MACRO Detector Research Articles

Feasibility of multi‐contrast imaging on dual‐source photon counting detector (PCD) CT: An initial phantom study

Photon-counting-detector-computed tomography (PCD-CT) allows separation of multiple, simultaneously imaged contrast agents, such as iodine (I), gadolinium (Gd), and bismuth (Bi). However, PCDs suffer from several technical limitations such as charge sharing, K-edge escape, and pulse pile-up, which compromise spectral separation of multi-energy data and degrade multi-contrast imaging performance. The purpose of this work was to determine the performance of a dual-source (DS) PCD-CT relative to a single-source (SS) PCD-CT for the separation of simultaneously imaged I,Gd, andBi contrast agents. Phantom experiments were performed using a research whole-body PCD-CT and head/abdomen-sized phantoms containing vials of different I, Gd, Bi concentrations. To emulate a DS-PCD-CT, the phantoms were scanned twice on the SS-PCD-CT using different tube potentials for each scan. A tube potential of 80kV (energy thresholds=25/50keV) was used for low-energy tube, while the high-energy tube used Sn140 kV (Sn indicates tin filter) and thresholds of 25/90keV. The same phantoms were scanned also on the SS-PCD-CT using the chess acquisition mode. In chess mode, the 4×4 subpixels within a macro detector pixel are split into two sets based on a chess-board pattern. With each subpixel set having two energy thresholds, chess mode allows four energy-bin data sets, which permits simultaneous multi-contrast imaging. Because of this design, only 50% area of each detector pixel is configured to receive photons of a pre-defined threshold, leading to 50% dose utilization efficiency. To compensate for this dose inefficiency, the radiation dose for this scan was doubled compared to DS-PCD-CT. A 140kV tube potential and thresholds=25/50/75/90keV were used. These settings were determined based on the K-edges of Gd, andBi, and were found to yield good differentiation of I/Gd/Bi based on phantom experiments and other literature. The energy-bin images obtained from each scan (scan pair) were used to generate I-, Gd-, Bi-specific image via material decomposition. Root-mean-square-error (RMSE) between the known and measured concentrations was calculated for each scenario. A 20-cm water cylinder phantom was scanned on both systems, which was used for evaluating the magnitude of noise, and noise power spectra (NPS) of I/Gd/Bi-specific images. Phantom results showed that DS-PCD-CT reduced noise in material-specific images for both head and body phantoms compared to SS-PCD-CT. The noise level of SS-PCD was reduced from 2.55 to 0.90mg/mL (I), 1.97 to 0.78mg/mL (Gd), and 0.85 to 0.74mg/mL (Bi) using DS-PCD. NPS analysis showed that the noise texture of images acquired on both systems is similar. For the body phantom, the RMSE for SS-PCD-CT was reduced relative to DS-PCD-CT from 10.52 to 2.76mg/mL (I), 7.90 to 2.01mg/mL (Gd), and 1.91 to 1.16mg/mL (Bi). A similar trend was observed for the head phantom: RMSE reduced from 2.59 (SS-PCD) to 0.72 (DS-PCD) mg/mL (I), 2.02 to 0.58mg/mL (Gd), and 0.85 to 0.57mg/mL (Bi). We demonstrate the feasibility of performing simultaneous imaging of I,Gd, andBi materials on DS-PCD-CT. Under the condition without cross scattering, DS-PCD reduced the RMSE for quantification of material concentration in relative to a SS-PCD-CT system using chess mode.

UNDERGROUND MUON ENERGY SPECTRA WITH THE MACRO TRD

The MACRO detector was located in the Hall B of the Gran Sasso underground Laboratories under an average rock overburden of 3700 hg/cm2. A TRD composed by three identical modules, covering an horizontal area of 36 m2, was added to the MACRO detector in order to measure the residual energy of muons entering MACRO. This kind of measurement provides a useful tool to study the primary cosmic ray energy spectra and composition, their interactions with the Earth's atmosphere and the propagation of muons inside the rock. The results of the measurement of the energy of single and double muons crossing MACRO will be presented. Our data show that double muons are more energetic than single ones in the rock depth range from 3000 to 6500 hg/cm2. Single muon data confirm the reliability of the models adopted to describe the cosmic ray interactions with the atmosphere and the muon propagation inside the rock.

