The Time-Of-Flight system consisting of plastic scintillation counters plays
an important role for particle identification in the BESIII experiment at the
BEPCII double ring e+e− collider. Degradation of the detection efficiency
of the barrel TOF system has been observed since the start of physical data
taking and this effect has triggered intensive and systematic studies about
aging effects of the detector. The aging rates of the attenuation lengths and
relative gains are obtained based on the data acquired in past several years.
This study is essential for ensuring an extended operation of the barrel TOF
system in optimal conditions.Comment: 14 pages, 8 figure