Abstract
The DIRAC spectrometer installed at CERN PS was upgraded in order to study simultaneously A2π and AπK atoms, namely the bound states of two π mesons, and of π and K mesons, respectively. The detector system can now accept a high intensity beam of 2–6×1011 primary protons per second. The electronics and the data-acquisition system can handle a very large amount of data to identify π, K, p, e and µ, allowing the selection of ππ and πK pairs in the offline analysis. The resolution of the longitudinal and transverse components of the relative momentum Q of each meson pair in their center-of-mass system with respect to the direction of the pair was substantially improved. The analysis of their distributions allowed an reliable separation between the meson pairs originating from hadronic atoms and the backgrounds permitting the measurement of the lifetimes of hadronic atoms in the ground state and π–π, π–K s-wave scattering lengths. The upgraded setup also allowed the study of the long-lived excited states of ππ atoms.
Highlights
The objective of the DIRAC experiment at the CERN Proton Synchrotron was a study of the hydrogen-like atom pionium formed by π+ and π– mesons (A2π)
This electronics is used for the X plane of the scintillating fibre detector (SFD), the ionization hodoscope (IH), the Vertical Hodoscopes (VH) and Horizontal Hodoscope (HH) and the Cerenkov detectors (726 channels in total on 51 boards) and grouped in 2 readout branches connected to data transfer system (DTS) transmitters (N415: see section)
The resolution of the setup is determined by the resolution of the opening angle of the pair measured with the upstream coordinate detectors, the multiple scattering in the mylar membrane after the target, in the Microdrift Chambers (MDC) detector, in the SFD detector and in the surrounding air
Summary
The objective of the DIRAC experiment at the CERN Proton Synchrotron was a study of the hydrogen-like atom pionium formed by π+ and π– mesons (A2π). General layout and the principal updates The DIRAC setup [ADE03B] was originally designed to detect π+π– pairs with small relative momenta It was a double arm magnetic spectrometer with two identical arms symmetrically located with respect to the secondary particle beam. When the distance between the central axis of the primary beam and the lower edge of the Pt foil is reduced to 3.5 mm, the counting rate on an IH slab starts increasing above the standard noise level This rate measurement as a function of the height with respect to the primary beam line was carefully carried out, and it was found that the intensity of the primary beam has a Gaussian distribution in y direction with a width σ < 1.75 mm, it varies very smoothly, and no separate spot (isolated halo) has been observed. It was again confirmed that the intensity distribution of the protons within the primary beam is smooth and follows a Gaussian distribution with σ < 1.75 mm
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
