron.
Keeping the EKS98 nuclear modifications for as a baseline, we find
that some 20-30 % nuclear modifications to the and distributions
account for the change induced in the PW ratio by the NuTeV-suggested increase
. We show that introduction of such
nuclear modifications in and individually, does not lead into
contradiction with the present global DGLAP analyses of the nuclear parton
distributions, where deep inelastic scattering data and Drell-Yan dilepton
data from collisions are used as constraints. We thus suggest that the
NuTeV result serves as an important further constraint in pinning down the
nuclear effects of the bound nucleon PDFs. We also predict that if the NuTeV
anomaly is explained by this mechanism, the NOMAD experiment should see an
increase in the weak mixing angle quite close to the NuTeV result.Comment: 17 pages, 7 figure
Pentaquarks: review of the experimental evidence
Pentaquarks, namely baryons made by 4 quarks and one antiquark have been
predicted and searched for since several decades without success. Theoretical
and experimental advances in the last 2 years led to the observation of a
number of pentaquark candidates. We review the experimental evidence for
pentaquarks as well as their non-observations by some experiments, and discuss
to which extend these sometimes contradicting informations may lead to a
consistent picture.Comment: Contribution to the International Conference on 'Strangeness in Quark
Matter', 15-21 Sept. 2004, Cape Tawn, South Afric
Statistical Pattern Recognition: Application to Oscillation Searches Based on Kinematic Criteria
Classic statistical techniques (like the multi-dimensional likelihood and the
Fisher discriminant method) together with Multi-layer Perceptron and Learning
Vector Quantization Neural Networks have been systematically used in order to
find the best sensitivity when searching for
oscillations. We discovered that for a general direct appearance
search based on kinematic criteria: a) An optimal discrimination power is
obtained using only three variables (, and
) and their correlations. Increasing the number of variables (or
combinations of variables) only increases the complexity of the problem, but
does not result in a sensible change of the expected sensitivity. b) The
multi-layer perceptron approach offers the best performance. As an example to
assert numerically those points, we have considered the problem of
appearance at the CNGS beam using a Liquid Argon TPC detector.Comment: 24 pages, 15 figure
Nucleon Decay Searches with large Liquid Argon TPC Detectors at Shallow Depths: atmospheric neutrinos and cosmogenic backgrounds
Grand Unification of the strong, weak and electromagnetic interactions into a single unified gauge group is an extremely appealing idea which has been vigorously pursued theoretically and experimentally for many years. The detection of proton or bound-neutron decays would represent its most direct experimental evidence. In this context, we studied the physics potentialities of very large underground Liquid Argon Time Projection Chambers (LAr TPC). We carried out a detailed simulation of signal efficiency and background sources, including atmospheric neutrinos and cosmogenic backgrounds. We point out that a liquid Argon TPC, offering good granularity and energy resolution, low particle detection threshold, and excellent background discrimination, should yield very good signal over background ratios in many possible decay modes, allowing to reach partial lifetime sensitivities in the range of 1034â1035 years with exposures up to 1000 ktonĂyear, often in quasi-background-free conditions optimal for discoveries at the few events level, corresponding to atmospheric neutrino background rejections of the order of 105. Multi-prong decay modes like e.g. pâÎŒâÏ+K+ or pâe+Ï+Ïâ and channels involving kaons like e.g. pâK+ÎœÂŻ, pâe+K0 and pâÎŒ+K0 are particularly suitable, since liquid Argon imaging (...)This work was in part supported by ETH and the Swiss National Foundation. AB, AJM and SN have been supported by CICYT Grants FPA-2002-01835 and FPA-2005-07605-C02-01. SN acknowledges support from the Ramon y Cajal Programme. We thank P. Sala for help with FLUKA while she was an ETH employee