Recent developments of the nuclear emulsion technology led to the production of films with nanometric silver halide grains suitable to track low energy nuclear recoils with submicrometric length. ...This improvement opens the way to a directional Dark Matter detection, thus providing an innovative and complementary approach to the on-going WIMP searches. An important background source for these searches is represented by neutron-induced nuclear recoils that can mimic the WIMP signal. In this paper we provide an estimation of the contribution to this background from the intrinsic radioactive contamination of nuclear emulsions. We also report the neutron-induced background as a function of the read-out threshold, by using a GEANT4 simulation of the nuclear emulsion, showing that it amounts to about 0.06 per year per kilogram, fully compatible with the design of a 10 kg × year exposure.
We present a measurement of the flux of neutrino-induced upgoing muons (<E
ν
>∼ 100 GeV) using the MACRO detector. The ratio of the number of observed to expected events integrated over all zenith ...angles is 0.74 ±0.036 (stat) ±0.046 (systematic) ±0.13 (theoretical). The observed zenith distribution for −1.0≤cos
θ≤−0.1 does not fit well with the no oscillation expectation, giving a maximum probability for
χ
2 of 0.1%. The acceptance of the detector has been extensively studied using downgoing muons, independent analyses and Monte Carlo simulations. The other systematic uncertainties cannot be the source of the discrepancies between the data and expectations.
We have investigated whether the observed number of events and the shape of the zenith distribution can be explained by a neutrino oscillation hypothesis. Fitting either the flux or zenith distribution independently yields mixing parameters of sin
22
θ=1.0 and
Δm
2 of a few times 10
−3 eV
2. However, the observed zenith distribution does not fit well with any expectations, giving a maximum probability for
χ
2 of 5% for the best oscillation hypothesis, and the combined probability for the shape and number of events is 17%. We conclude that these data favor a neutrino oscillation hypothesis, but with unexplained structure in the zenith distribution not easily explained by either the statistics or systematics of the experiment.
A
bstract
The OPERA neutrino experiment at the underground Gran Sasso Laboratory has measured the velocity of neutrinos from the CERN CNGS beam over a baseline of about 730 km. The measurement is ...based on data taken by OPERA in the years 2009, 2010 and 2011. Dedicated upgrades of the CNGS timing system and of the OPERA detector, as well as a high precision geodesy campaign for the measurement of the neutrino baseline, allowed reaching comparable systematic and statistical accuracies.
An arrival time of CNGS muon neutrinos with respect to the one computed assuming the speed of light in vacuum of
was measured corresponding to a relative difference of the muon neutrino velocity with respect to the speed of light
. The above result, obtained by comparing the time distributions of neutrino interactions and of protons hitting the CNGS target in 10.5
μ
s long extractions, was confirmed by a test performed at the end of 2011 using a short bunch beam allowing to measure the neutrino time of flight at the single interaction level.
Direct Dark Matter searches are nowadays one of the most fervid research topics with many experimental efforts devoted to the search for nuclear recoils induced by the scattering of Weakly ...Interactive Massive Particles (WIMPs). Detectors able to reconstruct the direction of the nucleus recoiling against the scattering WIMP are opening a new frontier to possibly extend Dark Matter searches beyond the neutrino background. Exploiting directionality would also prove the galactic origin of Dark Matter with an unambiguous signal-to-background separation. Indeed, the angular distribution of recoiled nuclei is centered around the direction of the Cygnus constellation, while the background distribution is expected to be isotropic. Current directional experiments are based on gas TPC whose sensitivity is limited by the small achievable detector mass. In this paper we present the discovery potential of a directional experiment based on the use of a solid target made of newly developed nuclear emulsions and of optical read-out systems reaching unprecedented nanometric resolution.
The OPERA magnetic spectrometer Ambrosio, M.; Brugnera, R.; Dusini, S. ...
