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
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).
Calorimeter and DAQ layout
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 seconds.
Decay of the 0 meson 00 s
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
invariant mass distributions Different spectra with different 0 minimum E: Less events Less uncorrelated photons Similar mass values
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)
Signal and background We can observe two different areas: The signal (real decay of the 0 ) The background (uncorrelated photons)
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
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