There is an idea to implement additional TOF in the west-arm in order to extend hadron PID capability of the arm. The difference of flight time in 5 meter is shown in Fig. 12.
The identification of pion and kaon is done up to 2.5 GeV/c, and proton is identified up to 4.2 GeV/c with 3 sigma separation for 100 ps resolution, which the additional TOF is aiming for. In case of 400 ps resolution, which EMCal-time-of-flight would give with out the additional implementation of TOF, pion and kaon is identified up to 1.2 GeV/c, and proton is identified up tp 2 GeV/c for the 3 sigma separation.
The disadvantages of the configuration without the additional TOF is following 3 points. These disadvantages are mainly for the kaon where both TOF and AEROGEL are required for PID.
(1) Increase of systematic error in single spectra of kaon in the region. For the inclusive spectra, the measurement by the existing RICH + TOF configuration in the east-arm would enables (when a certain requirement in systematic error (as well as statistical error) is satisfied) to supplement the lack of TOF coverage in the west-arm. This is the case mainly for the kaon in the region between 2 GeV/c and 3.7 GeV/c. (Make a comparison between Fig. 13 and Fig. 14. Namely up to 2 GeV/c, kaon is measurable without TOF as shown in Fig. 13. And up to 3.7 GeV/c, kaon is measurable with TOF as shown in Fig. 14.) But the systematic error is to be increasing.
(2)And once we are interested in the track-by-track physics, the lack of the TOF detector results in the large disadvantages for the kinematic coverage in the region. The track-by-track physics contains, i.e. event-by-event fluctuation of variety of observables, flow, and jet physics. And lost is for the strangeness particle, kaon.
(3)And there are technical disadvantages as well, if there is no additional TOF in the west-arm. . In the analysis, (i) consistency checks in track-by-track bases possibly give smaller systematic error, and (ii) the large overlap coverage for kaon between 1 GeV/c and 3.7 GeV/c in three logics (the first one is by kaon-by-TOF, and the second is by the coincidence of veto-proton-by-TOF and veto-pion-by-TOF and the third is the coincidence of veto-proton-by-TOF and veto-pion-by-Aerogel) gives smaller systematic error.
Those two capabilities ((i) and (ii)) for systematic checks are lost, when there is no additional TOF in the west-arm.