Last Update: October 2000

### MACRO

Collaboration:

INFN - Bari, Bologna, Lecce, LNF, LNGS, Napoli, Pisa, Torino

USA - Boston, Caltech, Drexel, Indiana, Michigan, Texas A&M

Laboratory: LNGS

1. Goal of the experiment

`MACRO is a large area multipurpose underground detector designed to search for rare events in the cosmic radiation. It has been optimized to look for the supermassive magnetic monopoles predicted by Grand Unified Theories (GUT) of the electroweak and strong interactions; it can also perform measurements in areas of astrophysics, nuclear, particle and cosmic ray physics. These include the study of atmospheric neutrinos and neutrino oscillations, high energy (E` `n``` `>~` `1 GeV) neutrino astronomy, indirect searches for WIMPs, search for low energy (E` `n``` `>~` `7 MeV) stellar collapse neutrinos, studies of various aspects of the high energy underground muon flux (which is an indirect tool to study the primary cosmic ray composition, origin and interactions), searches for fractionally charged particles and other rare particles that may exist in the cosmic radiation. The mean rock depth of the overburden is` `~``3700 m.w.e., while the minimum is 3150 m.w.e. This defines the minimum muon energy at the surface at` `~``1.3 TeV in order to reach MACRO. The average residual energy and the muon flux at the MACRO depth are` `~``310 GeV and` `~``1 m``-2``h``-1``, respectively. The detector has been built and equipped with electronics during the years 1988 - 1995. It was completed in August 1995 and since the fall of 1995 it is running in its full configuration.`

`The MACRO detector has a modular structure: it is divided into six sections referred to as supermodules. Each active part of one supermodule has a size of 12.6 x 12.6 x 9.3 m``3``and comes with separate mechanical structure and electronics readout. The full detector has global dimensions of 76.5 x 12.6 x 9.3 m``3` `and provides a total acceptance to an isotropic flux of particles of``~``10. 000 m``2``sr. The total mass is` `~``5300 t.`

`The detector is composed of three sub-detectors: liquid scintillation counters, limited streamer tubes and nuclear track detectors. Each one of them can be used in "standalone" and in "combined" mode.`

`Redundancy and complementarity have been the primary goals in designing the experiment. For example, since no more than few magnetic monopoles can be expected, multiple signatures and ability to perform cross checks among various parts of the apparatus are important.`

2. Physics achievements

In the past years several significative results have been obtained for each of the physics items outlined in the section of the goal of the experiment and addressed in the proposal of the experiment dated 1984.

For the year 2000 the most important result is related to the neutrino oscillation field. After the results published in 1998, the increase of statistics and more extensive analysis allowed to reach, using the angular distribution of upgoing muons, a probability of 36% in favor of numu-nutau oscillation, 7% for numu-nusterile oscillation and 0.36% for no oscillation. The best oscillation parameters, related to the higher probability case, are Dm2=0.0025 eV2 and sin2(2q)=1. The analysis of the two type of low energy events (i.e. semicontained events and events with a muon stopping in the massive part of the detector) gives a strong internal coherence to the oscillation hypothesis, since the observed deficits are well in agreement with the expectations using the above mentioned parameters. The analisys was object of publication on a referred journal during this year.

Other published results are related to the high energy muon neutrino astronomy, to a search for nuclearites in the penetrating cosmic radiation using the scintillator and nuclear track subdetectors and to a search for lightly ionizing particles.

Given the importance of the neutrino physics, the experiment has been approved for a data taking prolonged up to the end of 2000.

3. INFN contribution to the experiment in terms of manpower and financial support

- Manpower (Year 2000): 78 researchers(~28 FTE), 8 Technicians (~3.5 FTE)

- Financial Support (Year 2000): 1066 MLit

4. Number of publication in referred journals: 5

5. Number of talks to conferences: 16

6. Number of undergraduate and doctoral thesis on the experiment

- Undergraduate thesis - Year 2000: 3 in progress

- Doctoral thesis - Year 2000: 3 completed; 3 in progress.

7. Leadership role in the experiment

G. Giacomelli - Co-Spokesman

M. Spinetti - Technical Supervisor and National Responsible

8. Innovative instruments

The experiment has been completed in 1995 and up-to-date techniques for particle detection have been used at the time of installation.

Examples: the largest (~20000 m2) tracking system, based on 3x3 cm2 limited streamer tubes, deployed in an underground laoratory; the data acquisition system based on a server/client architecture with VME computers distributed on a network, the readout of the streamer tube system based on custom modules; the processing of the scintillator signals based on 300 MCycles VME WFD; a scintillator signal processing and trigger system dedicated to the detection of stellar collapses with a live time close to 100%.

9. Competing experiments

For some physics items, like magnetic monopole search and the obsevation of penetrating cosmic ray radiation, MACRO has no competitors due to the large surface, the complementarity of the detection techniques and the location in an underground laboratory. For the neutrino oscillation physics MACRO is competitive with SK in the atmospheric neutrino energy range 5-100 GeV, given the accumulated statistics and comparable rates for upgoing muons.

MACRO has initiated, together with SK, the international network for early alarm in case of stellar collapse.

10. International committee which has reviewed the experiment

The experiment is reviewed by the funding authorities of INFN and DOE; it is also periodically reviewed by the Scientific Committee of the LNGS