IEEE transactions on nuclear science,
06/2004, Letnik:
51, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The OPERA neutrino oscillation experiment foresees the construction of two magnetized iron spectrometers located after the lead-nuclear emulsion targets. The magnet is made up of two vertical walls ...of rectangular cross section connected by return yokes. The particle trajectories are measured by high precision drift tubes located before and after the arms of the magnet. Moreover, the magnet steel is instrumented with resistive plate chambers that ease pattern recognition and allow a calorimetric measurement of the hadronic showers. In this paper, we review the construction of the spectrometers. In particular, we describe the results obtained from the magnet and RPC prototypes and the installation of the final apparatus at the Gran Sasso laboratories. We discuss the mechanical and magnetic properties of the steel and the techniques employed to calibrate the field in the bulk of the magnet. Moreover, results of the tests and issues concerning the mass production of the resistive plate chambers are reported. Finally, the expected physics performance of the detector is described; estimates rely on numerical simulations and the outcome of the tests described above.
A new method of momentum measurement of charged particles through multiple Coulomb scattering (MCS) in the OPERA lead-emulsion target is presented. It is based on precise measurements of track ...angular deviations carried out thanks to the very high resolution of nuclear emulsions. The algorithm has been tested with Monte Carlo pions. The results are found to describe within the expected uncertainties the data obtained from test beams. We also present a comparison of muon momenta evaluated through MCS in the OPERA lead-emulsion target with those determined by the electronic detectors for neutrino-charged current interaction events. The two independent measurements agree within the experimental uncertainties, and the results validate the algorithm developed for the emulsion detector of OPERA.
The OPERA experiment, designed to perform the first observation of
ν
μ
→
ν
τ
oscillations in appearance mode through the detection of the
τ
leptons produced in
ν
τ
charged current interactions, has ...collected data from 2008 to 2012. In the present paper, the procedure developed to detect
τ
particle decays, occurring over distances of the order of
1
mm
from the neutrino interaction point, is described in detail and applied to the search for charmed hadrons, showing similar decay topologies as the
τ
lepton. In the analysed sample, 50 charm decay candidate events are observed while
54
±
4
are expected, proving that the detector performance and the analysis chain applied to neutrino events are well reproduced by the OPERA simulation and thus validating the methods for
ν
τ
appearance detection.
Tests of OPERA RPC detectors Bergnoli, A.; Borsato, E.; Brugnera, R. ...
IEEE transactions on nuclear science,
12/2005, Letnik:
52, Številka:
6
Journal Article
Recenzirano
OPERA is part of the CNGS project and it is an experiment dedicated to the observation of long-baseline nu mu into nu tau oscillations through tau appearance. Resistive Plate Chambers (RPCs) with ...bakelite electrodes are used to instrument the 2 cm gaps between the magnetized iron slabs of the two spectrometers. The RPC installation ended in may 2004 on the first spectrometer and in march 2005 on the second one. Before the installation, every RPC is subjected to a complete test chain in order to reject the poorer quality detectors. The tests are performed in dedicated facilities to ensure the proper RPC gluing, to measure its electrical properties and to verify the response to cosmic rays and the intrinsic noise levels. We have also tested the long term stability of real size OPERA RPC prototypes operated at cosmic ray fluxes for more than one year. On small size prototypes we are performing studies on the gas mixtures in order to reduce the total charge released in the gas for each detector count. The validation of the installed RPCs has been performed with pure nitrogen. A small part of them has been also tested with the gas mixture Ar/C 2 H 2 F 4 /i-C 4 H 10 /SF 6 =75.4/20/4/0.6
The OPERA experiment was designed to search for
ν
μ
→
ν
τ
oscillations in appearance mode through the direct observation of tau neutrinos in the CNGS neutrino beam. In this paper, we report a study ...of the multiplicity of charged particles produced in charged-current neutrino interactions in lead. We present charged hadron average multiplicities, their dispersion and investigate the KNO scaling in different kinematical regions. The results are presented in detail in the form of tables that can be used in the validation of Monte Carlo generators of neutrino–lead interactions.
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