Particle identification

A major goal of the physics program is to cleanly measure rare decays to test the Standard Model and be sensitive to possible new physics. This requires excellent charged hadron identification with 4 separation of pions and kaons up to 2.8 GeV/c. Even though a d/d capability will be retained in the readout of the new drift chamber, the momentum range over which we have good identification needs to be extended upward in order to access many of the most important physics issues. The new system must also be no thicker than 12%of a radiation length-the present time-of-flight scintillator thickness-in order not to compromise the performance of the CsI calorimeter.

The required performance of a particle identification system depends on the process being studied. The number of standard deviations of separation, n, is defined as

where , , , are the means and standard deviations of the and distributions respectively. Excellent work on all decay physics can be accomplished if one has 4 separation at 2.8 GeV/c, the maximum momentum reached in decays. As an example, consider the problem of separating from . The separation needed depends on the relative populations in the two channels, and the signal purity desired. In Fig. , the plot of separation versus fraction of the signal which is is shown. If the fraction is only 10%, the rejection required is at the 3-4 level for reasonable (%) purities (ignoring other sources of background). For the modes, the background just from is about 20 times the signal without particle identification and thus 4 rejection is essential. The separation at even higher momentum is also useful for other physics such as light quark fragmentation, charm decays, and decays. Although we have specifically mentioned separation, another important consideration is the ability to separate protons from kaons.