LVD Experiment Research Articles

Effect of pressure and ventilation in the experimental hall on the background events count rate of the LVD detector

In the LVD experiment (Gran Sasso, Italy), variations in the counting rate of detector background pulses associated with the injection of radon from the rock into the experimental hall are studied. We present dependences of changes in atmospheric pressure on the surface and in the experimental hall of the setup, as well as variations in the counting rate of LVD events associated with changes in radon concentration.

On the Mechanism of Temperature Variations in the Average Energy of Muons at Large Depths

Sources of seasonal temperature variations in the average energy of the muon flux detected in the LVD experiment have been discussed. It has been shown that variations are due to the processes of generation of muons in upper layers of the atmosphere and the passage of muons through a thick rock layer.

Neutrino velocity and local Lorentz invariance

We discuss the possible violation of local Lorentz invariance (LLI) arising from a faster-than-light neutrino speed. A toy calculation of the LLI violation parameter [Formula: see text], based on the (disclaimed) OPERA data, suggests that the values of [Formula: see text] are determined by the interaction involved, and not by the energy range. This hypothesis is further corroborated by the analysis of the more recent results of the BOREXINO, LVD and ICARUS experiments.

Generation of neutrons produced by muons from CERN neutrino beam

Preliminary results of neutron generation by muons, produced in CERN neutrino beam with average energy 17 GeV in LVD experiment are presented for the period 2008–2011 yrs. A Monte Carlo simulation of neutrons produced by horizontal muons was performed using the Geant4 software package. The efficiency of neutron detection in the LVD was calculated. For iron-based and white spirit scintillators, the measured neutron yields prove to be Ysc = (3.6 ± 0.7) × 10−5n/μ (g−1 cm2) and YFe = (23.2 ± 4.6) × 10−5n/μ (g−1 cm2).

Light output response of the LVD liquid scintillator to neutron-induced nuclear recoils

The organic liquid scintillator used in the LVD experiment (INFN Gran Sasso National Laboratory) has been exposed to an Am-Be neutron source to measure the light response function for neutron energies in the region from about 4 to 11 MeV.A full Monte Carlo simulation, incorporating the detector response, is used to generate neutron scattering spectra which are matched to the observed ones to determine the quenching factors.The obtained light output response is well described by the semi-empirical Birks model.The results, consistent with those obtained by other authors using similar hydrocarbonate scintillators, can be of interest for fast and high-energy neutron spectroscopy that could be performed with this detector.

Neutrino speed: a report on the [formula omitted] speed measurements of the BOREXINO, ICARUS and LVD experiments with the CNGS beam

We report the measurement of the speed of muon neutrinos performed by the Borexino, ICARUS and LVD experiments, using narrow bunch CNGS neutrino beams with an average energy E = 17 GeV and a baseline of ∼ 730 km between Cern and Laboratori Nazionali del Gran Sasso (LNGS). The final result for the difference in time-of-flight between such muon neutrinos and a particle moving at the speed of light in vacuum is δt=0.8±0.7stat±2.9sys ns for Borexino, δt=−0.1±0.7stat±2.7sys ns for ICARUS and δt=−0.3±0.6stat±3.2−sys ns for LVD, well consistent with zero.

Determination of a time-shift in the OPERA set-up using high-energy horizontal muons in the LVD and OPERA detectors

The purpose of this work is to report the measurement of a time-shift in the OPERA set-up in a totally independent way from Time Of Flight (TOF) measurements of CNGS neutrino events. The LVD and OPERA experiments are both installed in the same laboratory: LNGS. The relative position of the two detectors, separated by an average distance of ~ 160 m, allows the use of very high energy horizontal muons to cross-calibrate the timing systems of the two detectors, using a TOF technique which is totally independent from TOF of CNGS neutrino events. Indeed, the OPERA-LVD direction lies along the so-called "Teramo anomaly", a region in the Gran Sasso massif where LVD has established, many years ago, the existence of an anomaly in the mountain structure, which exhibits a low m. w. e. thickness for horizontal directions. The "abundant" high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA exist because of this anomaly in the mountain orography. The total live time of the data in coincidence correspond to 1200 days from mid 2007 until March 2012. The time coincidence study of LVD and OPERA detectors is based on 306 cosmic horizontal muon events and shows the existence of a negative time shift in the OPERA set-up of the order of deltaT(AB) = - (73 \pm 9) ns when two calendar periods, A and B, are compared. This result shows a systematic effect in the OPERA timing system from August 2008 until December 2011. The size of the effect is comparable with the neutrino velocity excess recently measured by OPERA. It is probably interesting not to forget that with the MRPC technology developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was reached. That technology can be implemented at LNGS for a high precision determination of TOF with the CNGS neutrino beams of an order of magnitude smaller than the value of the OPERA systematic effect.

