1. A Data Acquisition system with an e.m. calorimeter for cosmic rays and  0 mesons study Lorenzo Centioni 1, Elena Eramo 2, Azzurra Giordani 1 1 Lic. Sc. B. Touschek, Grottaferrata (RM) 2 Lic. Sc. E. Amaldi, Roma Tutor: Pasquale Di Nezza Technician: Aldo Orlandi

2. Aim of the experiment  Realize a DAQ to analyze cosmic rays signals reconstructed by an e.m. calorimeter  In order to perform a study on a calorimeter working in a real experiment, we have reconstructed the  0 particle invariant mass (data from the Hermes experiment).

3. Calorimeter and DAQ layout

4. The particle  0 The particle  0 is a meson formed by a mix of u and d quarks: It decays by electromagnetic force in two photons in the 98.8% of the time (Particle Data Book). Its life time is about 10 -17 seconds.

5. Decay of the  0 meson 00   10 -17 s

6.  0 spectrum  The spectrum fit is a superposition of a gaussian curve and a first order polynomial  The mean value of the distribution is the  0 mass

7.  invariant mass distributions Different spectra with different  0 minimum E:  Less events  Less uncorrelated photons  Similar mass values

8.  0 M as a function of  0 minimum E  The  0 mass does not depends on the energy of the particle  The results coincide with the expected value (0.135 GeV)

9. Signal and background We can observe two different areas:  The signal (real decay of the  0 )  The background (uncorrelated photons)

10. Ratio sign/back as a function of  0 minimum E  Sign/bg ratio of different spectra with different  0 minimum E  We obtained a second order polynomial  Uncorrelated photon pairs mainly at low energy

11. Conclusions  We have created a DAQ made by a sampling e.m. calorimeter  Collected data analyzed within the Linux operating system (LabView, Paw++)  Studies on  0 meson: invariant mass reconstruction, energy dependence, sign/bg ratio