Final Search for Lightly Ionizing Particles with the MACRO detector
We present the final results of a search for lightly ionizing particles using
the entire cosmic ray data set the MACRO detector collected during its
1995-2000 run. Like the original search performed with the data of 1995-96,
this search was sensitive to fractionally charged particles with an electric
charge q as low as e/5 and with velocities between approximately 0.25c and c.
The efficiency of this search was approx 70% for q = e/5 and increased rapidly
to 100% for higher charges. No candidate events were observed. This corresponds
to a 90% C. L. upper limit on their isotropic flux of 6.1x10^-16 cm^-2 sec^-1
sr^-1 which represents the most stringent experimental limit ever obtained.