Updated results from the 3-ton Gd loaded liquid scintillator target after 2 years of data taking at LNGS

We performed a 3-m3 Gd experiment by doping (up to 0.1% in weight) two counters of the LVD experiment, at LNGS, with a Gd organic salt developed and produced as the result of a joint INFN/INR research activity. Feasibility of the experiment and performances of the Gd doped liquid scintillator (Gd-LS) have been presented. The chemical and physical properties of the Gd-LS and its performance as a neutron detector, namely neutron capture efficiency and average capture time are being monitored since the doping time in 2005. From laboratory survey we can state the stability of the trasmittance (T) at the reference wavelength (425 nm) with a C.L. of 81% and 96% respectively for the first and the second doped counter. This is the largest stable Gd-doped organic liquid scintillator target ever produced and continuously operated for a long period.

Supernova neutrinos: Earth matter effects and neutrino mass spectrum

We perform a detailed study of the Earth matter effects on supernova neutrinos. The dependences of these effects on the properties of the original neutrino fluxes, on the trajectory of the neutrinos inside the Earth and on the oscillation parameters are described. We show that, for a large fraction (∼60%) of the possible arrival times of the signal, the neutrino flux crosses a substantial amount of the matter of the Earth at least for one of the existing detectors. For oscillation parameters from the LMA solution of the solar neutrino problem the Earth matter effect consists in an oscillatory modulation of the ν ̄ e and/or ν e energy spectra. The relative deviation with respect to the undistorted spectra can be as large as 20–30% for E≳20 MeV and 70–100% for E≳40 MeV. For parameters from the SMA and LOW solutions the effect is localized at low energies ( E≲10 MeV) and is not larger than ∼10%. The Earth matter effects can be revealed (i) by the observation of oscillatory distortions of the energy spectra in a single experiment and (ii) by the comparison between the spectra at different detectors. For a supernova at distance D=10 Kpc, comparing the results of SuperKamiokande (SK), SNO and LVD experiments one can establish the effect at (2–3) σ level, whereas larger statistical significance ((4–5) σ) is obtained if two experiments of SK-size or larger are available. Studies of the Earth matter effect will select or confirm the solution of the solar neutrino problem, probe the mixing U e3 and identify the hierarchy of the neutrino mass spectrum.

On the depth-intensity curve of multiple muons with LVD

Using the LVD experiment under Gran Sasso, the measurement of high energy cosmic ray muons was done. We obtained a different dehaviour of the depth-intensity curves for single and multiple muon events above 7000 m w.e. The ratio of multiple to single muon events increases by a factor of about 7 when the depth changes from 7000 to 10,000 m w.e.

Study of the c.r. composition and interaction at E0 = 10 – 100 TeV from the observation of H.E. muons and atmospheric Cherenkov light in EAS

In the energy region 10 – 100 TeV both the c.r. composition from direct measurements and the cross section for high energy secondary production in the very forward region for p-air interactions are rather uncertain. Contemporaneous measurements of the total energy and of the threshold energy/nucleon of the primary particle can be provided by the atmospheric Cherenkov light and high energy muons. These measurements are performed by the combined operation of the Cherenkov array of the EAS-TOP experiment on the surface (810 gcm2 atmospheric depth) and of the LVD experiment in the underground Gran Sasso Laboratories (3300 m w.e.; Eμth = 1.3 TeV) leading to the measurement of (Eμ > 1.3 TeV, E0) in the given energy range. The combined operation of the experiments and preliminary results are reported.

Neutrino burst identification in underground detectors

We discuss the problem of neutrino burst identification in underground ν-telescopes. First the usual statistical analysis based on the time structure of the events is reviewed, with special attention to the statistical significance of burst candidates. Next, we propose a second level analysis that can provide independent confirmation of burst detection. This exploits the spatial distribution of the single events of a burst candidate, and uses the formalism of the entropy of information. Examples of both techniques are shown, based on the LVD experiment at Gran Sasso.