Time correlations of high energy muons in an underground detector

We present the result of a search for correlations in the arrival times of high energy muons collected from 1995 till 2000 with the streamer tube system of the complete MACRO detector at the underground Gran Sasso Lab. Large samples of single muons (8.6 million), double muons (0.46 million) and multiple muons with multiplicities from 3 to 6 (0.08 million) were selected. These samples were used to search for time correlations of cosmic ray particles coming from the whole upper hemisphere or from selected space cones. The results of our analyses confirm with high statistics a random arrival time distribution of high energy cosmic rays.

Measurements of atmospheric muon neutrino oscillations, global analysis of the data collected with MACRO detector

The final analysis of atmospheric neutrino events collected with the MACRO detector is presented. Three different classes of events, generated by neutrinos in different energy ranges, are studied l ...

Atmospheric neutrino oscillations with MACRO

We present the latest results on the study of atmospheric neutrino oscillations with the MACRO detector at Gran Sasso. Two sub-samples of events have been analysed, both in terms of absolute flux and zenith angle distribution: high energy events (with 〈 E ν 〉 ⋍ 50 GeV) and low energy events (with 〈 E v 〉 ⋍ 4 GeV). The high energy sample has been used also to check the ν μ Hν sterile oscillation hypothesis and to estimate neutrino energies using Multiple Coulomb Scattering (MCS) informations. All these analyses are mutually consistent and strongly favour the ν μ ⇌ ν τ oscillation hypothesis with maximal mixing and Δm 2 = 2.5 · 10 −3eV 2.

Study of atmospheric neutrinos with the MACRO detector

The MACRO experiment detected different categories of atmospheric muon neutrinos. We describe in this paper the energy estimate of upward throughgoing muons by using the multiple coulomb scattering. Combining the results of such analysis with the upgoing muon angular distribution, both not using the absolute ν flux normalization informations, an evidence above 4σ for atmospheric neutrino oscillation is found.

Moon and Sun shadowing effect in the MACRO detector

Using data collected by the MACRO experiment from 1989 to the end of its operations in 2000, we have studied in the underground muon flux the shadowing effects due to both the Moon and the Sun. We have observed the shadow cast by the Moon at its apparent position with a significance of 6.5 σ. The Moon shadowing effect has been used to verify the pointing capability of the detector and to determine the instrument resolution for the search of muon excesses from any direction of the celestial sphere. The dependence of the effect on the geomagnetic field is clearly shown by splitting the data sample in day and night observations. The Sun shadow, observed with a significance of 4.6 σ is displaced by about 0.6° from its apparent position. In this case however the explanation resides in the configuration of the Solar and Interplanetary Magnetic Fields, which affect the propagation of cosmic ray particles between the Sun, and the Earth. The displacement of the Sun shadow with respect to the real Sun position has been used to establish an upper limit on the antimatter flux in cosmic rays of about 48% at 68% c.l. and primary energies of about 20 TeV.

Measurement of the residual energy of muons in the Gran Sasso underground laboratories

The MACRO detector was located in the Hall B of the Gran Sasso underground laboratories under an average rock overburden of 3700 hg/cm 2. A transition radiation detector composed of three identical modules, covering a total horizontal area of 36 m 2, was installed inside the empty upper part of the detector in order to measure the residual energy of muons. This paper presents the measurement of the residual energy of single and double muons crossing the apparatus. Our data show that double muons are more energetic than single ones. This measurement is performed over a standard rock depth range from 3000 to 6500 hg/cm 2.

