1. Schematic design of the upgraded ADAMO (right picture). We can see the magnetic system, the five planes of silicon detectors, the Time Of Flight apparatus, with three organic scintillators coupled with PMT’s and the threshold Čerenkov system, that will be based on an aerogel radiator coupled with six PMT’s. The upgrade is presently in progress and the work is focused in the development of the TOF system. The next step will be the production of the Čerenkov counter. The geometrical factor (i.e. the acceptance) measured in cm 2 sr as a function of the particles’ momentum (for both the old ADAMO version and the new one) is shown in the left graph. Its improvement, about of a factor 8, is evident and will permit to collect more significant data samples in the same exposure time. This greater acceptance is very important for the detector’s purposes; in fact it is designed also for acquisition of rare components (such as protons, whose flux is estimated to be about 1/100 compared to the muon one). ADAMO, an Altazimuthal Detector for Atmospheric Cosmic-Ray Observation Lorenzo Bonechi, Mauro Grandi, Francesco Taccetti and Elena Vannuccini Università di Firenze e INFN ADAMO is a magnetic spectrometer designed to study cosmic rays at ground level. It was conceived in 1999 on the basis of the experience gained by the Wizard group in Florence, involved in the construction of the PAMELA tracking system. The first version of the telescope (left photo) was composed of a permanent magnet enclosed in a mechanical amagnetic structure movable along both zenithal and azimuthal angles. It allowed the detection at ground of cosmic particles coming from different directions. The purpose of this detector is the study of the main charged components of cosmic rays at ground level, i.e. muons, electrons and protons, with momenta between about 100 MeV/c and 100 GeV/c. The measurement of these components allows a fine tuning of the propagation models of cosmic rays in the Earth's atmosphere. Furthermore, because of the relationship between the amounts of secondary muons and neutrinos, measurements of muon flux at different atmospheric depths and different geographical locations are useful to constrain models of neutrino oscillation put in evidence by large underground experiments. An upgrade of the telescope is in progress (a CAD design of the new detector is shown at right). Changes are intended to increase the acceptance, limited by the size of the magnetic cavity, and to perform particle discrimination through a Time Of Flight measurement and a threshold Čerenkov detector. The project of the upgraded system is briefly presented. The magnetic spectrometer assembled on the platform which permits rotations along two angles. Five silicon planes allow particle tracking inside the strong magnetic field produced (about 0.6 T). CAD design of the upgraded ADAMO telescope. The improvements will concern the increase of the acceptance (enlargement of the magnetic cavity to match the dimensions of the silicon detectors) and the achievement of particle identification by means of additional subsystems (TOF and Čerenkov counters). The subdetectors are indicated in the picture. TECHNICAL CHARACTERISTICS OF THE DETECTORS Each detector (ladder) is composed of two double sided microstrip silicon sensors, 300  m thick, and one hybrid circuit housing the front-end electronics. The n-type silicon wafer is segmented in 2035 p-type strips on the junction side (implantation pitch: 25.5  m) and 1024 n-type strips on the ohmic side, interleaved with p-stop strips to prevent charge from spreading over the backplane. The read-out pitches are 51  m and 67  m on junction and ohmic sides respectively. Decoupling capacitors are integrated directly on the sensors by means of a thin dioxide layer ; a double metallization is present on the ohmic side to bring the read-out lines on the same side for both views. Detectors operate in full depletion mode (bias voltage: 80 V). PERFORMANCES OF THE DETECTORS The spatial resolution achieved by these detectors on beam tests is 3  m for the junction side (used as bending view of charged particles) and about 12  m for the ohmic side. In the ADAMO configuration this resolution results in a Maximum Detectable Rigidity of 650 GV/c.  The external ladders are covered by a thin metal shield  the internal ones are protected only by a mylar foil (at bottom in the side photo), so to reduce the amount of dead materials  all the ladders are substained by an aluminum structure and inserted at the ends and between the magnetic modules  the low-noise electronics is based on 8 VA1 chips per ladder side FEATURES OF THE LADDER Tracking of particles is based on the relationship p cos   z B r between magnetic field B, radius r, momentum p, pitch angle  and charge z. The knowledge of the magnetic field is provided by a 3-dim. mapping procedure; an interpolation method is exploited to infer the intensity in all the points crossed by the incident particle. Particle flux measured at ground level by ADAMO, compared with the muon flux obtained by some balloon-borne experiments (left). ADAMO could measure momentum and charge sign of the particles entering the spectrometer, but it was not able to identify them. For this reason red points in figure contain the contribution from all kinds of incident particles, while the black ones, measured by balloon borne experiment, refer only to muons. Nevertheless, a comparison between these two sets of data is possible, since above 100 MeV/c particles other than muons (mainly protons and electrons) contribute less than 2% to the total flux. In fact, between 10 GeV/c and 100 GeV/c, ADAMO’s values are in agreement with the other data within the error bars. At lower momenta, some discrepances can be noticed. This can be explained with the presence of additional material that particles had to cross before reaching the detector. In fact, ADAMO was located during the data taking at the ground floor of a building: this location resulted in a dead layer where particles lost some energy. Estimations of the equivalent thickness are consistent with the observed spectrum. At momentum values lower than 400 MeV/c, ADAMO’s flux increases due to electrons’ contribution, which is comparable with muon’s one at these energies. Charge ratio (positive to negative particles) as a function of momentum; red points, referring to ADAMO, are compared with measurements from balloons. A weighted mean on the four values give the value: N + /N – = 1.16 ± 0.06 Right photo: magnetic system and support structure for photomultipliers in the upgraded ADAMO. Two iron cylinders that surround the PMT’s are visible: they are intended to reduce the magnetic field on the photocathode to about 0.1 mT. SCIENTIFIC OBJECTIVES OF THE DETECTOR THE SILICON MICROSTRIP DETECTORS PRELIMINARY RESULTS MAGNETIC SYSTEM PMTPMT TOF AEROGEL TRACKER ADAMO UPGRADE  TOF 1 TOF 2 TOF 3 Čerenkov Spectrometer The gain in the geometrical factor for the new magnetic configuration is counterbalanced by a worsening in the magnetic field intensity (see graph on the left, top) with respect to the old one. Along the main axis of the cavity the mean value of the active component of the field is 0.35 T. Rigidity is defined as the ratio between momentum and charge of the incident particle. The MDR (Maximum Detectable Rigidity) is the rigidity value for which the relative uncertainty on the momentum determination is 100%. In the left plot the uncertainty  p/p is reported as a function of momentum: the MDR is reached when p = 265 GeV/c. For our purposes a less intense magnetic field (which results in a lower MDR, 265 GV/c) is not so important, because an effective particle discrimination is obtained by TOF and Čerenkov system up to some GeV/c.