Neutrino-induced and atmospheric single-muon fluxes measured over five decades of intensity by LVD at Gran Sasso Laboratory

We report data taken by the LVD Experiment during a live-time period of 11 556 h. We have measured the muon intensity at slant depths of standard rock from about 3000 hg/cm2 to about 20 000 hg/cm2. This is an exclusive study, namely our data include only events containing single muons. This interval of slant depth extends into the region where the dominant source of underground muons seen by LVD is the interaction of atmospheric neutrinos with the rock surrounding LVD. The interesting result is that this flux is independent of slant depth beyond a slant depth of about 14 000 hg/cm2 of standard rock. Due to the unique topology of the Gran Sasso Laboratory the muons beyond about 14 000 hg/cm2 of standard rock are at a zenithal angle near 90°. Hence we have, for this fixed angle, a muon flux which is independent of slant depth. This is direct evidence that this flux is due to atmospheric neutrinos interacting in the rock surrounding LVD. The value of this flux near 90° is (8.3 ± 2.6) × 10−13 cm−2 s−1 sr−1, which is the first reported measurement at a zenithal angle near 90° and for slant depths between 14 000 and 20 000 hg/cm2. Our data cover over five decades of vertical intensity, and can be fit with just three parameters over the full range of our experiment. This is the first time a single experiment reports the parameters of a fit made to the vertical intensity over such a large range of standard rock slant depth. The results are compared with a Monte Carlo simulation which has as one of the two free parameters γπκ, the power index of the differential energy spectrum of the pions and kaons in the atmosphere. This comparison yields a value of 2.75 ± 0.03 for γπκ, where the error includes the systematic uncertainties. Our data are compared to other measurements made in our slant depth interval. We also report the value of the muon flux in Gran Sasso at θ = 90° as a function of the azimuthal angle.

Multiple muon events observed in the LVD experiment

This is a progress report on the multiple muon events recorded by the first tower of the LVD detector at the Gran Sasso Laboratory. About 17,000 multiple muon events have been observed since the LVD first tower started operation in June 1992. Presented here are the measured multiplicity distribution and separation distribution of muon pairs in the bundles.

Search for neutrino oscillations with the LVD liquid scintillation component

In this work the sensitivity of the liquid scintillation component of the LVD experiment at Gran Sasso, to search for atmospheric neutrino oscillations, has been evaluated. The computations have been performed both for confined events (for which we expect ∼160 interations/year) and for upward going muons (for which we expect ∼200 upward muons/year). The latest events are produced by neutrino interactions in the rock surrounding the apparatus. The results of these calculations show that, in three years life-time, limits on neutrino oscillations down to a sensitivity δm 2 ∼ 5×10 −5 eV 2 for maximum mixing angle will be reached at the 3 σ level.

The LVD experiment data acquisition system

Data acquisition for the LVD, a massive underground neutrino/muon detector containing 1800 tons of liquid scintillator in 1520 separate tanks and approximately 20000 (8-wire) Iarocci-type streamer chamber assemblies, is discussed. The detector is designed to look for stellar collapse neutrinos as well as for a broad range of physics experiments including searches for muon point sources, neutrino oscillations, and supersymmetric decay modes of the proton. The data acquisition challenge comes from the large physical size (49 m*12 m*13 m) and the large number of individual detectors involved. Data rates will be low enough to allow the use of CAMAC for the front-end hardware. However, peak data transfer design requirements for worst-case stellar collapse scenarios, along with the constant overhead of detector status monitoring, dictates the use of dedicated front-end processors (CES-STARBURST). The physical size of the detector system further suggests the use of a distributed data acquisition computer environment (VAXCluster). The CERN-developed MODEL online data acquisition system has been selected for the basic software architecture. The detector design and data acquisition hardware and software are described. >

The large-volume detector (LVD) of the Gran Sasso Laboratory

We describe here the LVD experiment (Large-Volume Detector) of the Gran Sasso Laboratory, which is the natural improvement of the LSD experiment (Liquid Scintillation Detector) running in the Mont Blanc Laboratory. The LVD ((31×13) m2 area, height 12 m) consists of ≈1800 tons of liquid scintillator and of a system of streamer tubes on 5 layers for reconstructing tracks of charged particles. As any experiment in an underground laboratory, which has a low statistics of events and requires long running times, the LVD is a multipurpose experiment but with different priorities of the researches. The main goal is neutrino astronomy, firstly detection of neutrinos from collapsing stars and secondly high-energy neutrinos and solar neutrinos. Since the expected number of interactions of neutrinos, from a stellar collapse is very high (of order of 900 for a collapse at the distance of the galactic centre), the LVD is, contrary to the present experiments, a real neutrino observatory, able to make a detailed analysis of the energy and temporal distributions of the burst. In addition to neutrino astrophysics, with the LVD experiment excellent possibilities exist to perform researches in cosmic-ray and high-energy elementary-particle physics.