Search for nucleon decays induced by GUT magnetic monopoles with the MACRO experiment

The interaction of a Grand Unification Magnetic Monopole with a nucleon can lead to a barion-number violating process in which the nucleon decays into a lepton and one or more mesons (catalysis of nucleon decay). In this paper we report an experimental study of the effects of a catalysis process in the MACRO detector. Using a dedicated analysis we obtain new magnetic monopole (MM) flux upper limits at the level of $\sim 3\cdot 10^{-16} cm^{-2} s^{-1} sr^{-1}$ for $1.1\cdot 10^{-4} \le |\beta| \le 5\cdot 10^{-3}$, based on the search for catalysis events in the MACRO data. We also analyze the dependence of the MM flux limit on the catalysis cross section.

Muon energy estimate through multiple scattering with the MACRO detector

Muon energy measurement represents an important issue for any experiment addressing neutrino-induced up-going muon studies. Since the neutrino oscillation probability depends on the neutrino energy, a measurement of the muon energy adds an important piece of information concerning the neutrino system. We show in this paper how the MACRO limited streamer tube system can be operated in drift mode by using the TDCs included in the QTPs, an electronics designed for magnetic monopole search. An improvement of the space resolution is obtained, through an analysis of the multiple scattering of muon tracks as they pass through our detector. This information can be used further to obtain an estimate of the energy of muons crossing the detector. Here we present the results of two dedicated tests, performed at CERN PS-T9 and SPS-X7 beam lines, to provide a full check of the electronics and to exploit the feasibility of such a multiple scattering analysis. We show that by using a neural network approach, we are able to reconstruct the muon energy for E μ<40 GeV . The test beam data provide an absolute energy calibration, which allows us to apply this method to MACRO data.

A combined analysis technique for the search for fast magnetic monopoles with the MACRO detector

We describe a search method for fast moving ( β= v/ c>5×10 −3) magnetic monopoles using simultaneously the scintillator, streamer tube and track-etch subdetectors of the MACRO apparatus. The first two subdetectors are used primarily for the identification of candidates while the track-etch one is used as the final tool for their rejection or confirmation. Using this technique, a first sample of more than two years of data has been analyzed without any evidence of a magnetic monopole. We set a 90% CL upper limit to the local monopole flux of 1.5×10 −15 cm −2 s −1 sr −1 in the velocity range 5×10 −3⩽ β⩽0.99 and for nucleon decay catalysis cross-section smaller than ∼1 mb

The MACRO detector at Gran Sasso

MACRO was an experiment that ran in the Laboratori Nazionali del Gran Sasso from 1988 to 2000. Its principal goal was to observe magnetic monopoles or set significantly lower experimental flux limits than had been previously available in the velocity range from about β=10 −4 to unity. In addition it made a variety of other observations. Examples are: setting flux limits on other so far unobserved particles such as nuclearites and lightly ionizing particles, searching for WIMP annihilations in the Earth and the Sun and for neutrino bursts from stellar collapses in or near our Galaxy, and making measurements relevant to high energy muon and neutrino astronomy and of the flux of up-going muons as a function of nadir angle showing evidence for neutrino oscillations. The apparatus consisted of three principal types of detectors: liquid scintillator counters, limited streamer tubes, and nuclear track etch detectors. In addition, over part of its area it contained a transition radiation detector. The general design philosophy emphasized redundancy and complementarity. This paper describes the technical aspects of the complete MACRO detector, its operational performance, and the techniques used to calibrate it and verify its proper operation. It supplements a previously published paper which described the first portion of the detector that was built and operated.

SEMI-CONTAINED NEUTRINO EVENTS IN MACRO

Updated results are presented of low-energy [Formula: see text] neutrino interactions observed by the MACRO detector. Two analyses (of different topologies) are presented; individually, and especially in their ratio, they are inconsistent with no oscillations and consistent with maximal mixing at Δm2 of a few times 10-3.

Matter effects in upward-going muons and sterile neutrino oscillations

The angular distribution of upward-going muons produced by atmospheric neutrinos in the rock below the MACRO detector show anomalies in good agreement with two flavor neutrino-mu ==> neutrino-tau oscillations with maximum mixing and Delta m**2 around 0.0024 eV**2. Exploiting the dependence of magnitude of the matter effect on oscillation channel, and using a set of 809 upward-going muons observed in MACRO, we show that the two flavor neutrino-mu ==> neutrino-sterile oscillation is disfavored with 99% C.L. with respect to neutrino-mu ==> neutrino-tau.

Search for massive rare particles with the MACRO track-etch detector at Gran Sasso

Searches for massive penetrating particles in the cosmic radiation have been performed with the MACRO nuclear track detector used as a “stand alone” detector. The complete experimental procedure is presented. In absence of candidates, updated estimates of the flux upper limits both for the CR-39 “stand alone” detector and for the global MACRO detector are presented for magnetic monopoles, nuclearites and charged Q-balls.

Analysis of the atmospheric neutrino data in terms of 3ν oscillations

A global analysis of atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We consider in our analysis both contained events and upward-going ν-induced muon events, including the previous data samples of Fréjus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data set, the recent 5.1 kton-yr contained events of Soudan-2 and the results on upgoing muons from the MACRO detector. After presenting the results for the analysis of atmospheric data alone, we add to our data sample the reactor bound of the CHOOZ experiment, showing and important complementarity between the atmospheric and reactor limits which results in a stronger constraint on the allowed value of θ 13.

Global three-neutrino oscillation analysis of neutrino data

A global analysis of the solar, atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We include the most recent solar neutrino rates of Homestake, SAGE, GALLEX and GNO, as well as the recent 1117 day Super-Kamiokande data sample, including the recoil electron energy spectrum both for day and night periods and we treat in a unified way the full parameter space for oscillations, correctly accounting for the transition from the matter enhanced (MSW) to the vacuum oscillations regime. Likewise, we include in our description conversions with $\theta_{12} > \pi/4$. For the atmospheric data we perform our analysis of the contained events and the upward-going $\nu$-induced muon fluxes, including the previous data samples of Frejus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data set, the recent 5.1 kton-yr contained events of Soudan2 and the results on upgoing muons from the MACRO detector. We first present the allowed regions of solar and atmospheric oscillation parameters $\theta_{12}$, $\Delta m^2_{21}$ and $\theta_{23}$, $\Delta m^2_{32}$, respectively, as a function of $\theta_{13}$ and determine the constraints from atmospheric and solar data on the mixing angle $\theta_{13}$, common to solar and atmospheric analyses. We also obtain the allowed ranges of parameters from the full five-dimensional combined analysis of the solar, atmospheric and reactor data.

Search for lightly ionizing particles with the MACRO detector

A search for lightly ionizing particles has been performed with the MACRO detector. This search was sensitive to particles with charges between $\fractional{5}$$e$ and close to the charge of an electron, with $\beta$ between approximately 0.25 and 1.0. Unlike previous searches both single track events and tracks buried within high multiplicity muon showers were examined. In a period of approximately one year no candidates were observed. Assuming an isotropic flux, for the single track sample this corresponds to a 90% C.L. upper flux limit $\Phi \leq 9.2 \times 10^{-15} cm^{-2} sec^{-1} sr^{-1}$ .

Search for magnetic monopoles with MACRO

Data from the complete MACRO detector have been used to search for magnetic monopoles (MMs) of all expected velocities. Scintillator, streamer tube (instrumented with specialized electronics) and nuclear track detectors have been used to search for signatures coming from MMs; the scintillator and nuclear track subdetectors were used also for searches for other rare particles (nuclearites, charged Q-balls). Based on no observation of such signals, we establish stringent flux limits, for MMs as slow as a few 10 −5 c.

Search for massive rare particles with the MACRO detector at Gran Sasso

Searches for massive penetrating particles in the cosmic radiation have been performed with the MACRO detector. Scintillators, streamer tubes (instrumented with specialized electronics) and nuclear track detectors have been used to search for signatures coming from magnetic monopoles (MMs); the scintillator and the nuclear track subdetectors were also used for searches for other rare particles (nuclearites, charged Q-balls). Based on no observation of such signals, we establish stringent flux limits, for MMs as slow as a few 10 −5 c.